This patchset adds a new mode to KASAN [1], which is called KHWASAN
(Kernel HardWare assisted Address SANitizer).
The plan is to implement HWASan [2] for the kernel with the incentive,
that it's going to have comparable to KASAN performance, but in the same
time consume much less memory, trading that off for somewhat imprecise
bug detection and being supported only for arm64.
The overall idea of the approach used by KHWASAN is the following:
1. By using the Top Byte Ignore arm64 CPU feature, we can store pointer
tags in the top byte of each kernel pointer.
2. Using shadow memory, we can store memory tags for each chunk of kernel
memory.
3. On each memory allocation, we can generate a random tag, embed it into
the returned pointer and set the memory tags that correspond to this
chunk of memory to the same value.
4. By using compiler instrumentation, before each memory access we can add
a check that the pointer tag matches the tag of the memory that is being
accessed.
5. On a tag mismatch we report an error.
[1] https://www.kernel.org/doc/html/latest/dev-tools/kasan.html
[2] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html
====== Rationale
On mobile devices KASAN's memory usage is significant problem. One of the
main reasons to have KWHASAN is to be able to perform a similar set of
checks that KASAN does, but with lower memory requirements.
Comment from Vishwath Mohan <[email protected]>:
I don't have data on-hand, but anecdotally both ASAN and KASAN have proven
problematic to enable for environments that don't tolerate the increased
memory pressure well. This includes,
(a) Low-memory form factors - Wear, TV, Things, lower-tier phones like Go,
(c) Connected components like Pixel's visual core [1].
These are both places I'd love to have a low(er) memory footprint option at
my disposal.
Comment from Evgenii Stepanov <[email protected]>:
Looking at a live Android device under load, slab (according to
/proc/meminfo) + kernel stack take 8-10% available RAM (~350MB). KASAN's
overhead of 2x - 3x on top of it is not insignificant.
Not having this overhead enables near-production use - ex. running
KASAN/KHWASAN kernel on a personal, daily-use device to catch bugs that do
not reproduce in test configuration. These are the ones that often cost
the most engineering time to track down.
CPU overhead is bad, but generally tolerable. RAM is critical, in our
experience. Once it gets low enough, OOM-killer makes your life miserable.
[1] https://www.blog.google/products/pixel/pixel-visual-core-image-processing-and-machine-learning-pixel-2/
====== Technical details
KHWASAN is implemented in a very similar way to KASAN. This patchset
essentially does the following:
1. TCR_TBI1 is set to enable Top Byte Ignore.
2. Shadow memory is used (with a different scale, 1:16, so each shadow
byte corresponds to 16 bytes of kernel memory) to store memory tags.
3. All slab objects are aligned to shadow scale, which is 16 bytes.
4. All pointers returned from the slab allocator are tagged with a random
tag and the corresponding shadow memory is poisoned with the same value.
5. Compiler instrumentation is used to insert tag checks. Either by
calling callbacks or by inlining them (CONFIG_KASAN_OUTLINE and
CONFIG_KASAN_INLINE flags are reused).
6. When a tag mismatch is detected in callback instrumentation mode
KHWASAN simply prints a bug report. In case of inline instrumentation,
clang inserts a brk instruction, and KHWASAN has it's own brk handler,
which reports the bug.
7. The memory in between slab objects is marked with a reserved tag, and
acts as a redzone.
8. When a slab object is freed it's marked with a reserved tag.
Bug detection is imprecise for two reasons:
1. We won't catch some small out-of-bounds accesses, that fall into the
same shadow cell, as the last byte of a slab object.
2. We only have 1 byte to store tags, which means we have a 1/256
probability of a tag match for an incorrect access (actually even
slightly less due to reserved tag values).
Despite that there's a particular type of bugs that KHWASAN can detect
compared to KASAN: use-after-free after the object has been allocated by
someone else.
====== Testing
Some kernel developers voiced a concern that changing the top byte of
kernel pointers may lead to subtle bugs that are difficult to discover.
To address this concern deliberate testing has been performed.
It doesn't seem feasible to do some kind of static checking to find
potential issues with pointer tagging, so a dynamic approach was taken.
All pointer comparisons/subtractions have been instrumented in an LLVM
compiler pass and a kernel module that would print a bug report whenever
two pointers with different tags are being compared/subtracted (ignoring
comparisons with NULL pointers and with pointers obtained by casting an
error code to a pointer type) has been used. Then the kernel has been
booted in QEMU and on an Odroid C2 board and syzkaller has been run.
This yielded the following results.
The two places that look interesting are:
is_vmalloc_addr in include/linux/mm.h
is_kernel_rodata in mm/util.c
Here we compare a pointer with some fixed untagged values to make sure
that the pointer lies in a particular part of the kernel address space.
Since KWHASAN doesn't add tags to pointers that belong to rodata or
vmalloc regions, this should work as is. To make sure debug checks to
those two functions that check that the result doesn't change whether
we operate on pointers with or without untagging has been added.
A few other cases that don't look that interesting:
Comparing pointers to achieve unique sorting order of pointee objects
(e.g. sorting locks addresses before performing a double lock):
tty_ldisc_lock_pair_timeout in drivers/tty/tty_ldisc.c
pipe_double_lock in fs/pipe.c
unix_state_double_lock in net/unix/af_unix.c
lock_two_nondirectories in fs/inode.c
mutex_lock_double in kernel/events/core.c
ep_cmp_ffd in fs/eventpoll.c
fsnotify_compare_groups fs/notify/mark.c
Nothing needs to be done here, since the tags embedded into pointers
don't change, so the sorting order would still be unique.
Checks that a pointer belongs to some particular allocation:
is_sibling_entry in lib/radix-tree.c
object_is_on_stack in include/linux/sched/task_stack.h
Nothing needs to be done here either, since two pointers can only belong
to the same allocation if they have the same tag.
Overall, since the kernel boots and works, there are no critical bugs.
As for the rest, the traditional kernel testing way (use until fails) is
the only one that looks feasible.
Another point here is that KWHASAN is available under a separate config
option that needs to be deliberately enabled. Even though it might be used
in a "near-production" environment to find bugs that are not found during
fuzzing or running tests, it is still a debug tool.
====== Benchmarks
The following numbers were collected on Odroid C2 board. Both KASAN and
KHWASAN were used in inline instrumentation mode.
Boot time [1]:
* ~1.7 sec for clean kernel
* ~5.0 sec for KASAN
* ~5.0 sec for KHWASAN
Network performance [2]:
* 8.33 Gbits/sec for clean kernel
* 3.17 Gbits/sec for KASAN
* 2.85 Gbits/sec for KHWASAN
Slab memory usage after boot [3]:
* ~40 kb for clean kernel
* ~105 kb (~260% overhead) for KASAN
* ~47 kb (~20% overhead) for KHWASAN
KASAN memory overhead consists of three main parts:
1. Increased slab memory usage due to redzones.
2. Shadow memory (the whole reserved once during boot).
3. Quaratine (grows gradually until some preset limit; the more the limit,
the more the chance to detect a use-after-free).
Comparing KWHASAN vs KASAN for each of these points:
1. 20% vs 260% overhead.
2. 1/16th vs 1/8th of physical memory.
3. KHWASAN doesn't require quarantine.
[1] Time before the ext4 driver is initialized.
[2] Measured as `iperf -s & iperf -c 127.0.0.1 -t 30`.
[3] Measured as `cat /proc/meminfo | grep Slab`.
====== Some notes
A few notes:
1. The patchset can be found here:
https://github.com/xairy/kasan-prototype/tree/khwasan
2. Building requires a recent LLVM version (r330044 or later).
3. Stack instrumentation is not supported yet and will be added later.
====== Changes
Changes in v6:
- Rebased onto 050cdc6c (4.19-rc1+).
- Added notes regarding patchset testing into the cover letter.
Changes in v5:
- Rebased onto 1ffaddd029 (4.18-rc8).
- Preassign tags for objects from caches with constructors and
SLAB_TYPESAFE_BY_RCU caches.
- Fix SLAB allocator support by untagging page->s_mem in
kasan_poison_slab().
- Performed dynamic testing to find potential places where pointer tagging
might result in bugs [1].
- Clarified and fixed memory usage benchmarks in the cover letter.
- Added a rationale for having KHWASAN to the cover letter.
Changes in v4:
- Fixed SPDX comment style in mm/kasan/kasan.h.
- Fixed mm/kasan/kasan.h changes being included in a wrong patch.
- Swapped "khwasan, arm64: fix up fault handling logic" and "khwasan: add
tag related helper functions" patches order.
- Rebased onto 6f0d349d (4.18-rc2+).
Changes in v3:
- Minor documentation fixes.
- Fixed CFLAGS variable name in KASAN makefile.
- Added a "SPDX-License-Identifier: GPL-2.0" line to all source files
under mm/kasan.
- Rebased onto 81e97f013 (4.18-rc1+).
Changes in v2:
- Changed kmalloc_large_node_hook to return tagged pointer instead of
using an output argument.
- Fix checking whether -fsanitize=hwaddress is supported by the compiler.
- Removed duplication of -fno-builtin for KASAN and KHWASAN.
- Removed {} block for one line for_each_possible_cpu loop.
- Made set_track() static inline as it is used only in common.c.
- Moved optimal_redzone() to common.c.
- Fixed using tagged pointer for shadow calculation in
kasan_unpoison_shadow().
- Restored setting cache->align in kasan_cache_create(), which was
accidentally lost.
- Simplified __kasan_slab_free(), kasan_alloc_pages() and kasan_kmalloc().
- Removed tagging from kasan_kmalloc_large().
- Added page_kasan_tag_reset() to kasan_poison_slab() and removed
!PageSlab() check from page_to_virt.
- Reset pointer tag in _virt_addr_is_linear.
- Set page tag for each page when multiple pages are allocated or freed.
- Added a comment as to why we ignore cma allocated pages.
Changes in v1:
- Rebased onto 4.17-rc4.
- Updated benchmarking stats.
- Documented compiler version requirements, memory usage and slowdown.
- Dropped kvm patches, as clang + arm64 + kvm is completely broken [1].
Changes in RFC v3:
- Renamed CONFIG_KASAN_CLASSIC and CONFIG_KASAN_TAGS to
CONFIG_KASAN_GENERIC and CONFIG_KASAN_HW respectively.
- Switch to -fsanitize=kernel-hwaddress instead of -fsanitize=hwaddress.
- Removed unnecessary excessive shadow initialization.
- Removed khwasan_enabled flag (it’s not needed since KHWASAN is
initialized before any slab caches are used).
- Split out kasan_report.c and khwasan_report.c from report.c.
- Moved more common KASAN and KHWASAN functions to common.c.
- Added tagging to pagealloc.
- Rebased onto 4.17-rc1.
- Temporarily dropped patch that adds kvm support (arm64 + kvm + clang
combo is broken right now [2]).
Changes in RFC v2:
- Removed explicit casts to u8 * for kasan_mem_to_shadow() calls.
- Introduced KASAN_TCR_FLAGS for setting the TCR_TBI1 flag.
- Added a comment regarding the non-atomic RMW sequence in
khwasan_random_tag().
- Made all tag related functions accept const void *.
- Untagged pointers in __kimg_to_phys, which is used by virt_to_phys.
- Untagged pointers in show_ptr in fault handling logic.
- Untagged pointers passed to KVM.
- Added two reserved tag values: 0xFF and 0xFE.
- Used the reserved tag 0xFF to disable validity checking (to resolve the
issue with pointer tag being lost after page_address + kmap usage).
- Used the reserved tag 0xFE to mark redzones and freed objects.
- Added mnemonics for esr manipulation in KHWASAN brk handler.
- Added a comment about the -recover flag.
- Some minor cleanups and fixes.
- Rebased onto 3215b9d5 (4.16-rc6+).
- Tested on real hardware (Odroid C2 board).
- Added better benchmarks.
[1] https://lkml.org/lkml/2018/7/18/765
[2] https://lkml.org/lkml/2018/4/19/775
Andrey Konovalov (18):
khwasan, mm: change kasan hooks signatures
khwasan: move common kasan and khwasan code to common.c
khwasan: add CONFIG_KASAN_GENERIC and CONFIG_KASAN_HW
khwasan, arm64: adjust shadow size for CONFIG_KASAN_HW
khwasan: initialize shadow to 0xff
khwasan, arm64: untag virt address in __kimg_to_phys and
_virt_addr_is_linear
khwasan: add tag related helper functions
khwasan: preassign tags to objects with ctors or SLAB_TYPESAFE_BY_RCU
khwasan, arm64: fix up fault handling logic
khwasan, arm64: enable top byte ignore for the kernel
khwasan, mm: perform untagged pointers comparison in krealloc
khwasan: split out kasan_report.c from report.c
khwasan: add bug reporting routines
khwasan: add hooks implementation
khwasan, arm64: add brk handler for inline instrumentation
khwasan, mm, arm64: tag non slab memory allocated via pagealloc
khwasan: update kasan documentation
kasan: add SPDX-License-Identifier mark to source files
Documentation/dev-tools/kasan.rst | 213 ++++----
arch/arm64/Kconfig | 1 +
arch/arm64/Makefile | 2 +-
arch/arm64/include/asm/brk-imm.h | 2 +
arch/arm64/include/asm/memory.h | 41 +-
arch/arm64/include/asm/pgtable-hwdef.h | 1 +
arch/arm64/kernel/traps.c | 69 ++-
arch/arm64/mm/fault.c | 3 +
arch/arm64/mm/kasan_init.c | 18 +-
arch/arm64/mm/proc.S | 8 +-
include/linux/compiler-clang.h | 3 +-
include/linux/compiler-gcc.h | 4 +
include/linux/compiler.h | 3 +-
include/linux/kasan.h | 90 +++-
include/linux/mm.h | 29 ++
include/linux/page-flags-layout.h | 10 +
lib/Kconfig.kasan | 77 ++-
mm/cma.c | 11 +
mm/kasan/Makefile | 9 +-
mm/kasan/common.c | 663 +++++++++++++++++++++++++
mm/kasan/kasan.c | 565 +--------------------
mm/kasan/kasan.h | 85 +++-
mm/kasan/kasan_init.c | 1 +
mm/kasan/kasan_report.c | 156 ++++++
mm/kasan/khwasan.c | 181 +++++++
mm/kasan/khwasan_report.c | 61 +++
mm/kasan/quarantine.c | 1 +
mm/kasan/report.c | 272 +++-------
mm/page_alloc.c | 1 +
mm/slab.c | 18 +-
mm/slab.h | 2 +-
mm/slab_common.c | 6 +-
mm/slub.c | 21 +-
scripts/Makefile.kasan | 27 +-
34 files changed, 1734 insertions(+), 920 deletions(-)
create mode 100644 mm/kasan/common.c
create mode 100644 mm/kasan/kasan_report.c
create mode 100644 mm/kasan/khwasan.c
create mode 100644 mm/kasan/khwasan_report.c
--
2.19.0.rc0.228.g281dcd1b4d0-goog
A KHWASAN shadow memory cell contains a memory tag, that corresponds to
the tag in the top byte of the pointer, that points to that memory. The
native top byte value of kernel pointers is 0xff, so with KHWASAN we
need to initialize shadow memory to 0xff. This commit does that.
Signed-off-by: Andrey Konovalov <[email protected]>
---
arch/arm64/mm/kasan_init.c | 16 ++++++++++++++--
include/linux/kasan.h | 8 ++++++++
mm/kasan/common.c | 3 ++-
3 files changed, 24 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index 12145874c02b..7a31e8ccbad2 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -44,6 +44,15 @@ static phys_addr_t __init kasan_alloc_zeroed_page(int node)
return __pa(p);
}
+static phys_addr_t __init kasan_alloc_raw_page(int node)
+{
+ void *p = memblock_virt_alloc_try_nid_raw(PAGE_SIZE, PAGE_SIZE,
+ __pa(MAX_DMA_ADDRESS),
+ MEMBLOCK_ALLOC_ACCESSIBLE,
+ node);
+ return __pa(p);
+}
+
static pte_t *__init kasan_pte_offset(pmd_t *pmdp, unsigned long addr, int node,
bool early)
{
@@ -89,7 +98,9 @@ static void __init kasan_pte_populate(pmd_t *pmdp, unsigned long addr,
do {
phys_addr_t page_phys = early ? __pa_symbol(kasan_zero_page)
- : kasan_alloc_zeroed_page(node);
+ : kasan_alloc_raw_page(node);
+ if (!early)
+ memset(__va(page_phys), KASAN_SHADOW_INIT, PAGE_SIZE);
next = addr + PAGE_SIZE;
set_pte(ptep, pfn_pte(__phys_to_pfn(page_phys), PAGE_KERNEL));
} while (ptep++, addr = next, addr != end && pte_none(READ_ONCE(*ptep)));
@@ -139,6 +150,7 @@ asmlinkage void __init kasan_early_init(void)
KASAN_SHADOW_END - (1UL << (64 - KASAN_SHADOW_SCALE_SHIFT)));
BUILD_BUG_ON(!IS_ALIGNED(KASAN_SHADOW_START, PGDIR_SIZE));
BUILD_BUG_ON(!IS_ALIGNED(KASAN_SHADOW_END, PGDIR_SIZE));
+
kasan_pgd_populate(KASAN_SHADOW_START, KASAN_SHADOW_END, NUMA_NO_NODE,
true);
}
@@ -235,7 +247,7 @@ void __init kasan_init(void)
set_pte(&kasan_zero_pte[i],
pfn_pte(sym_to_pfn(kasan_zero_page), PAGE_KERNEL_RO));
- memset(kasan_zero_page, 0, PAGE_SIZE);
+ memset(kasan_zero_page, KASAN_SHADOW_INIT, PAGE_SIZE);
cpu_replace_ttbr1(lm_alias(swapper_pg_dir));
/* At this point kasan is fully initialized. Enable error messages */
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index beb56a26fe9b..1c31bb089154 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -150,6 +150,8 @@ static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
#ifdef CONFIG_KASAN_GENERIC
+#define KASAN_SHADOW_INIT 0
+
void kasan_cache_shrink(struct kmem_cache *cache);
void kasan_cache_shutdown(struct kmem_cache *cache);
@@ -160,4 +162,10 @@ static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
#endif /* CONFIG_KASAN_GENERIC */
+#ifdef CONFIG_KASAN_HW
+
+#define KASAN_SHADOW_INIT 0xFF
+
+#endif /* CONFIG_KASAN_HW */
+
#endif /* LINUX_KASAN_H */
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 154010ba6c1f..bed8e13c6e1d 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -474,11 +474,12 @@ int kasan_module_alloc(void *addr, size_t size)
ret = __vmalloc_node_range(shadow_size, 1, shadow_start,
shadow_start + shadow_size,
- GFP_KERNEL | __GFP_ZERO,
+ GFP_KERNEL,
PAGE_KERNEL, VM_NO_GUARD, NUMA_NO_NODE,
__builtin_return_address(0));
if (ret) {
+ __memset(ret, KASAN_SHADOW_INIT, shadow_size);
find_vm_area(addr)->flags |= VM_KASAN;
kmemleak_ignore(ret);
return 0;
--
2.19.0.rc0.228.g281dcd1b4d0-goog
show_pte in arm64 fault handling relies on the fact that the top byte of
a kernel pointer is 0xff, which isn't always the case with KHWASAN enabled.
Reset the top byte.
Signed-off-by: Andrey Konovalov <[email protected]>
---
arch/arm64/mm/fault.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 50b30ff30de4..35feee78a9bd 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -32,6 +32,7 @@
#include <linux/perf_event.h>
#include <linux/preempt.h>
#include <linux/hugetlb.h>
+#include <linux/kasan.h>
#include <asm/bug.h>
#include <asm/cmpxchg.h>
@@ -134,6 +135,8 @@ void show_pte(unsigned long addr)
pgd_t *pgdp;
pgd_t pgd;
+ addr = (unsigned long)khwasan_reset_tag((void *)addr);
+
if (addr < TASK_SIZE) {
/* TTBR0 */
mm = current->active_mm;
--
2.19.0.rc0.228.g281dcd1b4d0-goog
The krealloc function checks where the same buffer was reused or a new one
allocated by comparing kernel pointers. KHWASAN changes memory tag on the
krealloc'ed chunk of memory and therefore also changes the pointer tag of
the returned pointer. Therefore we need to perform comparison on untagged
(with tags reset) pointers to check whether it's the same memory region or
not.
Signed-off-by: Andrey Konovalov <[email protected]>
---
mm/slab_common.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 3abfa0f86118..0d588dfebd7d 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1513,7 +1513,7 @@ void *krealloc(const void *p, size_t new_size, gfp_t flags)
}
ret = __do_krealloc(p, new_size, flags);
- if (ret && p != ret)
+ if (ret && khwasan_reset_tag(p) != khwasan_reset_tag(ret))
kfree(p);
return ret;
--
2.19.0.rc0.228.g281dcd1b4d0-goog
KWHASAN doesn't check memory accesses through pointers tagged with 0xff.
When page_address is used to get pointer to memory that corresponds to
some page, the tag of the resulting pointer gets set to 0xff, even though
the allocated memory might have been tagged differently.
For slab pages it's impossible to recover the correct tag to return from
page_address, since the page might contain multiple slab objects tagged
with different values, and we can't know in advance which one of them is
going to get accessed. For non slab pages however, we can recover the tag
in page_address, since the whole page was marked with the same tag.
This patch adds tagging to non slab memory allocated with pagealloc. To
set the tag of the pointer returned from page_address, the tag gets stored
to page->flags when the memory gets allocated.
Signed-off-by: Andrey Konovalov <[email protected]>
---
arch/arm64/include/asm/memory.h | 10 ++++++++++
include/linux/mm.h | 29 +++++++++++++++++++++++++++++
include/linux/page-flags-layout.h | 10 ++++++++++
mm/cma.c | 11 +++++++++++
mm/kasan/common.c | 17 +++++++++++++++--
mm/page_alloc.c | 1 +
6 files changed, 76 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index f5e2953b7009..ea7f928aba31 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -312,7 +312,17 @@ static inline void *phys_to_virt(phys_addr_t x)
#define __virt_to_pgoff(kaddr) (((u64)(kaddr) & ~PAGE_OFFSET) / PAGE_SIZE * sizeof(struct page))
#define __page_to_voff(kaddr) (((u64)(kaddr) & ~VMEMMAP_START) * PAGE_SIZE / sizeof(struct page))
+#ifndef CONFIG_KASAN_HW
#define page_to_virt(page) ((void *)((__page_to_voff(page)) | PAGE_OFFSET))
+#else
+#define page_to_virt(page) ({ \
+ unsigned long __addr = \
+ ((__page_to_voff(page)) | PAGE_OFFSET); \
+ __addr = KASAN_SET_TAG(__addr, page_kasan_tag(page)); \
+ ((void *)__addr); \
+})
+#endif
+
#define virt_to_page(vaddr) ((struct page *)((__virt_to_pgoff(vaddr)) | VMEMMAP_START))
#define _virt_addr_valid(kaddr) pfn_valid((((u64)(kaddr) & ~PAGE_OFFSET) \
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a61ebe8ad4ca..a1e7c590d925 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -804,6 +804,7 @@ vm_fault_t finish_mkwrite_fault(struct vm_fault *vmf);
#define NODES_PGOFF (SECTIONS_PGOFF - NODES_WIDTH)
#define ZONES_PGOFF (NODES_PGOFF - ZONES_WIDTH)
#define LAST_CPUPID_PGOFF (ZONES_PGOFF - LAST_CPUPID_WIDTH)
+#define KASAN_TAG_PGOFF (LAST_CPUPID_PGOFF - KASAN_TAG_WIDTH)
/*
* Define the bit shifts to access each section. For non-existent
@@ -814,6 +815,7 @@ vm_fault_t finish_mkwrite_fault(struct vm_fault *vmf);
#define NODES_PGSHIFT (NODES_PGOFF * (NODES_WIDTH != 0))
#define ZONES_PGSHIFT (ZONES_PGOFF * (ZONES_WIDTH != 0))
#define LAST_CPUPID_PGSHIFT (LAST_CPUPID_PGOFF * (LAST_CPUPID_WIDTH != 0))
+#define KASAN_TAG_PGSHIFT (KASAN_TAG_PGOFF * (KASAN_TAG_WIDTH != 0))
/* NODE:ZONE or SECTION:ZONE is used to ID a zone for the buddy allocator */
#ifdef NODE_NOT_IN_PAGE_FLAGS
@@ -836,6 +838,7 @@ vm_fault_t finish_mkwrite_fault(struct vm_fault *vmf);
#define NODES_MASK ((1UL << NODES_WIDTH) - 1)
#define SECTIONS_MASK ((1UL << SECTIONS_WIDTH) - 1)
#define LAST_CPUPID_MASK ((1UL << LAST_CPUPID_SHIFT) - 1)
+#define KASAN_TAG_MASK ((1UL << KASAN_TAG_WIDTH) - 1)
#define ZONEID_MASK ((1UL << ZONEID_SHIFT) - 1)
static inline enum zone_type page_zonenum(const struct page *page)
@@ -1081,6 +1084,32 @@ static inline bool cpupid_match_pid(struct task_struct *task, int cpupid)
}
#endif /* CONFIG_NUMA_BALANCING */
+#ifdef CONFIG_KASAN_HW
+static inline u8 page_kasan_tag(const struct page *page)
+{
+ return (page->flags >> KASAN_TAG_PGSHIFT) & KASAN_TAG_MASK;
+}
+
+static inline void page_kasan_tag_set(struct page *page, u8 tag)
+{
+ page->flags &= ~(KASAN_TAG_MASK << KASAN_TAG_PGSHIFT);
+ page->flags |= (tag & KASAN_TAG_MASK) << KASAN_TAG_PGSHIFT;
+}
+
+static inline void page_kasan_tag_reset(struct page *page)
+{
+ page_kasan_tag_set(page, 0xff);
+}
+#else
+static inline u8 page_kasan_tag(const struct page *page)
+{
+ return 0xff;
+}
+
+static inline void page_kasan_tag_set(struct page *page, u8 tag) { }
+static inline void page_kasan_tag_reset(struct page *page) { }
+#endif
+
static inline struct zone *page_zone(const struct page *page)
{
return &NODE_DATA(page_to_nid(page))->node_zones[page_zonenum(page)];
diff --git a/include/linux/page-flags-layout.h b/include/linux/page-flags-layout.h
index 7ec86bf31ce4..8dbad17664c2 100644
--- a/include/linux/page-flags-layout.h
+++ b/include/linux/page-flags-layout.h
@@ -82,6 +82,16 @@
#define LAST_CPUPID_WIDTH 0
#endif
+#ifdef CONFIG_KASAN_HW
+#define KASAN_TAG_WIDTH 8
+#if SECTIONS_WIDTH+NODES_WIDTH+ZONES_WIDTH+LAST_CPUPID_WIDTH+KASAN_TAG_WIDTH \
+ > BITS_PER_LONG - NR_PAGEFLAGS
+#error "KASAN: not enough bits in page flags for tag"
+#endif
+#else
+#define KASAN_TAG_WIDTH 0
+#endif
+
/*
* We are going to use the flags for the page to node mapping if its in
* there. This includes the case where there is no node, so it is implicit.
diff --git a/mm/cma.c b/mm/cma.c
index 4cb76121a3ab..c7b39dd3b4f6 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -407,6 +407,7 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
unsigned long pfn = -1;
unsigned long start = 0;
unsigned long bitmap_maxno, bitmap_no, bitmap_count;
+ size_t i;
struct page *page = NULL;
int ret = -ENOMEM;
@@ -466,6 +467,16 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
trace_cma_alloc(pfn, page, count, align);
+ /*
+ * CMA can allocate multiple page blocks, which results in different
+ * blocks being marked with different tags. Reset the tags to ignore
+ * those page blocks.
+ */
+ if (page) {
+ for (i = 0; i < count; i++)
+ page_kasan_tag_reset(page + i);
+ }
+
if (ret && !no_warn) {
pr_err("%s: alloc failed, req-size: %zu pages, ret: %d\n",
__func__, count, ret);
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 938229b26f3a..e5648f4218eb 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -212,8 +212,15 @@ void kasan_unpoison_stack_above_sp_to(const void *watermark)
void kasan_alloc_pages(struct page *page, unsigned int order)
{
+ u8 tag;
+ unsigned long i;
+
if (unlikely(PageHighMem(page)))
return;
+
+ tag = random_tag();
+ for (i = 0; i < (1 << order); i++)
+ page_kasan_tag_set(page + i, tag);
kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order);
}
@@ -311,6 +318,12 @@ struct kasan_free_meta *get_free_info(struct kmem_cache *cache,
void kasan_poison_slab(struct page *page)
{
+ unsigned long i;
+
+ if (IS_ENABLED(CONFIG_SLAB))
+ page->s_mem = reset_tag(page->s_mem);
+ for (i = 0; i < (1 << compound_order(page)); i++)
+ page_kasan_tag_reset(page + i);
kasan_poison_shadow(page_address(page),
PAGE_SIZE << compound_order(page),
KASAN_KMALLOC_REDZONE);
@@ -484,7 +497,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip)
page = virt_to_head_page(ptr);
if (unlikely(!PageSlab(page))) {
- if (reset_tag(ptr) != page_address(page)) {
+ if (ptr != page_address(page)) {
kasan_report_invalid_free(ptr, ip);
return;
}
@@ -497,7 +510,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip)
void kasan_kfree_large(void *ptr, unsigned long ip)
{
- if (reset_tag(ptr) != page_address(virt_to_head_page(ptr)))
+ if (ptr != page_address(virt_to_head_page(ptr)))
kasan_report_invalid_free(ptr, ip);
/* The object will be poisoned by page_alloc. */
}
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e75865d58ba7..eb5627f89853 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1177,6 +1177,7 @@ static void __meminit __init_single_page(struct page *page, unsigned long pfn,
init_page_count(page);
page_mapcount_reset(page);
page_cpupid_reset_last(page);
+ page_kasan_tag_reset(page);
INIT_LIST_HEAD(&page->lru);
#ifdef WANT_PAGE_VIRTUAL
--
2.19.0.rc0.228.g281dcd1b4d0-goog
KHWASAN inline instrumentation mode (which embeds checks of shadow memory
into the generated code, instead of inserting a callback) generates a brk
instruction when a tag mismatch is detected.
This commit add a KHWASAN brk handler, that decodes the immediate value
passed to the brk instructions (to extract information about the memory
access that triggered the mismatch), reads the register values (x0 contains
the guilty address) and reports the bug.
Signed-off-by: Andrey Konovalov <[email protected]>
---
arch/arm64/include/asm/brk-imm.h | 2 +
arch/arm64/kernel/traps.c | 69 +++++++++++++++++++++++++++++++-
2 files changed, 69 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/include/asm/brk-imm.h b/arch/arm64/include/asm/brk-imm.h
index ed693c5bcec0..e4a7013321dc 100644
--- a/arch/arm64/include/asm/brk-imm.h
+++ b/arch/arm64/include/asm/brk-imm.h
@@ -16,10 +16,12 @@
* 0x400: for dynamic BRK instruction
* 0x401: for compile time BRK instruction
* 0x800: kernel-mode BUG() and WARN() traps
+ * 0x9xx: KHWASAN trap (allowed values 0x900 - 0x9ff)
*/
#define FAULT_BRK_IMM 0x100
#define KGDB_DYN_DBG_BRK_IMM 0x400
#define KGDB_COMPILED_DBG_BRK_IMM 0x401
#define BUG_BRK_IMM 0x800
+#define KHWASAN_BRK_IMM 0x900
#endif
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 039e9ff379cc..fd70347d1ce7 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -35,6 +35,7 @@
#include <linux/sizes.h>
#include <linux/syscalls.h>
#include <linux/mm_types.h>
+#include <linux/kasan.h>
#include <asm/atomic.h>
#include <asm/bug.h>
@@ -269,10 +270,14 @@ void arm64_notify_die(const char *str, struct pt_regs *regs,
}
}
-void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
+void __arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
{
regs->pc += size;
+}
+void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
+{
+ __arm64_skip_faulting_instruction(regs, size);
/*
* If we were single stepping, we want to get the step exception after
* we return from the trap.
@@ -775,7 +780,7 @@ static int bug_handler(struct pt_regs *regs, unsigned int esr)
}
/* If thread survives, skip over the BUG instruction and continue: */
- arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
+ __arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
return DBG_HOOK_HANDLED;
}
@@ -785,6 +790,59 @@ static struct break_hook bug_break_hook = {
.fn = bug_handler,
};
+#ifdef CONFIG_KASAN_HW
+
+#define KHWASAN_ESR_RECOVER 0x20
+#define KHWASAN_ESR_WRITE 0x10
+#define KHWASAN_ESR_SIZE_MASK 0x0f
+#define KHWASAN_ESR_SIZE(esr) (1 << ((esr) & KHWASAN_ESR_SIZE_MASK))
+
+static int khwasan_handler(struct pt_regs *regs, unsigned int esr)
+{
+ bool recover = esr & KHWASAN_ESR_RECOVER;
+ bool write = esr & KHWASAN_ESR_WRITE;
+ size_t size = KHWASAN_ESR_SIZE(esr);
+ u64 addr = regs->regs[0];
+ u64 pc = regs->pc;
+
+ if (user_mode(regs))
+ return DBG_HOOK_ERROR;
+
+ kasan_report(addr, size, write, pc);
+
+ /*
+ * The instrumentation allows to control whether we can proceed after
+ * a crash was detected. This is done by passing the -recover flag to
+ * the compiler. Disabling recovery allows to generate more compact
+ * code.
+ *
+ * Unfortunately disabling recovery doesn't work for the kernel right
+ * now. KHWASAN reporting is disabled in some contexts (for example when
+ * the allocator accesses slab object metadata; same is true for KASAN;
+ * this is controlled by current->kasan_depth). All these accesses are
+ * detected by the tool, even though the reports for them are not
+ * printed.
+ *
+ * This is something that might be fixed at some point in the future.
+ */
+ if (!recover)
+ die("Oops - KHWASAN", regs, 0);
+
+ /* If thread survives, skip over the brk instruction and continue: */
+ __arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
+ return DBG_HOOK_HANDLED;
+}
+
+#define KHWASAN_ESR_VAL (0xf2000000 | KHWASAN_BRK_IMM)
+#define KHWASAN_ESR_MASK 0xffffff00
+
+static struct break_hook khwasan_break_hook = {
+ .esr_val = KHWASAN_ESR_VAL,
+ .esr_mask = KHWASAN_ESR_MASK,
+ .fn = khwasan_handler,
+};
+#endif
+
/*
* Initial handler for AArch64 BRK exceptions
* This handler only used until debug_traps_init().
@@ -792,6 +850,10 @@ static struct break_hook bug_break_hook = {
int __init early_brk64(unsigned long addr, unsigned int esr,
struct pt_regs *regs)
{
+#ifdef CONFIG_KASAN_HW
+ if ((esr & KHWASAN_ESR_MASK) == KHWASAN_ESR_VAL)
+ return khwasan_handler(regs, esr) != DBG_HOOK_HANDLED;
+#endif
return bug_handler(regs, esr) != DBG_HOOK_HANDLED;
}
@@ -799,4 +861,7 @@ int __init early_brk64(unsigned long addr, unsigned int esr,
void __init trap_init(void)
{
register_break_hook(&bug_break_hook);
+#ifdef CONFIG_KASAN_HW
+ register_break_hook(&khwasan_break_hook);
+#endif
}
--
2.19.0.rc0.228.g281dcd1b4d0-goog
This patch updates KASAN documentation to reflect the addition of KHWASAN.
Signed-off-by: Andrey Konovalov <[email protected]>
---
Documentation/dev-tools/kasan.rst | 213 +++++++++++++++++-------------
1 file changed, 123 insertions(+), 90 deletions(-)
diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index aabc8738b3d8..842d95af74d3 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -8,11 +8,19 @@ KernelAddressSANitizer (KASAN) is a dynamic memory error detector. It provides
a fast and comprehensive solution for finding use-after-free and out-of-bounds
bugs.
-KASAN uses compile-time instrumentation for checking every memory access,
-therefore you will need a GCC version 4.9.2 or later. GCC 5.0 or later is
-required for detection of out-of-bounds accesses to stack or global variables.
+KASAN has two modes: classic KASAN (a classic version, similar to user space
+ASan) and KHWASAN (a version based on memory tagging, similar to user space
+HWASan).
-Currently KASAN is supported only for the x86_64 and arm64 architectures.
+KASAN uses compile-time instrumentation to insert validity checks before every
+memory access, and therefore requires a compiler version that supports that.
+For classic KASAN you need GCC version 4.9.2 or later. GCC 5.0 or later is
+required for detection of out-of-bounds accesses on stack and global variables.
+KHWASAN in turns is only supported in clang and requires revision 330044 or
+later.
+
+Currently classic KASAN is supported for the x86_64, arm64 and xtensa
+architectures, and KHWASAN is supported only for arm64.
Usage
-----
@@ -21,12 +29,14 @@ To enable KASAN configure kernel with::
CONFIG_KASAN = y
-and choose between CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE. Outline and
-inline are compiler instrumentation types. The former produces smaller binary
-the latter is 1.1 - 2 times faster. Inline instrumentation requires a GCC
+and choose between CONFIG_KASAN_GENERIC (to enable classic KASAN) and
+CONFIG_KASAN_HW (to enabled KHWASAN). You also need to choose choose between
+CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE. Outline and inline are compiler
+instrumentation types. The former produces smaller binary while the latter is
+1.1 - 2 times faster. For classic KASAN inline instrumentation requires GCC
version 5.0 or later.
-KASAN works with both SLUB and SLAB memory allocators.
+Both KASAN modes work with both SLUB and SLAB memory allocators.
For better bug detection and nicer reporting, enable CONFIG_STACKTRACE.
To disable instrumentation for specific files or directories, add a line
@@ -43,85 +53,80 @@ similar to the following to the respective kernel Makefile:
Error reports
~~~~~~~~~~~~~
-A typical out of bounds access report looks like this::
+A typical out-of-bounds access classic KASAN report looks like this::
==================================================================
- BUG: AddressSanitizer: out of bounds access in kmalloc_oob_right+0x65/0x75 [test_kasan] at addr ffff8800693bc5d3
- Write of size 1 by task modprobe/1689
- =============================================================================
- BUG kmalloc-128 (Not tainted): kasan error
- -----------------------------------------------------------------------------
-
- Disabling lock debugging due to kernel taint
- INFO: Allocated in kmalloc_oob_right+0x3d/0x75 [test_kasan] age=0 cpu=0 pid=1689
- __slab_alloc+0x4b4/0x4f0
- kmem_cache_alloc_trace+0x10b/0x190
- kmalloc_oob_right+0x3d/0x75 [test_kasan]
- init_module+0x9/0x47 [test_kasan]
- do_one_initcall+0x99/0x200
- load_module+0x2cb3/0x3b20
- SyS_finit_module+0x76/0x80
- system_call_fastpath+0x12/0x17
- INFO: Slab 0xffffea0001a4ef00 objects=17 used=7 fp=0xffff8800693bd728 flags=0x100000000004080
- INFO: Object 0xffff8800693bc558 @offset=1368 fp=0xffff8800693bc720
-
- Bytes b4 ffff8800693bc548: 00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ
- Object ffff8800693bc558: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
- Object ffff8800693bc568: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
- Object ffff8800693bc578: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
- Object ffff8800693bc588: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
- Object ffff8800693bc598: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
- Object ffff8800693bc5a8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
- Object ffff8800693bc5b8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
- Object ffff8800693bc5c8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5 kkkkkkkkkkkkkkk.
- Redzone ffff8800693bc5d8: cc cc cc cc cc cc cc cc ........
- Padding ffff8800693bc718: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ
- CPU: 0 PID: 1689 Comm: modprobe Tainted: G B 3.18.0-rc1-mm1+ #98
- Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014
- ffff8800693bc000 0000000000000000 ffff8800693bc558 ffff88006923bb78
- ffffffff81cc68ae 00000000000000f3 ffff88006d407600 ffff88006923bba8
- ffffffff811fd848 ffff88006d407600 ffffea0001a4ef00 ffff8800693bc558
+ BUG: KASAN: slab-out-of-bounds in kmalloc_oob_right+0xa8/0xbc [test_kasan]
+ Write of size 1 at addr ffff8800696f3d3b by task insmod/2734
+
+ CPU: 0 PID: 2734 Comm: insmod Not tainted 4.15.0+ #98
+ Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
Call Trace:
- [<ffffffff81cc68ae>] dump_stack+0x46/0x58
- [<ffffffff811fd848>] print_trailer+0xf8/0x160
- [<ffffffffa00026a7>] ? kmem_cache_oob+0xc3/0xc3 [test_kasan]
- [<ffffffff811ff0f5>] object_err+0x35/0x40
- [<ffffffffa0002065>] ? kmalloc_oob_right+0x65/0x75 [test_kasan]
- [<ffffffff8120b9fa>] kasan_report_error+0x38a/0x3f0
- [<ffffffff8120a79f>] ? kasan_poison_shadow+0x2f/0x40
- [<ffffffff8120b344>] ? kasan_unpoison_shadow+0x14/0x40
- [<ffffffff8120a79f>] ? kasan_poison_shadow+0x2f/0x40
- [<ffffffffa00026a7>] ? kmem_cache_oob+0xc3/0xc3 [test_kasan]
- [<ffffffff8120a995>] __asan_store1+0x75/0xb0
- [<ffffffffa0002601>] ? kmem_cache_oob+0x1d/0xc3 [test_kasan]
- [<ffffffffa0002065>] ? kmalloc_oob_right+0x65/0x75 [test_kasan]
- [<ffffffffa0002065>] kmalloc_oob_right+0x65/0x75 [test_kasan]
- [<ffffffffa00026b0>] init_module+0x9/0x47 [test_kasan]
- [<ffffffff810002d9>] do_one_initcall+0x99/0x200
- [<ffffffff811e4e5c>] ? __vunmap+0xec/0x160
- [<ffffffff81114f63>] load_module+0x2cb3/0x3b20
- [<ffffffff8110fd70>] ? m_show+0x240/0x240
- [<ffffffff81115f06>] SyS_finit_module+0x76/0x80
- [<ffffffff81cd3129>] system_call_fastpath+0x12/0x17
+ __dump_stack lib/dump_stack.c:17
+ dump_stack+0x83/0xbc lib/dump_stack.c:53
+ print_address_description+0x73/0x280 mm/kasan/report.c:254
+ kasan_report_error mm/kasan/report.c:352
+ kasan_report+0x10e/0x220 mm/kasan/report.c:410
+ __asan_report_store1_noabort+0x17/0x20 mm/kasan/report.c:505
+ kmalloc_oob_right+0xa8/0xbc [test_kasan] lib/test_kasan.c:42
+ kmalloc_tests_init+0x16/0x769 [test_kasan]
+ do_one_initcall+0x9e/0x240 init/main.c:832
+ do_init_module+0x1b6/0x542 kernel/module.c:3462
+ load_module+0x6042/0x9030 kernel/module.c:3786
+ SYSC_init_module+0x18f/0x1c0 kernel/module.c:3858
+ SyS_init_module+0x9/0x10 kernel/module.c:3841
+ do_syscall_64+0x198/0x480 arch/x86/entry/common.c:287
+ entry_SYSCALL_64_after_hwframe+0x21/0x86 arch/x86/entry/entry_64.S:251
+ RIP: 0033:0x7fdd79df99da
+ RSP: 002b:00007fff2229bdf8 EFLAGS: 00000202 ORIG_RAX: 00000000000000af
+ RAX: ffffffffffffffda RBX: 000055c408121190 RCX: 00007fdd79df99da
+ RDX: 00007fdd7a0b8f88 RSI: 0000000000055670 RDI: 00007fdd7a47e000
+ RBP: 000055c4081200b0 R08: 0000000000000003 R09: 0000000000000000
+ R10: 00007fdd79df5d0a R11: 0000000000000202 R12: 00007fdd7a0b8f88
+ R13: 000055c408120090 R14: 0000000000000000 R15: 0000000000000000
+
+ Allocated by task 2734:
+ save_stack+0x43/0xd0 mm/kasan/common.c:176
+ set_track+0x20/0x30 mm/kasan/common.c:188
+ kasan_kmalloc+0x9a/0xc0 mm/kasan/kasan.c:372
+ kmem_cache_alloc_trace+0xcd/0x1a0 mm/slub.c:2761
+ kmalloc ./include/linux/slab.h:512
+ kmalloc_oob_right+0x56/0xbc [test_kasan] lib/test_kasan.c:36
+ kmalloc_tests_init+0x16/0x769 [test_kasan]
+ do_one_initcall+0x9e/0x240 init/main.c:832
+ do_init_module+0x1b6/0x542 kernel/module.c:3462
+ load_module+0x6042/0x9030 kernel/module.c:3786
+ SYSC_init_module+0x18f/0x1c0 kernel/module.c:3858
+ SyS_init_module+0x9/0x10 kernel/module.c:3841
+ do_syscall_64+0x198/0x480 arch/x86/entry/common.c:287
+ entry_SYSCALL_64_after_hwframe+0x21/0x86 arch/x86/entry/entry_64.S:251
+
+ The buggy address belongs to the object at ffff8800696f3cc0
+ which belongs to the cache kmalloc-128 of size 128
+ The buggy address is located 123 bytes inside of
+ 128-byte region [ffff8800696f3cc0, ffff8800696f3d40)
+ The buggy address belongs to the page:
+ page:ffffea0001a5bcc0 count:1 mapcount:0 mapping: (null) index:0x0
+ flags: 0x100000000000100(slab)
+ raw: 0100000000000100 0000000000000000 0000000000000000 0000000180150015
+ raw: ffffea0001a8ce40 0000000300000003 ffff88006d001640 0000000000000000
+ page dumped because: kasan: bad access detected
+
Memory state around the buggy address:
- ffff8800693bc300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
- ffff8800693bc380: fc fc 00 00 00 00 00 00 00 00 00 00 00 00 00 fc
- ffff8800693bc400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
- ffff8800693bc480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
- ffff8800693bc500: fc fc fc fc fc fc fc fc fc fc fc 00 00 00 00 00
- >ffff8800693bc580: 00 00 00 00 00 00 00 00 00 00 03 fc fc fc fc fc
- ^
- ffff8800693bc600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
- ffff8800693bc680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
- ffff8800693bc700: fc fc fc fc fb fb fb fb fb fb fb fb fb fb fb fb
- ffff8800693bc780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
- ffff8800693bc800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
+ ffff8800696f3c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fc
+ ffff8800696f3c80: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
+ >ffff8800696f3d00: 00 00 00 00 00 00 00 03 fc fc fc fc fc fc fc fc
+ ^
+ ffff8800696f3d80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fc fc
+ ffff8800696f3e00: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
==================================================================
-The header of the report discribe what kind of bug happened and what kind of
-access caused it. It's followed by the description of the accessed slub object
-(see 'SLUB Debug output' section in Documentation/vm/slub.rst for details) and
-the description of the accessed memory page.
+The header of the report provides a short summary of what kind of bug happened
+and what kind of access caused it. It's followed by a stack trace of the bad
+access, a stack trace of where the accessed memory was allocated (in case bad
+access happens on a slab object), and a stack trace of where the object was
+freed (in case of a use-after-free bug report). Next comes a description of
+the accessed slab object and information about the accessed memory page.
In the last section the report shows memory state around the accessed address.
Reading this part requires some understanding of how KASAN works.
@@ -138,18 +143,24 @@ inaccessible memory like redzones or freed memory (see mm/kasan/kasan.h).
In the report above the arrows point to the shadow byte 03, which means that
the accessed address is partially accessible.
+For KHWASAN this last report section shows the memory tags around the accessed
+address (see Implementation details section).
+
Implementation details
----------------------
+Classic KASAN
+~~~~~~~~~~~~~
+
From a high level, our approach to memory error detection is similar to that
of kmemcheck: use shadow memory to record whether each byte of memory is safe
-to access, and use compile-time instrumentation to check shadow memory on each
-memory access.
+to access, and use compile-time instrumentation to insert checks of shadow
+memory on each memory access.
-AddressSanitizer dedicates 1/8 of kernel memory to its shadow memory
-(e.g. 16TB to cover 128TB on x86_64) and uses direct mapping with a scale and
-offset to translate a memory address to its corresponding shadow address.
+Classic KASAN dedicates 1/8th of kernel memory to its shadow memory (e.g. 16TB
+to cover 128TB on x86_64) and uses direct mapping with a scale and offset to
+translate a memory address to its corresponding shadow address.
Here is the function which translates an address to its corresponding shadow
address::
@@ -162,12 +173,34 @@ address::
where ``KASAN_SHADOW_SCALE_SHIFT = 3``.
-Compile-time instrumentation used for checking memory accesses. Compiler inserts
-function calls (__asan_load*(addr), __asan_store*(addr)) before each memory
-access of size 1, 2, 4, 8 or 16. These functions check whether memory access is
-valid or not by checking corresponding shadow memory.
+Compile-time instrumentation is used to insert memory access checks. Compiler
+inserts function calls (__asan_load*(addr), __asan_store*(addr)) before each
+memory access of size 1, 2, 4, 8 or 16. These functions check whether memory
+access is valid or not by checking corresponding shadow memory.
GCC 5.0 has possibility to perform inline instrumentation. Instead of making
function calls GCC directly inserts the code to check the shadow memory.
This option significantly enlarges kernel but it gives x1.1-x2 performance
boost over outline instrumented kernel.
+
+KHWASAN
+~~~~~~~
+
+KHWASAN uses the Top Byte Ignore (TBI) feature of modern arm64 CPUs to store
+a pointer tag in the top byte of kernel pointers. KHWASAN also uses shadow
+memory to store memory tags associated with each 16-byte memory cell (therefore
+it dedicates 1/16th of the kernel memory for shadow memory).
+
+On each memory allocation KHWASAN generates a random tag, tags allocated memory
+with this tag, and embeds this tag into the returned pointer. KHWASAN uses
+compile-time instrumentation to insert checks before each memory access. These
+checks make sure that tag of the memory that is being accessed is equal to tag
+of the pointer that is used to access this memory. In case of a tag mismatch
+KHWASAN prints a bug report.
+
+KHWASAN also has two instrumentation modes (outline, that emits callbacks to
+check memory accesses; and inline, that performs the shadow memory checks
+inline). With outline instrumentation mode, a bug report is simply printed
+from the function that performs the access check. With inline instrumentation
+a brk instruction is emitted by the compiler, and a dedicated brk handler is
+used to print KHWASAN reports.
--
2.19.0.rc0.228.g281dcd1b4d0-goog
This commit adds KHWASAN specific hooks implementation and adjusts
common KASAN and KHWASAN ones.
1. When a new slab cache is created, KHWASAN rounds up the size of the
objects in this cache to KASAN_SHADOW_SCALE_SIZE (== 16).
2. On each kmalloc KHWASAN generates a random tag, sets the shadow memory,
that corresponds to this object to this tag, and embeds this tag value
into the top byte of the returned pointer.
3. On each kfree KHWASAN poisons the shadow memory with a random tag to
allow detection of use-after-free bugs.
The rest of the logic of the hook implementation is very much similar to
the one provided by KASAN. KHWASAN saves allocation and free stack metadata
to the slab object the same was KASAN does this.
Signed-off-by: Andrey Konovalov <[email protected]>
---
mm/kasan/common.c | 82 +++++++++++++++++++++++++++++++++++-----------
mm/kasan/kasan.h | 8 +++++
mm/kasan/khwasan.c | 40 ++++++++++++++++++++++
3 files changed, 111 insertions(+), 19 deletions(-)
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index bed8e13c6e1d..938229b26f3a 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -140,6 +140,9 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value)
{
void *shadow_start, *shadow_end;
+ /* Perform shadow offset calculation based on untagged address */
+ address = reset_tag(address);
+
shadow_start = kasan_mem_to_shadow(address);
shadow_end = kasan_mem_to_shadow(address + size);
@@ -148,11 +151,20 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value)
void kasan_unpoison_shadow(const void *address, size_t size)
{
- kasan_poison_shadow(address, size, 0);
+ u8 tag = get_tag(address);
+
+ /* Perform shadow offset calculation based on untagged address */
+ address = reset_tag(address);
+
+ kasan_poison_shadow(address, size, tag);
if (size & KASAN_SHADOW_MASK) {
u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size);
- *shadow = size & KASAN_SHADOW_MASK;
+
+ if (IS_ENABLED(CONFIG_KASAN_HW))
+ *shadow = tag;
+ else
+ *shadow = size & KASAN_SHADOW_MASK;
}
}
@@ -200,8 +212,9 @@ void kasan_unpoison_stack_above_sp_to(const void *watermark)
void kasan_alloc_pages(struct page *page, unsigned int order)
{
- if (likely(!PageHighMem(page)))
- kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order);
+ if (unlikely(PageHighMem(page)))
+ return;
+ kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order);
}
void kasan_free_pages(struct page *page, unsigned int order)
@@ -235,6 +248,7 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
slab_flags_t *flags)
{
unsigned int orig_size = *size;
+ unsigned int redzone_size = 0;
int redzone_adjust;
/* Add alloc meta. */
@@ -242,20 +256,20 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
*size += sizeof(struct kasan_alloc_meta);
/* Add free meta. */
- if (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
- cache->object_size < sizeof(struct kasan_free_meta)) {
+ if (IS_ENABLED(CONFIG_KASAN_GENERIC) &&
+ (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
+ cache->object_size < sizeof(struct kasan_free_meta))) {
cache->kasan_info.free_meta_offset = *size;
*size += sizeof(struct kasan_free_meta);
}
- redzone_adjust = optimal_redzone(cache->object_size) -
- (*size - cache->object_size);
+ redzone_size = optimal_redzone(cache->object_size);
+ redzone_adjust = redzone_size - (*size - cache->object_size);
if (redzone_adjust > 0)
*size += redzone_adjust;
*size = min_t(unsigned int, KMALLOC_MAX_SIZE,
- max(*size, cache->object_size +
- optimal_redzone(cache->object_size)));
+ max(*size, cache->object_size + redzone_size));
/*
* If the metadata doesn't fit, don't enable KASAN at all.
@@ -268,6 +282,8 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
return;
}
+ cache->align = round_up(cache->align, KASAN_SHADOW_SCALE_SIZE);
+
*flags |= SLAB_KASAN;
}
@@ -328,15 +344,30 @@ void *kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags)
return kasan_kmalloc(cache, object, cache->object_size, flags);
}
+static inline bool shadow_invalid(u8 tag, s8 shadow_byte)
+{
+ if (IS_ENABLED(CONFIG_KASAN_GENERIC))
+ return shadow_byte < 0 ||
+ shadow_byte >= KASAN_SHADOW_SCALE_SIZE;
+ else
+ return tag != (u8)shadow_byte;
+}
+
static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
unsigned long ip, bool quarantine)
{
s8 shadow_byte;
+ u8 tag;
+ void *tagged_object;
unsigned long rounded_up_size;
+ tag = get_tag(object);
+ tagged_object = object;
+ object = reset_tag(object);
+
if (unlikely(nearest_obj(cache, virt_to_head_page(object), object) !=
object)) {
- kasan_report_invalid_free(object, ip);
+ kasan_report_invalid_free(tagged_object, ip);
return true;
}
@@ -345,20 +376,22 @@ static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
return false;
shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
- if (shadow_byte < 0 || shadow_byte >= KASAN_SHADOW_SCALE_SIZE) {
- kasan_report_invalid_free(object, ip);
+ if (shadow_invalid(tag, shadow_byte)) {
+ kasan_report_invalid_free(tagged_object, ip);
return true;
}
rounded_up_size = round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE);
kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE);
- if (!quarantine || unlikely(!(cache->flags & SLAB_KASAN)))
+ if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine) ||
+ unlikely(!(cache->flags & SLAB_KASAN)))
return false;
set_track(&get_alloc_info(cache, object)->free_track, GFP_NOWAIT);
quarantine_put(get_free_info(cache, object), cache);
- return true;
+
+ return IS_ENABLED(CONFIG_KASAN_GENERIC);
}
bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
@@ -371,6 +404,7 @@ void *kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
{
unsigned long redzone_start;
unsigned long redzone_end;
+ u8 tag;
if (gfpflags_allow_blocking(flags))
quarantine_reduce();
@@ -383,14 +417,24 @@ void *kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
redzone_end = round_up((unsigned long)object + cache->object_size,
KASAN_SHADOW_SCALE_SIZE);
- kasan_unpoison_shadow(object, size);
+ /*
+ * Objects with contructors and objects from SLAB_TYPESAFE_BY_RCU slabs
+ * have tags preassigned and are already tagged.
+ */
+ if (IS_ENABLED(CONFIG_KASAN_HW) &&
+ (cache->ctor || cache->flags & SLAB_TYPESAFE_BY_RCU))
+ tag = get_tag(object);
+ else
+ tag = random_tag();
+
+ kasan_unpoison_shadow(set_tag(object, tag), size);
kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
KASAN_KMALLOC_REDZONE);
if (cache->flags & SLAB_KASAN)
set_track(&get_alloc_info(cache, object)->alloc_track, flags);
- return (void *)object;
+ return set_tag(object, tag);
}
EXPORT_SYMBOL(kasan_kmalloc);
@@ -440,7 +484,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip)
page = virt_to_head_page(ptr);
if (unlikely(!PageSlab(page))) {
- if (ptr != page_address(page)) {
+ if (reset_tag(ptr) != page_address(page)) {
kasan_report_invalid_free(ptr, ip);
return;
}
@@ -453,7 +497,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip)
void kasan_kfree_large(void *ptr, unsigned long ip)
{
- if (ptr != page_address(virt_to_head_page(ptr)))
+ if (reset_tag(ptr) != page_address(virt_to_head_page(ptr)))
kasan_report_invalid_free(ptr, ip);
/* The object will be poisoned by page_alloc. */
}
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index d60859d26be7..6f4f2ebf5f57 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -12,10 +12,18 @@
#define KHWASAN_TAG_INVALID 0xFE /* inaccessible memory tag */
#define KHWASAN_TAG_MAX 0xFD /* maximum value for random tags */
+#ifdef CONFIG_KASAN_GENERIC
#define KASAN_FREE_PAGE 0xFF /* page was freed */
#define KASAN_PAGE_REDZONE 0xFE /* redzone for kmalloc_large allocations */
#define KASAN_KMALLOC_REDZONE 0xFC /* redzone inside slub object */
#define KASAN_KMALLOC_FREE 0xFB /* object was freed (kmem_cache_free/kfree) */
+#else
+#define KASAN_FREE_PAGE KHWASAN_TAG_INVALID
+#define KASAN_PAGE_REDZONE KHWASAN_TAG_INVALID
+#define KASAN_KMALLOC_REDZONE KHWASAN_TAG_INVALID
+#define KASAN_KMALLOC_FREE KHWASAN_TAG_INVALID
+#endif
+
#define KASAN_GLOBAL_REDZONE 0xFA /* redzone for global variable */
/*
diff --git a/mm/kasan/khwasan.c b/mm/kasan/khwasan.c
index 9d91bf3c8246..6b1309278e39 100644
--- a/mm/kasan/khwasan.c
+++ b/mm/kasan/khwasan.c
@@ -106,15 +106,52 @@ void *khwasan_preset_slab_tag(struct kmem_cache *cache, unsigned int idx,
void check_memory_region(unsigned long addr, size_t size, bool write,
unsigned long ret_ip)
{
+ u8 tag;
+ u8 *shadow_first, *shadow_last, *shadow;
+ void *untagged_addr;
+
+ tag = get_tag((const void *)addr);
+
+ /* Ignore accesses for pointers tagged with 0xff (native kernel
+ * pointer tag) to suppress false positives caused by kmap.
+ *
+ * Some kernel code was written to account for archs that don't keep
+ * high memory mapped all the time, but rather map and unmap particular
+ * pages when needed. Instead of storing a pointer to the kernel memory,
+ * this code saves the address of the page structure and offset within
+ * that page for later use. Those pages are then mapped and unmapped
+ * with kmap/kunmap when necessary and virt_to_page is used to get the
+ * virtual address of the page. For arm64 (that keeps the high memory
+ * mapped all the time), kmap is turned into a page_address call.
+
+ * The issue is that with use of the page_address + virt_to_page
+ * sequence the top byte value of the original pointer gets lost (gets
+ * set to KHWASAN_TAG_KERNEL (0xFF).
+ */
+ if (tag == KHWASAN_TAG_KERNEL)
+ return;
+
+ untagged_addr = reset_tag((const void *)addr);
+ shadow_first = kasan_mem_to_shadow(untagged_addr);
+ shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1);
+
+ for (shadow = shadow_first; shadow <= shadow_last; shadow++) {
+ if (*shadow != tag) {
+ kasan_report(addr, size, write, ret_ip);
+ return;
+ }
+ }
}
#define DEFINE_HWASAN_LOAD_STORE(size) \
void __hwasan_load##size##_noabort(unsigned long addr) \
{ \
+ check_memory_region(addr, size, false, _RET_IP_); \
} \
EXPORT_SYMBOL(__hwasan_load##size##_noabort); \
void __hwasan_store##size##_noabort(unsigned long addr) \
{ \
+ check_memory_region(addr, size, true, _RET_IP_); \
} \
EXPORT_SYMBOL(__hwasan_store##size##_noabort)
@@ -126,15 +163,18 @@ DEFINE_HWASAN_LOAD_STORE(16);
void __hwasan_loadN_noabort(unsigned long addr, unsigned long size)
{
+ check_memory_region(addr, size, false, _RET_IP_);
}
EXPORT_SYMBOL(__hwasan_loadN_noabort);
void __hwasan_storeN_noabort(unsigned long addr, unsigned long size)
{
+ check_memory_region(addr, size, true, _RET_IP_);
}
EXPORT_SYMBOL(__hwasan_storeN_noabort);
void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
{
+ kasan_poison_shadow((void *)addr, size, tag);
}
EXPORT_SYMBOL(__hwasan_tag_memory);
--
2.19.0.rc0.228.g281dcd1b4d0-goog
This patch adds a "SPDX-License-Identifier: GPL-2.0" mark to all source
files under mm/kasan.
Signed-off-by: Andrey Konovalov <[email protected]>
---
mm/kasan/common.c | 1 +
mm/kasan/kasan.c | 1 +
mm/kasan/kasan_init.c | 1 +
mm/kasan/kasan_report.c | 1 +
mm/kasan/khwasan.c | 1 +
mm/kasan/khwasan_report.c | 1 +
mm/kasan/quarantine.c | 1 +
mm/kasan/report.c | 1 +
8 files changed, 8 insertions(+)
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index e5648f4218eb..f2576d93e74c 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
/*
* This file contains common KASAN and KHWASAN code.
*
diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index 44ec228de0a2..128a865c9e05 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
/*
* This file contains core KASAN code.
*
diff --git a/mm/kasan/kasan_init.c b/mm/kasan/kasan_init.c
index 7a2a2f13f86f..b3c068ab2a85 100644
--- a/mm/kasan/kasan_init.c
+++ b/mm/kasan/kasan_init.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
/*
* This file contains some kasan initialization code.
*
diff --git a/mm/kasan/kasan_report.c b/mm/kasan/kasan_report.c
index fdf2d77e3125..48da73f4ef7c 100644
--- a/mm/kasan/kasan_report.c
+++ b/mm/kasan/kasan_report.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
/*
* This file contains KASAN specific error reporting code.
*
diff --git a/mm/kasan/khwasan.c b/mm/kasan/khwasan.c
index 6b1309278e39..934f80b2d22e 100644
--- a/mm/kasan/khwasan.c
+++ b/mm/kasan/khwasan.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
/*
* This file contains core KHWASAN code.
*
diff --git a/mm/kasan/khwasan_report.c b/mm/kasan/khwasan_report.c
index 51238b404b08..4e193546d94e 100644
--- a/mm/kasan/khwasan_report.c
+++ b/mm/kasan/khwasan_report.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
/*
* This file contains KHWASAN specific error reporting code.
*
diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
index 3a8ddf8baf7d..0e4dc1a22615 100644
--- a/mm/kasan/quarantine.c
+++ b/mm/kasan/quarantine.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
/*
* KASAN quarantine.
*
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index e031c78f2e52..633b4b245798 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
/*
* This file contains common KASAN and KHWASAN error reporting code.
*
--
2.19.0.rc0.228.g281dcd1b4d0-goog
This commit adds rountines, that print KHWASAN error reports. Those are
quite similar to KASAN, the difference is:
1. The way KHWASAN finds the first bad shadow cell (with a mismatching
tag). KHWASAN compares memory tags from the shadow memory to the pointer
tag.
2. KHWASAN reports all bugs with the "KASAN: invalid-access" header. This
is done, so various external tools that already parse the kernel logs
looking for KASAN reports wouldn't need to be changed.
Signed-off-by: Andrey Konovalov <[email protected]>
---
include/linux/kasan.h | 3 +++
mm/kasan/kasan.h | 7 +++++
mm/kasan/kasan_report.c | 7 ++---
mm/kasan/khwasan_report.c | 21 +++++++++++++++
mm/kasan/report.c | 57 +++++++++++++++++++++------------------
5 files changed, 64 insertions(+), 31 deletions(-)
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 1f852244e739..4424359a9dfa 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -174,6 +174,9 @@ void *khwasan_preset_slub_tag(struct kmem_cache *cache, const void *addr);
void *khwasan_preset_slab_tag(struct kmem_cache *cache, unsigned int idx,
const void *addr);
+void kasan_report(unsigned long addr, size_t size,
+ bool write, unsigned long ip);
+
#else /* CONFIG_KASAN_HW */
static inline void khwasan_init(void) { }
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 82672473740c..d60859d26be7 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -119,8 +119,15 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value);
void check_memory_region(unsigned long addr, size_t size, bool write,
unsigned long ret_ip);
+void *find_first_bad_addr(void *addr, size_t size);
const char *get_bug_type(struct kasan_access_info *info);
+#ifdef CONFIG_KASAN_HW
+void print_tags(u8 addr_tag, const void *addr);
+#else
+static inline void print_tags(u8 addr_tag, const void *addr) { }
+#endif
+
void kasan_report(unsigned long addr, size_t size,
bool is_write, unsigned long ip);
void kasan_report_invalid_free(void *object, unsigned long ip);
diff --git a/mm/kasan/kasan_report.c b/mm/kasan/kasan_report.c
index 2d8decbecbd5..fdf2d77e3125 100644
--- a/mm/kasan/kasan_report.c
+++ b/mm/kasan/kasan_report.c
@@ -33,10 +33,10 @@
#include "kasan.h"
#include "../slab.h"
-static const void *find_first_bad_addr(const void *addr, size_t size)
+void *find_first_bad_addr(void *addr, size_t size)
{
u8 shadow_val = *(u8 *)kasan_mem_to_shadow(addr);
- const void *first_bad_addr = addr;
+ void *first_bad_addr = addr;
while (!shadow_val && first_bad_addr < addr + size) {
first_bad_addr += KASAN_SHADOW_SCALE_SIZE;
@@ -50,9 +50,6 @@ static const char *get_shadow_bug_type(struct kasan_access_info *info)
const char *bug_type = "unknown-crash";
u8 *shadow_addr;
- info->first_bad_addr = find_first_bad_addr(info->access_addr,
- info->access_size);
-
shadow_addr = (u8 *)kasan_mem_to_shadow(info->first_bad_addr);
/*
diff --git a/mm/kasan/khwasan_report.c b/mm/kasan/khwasan_report.c
index 2edbc3c76be5..51238b404b08 100644
--- a/mm/kasan/khwasan_report.c
+++ b/mm/kasan/khwasan_report.c
@@ -37,3 +37,24 @@ const char *get_bug_type(struct kasan_access_info *info)
{
return "invalid-access";
}
+
+void *find_first_bad_addr(void *addr, size_t size)
+{
+ u8 tag = get_tag(addr);
+ void *untagged_addr = reset_tag(addr);
+ u8 *shadow = (u8 *)kasan_mem_to_shadow(untagged_addr);
+ void *first_bad_addr = untagged_addr;
+
+ while (*shadow == tag && first_bad_addr < untagged_addr + size) {
+ first_bad_addr += KASAN_SHADOW_SCALE_SIZE;
+ shadow = (u8 *)kasan_mem_to_shadow(first_bad_addr);
+ }
+ return first_bad_addr;
+}
+
+void print_tags(u8 addr_tag, const void *addr)
+{
+ u8 *shadow = (u8 *)kasan_mem_to_shadow(addr);
+
+ pr_err("Pointer tag: [%02x], memory tag: [%02x]\n", addr_tag, *shadow);
+}
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 155247a6f8a8..e031c78f2e52 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -64,11 +64,10 @@ static int __init kasan_set_multi_shot(char *str)
}
__setup("kasan_multi_shot", kasan_set_multi_shot);
-static void print_error_description(struct kasan_access_info *info,
- const char *bug_type)
+static void print_error_description(struct kasan_access_info *info)
{
pr_err("BUG: KASAN: %s in %pS\n",
- bug_type, (void *)info->ip);
+ get_bug_type(info), (void *)info->ip);
pr_err("%s of size %zu at addr %px by task %s/%d\n",
info->is_write ? "Write" : "Read", info->access_size,
info->access_addr, current->comm, task_pid_nr(current));
@@ -272,6 +271,8 @@ void kasan_report_invalid_free(void *object, unsigned long ip)
start_report(&flags);
pr_err("BUG: KASAN: double-free or invalid-free in %pS\n", (void *)ip);
+ print_tags(get_tag(object), reset_tag(object));
+ object = reset_tag(object);
pr_err("\n");
print_address_description(object);
pr_err("\n");
@@ -279,41 +280,45 @@ void kasan_report_invalid_free(void *object, unsigned long ip)
end_report(&flags);
}
-static void kasan_report_error(struct kasan_access_info *info)
-{
- unsigned long flags;
-
- start_report(&flags);
-
- print_error_description(info, get_bug_type(info));
- pr_err("\n");
-
- if (!addr_has_shadow(info->access_addr)) {
- dump_stack();
- } else {
- print_address_description((void *)info->access_addr);
- pr_err("\n");
- print_shadow_for_address(info->first_bad_addr);
- }
-
- end_report(&flags);
-}
-
void kasan_report(unsigned long addr, size_t size,
bool is_write, unsigned long ip)
{
struct kasan_access_info info;
+ void *tagged_addr;
+ void *untagged_addr;
+ unsigned long flags;
if (likely(!report_enabled()))
return;
disable_trace_on_warning();
- info.access_addr = (void *)addr;
- info.first_bad_addr = (void *)addr;
+ tagged_addr = (void *)addr;
+ untagged_addr = reset_tag(tagged_addr);
+
+ info.access_addr = tagged_addr;
+ if (addr_has_shadow(untagged_addr))
+ info.first_bad_addr = find_first_bad_addr(tagged_addr, size);
+ else
+ info.first_bad_addr = untagged_addr;
info.access_size = size;
info.is_write = is_write;
info.ip = ip;
- kasan_report_error(&info);
+ start_report(&flags);
+
+ print_error_description(&info);
+ if (addr_has_shadow(untagged_addr))
+ print_tags(get_tag(tagged_addr), info.first_bad_addr);
+ pr_err("\n");
+
+ if (addr_has_shadow(untagged_addr)) {
+ print_address_description(untagged_addr);
+ pr_err("\n");
+ print_shadow_for_address(info.first_bad_addr);
+ } else {
+ dump_stack();
+ }
+
+ end_report(&flags);
}
--
2.19.0.rc0.228.g281dcd1b4d0-goog
KHWASAN uses the Top Byte Ignore feature of arm64 CPUs to store a pointer
tag in the top byte of each pointer. This commit enables the TCR_TBI1 bit,
which enables Top Byte Ignore for the kernel, when KHWASAN is used.
Signed-off-by: Andrey Konovalov <[email protected]>
---
arch/arm64/include/asm/pgtable-hwdef.h | 1 +
arch/arm64/mm/proc.S | 8 +++++++-
2 files changed, 8 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
index fd208eac9f2a..483aceedad76 100644
--- a/arch/arm64/include/asm/pgtable-hwdef.h
+++ b/arch/arm64/include/asm/pgtable-hwdef.h
@@ -289,6 +289,7 @@
#define TCR_A1 (UL(1) << 22)
#define TCR_ASID16 (UL(1) << 36)
#define TCR_TBI0 (UL(1) << 37)
+#define TCR_TBI1 (UL(1) << 38)
#define TCR_HA (UL(1) << 39)
#define TCR_HD (UL(1) << 40)
#define TCR_NFD1 (UL(1) << 54)
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 03646e6a2ef4..c5175e098d02 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -47,6 +47,12 @@
/* PTWs cacheable, inner/outer WBWA */
#define TCR_CACHE_FLAGS TCR_IRGN_WBWA | TCR_ORGN_WBWA
+#ifdef CONFIG_KASAN_HW
+#define TCR_KASAN_FLAGS TCR_TBI1
+#else
+#define TCR_KASAN_FLAGS 0
+#endif
+
#define MAIR(attr, mt) ((attr) << ((mt) * 8))
/*
@@ -440,7 +446,7 @@ ENTRY(__cpu_setup)
*/
ldr x10, =TCR_TxSZ(VA_BITS) | TCR_CACHE_FLAGS | TCR_SMP_FLAGS | \
TCR_TG_FLAGS | TCR_KASLR_FLAGS | TCR_ASID16 | \
- TCR_TBI0 | TCR_A1
+ TCR_TBI0 | TCR_A1 | TCR_KASAN_FLAGS
tcr_set_idmap_t0sz x10, x9
/*
--
2.19.0.rc0.228.g281dcd1b4d0-goog
This patch moves KASAN specific error reporting routines to kasan_report.c
without any functional changes, leaving common error reporting code in
report.c to be later reused by KHWASAN.
Signed-off-by: Andrey Konovalov <[email protected]>
---
mm/kasan/Makefile | 4 +-
mm/kasan/kasan.h | 7 ++
mm/kasan/kasan_report.c | 158 +++++++++++++++++++++++++
mm/kasan/khwasan_report.c | 39 +++++++
mm/kasan/report.c | 234 +++++++++-----------------------------
5 files changed, 257 insertions(+), 185 deletions(-)
create mode 100644 mm/kasan/kasan_report.c
create mode 100644 mm/kasan/khwasan_report.c
diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
index 14955add96d3..7ef536390365 100644
--- a/mm/kasan/Makefile
+++ b/mm/kasan/Makefile
@@ -14,5 +14,5 @@ CFLAGS_kasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
CFLAGS_khwasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
obj-$(CONFIG_KASAN) := common.o kasan_init.o report.o
-obj-$(CONFIG_KASAN_GENERIC) += kasan.o quarantine.o
-obj-$(CONFIG_KASAN_HW) += khwasan.o
+obj-$(CONFIG_KASAN_GENERIC) += kasan.o kasan_report.o quarantine.o
+obj-$(CONFIG_KASAN_HW) += khwasan.o khwasan_report.o
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index a7cc27d96608..82672473740c 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -109,11 +109,18 @@ static inline const void *kasan_shadow_to_mem(const void *shadow_addr)
<< KASAN_SHADOW_SCALE_SHIFT);
}
+static inline bool addr_has_shadow(const void *addr)
+{
+ return (addr >= kasan_shadow_to_mem((void *)KASAN_SHADOW_START));
+}
+
void kasan_poison_shadow(const void *address, size_t size, u8 value);
void check_memory_region(unsigned long addr, size_t size, bool write,
unsigned long ret_ip);
+const char *get_bug_type(struct kasan_access_info *info);
+
void kasan_report(unsigned long addr, size_t size,
bool is_write, unsigned long ip);
void kasan_report_invalid_free(void *object, unsigned long ip);
diff --git a/mm/kasan/kasan_report.c b/mm/kasan/kasan_report.c
new file mode 100644
index 000000000000..2d8decbecbd5
--- /dev/null
+++ b/mm/kasan/kasan_report.c
@@ -0,0 +1,158 @@
+/*
+ * This file contains KASAN specific error reporting code.
+ *
+ * Copyright (c) 2014 Samsung Electronics Co., Ltd.
+ * Author: Andrey Ryabinin <[email protected]>
+ *
+ * Some code borrowed from https://github.com/xairy/kasan-prototype by
+ * Andrey Konovalov <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/bitops.h>
+#include <linux/ftrace.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/printk.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/stackdepot.h>
+#include <linux/stacktrace.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/kasan.h>
+#include <linux/module.h>
+
+#include <asm/sections.h>
+
+#include "kasan.h"
+#include "../slab.h"
+
+static const void *find_first_bad_addr(const void *addr, size_t size)
+{
+ u8 shadow_val = *(u8 *)kasan_mem_to_shadow(addr);
+ const void *first_bad_addr = addr;
+
+ while (!shadow_val && first_bad_addr < addr + size) {
+ first_bad_addr += KASAN_SHADOW_SCALE_SIZE;
+ shadow_val = *(u8 *)kasan_mem_to_shadow(first_bad_addr);
+ }
+ return first_bad_addr;
+}
+
+static const char *get_shadow_bug_type(struct kasan_access_info *info)
+{
+ const char *bug_type = "unknown-crash";
+ u8 *shadow_addr;
+
+ info->first_bad_addr = find_first_bad_addr(info->access_addr,
+ info->access_size);
+
+ shadow_addr = (u8 *)kasan_mem_to_shadow(info->first_bad_addr);
+
+ /*
+ * If shadow byte value is in [0, KASAN_SHADOW_SCALE_SIZE) we can look
+ * at the next shadow byte to determine the type of the bad access.
+ */
+ if (*shadow_addr > 0 && *shadow_addr <= KASAN_SHADOW_SCALE_SIZE - 1)
+ shadow_addr++;
+
+ switch (*shadow_addr) {
+ case 0 ... KASAN_SHADOW_SCALE_SIZE - 1:
+ /*
+ * In theory it's still possible to see these shadow values
+ * due to a data race in the kernel code.
+ */
+ bug_type = "out-of-bounds";
+ break;
+ case KASAN_PAGE_REDZONE:
+ case KASAN_KMALLOC_REDZONE:
+ bug_type = "slab-out-of-bounds";
+ break;
+ case KASAN_GLOBAL_REDZONE:
+ bug_type = "global-out-of-bounds";
+ break;
+ case KASAN_STACK_LEFT:
+ case KASAN_STACK_MID:
+ case KASAN_STACK_RIGHT:
+ case KASAN_STACK_PARTIAL:
+ bug_type = "stack-out-of-bounds";
+ break;
+ case KASAN_FREE_PAGE:
+ case KASAN_KMALLOC_FREE:
+ bug_type = "use-after-free";
+ break;
+ case KASAN_USE_AFTER_SCOPE:
+ bug_type = "use-after-scope";
+ break;
+ case KASAN_ALLOCA_LEFT:
+ case KASAN_ALLOCA_RIGHT:
+ bug_type = "alloca-out-of-bounds";
+ break;
+ }
+
+ return bug_type;
+}
+
+static const char *get_wild_bug_type(struct kasan_access_info *info)
+{
+ const char *bug_type = "unknown-crash";
+
+ if ((unsigned long)info->access_addr < PAGE_SIZE)
+ bug_type = "null-ptr-deref";
+ else if ((unsigned long)info->access_addr < TASK_SIZE)
+ bug_type = "user-memory-access";
+ else
+ bug_type = "wild-memory-access";
+
+ return bug_type;
+}
+
+const char *get_bug_type(struct kasan_access_info *info)
+{
+ if (addr_has_shadow(info->access_addr))
+ return get_shadow_bug_type(info);
+ return get_wild_bug_type(info);
+}
+
+#define DEFINE_ASAN_REPORT_LOAD(size) \
+void __asan_report_load##size##_noabort(unsigned long addr) \
+{ \
+ kasan_report(addr, size, false, _RET_IP_); \
+} \
+EXPORT_SYMBOL(__asan_report_load##size##_noabort)
+
+#define DEFINE_ASAN_REPORT_STORE(size) \
+void __asan_report_store##size##_noabort(unsigned long addr) \
+{ \
+ kasan_report(addr, size, true, _RET_IP_); \
+} \
+EXPORT_SYMBOL(__asan_report_store##size##_noabort)
+
+DEFINE_ASAN_REPORT_LOAD(1);
+DEFINE_ASAN_REPORT_LOAD(2);
+DEFINE_ASAN_REPORT_LOAD(4);
+DEFINE_ASAN_REPORT_LOAD(8);
+DEFINE_ASAN_REPORT_LOAD(16);
+DEFINE_ASAN_REPORT_STORE(1);
+DEFINE_ASAN_REPORT_STORE(2);
+DEFINE_ASAN_REPORT_STORE(4);
+DEFINE_ASAN_REPORT_STORE(8);
+DEFINE_ASAN_REPORT_STORE(16);
+
+void __asan_report_load_n_noabort(unsigned long addr, size_t size)
+{
+ kasan_report(addr, size, false, _RET_IP_);
+}
+EXPORT_SYMBOL(__asan_report_load_n_noabort);
+
+void __asan_report_store_n_noabort(unsigned long addr, size_t size)
+{
+ kasan_report(addr, size, true, _RET_IP_);
+}
+EXPORT_SYMBOL(__asan_report_store_n_noabort);
diff --git a/mm/kasan/khwasan_report.c b/mm/kasan/khwasan_report.c
new file mode 100644
index 000000000000..2edbc3c76be5
--- /dev/null
+++ b/mm/kasan/khwasan_report.c
@@ -0,0 +1,39 @@
+/*
+ * This file contains KHWASAN specific error reporting code.
+ *
+ * Copyright (c) 2014 Samsung Electronics Co., Ltd.
+ * Author: Andrey Ryabinin <[email protected]>
+ *
+ * Some code borrowed from https://github.com/xairy/kasan-prototype by
+ * Andrey Konovalov <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/bitops.h>
+#include <linux/ftrace.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/printk.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/stackdepot.h>
+#include <linux/stacktrace.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/kasan.h>
+#include <linux/module.h>
+
+#include <asm/sections.h>
+
+#include "kasan.h"
+#include "../slab.h"
+
+const char *get_bug_type(struct kasan_access_info *info)
+{
+ return "invalid-access";
+}
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 5c169aa688fd..155247a6f8a8 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -1,5 +1,5 @@
/*
- * This file contains error reporting code.
+ * This file contains common KASAN and KHWASAN error reporting code.
*
* Copyright (c) 2014 Samsung Electronics Co., Ltd.
* Author: Andrey Ryabinin <[email protected]>
@@ -39,103 +39,34 @@
#define SHADOW_BYTES_PER_ROW (SHADOW_BLOCKS_PER_ROW * SHADOW_BYTES_PER_BLOCK)
#define SHADOW_ROWS_AROUND_ADDR 2
-static const void *find_first_bad_addr(const void *addr, size_t size)
-{
- u8 shadow_val = *(u8 *)kasan_mem_to_shadow(addr);
- const void *first_bad_addr = addr;
-
- while (!shadow_val && first_bad_addr < addr + size) {
- first_bad_addr += KASAN_SHADOW_SCALE_SIZE;
- shadow_val = *(u8 *)kasan_mem_to_shadow(first_bad_addr);
- }
- return first_bad_addr;
-}
+static unsigned long kasan_flags;
-static bool addr_has_shadow(struct kasan_access_info *info)
-{
- return (info->access_addr >=
- kasan_shadow_to_mem((void *)KASAN_SHADOW_START));
-}
+#define KASAN_BIT_REPORTED 0
+#define KASAN_BIT_MULTI_SHOT 1
-static const char *get_shadow_bug_type(struct kasan_access_info *info)
+bool kasan_save_enable_multi_shot(void)
{
- const char *bug_type = "unknown-crash";
- u8 *shadow_addr;
-
- info->first_bad_addr = find_first_bad_addr(info->access_addr,
- info->access_size);
-
- shadow_addr = (u8 *)kasan_mem_to_shadow(info->first_bad_addr);
-
- /*
- * If shadow byte value is in [0, KASAN_SHADOW_SCALE_SIZE) we can look
- * at the next shadow byte to determine the type of the bad access.
- */
- if (*shadow_addr > 0 && *shadow_addr <= KASAN_SHADOW_SCALE_SIZE - 1)
- shadow_addr++;
-
- switch (*shadow_addr) {
- case 0 ... KASAN_SHADOW_SCALE_SIZE - 1:
- /*
- * In theory it's still possible to see these shadow values
- * due to a data race in the kernel code.
- */
- bug_type = "out-of-bounds";
- break;
- case KASAN_PAGE_REDZONE:
- case KASAN_KMALLOC_REDZONE:
- bug_type = "slab-out-of-bounds";
- break;
- case KASAN_GLOBAL_REDZONE:
- bug_type = "global-out-of-bounds";
- break;
- case KASAN_STACK_LEFT:
- case KASAN_STACK_MID:
- case KASAN_STACK_RIGHT:
- case KASAN_STACK_PARTIAL:
- bug_type = "stack-out-of-bounds";
- break;
- case KASAN_FREE_PAGE:
- case KASAN_KMALLOC_FREE:
- bug_type = "use-after-free";
- break;
- case KASAN_USE_AFTER_SCOPE:
- bug_type = "use-after-scope";
- break;
- case KASAN_ALLOCA_LEFT:
- case KASAN_ALLOCA_RIGHT:
- bug_type = "alloca-out-of-bounds";
- break;
- }
-
- return bug_type;
+ return test_and_set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
}
+EXPORT_SYMBOL_GPL(kasan_save_enable_multi_shot);
-static const char *get_wild_bug_type(struct kasan_access_info *info)
+void kasan_restore_multi_shot(bool enabled)
{
- const char *bug_type = "unknown-crash";
-
- if ((unsigned long)info->access_addr < PAGE_SIZE)
- bug_type = "null-ptr-deref";
- else if ((unsigned long)info->access_addr < TASK_SIZE)
- bug_type = "user-memory-access";
- else
- bug_type = "wild-memory-access";
-
- return bug_type;
+ if (!enabled)
+ clear_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
}
+EXPORT_SYMBOL_GPL(kasan_restore_multi_shot);
-static const char *get_bug_type(struct kasan_access_info *info)
+static int __init kasan_set_multi_shot(char *str)
{
- if (addr_has_shadow(info))
- return get_shadow_bug_type(info);
- return get_wild_bug_type(info);
+ set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
+ return 1;
}
+__setup("kasan_multi_shot", kasan_set_multi_shot);
-static void print_error_description(struct kasan_access_info *info)
+static void print_error_description(struct kasan_access_info *info,
+ const char *bug_type)
{
- const char *bug_type = get_bug_type(info);
-
pr_err("BUG: KASAN: %s in %pS\n",
bug_type, (void *)info->ip);
pr_err("%s of size %zu at addr %px by task %s/%d\n",
@@ -143,25 +74,9 @@ static void print_error_description(struct kasan_access_info *info)
info->access_addr, current->comm, task_pid_nr(current));
}
-static inline bool kernel_or_module_addr(const void *addr)
-{
- if (addr >= (void *)_stext && addr < (void *)_end)
- return true;
- if (is_module_address((unsigned long)addr))
- return true;
- return false;
-}
-
-static inline bool init_task_stack_addr(const void *addr)
-{
- return addr >= (void *)&init_thread_union.stack &&
- (addr <= (void *)&init_thread_union.stack +
- sizeof(init_thread_union.stack));
-}
-
static DEFINE_SPINLOCK(report_lock);
-static void kasan_start_report(unsigned long *flags)
+static void start_report(unsigned long *flags)
{
/*
* Make sure we don't end up in loop.
@@ -171,7 +86,7 @@ static void kasan_start_report(unsigned long *flags)
pr_err("==================================================================\n");
}
-static void kasan_end_report(unsigned long *flags)
+static void end_report(unsigned long *flags)
{
pr_err("==================================================================\n");
add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
@@ -249,6 +164,22 @@ static void describe_object(struct kmem_cache *cache, void *object,
describe_object_addr(cache, object, addr);
}
+static inline bool kernel_or_module_addr(const void *addr)
+{
+ if (addr >= (void *)_stext && addr < (void *)_end)
+ return true;
+ if (is_module_address((unsigned long)addr))
+ return true;
+ return false;
+}
+
+static inline bool init_task_stack_addr(const void *addr)
+{
+ return addr >= (void *)&init_thread_union.stack &&
+ (addr <= (void *)&init_thread_union.stack +
+ sizeof(init_thread_union.stack));
+}
+
static void print_address_description(void *addr)
{
struct page *page = addr_to_page(addr);
@@ -326,29 +257,38 @@ static void print_shadow_for_address(const void *addr)
}
}
+static bool report_enabled(void)
+{
+ if (current->kasan_depth)
+ return false;
+ if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
+ return true;
+ return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
+}
+
void kasan_report_invalid_free(void *object, unsigned long ip)
{
unsigned long flags;
- kasan_start_report(&flags);
+ start_report(&flags);
pr_err("BUG: KASAN: double-free or invalid-free in %pS\n", (void *)ip);
pr_err("\n");
print_address_description(object);
pr_err("\n");
print_shadow_for_address(object);
- kasan_end_report(&flags);
+ end_report(&flags);
}
static void kasan_report_error(struct kasan_access_info *info)
{
unsigned long flags;
- kasan_start_report(&flags);
+ start_report(&flags);
- print_error_description(info);
+ print_error_description(info, get_bug_type(info));
pr_err("\n");
- if (!addr_has_shadow(info)) {
+ if (!addr_has_shadow(info->access_addr)) {
dump_stack();
} else {
print_address_description((void *)info->access_addr);
@@ -356,41 +296,7 @@ static void kasan_report_error(struct kasan_access_info *info)
print_shadow_for_address(info->first_bad_addr);
}
- kasan_end_report(&flags);
-}
-
-static unsigned long kasan_flags;
-
-#define KASAN_BIT_REPORTED 0
-#define KASAN_BIT_MULTI_SHOT 1
-
-bool kasan_save_enable_multi_shot(void)
-{
- return test_and_set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
-}
-EXPORT_SYMBOL_GPL(kasan_save_enable_multi_shot);
-
-void kasan_restore_multi_shot(bool enabled)
-{
- if (!enabled)
- clear_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
-}
-EXPORT_SYMBOL_GPL(kasan_restore_multi_shot);
-
-static int __init kasan_set_multi_shot(char *str)
-{
- set_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags);
- return 1;
-}
-__setup("kasan_multi_shot", kasan_set_multi_shot);
-
-static inline bool kasan_report_enabled(void)
-{
- if (current->kasan_depth)
- return false;
- if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
- return true;
- return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
+ end_report(&flags);
}
void kasan_report(unsigned long addr, size_t size,
@@ -398,7 +304,7 @@ void kasan_report(unsigned long addr, size_t size,
{
struct kasan_access_info info;
- if (likely(!kasan_report_enabled()))
+ if (likely(!report_enabled()))
return;
disable_trace_on_warning();
@@ -411,41 +317,3 @@ void kasan_report(unsigned long addr, size_t size,
kasan_report_error(&info);
}
-
-
-#define DEFINE_ASAN_REPORT_LOAD(size) \
-void __asan_report_load##size##_noabort(unsigned long addr) \
-{ \
- kasan_report(addr, size, false, _RET_IP_); \
-} \
-EXPORT_SYMBOL(__asan_report_load##size##_noabort)
-
-#define DEFINE_ASAN_REPORT_STORE(size) \
-void __asan_report_store##size##_noabort(unsigned long addr) \
-{ \
- kasan_report(addr, size, true, _RET_IP_); \
-} \
-EXPORT_SYMBOL(__asan_report_store##size##_noabort)
-
-DEFINE_ASAN_REPORT_LOAD(1);
-DEFINE_ASAN_REPORT_LOAD(2);
-DEFINE_ASAN_REPORT_LOAD(4);
-DEFINE_ASAN_REPORT_LOAD(8);
-DEFINE_ASAN_REPORT_LOAD(16);
-DEFINE_ASAN_REPORT_STORE(1);
-DEFINE_ASAN_REPORT_STORE(2);
-DEFINE_ASAN_REPORT_STORE(4);
-DEFINE_ASAN_REPORT_STORE(8);
-DEFINE_ASAN_REPORT_STORE(16);
-
-void __asan_report_load_n_noabort(unsigned long addr, size_t size)
-{
- kasan_report(addr, size, false, _RET_IP_);
-}
-EXPORT_SYMBOL(__asan_report_load_n_noabort);
-
-void __asan_report_store_n_noabort(unsigned long addr, size_t size)
-{
- kasan_report(addr, size, true, _RET_IP_);
-}
-EXPORT_SYMBOL(__asan_report_store_n_noabort);
--
2.19.0.rc0.228.g281dcd1b4d0-goog
__kimg_to_phys (which is used by virt_to_phys) and _virt_addr_is_linear
(which is used by virt_addr_valid) assume that the top byte of the address
is 0xff, which isn't always the case with KHWASAN enabled.
The solution is to reset the tag in those macros.
Signed-off-by: Andrey Konovalov <[email protected]>
---
arch/arm64/include/asm/memory.h | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index f5e262ee76c1..f5e2953b7009 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -92,6 +92,13 @@
#define KASAN_THREAD_SHIFT 0
#endif
+#ifdef CONFIG_KASAN_HW
+#define KASAN_TAG_SHIFTED(tag) ((unsigned long)(tag) << 56)
+#define KASAN_SET_TAG(addr, tag) (((addr) & ~KASAN_TAG_SHIFTED(0xff)) | \
+ KASAN_TAG_SHIFTED(tag))
+#define KASAN_RESET_TAG(addr) KASAN_SET_TAG(addr, 0xff)
+#endif
+
#define MIN_THREAD_SHIFT (14 + KASAN_THREAD_SHIFT)
/*
@@ -232,7 +239,12 @@ static inline unsigned long kaslr_offset(void)
#define __is_lm_address(addr) (!!((addr) & BIT(VA_BITS - 1)))
#define __lm_to_phys(addr) (((addr) & ~PAGE_OFFSET) + PHYS_OFFSET)
+
+#ifdef CONFIG_KASAN_HW
+#define __kimg_to_phys(addr) (KASAN_RESET_TAG(addr) - kimage_voffset)
+#else
#define __kimg_to_phys(addr) ((addr) - kimage_voffset)
+#endif
#define __virt_to_phys_nodebug(x) ({ \
phys_addr_t __x = (phys_addr_t)(x); \
@@ -308,7 +320,13 @@ static inline void *phys_to_virt(phys_addr_t x)
#endif
#endif
+#ifdef CONFIG_KASAN_HW
+#define _virt_addr_is_linear(kaddr) (KASAN_RESET_TAG((u64)(kaddr)) >= \
+ PAGE_OFFSET)
+#else
#define _virt_addr_is_linear(kaddr) (((u64)(kaddr)) >= PAGE_OFFSET)
+#endif
+
#define virt_addr_valid(kaddr) (_virt_addr_is_linear(kaddr) && \
_virt_addr_valid(kaddr))
--
2.19.0.rc0.228.g281dcd1b4d0-goog
This commit adds a few helper functions, that are meant to be used to
work with tags embedded in the top byte of kernel pointers: to set, to
get or to reset (set to 0xff) the top byte.
Signed-off-by: Andrey Konovalov <[email protected]>
---
arch/arm64/mm/kasan_init.c | 2 ++
include/linux/kasan.h | 29 +++++++++++++++++
mm/kasan/kasan.h | 55 ++++++++++++++++++++++++++++++++
mm/kasan/khwasan.c | 65 ++++++++++++++++++++++++++++++++++++++
4 files changed, 151 insertions(+)
diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index 7a31e8ccbad2..e7f37c0b7e14 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -250,6 +250,8 @@ void __init kasan_init(void)
memset(kasan_zero_page, KASAN_SHADOW_INIT, PAGE_SIZE);
cpu_replace_ttbr1(lm_alias(swapper_pg_dir));
+ khwasan_init();
+
/* At this point kasan is fully initialized. Enable error messages */
init_task.kasan_depth = 0;
pr_info("KernelAddressSanitizer initialized\n");
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 1c31bb089154..1f852244e739 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -166,6 +166,35 @@ static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
#define KASAN_SHADOW_INIT 0xFF
+void khwasan_init(void);
+
+void *khwasan_reset_tag(const void *addr);
+
+void *khwasan_preset_slub_tag(struct kmem_cache *cache, const void *addr);
+void *khwasan_preset_slab_tag(struct kmem_cache *cache, unsigned int idx,
+ const void *addr);
+
+#else /* CONFIG_KASAN_HW */
+
+static inline void khwasan_init(void) { }
+
+static inline void *khwasan_reset_tag(const void *addr)
+{
+ return (void *)addr;
+}
+
+static inline void *khwasan_preset_slub_tag(struct kmem_cache *cache,
+ const void *addr)
+{
+ return (void *)addr;
+}
+
+static inline void *khwasan_preset_slab_tag(struct kmem_cache *cache,
+ unsigned int idx, const void *addr)
+{
+ return (void *)addr;
+}
+
#endif /* CONFIG_KASAN_HW */
#endif /* LINUX_KASAN_H */
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 19b950eaccff..a7cc27d96608 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -8,6 +8,10 @@
#define KASAN_SHADOW_SCALE_SIZE (1UL << KASAN_SHADOW_SCALE_SHIFT)
#define KASAN_SHADOW_MASK (KASAN_SHADOW_SCALE_SIZE - 1)
+#define KHWASAN_TAG_KERNEL 0xFF /* native kernel pointers tag */
+#define KHWASAN_TAG_INVALID 0xFE /* inaccessible memory tag */
+#define KHWASAN_TAG_MAX 0xFD /* maximum value for random tags */
+
#define KASAN_FREE_PAGE 0xFF /* page was freed */
#define KASAN_PAGE_REDZONE 0xFE /* redzone for kmalloc_large allocations */
#define KASAN_KMALLOC_REDZONE 0xFC /* redzone inside slub object */
@@ -126,6 +130,57 @@ static inline void quarantine_reduce(void) { }
static inline void quarantine_remove_cache(struct kmem_cache *cache) { }
#endif
+#ifdef CONFIG_KASAN_HW
+
+#define KHWASAN_TAG_SHIFT 56
+#define KHWASAN_TAG_MASK (0xFFUL << KHWASAN_TAG_SHIFT)
+
+u8 random_tag(void);
+
+static inline void *set_tag(const void *addr, u8 tag)
+{
+ u64 a = (u64)addr;
+
+ a &= ~KHWASAN_TAG_MASK;
+ a |= ((u64)tag << KHWASAN_TAG_SHIFT);
+
+ return (void *)a;
+}
+
+static inline u8 get_tag(const void *addr)
+{
+ return (u8)((u64)addr >> KHWASAN_TAG_SHIFT);
+}
+
+static inline void *reset_tag(const void *addr)
+{
+ return set_tag(addr, KHWASAN_TAG_KERNEL);
+}
+
+#else /* CONFIG_KASAN_HW */
+
+static inline u8 random_tag(void)
+{
+ return 0;
+}
+
+static inline void *set_tag(const void *addr, u8 tag)
+{
+ return (void *)addr;
+}
+
+static inline u8 get_tag(const void *addr)
+{
+ return 0;
+}
+
+static inline void *reset_tag(const void *addr)
+{
+ return (void *)addr;
+}
+
+#endif /* CONFIG_KASAN_HW */
+
/*
* Exported functions for interfaces called from assembly or from generated
* code. Declarations here to avoid warning about missing declarations.
diff --git a/mm/kasan/khwasan.c b/mm/kasan/khwasan.c
index e2c3a7f7fd1f..9d91bf3c8246 100644
--- a/mm/kasan/khwasan.c
+++ b/mm/kasan/khwasan.c
@@ -38,6 +38,71 @@
#include "kasan.h"
#include "../slab.h"
+static DEFINE_PER_CPU(u32, prng_state);
+
+void khwasan_init(void)
+{
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ per_cpu(prng_state, cpu) = get_random_u32();
+}
+
+/*
+ * If a preemption happens between this_cpu_read and this_cpu_write, the only
+ * side effect is that we'll give a few allocated in different contexts objects
+ * the same tag. Since KHWASAN is meant to be used a probabilistic bug-detection
+ * debug feature, this doesn’t have significant negative impact.
+ *
+ * Ideally the tags use strong randomness to prevent any attempts to predict
+ * them during explicit exploit attempts. But strong randomness is expensive,
+ * and we did an intentional trade-off to use a PRNG. This non-atomic RMW
+ * sequence has in fact positive effect, since interrupts that randomly skew
+ * PRNG at unpredictable points do only good.
+ */
+u8 random_tag(void)
+{
+ u32 state = this_cpu_read(prng_state);
+
+ state = 1664525 * state + 1013904223;
+ this_cpu_write(prng_state, state);
+
+ return (u8)(state % (KHWASAN_TAG_MAX + 1));
+}
+
+void *khwasan_reset_tag(const void *addr)
+{
+ return reset_tag(addr);
+}
+
+void *khwasan_preset_slub_tag(struct kmem_cache *cache, const void *addr)
+{
+ /*
+ * Since it's desirable to only call object contructors ones during
+ * slab allocation, we preassign tags to all such objects.
+ * Also preassign tags for SLAB_TYPESAFE_BY_RCU slabs to avoid
+ * use-after-free reports.
+ */
+ if (cache->ctor || cache->flags & SLAB_TYPESAFE_BY_RCU)
+ return set_tag(addr, random_tag());
+ return (void *)addr;
+}
+
+void *khwasan_preset_slab_tag(struct kmem_cache *cache, unsigned int idx,
+ const void *addr)
+{
+ /*
+ * See comment in khwasan_preset_slub_tag.
+ * For SLAB allocator we can't preassign tags randomly since the
+ * freelist is stored as an array of indexes instead of a linked
+ * list. Assign tags based on objects indexes, so that objects that
+ * are next to each other get different tags.
+ */
+ if (cache->ctor || cache->flags & SLAB_TYPESAFE_BY_RCU)
+ return set_tag(addr, (u8)idx);
+ return (void *)addr;
+}
+
void check_memory_region(unsigned long addr, size_t size, bool write,
unsigned long ret_ip)
{
--
2.19.0.rc0.228.g281dcd1b4d0-goog
An object constructor can initialize pointers within this objects based on
the address of the object. Since the object address might be tagged, we
need to assign a tag before calling constructor.
The implemented approach is to assign tags to objects with constructors
when a slab is allocated and call constructors once as usual. The
downside is that such object would always have the same tag when it is
reallocated, so we won't catch use-after-frees on it.
Also pressign tags for objects from SLAB_TYPESAFE_BY_RCU caches, since
they can be validy accessed after having been freed.
Signed-off-by: Andrey Konovalov <[email protected]>
---
mm/slab.c | 6 +++++-
mm/slub.c | 4 ++++
2 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/mm/slab.c b/mm/slab.c
index 6fdca9ec2ea4..3b4227059f2e 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -403,7 +403,11 @@ static inline struct kmem_cache *virt_to_cache(const void *obj)
static inline void *index_to_obj(struct kmem_cache *cache, struct page *page,
unsigned int idx)
{
- return page->s_mem + cache->size * idx;
+ void *obj;
+
+ obj = page->s_mem + cache->size * idx;
+ obj = khwasan_preset_slab_tag(cache, idx, obj);
+ return obj;
}
/*
diff --git a/mm/slub.c b/mm/slub.c
index 4206e1b616e7..086d6558a6b6 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1531,12 +1531,14 @@ static bool shuffle_freelist(struct kmem_cache *s, struct page *page)
/* First entry is used as the base of the freelist */
cur = next_freelist_entry(s, page, &pos, start, page_limit,
freelist_count);
+ cur = khwasan_preset_slub_tag(s, cur);
page->freelist = cur;
for (idx = 1; idx < page->objects; idx++) {
setup_object(s, page, cur);
next = next_freelist_entry(s, page, &pos, start, page_limit,
freelist_count);
+ next = khwasan_preset_slub_tag(s, next);
set_freepointer(s, cur, next);
cur = next;
}
@@ -1613,8 +1615,10 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
shuffle = shuffle_freelist(s, page);
if (!shuffle) {
+ start = khwasan_preset_slub_tag(s, start);
for_each_object_idx(p, idx, s, start, page->objects) {
setup_object(s, page, p);
+ p = khwasan_preset_slub_tag(s, p);
if (likely(idx < page->objects))
set_freepointer(s, p, p + s->size);
else
--
2.19.0.rc0.228.g281dcd1b4d0-goog
KWHASAN uses 1 shadow byte for 16 bytes of kernel memory, so it requires
1/16th of the kernel virtual address space for the shadow memory.
This commit sets KASAN_SHADOW_SCALE_SHIFT to 4 when KHWASAN is enabled.
Signed-off-by: Andrey Konovalov <[email protected]>
---
arch/arm64/Makefile | 2 +-
arch/arm64/include/asm/memory.h | 13 +++++++++----
2 files changed, 10 insertions(+), 5 deletions(-)
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 106039d25e2f..17047b8ab984 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -94,7 +94,7 @@ endif
# KASAN_SHADOW_OFFSET = VA_START + (1 << (VA_BITS - KASAN_SHADOW_SCALE_SHIFT))
# - (1 << (64 - KASAN_SHADOW_SCALE_SHIFT))
# in 32-bit arithmetic
-KASAN_SHADOW_SCALE_SHIFT := 3
+KASAN_SHADOW_SCALE_SHIFT := $(if $(CONFIG_KASAN_HW), 4, 3)
KASAN_SHADOW_OFFSET := $(shell printf "0x%08x00000000\n" $$(( \
(0xffffffff & (-1 << ($(CONFIG_ARM64_VA_BITS) - 32))) \
+ (1 << ($(CONFIG_ARM64_VA_BITS) - 32 - $(KASAN_SHADOW_SCALE_SHIFT))) \
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index b96442960aea..f5e262ee76c1 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -74,12 +74,17 @@
#define KERNEL_END _end
/*
- * KASAN requires 1/8th of the kernel virtual address space for the shadow
- * region. KASAN can bloat the stack significantly, so double the (minimum)
- * stack size when KASAN is in use.
+ * KASAN and KHWASAN require 1/8th and 1/16th of the kernel virtual address
+ * space for the shadow region respectively. They can bloat the stack
+ * significantly, so double the (minimum) stack size when they are in use.
*/
-#ifdef CONFIG_KASAN
+#ifdef CONFIG_KASAN_GENERIC
#define KASAN_SHADOW_SCALE_SHIFT 3
+#endif
+#ifdef CONFIG_KASAN_HW
+#define KASAN_SHADOW_SCALE_SHIFT 4
+#endif
+#ifdef CONFIG_KASAN
#define KASAN_SHADOW_SIZE (UL(1) << (VA_BITS - KASAN_SHADOW_SCALE_SHIFT))
#define KASAN_THREAD_SHIFT 1
#else
--
2.19.0.rc0.228.g281dcd1b4d0-goog
KHWASAN will change the value of the top byte of pointers returned from the
kernel allocation functions (such as kmalloc). This patch updates KASAN
hooks signatures and their usage in SLAB and SLUB code to reflect that.
Signed-off-by: Andrey Konovalov <[email protected]>
---
include/linux/kasan.h | 34 +++++++++++++++++++++++-----------
mm/kasan/kasan.c | 24 ++++++++++++++----------
mm/slab.c | 12 ++++++------
mm/slab.h | 2 +-
mm/slab_common.c | 4 ++--
mm/slub.c | 15 +++++++--------
6 files changed, 53 insertions(+), 38 deletions(-)
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 46aae129917c..54d577ad2181 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -53,14 +53,14 @@ void kasan_unpoison_object_data(struct kmem_cache *cache, void *object);
void kasan_poison_object_data(struct kmem_cache *cache, void *object);
void kasan_init_slab_obj(struct kmem_cache *cache, const void *object);
-void kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags);
+void *kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags);
void kasan_kfree_large(void *ptr, unsigned long ip);
void kasan_poison_kfree(void *ptr, unsigned long ip);
-void kasan_kmalloc(struct kmem_cache *s, const void *object, size_t size,
+void *kasan_kmalloc(struct kmem_cache *s, const void *object, size_t size,
gfp_t flags);
-void kasan_krealloc(const void *object, size_t new_size, gfp_t flags);
+void *kasan_krealloc(const void *object, size_t new_size, gfp_t flags);
-void kasan_slab_alloc(struct kmem_cache *s, void *object, gfp_t flags);
+void *kasan_slab_alloc(struct kmem_cache *s, void *object, gfp_t flags);
bool kasan_slab_free(struct kmem_cache *s, void *object, unsigned long ip);
struct kasan_cache {
@@ -108,16 +108,28 @@ static inline void kasan_poison_object_data(struct kmem_cache *cache,
static inline void kasan_init_slab_obj(struct kmem_cache *cache,
const void *object) {}
-static inline void kasan_kmalloc_large(void *ptr, size_t size, gfp_t flags) {}
+static inline void *kasan_kmalloc_large(void *ptr, size_t size, gfp_t flags)
+{
+ return ptr;
+}
static inline void kasan_kfree_large(void *ptr, unsigned long ip) {}
static inline void kasan_poison_kfree(void *ptr, unsigned long ip) {}
-static inline void kasan_kmalloc(struct kmem_cache *s, const void *object,
- size_t size, gfp_t flags) {}
-static inline void kasan_krealloc(const void *object, size_t new_size,
- gfp_t flags) {}
+static inline void *kasan_kmalloc(struct kmem_cache *s, const void *object,
+ size_t size, gfp_t flags)
+{
+ return (void *)object;
+}
+static inline void *kasan_krealloc(const void *object, size_t new_size,
+ gfp_t flags)
+{
+ return (void *)object;
+}
-static inline void kasan_slab_alloc(struct kmem_cache *s, void *object,
- gfp_t flags) {}
+static inline void *kasan_slab_alloc(struct kmem_cache *s, void *object,
+ gfp_t flags)
+{
+ return object;
+}
static inline bool kasan_slab_free(struct kmem_cache *s, void *object,
unsigned long ip)
{
diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index c3bd5209da38..f696c7c143c2 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -485,9 +485,9 @@ void kasan_init_slab_obj(struct kmem_cache *cache, const void *object)
__memset(alloc_info, 0, sizeof(*alloc_info));
}
-void kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags)
+void *kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags)
{
- kasan_kmalloc(cache, object, cache->object_size, flags);
+ return kasan_kmalloc(cache, object, cache->object_size, flags);
}
static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
@@ -528,7 +528,7 @@ bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
return __kasan_slab_free(cache, object, ip, true);
}
-void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
+void *kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
gfp_t flags)
{
unsigned long redzone_start;
@@ -538,7 +538,7 @@ void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
quarantine_reduce();
if (unlikely(object == NULL))
- return;
+ return NULL;
redzone_start = round_up((unsigned long)(object + size),
KASAN_SHADOW_SCALE_SIZE);
@@ -551,10 +551,12 @@ void kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
if (cache->flags & SLAB_KASAN)
set_track(&get_alloc_info(cache, object)->alloc_track, flags);
+
+ return (void *)object;
}
EXPORT_SYMBOL(kasan_kmalloc);
-void kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags)
+void *kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags)
{
struct page *page;
unsigned long redzone_start;
@@ -564,7 +566,7 @@ void kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags)
quarantine_reduce();
if (unlikely(ptr == NULL))
- return;
+ return NULL;
page = virt_to_page(ptr);
redzone_start = round_up((unsigned long)(ptr + size),
@@ -574,21 +576,23 @@ void kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags)
kasan_unpoison_shadow(ptr, size);
kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
KASAN_PAGE_REDZONE);
+
+ return (void *)ptr;
}
-void kasan_krealloc(const void *object, size_t size, gfp_t flags)
+void *kasan_krealloc(const void *object, size_t size, gfp_t flags)
{
struct page *page;
if (unlikely(object == ZERO_SIZE_PTR))
- return;
+ return ZERO_SIZE_PTR;
page = virt_to_head_page(object);
if (unlikely(!PageSlab(page)))
- kasan_kmalloc_large(object, size, flags);
+ return kasan_kmalloc_large(object, size, flags);
else
- kasan_kmalloc(page->slab_cache, object, size, flags);
+ return kasan_kmalloc(page->slab_cache, object, size, flags);
}
void kasan_poison_kfree(void *ptr, unsigned long ip)
diff --git a/mm/slab.c b/mm/slab.c
index aa76a70e087e..6fdca9ec2ea4 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3551,7 +3551,7 @@ void *kmem_cache_alloc(struct kmem_cache *cachep, gfp_t flags)
{
void *ret = slab_alloc(cachep, flags, _RET_IP_);
- kasan_slab_alloc(cachep, ret, flags);
+ ret = kasan_slab_alloc(cachep, ret, flags);
trace_kmem_cache_alloc(_RET_IP_, ret,
cachep->object_size, cachep->size, flags);
@@ -3617,7 +3617,7 @@ kmem_cache_alloc_trace(struct kmem_cache *cachep, gfp_t flags, size_t size)
ret = slab_alloc(cachep, flags, _RET_IP_);
- kasan_kmalloc(cachep, ret, size, flags);
+ ret = kasan_kmalloc(cachep, ret, size, flags);
trace_kmalloc(_RET_IP_, ret,
size, cachep->size, flags);
return ret;
@@ -3641,7 +3641,7 @@ void *kmem_cache_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid)
{
void *ret = slab_alloc_node(cachep, flags, nodeid, _RET_IP_);
- kasan_slab_alloc(cachep, ret, flags);
+ ret = kasan_slab_alloc(cachep, ret, flags);
trace_kmem_cache_alloc_node(_RET_IP_, ret,
cachep->object_size, cachep->size,
flags, nodeid);
@@ -3660,7 +3660,7 @@ void *kmem_cache_alloc_node_trace(struct kmem_cache *cachep,
ret = slab_alloc_node(cachep, flags, nodeid, _RET_IP_);
- kasan_kmalloc(cachep, ret, size, flags);
+ ret = kasan_kmalloc(cachep, ret, size, flags);
trace_kmalloc_node(_RET_IP_, ret,
size, cachep->size,
flags, nodeid);
@@ -3679,7 +3679,7 @@ __do_kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller)
if (unlikely(ZERO_OR_NULL_PTR(cachep)))
return cachep;
ret = kmem_cache_alloc_node_trace(cachep, flags, node, size);
- kasan_kmalloc(cachep, ret, size, flags);
+ ret = kasan_kmalloc(cachep, ret, size, flags);
return ret;
}
@@ -3715,7 +3715,7 @@ static __always_inline void *__do_kmalloc(size_t size, gfp_t flags,
return cachep;
ret = slab_alloc(cachep, flags, caller);
- kasan_kmalloc(cachep, ret, size, flags);
+ ret = kasan_kmalloc(cachep, ret, size, flags);
trace_kmalloc(caller, ret,
size, cachep->size, flags);
diff --git a/mm/slab.h b/mm/slab.h
index 58c6c1c2a78e..4190c24ef0e9 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -441,7 +441,7 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s, gfp_t flags,
kmemleak_alloc_recursive(object, s->object_size, 1,
s->flags, flags);
- kasan_slab_alloc(s, object, flags);
+ p[i] = kasan_slab_alloc(s, object, flags);
}
if (memcg_kmem_enabled())
diff --git a/mm/slab_common.c b/mm/slab_common.c
index fea3376f9816..3abfa0f86118 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1183,7 +1183,7 @@ void *kmalloc_order(size_t size, gfp_t flags, unsigned int order)
page = alloc_pages(flags, order);
ret = page ? page_address(page) : NULL;
kmemleak_alloc(ret, size, 1, flags);
- kasan_kmalloc_large(ret, size, flags);
+ ret = kasan_kmalloc_large(ret, size, flags);
return ret;
}
EXPORT_SYMBOL(kmalloc_order);
@@ -1461,7 +1461,7 @@ static __always_inline void *__do_krealloc(const void *p, size_t new_size,
ks = ksize(p);
if (ks >= new_size) {
- kasan_krealloc((void *)p, new_size, flags);
+ p = kasan_krealloc((void *)p, new_size, flags);
return (void *)p;
}
diff --git a/mm/slub.c b/mm/slub.c
index ce2b9e5cea77..30b9bf777bab 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1335,10 +1335,10 @@ static inline void dec_slabs_node(struct kmem_cache *s, int node,
* Hooks for other subsystems that check memory allocations. In a typical
* production configuration these hooks all should produce no code at all.
*/
-static inline void kmalloc_large_node_hook(void *ptr, size_t size, gfp_t flags)
+static inline void *kmalloc_large_node_hook(void *ptr, size_t size, gfp_t flags)
{
kmemleak_alloc(ptr, size, 1, flags);
- kasan_kmalloc_large(ptr, size, flags);
+ return kasan_kmalloc_large(ptr, size, flags);
}
static __always_inline void kfree_hook(void *x)
@@ -2731,7 +2731,7 @@ void *kmem_cache_alloc_trace(struct kmem_cache *s, gfp_t gfpflags, size_t size)
{
void *ret = slab_alloc(s, gfpflags, _RET_IP_);
trace_kmalloc(_RET_IP_, ret, size, s->size, gfpflags);
- kasan_kmalloc(s, ret, size, gfpflags);
+ ret = kasan_kmalloc(s, ret, size, gfpflags);
return ret;
}
EXPORT_SYMBOL(kmem_cache_alloc_trace);
@@ -2759,7 +2759,7 @@ void *kmem_cache_alloc_node_trace(struct kmem_cache *s,
trace_kmalloc_node(_RET_IP_, ret,
size, s->size, gfpflags, node);
- kasan_kmalloc(s, ret, size, gfpflags);
+ ret = kasan_kmalloc(s, ret, size, gfpflags);
return ret;
}
EXPORT_SYMBOL(kmem_cache_alloc_node_trace);
@@ -3749,7 +3749,7 @@ void *__kmalloc(size_t size, gfp_t flags)
trace_kmalloc(_RET_IP_, ret, size, s->size, flags);
- kasan_kmalloc(s, ret, size, flags);
+ ret = kasan_kmalloc(s, ret, size, flags);
return ret;
}
@@ -3766,8 +3766,7 @@ static void *kmalloc_large_node(size_t size, gfp_t flags, int node)
if (page)
ptr = page_address(page);
- kmalloc_large_node_hook(ptr, size, flags);
- return ptr;
+ return kmalloc_large_node_hook(ptr, size, flags);
}
void *__kmalloc_node(size_t size, gfp_t flags, int node)
@@ -3794,7 +3793,7 @@ void *__kmalloc_node(size_t size, gfp_t flags, int node)
trace_kmalloc_node(_RET_IP_, ret, size, s->size, flags, node);
- kasan_kmalloc(s, ret, size, flags);
+ ret = kasan_kmalloc(s, ret, size, flags);
return ret;
}
--
2.19.0.rc0.228.g281dcd1b4d0-goog
This commit splits the current CONFIG_KASAN config option into two:
1. CONFIG_KASAN_GENERIC, that enables the generic software-only KASAN
version (the one that exists now);
2. CONFIG_KASAN_HW, that enables KHWASAN.
With CONFIG_KASAN_HW enabled, compiler options are changed to instrument
kernel files wiht -fsantize=hwaddress (except the ones for which
KASAN_SANITIZE := n is set).
Both CONFIG_KASAN_GENERIC and CONFIG_KASAN_HW support both
CONFIG_KASAN_INLINE and CONFIG_KASAN_OUTLINE instrumentation modes.
This commit also adds empty placeholder (for now) implementation of
KHWASAN specific hooks inserted by the compiler and adjusts common hooks
implementation to compile correctly with each of the config options.
Signed-off-by: Andrey Konovalov <[email protected]>
---
arch/arm64/Kconfig | 1 +
include/linux/compiler-clang.h | 3 +-
include/linux/compiler-gcc.h | 4 ++
include/linux/compiler.h | 3 +-
include/linux/kasan.h | 16 +++++--
lib/Kconfig.kasan | 77 ++++++++++++++++++++++++++--------
mm/kasan/Makefile | 6 ++-
mm/kasan/kasan.h | 3 +-
mm/kasan/khwasan.c | 75 +++++++++++++++++++++++++++++++++
mm/slub.c | 2 +-
scripts/Makefile.kasan | 27 +++++++++++-
11 files changed, 188 insertions(+), 29 deletions(-)
create mode 100644 mm/kasan/khwasan.c
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 29e75b47becd..991564148f54 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -105,6 +105,7 @@ config ARM64
select HAVE_ARCH_HUGE_VMAP
select HAVE_ARCH_JUMP_LABEL
select HAVE_ARCH_KASAN if !(ARM64_16K_PAGES && ARM64_VA_BITS_48)
+ select HAVE_ARCH_KASAN_HW if !(ARM64_16K_PAGES && ARM64_VA_BITS_48)
select HAVE_ARCH_KGDB
select HAVE_ARCH_MMAP_RND_BITS
select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index b1ce500fe8b3..2c258a9d4c67 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -17,11 +17,12 @@
#define KASAN_ABI_VERSION 5
/* emulate gcc's __SANITIZE_ADDRESS__ flag */
-#if __has_feature(address_sanitizer)
+#if __has_feature(address_sanitizer) || __has_feature(hwaddress_sanitizer)
#define __SANITIZE_ADDRESS__
#endif
#define __no_sanitize_address __attribute__((no_sanitize("address")))
+#define __no_sanitize_hwaddress __attribute__((no_sanitize("hwaddress")))
/*
* Not all versions of clang implement the the type-generic versions
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 763bbad1e258..a186b55c8c4c 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -227,6 +227,10 @@
#define __no_sanitize_address
#endif
+#if !defined(__no_sanitize_hwaddress)
+#define __no_sanitize_hwaddress /* gcc doesn't support KHWASAN */
+#endif
+
/*
* Turn individual warnings and errors on and off locally, depending
* on version.
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 681d866efb1e..3f2ba192d57d 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -195,7 +195,8 @@ void __read_once_size(const volatile void *p, void *res, int size)
* https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
* '__maybe_unused' allows us to avoid defined-but-not-used warnings.
*/
-# define __no_kasan_or_inline __no_sanitize_address __maybe_unused
+# define __no_kasan_or_inline __no_sanitize_address __no_sanitize_hwaddress \
+ __maybe_unused
#else
# define __no_kasan_or_inline __always_inline
#endif
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 54d577ad2181..beb56a26fe9b 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -45,8 +45,6 @@ void kasan_free_pages(struct page *page, unsigned int order);
void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
slab_flags_t *flags);
-void kasan_cache_shrink(struct kmem_cache *cache);
-void kasan_cache_shutdown(struct kmem_cache *cache);
void kasan_poison_slab(struct page *page);
void kasan_unpoison_object_data(struct kmem_cache *cache, void *object);
@@ -97,8 +95,6 @@ static inline void kasan_free_pages(struct page *page, unsigned int order) {}
static inline void kasan_cache_create(struct kmem_cache *cache,
unsigned int *size,
slab_flags_t *flags) {}
-static inline void kasan_cache_shrink(struct kmem_cache *cache) {}
-static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
static inline void kasan_poison_slab(struct page *page) {}
static inline void kasan_unpoison_object_data(struct kmem_cache *cache,
@@ -152,4 +148,16 @@ static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
#endif /* CONFIG_KASAN */
+#ifdef CONFIG_KASAN_GENERIC
+
+void kasan_cache_shrink(struct kmem_cache *cache);
+void kasan_cache_shutdown(struct kmem_cache *cache);
+
+#else /* CONFIG_KASAN_GENERIC */
+
+static inline void kasan_cache_shrink(struct kmem_cache *cache) {}
+static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
+
+#endif /* CONFIG_KASAN_GENERIC */
+
#endif /* LINUX_KASAN_H */
diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index befb127507c0..5a22629f30e7 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -1,34 +1,75 @@
config HAVE_ARCH_KASAN
bool
+config HAVE_ARCH_KASAN_HW
+ bool
+
if HAVE_ARCH_KASAN
config KASAN
- bool "KASan: runtime memory debugger"
+ bool "KASAN: runtime memory debugger"
+ help
+ Enables KASAN (KernelAddressSANitizer) - runtime memory debugger,
+ designed to find out-of-bounds accesses and use-after-free bugs.
+
+choice
+ prompt "KASAN mode"
+ depends on KASAN
+ default KASAN_GENERIC
+ help
+ KASAN has two modes: KASAN (a classic version, similar to userspace
+ ASan, enabled with CONFIG_KASAN_GENERIC) and KHWASAN (a version
+ based on pointer tagging, only for arm64, similar to userspace
+ HWASan, enabled with CONFIG_KASAN_HW).
+
+config KASAN_GENERIC
+ bool "KASAN: the generic mode"
depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
select SLUB_DEBUG if SLUB
select CONSTRUCTORS
select STACKDEPOT
help
- Enables kernel address sanitizer - runtime memory debugger,
- designed to find out-of-bounds accesses and use-after-free bugs.
- This is strictly a debugging feature and it requires a gcc version
- of 4.9.2 or later. Detection of out of bounds accesses to stack or
- global variables requires gcc 5.0 or later.
- This feature consumes about 1/8 of available memory and brings about
- ~x3 performance slowdown.
+ Enables the generic mode of KASAN.
+ This is strictly a debugging feature and it requires a GCC version
+ of 4.9.2 or later. Detection of out-of-bounds accesses to stack or
+ global variables requires GCC 5.0 or later.
+ This mode consumes about 1/8 of available memory at kernel start
+ and introduces an overhead of ~x1.5 for the rest of the allocations.
+ The performance slowdown is ~x3.
For better error detection enable CONFIG_STACKTRACE.
- Currently CONFIG_KASAN doesn't work with CONFIG_DEBUG_SLAB
+ Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB
(the resulting kernel does not boot).
+if HAVE_ARCH_KASAN_HW
+
+config KASAN_HW
+ bool "KHWASAN: the hardware assisted mode"
+ depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
+ select SLUB_DEBUG if SLUB
+ select CONSTRUCTORS
+ select STACKDEPOT
+ help
+ Enabled KHWASAN (KASAN mode based on pointer tagging).
+ This mode requires Top Byte Ignore support by the CPU and therefore
+ only supported for arm64.
+ This feature requires clang revision 330044 or later.
+ This mode consumes about 1/16 of available memory at kernel start
+ and introduces an overhead of ~20% for the rest of the allocations.
+ For better error detection enable CONFIG_STACKTRACE.
+ Currently CONFIG_KASAN_HW doesn't work with CONFIG_DEBUG_SLAB
+ (the resulting kernel does not boot).
+
+endif
+
+endchoice
+
config KASAN_EXTRA
- bool "KAsan: extra checks"
- depends on KASAN && DEBUG_KERNEL && !COMPILE_TEST
+ bool "KASAN: extra checks"
+ depends on KASAN_GENERIC && DEBUG_KERNEL && !COMPILE_TEST
help
- This enables further checks in the kernel address sanitizer, for now
- it only includes the address-use-after-scope check that can lead
- to excessive kernel stack usage, frame size warnings and longer
- compile time.
+ This enables further checks in KASAN, for now it only includes the
+ address-use-after-scope check that can lead to excessive kernel
+ stack usage, frame size warnings and longer compile time.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715 has more
@@ -53,16 +94,16 @@ config KASAN_INLINE
memory accesses. This is faster than outline (in some workloads
it gives about x2 boost over outline instrumentation), but
make kernel's .text size much bigger.
- This requires a gcc version of 5.0 or later.
+ For CONFIG_KASAN_GENERIC this requires GCC 5.0 or later.
endchoice
config TEST_KASAN
- tristate "Module for testing kasan for bug detection"
+ tristate "Module for testing KASAN for bug detection"
depends on m && KASAN
help
This is a test module doing various nasty things like
out of bounds accesses, use after free. It is useful for testing
- kernel debugging features like kernel address sanitizer.
+ kernel debugging features like KASAN.
endif
diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
index a6df14bffb6b..14955add96d3 100644
--- a/mm/kasan/Makefile
+++ b/mm/kasan/Makefile
@@ -2,6 +2,7 @@
KASAN_SANITIZE := n
UBSAN_SANITIZE_common.o := n
UBSAN_SANITIZE_kasan.o := n
+UBSAN_SANITIZE_khwasan.o := n
KCOV_INSTRUMENT := n
CFLAGS_REMOVE_kasan.o = -pg
@@ -10,5 +11,8 @@ CFLAGS_REMOVE_kasan.o = -pg
CFLAGS_common.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
CFLAGS_kasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
+CFLAGS_khwasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
-obj-y := common.o kasan.o report.o kasan_init.o quarantine.o
+obj-$(CONFIG_KASAN) := common.o kasan_init.o report.o
+obj-$(CONFIG_KASAN_GENERIC) += kasan.o quarantine.o
+obj-$(CONFIG_KASAN_HW) += khwasan.o
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 659463800f10..19b950eaccff 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -114,7 +114,8 @@ void kasan_report(unsigned long addr, size_t size,
bool is_write, unsigned long ip);
void kasan_report_invalid_free(void *object, unsigned long ip);
-#if defined(CONFIG_SLAB) || defined(CONFIG_SLUB)
+#if defined(CONFIG_KASAN_GENERIC) && \
+ (defined(CONFIG_SLAB) || defined(CONFIG_SLUB))
void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache);
void quarantine_reduce(void);
void quarantine_remove_cache(struct kmem_cache *cache);
diff --git a/mm/kasan/khwasan.c b/mm/kasan/khwasan.c
new file mode 100644
index 000000000000..e2c3a7f7fd1f
--- /dev/null
+++ b/mm/kasan/khwasan.c
@@ -0,0 +1,75 @@
+/*
+ * This file contains core KHWASAN code.
+ *
+ * Copyright (c) 2018 Google, Inc.
+ * Author: Andrey Konovalov <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+#define DISABLE_BRANCH_PROFILING
+
+#include <linux/export.h>
+#include <linux/interrupt.h>
+#include <linux/init.h>
+#include <linux/kasan.h>
+#include <linux/kernel.h>
+#include <linux/kmemleak.h>
+#include <linux/linkage.h>
+#include <linux/memblock.h>
+#include <linux/memory.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/random.h>
+#include <linux/sched.h>
+#include <linux/sched/task_stack.h>
+#include <linux/slab.h>
+#include <linux/stacktrace.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/vmalloc.h>
+#include <linux/bug.h>
+
+#include "kasan.h"
+#include "../slab.h"
+
+void check_memory_region(unsigned long addr, size_t size, bool write,
+ unsigned long ret_ip)
+{
+}
+
+#define DEFINE_HWASAN_LOAD_STORE(size) \
+ void __hwasan_load##size##_noabort(unsigned long addr) \
+ { \
+ } \
+ EXPORT_SYMBOL(__hwasan_load##size##_noabort); \
+ void __hwasan_store##size##_noabort(unsigned long addr) \
+ { \
+ } \
+ EXPORT_SYMBOL(__hwasan_store##size##_noabort)
+
+DEFINE_HWASAN_LOAD_STORE(1);
+DEFINE_HWASAN_LOAD_STORE(2);
+DEFINE_HWASAN_LOAD_STORE(4);
+DEFINE_HWASAN_LOAD_STORE(8);
+DEFINE_HWASAN_LOAD_STORE(16);
+
+void __hwasan_loadN_noabort(unsigned long addr, unsigned long size)
+{
+}
+EXPORT_SYMBOL(__hwasan_loadN_noabort);
+
+void __hwasan_storeN_noabort(unsigned long addr, unsigned long size)
+{
+}
+EXPORT_SYMBOL(__hwasan_storeN_noabort);
+
+void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
+{
+}
+EXPORT_SYMBOL(__hwasan_tag_memory);
diff --git a/mm/slub.c b/mm/slub.c
index 30b9bf777bab..4206e1b616e7 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2955,7 +2955,7 @@ static __always_inline void slab_free(struct kmem_cache *s, struct page *page,
do_slab_free(s, page, head, tail, cnt, addr);
}
-#ifdef CONFIG_KASAN
+#ifdef CONFIG_KASAN_GENERIC
void ___cache_free(struct kmem_cache *cache, void *x, unsigned long addr)
{
do_slab_free(cache, virt_to_head_page(x), x, NULL, 1, addr);
diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
index 69552a39951d..49c6e056c697 100644
--- a/scripts/Makefile.kasan
+++ b/scripts/Makefile.kasan
@@ -1,5 +1,5 @@
# SPDX-License-Identifier: GPL-2.0
-ifdef CONFIG_KASAN
+ifdef CONFIG_KASAN_GENERIC
ifdef CONFIG_KASAN_INLINE
call_threshold := 10000
else
@@ -42,6 +42,29 @@ ifdef CONFIG_KASAN_EXTRA
CFLAGS_KASAN += $(call cc-option, -fsanitize-address-use-after-scope)
endif
-CFLAGS_KASAN_NOSANITIZE := -fno-builtin
+endif
+
+ifdef CONFIG_KASAN_HW
+
+ifdef CONFIG_KASAN_INLINE
+ instrumentation_flags := -mllvm -hwasan-mapping-offset=$(KASAN_SHADOW_OFFSET)
+else
+ instrumentation_flags := -mllvm -hwasan-instrument-with-calls=1
+endif
+CFLAGS_KASAN := -fsanitize=kernel-hwaddress \
+ -mllvm -hwasan-instrument-stack=0 \
+ $(instrumentation_flags)
+
+ifeq ($(call cc-option, $(CFLAGS_KASAN) -Werror),)
+ ifneq ($(CONFIG_COMPILE_TEST),y)
+ $(warning Cannot use CONFIG_KASAN_HW: \
+ -fsanitize=hwaddress is not supported by compiler)
+ endif
+endif
+
+endif
+
+ifdef CONFIG_KASAN
+CFLAGS_KASAN_NOSANITIZE := -fno-builtin
endif
--
2.19.0.rc0.228.g281dcd1b4d0-goog
KHWASAN will reuse a significant part of KASAN code, so move the common
parts to common.c without any functional changes.
Signed-off-by: Andrey Konovalov <[email protected]>
---
mm/kasan/Makefile | 5 +-
mm/kasan/common.c | 604 ++++++++++++++++++++++++++++++++++++++++++++++
mm/kasan/kasan.c | 568 +------------------------------------------
mm/kasan/kasan.h | 5 +
4 files changed, 615 insertions(+), 567 deletions(-)
create mode 100644 mm/kasan/common.c
diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
index 3289db38bc87..a6df14bffb6b 100644
--- a/mm/kasan/Makefile
+++ b/mm/kasan/Makefile
@@ -1,11 +1,14 @@
# SPDX-License-Identifier: GPL-2.0
KASAN_SANITIZE := n
+UBSAN_SANITIZE_common.o := n
UBSAN_SANITIZE_kasan.o := n
KCOV_INSTRUMENT := n
CFLAGS_REMOVE_kasan.o = -pg
# Function splitter causes unnecessary splits in __asan_load1/__asan_store1
# see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63533
+
+CFLAGS_common.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
CFLAGS_kasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
-obj-y := kasan.o report.o kasan_init.o quarantine.o
+obj-y := common.o kasan.o report.o kasan_init.o quarantine.o
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
new file mode 100644
index 000000000000..154010ba6c1f
--- /dev/null
+++ b/mm/kasan/common.c
@@ -0,0 +1,604 @@
+/*
+ * This file contains common KASAN and KHWASAN code.
+ *
+ * Copyright (c) 2014 Samsung Electronics Co., Ltd.
+ * Author: Andrey Ryabinin <[email protected]>
+ *
+ * Some code borrowed from https://github.com/xairy/kasan-prototype by
+ * Andrey Konovalov <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#include <linux/export.h>
+#include <linux/interrupt.h>
+#include <linux/init.h>
+#include <linux/kasan.h>
+#include <linux/kernel.h>
+#include <linux/kmemleak.h>
+#include <linux/linkage.h>
+#include <linux/memblock.h>
+#include <linux/memory.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/sched.h>
+#include <linux/sched/task_stack.h>
+#include <linux/slab.h>
+#include <linux/stacktrace.h>
+#include <linux/string.h>
+#include <linux/types.h>
+#include <linux/vmalloc.h>
+#include <linux/bug.h>
+
+#include "kasan.h"
+#include "../slab.h"
+
+static inline int in_irqentry_text(unsigned long ptr)
+{
+ return (ptr >= (unsigned long)&__irqentry_text_start &&
+ ptr < (unsigned long)&__irqentry_text_end) ||
+ (ptr >= (unsigned long)&__softirqentry_text_start &&
+ ptr < (unsigned long)&__softirqentry_text_end);
+}
+
+static inline void filter_irq_stacks(struct stack_trace *trace)
+{
+ int i;
+
+ if (!trace->nr_entries)
+ return;
+ for (i = 0; i < trace->nr_entries; i++)
+ if (in_irqentry_text(trace->entries[i])) {
+ /* Include the irqentry function into the stack. */
+ trace->nr_entries = i + 1;
+ break;
+ }
+}
+
+static inline depot_stack_handle_t save_stack(gfp_t flags)
+{
+ unsigned long entries[KASAN_STACK_DEPTH];
+ struct stack_trace trace = {
+ .nr_entries = 0,
+ .entries = entries,
+ .max_entries = KASAN_STACK_DEPTH,
+ .skip = 0
+ };
+
+ save_stack_trace(&trace);
+ filter_irq_stacks(&trace);
+ if (trace.nr_entries != 0 &&
+ trace.entries[trace.nr_entries-1] == ULONG_MAX)
+ trace.nr_entries--;
+
+ return depot_save_stack(&trace, flags);
+}
+
+static inline void set_track(struct kasan_track *track, gfp_t flags)
+{
+ track->pid = current->pid;
+ track->stack = save_stack(flags);
+}
+
+void kasan_enable_current(void)
+{
+ current->kasan_depth++;
+}
+
+void kasan_disable_current(void)
+{
+ current->kasan_depth--;
+}
+
+void kasan_check_read(const volatile void *p, unsigned int size)
+{
+ check_memory_region((unsigned long)p, size, false, _RET_IP_);
+}
+EXPORT_SYMBOL(kasan_check_read);
+
+void kasan_check_write(const volatile void *p, unsigned int size)
+{
+ check_memory_region((unsigned long)p, size, true, _RET_IP_);
+}
+EXPORT_SYMBOL(kasan_check_write);
+
+#undef memset
+void *memset(void *addr, int c, size_t len)
+{
+ check_memory_region((unsigned long)addr, len, true, _RET_IP_);
+
+ return __memset(addr, c, len);
+}
+
+#undef memmove
+void *memmove(void *dest, const void *src, size_t len)
+{
+ check_memory_region((unsigned long)src, len, false, _RET_IP_);
+ check_memory_region((unsigned long)dest, len, true, _RET_IP_);
+
+ return __memmove(dest, src, len);
+}
+
+#undef memcpy
+void *memcpy(void *dest, const void *src, size_t len)
+{
+ check_memory_region((unsigned long)src, len, false, _RET_IP_);
+ check_memory_region((unsigned long)dest, len, true, _RET_IP_);
+
+ return __memcpy(dest, src, len);
+}
+
+/*
+ * Poisons the shadow memory for 'size' bytes starting from 'addr'.
+ * Memory addresses should be aligned to KASAN_SHADOW_SCALE_SIZE.
+ */
+void kasan_poison_shadow(const void *address, size_t size, u8 value)
+{
+ void *shadow_start, *shadow_end;
+
+ shadow_start = kasan_mem_to_shadow(address);
+ shadow_end = kasan_mem_to_shadow(address + size);
+
+ __memset(shadow_start, value, shadow_end - shadow_start);
+}
+
+void kasan_unpoison_shadow(const void *address, size_t size)
+{
+ kasan_poison_shadow(address, size, 0);
+
+ if (size & KASAN_SHADOW_MASK) {
+ u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size);
+ *shadow = size & KASAN_SHADOW_MASK;
+ }
+}
+
+static void __kasan_unpoison_stack(struct task_struct *task, const void *sp)
+{
+ void *base = task_stack_page(task);
+ size_t size = sp - base;
+
+ kasan_unpoison_shadow(base, size);
+}
+
+/* Unpoison the entire stack for a task. */
+void kasan_unpoison_task_stack(struct task_struct *task)
+{
+ __kasan_unpoison_stack(task, task_stack_page(task) + THREAD_SIZE);
+}
+
+/* Unpoison the stack for the current task beyond a watermark sp value. */
+asmlinkage void kasan_unpoison_task_stack_below(const void *watermark)
+{
+ /*
+ * Calculate the task stack base address. Avoid using 'current'
+ * because this function is called by early resume code which hasn't
+ * yet set up the percpu register (%gs).
+ */
+ void *base = (void *)((unsigned long)watermark & ~(THREAD_SIZE - 1));
+
+ kasan_unpoison_shadow(base, watermark - base);
+}
+
+/*
+ * Clear all poison for the region between the current SP and a provided
+ * watermark value, as is sometimes required prior to hand-crafted asm function
+ * returns in the middle of functions.
+ */
+void kasan_unpoison_stack_above_sp_to(const void *watermark)
+{
+ const void *sp = __builtin_frame_address(0);
+ size_t size = watermark - sp;
+
+ if (WARN_ON(sp > watermark))
+ return;
+ kasan_unpoison_shadow(sp, size);
+}
+
+void kasan_alloc_pages(struct page *page, unsigned int order)
+{
+ if (likely(!PageHighMem(page)))
+ kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order);
+}
+
+void kasan_free_pages(struct page *page, unsigned int order)
+{
+ if (likely(!PageHighMem(page)))
+ kasan_poison_shadow(page_address(page),
+ PAGE_SIZE << order,
+ KASAN_FREE_PAGE);
+}
+
+/*
+ * Adaptive redzone policy taken from the userspace AddressSanitizer runtime.
+ * For larger allocations larger redzones are used.
+ */
+static inline unsigned int optimal_redzone(unsigned int object_size)
+{
+ if (IS_ENABLED(CONFIG_KASAN_HW))
+ return 0;
+
+ return
+ object_size <= 64 - 16 ? 16 :
+ object_size <= 128 - 32 ? 32 :
+ object_size <= 512 - 64 ? 64 :
+ object_size <= 4096 - 128 ? 128 :
+ object_size <= (1 << 14) - 256 ? 256 :
+ object_size <= (1 << 15) - 512 ? 512 :
+ object_size <= (1 << 16) - 1024 ? 1024 : 2048;
+}
+
+void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
+ slab_flags_t *flags)
+{
+ unsigned int orig_size = *size;
+ int redzone_adjust;
+
+ /* Add alloc meta. */
+ cache->kasan_info.alloc_meta_offset = *size;
+ *size += sizeof(struct kasan_alloc_meta);
+
+ /* Add free meta. */
+ if (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
+ cache->object_size < sizeof(struct kasan_free_meta)) {
+ cache->kasan_info.free_meta_offset = *size;
+ *size += sizeof(struct kasan_free_meta);
+ }
+ redzone_adjust = optimal_redzone(cache->object_size) -
+ (*size - cache->object_size);
+
+ if (redzone_adjust > 0)
+ *size += redzone_adjust;
+
+ *size = min_t(unsigned int, KMALLOC_MAX_SIZE,
+ max(*size, cache->object_size +
+ optimal_redzone(cache->object_size)));
+
+ /*
+ * If the metadata doesn't fit, don't enable KASAN at all.
+ */
+ if (*size <= cache->kasan_info.alloc_meta_offset ||
+ *size <= cache->kasan_info.free_meta_offset) {
+ cache->kasan_info.alloc_meta_offset = 0;
+ cache->kasan_info.free_meta_offset = 0;
+ *size = orig_size;
+ return;
+ }
+
+ *flags |= SLAB_KASAN;
+}
+
+size_t kasan_metadata_size(struct kmem_cache *cache)
+{
+ return (cache->kasan_info.alloc_meta_offset ?
+ sizeof(struct kasan_alloc_meta) : 0) +
+ (cache->kasan_info.free_meta_offset ?
+ sizeof(struct kasan_free_meta) : 0);
+}
+
+struct kasan_alloc_meta *get_alloc_info(struct kmem_cache *cache,
+ const void *object)
+{
+ BUILD_BUG_ON(sizeof(struct kasan_alloc_meta) > 32);
+ return (void *)object + cache->kasan_info.alloc_meta_offset;
+}
+
+struct kasan_free_meta *get_free_info(struct kmem_cache *cache,
+ const void *object)
+{
+ BUILD_BUG_ON(sizeof(struct kasan_free_meta) > 32);
+ return (void *)object + cache->kasan_info.free_meta_offset;
+}
+
+void kasan_poison_slab(struct page *page)
+{
+ kasan_poison_shadow(page_address(page),
+ PAGE_SIZE << compound_order(page),
+ KASAN_KMALLOC_REDZONE);
+}
+
+void kasan_unpoison_object_data(struct kmem_cache *cache, void *object)
+{
+ kasan_unpoison_shadow(object, cache->object_size);
+}
+
+void kasan_poison_object_data(struct kmem_cache *cache, void *object)
+{
+ kasan_poison_shadow(object,
+ round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE),
+ KASAN_KMALLOC_REDZONE);
+}
+
+void kasan_init_slab_obj(struct kmem_cache *cache, const void *object)
+{
+ struct kasan_alloc_meta *alloc_info;
+
+ if (!(cache->flags & SLAB_KASAN))
+ return;
+
+ alloc_info = get_alloc_info(cache, object);
+ __memset(alloc_info, 0, sizeof(*alloc_info));
+}
+
+void *kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags)
+{
+ return kasan_kmalloc(cache, object, cache->object_size, flags);
+}
+
+static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
+ unsigned long ip, bool quarantine)
+{
+ s8 shadow_byte;
+ unsigned long rounded_up_size;
+
+ if (unlikely(nearest_obj(cache, virt_to_head_page(object), object) !=
+ object)) {
+ kasan_report_invalid_free(object, ip);
+ return true;
+ }
+
+ /* RCU slabs could be legally used after free within the RCU period */
+ if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU))
+ return false;
+
+ shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
+ if (shadow_byte < 0 || shadow_byte >= KASAN_SHADOW_SCALE_SIZE) {
+ kasan_report_invalid_free(object, ip);
+ return true;
+ }
+
+ rounded_up_size = round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE);
+ kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE);
+
+ if (!quarantine || unlikely(!(cache->flags & SLAB_KASAN)))
+ return false;
+
+ set_track(&get_alloc_info(cache, object)->free_track, GFP_NOWAIT);
+ quarantine_put(get_free_info(cache, object), cache);
+ return true;
+}
+
+bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
+{
+ return __kasan_slab_free(cache, object, ip, true);
+}
+
+void *kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
+ gfp_t flags)
+{
+ unsigned long redzone_start;
+ unsigned long redzone_end;
+
+ if (gfpflags_allow_blocking(flags))
+ quarantine_reduce();
+
+ if (unlikely(object == NULL))
+ return NULL;
+
+ redzone_start = round_up((unsigned long)(object + size),
+ KASAN_SHADOW_SCALE_SIZE);
+ redzone_end = round_up((unsigned long)object + cache->object_size,
+ KASAN_SHADOW_SCALE_SIZE);
+
+ kasan_unpoison_shadow(object, size);
+ kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
+ KASAN_KMALLOC_REDZONE);
+
+ if (cache->flags & SLAB_KASAN)
+ set_track(&get_alloc_info(cache, object)->alloc_track, flags);
+
+ return (void *)object;
+}
+EXPORT_SYMBOL(kasan_kmalloc);
+
+void *kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags)
+{
+ struct page *page;
+ unsigned long redzone_start;
+ unsigned long redzone_end;
+
+ if (gfpflags_allow_blocking(flags))
+ quarantine_reduce();
+
+ if (unlikely(ptr == NULL))
+ return NULL;
+
+ page = virt_to_page(ptr);
+ redzone_start = round_up((unsigned long)(ptr + size),
+ KASAN_SHADOW_SCALE_SIZE);
+ redzone_end = (unsigned long)ptr + (PAGE_SIZE << compound_order(page));
+
+ kasan_unpoison_shadow(ptr, size);
+ kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
+ KASAN_PAGE_REDZONE);
+
+ return (void *)ptr;
+}
+
+void *kasan_krealloc(const void *object, size_t size, gfp_t flags)
+{
+ struct page *page;
+
+ if (unlikely(object == ZERO_SIZE_PTR))
+ return (void *)object;
+
+ page = virt_to_head_page(object);
+
+ if (unlikely(!PageSlab(page)))
+ return kasan_kmalloc_large(object, size, flags);
+ else
+ return kasan_kmalloc(page->slab_cache, object, size, flags);
+}
+
+void kasan_poison_kfree(void *ptr, unsigned long ip)
+{
+ struct page *page;
+
+ page = virt_to_head_page(ptr);
+
+ if (unlikely(!PageSlab(page))) {
+ if (ptr != page_address(page)) {
+ kasan_report_invalid_free(ptr, ip);
+ return;
+ }
+ kasan_poison_shadow(ptr, PAGE_SIZE << compound_order(page),
+ KASAN_FREE_PAGE);
+ } else {
+ __kasan_slab_free(page->slab_cache, ptr, ip, false);
+ }
+}
+
+void kasan_kfree_large(void *ptr, unsigned long ip)
+{
+ if (ptr != page_address(virt_to_head_page(ptr)))
+ kasan_report_invalid_free(ptr, ip);
+ /* The object will be poisoned by page_alloc. */
+}
+
+int kasan_module_alloc(void *addr, size_t size)
+{
+ void *ret;
+ size_t scaled_size;
+ size_t shadow_size;
+ unsigned long shadow_start;
+
+ shadow_start = (unsigned long)kasan_mem_to_shadow(addr);
+ scaled_size = (size + KASAN_SHADOW_MASK) >> KASAN_SHADOW_SCALE_SHIFT;
+ shadow_size = round_up(scaled_size, PAGE_SIZE);
+
+ if (WARN_ON(!PAGE_ALIGNED(shadow_start)))
+ return -EINVAL;
+
+ ret = __vmalloc_node_range(shadow_size, 1, shadow_start,
+ shadow_start + shadow_size,
+ GFP_KERNEL | __GFP_ZERO,
+ PAGE_KERNEL, VM_NO_GUARD, NUMA_NO_NODE,
+ __builtin_return_address(0));
+
+ if (ret) {
+ find_vm_area(addr)->flags |= VM_KASAN;
+ kmemleak_ignore(ret);
+ return 0;
+ }
+
+ return -ENOMEM;
+}
+
+void kasan_free_shadow(const struct vm_struct *vm)
+{
+ if (vm->flags & VM_KASAN)
+ vfree(kasan_mem_to_shadow(vm->addr));
+}
+
+#ifdef CONFIG_MEMORY_HOTPLUG
+static bool shadow_mapped(unsigned long addr)
+{
+ pgd_t *pgd = pgd_offset_k(addr);
+ p4d_t *p4d;
+ pud_t *pud;
+ pmd_t *pmd;
+ pte_t *pte;
+
+ if (pgd_none(*pgd))
+ return false;
+ p4d = p4d_offset(pgd, addr);
+ if (p4d_none(*p4d))
+ return false;
+ pud = pud_offset(p4d, addr);
+ if (pud_none(*pud))
+ return false;
+
+ /*
+ * We can't use pud_large() or pud_huge(), the first one is
+ * arch-specific, the last one depends on HUGETLB_PAGE. So let's abuse
+ * pud_bad(), if pud is bad then it's bad because it's huge.
+ */
+ if (pud_bad(*pud))
+ return true;
+ pmd = pmd_offset(pud, addr);
+ if (pmd_none(*pmd))
+ return false;
+
+ if (pmd_bad(*pmd))
+ return true;
+ pte = pte_offset_kernel(pmd, addr);
+ return !pte_none(*pte);
+}
+
+static int __meminit kasan_mem_notifier(struct notifier_block *nb,
+ unsigned long action, void *data)
+{
+ struct memory_notify *mem_data = data;
+ unsigned long nr_shadow_pages, start_kaddr, shadow_start;
+ unsigned long shadow_end, shadow_size;
+
+ nr_shadow_pages = mem_data->nr_pages >> KASAN_SHADOW_SCALE_SHIFT;
+ start_kaddr = (unsigned long)pfn_to_kaddr(mem_data->start_pfn);
+ shadow_start = (unsigned long)kasan_mem_to_shadow((void *)start_kaddr);
+ shadow_size = nr_shadow_pages << PAGE_SHIFT;
+ shadow_end = shadow_start + shadow_size;
+
+ if (WARN_ON(mem_data->nr_pages % KASAN_SHADOW_SCALE_SIZE) ||
+ WARN_ON(start_kaddr % (KASAN_SHADOW_SCALE_SIZE << PAGE_SHIFT)))
+ return NOTIFY_BAD;
+
+ switch (action) {
+ case MEM_GOING_ONLINE: {
+ void *ret;
+
+ /*
+ * If shadow is mapped already than it must have been mapped
+ * during the boot. This could happen if we onlining previously
+ * offlined memory.
+ */
+ if (shadow_mapped(shadow_start))
+ return NOTIFY_OK;
+
+ ret = __vmalloc_node_range(shadow_size, PAGE_SIZE, shadow_start,
+ shadow_end, GFP_KERNEL,
+ PAGE_KERNEL, VM_NO_GUARD,
+ pfn_to_nid(mem_data->start_pfn),
+ __builtin_return_address(0));
+ if (!ret)
+ return NOTIFY_BAD;
+
+ kmemleak_ignore(ret);
+ return NOTIFY_OK;
+ }
+ case MEM_CANCEL_ONLINE:
+ case MEM_OFFLINE: {
+ struct vm_struct *vm;
+
+ /*
+ * shadow_start was either mapped during boot by kasan_init()
+ * or during memory online by __vmalloc_node_range().
+ * In the latter case we can use vfree() to free shadow.
+ * Non-NULL result of the find_vm_area() will tell us if
+ * that was the second case.
+ *
+ * Currently it's not possible to free shadow mapped
+ * during boot by kasan_init(). It's because the code
+ * to do that hasn't been written yet. So we'll just
+ * leak the memory.
+ */
+ vm = find_vm_area((void *)shadow_start);
+ if (vm)
+ vfree((void *)shadow_start);
+ }
+ }
+
+ return NOTIFY_OK;
+}
+
+static int __init kasan_memhotplug_init(void)
+{
+ hotplug_memory_notifier(kasan_mem_notifier, 0);
+
+ return 0;
+}
+
+core_initcall(kasan_memhotplug_init);
+#endif
diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index f696c7c143c2..44ec228de0a2 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -1,5 +1,5 @@
/*
- * This file contains shadow memory manipulation code.
+ * This file contains core KASAN code.
*
* Copyright (c) 2014 Samsung Electronics Co., Ltd.
* Author: Andrey Ryabinin <[email protected]>
@@ -40,82 +40,6 @@
#include "kasan.h"
#include "../slab.h"
-void kasan_enable_current(void)
-{
- current->kasan_depth++;
-}
-
-void kasan_disable_current(void)
-{
- current->kasan_depth--;
-}
-
-/*
- * Poisons the shadow memory for 'size' bytes starting from 'addr'.
- * Memory addresses should be aligned to KASAN_SHADOW_SCALE_SIZE.
- */
-static void kasan_poison_shadow(const void *address, size_t size, u8 value)
-{
- void *shadow_start, *shadow_end;
-
- shadow_start = kasan_mem_to_shadow(address);
- shadow_end = kasan_mem_to_shadow(address + size);
-
- memset(shadow_start, value, shadow_end - shadow_start);
-}
-
-void kasan_unpoison_shadow(const void *address, size_t size)
-{
- kasan_poison_shadow(address, size, 0);
-
- if (size & KASAN_SHADOW_MASK) {
- u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size);
- *shadow = size & KASAN_SHADOW_MASK;
- }
-}
-
-static void __kasan_unpoison_stack(struct task_struct *task, const void *sp)
-{
- void *base = task_stack_page(task);
- size_t size = sp - base;
-
- kasan_unpoison_shadow(base, size);
-}
-
-/* Unpoison the entire stack for a task. */
-void kasan_unpoison_task_stack(struct task_struct *task)
-{
- __kasan_unpoison_stack(task, task_stack_page(task) + THREAD_SIZE);
-}
-
-/* Unpoison the stack for the current task beyond a watermark sp value. */
-asmlinkage void kasan_unpoison_task_stack_below(const void *watermark)
-{
- /*
- * Calculate the task stack base address. Avoid using 'current'
- * because this function is called by early resume code which hasn't
- * yet set up the percpu register (%gs).
- */
- void *base = (void *)((unsigned long)watermark & ~(THREAD_SIZE - 1));
-
- kasan_unpoison_shadow(base, watermark - base);
-}
-
-/*
- * Clear all poison for the region between the current SP and a provided
- * watermark value, as is sometimes required prior to hand-crafted asm function
- * returns in the middle of functions.
- */
-void kasan_unpoison_stack_above_sp_to(const void *watermark)
-{
- const void *sp = __builtin_frame_address(0);
- size_t size = watermark - sp;
-
- if (WARN_ON(sp > watermark))
- return;
- kasan_unpoison_shadow(sp, size);
-}
-
/*
* All functions below always inlined so compiler could
* perform better optimizations in each of __asan_loadX/__assn_storeX
@@ -260,121 +184,12 @@ static __always_inline void check_memory_region_inline(unsigned long addr,
kasan_report(addr, size, write, ret_ip);
}
-static void check_memory_region(unsigned long addr,
- size_t size, bool write,
+void check_memory_region(unsigned long addr, size_t size, bool write,
unsigned long ret_ip)
{
check_memory_region_inline(addr, size, write, ret_ip);
}
-void kasan_check_read(const volatile void *p, unsigned int size)
-{
- check_memory_region((unsigned long)p, size, false, _RET_IP_);
-}
-EXPORT_SYMBOL(kasan_check_read);
-
-void kasan_check_write(const volatile void *p, unsigned int size)
-{
- check_memory_region((unsigned long)p, size, true, _RET_IP_);
-}
-EXPORT_SYMBOL(kasan_check_write);
-
-#undef memset
-void *memset(void *addr, int c, size_t len)
-{
- check_memory_region((unsigned long)addr, len, true, _RET_IP_);
-
- return __memset(addr, c, len);
-}
-
-#undef memmove
-void *memmove(void *dest, const void *src, size_t len)
-{
- check_memory_region((unsigned long)src, len, false, _RET_IP_);
- check_memory_region((unsigned long)dest, len, true, _RET_IP_);
-
- return __memmove(dest, src, len);
-}
-
-#undef memcpy
-void *memcpy(void *dest, const void *src, size_t len)
-{
- check_memory_region((unsigned long)src, len, false, _RET_IP_);
- check_memory_region((unsigned long)dest, len, true, _RET_IP_);
-
- return __memcpy(dest, src, len);
-}
-
-void kasan_alloc_pages(struct page *page, unsigned int order)
-{
- if (likely(!PageHighMem(page)))
- kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order);
-}
-
-void kasan_free_pages(struct page *page, unsigned int order)
-{
- if (likely(!PageHighMem(page)))
- kasan_poison_shadow(page_address(page),
- PAGE_SIZE << order,
- KASAN_FREE_PAGE);
-}
-
-/*
- * Adaptive redzone policy taken from the userspace AddressSanitizer runtime.
- * For larger allocations larger redzones are used.
- */
-static unsigned int optimal_redzone(unsigned int object_size)
-{
- return
- object_size <= 64 - 16 ? 16 :
- object_size <= 128 - 32 ? 32 :
- object_size <= 512 - 64 ? 64 :
- object_size <= 4096 - 128 ? 128 :
- object_size <= (1 << 14) - 256 ? 256 :
- object_size <= (1 << 15) - 512 ? 512 :
- object_size <= (1 << 16) - 1024 ? 1024 : 2048;
-}
-
-void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
- slab_flags_t *flags)
-{
- unsigned int orig_size = *size;
- int redzone_adjust;
-
- /* Add alloc meta. */
- cache->kasan_info.alloc_meta_offset = *size;
- *size += sizeof(struct kasan_alloc_meta);
-
- /* Add free meta. */
- if (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
- cache->object_size < sizeof(struct kasan_free_meta)) {
- cache->kasan_info.free_meta_offset = *size;
- *size += sizeof(struct kasan_free_meta);
- }
- redzone_adjust = optimal_redzone(cache->object_size) -
- (*size - cache->object_size);
-
- if (redzone_adjust > 0)
- *size += redzone_adjust;
-
- *size = min_t(unsigned int, KMALLOC_MAX_SIZE,
- max(*size, cache->object_size +
- optimal_redzone(cache->object_size)));
-
- /*
- * If the metadata doesn't fit, don't enable KASAN at all.
- */
- if (*size <= cache->kasan_info.alloc_meta_offset ||
- *size <= cache->kasan_info.free_meta_offset) {
- cache->kasan_info.alloc_meta_offset = 0;
- cache->kasan_info.free_meta_offset = 0;
- *size = orig_size;
- return;
- }
-
- *flags |= SLAB_KASAN;
-}
-
void kasan_cache_shrink(struct kmem_cache *cache)
{
quarantine_remove_cache(cache);
@@ -386,275 +201,6 @@ void kasan_cache_shutdown(struct kmem_cache *cache)
quarantine_remove_cache(cache);
}
-size_t kasan_metadata_size(struct kmem_cache *cache)
-{
- return (cache->kasan_info.alloc_meta_offset ?
- sizeof(struct kasan_alloc_meta) : 0) +
- (cache->kasan_info.free_meta_offset ?
- sizeof(struct kasan_free_meta) : 0);
-}
-
-void kasan_poison_slab(struct page *page)
-{
- kasan_poison_shadow(page_address(page),
- PAGE_SIZE << compound_order(page),
- KASAN_KMALLOC_REDZONE);
-}
-
-void kasan_unpoison_object_data(struct kmem_cache *cache, void *object)
-{
- kasan_unpoison_shadow(object, cache->object_size);
-}
-
-void kasan_poison_object_data(struct kmem_cache *cache, void *object)
-{
- kasan_poison_shadow(object,
- round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE),
- KASAN_KMALLOC_REDZONE);
-}
-
-static inline int in_irqentry_text(unsigned long ptr)
-{
- return (ptr >= (unsigned long)&__irqentry_text_start &&
- ptr < (unsigned long)&__irqentry_text_end) ||
- (ptr >= (unsigned long)&__softirqentry_text_start &&
- ptr < (unsigned long)&__softirqentry_text_end);
-}
-
-static inline void filter_irq_stacks(struct stack_trace *trace)
-{
- int i;
-
- if (!trace->nr_entries)
- return;
- for (i = 0; i < trace->nr_entries; i++)
- if (in_irqentry_text(trace->entries[i])) {
- /* Include the irqentry function into the stack. */
- trace->nr_entries = i + 1;
- break;
- }
-}
-
-static inline depot_stack_handle_t save_stack(gfp_t flags)
-{
- unsigned long entries[KASAN_STACK_DEPTH];
- struct stack_trace trace = {
- .nr_entries = 0,
- .entries = entries,
- .max_entries = KASAN_STACK_DEPTH,
- .skip = 0
- };
-
- save_stack_trace(&trace);
- filter_irq_stacks(&trace);
- if (trace.nr_entries != 0 &&
- trace.entries[trace.nr_entries-1] == ULONG_MAX)
- trace.nr_entries--;
-
- return depot_save_stack(&trace, flags);
-}
-
-static inline void set_track(struct kasan_track *track, gfp_t flags)
-{
- track->pid = current->pid;
- track->stack = save_stack(flags);
-}
-
-struct kasan_alloc_meta *get_alloc_info(struct kmem_cache *cache,
- const void *object)
-{
- BUILD_BUG_ON(sizeof(struct kasan_alloc_meta) > 32);
- return (void *)object + cache->kasan_info.alloc_meta_offset;
-}
-
-struct kasan_free_meta *get_free_info(struct kmem_cache *cache,
- const void *object)
-{
- BUILD_BUG_ON(sizeof(struct kasan_free_meta) > 32);
- return (void *)object + cache->kasan_info.free_meta_offset;
-}
-
-void kasan_init_slab_obj(struct kmem_cache *cache, const void *object)
-{
- struct kasan_alloc_meta *alloc_info;
-
- if (!(cache->flags & SLAB_KASAN))
- return;
-
- alloc_info = get_alloc_info(cache, object);
- __memset(alloc_info, 0, sizeof(*alloc_info));
-}
-
-void *kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags)
-{
- return kasan_kmalloc(cache, object, cache->object_size, flags);
-}
-
-static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
- unsigned long ip, bool quarantine)
-{
- s8 shadow_byte;
- unsigned long rounded_up_size;
-
- if (unlikely(nearest_obj(cache, virt_to_head_page(object), object) !=
- object)) {
- kasan_report_invalid_free(object, ip);
- return true;
- }
-
- /* RCU slabs could be legally used after free within the RCU period */
- if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU))
- return false;
-
- shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
- if (shadow_byte < 0 || shadow_byte >= KASAN_SHADOW_SCALE_SIZE) {
- kasan_report_invalid_free(object, ip);
- return true;
- }
-
- rounded_up_size = round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE);
- kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE);
-
- if (!quarantine || unlikely(!(cache->flags & SLAB_KASAN)))
- return false;
-
- set_track(&get_alloc_info(cache, object)->free_track, GFP_NOWAIT);
- quarantine_put(get_free_info(cache, object), cache);
- return true;
-}
-
-bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
-{
- return __kasan_slab_free(cache, object, ip, true);
-}
-
-void *kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
- gfp_t flags)
-{
- unsigned long redzone_start;
- unsigned long redzone_end;
-
- if (gfpflags_allow_blocking(flags))
- quarantine_reduce();
-
- if (unlikely(object == NULL))
- return NULL;
-
- redzone_start = round_up((unsigned long)(object + size),
- KASAN_SHADOW_SCALE_SIZE);
- redzone_end = round_up((unsigned long)object + cache->object_size,
- KASAN_SHADOW_SCALE_SIZE);
-
- kasan_unpoison_shadow(object, size);
- kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
- KASAN_KMALLOC_REDZONE);
-
- if (cache->flags & SLAB_KASAN)
- set_track(&get_alloc_info(cache, object)->alloc_track, flags);
-
- return (void *)object;
-}
-EXPORT_SYMBOL(kasan_kmalloc);
-
-void *kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags)
-{
- struct page *page;
- unsigned long redzone_start;
- unsigned long redzone_end;
-
- if (gfpflags_allow_blocking(flags))
- quarantine_reduce();
-
- if (unlikely(ptr == NULL))
- return NULL;
-
- page = virt_to_page(ptr);
- redzone_start = round_up((unsigned long)(ptr + size),
- KASAN_SHADOW_SCALE_SIZE);
- redzone_end = (unsigned long)ptr + (PAGE_SIZE << compound_order(page));
-
- kasan_unpoison_shadow(ptr, size);
- kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
- KASAN_PAGE_REDZONE);
-
- return (void *)ptr;
-}
-
-void *kasan_krealloc(const void *object, size_t size, gfp_t flags)
-{
- struct page *page;
-
- if (unlikely(object == ZERO_SIZE_PTR))
- return ZERO_SIZE_PTR;
-
- page = virt_to_head_page(object);
-
- if (unlikely(!PageSlab(page)))
- return kasan_kmalloc_large(object, size, flags);
- else
- return kasan_kmalloc(page->slab_cache, object, size, flags);
-}
-
-void kasan_poison_kfree(void *ptr, unsigned long ip)
-{
- struct page *page;
-
- page = virt_to_head_page(ptr);
-
- if (unlikely(!PageSlab(page))) {
- if (ptr != page_address(page)) {
- kasan_report_invalid_free(ptr, ip);
- return;
- }
- kasan_poison_shadow(ptr, PAGE_SIZE << compound_order(page),
- KASAN_FREE_PAGE);
- } else {
- __kasan_slab_free(page->slab_cache, ptr, ip, false);
- }
-}
-
-void kasan_kfree_large(void *ptr, unsigned long ip)
-{
- if (ptr != page_address(virt_to_head_page(ptr)))
- kasan_report_invalid_free(ptr, ip);
- /* The object will be poisoned by page_alloc. */
-}
-
-int kasan_module_alloc(void *addr, size_t size)
-{
- void *ret;
- size_t scaled_size;
- size_t shadow_size;
- unsigned long shadow_start;
-
- shadow_start = (unsigned long)kasan_mem_to_shadow(addr);
- scaled_size = (size + KASAN_SHADOW_MASK) >> KASAN_SHADOW_SCALE_SHIFT;
- shadow_size = round_up(scaled_size, PAGE_SIZE);
-
- if (WARN_ON(!PAGE_ALIGNED(shadow_start)))
- return -EINVAL;
-
- ret = __vmalloc_node_range(shadow_size, 1, shadow_start,
- shadow_start + shadow_size,
- GFP_KERNEL | __GFP_ZERO,
- PAGE_KERNEL, VM_NO_GUARD, NUMA_NO_NODE,
- __builtin_return_address(0));
-
- if (ret) {
- find_vm_area(addr)->flags |= VM_KASAN;
- kmemleak_ignore(ret);
- return 0;
- }
-
- return -ENOMEM;
-}
-
-void kasan_free_shadow(const struct vm_struct *vm)
-{
- if (vm->flags & VM_KASAN)
- vfree(kasan_mem_to_shadow(vm->addr));
-}
-
static void register_global(struct kasan_global *global)
{
size_t aligned_size = round_up(global->size, KASAN_SHADOW_SCALE_SIZE);
@@ -795,113 +341,3 @@ DEFINE_ASAN_SET_SHADOW(f2);
DEFINE_ASAN_SET_SHADOW(f3);
DEFINE_ASAN_SET_SHADOW(f5);
DEFINE_ASAN_SET_SHADOW(f8);
-
-#ifdef CONFIG_MEMORY_HOTPLUG
-static bool shadow_mapped(unsigned long addr)
-{
- pgd_t *pgd = pgd_offset_k(addr);
- p4d_t *p4d;
- pud_t *pud;
- pmd_t *pmd;
- pte_t *pte;
-
- if (pgd_none(*pgd))
- return false;
- p4d = p4d_offset(pgd, addr);
- if (p4d_none(*p4d))
- return false;
- pud = pud_offset(p4d, addr);
- if (pud_none(*pud))
- return false;
-
- /*
- * We can't use pud_large() or pud_huge(), the first one is
- * arch-specific, the last one depends on HUGETLB_PAGE. So let's abuse
- * pud_bad(), if pud is bad then it's bad because it's huge.
- */
- if (pud_bad(*pud))
- return true;
- pmd = pmd_offset(pud, addr);
- if (pmd_none(*pmd))
- return false;
-
- if (pmd_bad(*pmd))
- return true;
- pte = pte_offset_kernel(pmd, addr);
- return !pte_none(*pte);
-}
-
-static int __meminit kasan_mem_notifier(struct notifier_block *nb,
- unsigned long action, void *data)
-{
- struct memory_notify *mem_data = data;
- unsigned long nr_shadow_pages, start_kaddr, shadow_start;
- unsigned long shadow_end, shadow_size;
-
- nr_shadow_pages = mem_data->nr_pages >> KASAN_SHADOW_SCALE_SHIFT;
- start_kaddr = (unsigned long)pfn_to_kaddr(mem_data->start_pfn);
- shadow_start = (unsigned long)kasan_mem_to_shadow((void *)start_kaddr);
- shadow_size = nr_shadow_pages << PAGE_SHIFT;
- shadow_end = shadow_start + shadow_size;
-
- if (WARN_ON(mem_data->nr_pages % KASAN_SHADOW_SCALE_SIZE) ||
- WARN_ON(start_kaddr % (KASAN_SHADOW_SCALE_SIZE << PAGE_SHIFT)))
- return NOTIFY_BAD;
-
- switch (action) {
- case MEM_GOING_ONLINE: {
- void *ret;
-
- /*
- * If shadow is mapped already than it must have been mapped
- * during the boot. This could happen if we onlining previously
- * offlined memory.
- */
- if (shadow_mapped(shadow_start))
- return NOTIFY_OK;
-
- ret = __vmalloc_node_range(shadow_size, PAGE_SIZE, shadow_start,
- shadow_end, GFP_KERNEL,
- PAGE_KERNEL, VM_NO_GUARD,
- pfn_to_nid(mem_data->start_pfn),
- __builtin_return_address(0));
- if (!ret)
- return NOTIFY_BAD;
-
- kmemleak_ignore(ret);
- return NOTIFY_OK;
- }
- case MEM_CANCEL_ONLINE:
- case MEM_OFFLINE: {
- struct vm_struct *vm;
-
- /*
- * shadow_start was either mapped during boot by kasan_init()
- * or during memory online by __vmalloc_node_range().
- * In the latter case we can use vfree() to free shadow.
- * Non-NULL result of the find_vm_area() will tell us if
- * that was the second case.
- *
- * Currently it's not possible to free shadow mapped
- * during boot by kasan_init(). It's because the code
- * to do that hasn't been written yet. So we'll just
- * leak the memory.
- */
- vm = find_vm_area((void *)shadow_start);
- if (vm)
- vfree((void *)shadow_start);
- }
- }
-
- return NOTIFY_OK;
-}
-
-static int __init kasan_memhotplug_init(void)
-{
- hotplug_memory_notifier(kasan_mem_notifier, 0);
-
- return 0;
-}
-
-core_initcall(kasan_memhotplug_init);
-#endif
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index c12dcfde2ebd..659463800f10 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -105,6 +105,11 @@ static inline const void *kasan_shadow_to_mem(const void *shadow_addr)
<< KASAN_SHADOW_SCALE_SHIFT);
}
+void kasan_poison_shadow(const void *address, size_t size, u8 value);
+
+void check_memory_region(unsigned long addr, size_t size, bool write,
+ unsigned long ret_ip);
+
void kasan_report(unsigned long addr, size_t size,
bool is_write, unsigned long ip);
void kasan_report_invalid_free(void *object, unsigned long ip);
--
2.19.0.rc0.228.g281dcd1b4d0-goog
On Wed, 29 Aug 2018 13:35:04 +0200 Andrey Konovalov <[email protected]> wrote:
> This patchset adds a new mode to KASAN [1], which is called KHWASAN
> (Kernel HardWare assisted Address SANitizer).
We're at v6 and there are no reviewed-by's or acked-by's to be seen.
Is that a fair commentary on what has been happening, or have people
been remiss in sending and gathering such things?
On Wed, Sep 5, 2018 at 2:10 PM Andrew Morton <[email protected]> wrote:
>
> On Wed, 29 Aug 2018 13:35:04 +0200 Andrey Konovalov <[email protected]> wrote:
>
> > This patchset adds a new mode to KASAN [1], which is called KHWASAN
> > (Kernel HardWare assisted Address SANitizer).
>
> We're at v6 and there are no reviewed-by's or acked-by's to be seen.
> Is that a fair commentary on what has been happening, or have people
> been remiss in sending and gathering such things?
>
I'm anxious to use these for Pixel Android devices. Looks like the
series has been aggregating changes from valuable feedback. Maybe if
the ARM maintainers and KASAN maintainers could Ack or Nack these, we
could decide to merge these or what needs more work?
--
Thanks,
~Nick Desaulniers
On Wed, Sep 05, 2018 at 02:10:32PM -0700, Andrew Morton wrote:
> On Wed, 29 Aug 2018 13:35:04 +0200 Andrey Konovalov <[email protected]> wrote:
>
> > This patchset adds a new mode to KASAN [1], which is called KHWASAN
> > (Kernel HardWare assisted Address SANitizer).
>
> We're at v6 and there are no reviewed-by's or acked-by's to be seen.
> Is that a fair commentary on what has been happening, or have people
> been remiss in sending and gathering such things?
I still have concerns about the consequences of merging this as anything
other than a debug option [1]. Unfortunately, merging it as a debug option
defeats the whole point, so I think we need to spend more effort on developing
tools that can help us to find and fix the subtle bugs which will arise from
enabling tagged pointers in the kernel.
Will
[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2018-August/596077.html
On Thu, Sep 6, 2018 at 12:05 PM, Will Deacon <[email protected]> wrote:
> On Wed, Sep 05, 2018 at 02:10:32PM -0700, Andrew Morton wrote:
>> On Wed, 29 Aug 2018 13:35:04 +0200 Andrey Konovalov <[email protected]> wrote:
>>
>> > This patchset adds a new mode to KASAN [1], which is called KHWASAN
>> > (Kernel HardWare assisted Address SANitizer).
>>
>> We're at v6 and there are no reviewed-by's or acked-by's to be seen.
>> Is that a fair commentary on what has been happening, or have people
>> been remiss in sending and gathering such things?
>
> I still have concerns about the consequences of merging this as anything
> other than a debug option [1]. Unfortunately, merging it as a debug option
> defeats the whole point, so I think we need to spend more effort on developing
> tools that can help us to find and fix the subtle bugs which will arise from
> enabling tagged pointers in the kernel.
I totally don't mind calling it a debug option. Do I need to somehow
specify it somewhere?
Why does it defeat the point? The point is to ease KASAN-like testing
on devices with limited memory.
On Thu, Sep 6, 2018 at 4:06 AM Andrey Konovalov <[email protected]> wrote:
>
> On Thu, Sep 6, 2018 at 12:05 PM, Will Deacon <[email protected]> wrote:
> > On Wed, Sep 05, 2018 at 02:10:32PM -0700, Andrew Morton wrote:
> >> On Wed, 29 Aug 2018 13:35:04 +0200 Andrey Konovalov <[email protected]> wrote:
> >>
> >> > This patchset adds a new mode to KASAN [1], which is called KHWASAN
> >> > (Kernel HardWare assisted Address SANitizer).
> >>
> >> We're at v6 and there are no reviewed-by's or acked-by's to be seen.
> >> Is that a fair commentary on what has been happening, or have people
> >> been remiss in sending and gathering such things?
> >
> > I still have concerns about the consequences of merging this as anything
> > other than a debug option [1]. Unfortunately, merging it as a debug option
> > defeats the whole point, so I think we need to spend more effort on developing
> > tools that can help us to find and fix the subtle bugs which will arise from
> > enabling tagged pointers in the kernel.
>
> I totally don't mind calling it a debug option. Do I need to somehow
> specify it somewhere?
>
> Why does it defeat the point? The point is to ease KASAN-like testing
> on devices with limited memory.
I don't disagree with using it strictly for debug. When I say I want
the series for Pixel phones, I should have been clearer that my intent
is for a limited pool of internal testers to walk around with KHWASAN
enabled devices; not general end users. It's hard enough today to get
anyone to test KASAN/ASAN on their "daily driver" due to the memory
usage and resulting performance.
We don't ship KASAN or KUBSAN on by default to end users (nor plan
to); it's used strictly for fuzzing through syzkaller (or by brave
"dogfooders" on the internal kernel teams). KHWASAN would let these
dogfooders go from being brave to fearless.
--
Thanks,
~Nick Desaulniers
On 08/29/2018 02:35 PM, Andrey Konovalov wrote:
> void kasan_poison_slab(struct page *page)
> {
> + unsigned long i;
> +
> + if (IS_ENABLED(CONFIG_SLAB))
> + page->s_mem = reset_tag(page->s_mem);
Why reinitialize here, instead of single initialization in alloc_slabmgmt()?
> + for (i = 0; i < (1 << compound_order(page)); i++)
> + page_kasan_tag_reset(page + i);
> kasan_poison_shadow(page_address(page),
> PAGE_SIZE << compound_order(page),
> KASAN_KMALLOC_REDZONE);
On 08/29/2018 02:35 PM, Andrey Konovalov wrote:
> Andrey Konovalov (18):
> khwasan, mm: change kasan hooks signatures
> khwasan: move common kasan and khwasan code to common.c
> khwasan: add CONFIG_KASAN_GENERIC and CONFIG_KASAN_HW
> khwasan, arm64: adjust shadow size for CONFIG_KASAN_HW
> khwasan: initialize shadow to 0xff
> khwasan, arm64: untag virt address in __kimg_to_phys and
> _virt_addr_is_linear
> khwasan: add tag related helper functions
> khwasan: preassign tags to objects with ctors or SLAB_TYPESAFE_BY_RCU
> khwasan, arm64: fix up fault handling logic
> khwasan, arm64: enable top byte ignore for the kernel
> khwasan, mm: perform untagged pointers comparison in krealloc
> khwasan: split out kasan_report.c from report.c
> khwasan: add bug reporting routines
> khwasan: add hooks implementation
> khwasan, arm64: add brk handler for inline instrumentation
> khwasan, mm, arm64: tag non slab memory allocated via pagealloc
> khwasan: update kasan documentation
> kasan: add SPDX-License-Identifier mark to source files
>
Aside from nit in 16/18 patch looks fine for me.
Reviewed-by: Andrey Ryabinin <[email protected]>
On Fri, Sep 7, 2018 at 6:06 PM, Andrey Ryabinin <[email protected]> wrote:
>
>
> On 08/29/2018 02:35 PM, Andrey Konovalov wrote:
>
>> void kasan_poison_slab(struct page *page)
>> {
>> + unsigned long i;
>> +
>> + if (IS_ENABLED(CONFIG_SLAB))
>> + page->s_mem = reset_tag(page->s_mem);
>
> Why reinitialize here, instead of single initialization in alloc_slabmgmt()?
Hm, don't see why I did it this way, looks odd to me as well. Will fix
in v7, thanks!
On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
> This commit splits the current CONFIG_KASAN config option into two:
> 1. CONFIG_KASAN_GENERIC, that enables the generic software-only KASAN
> version (the one that exists now);
> 2. CONFIG_KASAN_HW, that enables KHWASAN.
>
> With CONFIG_KASAN_HW enabled, compiler options are changed to instrument
> kernel files wiht -fsantize=hwaddress (except the ones for which
> KASAN_SANITIZE := n is set).
>
> Both CONFIG_KASAN_GENERIC and CONFIG_KASAN_HW support both
> CONFIG_KASAN_INLINE and CONFIG_KASAN_OUTLINE instrumentation modes.
>
> This commit also adds empty placeholder (for now) implementation of
> KHWASAN specific hooks inserted by the compiler and adjusts common hooks
> implementation to compile correctly with each of the config options.
>
> Signed-off-by: Andrey Konovalov <[email protected]>
> ---
> arch/arm64/Kconfig | 1 +
> include/linux/compiler-clang.h | 3 +-
> include/linux/compiler-gcc.h | 4 ++
> include/linux/compiler.h | 3 +-
> include/linux/kasan.h | 16 +++++--
> lib/Kconfig.kasan | 77 ++++++++++++++++++++++++++--------
> mm/kasan/Makefile | 6 ++-
> mm/kasan/kasan.h | 3 +-
> mm/kasan/khwasan.c | 75 +++++++++++++++++++++++++++++++++
> mm/slub.c | 2 +-
> scripts/Makefile.kasan | 27 +++++++++++-
> 11 files changed, 188 insertions(+), 29 deletions(-)
> create mode 100644 mm/kasan/khwasan.c
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 29e75b47becd..991564148f54 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -105,6 +105,7 @@ config ARM64
> select HAVE_ARCH_HUGE_VMAP
> select HAVE_ARCH_JUMP_LABEL
> select HAVE_ARCH_KASAN if !(ARM64_16K_PAGES && ARM64_VA_BITS_48)
> + select HAVE_ARCH_KASAN_HW if !(ARM64_16K_PAGES && ARM64_VA_BITS_48)
> select HAVE_ARCH_KGDB
> select HAVE_ARCH_MMAP_RND_BITS
> select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
> diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
> index b1ce500fe8b3..2c258a9d4c67 100644
> --- a/include/linux/compiler-clang.h
> +++ b/include/linux/compiler-clang.h
> @@ -17,11 +17,12 @@
> #define KASAN_ABI_VERSION 5
>
> /* emulate gcc's __SANITIZE_ADDRESS__ flag */
> -#if __has_feature(address_sanitizer)
> +#if __has_feature(address_sanitizer) || __has_feature(hwaddress_sanitizer)
> #define __SANITIZE_ADDRESS__
> #endif
>
> #define __no_sanitize_address __attribute__((no_sanitize("address")))
> +#define __no_sanitize_hwaddress __attribute__((no_sanitize("hwaddress")))
It seems that it would be better to have just 1 attribute for both types.
Currently __no_sanitize_address is used just in a single place. But if
it ever used more, people will need to always spell both which looks
unnecessary, or, worse will only fix asan but forget about khwasan.
If we do just:
#define __no_sanitize_address __attribute__((no_sanitize("address",
"hwaddress")))
Then we don't need any changes in compiler-gcc.h nor in compiler.h,
and no chance or forgetting one of them.
> /*
> * Not all versions of clang implement the the type-generic versions
> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
> index 763bbad1e258..a186b55c8c4c 100644
> --- a/include/linux/compiler-gcc.h
> +++ b/include/linux/compiler-gcc.h
> @@ -227,6 +227,10 @@
> #define __no_sanitize_address
> #endif
>
> +#if !defined(__no_sanitize_hwaddress)
> +#define __no_sanitize_hwaddress /* gcc doesn't support KHWASAN */
> +#endif
> +
> /*
> * Turn individual warnings and errors on and off locally, depending
> * on version.
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index 681d866efb1e..3f2ba192d57d 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -195,7 +195,8 @@ void __read_once_size(const volatile void *p, void *res, int size)
> * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
> * '__maybe_unused' allows us to avoid defined-but-not-used warnings.
> */
> -# define __no_kasan_or_inline __no_sanitize_address __maybe_unused
> +# define __no_kasan_or_inline __no_sanitize_address __no_sanitize_hwaddress \
> + __maybe_unused
> #else
> # define __no_kasan_or_inline __always_inline
> #endif
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 54d577ad2181..beb56a26fe9b 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -45,8 +45,6 @@ void kasan_free_pages(struct page *page, unsigned int order);
>
> void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
> slab_flags_t *flags);
> -void kasan_cache_shrink(struct kmem_cache *cache);
> -void kasan_cache_shutdown(struct kmem_cache *cache);
>
> void kasan_poison_slab(struct page *page);
> void kasan_unpoison_object_data(struct kmem_cache *cache, void *object);
> @@ -97,8 +95,6 @@ static inline void kasan_free_pages(struct page *page, unsigned int order) {}
> static inline void kasan_cache_create(struct kmem_cache *cache,
> unsigned int *size,
> slab_flags_t *flags) {}
> -static inline void kasan_cache_shrink(struct kmem_cache *cache) {}
> -static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
>
> static inline void kasan_poison_slab(struct page *page) {}
> static inline void kasan_unpoison_object_data(struct kmem_cache *cache,
> @@ -152,4 +148,16 @@ static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
>
> #endif /* CONFIG_KASAN */
>
> +#ifdef CONFIG_KASAN_GENERIC
> +
> +void kasan_cache_shrink(struct kmem_cache *cache);
> +void kasan_cache_shutdown(struct kmem_cache *cache);
> +
> +#else /* CONFIG_KASAN_GENERIC */
> +
> +static inline void kasan_cache_shrink(struct kmem_cache *cache) {}
> +static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
> +
> +#endif /* CONFIG_KASAN_GENERIC */
> +
> #endif /* LINUX_KASAN_H */
> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
> index befb127507c0..5a22629f30e7 100644
> --- a/lib/Kconfig.kasan
> +++ b/lib/Kconfig.kasan
> @@ -1,34 +1,75 @@
> config HAVE_ARCH_KASAN
> bool
>
> +config HAVE_ARCH_KASAN_HW
> + bool
> +
> if HAVE_ARCH_KASAN
>
> config KASAN
> - bool "KASan: runtime memory debugger"
> + bool "KASAN: runtime memory debugger"
> + help
> + Enables KASAN (KernelAddressSANitizer) - runtime memory debugger,
> + designed to find out-of-bounds accesses and use-after-free bugs.
Perhaps also give link to Documentation/dev-tools/kasan.rst while we are here.
> +
> +choice
> + prompt "KASAN mode"
> + depends on KASAN
> + default KASAN_GENERIC
> + help
> + KASAN has two modes: KASAN (a classic version, similar to userspace
In these few sentences we call the old mode with 3 different terms:
"generic", "classic" and "KASAN" :)
This is somewhat confusing. Let's call it "generic" throughout (here
and in the docs patch). "Generic" as in "supported on multiple arch
and not-dependent on hardware features". "Classic" makes sense for
people who knew KASAN before, but for future readers in won't make
sense.
> + ASan, enabled with CONFIG_KASAN_GENERIC) and KHWASAN (a version
> + based on pointer tagging, only for arm64, similar to userspace
> + HWASan, enabled with CONFIG_KASAN_HW).
> +
> +config KASAN_GENERIC
> + bool "KASAN: the generic mode"
> depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
> select SLUB_DEBUG if SLUB
> select CONSTRUCTORS
> select STACKDEPOT
> help
> - Enables kernel address sanitizer - runtime memory debugger,
> - designed to find out-of-bounds accesses and use-after-free bugs.
> - This is strictly a debugging feature and it requires a gcc version
> - of 4.9.2 or later. Detection of out of bounds accesses to stack or
> - global variables requires gcc 5.0 or later.
> - This feature consumes about 1/8 of available memory and brings about
> - ~x3 performance slowdown.
> + Enables the generic mode of KASAN.
> + This is strictly a debugging feature and it requires a GCC version
> + of 4.9.2 or later. Detection of out-of-bounds accesses to stack or
> + global variables requires GCC 5.0 or later.
> + This mode consumes about 1/8 of available memory at kernel start
> + and introduces an overhead of ~x1.5 for the rest of the allocations.
> + The performance slowdown is ~x3.
> For better error detection enable CONFIG_STACKTRACE.
> - Currently CONFIG_KASAN doesn't work with CONFIG_DEBUG_SLAB
> + Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB
> (the resulting kernel does not boot).
>
> +if HAVE_ARCH_KASAN_HW
This choice looks somewhat weird on non-arm64. It's kinda a choice
menu, but one can't really choose anything. Should we put the whole
choice under HAVE_ARCH_KASAN_HW, and just select KASAN_GENERIC
otherwise? I don't know what't the practice here. Andrey R?
> +config KASAN_HW
> + bool "KHWASAN: the hardware assisted mode"
> + depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
> + select SLUB_DEBUG if SLUB
> + select CONSTRUCTORS
> + select STACKDEPOT
> + help
> + Enabled KHWASAN (KASAN mode based on pointer tagging).
> + This mode requires Top Byte Ignore support by the CPU and therefore
> + only supported for arm64.
> + This feature requires clang revision 330044 or later.
> + This mode consumes about 1/16 of available memory at kernel start
> + and introduces an overhead of ~20% for the rest of the allocations.
> + For better error detection enable CONFIG_STACKTRACE.
> + Currently CONFIG_KASAN_HW doesn't work with CONFIG_DEBUG_SLAB
> + (the resulting kernel does not boot).
> +
> +endif
> +
> +endchoice
> +
> config KASAN_EXTRA
> - bool "KAsan: extra checks"
> - depends on KASAN && DEBUG_KERNEL && !COMPILE_TEST
> + bool "KASAN: extra checks"
> + depends on KASAN_GENERIC && DEBUG_KERNEL && !COMPILE_TEST
> help
> - This enables further checks in the kernel address sanitizer, for now
> - it only includes the address-use-after-scope check that can lead
> - to excessive kernel stack usage, frame size warnings and longer
> - compile time.
> + This enables further checks in KASAN, for now it only includes the
> + address-use-after-scope check that can lead to excessive kernel
> + stack usage, frame size warnings and longer compile time.
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715 has more
>
>
> @@ -53,16 +94,16 @@ config KASAN_INLINE
> memory accesses. This is faster than outline (in some workloads
> it gives about x2 boost over outline instrumentation), but
> make kernel's .text size much bigger.
> - This requires a gcc version of 5.0 or later.
> + For CONFIG_KASAN_GENERIC this requires GCC 5.0 or later.
>
> endchoice
>
> config TEST_KASAN
> - tristate "Module for testing kasan for bug detection"
> + tristate "Module for testing KASAN for bug detection"
> depends on m && KASAN
> help
> This is a test module doing various nasty things like
> out of bounds accesses, use after free. It is useful for testing
> - kernel debugging features like kernel address sanitizer.
> + kernel debugging features like KASAN.
>
> endif
> diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
> index a6df14bffb6b..14955add96d3 100644
> --- a/mm/kasan/Makefile
> +++ b/mm/kasan/Makefile
> @@ -2,6 +2,7 @@
> KASAN_SANITIZE := n
> UBSAN_SANITIZE_common.o := n
> UBSAN_SANITIZE_kasan.o := n
> +UBSAN_SANITIZE_khwasan.o := n
> KCOV_INSTRUMENT := n
>
> CFLAGS_REMOVE_kasan.o = -pg
> @@ -10,5 +11,8 @@ CFLAGS_REMOVE_kasan.o = -pg
>
> CFLAGS_common.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
> CFLAGS_kasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
> +CFLAGS_khwasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
>
> -obj-y := common.o kasan.o report.o kasan_init.o quarantine.o
> +obj-$(CONFIG_KASAN) := common.o kasan_init.o report.o
> +obj-$(CONFIG_KASAN_GENERIC) += kasan.o quarantine.o
> +obj-$(CONFIG_KASAN_HW) += khwasan.o
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 659463800f10..19b950eaccff 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -114,7 +114,8 @@ void kasan_report(unsigned long addr, size_t size,
> bool is_write, unsigned long ip);
> void kasan_report_invalid_free(void *object, unsigned long ip);
>
> -#if defined(CONFIG_SLAB) || defined(CONFIG_SLUB)
> +#if defined(CONFIG_KASAN_GENERIC) && \
> + (defined(CONFIG_SLAB) || defined(CONFIG_SLUB))
> void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache);
> void quarantine_reduce(void);
> void quarantine_remove_cache(struct kmem_cache *cache);
> diff --git a/mm/kasan/khwasan.c b/mm/kasan/khwasan.c
> new file mode 100644
> index 000000000000..e2c3a7f7fd1f
> --- /dev/null
> +++ b/mm/kasan/khwasan.c
> @@ -0,0 +1,75 @@
> +/*
> + * This file contains core KHWASAN code.
> + *
> + * Copyright (c) 2018 Google, Inc.
> + * Author: Andrey Konovalov <[email protected]>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +#define DISABLE_BRANCH_PROFILING
> +
> +#include <linux/export.h>
> +#include <linux/interrupt.h>
> +#include <linux/init.h>
> +#include <linux/kasan.h>
> +#include <linux/kernel.h>
> +#include <linux/kmemleak.h>
> +#include <linux/linkage.h>
> +#include <linux/memblock.h>
> +#include <linux/memory.h>
> +#include <linux/mm.h>
> +#include <linux/module.h>
> +#include <linux/printk.h>
> +#include <linux/random.h>
> +#include <linux/sched.h>
> +#include <linux/sched/task_stack.h>
> +#include <linux/slab.h>
> +#include <linux/stacktrace.h>
> +#include <linux/string.h>
> +#include <linux/types.h>
> +#include <linux/vmalloc.h>
> +#include <linux/bug.h>
> +
> +#include "kasan.h"
> +#include "../slab.h"
> +
> +void check_memory_region(unsigned long addr, size_t size, bool write,
> + unsigned long ret_ip)
> +{
> +}
> +
> +#define DEFINE_HWASAN_LOAD_STORE(size) \
> + void __hwasan_load##size##_noabort(unsigned long addr) \
> + { \
> + } \
> + EXPORT_SYMBOL(__hwasan_load##size##_noabort); \
> + void __hwasan_store##size##_noabort(unsigned long addr) \
> + { \
> + } \
> + EXPORT_SYMBOL(__hwasan_store##size##_noabort)
> +
> +DEFINE_HWASAN_LOAD_STORE(1);
> +DEFINE_HWASAN_LOAD_STORE(2);
> +DEFINE_HWASAN_LOAD_STORE(4);
> +DEFINE_HWASAN_LOAD_STORE(8);
> +DEFINE_HWASAN_LOAD_STORE(16);
> +
> +void __hwasan_loadN_noabort(unsigned long addr, unsigned long size)
> +{
> +}
> +EXPORT_SYMBOL(__hwasan_loadN_noabort);
> +
> +void __hwasan_storeN_noabort(unsigned long addr, unsigned long size)
> +{
> +}
> +EXPORT_SYMBOL(__hwasan_storeN_noabort);
> +
> +void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
> +{
> +}
> +EXPORT_SYMBOL(__hwasan_tag_memory);
> diff --git a/mm/slub.c b/mm/slub.c
> index 30b9bf777bab..4206e1b616e7 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2955,7 +2955,7 @@ static __always_inline void slab_free(struct kmem_cache *s, struct page *page,
> do_slab_free(s, page, head, tail, cnt, addr);
> }
>
> -#ifdef CONFIG_KASAN
> +#ifdef CONFIG_KASAN_GENERIC
> void ___cache_free(struct kmem_cache *cache, void *x, unsigned long addr)
> {
> do_slab_free(cache, virt_to_head_page(x), x, NULL, 1, addr);
> diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
> index 69552a39951d..49c6e056c697 100644
> --- a/scripts/Makefile.kasan
> +++ b/scripts/Makefile.kasan
> @@ -1,5 +1,5 @@
> # SPDX-License-Identifier: GPL-2.0
> -ifdef CONFIG_KASAN
> +ifdef CONFIG_KASAN_GENERIC
> ifdef CONFIG_KASAN_INLINE
> call_threshold := 10000
> else
> @@ -42,6 +42,29 @@ ifdef CONFIG_KASAN_EXTRA
> CFLAGS_KASAN += $(call cc-option, -fsanitize-address-use-after-scope)
> endif
>
> -CFLAGS_KASAN_NOSANITIZE := -fno-builtin
> +endif
> +
> +ifdef CONFIG_KASAN_HW
> +
> +ifdef CONFIG_KASAN_INLINE
> + instrumentation_flags := -mllvm -hwasan-mapping-offset=$(KASAN_SHADOW_OFFSET)
> +else
> + instrumentation_flags := -mllvm -hwasan-instrument-with-calls=1
> +endif
>
> +CFLAGS_KASAN := -fsanitize=kernel-hwaddress \
> + -mllvm -hwasan-instrument-stack=0 \
> + $(instrumentation_flags)
> +
> +ifeq ($(call cc-option, $(CFLAGS_KASAN) -Werror),)
> + ifneq ($(CONFIG_COMPILE_TEST),y)
> + $(warning Cannot use CONFIG_KASAN_HW: \
> + -fsanitize=hwaddress is not supported by compiler)
> + endif
> +endif
> +
> +endif
> +
> +ifdef CONFIG_KASAN
> +CFLAGS_KASAN_NOSANITIZE := -fno-builtin
> endif
> --
> 2.19.0.rc0.228.g281dcd1b4d0-goog
>
On Wed, Sep 12, 2018 at 4:47 PM, Dmitry Vyukov <[email protected]> wrote:
> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
>> This commit splits the current CONFIG_KASAN config option into two:
>> 1. CONFIG_KASAN_GENERIC, that enables the generic software-only KASAN
>> version (the one that exists now);
>> 2. CONFIG_KASAN_HW, that enables KHWASAN.
>>
>> With CONFIG_KASAN_HW enabled, compiler options are changed to instrument
>> kernel files wiht -fsantize=hwaddress (except the ones for which
>> KASAN_SANITIZE := n is set).
>>
>> Both CONFIG_KASAN_GENERIC and CONFIG_KASAN_HW support both
>> CONFIG_KASAN_INLINE and CONFIG_KASAN_OUTLINE instrumentation modes.
>>
>> This commit also adds empty placeholder (for now) implementation of
>> KHWASAN specific hooks inserted by the compiler and adjusts common hooks
>> implementation to compile correctly with each of the config options.
>>
>> Signed-off-by: Andrey Konovalov <[email protected]>
>> ---
>> arch/arm64/Kconfig | 1 +
>> include/linux/compiler-clang.h | 3 +-
>> include/linux/compiler-gcc.h | 4 ++
>> include/linux/compiler.h | 3 +-
>> include/linux/kasan.h | 16 +++++--
>> lib/Kconfig.kasan | 77 ++++++++++++++++++++++++++--------
>> mm/kasan/Makefile | 6 ++-
>> mm/kasan/kasan.h | 3 +-
>> mm/kasan/khwasan.c | 75 +++++++++++++++++++++++++++++++++
>> mm/slub.c | 2 +-
>> scripts/Makefile.kasan | 27 +++++++++++-
>> 11 files changed, 188 insertions(+), 29 deletions(-)
>> create mode 100644 mm/kasan/khwasan.c
>>
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index 29e75b47becd..991564148f54 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -105,6 +105,7 @@ config ARM64
>> select HAVE_ARCH_HUGE_VMAP
>> select HAVE_ARCH_JUMP_LABEL
>> select HAVE_ARCH_KASAN if !(ARM64_16K_PAGES && ARM64_VA_BITS_48)
>> + select HAVE_ARCH_KASAN_HW if !(ARM64_16K_PAGES && ARM64_VA_BITS_48)
>> select HAVE_ARCH_KGDB
>> select HAVE_ARCH_MMAP_RND_BITS
>> select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
>> diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
>> index b1ce500fe8b3..2c258a9d4c67 100644
>> --- a/include/linux/compiler-clang.h
>> +++ b/include/linux/compiler-clang.h
>> @@ -17,11 +17,12 @@
>> #define KASAN_ABI_VERSION 5
>>
>> /* emulate gcc's __SANITIZE_ADDRESS__ flag */
>> -#if __has_feature(address_sanitizer)
>> +#if __has_feature(address_sanitizer) || __has_feature(hwaddress_sanitizer)
>> #define __SANITIZE_ADDRESS__
>> #endif
>>
>> #define __no_sanitize_address __attribute__((no_sanitize("address")))
>> +#define __no_sanitize_hwaddress __attribute__((no_sanitize("hwaddress")))
>
> It seems that it would be better to have just 1 attribute for both types.
> Currently __no_sanitize_address is used just in a single place. But if
> it ever used more, people will need to always spell both which looks
> unnecessary, or, worse will only fix asan but forget about khwasan.
>
> If we do just:
>
> #define __no_sanitize_address __attribute__((no_sanitize("address",
> "hwaddress")))
>
> Then we don't need any changes in compiler-gcc.h nor in compiler.h,
> and no chance or forgetting one of them.
>
>> /*
>> * Not all versions of clang implement the the type-generic versions
>> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
>> index 763bbad1e258..a186b55c8c4c 100644
>> --- a/include/linux/compiler-gcc.h
>> +++ b/include/linux/compiler-gcc.h
>> @@ -227,6 +227,10 @@
>> #define __no_sanitize_address
>> #endif
>>
>> +#if !defined(__no_sanitize_hwaddress)
>> +#define __no_sanitize_hwaddress /* gcc doesn't support KHWASAN */
>> +#endif
>> +
>> /*
>> * Turn individual warnings and errors on and off locally, depending
>> * on version.
>> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
>> index 681d866efb1e..3f2ba192d57d 100644
>> --- a/include/linux/compiler.h
>> +++ b/include/linux/compiler.h
>> @@ -195,7 +195,8 @@ void __read_once_size(const volatile void *p, void *res, int size)
>> * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368
>> * '__maybe_unused' allows us to avoid defined-but-not-used warnings.
>> */
>> -# define __no_kasan_or_inline __no_sanitize_address __maybe_unused
>> +# define __no_kasan_or_inline __no_sanitize_address __no_sanitize_hwaddress \
>> + __maybe_unused
>> #else
>> # define __no_kasan_or_inline __always_inline
>> #endif
>> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
>> index 54d577ad2181..beb56a26fe9b 100644
>> --- a/include/linux/kasan.h
>> +++ b/include/linux/kasan.h
>> @@ -45,8 +45,6 @@ void kasan_free_pages(struct page *page, unsigned int order);
>>
>> void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
>> slab_flags_t *flags);
>> -void kasan_cache_shrink(struct kmem_cache *cache);
>> -void kasan_cache_shutdown(struct kmem_cache *cache);
>>
>> void kasan_poison_slab(struct page *page);
>> void kasan_unpoison_object_data(struct kmem_cache *cache, void *object);
>> @@ -97,8 +95,6 @@ static inline void kasan_free_pages(struct page *page, unsigned int order) {}
>> static inline void kasan_cache_create(struct kmem_cache *cache,
>> unsigned int *size,
>> slab_flags_t *flags) {}
>> -static inline void kasan_cache_shrink(struct kmem_cache *cache) {}
>> -static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
>>
>> static inline void kasan_poison_slab(struct page *page) {}
>> static inline void kasan_unpoison_object_data(struct kmem_cache *cache,
>> @@ -152,4 +148,16 @@ static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
>>
>> #endif /* CONFIG_KASAN */
>>
>> +#ifdef CONFIG_KASAN_GENERIC
>> +
>> +void kasan_cache_shrink(struct kmem_cache *cache);
>> +void kasan_cache_shutdown(struct kmem_cache *cache);
>> +
>> +#else /* CONFIG_KASAN_GENERIC */
>> +
>> +static inline void kasan_cache_shrink(struct kmem_cache *cache) {}
>> +static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
>> +
>> +#endif /* CONFIG_KASAN_GENERIC */
>> +
>> #endif /* LINUX_KASAN_H */
>> diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
>> index befb127507c0..5a22629f30e7 100644
>> --- a/lib/Kconfig.kasan
>> +++ b/lib/Kconfig.kasan
>> @@ -1,34 +1,75 @@
>> config HAVE_ARCH_KASAN
>> bool
>>
>> +config HAVE_ARCH_KASAN_HW
>> + bool
>> +
>> if HAVE_ARCH_KASAN
>>
>> config KASAN
>> - bool "KASan: runtime memory debugger"
>> + bool "KASAN: runtime memory debugger"
>> + help
>> + Enables KASAN (KernelAddressSANitizer) - runtime memory debugger,
>> + designed to find out-of-bounds accesses and use-after-free bugs.
>
> Perhaps also give link to Documentation/dev-tools/kasan.rst while we are here.
>
>> +
>> +choice
>> + prompt "KASAN mode"
>> + depends on KASAN
>> + default KASAN_GENERIC
>> + help
>> + KASAN has two modes: KASAN (a classic version, similar to userspace
>
> In these few sentences we call the old mode with 3 different terms:
> "generic", "classic" and "KASAN" :)
> This is somewhat confusing. Let's call it "generic" throughout (here
> and in the docs patch). "Generic" as in "supported on multiple arch
> and not-dependent on hardware features". "Classic" makes sense for
> people who knew KASAN before, but for future readers in won't make
> sense.
>
>
>> + ASan, enabled with CONFIG_KASAN_GENERIC) and KHWASAN (a version
>> + based on pointer tagging, only for arm64, similar to userspace
>> + HWASan, enabled with CONFIG_KASAN_HW).
>> +
>> +config KASAN_GENERIC
>> + bool "KASAN: the generic mode"
>> depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
>> select SLUB_DEBUG if SLUB
>> select CONSTRUCTORS
>> select STACKDEPOT
>> help
>> - Enables kernel address sanitizer - runtime memory debugger,
>> - designed to find out-of-bounds accesses and use-after-free bugs.
>> - This is strictly a debugging feature and it requires a gcc version
>> - of 4.9.2 or later. Detection of out of bounds accesses to stack or
>> - global variables requires gcc 5.0 or later.
>> - This feature consumes about 1/8 of available memory and brings about
>> - ~x3 performance slowdown.
>> + Enables the generic mode of KASAN.
>> + This is strictly a debugging feature and it requires a GCC version
>> + of 4.9.2 or later. Detection of out-of-bounds accesses to stack or
>> + global variables requires GCC 5.0 or later.
>> + This mode consumes about 1/8 of available memory at kernel start
>> + and introduces an overhead of ~x1.5 for the rest of the allocations.
>> + The performance slowdown is ~x3.
>> For better error detection enable CONFIG_STACKTRACE.
>> - Currently CONFIG_KASAN doesn't work with CONFIG_DEBUG_SLAB
>> + Currently CONFIG_KASAN_GENERIC doesn't work with CONFIG_DEBUG_SLAB
>> (the resulting kernel does not boot).
>>
>> +if HAVE_ARCH_KASAN_HW
>
> This choice looks somewhat weird on non-arm64. It's kinda a choice
> menu, but one can't really choose anything. Should we put the whole
> choice under HAVE_ARCH_KASAN_HW, and just select KASAN_GENERIC
> otherwise? I don't know what't the practice here. Andrey R?
>
>> +config KASAN_HW
>> + bool "KHWASAN: the hardware assisted mode"
Do we need a hyphen here? hardware-assisted?
>> + depends on (SLUB && SYSFS) || (SLAB && !DEBUG_SLAB)
>> + select SLUB_DEBUG if SLUB
>> + select CONSTRUCTORS
>> + select STACKDEPOT
>> + help
>> + Enabled KHWASAN (KASAN mode based on pointer tagging).
>> + This mode requires Top Byte Ignore support by the CPU and therefore
>> + only supported for arm64.
>> + This feature requires clang revision 330044 or later.
>> + This mode consumes about 1/16 of available memory at kernel start
>> + and introduces an overhead of ~20% for the rest of the allocations.
>> + For better error detection enable CONFIG_STACKTRACE.
>> + Currently CONFIG_KASAN_HW doesn't work with CONFIG_DEBUG_SLAB
>> + (the resulting kernel does not boot).
>> +
>> +endif
>> +
>> +endchoice
>> +
>> config KASAN_EXTRA
>> - bool "KAsan: extra checks"
>> - depends on KASAN && DEBUG_KERNEL && !COMPILE_TEST
>> + bool "KASAN: extra checks"
>> + depends on KASAN_GENERIC && DEBUG_KERNEL && !COMPILE_TEST
>> help
>> - This enables further checks in the kernel address sanitizer, for now
>> - it only includes the address-use-after-scope check that can lead
>> - to excessive kernel stack usage, frame size warnings and longer
>> - compile time.
>> + This enables further checks in KASAN, for now it only includes the
>> + address-use-after-scope check that can lead to excessive kernel
>> + stack usage, frame size warnings and longer compile time.
>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715 has more
>>
>>
>> @@ -53,16 +94,16 @@ config KASAN_INLINE
>> memory accesses. This is faster than outline (in some workloads
>> it gives about x2 boost over outline instrumentation), but
>> make kernel's .text size much bigger.
>> - This requires a gcc version of 5.0 or later.
>> + For CONFIG_KASAN_GENERIC this requires GCC 5.0 or later.
>>
>> endchoice
>>
>> config TEST_KASAN
>> - tristate "Module for testing kasan for bug detection"
>> + tristate "Module for testing KASAN for bug detection"
>> depends on m && KASAN
>> help
>> This is a test module doing various nasty things like
>> out of bounds accesses, use after free. It is useful for testing
>> - kernel debugging features like kernel address sanitizer.
>> + kernel debugging features like KASAN.
>>
>> endif
>> diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
>> index a6df14bffb6b..14955add96d3 100644
>> --- a/mm/kasan/Makefile
>> +++ b/mm/kasan/Makefile
>> @@ -2,6 +2,7 @@
>> KASAN_SANITIZE := n
>> UBSAN_SANITIZE_common.o := n
>> UBSAN_SANITIZE_kasan.o := n
>> +UBSAN_SANITIZE_khwasan.o := n
>> KCOV_INSTRUMENT := n
>>
>> CFLAGS_REMOVE_kasan.o = -pg
>> @@ -10,5 +11,8 @@ CFLAGS_REMOVE_kasan.o = -pg
>>
>> CFLAGS_common.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
>> CFLAGS_kasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
>> +CFLAGS_khwasan.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector)
>>
>> -obj-y := common.o kasan.o report.o kasan_init.o quarantine.o
>> +obj-$(CONFIG_KASAN) := common.o kasan_init.o report.o
>> +obj-$(CONFIG_KASAN_GENERIC) += kasan.o quarantine.o
>> +obj-$(CONFIG_KASAN_HW) += khwasan.o
>> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
>> index 659463800f10..19b950eaccff 100644
>> --- a/mm/kasan/kasan.h
>> +++ b/mm/kasan/kasan.h
>> @@ -114,7 +114,8 @@ void kasan_report(unsigned long addr, size_t size,
>> bool is_write, unsigned long ip);
>> void kasan_report_invalid_free(void *object, unsigned long ip);
>>
>> -#if defined(CONFIG_SLAB) || defined(CONFIG_SLUB)
>> +#if defined(CONFIG_KASAN_GENERIC) && \
>> + (defined(CONFIG_SLAB) || defined(CONFIG_SLUB))
>> void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache);
>> void quarantine_reduce(void);
>> void quarantine_remove_cache(struct kmem_cache *cache);
>> diff --git a/mm/kasan/khwasan.c b/mm/kasan/khwasan.c
>> new file mode 100644
>> index 000000000000..e2c3a7f7fd1f
>> --- /dev/null
>> +++ b/mm/kasan/khwasan.c
>> @@ -0,0 +1,75 @@
>> +/*
>> + * This file contains core KHWASAN code.
>> + *
>> + * Copyright (c) 2018 Google, Inc.
>> + * Author: Andrey Konovalov <[email protected]>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + *
>> + */
>> +
>> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>> +#define DISABLE_BRANCH_PROFILING
>> +
>> +#include <linux/export.h>
>> +#include <linux/interrupt.h>
>> +#include <linux/init.h>
>> +#include <linux/kasan.h>
>> +#include <linux/kernel.h>
>> +#include <linux/kmemleak.h>
>> +#include <linux/linkage.h>
>> +#include <linux/memblock.h>
>> +#include <linux/memory.h>
>> +#include <linux/mm.h>
>> +#include <linux/module.h>
>> +#include <linux/printk.h>
>> +#include <linux/random.h>
>> +#include <linux/sched.h>
>> +#include <linux/sched/task_stack.h>
>> +#include <linux/slab.h>
>> +#include <linux/stacktrace.h>
>> +#include <linux/string.h>
>> +#include <linux/types.h>
>> +#include <linux/vmalloc.h>
>> +#include <linux/bug.h>
>> +
>> +#include "kasan.h"
>> +#include "../slab.h"
>> +
>> +void check_memory_region(unsigned long addr, size_t size, bool write,
>> + unsigned long ret_ip)
>> +{
>> +}
>> +
>> +#define DEFINE_HWASAN_LOAD_STORE(size) \
>> + void __hwasan_load##size##_noabort(unsigned long addr) \
>> + { \
>> + } \
>> + EXPORT_SYMBOL(__hwasan_load##size##_noabort); \
>> + void __hwasan_store##size##_noabort(unsigned long addr) \
>> + { \
>> + } \
>> + EXPORT_SYMBOL(__hwasan_store##size##_noabort)
>> +
>> +DEFINE_HWASAN_LOAD_STORE(1);
>> +DEFINE_HWASAN_LOAD_STORE(2);
>> +DEFINE_HWASAN_LOAD_STORE(4);
>> +DEFINE_HWASAN_LOAD_STORE(8);
>> +DEFINE_HWASAN_LOAD_STORE(16);
>> +
>> +void __hwasan_loadN_noabort(unsigned long addr, unsigned long size)
>> +{
>> +}
>> +EXPORT_SYMBOL(__hwasan_loadN_noabort);
>> +
>> +void __hwasan_storeN_noabort(unsigned long addr, unsigned long size)
>> +{
>> +}
>> +EXPORT_SYMBOL(__hwasan_storeN_noabort);
>> +
>> +void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
>> +{
>> +}
>> +EXPORT_SYMBOL(__hwasan_tag_memory);
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 30b9bf777bab..4206e1b616e7 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -2955,7 +2955,7 @@ static __always_inline void slab_free(struct kmem_cache *s, struct page *page,
>> do_slab_free(s, page, head, tail, cnt, addr);
>> }
>>
>> -#ifdef CONFIG_KASAN
>> +#ifdef CONFIG_KASAN_GENERIC
>> void ___cache_free(struct kmem_cache *cache, void *x, unsigned long addr)
>> {
>> do_slab_free(cache, virt_to_head_page(x), x, NULL, 1, addr);
>> diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
>> index 69552a39951d..49c6e056c697 100644
>> --- a/scripts/Makefile.kasan
>> +++ b/scripts/Makefile.kasan
>> @@ -1,5 +1,5 @@
>> # SPDX-License-Identifier: GPL-2.0
>> -ifdef CONFIG_KASAN
>> +ifdef CONFIG_KASAN_GENERIC
>> ifdef CONFIG_KASAN_INLINE
>> call_threshold := 10000
>> else
>> @@ -42,6 +42,29 @@ ifdef CONFIG_KASAN_EXTRA
>> CFLAGS_KASAN += $(call cc-option, -fsanitize-address-use-after-scope)
>> endif
>>
>> -CFLAGS_KASAN_NOSANITIZE := -fno-builtin
>> +endif
>> +
>> +ifdef CONFIG_KASAN_HW
>> +
>> +ifdef CONFIG_KASAN_INLINE
>> + instrumentation_flags := -mllvm -hwasan-mapping-offset=$(KASAN_SHADOW_OFFSET)
>> +else
>> + instrumentation_flags := -mllvm -hwasan-instrument-with-calls=1
>> +endif
>>
>> +CFLAGS_KASAN := -fsanitize=kernel-hwaddress \
>> + -mllvm -hwasan-instrument-stack=0 \
>> + $(instrumentation_flags)
>> +
>> +ifeq ($(call cc-option, $(CFLAGS_KASAN) -Werror),)
>> + ifneq ($(CONFIG_COMPILE_TEST),y)
>> + $(warning Cannot use CONFIG_KASAN_HW: \
>> + -fsanitize=hwaddress is not supported by compiler)
>> + endif
>> +endif
>> +
>> +endif
>> +
>> +ifdef CONFIG_KASAN
>> +CFLAGS_KASAN_NOSANITIZE := -fno-builtin
>> endif
>> --
>> 2.19.0.rc0.228.g281dcd1b4d0-goog
>>
On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
> KWHASAN uses 1 shadow byte for 16 bytes of kernel memory, so it requires
> 1/16th of the kernel virtual address space for the shadow memory.
>
> This commit sets KASAN_SHADOW_SCALE_SHIFT to 4 when KHWASAN is enabled.
>
> Signed-off-by: Andrey Konovalov <[email protected]>
> ---
> arch/arm64/Makefile | 2 +-
> arch/arm64/include/asm/memory.h | 13 +++++++++----
> 2 files changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 106039d25e2f..17047b8ab984 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -94,7 +94,7 @@ endif
> # KASAN_SHADOW_OFFSET = VA_START + (1 << (VA_BITS - KASAN_SHADOW_SCALE_SHIFT))
> # - (1 << (64 - KASAN_SHADOW_SCALE_SHIFT))
> # in 32-bit arithmetic
> -KASAN_SHADOW_SCALE_SHIFT := 3
> +KASAN_SHADOW_SCALE_SHIFT := $(if $(CONFIG_KASAN_HW), 4, 3)
> KASAN_SHADOW_OFFSET := $(shell printf "0x%08x00000000\n" $$(( \
> (0xffffffff & (-1 << ($(CONFIG_ARM64_VA_BITS) - 32))) \
> + (1 << ($(CONFIG_ARM64_VA_BITS) - 32 - $(KASAN_SHADOW_SCALE_SHIFT))) \
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index b96442960aea..f5e262ee76c1 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -74,12 +74,17 @@
> #define KERNEL_END _end
>
> /*
> - * KASAN requires 1/8th of the kernel virtual address space for the shadow
> - * region. KASAN can bloat the stack significantly, so double the (minimum)
> - * stack size when KASAN is in use.
> + * KASAN and KHWASAN require 1/8th and 1/16th of the kernel virtual address
I am somewhat confused by the terminology.
"KASAN" is not actually "CONFIG_KASAN" below, it is actually
"CONFIG_KASAN_GENERIC". While "KHWASAN" translates to "KASAN_HW" few
lines later.
I think we need some consistent terminology for comments and config
names until it's too late.
> + * space for the shadow region respectively. They can bloat the stack
> + * significantly, so double the (minimum) stack size when they are in use.
> */
> -#ifdef CONFIG_KASAN
> +#ifdef CONFIG_KASAN_GENERIC
> #define KASAN_SHADOW_SCALE_SHIFT 3
> +#endif
> +#ifdef CONFIG_KASAN_HW
> +#define KASAN_SHADOW_SCALE_SHIFT 4
> +#endif
> +#ifdef CONFIG_KASAN
> #define KASAN_SHADOW_SIZE (UL(1) << (VA_BITS - KASAN_SHADOW_SCALE_SHIFT))
> #define KASAN_THREAD_SHIFT 1
> #else
> --
> 2.19.0.rc0.228.g281dcd1b4d0-goog
>
On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
> This commit adds a few helper functions, that are meant to be used to
> work with tags embedded in the top byte of kernel pointers: to set, to
> get or to reset (set to 0xff) the top byte.
>
> Signed-off-by: Andrey Konovalov <[email protected]>
> ---
> arch/arm64/mm/kasan_init.c | 2 ++
> include/linux/kasan.h | 29 +++++++++++++++++
> mm/kasan/kasan.h | 55 ++++++++++++++++++++++++++++++++
> mm/kasan/khwasan.c | 65 ++++++++++++++++++++++++++++++++++++++
> 4 files changed, 151 insertions(+)
>
> diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
> index 7a31e8ccbad2..e7f37c0b7e14 100644
> --- a/arch/arm64/mm/kasan_init.c
> +++ b/arch/arm64/mm/kasan_init.c
> @@ -250,6 +250,8 @@ void __init kasan_init(void)
> memset(kasan_zero_page, KASAN_SHADOW_INIT, PAGE_SIZE);
> cpu_replace_ttbr1(lm_alias(swapper_pg_dir));
>
> + khwasan_init();
> +
> /* At this point kasan is fully initialized. Enable error messages */
> init_task.kasan_depth = 0;
> pr_info("KernelAddressSanitizer initialized\n");
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 1c31bb089154..1f852244e739 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -166,6 +166,35 @@ static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
>
> #define KASAN_SHADOW_INIT 0xFF
>
> +void khwasan_init(void);
> +
> +void *khwasan_reset_tag(const void *addr);
> +
> +void *khwasan_preset_slub_tag(struct kmem_cache *cache, const void *addr);
> +void *khwasan_preset_slab_tag(struct kmem_cache *cache, unsigned int idx,
> + const void *addr);
> +
> +#else /* CONFIG_KASAN_HW */
> +
> +static inline void khwasan_init(void) { }
> +
> +static inline void *khwasan_reset_tag(const void *addr)
> +{
> + return (void *)addr;
> +}
> +
> +static inline void *khwasan_preset_slub_tag(struct kmem_cache *cache,
> + const void *addr)
> +{
> + return (void *)addr;
> +}
> +
> +static inline void *khwasan_preset_slab_tag(struct kmem_cache *cache,
> + unsigned int idx, const void *addr)
> +{
> + return (void *)addr;
> +}
> +
> #endif /* CONFIG_KASAN_HW */
>
> #endif /* LINUX_KASAN_H */
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 19b950eaccff..a7cc27d96608 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -8,6 +8,10 @@
> #define KASAN_SHADOW_SCALE_SIZE (1UL << KASAN_SHADOW_SCALE_SHIFT)
> #define KASAN_SHADOW_MASK (KASAN_SHADOW_SCALE_SIZE - 1)
>
> +#define KHWASAN_TAG_KERNEL 0xFF /* native kernel pointers tag */
> +#define KHWASAN_TAG_INVALID 0xFE /* inaccessible memory tag */
> +#define KHWASAN_TAG_MAX 0xFD /* maximum value for random tags */
> +
> #define KASAN_FREE_PAGE 0xFF /* page was freed */
> #define KASAN_PAGE_REDZONE 0xFE /* redzone for kmalloc_large allocations */
> #define KASAN_KMALLOC_REDZONE 0xFC /* redzone inside slub object */
> @@ -126,6 +130,57 @@ static inline void quarantine_reduce(void) { }
> static inline void quarantine_remove_cache(struct kmem_cache *cache) { }
> #endif
>
> +#ifdef CONFIG_KASAN_HW
> +
> +#define KHWASAN_TAG_SHIFT 56
> +#define KHWASAN_TAG_MASK (0xFFUL << KHWASAN_TAG_SHIFT)
> +
> +u8 random_tag(void);
> +
> +static inline void *set_tag(const void *addr, u8 tag)
> +{
> + u64 a = (u64)addr;
> +
> + a &= ~KHWASAN_TAG_MASK;
> + a |= ((u64)tag << KHWASAN_TAG_SHIFT);
> +
> + return (void *)a;
> +}
> +
> +static inline u8 get_tag(const void *addr)
> +{
> + return (u8)((u64)addr >> KHWASAN_TAG_SHIFT);
> +}
> +
> +static inline void *reset_tag(const void *addr)
> +{
> + return set_tag(addr, KHWASAN_TAG_KERNEL);
> +}
> +
> +#else /* CONFIG_KASAN_HW */
> +
> +static inline u8 random_tag(void)
> +{
> + return 0;
> +}
> +
> +static inline void *set_tag(const void *addr, u8 tag)
> +{
> + return (void *)addr;
> +}
> +
> +static inline u8 get_tag(const void *addr)
> +{
> + return 0;
> +}
> +
> +static inline void *reset_tag(const void *addr)
> +{
> + return (void *)addr;
> +}
> +
> +#endif /* CONFIG_KASAN_HW */
> +
> /*
> * Exported functions for interfaces called from assembly or from generated
> * code. Declarations here to avoid warning about missing declarations.
> diff --git a/mm/kasan/khwasan.c b/mm/kasan/khwasan.c
> index e2c3a7f7fd1f..9d91bf3c8246 100644
> --- a/mm/kasan/khwasan.c
> +++ b/mm/kasan/khwasan.c
> @@ -38,6 +38,71 @@
> #include "kasan.h"
> #include "../slab.h"
>
> +static DEFINE_PER_CPU(u32, prng_state);
> +
> +void khwasan_init(void)
> +{
> + int cpu;
> +
> + for_each_possible_cpu(cpu)
> + per_cpu(prng_state, cpu) = get_random_u32();
> +}
> +
> +/*
> + * If a preemption happens between this_cpu_read and this_cpu_write, the only
> + * side effect is that we'll give a few allocated in different contexts objects
> + * the same tag. Since KHWASAN is meant to be used a probabilistic bug-detection
> + * debug feature, this doesn’t have significant negative impact.
> + *
> + * Ideally the tags use strong randomness to prevent any attempts to predict
> + * them during explicit exploit attempts. But strong randomness is expensive,
> + * and we did an intentional trade-off to use a PRNG. This non-atomic RMW
> + * sequence has in fact positive effect, since interrupts that randomly skew
> + * PRNG at unpredictable points do only good.
> + */
> +u8 random_tag(void)
> +{
> + u32 state = this_cpu_read(prng_state);
> +
> + state = 1664525 * state + 1013904223;
> + this_cpu_write(prng_state, state);
> +
> + return (u8)(state % (KHWASAN_TAG_MAX + 1));
> +}
> +
> +void *khwasan_reset_tag(const void *addr)
> +{
> + return reset_tag(addr);
> +}
> +
> +void *khwasan_preset_slub_tag(struct kmem_cache *cache, const void *addr)
Can't we do this in the existing kasan_init_slab_obj() hook? It looks
like it should do exactly this -- allow any one-time initialization
for objects. We could extend it to accept index and return a new
pointer.
If that does not work for some reason, I would try to at least unify
the hook for slab/slub, e.g. pass idx=-1 from slub and then use
random_tag().
It also seems that we do preset tag for slab multiple times (from
slab_get_obj()). Using kasan_init_slab_obj() should resolve this too
(hopefully we don't call it multiple times).
> +{
> + /*
> + * Since it's desirable to only call object contructors ones during
> + * slab allocation, we preassign tags to all such objects.
> + * Also preassign tags for SLAB_TYPESAFE_BY_RCU slabs to avoid
> + * use-after-free reports.
> + */
> + if (cache->ctor || cache->flags & SLAB_TYPESAFE_BY_RCU)
> + return set_tag(addr, random_tag());
> + return (void *)addr;
> +}
> +
> +void *khwasan_preset_slab_tag(struct kmem_cache *cache, unsigned int idx,
> + const void *addr)
> +{
> + /*
> + * See comment in khwasan_preset_slub_tag.
> + * For SLAB allocator we can't preassign tags randomly since the
> + * freelist is stored as an array of indexes instead of a linked
> + * list. Assign tags based on objects indexes, so that objects that
> + * are next to each other get different tags.
> + */
> + if (cache->ctor || cache->flags & SLAB_TYPESAFE_BY_RCU)
> + return set_tag(addr, (u8)idx);
> + return (void *)addr;
> +}
> +
> void check_memory_region(unsigned long addr, size_t size, bool write,
> unsigned long ret_ip)
> {
> --
> 2.19.0.rc0.228.g281dcd1b4d0-goog
>
On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
> __kimg_to_phys (which is used by virt_to_phys) and _virt_addr_is_linear
> (which is used by virt_addr_valid) assume that the top byte of the address
> is 0xff, which isn't always the case with KHWASAN enabled.
>
> The solution is to reset the tag in those macros.
>
> Signed-off-by: Andrey Konovalov <[email protected]>
> ---
> arch/arm64/include/asm/memory.h | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index f5e262ee76c1..f5e2953b7009 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -92,6 +92,13 @@
> #define KASAN_THREAD_SHIFT 0
> #endif
>
> +#ifdef CONFIG_KASAN_HW
> +#define KASAN_TAG_SHIFTED(tag) ((unsigned long)(tag) << 56)
> +#define KASAN_SET_TAG(addr, tag) (((addr) & ~KASAN_TAG_SHIFTED(0xff)) | \
> + KASAN_TAG_SHIFTED(tag))
> +#define KASAN_RESET_TAG(addr) KASAN_SET_TAG(addr, 0xff)
> +#endif
> +
Wouldn't it be better to
#define KASAN_RESET_TAG(addr) addr
when CONFIG_KASAN_HW is not enabled, and then not duplicate the macros
below? That's what we do in kasan.h for all hooks.
I see that a subsequent patch duplicates yet another macro in this
file. While we could use:
#define __kimg_to_phys(addr) (KASAN_RESET_TAG(addr) - kimage_voffset)
with and without kasan. Duplicating them increases risk that somebody
will change only the non-kasan version but forget kasan version.
> #define MIN_THREAD_SHIFT (14 + KASAN_THREAD_SHIFT)
>
> /*
> @@ -232,7 +239,12 @@ static inline unsigned long kaslr_offset(void)
> #define __is_lm_address(addr) (!!((addr) & BIT(VA_BITS - 1)))
>
> #define __lm_to_phys(addr) (((addr) & ~PAGE_OFFSET) + PHYS_OFFSET)
> +
> +#ifdef CONFIG_KASAN_HW
> +#define __kimg_to_phys(addr) (KASAN_RESET_TAG(addr) - kimage_voffset)
> +#else
> #define __kimg_to_phys(addr) ((addr) - kimage_voffset)
> +#endif
>
> #define __virt_to_phys_nodebug(x) ({ \
> phys_addr_t __x = (phys_addr_t)(x); \
> @@ -308,7 +320,13 @@ static inline void *phys_to_virt(phys_addr_t x)
> #endif
> #endif
>
> +#ifdef CONFIG_KASAN_HW
> +#define _virt_addr_is_linear(kaddr) (KASAN_RESET_TAG((u64)(kaddr)) >= \
> + PAGE_OFFSET)
> +#else
> #define _virt_addr_is_linear(kaddr) (((u64)(kaddr)) >= PAGE_OFFSET)
> +#endif
> +
> #define virt_addr_valid(kaddr) (_virt_addr_is_linear(kaddr) && \
> _virt_addr_valid(kaddr))
>
> --
> 2.19.0.rc0.228.g281dcd1b4d0-goog
>
On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
> An object constructor can initialize pointers within this objects based on
> the address of the object. Since the object address might be tagged, we
> need to assign a tag before calling constructor.
>
> The implemented approach is to assign tags to objects with constructors
> when a slab is allocated and call constructors once as usual. The
> downside is that such object would always have the same tag when it is
> reallocated, so we won't catch use-after-frees on it.
>
> Also pressign tags for objects from SLAB_TYPESAFE_BY_RCU caches, since
> they can be validy accessed after having been freed.
>
> Signed-off-by: Andrey Konovalov <[email protected]>
> ---
> mm/slab.c | 6 +++++-
> mm/slub.c | 4 ++++
> 2 files changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/mm/slab.c b/mm/slab.c
> index 6fdca9ec2ea4..3b4227059f2e 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -403,7 +403,11 @@ static inline struct kmem_cache *virt_to_cache(const void *obj)
> static inline void *index_to_obj(struct kmem_cache *cache, struct page *page,
> unsigned int idx)
> {
> - return page->s_mem + cache->size * idx;
> + void *obj;
> +
> + obj = page->s_mem + cache->size * idx;
> + obj = khwasan_preset_slab_tag(cache, idx, obj);
> + return obj;
> }
>
> /*
> diff --git a/mm/slub.c b/mm/slub.c
> index 4206e1b616e7..086d6558a6b6 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1531,12 +1531,14 @@ static bool shuffle_freelist(struct kmem_cache *s, struct page *page)
> /* First entry is used as the base of the freelist */
> cur = next_freelist_entry(s, page, &pos, start, page_limit,
> freelist_count);
> + cur = khwasan_preset_slub_tag(s, cur);
> page->freelist = cur;
>
> for (idx = 1; idx < page->objects; idx++) {
> setup_object(s, page, cur);
> next = next_freelist_entry(s, page, &pos, start, page_limit,
> freelist_count);
> + next = khwasan_preset_slub_tag(s, next);
> set_freepointer(s, cur, next);
> cur = next;
> }
> @@ -1613,8 +1615,10 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
> shuffle = shuffle_freelist(s, page);
>
> if (!shuffle) {
> + start = khwasan_preset_slub_tag(s, start);
> for_each_object_idx(p, idx, s, start, page->objects) {
> setup_object(s, page, p);
> + p = khwasan_preset_slub_tag(s, p);
As I commented in the previous patch, can't we do this in
kasan_init_slab_obj(), which should be called in all the right places
already?
> if (likely(idx < page->objects))
> set_freepointer(s, p, p + s->size);
> else
> --
> 2.19.0.rc0.228.g281dcd1b4d0-goog
>
On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
> KHWASAN inline instrumentation mode (which embeds checks of shadow memory
> into the generated code, instead of inserting a callback) generates a brk
> instruction when a tag mismatch is detected.
>
> This commit add a KHWASAN brk handler, that decodes the immediate value
> passed to the brk instructions (to extract information about the memory
> access that triggered the mismatch), reads the register values (x0 contains
> the guilty address) and reports the bug.
>
> Signed-off-by: Andrey Konovalov <[email protected]>
> ---
> arch/arm64/include/asm/brk-imm.h | 2 +
> arch/arm64/kernel/traps.c | 69 +++++++++++++++++++++++++++++++-
> 2 files changed, 69 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/brk-imm.h b/arch/arm64/include/asm/brk-imm.h
> index ed693c5bcec0..e4a7013321dc 100644
> --- a/arch/arm64/include/asm/brk-imm.h
> +++ b/arch/arm64/include/asm/brk-imm.h
> @@ -16,10 +16,12 @@
> * 0x400: for dynamic BRK instruction
> * 0x401: for compile time BRK instruction
> * 0x800: kernel-mode BUG() and WARN() traps
> + * 0x9xx: KHWASAN trap (allowed values 0x900 - 0x9ff)
> */
> #define FAULT_BRK_IMM 0x100
> #define KGDB_DYN_DBG_BRK_IMM 0x400
> #define KGDB_COMPILED_DBG_BRK_IMM 0x401
> #define BUG_BRK_IMM 0x800
> +#define KHWASAN_BRK_IMM 0x900
>
> #endif
> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index 039e9ff379cc..fd70347d1ce7 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -35,6 +35,7 @@
> #include <linux/sizes.h>
> #include <linux/syscalls.h>
> #include <linux/mm_types.h>
> +#include <linux/kasan.h>
>
> #include <asm/atomic.h>
> #include <asm/bug.h>
> @@ -269,10 +270,14 @@ void arm64_notify_die(const char *str, struct pt_regs *regs,
> }
> }
>
> -void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
> +void __arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
> {
> regs->pc += size;
> +}
>
> +void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
> +{
> + __arm64_skip_faulting_instruction(regs, size);
> /*
> * If we were single stepping, we want to get the step exception after
> * we return from the trap.
> @@ -775,7 +780,7 @@ static int bug_handler(struct pt_regs *regs, unsigned int esr)
> }
>
> /* If thread survives, skip over the BUG instruction and continue: */
> - arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
> + __arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
> return DBG_HOOK_HANDLED;
> }
>
> @@ -785,6 +790,59 @@ static struct break_hook bug_break_hook = {
> .fn = bug_handler,
> };
>
> +#ifdef CONFIG_KASAN_HW
> +
> +#define KHWASAN_ESR_RECOVER 0x20
> +#define KHWASAN_ESR_WRITE 0x10
> +#define KHWASAN_ESR_SIZE_MASK 0x0f
> +#define KHWASAN_ESR_SIZE(esr) (1 << ((esr) & KHWASAN_ESR_SIZE_MASK))
> +
> +static int khwasan_handler(struct pt_regs *regs, unsigned int esr)
> +{
> + bool recover = esr & KHWASAN_ESR_RECOVER;
> + bool write = esr & KHWASAN_ESR_WRITE;
> + size_t size = KHWASAN_ESR_SIZE(esr);
> + u64 addr = regs->regs[0];
> + u64 pc = regs->pc;
> +
> + if (user_mode(regs))
> + return DBG_HOOK_ERROR;
> +
> + kasan_report(addr, size, write, pc);
> +
> + /*
> + * The instrumentation allows to control whether we can proceed after
> + * a crash was detected. This is done by passing the -recover flag to
> + * the compiler. Disabling recovery allows to generate more compact
> + * code.
> + *
> + * Unfortunately disabling recovery doesn't work for the kernel right
> + * now. KHWASAN reporting is disabled in some contexts (for example when
> + * the allocator accesses slab object metadata; same is true for KASAN;
> + * this is controlled by current->kasan_depth). All these accesses are
> + * detected by the tool, even though the reports for them are not
> + * printed.
I am not following this part.
Slab accesses metadata. OK.
This is detected as bad access. OK.
Report is not printed. OK.
We skip BRK and resume execution.
What is the problem?
> + *
> + * This is something that might be fixed at some point in the future.
> + */
> + if (!recover)
> + die("Oops - KHWASAN", regs, 0);
> +
> + /* If thread survives, skip over the brk instruction and continue: */
> + __arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
> + return DBG_HOOK_HANDLED;
> +}
> +
> +#define KHWASAN_ESR_VAL (0xf2000000 | KHWASAN_BRK_IMM)
> +#define KHWASAN_ESR_MASK 0xffffff00
> +
> +static struct break_hook khwasan_break_hook = {
> + .esr_val = KHWASAN_ESR_VAL,
> + .esr_mask = KHWASAN_ESR_MASK,
> + .fn = khwasan_handler,
> +};
> +#endif
> +
> /*
> * Initial handler for AArch64 BRK exceptions
> * This handler only used until debug_traps_init().
> @@ -792,6 +850,10 @@ static struct break_hook bug_break_hook = {
> int __init early_brk64(unsigned long addr, unsigned int esr,
> struct pt_regs *regs)
> {
> +#ifdef CONFIG_KASAN_HW
> + if ((esr & KHWASAN_ESR_MASK) == KHWASAN_ESR_VAL)
> + return khwasan_handler(regs, esr) != DBG_HOOK_HANDLED;
> +#endif
> return bug_handler(regs, esr) != DBG_HOOK_HANDLED;
> }
>
> @@ -799,4 +861,7 @@ int __init early_brk64(unsigned long addr, unsigned int esr,
> void __init trap_init(void)
> {
> register_break_hook(&bug_break_hook);
> +#ifdef CONFIG_KASAN_HW
> + register_break_hook(&khwasan_break_hook);
> +#endif
> }
> --
> 2.19.0.rc0.228.g281dcd1b4d0-goog
>
On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
> KHWASAN inline instrumentation mode (which embeds checks of shadow memory
> into the generated code, instead of inserting a callback) generates a brk
> instruction when a tag mismatch is detected.
>
> This commit add a KHWASAN brk handler, that decodes the immediate value
> passed to the brk instructions (to extract information about the memory
> access that triggered the mismatch), reads the register values (x0 contains
> the guilty address) and reports the bug.
>
> Signed-off-by: Andrey Konovalov <[email protected]>
> ---
> arch/arm64/include/asm/brk-imm.h | 2 +
> arch/arm64/kernel/traps.c | 69 +++++++++++++++++++++++++++++++-
> 2 files changed, 69 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/brk-imm.h b/arch/arm64/include/asm/brk-imm.h
> index ed693c5bcec0..e4a7013321dc 100644
> --- a/arch/arm64/include/asm/brk-imm.h
> +++ b/arch/arm64/include/asm/brk-imm.h
> @@ -16,10 +16,12 @@
> * 0x400: for dynamic BRK instruction
> * 0x401: for compile time BRK instruction
> * 0x800: kernel-mode BUG() and WARN() traps
> + * 0x9xx: KHWASAN trap (allowed values 0x900 - 0x9ff)
> */
> #define FAULT_BRK_IMM 0x100
> #define KGDB_DYN_DBG_BRK_IMM 0x400
> #define KGDB_COMPILED_DBG_BRK_IMM 0x401
> #define BUG_BRK_IMM 0x800
> +#define KHWASAN_BRK_IMM 0x900
>
> #endif
> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index 039e9ff379cc..fd70347d1ce7 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -35,6 +35,7 @@
> #include <linux/sizes.h>
> #include <linux/syscalls.h>
> #include <linux/mm_types.h>
> +#include <linux/kasan.h>
>
> #include <asm/atomic.h>
> #include <asm/bug.h>
> @@ -269,10 +270,14 @@ void arm64_notify_die(const char *str, struct pt_regs *regs,
> }
> }
>
> -void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
> +void __arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
> {
> regs->pc += size;
> +}
>
> +void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
> +{
> + __arm64_skip_faulting_instruction(regs, size);
> /*
> * If we were single stepping, we want to get the step exception after
> * we return from the trap.
> @@ -775,7 +780,7 @@ static int bug_handler(struct pt_regs *regs, unsigned int esr)
> }
>
> /* If thread survives, skip over the BUG instruction and continue: */
> - arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
> + __arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
> return DBG_HOOK_HANDLED;
> }
>
> @@ -785,6 +790,59 @@ static struct break_hook bug_break_hook = {
> .fn = bug_handler,
> };
>
> +#ifdef CONFIG_KASAN_HW
> +
> +#define KHWASAN_ESR_RECOVER 0x20
> +#define KHWASAN_ESR_WRITE 0x10
> +#define KHWASAN_ESR_SIZE_MASK 0x0f
> +#define KHWASAN_ESR_SIZE(esr) (1 << ((esr) & KHWASAN_ESR_SIZE_MASK))
> +
> +static int khwasan_handler(struct pt_regs *regs, unsigned int esr)
> +{
> + bool recover = esr & KHWASAN_ESR_RECOVER;
> + bool write = esr & KHWASAN_ESR_WRITE;
> + size_t size = KHWASAN_ESR_SIZE(esr);
> + u64 addr = regs->regs[0];
> + u64 pc = regs->pc;
> +
> + if (user_mode(regs))
> + return DBG_HOOK_ERROR;
> +
> + kasan_report(addr, size, write, pc);
> +
> + /*
> + * The instrumentation allows to control whether we can proceed after
> + * a crash was detected. This is done by passing the -recover flag to
> + * the compiler. Disabling recovery allows to generate more compact
> + * code.
> + *
> + * Unfortunately disabling recovery doesn't work for the kernel right
> + * now. KHWASAN reporting is disabled in some contexts (for example when
> + * the allocator accesses slab object metadata; same is true for KASAN;
> + * this is controlled by current->kasan_depth). All these accesses are
> + * detected by the tool, even though the reports for them are not
> + * printed.
> + *
> + * This is something that might be fixed at some point in the future.
> + */
> + if (!recover)
> + die("Oops - KHWASAN", regs, 0);
Why die and not panic? Die seems to be much less used function, and it
calls panic anyway, and we call panic in kasan_report if panic_on_warn
is set.
> + /* If thread survives, skip over the brk instruction and continue: */
> + __arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
> + return DBG_HOOK_HANDLED;
> +}
> +
> +#define KHWASAN_ESR_VAL (0xf2000000 | KHWASAN_BRK_IMM)
> +#define KHWASAN_ESR_MASK 0xffffff00
> +
> +static struct break_hook khwasan_break_hook = {
> + .esr_val = KHWASAN_ESR_VAL,
> + .esr_mask = KHWASAN_ESR_MASK,
> + .fn = khwasan_handler,
> +};
> +#endif
> +
> /*
> * Initial handler for AArch64 BRK exceptions
> * This handler only used until debug_traps_init().
> @@ -792,6 +850,10 @@ static struct break_hook bug_break_hook = {
> int __init early_brk64(unsigned long addr, unsigned int esr,
> struct pt_regs *regs)
> {
> +#ifdef CONFIG_KASAN_HW
> + if ((esr & KHWASAN_ESR_MASK) == KHWASAN_ESR_VAL)
> + return khwasan_handler(regs, esr) != DBG_HOOK_HANDLED;
> +#endif
> return bug_handler(regs, esr) != DBG_HOOK_HANDLED;
> }
>
> @@ -799,4 +861,7 @@ int __init early_brk64(unsigned long addr, unsigned int esr,
> void __init trap_init(void)
> {
> register_break_hook(&bug_break_hook);
> +#ifdef CONFIG_KASAN_HW
> + register_break_hook(&khwasan_break_hook);
> +#endif
> }
> --
> 2.19.0.rc0.228.g281dcd1b4d0-goog
>
On Wed, Sep 12, 2018 at 7:16 PM Dmitry Vyukov <[email protected]> wrote:
> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
[...]
> > +static int khwasan_handler(struct pt_regs *regs, unsigned int esr)
> > +{
> > + bool recover = esr & KHWASAN_ESR_RECOVER;
> > + bool write = esr & KHWASAN_ESR_WRITE;
> > + size_t size = KHWASAN_ESR_SIZE(esr);
> > + u64 addr = regs->regs[0];
> > + u64 pc = regs->pc;
> > +
> > + if (user_mode(regs))
> > + return DBG_HOOK_ERROR;
> > +
> > + kasan_report(addr, size, write, pc);
> > +
> > + /*
> > + * The instrumentation allows to control whether we can proceed after
> > + * a crash was detected. This is done by passing the -recover flag to
> > + * the compiler. Disabling recovery allows to generate more compact
> > + * code.
> > + *
> > + * Unfortunately disabling recovery doesn't work for the kernel right
> > + * now. KHWASAN reporting is disabled in some contexts (for example when
> > + * the allocator accesses slab object metadata; same is true for KASAN;
> > + * this is controlled by current->kasan_depth). All these accesses are
> > + * detected by the tool, even though the reports for them are not
> > + * printed.
> > + *
> > + * This is something that might be fixed at some point in the future.
> > + */
> > + if (!recover)
> > + die("Oops - KHWASAN", regs, 0);
>
> Why die and not panic? Die seems to be much less used function, and it
> calls panic anyway, and we call panic in kasan_report if panic_on_warn
> is set.
die() is vaguely equivalent to BUG(); die() and BUG() normally only
terminate the current process, which may or may not leave the system
somewhat usable, while panic() always brings down the whole system.
AFAIK panic() shouldn't be used unless you're in some very low-level
code where you know that trying to just kill the current process can't
work and the entire system is broken beyond repair.
If KASAN traps on some random memory access, there's a good chance
that just killing the current process will allow at least parts of the
system to continue. I'm not sure whether BUG() or die() is more
appropriate here, but I think it definitely should not be a panic().
On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
> This commit adds rountines, that print KHWASAN error reports. Those are
> quite similar to KASAN, the difference is:
>
> 1. The way KHWASAN finds the first bad shadow cell (with a mismatching
> tag). KHWASAN compares memory tags from the shadow memory to the pointer
> tag.
>
> 2. KHWASAN reports all bugs with the "KASAN: invalid-access" header. This
> is done, so various external tools that already parse the kernel logs
> looking for KASAN reports wouldn't need to be changed.
>
> Signed-off-by: Andrey Konovalov <[email protected]>
> ---
> include/linux/kasan.h | 3 +++
> mm/kasan/kasan.h | 7 +++++
> mm/kasan/kasan_report.c | 7 ++---
> mm/kasan/khwasan_report.c | 21 +++++++++++++++
> mm/kasan/report.c | 57 +++++++++++++++++++++------------------
> 5 files changed, 64 insertions(+), 31 deletions(-)
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 1f852244e739..4424359a9dfa 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -174,6 +174,9 @@ void *khwasan_preset_slub_tag(struct kmem_cache *cache, const void *addr);
> void *khwasan_preset_slab_tag(struct kmem_cache *cache, unsigned int idx,
> const void *addr);
>
> +void kasan_report(unsigned long addr, size_t size,
> + bool write, unsigned long ip);
> +
> #else /* CONFIG_KASAN_HW */
>
> static inline void khwasan_init(void) { }
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 82672473740c..d60859d26be7 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -119,8 +119,15 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value);
> void check_memory_region(unsigned long addr, size_t size, bool write,
> unsigned long ret_ip);
>
> +void *find_first_bad_addr(void *addr, size_t size);
> const char *get_bug_type(struct kasan_access_info *info);
>
> +#ifdef CONFIG_KASAN_HW
We already have #ifdef CONFIG_KASAN_HW section below with additional
functions for KASAN_HW and empty stubs otherwise. I would add this one
there as well.
> +void print_tags(u8 addr_tag, const void *addr);
> +#else
> +static inline void print_tags(u8 addr_tag, const void *addr) { }
> +#endif
> +
> void kasan_report(unsigned long addr, size_t size,
> bool is_write, unsigned long ip);
> void kasan_report_invalid_free(void *object, unsigned long ip);
> diff --git a/mm/kasan/kasan_report.c b/mm/kasan/kasan_report.c
> index 2d8decbecbd5..fdf2d77e3125 100644
> --- a/mm/kasan/kasan_report.c
> +++ b/mm/kasan/kasan_report.c
> @@ -33,10 +33,10 @@
> #include "kasan.h"
> #include "../slab.h"
>
> -static const void *find_first_bad_addr(const void *addr, size_t size)
> +void *find_first_bad_addr(void *addr, size_t size)
> {
> u8 shadow_val = *(u8 *)kasan_mem_to_shadow(addr);
> - const void *first_bad_addr = addr;
> + void *first_bad_addr = addr;
>
> while (!shadow_val && first_bad_addr < addr + size) {
> first_bad_addr += KASAN_SHADOW_SCALE_SIZE;
> @@ -50,9 +50,6 @@ static const char *get_shadow_bug_type(struct kasan_access_info *info)
> const char *bug_type = "unknown-crash";
> u8 *shadow_addr;
>
> - info->first_bad_addr = find_first_bad_addr(info->access_addr,
> - info->access_size);
> -
> shadow_addr = (u8 *)kasan_mem_to_shadow(info->first_bad_addr);
>
> /*
> diff --git a/mm/kasan/khwasan_report.c b/mm/kasan/khwasan_report.c
> index 2edbc3c76be5..51238b404b08 100644
> --- a/mm/kasan/khwasan_report.c
> +++ b/mm/kasan/khwasan_report.c
> @@ -37,3 +37,24 @@ const char *get_bug_type(struct kasan_access_info *info)
> {
> return "invalid-access";
> }
> +
> +void *find_first_bad_addr(void *addr, size_t size)
> +{
> + u8 tag = get_tag(addr);
> + void *untagged_addr = reset_tag(addr);
> + u8 *shadow = (u8 *)kasan_mem_to_shadow(untagged_addr);
> + void *first_bad_addr = untagged_addr;
> +
> + while (*shadow == tag && first_bad_addr < untagged_addr + size) {
I think it's better to check that are within bounds before accessing
shadow. Otherwise it's kinda potential out-of-bounds access ;)
I know that we _should_ not do an oob here, but still.
Also feels that this function can be shortened to something like:
u8 tag = get_tag(addr);
void *p = reset_tag(addr);
void *end = p + size;
while (p < end && tag == *(u8 *)kasan_mem_to_shadow(p))
p += KASAN_SHADOW_SCALE_SIZE;
return p;
> + first_bad_addr += KASAN_SHADOW_SCALE_SIZE;
> + shadow = (u8 *)kasan_mem_to_shadow(first_bad_addr);
> + }
> + return first_bad_addr;
> +}
> +
> +void print_tags(u8 addr_tag, const void *addr)
> +{
> + u8 *shadow = (u8 *)kasan_mem_to_shadow(addr);
> +
> + pr_err("Pointer tag: [%02x], memory tag: [%02x]\n", addr_tag, *shadow);
> +}
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index 155247a6f8a8..e031c78f2e52 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -64,11 +64,10 @@ static int __init kasan_set_multi_shot(char *str)
> }
> __setup("kasan_multi_shot", kasan_set_multi_shot);
>
> -static void print_error_description(struct kasan_access_info *info,
> - const char *bug_type)
> +static void print_error_description(struct kasan_access_info *info)
> {
> pr_err("BUG: KASAN: %s in %pS\n",
> - bug_type, (void *)info->ip);
> + get_bug_type(info), (void *)info->ip);
> pr_err("%s of size %zu at addr %px by task %s/%d\n",
> info->is_write ? "Write" : "Read", info->access_size,
> info->access_addr, current->comm, task_pid_nr(current));
> @@ -272,6 +271,8 @@ void kasan_report_invalid_free(void *object, unsigned long ip)
>
> start_report(&flags);
> pr_err("BUG: KASAN: double-free or invalid-free in %pS\n", (void *)ip);
> + print_tags(get_tag(object), reset_tag(object));
> + object = reset_tag(object);
> pr_err("\n");
> print_address_description(object);
> pr_err("\n");
> @@ -279,41 +280,45 @@ void kasan_report_invalid_free(void *object, unsigned long ip)
> end_report(&flags);
> }
>
> -static void kasan_report_error(struct kasan_access_info *info)
> -{
> - unsigned long flags;
> -
> - start_report(&flags);
> -
> - print_error_description(info, get_bug_type(info));
> - pr_err("\n");
> -
> - if (!addr_has_shadow(info->access_addr)) {
> - dump_stack();
> - } else {
> - print_address_description((void *)info->access_addr);
> - pr_err("\n");
> - print_shadow_for_address(info->first_bad_addr);
> - }
> -
> - end_report(&flags);
> -}
> -
> void kasan_report(unsigned long addr, size_t size,
> bool is_write, unsigned long ip)
> {
> struct kasan_access_info info;
> + void *tagged_addr;
> + void *untagged_addr;
> + unsigned long flags;
>
> if (likely(!report_enabled()))
> return;
>
> disable_trace_on_warning();
>
> - info.access_addr = (void *)addr;
> - info.first_bad_addr = (void *)addr;
> + tagged_addr = (void *)addr;
> + untagged_addr = reset_tag(tagged_addr);
> +
> + info.access_addr = tagged_addr;
> + if (addr_has_shadow(untagged_addr))
> + info.first_bad_addr = find_first_bad_addr(tagged_addr, size);
> + else
> + info.first_bad_addr = untagged_addr;
> info.access_size = size;
> info.is_write = is_write;
> info.ip = ip;
>
> - kasan_report_error(&info);
> + start_report(&flags);
> +
> + print_error_description(&info);
> + if (addr_has_shadow(untagged_addr))
> + print_tags(get_tag(tagged_addr), info.first_bad_addr);
> + pr_err("\n");
> +
> + if (addr_has_shadow(untagged_addr)) {
> + print_address_description(untagged_addr);
> + pr_err("\n");
> + print_shadow_for_address(info.first_bad_addr);
> + } else {
> + dump_stack();
> + }
> +
> + end_report(&flags);
> }
> --
> 2.19.0.rc0.228.g281dcd1b4d0-goog
>
On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
> This commit adds KHWASAN specific hooks implementation and adjusts
> common KASAN and KHWASAN ones.
>
> 1. When a new slab cache is created, KHWASAN rounds up the size of the
> objects in this cache to KASAN_SHADOW_SCALE_SIZE (== 16).
>
> 2. On each kmalloc KHWASAN generates a random tag, sets the shadow memory,
> that corresponds to this object to this tag, and embeds this tag value
> into the top byte of the returned pointer.
>
> 3. On each kfree KHWASAN poisons the shadow memory with a random tag to
> allow detection of use-after-free bugs.
>
> The rest of the logic of the hook implementation is very much similar to
> the one provided by KASAN. KHWASAN saves allocation and free stack metadata
> to the slab object the same was KASAN does this.
>
> Signed-off-by: Andrey Konovalov <[email protected]>
> ---
> mm/kasan/common.c | 82 +++++++++++++++++++++++++++++++++++-----------
> mm/kasan/kasan.h | 8 +++++
> mm/kasan/khwasan.c | 40 ++++++++++++++++++++++
> 3 files changed, 111 insertions(+), 19 deletions(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index bed8e13c6e1d..938229b26f3a 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -140,6 +140,9 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value)
> {
> void *shadow_start, *shadow_end;
>
> + /* Perform shadow offset calculation based on untagged address */
> + address = reset_tag(address);
> +
> shadow_start = kasan_mem_to_shadow(address);
> shadow_end = kasan_mem_to_shadow(address + size);
>
> @@ -148,11 +151,20 @@ void kasan_poison_shadow(const void *address, size_t size, u8 value)
>
> void kasan_unpoison_shadow(const void *address, size_t size)
> {
> - kasan_poison_shadow(address, size, 0);
> + u8 tag = get_tag(address);
> +
> + /* Perform shadow offset calculation based on untagged address */
The comment is not super-useful. It would be more useful to say why we
need to do this.
Most callers explicitly untag pointer passed to this function, for
some it's unclear if the pointer contains tag or not.
For example, __hwasan_tag_memory -- what does it accept? Tagged or untagged?
> + address = reset_tag(address);
> +
> + kasan_poison_shadow(address, size, tag);
>
> if (size & KASAN_SHADOW_MASK) {
> u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size);
> - *shadow = size & KASAN_SHADOW_MASK;
> +
> + if (IS_ENABLED(CONFIG_KASAN_HW))
> + *shadow = tag;
> + else
> + *shadow = size & KASAN_SHADOW_MASK;
> }
> }
It seems that this function is just different for kasan and khwasan.
Currently for kasan we have:
kasan_poison_shadow(address, size, tag);
if (size & KASAN_SHADOW_MASK) {
u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size);
*shadow = size & KASAN_SHADOW_MASK;
}
But what we want to say for khwasan is:
kasan_poison_shadow(address, round_up(size, KASAN_SHADOW_SCALE_SIZE),
get_tag(address));
Not sure if we want to keep a common implementation or just have
separate implementations...
>
> @@ -200,8 +212,9 @@ void kasan_unpoison_stack_above_sp_to(const void *watermark)
>
> void kasan_alloc_pages(struct page *page, unsigned int order)
> {
> - if (likely(!PageHighMem(page)))
> - kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order);
> + if (unlikely(PageHighMem(page)))
> + return;
> + kasan_unpoison_shadow(page_address(page), PAGE_SIZE << order);
> }
>
> void kasan_free_pages(struct page *page, unsigned int order)
> @@ -235,6 +248,7 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
> slab_flags_t *flags)
> {
> unsigned int orig_size = *size;
> + unsigned int redzone_size = 0;
This variable seems to be always initialized below. We don't general
initialize local variables in this case.
> int redzone_adjust;
>
> /* Add alloc meta. */
> @@ -242,20 +256,20 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
> *size += sizeof(struct kasan_alloc_meta);
>
> /* Add free meta. */
> - if (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
> - cache->object_size < sizeof(struct kasan_free_meta)) {
> + if (IS_ENABLED(CONFIG_KASAN_GENERIC) &&
> + (cache->flags & SLAB_TYPESAFE_BY_RCU || cache->ctor ||
> + cache->object_size < sizeof(struct kasan_free_meta))) {
> cache->kasan_info.free_meta_offset = *size;
> *size += sizeof(struct kasan_free_meta);
> }
> - redzone_adjust = optimal_redzone(cache->object_size) -
> - (*size - cache->object_size);
>
> + redzone_size = optimal_redzone(cache->object_size);
> + redzone_adjust = redzone_size - (*size - cache->object_size);
> if (redzone_adjust > 0)
> *size += redzone_adjust;
>
> *size = min_t(unsigned int, KMALLOC_MAX_SIZE,
> - max(*size, cache->object_size +
> - optimal_redzone(cache->object_size)));
> + max(*size, cache->object_size + redzone_size));
>
> /*
> * If the metadata doesn't fit, don't enable KASAN at all.
> @@ -268,6 +282,8 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
> return;
> }
>
> + cache->align = round_up(cache->align, KASAN_SHADOW_SCALE_SIZE);
> +
> *flags |= SLAB_KASAN;
> }
>
> @@ -328,15 +344,30 @@ void *kasan_slab_alloc(struct kmem_cache *cache, void *object, gfp_t flags)
> return kasan_kmalloc(cache, object, cache->object_size, flags);
> }
>
> +static inline bool shadow_invalid(u8 tag, s8 shadow_byte)
> +{
> + if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> + return shadow_byte < 0 ||
> + shadow_byte >= KASAN_SHADOW_SCALE_SIZE;
> + else
> + return tag != (u8)shadow_byte;
> +}
> +
> static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
> unsigned long ip, bool quarantine)
> {
> s8 shadow_byte;
> + u8 tag;
> + void *tagged_object;
> unsigned long rounded_up_size;
>
> + tag = get_tag(object);
> + tagged_object = object;
> + object = reset_tag(object);
> +
> if (unlikely(nearest_obj(cache, virt_to_head_page(object), object) !=
> object)) {
> - kasan_report_invalid_free(object, ip);
> + kasan_report_invalid_free(tagged_object, ip);
> return true;
> }
>
> @@ -345,20 +376,22 @@ static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
> return false;
>
> shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
> - if (shadow_byte < 0 || shadow_byte >= KASAN_SHADOW_SCALE_SIZE) {
> - kasan_report_invalid_free(object, ip);
> + if (shadow_invalid(tag, shadow_byte)) {
> + kasan_report_invalid_free(tagged_object, ip);
> return true;
> }
>
> rounded_up_size = round_up(cache->object_size, KASAN_SHADOW_SCALE_SIZE);
> kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE);
>
> - if (!quarantine || unlikely(!(cache->flags & SLAB_KASAN)))
> + if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine) ||
> + unlikely(!(cache->flags & SLAB_KASAN)))
> return false;
>
> set_track(&get_alloc_info(cache, object)->free_track, GFP_NOWAIT);
> quarantine_put(get_free_info(cache, object), cache);
> - return true;
> +
> + return IS_ENABLED(CONFIG_KASAN_GENERIC);
> }
>
> bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
> @@ -371,6 +404,7 @@ void *kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
> {
> unsigned long redzone_start;
> unsigned long redzone_end;
> + u8 tag;
>
> if (gfpflags_allow_blocking(flags))
> quarantine_reduce();
> @@ -383,14 +417,24 @@ void *kasan_kmalloc(struct kmem_cache *cache, const void *object, size_t size,
> redzone_end = round_up((unsigned long)object + cache->object_size,
> KASAN_SHADOW_SCALE_SIZE);
>
> - kasan_unpoison_shadow(object, size);
> + /*
> + * Objects with contructors and objects from SLAB_TYPESAFE_BY_RCU slabs
> + * have tags preassigned and are already tagged.
> + */
> + if (IS_ENABLED(CONFIG_KASAN_HW) &&
> + (cache->ctor || cache->flags & SLAB_TYPESAFE_BY_RCU))
> + tag = get_tag(object);
> + else
> + tag = random_tag();
> +
> + kasan_unpoison_shadow(set_tag(object, tag), size);
> kasan_poison_shadow((void *)redzone_start, redzone_end - redzone_start,
> KASAN_KMALLOC_REDZONE);
>
> if (cache->flags & SLAB_KASAN)
> set_track(&get_alloc_info(cache, object)->alloc_track, flags);
>
> - return (void *)object;
> + return set_tag(object, tag);
> }
> EXPORT_SYMBOL(kasan_kmalloc);
>
> @@ -440,7 +484,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip)
> page = virt_to_head_page(ptr);
>
> if (unlikely(!PageSlab(page))) {
> - if (ptr != page_address(page)) {
> + if (reset_tag(ptr) != page_address(page)) {
> kasan_report_invalid_free(ptr, ip);
> return;
> }
> @@ -453,7 +497,7 @@ void kasan_poison_kfree(void *ptr, unsigned long ip)
>
> void kasan_kfree_large(void *ptr, unsigned long ip)
> {
> - if (ptr != page_address(virt_to_head_page(ptr)))
> + if (reset_tag(ptr) != page_address(virt_to_head_page(ptr)))
> kasan_report_invalid_free(ptr, ip);
> /* The object will be poisoned by page_alloc. */
> }
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index d60859d26be7..6f4f2ebf5f57 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -12,10 +12,18 @@
> #define KHWASAN_TAG_INVALID 0xFE /* inaccessible memory tag */
> #define KHWASAN_TAG_MAX 0xFD /* maximum value for random tags */
>
> +#ifdef CONFIG_KASAN_GENERIC
> #define KASAN_FREE_PAGE 0xFF /* page was freed */
> #define KASAN_PAGE_REDZONE 0xFE /* redzone for kmalloc_large allocations */
> #define KASAN_KMALLOC_REDZONE 0xFC /* redzone inside slub object */
> #define KASAN_KMALLOC_FREE 0xFB /* object was freed (kmem_cache_free/kfree) */
> +#else
> +#define KASAN_FREE_PAGE KHWASAN_TAG_INVALID
> +#define KASAN_PAGE_REDZONE KHWASAN_TAG_INVALID
> +#define KASAN_KMALLOC_REDZONE KHWASAN_TAG_INVALID
> +#define KASAN_KMALLOC_FREE KHWASAN_TAG_INVALID
> +#endif
> +
> #define KASAN_GLOBAL_REDZONE 0xFA /* redzone for global variable */
>
> /*
> diff --git a/mm/kasan/khwasan.c b/mm/kasan/khwasan.c
> index 9d91bf3c8246..6b1309278e39 100644
> --- a/mm/kasan/khwasan.c
> +++ b/mm/kasan/khwasan.c
> @@ -106,15 +106,52 @@ void *khwasan_preset_slab_tag(struct kmem_cache *cache, unsigned int idx,
> void check_memory_region(unsigned long addr, size_t size, bool write,
> unsigned long ret_ip)
> {
> + u8 tag;
> + u8 *shadow_first, *shadow_last, *shadow;
> + void *untagged_addr;
> +
> + tag = get_tag((const void *)addr);
> +
> + /* Ignore accesses for pointers tagged with 0xff (native kernel
/* on a separate line
> + * pointer tag) to suppress false positives caused by kmap.
> + *
> + * Some kernel code was written to account for archs that don't keep
> + * high memory mapped all the time, but rather map and unmap particular
> + * pages when needed. Instead of storing a pointer to the kernel memory,
> + * this code saves the address of the page structure and offset within
> + * that page for later use. Those pages are then mapped and unmapped
> + * with kmap/kunmap when necessary and virt_to_page is used to get the
> + * virtual address of the page. For arm64 (that keeps the high memory
> + * mapped all the time), kmap is turned into a page_address call.
> +
> + * The issue is that with use of the page_address + virt_to_page
> + * sequence the top byte value of the original pointer gets lost (gets
> + * set to KHWASAN_TAG_KERNEL (0xFF).
Missed closing bracket.
> + */
> + if (tag == KHWASAN_TAG_KERNEL)
> + return;
> +
> + untagged_addr = reset_tag((const void *)addr);
> + shadow_first = kasan_mem_to_shadow(untagged_addr);
> + shadow_last = kasan_mem_to_shadow(untagged_addr + size - 1);
> +
> + for (shadow = shadow_first; shadow <= shadow_last; shadow++) {
> + if (*shadow != tag) {
> + kasan_report(addr, size, write, ret_ip);
> + return;
> + }
> + }
> }
>
> #define DEFINE_HWASAN_LOAD_STORE(size) \
> void __hwasan_load##size##_noabort(unsigned long addr) \
> { \
> + check_memory_region(addr, size, false, _RET_IP_); \
> } \
> EXPORT_SYMBOL(__hwasan_load##size##_noabort); \
> void __hwasan_store##size##_noabort(unsigned long addr) \
> { \
> + check_memory_region(addr, size, true, _RET_IP_); \
> } \
> EXPORT_SYMBOL(__hwasan_store##size##_noabort)
>
> @@ -126,15 +163,18 @@ DEFINE_HWASAN_LOAD_STORE(16);
>
> void __hwasan_loadN_noabort(unsigned long addr, unsigned long size)
> {
> + check_memory_region(addr, size, false, _RET_IP_);
> }
> EXPORT_SYMBOL(__hwasan_loadN_noabort);
>
> void __hwasan_storeN_noabort(unsigned long addr, unsigned long size)
> {
> + check_memory_region(addr, size, true, _RET_IP_);
> }
> EXPORT_SYMBOL(__hwasan_storeN_noabort);
>
> void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size)
> {
> + kasan_poison_shadow((void *)addr, size, tag);
> }
> EXPORT_SYMBOL(__hwasan_tag_memory);
> --
> 2.19.0.rc0.228.g281dcd1b4d0-goog
>
On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
> This patch updates KASAN documentation to reflect the addition of KHWASAN.
>
> Signed-off-by: Andrey Konovalov <[email protected]>
> ---
> Documentation/dev-tools/kasan.rst | 213 +++++++++++++++++-------------
> 1 file changed, 123 insertions(+), 90 deletions(-)
>
> diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
> index aabc8738b3d8..842d95af74d3 100644
> --- a/Documentation/dev-tools/kasan.rst
> +++ b/Documentation/dev-tools/kasan.rst
> @@ -8,11 +8,19 @@ KernelAddressSANitizer (KASAN) is a dynamic memory error detector. It provides
> a fast and comprehensive solution for finding use-after-free and out-of-bounds
> bugs.
>
> -KASAN uses compile-time instrumentation for checking every memory access,
> -therefore you will need a GCC version 4.9.2 or later. GCC 5.0 or later is
> -required for detection of out-of-bounds accesses to stack or global variables.
> +KASAN has two modes: classic KASAN (a classic version, similar to user space
> +ASan) and KHWASAN (a version based on memory tagging, similar to user space
> +HWASan).
>
> -Currently KASAN is supported only for the x86_64 and arm64 architectures.
> +KASAN uses compile-time instrumentation to insert validity checks before every
> +memory access, and therefore requires a compiler version that supports that.
> +For classic KASAN you need GCC version 4.9.2 or later. GCC 5.0 or later is
> +required for detection of out-of-bounds accesses on stack and global variables.
> +KHWASAN in turns is only supported in clang and requires revision 330044 or
in turn?
> +later.
> +
> +Currently classic KASAN is supported for the x86_64, arm64 and xtensa
> +architectures, and KHWASAN is supported only for arm64.
>
> Usage
> -----
> @@ -21,12 +29,14 @@ To enable KASAN configure kernel with::
>
> CONFIG_KASAN = y
>
> -and choose between CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE. Outline and
> -inline are compiler instrumentation types. The former produces smaller binary
> -the latter is 1.1 - 2 times faster. Inline instrumentation requires a GCC
> +and choose between CONFIG_KASAN_GENERIC (to enable classic KASAN) and
> +CONFIG_KASAN_HW (to enabled KHWASAN). You also need to choose choose between
to enable
> +CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE. Outline and inline are compiler
> +instrumentation types. The former produces smaller binary while the latter is
> +1.1 - 2 times faster. For classic KASAN inline instrumentation requires GCC
> version 5.0 or later.
>
> -KASAN works with both SLUB and SLAB memory allocators.
> +Both KASAN modes work with both SLUB and SLAB memory allocators.
> For better bug detection and nicer reporting, enable CONFIG_STACKTRACE.
>
> To disable instrumentation for specific files or directories, add a line
> @@ -43,85 +53,80 @@ similar to the following to the respective kernel Makefile:
> Error reports
> ~~~~~~~~~~~~~
>
> -A typical out of bounds access report looks like this::
> +A typical out-of-bounds access classic KASAN report looks like this::
>
> ==================================================================
> - BUG: AddressSanitizer: out of bounds access in kmalloc_oob_right+0x65/0x75 [test_kasan] at addr ffff8800693bc5d3
> - Write of size 1 by task modprobe/1689
> - =============================================================================
> - BUG kmalloc-128 (Not tainted): kasan error
> - -----------------------------------------------------------------------------
> -
> - Disabling lock debugging due to kernel taint
> - INFO: Allocated in kmalloc_oob_right+0x3d/0x75 [test_kasan] age=0 cpu=0 pid=1689
> - __slab_alloc+0x4b4/0x4f0
> - kmem_cache_alloc_trace+0x10b/0x190
> - kmalloc_oob_right+0x3d/0x75 [test_kasan]
> - init_module+0x9/0x47 [test_kasan]
> - do_one_initcall+0x99/0x200
> - load_module+0x2cb3/0x3b20
> - SyS_finit_module+0x76/0x80
> - system_call_fastpath+0x12/0x17
> - INFO: Slab 0xffffea0001a4ef00 objects=17 used=7 fp=0xffff8800693bd728 flags=0x100000000004080
> - INFO: Object 0xffff8800693bc558 @offset=1368 fp=0xffff8800693bc720
> -
> - Bytes b4 ffff8800693bc548: 00 00 00 00 00 00 00 00 5a 5a 5a 5a 5a 5a 5a 5a ........ZZZZZZZZ
> - Object ffff8800693bc558: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> - Object ffff8800693bc568: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> - Object ffff8800693bc578: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> - Object ffff8800693bc588: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> - Object ffff8800693bc598: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> - Object ffff8800693bc5a8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> - Object ffff8800693bc5b8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
> - Object ffff8800693bc5c8: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5 kkkkkkkkkkkkkkk.
> - Redzone ffff8800693bc5d8: cc cc cc cc cc cc cc cc ........
> - Padding ffff8800693bc718: 5a 5a 5a 5a 5a 5a 5a 5a ZZZZZZZZ
> - CPU: 0 PID: 1689 Comm: modprobe Tainted: G B 3.18.0-rc1-mm1+ #98
> - Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014
> - ffff8800693bc000 0000000000000000 ffff8800693bc558 ffff88006923bb78
> - ffffffff81cc68ae 00000000000000f3 ffff88006d407600 ffff88006923bba8
> - ffffffff811fd848 ffff88006d407600 ffffea0001a4ef00 ffff8800693bc558
> + BUG: KASAN: slab-out-of-bounds in kmalloc_oob_right+0xa8/0xbc [test_kasan]
> + Write of size 1 at addr ffff8800696f3d3b by task insmod/2734
> +
> + CPU: 0 PID: 2734 Comm: insmod Not tainted 4.15.0+ #98
> + Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> Call Trace:
> - [<ffffffff81cc68ae>] dump_stack+0x46/0x58
> - [<ffffffff811fd848>] print_trailer+0xf8/0x160
> - [<ffffffffa00026a7>] ? kmem_cache_oob+0xc3/0xc3 [test_kasan]
> - [<ffffffff811ff0f5>] object_err+0x35/0x40
> - [<ffffffffa0002065>] ? kmalloc_oob_right+0x65/0x75 [test_kasan]
> - [<ffffffff8120b9fa>] kasan_report_error+0x38a/0x3f0
> - [<ffffffff8120a79f>] ? kasan_poison_shadow+0x2f/0x40
> - [<ffffffff8120b344>] ? kasan_unpoison_shadow+0x14/0x40
> - [<ffffffff8120a79f>] ? kasan_poison_shadow+0x2f/0x40
> - [<ffffffffa00026a7>] ? kmem_cache_oob+0xc3/0xc3 [test_kasan]
> - [<ffffffff8120a995>] __asan_store1+0x75/0xb0
> - [<ffffffffa0002601>] ? kmem_cache_oob+0x1d/0xc3 [test_kasan]
> - [<ffffffffa0002065>] ? kmalloc_oob_right+0x65/0x75 [test_kasan]
> - [<ffffffffa0002065>] kmalloc_oob_right+0x65/0x75 [test_kasan]
> - [<ffffffffa00026b0>] init_module+0x9/0x47 [test_kasan]
> - [<ffffffff810002d9>] do_one_initcall+0x99/0x200
> - [<ffffffff811e4e5c>] ? __vunmap+0xec/0x160
> - [<ffffffff81114f63>] load_module+0x2cb3/0x3b20
> - [<ffffffff8110fd70>] ? m_show+0x240/0x240
> - [<ffffffff81115f06>] SyS_finit_module+0x76/0x80
> - [<ffffffff81cd3129>] system_call_fastpath+0x12/0x17
> + __dump_stack lib/dump_stack.c:17
> + dump_stack+0x83/0xbc lib/dump_stack.c:53
> + print_address_description+0x73/0x280 mm/kasan/report.c:254
KASAN does not print line numbers per se.
I think we need to show unmodified output to not confuse readers
(probably remove the useless ? lines).
> + kasan_report_error mm/kasan/report.c:352
> + kasan_report+0x10e/0x220 mm/kasan/report.c:410
> + __asan_report_store1_noabort+0x17/0x20 mm/kasan/report.c:505
> + kmalloc_oob_right+0xa8/0xbc [test_kasan] lib/test_kasan.c:42
> + kmalloc_tests_init+0x16/0x769 [test_kasan]
> + do_one_initcall+0x9e/0x240 init/main.c:832
> + do_init_module+0x1b6/0x542 kernel/module.c:3462
> + load_module+0x6042/0x9030 kernel/module.c:3786
> + SYSC_init_module+0x18f/0x1c0 kernel/module.c:3858
> + SyS_init_module+0x9/0x10 kernel/module.c:3841
> + do_syscall_64+0x198/0x480 arch/x86/entry/common.c:287
> + entry_SYSCALL_64_after_hwframe+0x21/0x86 arch/x86/entry/entry_64.S:251
> + RIP: 0033:0x7fdd79df99da
> + RSP: 002b:00007fff2229bdf8 EFLAGS: 00000202 ORIG_RAX: 00000000000000af
> + RAX: ffffffffffffffda RBX: 000055c408121190 RCX: 00007fdd79df99da
> + RDX: 00007fdd7a0b8f88 RSI: 0000000000055670 RDI: 00007fdd7a47e000
> + RBP: 000055c4081200b0 R08: 0000000000000003 R09: 0000000000000000
> + R10: 00007fdd79df5d0a R11: 0000000000000202 R12: 00007fdd7a0b8f88
> + R13: 000055c408120090 R14: 0000000000000000 R15: 0000000000000000
> +
> + Allocated by task 2734:
> + save_stack+0x43/0xd0 mm/kasan/common.c:176
> + set_track+0x20/0x30 mm/kasan/common.c:188
> + kasan_kmalloc+0x9a/0xc0 mm/kasan/kasan.c:372
> + kmem_cache_alloc_trace+0xcd/0x1a0 mm/slub.c:2761
> + kmalloc ./include/linux/slab.h:512
> + kmalloc_oob_right+0x56/0xbc [test_kasan] lib/test_kasan.c:36
> + kmalloc_tests_init+0x16/0x769 [test_kasan]
> + do_one_initcall+0x9e/0x240 init/main.c:832
> + do_init_module+0x1b6/0x542 kernel/module.c:3462
> + load_module+0x6042/0x9030 kernel/module.c:3786
> + SYSC_init_module+0x18f/0x1c0 kernel/module.c:3858
> + SyS_init_module+0x9/0x10 kernel/module.c:3841
> + do_syscall_64+0x198/0x480 arch/x86/entry/common.c:287
> + entry_SYSCALL_64_after_hwframe+0x21/0x86 arch/x86/entry/entry_64.S:251
> +
> + The buggy address belongs to the object at ffff8800696f3cc0
> + which belongs to the cache kmalloc-128 of size 128
> + The buggy address is located 123 bytes inside of
> + 128-byte region [ffff8800696f3cc0, ffff8800696f3d40)
> + The buggy address belongs to the page:
> + page:ffffea0001a5bcc0 count:1 mapcount:0 mapping: (null) index:0x0
> + flags: 0x100000000000100(slab)
> + raw: 0100000000000100 0000000000000000 0000000000000000 0000000180150015
> + raw: ffffea0001a8ce40 0000000300000003 ffff88006d001640 0000000000000000
> + page dumped because: kasan: bad access detected
> +
> Memory state around the buggy address:
> - ffff8800693bc300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> - ffff8800693bc380: fc fc 00 00 00 00 00 00 00 00 00 00 00 00 00 fc
> - ffff8800693bc400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> - ffff8800693bc480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> - ffff8800693bc500: fc fc fc fc fc fc fc fc fc fc fc 00 00 00 00 00
> - >ffff8800693bc580: 00 00 00 00 00 00 00 00 00 00 03 fc fc fc fc fc
> - ^
> - ffff8800693bc600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> - ffff8800693bc680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> - ffff8800693bc700: fc fc fc fc fb fb fb fb fb fb fb fb fb fb fb fb
> - ffff8800693bc780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> - ffff8800693bc800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> + ffff8800696f3c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fc
> + ffff8800696f3c80: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
> + >ffff8800696f3d00: 00 00 00 00 00 00 00 03 fc fc fc fc fc fc fc fc
> + ^
> + ffff8800696f3d80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fc fc
> + ffff8800696f3e00: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
> ==================================================================
>
> -The header of the report discribe what kind of bug happened and what kind of
> -access caused it. It's followed by the description of the accessed slub object
> -(see 'SLUB Debug output' section in Documentation/vm/slub.rst for details) and
> -the description of the accessed memory page.
> +The header of the report provides a short summary of what kind of bug happened
> +and what kind of access caused it. It's followed by a stack trace of the bad
> +access, a stack trace of where the accessed memory was allocated (in case bad
> +access happens on a slab object), and a stack trace of where the object was
> +freed (in case of a use-after-free bug report). Next comes a description of
> +the accessed slab object and information about the accessed memory page.
>
> In the last section the report shows memory state around the accessed address.
> Reading this part requires some understanding of how KASAN works.
> @@ -138,18 +143,24 @@ inaccessible memory like redzones or freed memory (see mm/kasan/kasan.h).
> In the report above the arrows point to the shadow byte 03, which means that
> the accessed address is partially accessible.
>
> +For KHWASAN this last report section shows the memory tags around the accessed
> +address (see Implementation details section).
> Implementation details
> ----------------------
>
> +Classic KASAN
> +~~~~~~~~~~~~~
> +
> From a high level, our approach to memory error detection is similar to that
> of kmemcheck: use shadow memory to record whether each byte of memory is safe
> -to access, and use compile-time instrumentation to check shadow memory on each
> -memory access.
> +to access, and use compile-time instrumentation to insert checks of shadow
> +memory on each memory access.
>
> -AddressSanitizer dedicates 1/8 of kernel memory to its shadow memory
> -(e.g. 16TB to cover 128TB on x86_64) and uses direct mapping with a scale and
> -offset to translate a memory address to its corresponding shadow address.
> +Classic KASAN dedicates 1/8th of kernel memory to its shadow memory (e.g. 16TB
> +to cover 128TB on x86_64) and uses direct mapping with a scale and offset to
> +translate a memory address to its corresponding shadow address.
>
> Here is the function which translates an address to its corresponding shadow
> address::
> @@ -162,12 +173,34 @@ address::
>
> where ``KASAN_SHADOW_SCALE_SHIFT = 3``.
>
> -Compile-time instrumentation used for checking memory accesses. Compiler inserts
> -function calls (__asan_load*(addr), __asan_store*(addr)) before each memory
> -access of size 1, 2, 4, 8 or 16. These functions check whether memory access is
> -valid or not by checking corresponding shadow memory.
> +Compile-time instrumentation is used to insert memory access checks. Compiler
> +inserts function calls (__asan_load*(addr), __asan_store*(addr)) before each
> +memory access of size 1, 2, 4, 8 or 16. These functions check whether memory
> +access is valid or not by checking corresponding shadow memory.
>
> GCC 5.0 has possibility to perform inline instrumentation. Instead of making
> function calls GCC directly inserts the code to check the shadow memory.
> This option significantly enlarges kernel but it gives x1.1-x2 performance
> boost over outline instrumented kernel.
> +
> +KHWASAN
> +~~~~~~~
> +
> +KHWASAN uses the Top Byte Ignore (TBI) feature of modern arm64 CPUs to store
> +a pointer tag in the top byte of kernel pointers. KHWASAN also uses shadow
> +memory to store memory tags associated with each 16-byte memory cell (therefore
> +it dedicates 1/16th of the kernel memory for shadow memory).
> +
> +On each memory allocation KHWASAN generates a random tag, tags allocated memory
> +with this tag, and embeds this tag into the returned pointer. KHWASAN uses
> +compile-time instrumentation to insert checks before each memory access. These
> +checks make sure that tag of the memory that is being accessed is equal to tag
> +of the pointer that is used to access this memory. In case of a tag mismatch
> +KHWASAN prints a bug report.
> +
> +KHWASAN also has two instrumentation modes (outline, that emits callbacks to
> +check memory accesses; and inline, that performs the shadow memory checks
> +inline). With outline instrumentation mode, a bug report is simply printed
> +from the function that performs the access check. With inline instrumentation
> +a brk instruction is emitted by the compiler, and a dedicated brk handler is
> +used to print KHWASAN reports.
> --
> 2.19.0.rc0.228.g281dcd1b4d0-goog
>
On Wed, Sep 12, 2018 at 7:39 PM, Jann Horn <[email protected]> wrote:
> On Wed, Sep 12, 2018 at 7:16 PM Dmitry Vyukov <[email protected]> wrote:
>> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
> [...]
>> > +static int khwasan_handler(struct pt_regs *regs, unsigned int esr)
>> > +{
>> > + bool recover = esr & KHWASAN_ESR_RECOVER;
>> > + bool write = esr & KHWASAN_ESR_WRITE;
>> > + size_t size = KHWASAN_ESR_SIZE(esr);
>> > + u64 addr = regs->regs[0];
>> > + u64 pc = regs->pc;
>> > +
>> > + if (user_mode(regs))
>> > + return DBG_HOOK_ERROR;
>> > +
>> > + kasan_report(addr, size, write, pc);
>> > +
>> > + /*
>> > + * The instrumentation allows to control whether we can proceed after
>> > + * a crash was detected. This is done by passing the -recover flag to
>> > + * the compiler. Disabling recovery allows to generate more compact
>> > + * code.
>> > + *
>> > + * Unfortunately disabling recovery doesn't work for the kernel right
>> > + * now. KHWASAN reporting is disabled in some contexts (for example when
>> > + * the allocator accesses slab object metadata; same is true for KASAN;
>> > + * this is controlled by current->kasan_depth). All these accesses are
>> > + * detected by the tool, even though the reports for them are not
>> > + * printed.
>> > + *
>> > + * This is something that might be fixed at some point in the future.
>> > + */
>> > + if (!recover)
>> > + die("Oops - KHWASAN", regs, 0);
>>
>> Why die and not panic? Die seems to be much less used function, and it
>> calls panic anyway, and we call panic in kasan_report if panic_on_warn
>> is set.
>
> die() is vaguely equivalent to BUG(); die() and BUG() normally only
> terminate the current process, which may or may not leave the system
> somewhat usable, while panic() always brings down the whole system.
> AFAIK panic() shouldn't be used unless you're in some very low-level
> code where you know that trying to just kill the current process can't
> work and the entire system is broken beyond repair.
>
> If KASAN traps on some random memory access, there's a good chance
> that just killing the current process will allow at least parts of the
> system to continue. I'm not sure whether BUG() or die() is more
> appropriate here, but I think it definitely should not be a panic().
Nick, do you know if die() will be enough to catch problems on Android
phones? panic_on_warn would turn this into panic, but I guess one does
not want panic_on_warn on a canary phone.
On Thu, Sep 13, 2018 at 1:37 AM Dmitry Vyukov <[email protected]> wrote:
>
> On Wed, Sep 12, 2018 at 7:39 PM, Jann Horn <[email protected]> wrote:
> > On Wed, Sep 12, 2018 at 7:16 PM Dmitry Vyukov <[email protected]> wrote:
> >> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
> > [...]
> >> > +static int khwasan_handler(struct pt_regs *regs, unsigned int esr)
> >> > +{
> >> > + bool recover = esr & KHWASAN_ESR_RECOVER;
> >> > + bool write = esr & KHWASAN_ESR_WRITE;
> >> > + size_t size = KHWASAN_ESR_SIZE(esr);
> >> > + u64 addr = regs->regs[0];
> >> > + u64 pc = regs->pc;
> >> > +
> >> > + if (user_mode(regs))
> >> > + return DBG_HOOK_ERROR;
> >> > +
> >> > + kasan_report(addr, size, write, pc);
> >> > +
> >> > + /*
> >> > + * The instrumentation allows to control whether we can proceed after
> >> > + * a crash was detected. This is done by passing the -recover flag to
> >> > + * the compiler. Disabling recovery allows to generate more compact
> >> > + * code.
> >> > + *
> >> > + * Unfortunately disabling recovery doesn't work for the kernel right
> >> > + * now. KHWASAN reporting is disabled in some contexts (for example when
> >> > + * the allocator accesses slab object metadata; same is true for KASAN;
> >> > + * this is controlled by current->kasan_depth). All these accesses are
> >> > + * detected by the tool, even though the reports for them are not
> >> > + * printed.
> >> > + *
> >> > + * This is something that might be fixed at some point in the future.
> >> > + */
> >> > + if (!recover)
> >> > + die("Oops - KHWASAN", regs, 0);
> >>
> >> Why die and not panic? Die seems to be much less used function, and it
> >> calls panic anyway, and we call panic in kasan_report if panic_on_warn
> >> is set.
> >
> > die() is vaguely equivalent to BUG(); die() and BUG() normally only
> > terminate the current process, which may or may not leave the system
> > somewhat usable, while panic() always brings down the whole system.
> > AFAIK panic() shouldn't be used unless you're in some very low-level
> > code where you know that trying to just kill the current process can't
> > work and the entire system is broken beyond repair.
> >
> > If KASAN traps on some random memory access, there's a good chance
> > that just killing the current process will allow at least parts of the
> > system to continue. I'm not sure whether BUG() or die() is more
> > appropriate here, but I think it definitely should not be a panic().
>
>
> Nick, do you know if die() will be enough to catch problems on Android
> phones? panic_on_warn would turn this into panic, but I guess one does
> not want panic_on_warn on a canary phone.
die() has arch specific implementations, so looking at:
arch/arm64/kernel/traps.c:196#die
it looks like panic is invoked if in_interrupt() or panic_on_oops(),
which is a configure option. So maybe the config for KHWASAN should
also enable that? Otherwise seems easy to forget. But maybe that
should remain configurable separately?
Looking at the kernel configs for the Pixel 2, it does seem like
CONFIG_PANIC_ON_OOPS=y is already enabled.
https://android.googlesource.com/kernel/msm/+/android-msm-wahoo-4.4-pie/arch/arm64/configs/wahoo_defconfig#746
Specifically to catch problems on Android, our internal debug builds
can report on panics, but not oops, IIUC.
--
Thanks,
~Nick Desaulniers
On Thu, Sep 13, 2018 at 8:09 PM Nick Desaulniers
<[email protected]> wrote:
>
> On Thu, Sep 13, 2018 at 1:37 AM Dmitry Vyukov <[email protected]> wrote:
> >
> > On Wed, Sep 12, 2018 at 7:39 PM, Jann Horn <[email protected]> wrote:
> > > On Wed, Sep 12, 2018 at 7:16 PM Dmitry Vyukov <[email protected]> wrote:
> > >> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
> > > [...]
> > >> > +static int khwasan_handler(struct pt_regs *regs, unsigned int esr)
> > >> > +{
> > >> > + bool recover = esr & KHWASAN_ESR_RECOVER;
> > >> > + bool write = esr & KHWASAN_ESR_WRITE;
> > >> > + size_t size = KHWASAN_ESR_SIZE(esr);
> > >> > + u64 addr = regs->regs[0];
> > >> > + u64 pc = regs->pc;
> > >> > +
> > >> > + if (user_mode(regs))
> > >> > + return DBG_HOOK_ERROR;
> > >> > +
> > >> > + kasan_report(addr, size, write, pc);
> > >> > +
> > >> > + /*
> > >> > + * The instrumentation allows to control whether we can proceed after
> > >> > + * a crash was detected. This is done by passing the -recover flag to
> > >> > + * the compiler. Disabling recovery allows to generate more compact
> > >> > + * code.
> > >> > + *
> > >> > + * Unfortunately disabling recovery doesn't work for the kernel right
> > >> > + * now. KHWASAN reporting is disabled in some contexts (for example when
> > >> > + * the allocator accesses slab object metadata; same is true for KASAN;
> > >> > + * this is controlled by current->kasan_depth). All these accesses are
> > >> > + * detected by the tool, even though the reports for them are not
> > >> > + * printed.
> > >> > + *
> > >> > + * This is something that might be fixed at some point in the future.
> > >> > + */
> > >> > + if (!recover)
> > >> > + die("Oops - KHWASAN", regs, 0);
> > >>
> > >> Why die and not panic? Die seems to be much less used function, and it
> > >> calls panic anyway, and we call panic in kasan_report if panic_on_warn
> > >> is set.
> > >
> > > die() is vaguely equivalent to BUG(); die() and BUG() normally only
> > > terminate the current process, which may or may not leave the system
> > > somewhat usable, while panic() always brings down the whole system.
> > > AFAIK panic() shouldn't be used unless you're in some very low-level
> > > code where you know that trying to just kill the current process can't
> > > work and the entire system is broken beyond repair.
> > >
> > > If KASAN traps on some random memory access, there's a good chance
> > > that just killing the current process will allow at least parts of the
> > > system to continue. I'm not sure whether BUG() or die() is more
> > > appropriate here, but I think it definitely should not be a panic().
> >
> >
> > Nick, do you know if die() will be enough to catch problems on Android
> > phones? panic_on_warn would turn this into panic, but I guess one does
> > not want panic_on_warn on a canary phone.
>
> die() has arch specific implementations, so looking at:
>
> arch/arm64/kernel/traps.c:196#die
>
> it looks like panic is invoked if in_interrupt() or panic_on_oops(),
> which is a configure option. So maybe the config for KHWASAN should
> also enable that? Otherwise seems easy to forget. But maybe that
> should remain configurable separately?
In the upstream kernel, it is desirable to be able to discover bugs
and debug them from inside the running system. When you detect a bug
that makes it impossible for the current task to continue safely,
you're supposed to use something like BUG() to terminate the task; if
you can continue safely, you're supposed to use WARN(). Either way,
you should *not* just shoot down the whole kernel unless the system is
corrupted so badly that trying to keep running would be pointless.
You can configure the kernel such that it crashes the device when such
an event occurs, and doing so can sometimes be beneficial; but please
don't hardcode such policies into the upstream kernel.
On Thu, Sep 13, 2018 at 8:09 PM, 'Nick Desaulniers' via kasan-dev
<[email protected]> wrote:
> On Thu, Sep 13, 2018 at 1:37 AM Dmitry Vyukov <[email protected]> wrote:
>>
>> On Wed, Sep 12, 2018 at 7:39 PM, Jann Horn <[email protected]> wrote:
>> > On Wed, Sep 12, 2018 at 7:16 PM Dmitry Vyukov <[email protected]> wrote:
>> >> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
>> > [...]
>> >> > +static int khwasan_handler(struct pt_regs *regs, unsigned int esr)
>> >> > +{
>> >> > + bool recover = esr & KHWASAN_ESR_RECOVER;
>> >> > + bool write = esr & KHWASAN_ESR_WRITE;
>> >> > + size_t size = KHWASAN_ESR_SIZE(esr);
>> >> > + u64 addr = regs->regs[0];
>> >> > + u64 pc = regs->pc;
>> >> > +
>> >> > + if (user_mode(regs))
>> >> > + return DBG_HOOK_ERROR;
>> >> > +
>> >> > + kasan_report(addr, size, write, pc);
>> >> > +
>> >> > + /*
>> >> > + * The instrumentation allows to control whether we can proceed after
>> >> > + * a crash was detected. This is done by passing the -recover flag to
>> >> > + * the compiler. Disabling recovery allows to generate more compact
>> >> > + * code.
>> >> > + *
>> >> > + * Unfortunately disabling recovery doesn't work for the kernel right
>> >> > + * now. KHWASAN reporting is disabled in some contexts (for example when
>> >> > + * the allocator accesses slab object metadata; same is true for KASAN;
>> >> > + * this is controlled by current->kasan_depth). All these accesses are
>> >> > + * detected by the tool, even though the reports for them are not
>> >> > + * printed.
>> >> > + *
>> >> > + * This is something that might be fixed at some point in the future.
>> >> > + */
>> >> > + if (!recover)
>> >> > + die("Oops - KHWASAN", regs, 0);
>> >>
>> >> Why die and not panic? Die seems to be much less used function, and it
>> >> calls panic anyway, and we call panic in kasan_report if panic_on_warn
>> >> is set.
>> >
>> > die() is vaguely equivalent to BUG(); die() and BUG() normally only
>> > terminate the current process, which may or may not leave the system
>> > somewhat usable, while panic() always brings down the whole system.
>> > AFAIK panic() shouldn't be used unless you're in some very low-level
>> > code where you know that trying to just kill the current process can't
>> > work and the entire system is broken beyond repair.
>> >
>> > If KASAN traps on some random memory access, there's a good chance
>> > that just killing the current process will allow at least parts of the
>> > system to continue. I'm not sure whether BUG() or die() is more
>> > appropriate here, but I think it definitely should not be a panic().
>>
>>
>> Nick, do you know if die() will be enough to catch problems on Android
>> phones? panic_on_warn would turn this into panic, but I guess one does
>> not want panic_on_warn on a canary phone.
>
> die() has arch specific implementations, so looking at:
>
> arch/arm64/kernel/traps.c:196#die
>
> it looks like panic is invoked if in_interrupt() or panic_on_oops(),
> which is a configure option. So maybe the config for KHWASAN should
> also enable that? Otherwise seems easy to forget. But maybe that
> should remain configurable separately?
>
> Looking at the kernel configs for the Pixel 2, it does seem like
> CONFIG_PANIC_ON_OOPS=y is already enabled.
> https://android.googlesource.com/kernel/msm/+/android-msm-wahoo-4.4-pie/arch/arm64/configs/wahoo_defconfig#746
Then I think we are good here.
> Specifically to catch problems on Android, our internal debug builds
> can report on panics, but not oops, IIUC.
On Thu, Sep 06, 2018 at 01:06:23PM +0200, Andrey Konovalov wrote:
> On Thu, Sep 6, 2018 at 12:05 PM, Will Deacon <[email protected]> wrote:
> > On Wed, Sep 05, 2018 at 02:10:32PM -0700, Andrew Morton wrote:
> >> On Wed, 29 Aug 2018 13:35:04 +0200 Andrey Konovalov <[email protected]> wrote:
> >>
> >> > This patchset adds a new mode to KASAN [1], which is called KHWASAN
> >> > (Kernel HardWare assisted Address SANitizer).
> >>
> >> We're at v6 and there are no reviewed-by's or acked-by's to be seen.
> >> Is that a fair commentary on what has been happening, or have people
> >> been remiss in sending and gathering such things?
> >
> > I still have concerns about the consequences of merging this as anything
> > other than a debug option [1]. Unfortunately, merging it as a debug option
> > defeats the whole point, so I think we need to spend more effort on developing
> > tools that can help us to find and fix the subtle bugs which will arise from
> > enabling tagged pointers in the kernel.
>
> I totally don't mind calling it a debug option. Do I need to somehow
> specify it somewhere?
Ok, sorry, I completely misunderstood you earlier on then! For some reason
I thought you wanted this on by default.
In which case, I'm ok with the overall idea as long as we make the caveats
clear in the Kconfig text. In particular, that enabling this option may
introduce problems relating to pointer casting and comparison, but can
offer better coverage and lower memory consumption than a fully
software-based KASAN solution.
Will
On Wed, Sep 12, 2018 at 4:47 PM, Dmitry Vyukov <[email protected]> wrote:
> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
>>
>> #define __no_sanitize_address __attribute__((no_sanitize("address")))
>> +#define __no_sanitize_hwaddress __attribute__((no_sanitize("hwaddress")))
>
> It seems that it would be better to have just 1 attribute for both types.
> Currently __no_sanitize_address is used just in a single place. But if
> it ever used more, people will need to always spell both which looks
> unnecessary, or, worse will only fix asan but forget about khwasan.
>
> If we do just:
>
> #define __no_sanitize_address __attribute__((no_sanitize("address",
> "hwaddress")))
>
> Then we don't need any changes in compiler-gcc.h nor in compiler.h,
> and no chance or forgetting one of them.
Will do in v7.
>> config KASAN
>> - bool "KASan: runtime memory debugger"
>> + bool "KASAN: runtime memory debugger"
>> + help
>> + Enables KASAN (KernelAddressSANitizer) - runtime memory debugger,
>> + designed to find out-of-bounds accesses and use-after-free bugs.
>
> Perhaps also give link to Documentation/dev-tools/kasan.rst while we are here.
Will do in v7.
>
>> +
>> +choice
>> + prompt "KASAN mode"
>> + depends on KASAN
>> + default KASAN_GENERIC
>> + help
>> + KASAN has two modes: KASAN (a classic version, similar to userspace
>
> In these few sentences we call the old mode with 3 different terms:
> "generic", "classic" and "KASAN" :)
> This is somewhat confusing. Let's call it "generic" throughout (here
> and in the docs patch). "Generic" as in "supported on multiple arch
> and not-dependent on hardware features". "Classic" makes sense for
> people who knew KASAN before, but for future readers in won't make
> sense.
Will use "generic" in v7.
>>
>> +if HAVE_ARCH_KASAN_HW
>
> This choice looks somewhat weird on non-arm64. It's kinda a choice
> menu, but one can't really choose anything. Should we put the whole
> choice under HAVE_ARCH_KASAN_HW, and just select KASAN_GENERIC
> otherwise? I don't know what't the practice here. Andrey R?
I think having one option that is auto selected is fine.
>> +config KASAN_HW
>> + bool "KHWASAN: the hardware assisted mode"
Do we need a hyphen here? hardware-assisted?
Yes, will fix in v7.
On Wed, Sep 12, 2018 at 6:21 PM, Dmitry Vyukov <[email protected]> wrote:
> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
>> +void *khwasan_preset_slub_tag(struct kmem_cache *cache, const void *addr)
>
> Can't we do this in the existing kasan_init_slab_obj() hook? It looks
> like it should do exactly this -- allow any one-time initialization
> for objects. We could extend it to accept index and return a new
> pointer.
> If that does not work for some reason, I would try to at least unify
> the hook for slab/slub, e.g. pass idx=-1 from slub and then use
> random_tag().
> It also seems that we do preset tag for slab multiple times (from
> slab_get_obj()). Using kasan_init_slab_obj() should resolve this too
> (hopefully we don't call it multiple times).
The issue is that SLAB stores freelist as an array of indexes instead
of using an actual linked list like SLUB. So you can't store the tag
in the pointer while the object is in the freelist, since there's no
pointer. And, technically, we don't preset tags for SLAB, we just use
the id as the tag every time a pointer is used, so perhaps we should
rename the callback. As to unifying the callbacks, sure, we can do
that.
On Wed, Sep 12, 2018 at 7:13 PM, Dmitry Vyukov <[email protected]> wrote:
> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
>> +static int khwasan_handler(struct pt_regs *regs, unsigned int esr)
>> +{
>> + bool recover = esr & KHWASAN_ESR_RECOVER;
>> + bool write = esr & KHWASAN_ESR_WRITE;
>> + size_t size = KHWASAN_ESR_SIZE(esr);
>> + u64 addr = regs->regs[0];
>> + u64 pc = regs->pc;
>> +
>> + if (user_mode(regs))
>> + return DBG_HOOK_ERROR;
>> +
>> + kasan_report(addr, size, write, pc);
>> +
>> + /*
>> + * The instrumentation allows to control whether we can proceed after
>> + * a crash was detected. This is done by passing the -recover flag to
>> + * the compiler. Disabling recovery allows to generate more compact
>> + * code.
>> + *
>> + * Unfortunately disabling recovery doesn't work for the kernel right
>> + * now. KHWASAN reporting is disabled in some contexts (for example when
>> + * the allocator accesses slab object metadata; same is true for KASAN;
>> + * this is controlled by current->kasan_depth). All these accesses are
>> + * detected by the tool, even though the reports for them are not
>> + * printed.
>
>
> I am not following this part.
> Slab accesses metadata. OK.
> This is detected as bad access. OK.
> Report is not printed. OK.
> We skip BRK and resume execution.
> What is the problem?
When the kernel is compiled with -fsanitize=kernel-hwaddress without
any additional flags (like it's done now with KASAN_HW) everything
works as you described and there's no problem. However if one were to
recompile the kernel with hwasan recovery disabled, KHWASAN wouldn't
work due to the reasons described in the comment. Should I make it
more clear?
>
>
>
>> + *
>> + * This is something that might be fixed at some point in the future.
>> + */
>> + if (!recover)
>> + die("Oops - KHWASAN", regs, 0);
On Mon, Sep 17, 2018 at 8:59 PM, Andrey Konovalov <[email protected]> wrote:
> On Wed, Sep 12, 2018 at 6:21 PM, Dmitry Vyukov <[email protected]> wrote:
>> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
>
>>> +void *khwasan_preset_slub_tag(struct kmem_cache *cache, const void *addr)
>>
>> Can't we do this in the existing kasan_init_slab_obj() hook? It looks
>> like it should do exactly this -- allow any one-time initialization
>> for objects. We could extend it to accept index and return a new
>> pointer.
>> If that does not work for some reason, I would try to at least unify
>> the hook for slab/slub, e.g. pass idx=-1 from slub and then use
>> random_tag().
>> It also seems that we do preset tag for slab multiple times (from
>> slab_get_obj()). Using kasan_init_slab_obj() should resolve this too
>> (hopefully we don't call it multiple times).
>
> The issue is that SLAB stores freelist as an array of indexes instead
> of using an actual linked list like SLUB. So you can't store the tag
> in the pointer while the object is in the freelist, since there's no
> pointer. And, technically, we don't preset tags for SLAB, we just use
> the id as the tag every time a pointer is used, so perhaps we should
> rename the callback. As to unifying the callbacks, sure, we can do
> that.
As per offline discussion: potentially we can use
kasan_init_slab_obj() if we add tag in kmalloc hook by using
obj_to_idx().
On Wed, Sep 12, 2018 at 6:36 PM, Dmitry Vyukov <[email protected]> wrote:
> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
>> if (!shuffle) {
>> + start = khwasan_preset_slub_tag(s, start);
>> for_each_object_idx(p, idx, s, start, page->objects) {
>> setup_object(s, page, p);
>> + p = khwasan_preset_slub_tag(s, p);
>
>
> As I commented in the previous patch, can't we do this in
> kasan_init_slab_obj(), which should be called in all the right places
> already?
>
As per offline discussion, will do in v7.
On Wed, Sep 12, 2018 at 6:33 PM, Dmitry Vyukov <[email protected]> wrote:
> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
>> +#ifdef CONFIG_KASAN_HW
>> +#define KASAN_TAG_SHIFTED(tag) ((unsigned long)(tag) << 56)
>> +#define KASAN_SET_TAG(addr, tag) (((addr) & ~KASAN_TAG_SHIFTED(0xff)) | \
>> + KASAN_TAG_SHIFTED(tag))
>> +#define KASAN_RESET_TAG(addr) KASAN_SET_TAG(addr, 0xff)
>> +#endif
>> +
>
>
> Wouldn't it be better to
> #define KASAN_RESET_TAG(addr) addr
> when CONFIG_KASAN_HW is not enabled, and then not duplicate the macros
> below? That's what we do in kasan.h for all hooks.
> I see that a subsequent patch duplicates yet another macro in this
> file. While we could use:
>
> #define __kimg_to_phys(addr) (KASAN_RESET_TAG(addr) - kimage_voffset)
>
> with and without kasan. Duplicating them increases risk that somebody
> will change only the non-kasan version but forget kasan version.
Will do in v7.
On Wed, Sep 12, 2018 at 7:50 PM, Dmitry Vyukov <[email protected]> wrote:
> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
>> +#ifdef CONFIG_KASAN_HW
>
> We already have #ifdef CONFIG_KASAN_HW section below with additional
> functions for KASAN_HW and empty stubs otherwise. I would add this one
> there as well.
Will do in v7.
>
>> +void print_tags(u8 addr_tag, const void *addr);
>> +#else
>> +static inline void print_tags(u8 addr_tag, const void *addr) { }
>> +#endif
>> +void *find_first_bad_addr(void *addr, size_t size)
>> +{
>> + u8 tag = get_tag(addr);
>> + void *untagged_addr = reset_tag(addr);
>> + u8 *shadow = (u8 *)kasan_mem_to_shadow(untagged_addr);
>> + void *first_bad_addr = untagged_addr;
>> +
>> + while (*shadow == tag && first_bad_addr < untagged_addr + size) {
>
> I think it's better to check that are within bounds before accessing
> shadow. Otherwise it's kinda potential out-of-bounds access ;)
> I know that we _should_ not do an oob here, but still.
> Also feels that this function can be shortened to something like:
>
> u8 tag = get_tag(addr);
> void *p = reset_tag(addr);
> void *end = p + size;
>
> while (p < end && tag == *(u8 *)kasan_mem_to_shadow(p))
> p += KASAN_SHADOW_SCALE_SIZE;
> return p;
Will do in v7.
On Wed, Sep 12, 2018 at 8:39 PM, Dmitry Vyukov <[email protected]> wrote:
> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
>> This patch updates KASAN documentation to reflect the addition of KHWASAN.
>> -Currently KASAN is supported only for the x86_64 and arm64 architectures.
>> +KASAN uses compile-time instrumentation to insert validity checks before every
>> +memory access, and therefore requires a compiler version that supports that.
>> +For classic KASAN you need GCC version 4.9.2 or later. GCC 5.0 or later is
>> +required for detection of out-of-bounds accesses on stack and global variables.
>> +KHWASAN in turns is only supported in clang and requires revision 330044 or
>
> in turn?
>
>> -and choose between CONFIG_KASAN_OUTLINE and CONFIG_KASAN_INLINE. Outline and
>> -inline are compiler instrumentation types. The former produces smaller binary
>> -the latter is 1.1 - 2 times faster. Inline instrumentation requires a GCC
>> +and choose between CONFIG_KASAN_GENERIC (to enable classic KASAN) and
>> +CONFIG_KASAN_HW (to enabled KHWASAN). You also need to choose choose between
>
> to enable
>
>> + print_address_description+0x73/0x280 mm/kasan/report.c:254
>
>
> KASAN does not print line numbers per se.
> I think we need to show unmodified output to not confuse readers
> (probably remove the useless ? lines).
Will fix all in v7.
On Wed, Sep 12, 2018 at 8:30 PM, Dmitry Vyukov <[email protected]> wrote:
> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
>> void kasan_unpoison_shadow(const void *address, size_t size)
>> {
>> - kasan_poison_shadow(address, size, 0);
>> + u8 tag = get_tag(address);
>> +
>> + /* Perform shadow offset calculation based on untagged address */
>
> The comment is not super-useful. It would be more useful to say why we
> need to do this.
> Most callers explicitly untag pointer passed to this function, for
> some it's unclear if the pointer contains tag or not.
> For example, __hwasan_tag_memory -- what does it accept? Tagged or untagged?
There are some callers that pass tagged pointers to this functions,
e.g. ksize or kasan_unpoison_object_data. I'll expand the comment.
>
>
>> + address = reset_tag(address);
>> +
>> + kasan_poison_shadow(address, size, tag);
>>
>> if (size & KASAN_SHADOW_MASK) {
>> u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size);
>> - *shadow = size & KASAN_SHADOW_MASK;
>> +
>> + if (IS_ENABLED(CONFIG_KASAN_HW))
>> + *shadow = tag;
>> + else
>> + *shadow = size & KASAN_SHADOW_MASK;
>> }
>> }
>
>
> It seems that this function is just different for kasan and khwasan.
> Currently for kasan we have:
>
> kasan_poison_shadow(address, size, tag);
> if (size & KASAN_SHADOW_MASK) {
> u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size);
> *shadow = size & KASAN_SHADOW_MASK;
> }
>
> But what we want to say for khwasan is:
>
> kasan_poison_shadow(address, round_up(size, KASAN_SHADOW_SCALE_SIZE),
> get_tag(address));
>
> Not sure if we want to keep a common implementation or just have
> separate implementations...
As per offline discussion leaving as is.
>> void kasan_free_pages(struct page *page, unsigned int order)
>> @@ -235,6 +248,7 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
>> slab_flags_t *flags)
>> {
>> unsigned int orig_size = *size;
>> + unsigned int redzone_size = 0;
>
> This variable seems to be always initialized below. We don't general
> initialize local variables in this case.
Will fix in v7.
>> void check_memory_region(unsigned long addr, size_t size, bool write,
>> unsigned long ret_ip)
>> {
>> + u8 tag;
>> + u8 *shadow_first, *shadow_last, *shadow;
>> + void *untagged_addr;
>> +
>> + tag = get_tag((const void *)addr);
>> +
>> + /* Ignore accesses for pointers tagged with 0xff (native kernel
>
> /* on a separate line
Will fix in v7.
>
>> + * pointer tag) to suppress false positives caused by kmap.
>> + *
>> + * Some kernel code was written to account for archs that don't keep
>> + * high memory mapped all the time, but rather map and unmap particular
>> + * pages when needed. Instead of storing a pointer to the kernel memory,
>> + * this code saves the address of the page structure and offset within
>> + * that page for later use. Those pages are then mapped and unmapped
>> + * with kmap/kunmap when necessary and virt_to_page is used to get the
>> + * virtual address of the page. For arm64 (that keeps the high memory
>> + * mapped all the time), kmap is turned into a page_address call.
>> +
>> + * The issue is that with use of the page_address + virt_to_page
>> + * sequence the top byte value of the original pointer gets lost (gets
>> + * set to KHWASAN_TAG_KERNEL (0xFF).
>
> Missed closing bracket.
Will fix in v7.
On Wed, Sep 12, 2018 at 4:54 PM, Dmitry Vyukov <[email protected]> wrote:
> On Wed, Aug 29, 2018 at 1:35 PM, Andrey Konovalov <[email protected]> wrote:
>> /*
>> - * KASAN requires 1/8th of the kernel virtual address space for the shadow
>> - * region. KASAN can bloat the stack significantly, so double the (minimum)
>> - * stack size when KASAN is in use.
>> + * KASAN and KHWASAN require 1/8th and 1/16th of the kernel virtual address
>
>
> I am somewhat confused by the terminology.
> "KASAN" is not actually "CONFIG_KASAN" below, it is actually
> "CONFIG_KASAN_GENERIC". While "KHWASAN" translates to "KASAN_HW" few
> lines later.
> I think we need some consistent terminology for comments and config
> names until it's too late.
>
As per offline discussion will rename in v7.
On Fri, Sep 14, 2018 at 5:28 PM, Will Deacon <[email protected]> wrote:
> On Thu, Sep 06, 2018 at 01:06:23PM +0200, Andrey Konovalov wrote:
>> On Thu, Sep 6, 2018 at 12:05 PM, Will Deacon <[email protected]> wrote:
>> > On Wed, Sep 05, 2018 at 02:10:32PM -0700, Andrew Morton wrote:
>> >> On Wed, 29 Aug 2018 13:35:04 +0200 Andrey Konovalov <[email protected]> wrote:
>> >>
>> >> > This patchset adds a new mode to KASAN [1], which is called KHWASAN
>> >> > (Kernel HardWare assisted Address SANitizer).
>> >>
>> >> We're at v6 and there are no reviewed-by's or acked-by's to be seen.
>> >> Is that a fair commentary on what has been happening, or have people
>> >> been remiss in sending and gathering such things?
>> >
>> > I still have concerns about the consequences of merging this as anything
>> > other than a debug option [1]. Unfortunately, merging it as a debug option
>> > defeats the whole point, so I think we need to spend more effort on developing
>> > tools that can help us to find and fix the subtle bugs which will arise from
>> > enabling tagged pointers in the kernel.
>>
>> I totally don't mind calling it a debug option. Do I need to somehow
>> specify it somewhere?
>
> Ok, sorry, I completely misunderstood you earlier on then! For some reason
> I thought you wanted this on by default.
>
> In which case, I'm ok with the overall idea as long as we make the caveats
> clear in the Kconfig text. In particular, that enabling this option may
> introduce problems relating to pointer casting and comparison, but can
> offer better coverage and lower memory consumption than a fully
> software-based KASAN solution.
Great! I'll explicitly call it debug feature and mention the caveats
in v7. Thanks!