LinuxLists.cc - [PATCH 00/11] [v5] Use global pages with PTI

2018-04-06 21:06:11

Subject: [PATCH 00/11] [v5] Use global pages with PTI

Changes from v4
* Fix compile error reported by Tom Lendacky
* Avoid setting _PAGE_GLOBAL on non-present entries

Changes from v3:
* Fix whitespace issue noticed by willy
* Clarify comments about X86_FEATURE_PGE checks
* Clarify commit message around the necessity of _PAGE_GLOBAL
filtering when CR4.PGE=0 or PGE is unsupported.

Changes from v2:

* Add performance numbers to changelogs
* Fix compile error resulting from use of x86-specific
__default_kernel_pte_mask in arch-generic mm/early_ioremap.c
* Delay kernel text cloning until after we are done messing
with it (patch 11).
* Blacklist K8 explicitly from mapping all kernel text as
global (this should never happen because K8 does not use
pti when pti=auto, but we on the safe side). (patch 11)

--

The later versions of the KAISER patches (pre-PTI) allowed the
user/kernel shared areas to be GLOBAL. The thought was that this would
reduce the TLB overhead of keeping two copies of these mappings.

During the switch over to PTI, we seem to have lost our ability to have
GLOBAL mappings. This adds them back.

To measure the benefits of this, I took a modern Atom system without
PCIDs and ran a microbenchmark[1] (higher is better):

No Global Lines (baseline ): 6077741 lseeks/sec
88 Global Lines (kern entry): 7528609 lseeks/sec (+23.9%)
94 Global Lines (all ktext ): 8433111 lseeks/sec (+38.8%)

On a modern Skylake desktop with PCIDs, the benefits are tangible, but not
huge:

No Global pages (baseline): 15783951 lseeks/sec
28 Global pages (this set): 16054688 lseeks/sec
+270737 lseeks/sec (+1.71%)

I also double-checked with a kernel compile on the Skylake system (lower
is better):

No Global pages (baseline): 186.951 seconds time elapsed ( +- 0.35% )
28 Global pages (this set): 185.756 seconds time elapsed ( +- 0.09% )
-1.195 seconds (-0.64%)

1. https://github.com/antonblanchard/will-it-scale/blob/master/tests/lseek1.c

Cc: Andrea Arcangeli <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: [email protected]
Cc: Nadav Amit <[email protected]>

2018-04-06 21:01:46

by Dave Hansen

[permalink] [raw]

Subject: [PATCH 11/11] x86/pti: leave kernel text global for !PCID

Note: This has changed since the last version. It now clones the
kernel text PMDs at a much later point and also disables this
functionality on AMD K8 processors. Details in the patch.

--

I'm sticking this at the end of the series because it's a bit weird.
It can be dropped and the rest of the series is still useful without
it.

Global pages are bad for hardening because they potentially let an
exploit read the kernel image via a Meltdown-style attack which
makes it easier to find gadgets.

But, global pages are good for performance because they reduce TLB
misses when making user/kernel transitions, especially when PCIDs
are not available, such as on older hardware, or where a hypervisor
has disabled them for some reason.

This patch implements a basic, sane policy: If you have PCIDs, you
only map a minimal amount of kernel text global. If you do not have
PCIDs, you map all kernel text global.

This policy effectively makes PCIDs something that not only adds
performance but a little bit of hardening as well.

I ran a simple "lseek" microbenchmark[1] to test the benefit on
a modern Atom microserver. Most of the benefit comes from applying
the series before this patch ("entry only"), but there is still a
signifiant benefit from this patch.

No Global Lines (baseline ): 6077741 lseeks/sec
88 Global Lines (entry only): 7528609 lseeks/sec (+23.9%)
94 Global Lines (this patch): 8433111 lseeks/sec (+38.8%)

1. https://github.com/antonblanchard/will-it-scale/blob/master/tests/lseek1.c

Signed-off-by: Dave Hansen <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: [email protected]
Cc: Nadav Amit <[email protected]>
---

b/arch/x86/include/asm/pti.h | 2 +
b/arch/x86/mm/init_64.c | 6 +++
b/arch/x86/mm/pti.c | 78 ++++++++++++++++++++++++++++++++++++++++---
3 files changed, 82 insertions(+), 4 deletions(-)

diff -puN arch/x86/include/asm/pti.h~kpti-global-text-option arch/x86/include/asm/pti.h
--- a/arch/x86/include/asm/pti.h~kpti-global-text-option 2018-04-06 10:47:59.393796116 -0700
+++ b/arch/x86/include/asm/pti.h 2018-04-06 10:47:59.400796116 -0700
@@ -6,8 +6,10 @@
#ifdef CONFIG_PAGE_TABLE_ISOLATION
extern void pti_init(void);
extern void pti_check_boottime_disable(void);
+extern void pti_clone_kernel_text(void);
#else
static inline void pti_check_boottime_disable(void) { }
+static inline void pti_clone_kernel_text(void) { }
#endif

#endif /* __ASSEMBLY__ */
diff -puN arch/x86/mm/init_64.c~kpti-global-text-option arch/x86/mm/init_64.c
--- a/arch/x86/mm/init_64.c~kpti-global-text-option 2018-04-06 10:47:59.395796116 -0700
+++ b/arch/x86/mm/init_64.c 2018-04-06 10:47:59.400796116 -0700
@@ -1294,6 +1294,12 @@ void mark_rodata_ro(void)
(unsigned long) __va(__pa_symbol(_sdata)));

debug_checkwx();
+
+ /*
+ * Do this after all of the manipulation of the
+ * kernel text page tables are complete.
+ */
+ pti_clone_kernel_text();
}

int kern_addr_valid(unsigned long addr)
diff -puN arch/x86/mm/pti.c~kpti-global-text-option arch/x86/mm/pti.c
--- a/arch/x86/mm/pti.c~kpti-global-text-option 2018-04-06 10:47:59.397796116 -0700
+++ b/arch/x86/mm/pti.c 2018-04-06 10:47:59.401796116 -0700
@@ -66,12 +66,22 @@ static void __init pti_print_if_secure(c
pr_info("%s\n", reason);
}

+enum pti_mode {
+ PTI_AUTO = 0,
+ PTI_FORCE_OFF,
+ PTI_FORCE_ON
+} pti_mode;
+
void __init pti_check_boottime_disable(void)
{
char arg[5];
int ret;

+ /* Assume mode is auto unless overridden. */
+ pti_mode = PTI_AUTO;
+
if (hypervisor_is_type(X86_HYPER_XEN_PV)) {
+ pti_mode = PTI_FORCE_OFF;
pti_print_if_insecure("disabled on XEN PV.");
return;
}
@@ -79,18 +89,23 @@ void __init pti_check_boottime_disable(v
ret = cmdline_find_option(boot_command_line, "pti", arg, sizeof(arg));
if (ret > 0) {
if (ret == 3 && !strncmp(arg, "off", 3)) {
+ pti_mode = PTI_FORCE_OFF;
pti_print_if_insecure("disabled on command line.");
return;
}
if (ret == 2 && !strncmp(arg, "on", 2)) {
+ pti_mode = PTI_FORCE_ON;
pti_print_if_secure("force enabled on command line.");
goto enable;
}
- if (ret == 4 && !strncmp(arg, "auto", 4))
+ if (ret == 4 && !strncmp(arg, "auto", 4)) {
+ pti_mode = PTI_AUTO;
goto autosel;
+ }
}

if (cmdline_find_option_bool(boot_command_line, "nopti")) {
+ pti_mode = PTI_FORCE_OFF;
pti_print_if_insecure("disabled on command line.");
return;
}
@@ -149,7 +164,7 @@ pgd_t __pti_set_user_pgd(pgd_t *pgdp, pg
*
* Returns a pointer to a P4D on success, or NULL on failure.
*/
-static __init p4d_t *pti_user_pagetable_walk_p4d(unsigned long address)
+static p4d_t *pti_user_pagetable_walk_p4d(unsigned long address)
{
pgd_t *pgd = kernel_to_user_pgdp(pgd_offset_k(address));
gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);
@@ -177,7 +192,7 @@ static __init p4d_t *pti_user_pagetable_
*
* Returns a pointer to a PMD on success, or NULL on failure.
*/
-static __init pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)
+static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)
{
gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);
p4d_t *p4d = pti_user_pagetable_walk_p4d(address);
@@ -267,7 +282,7 @@ static void __init pti_setup_vsyscall(vo
static void __init pti_setup_vsyscall(void) { }
#endif

-static void __init
+static void
pti_clone_pmds(unsigned long start, unsigned long end, pmdval_t clear)
{
unsigned long addr;
@@ -373,6 +388,58 @@ static void __init pti_clone_entry_text(
}

/*
+ * Global pages and PCIDs are both ways to make kernel TLB entries
+ * live longer, reduce TLB misses and improve kernel performance.
+ * But, leaving all kernel text Global makes it potentially accessible
+ * to Meltdown-style attacks which make it trivial to find gadgets or
+ * defeat KASLR.
+ *
+ * Only use global pages when it is really worth it.
+ */
+static inline bool pti_kernel_image_global_ok(void)
+{
+ /*
+ * Systems with PCIDs get litlle benefit from global
+ * kernel text and are not worth the downsides.
+ */
+ if (cpu_feature_enabled(X86_FEATURE_PCID))
+ return false;
+
+ /*
+ * Only do global kernel image for pti=auto. Do the most
+ * secure thing (not global) if pti=on specified.
+ */
+ if (pti_mode != PTI_AUTO)
+ return false;
+
+ /*
+ * K8 may not tolerate the cleared _PAGE_RW on the userspace
+ * global kernel image pages. Do the safe thing (disable
+ * global kernel image). This is unlikely to ever be
+ * noticed because PTI is disabled by default on AMD CPUs.
+ */
+ if (boot_cpu_has(X86_FEATURE_K8))
+ return false;
+
+ return true;
+}
+
+/*
+ * For some configurations, map all of kernel text into the user page
+ * tables. This reduces TLB misses, especially on non-PCID systems.
+ */
+void pti_clone_kernel_text(void)
+{
+ unsigned long start = PFN_ALIGN(_text);
+ unsigned long end = ALIGN((unsigned long)_end, PMD_PAGE_SIZE);
+
+ if (!pti_kernel_image_global_ok())
+ return;
+
+ pti_clone_pmds(start, end, _PAGE_RW);
+}
+
+/*
* This is the only user for it and it is not arch-generic like
* the other set_memory.h functions. Just extern it.
*/
@@ -388,6 +455,9 @@ void pti_set_kernel_image_nonglobal(void
unsigned long start = PFN_ALIGN(_text);
unsigned long end = ALIGN((unsigned long)_end, PMD_PAGE_SIZE);

+ if (pti_kernel_image_global_ok())
+ return;
+
pr_debug("set kernel image non-global\n");

set_memory_nonglobal(start, (end - start) >> PAGE_SHIFT);
_

2018-04-06 21:01:46

by Dave Hansen

[permalink] [raw]

Subject: [PATCH 03/11] x86/mm: introduce "default" kernel PTE mask

From: Dave Hansen <[email protected]>

The __PAGE_KERNEL_* page permissions are "raw". They contain bits
that may or may not be supported on the current processor. They need
to be filtered by a mask (currently __supported_pte_mask) to turn them
into a value that we can actually set in a PTE.

These __PAGE_KERNEL_* values all contain _PAGE_GLOBAL. But, with PTI,
we want to be able to support _PAGE_GLOBAL (have the bit set in
__supported_pte_mask) but not have it appear in any of these masks by
default.

This patch creates a new mask, __default_kernel_pte_mask, and applies
it when creating all of the PAGE_KERNEL_* masks. This makes
PAGE_KERNEL_* safe to use anywhere (they only contain supported bits).
It also ensures that PAGE_KERNEL_* contains _PAGE_GLOBAL on PTI=n
kernels but clears _PAGE_GLOBAL when PTI=y.

We also make __default_kernel_pte_mask a non-GPL exported symbol
because there are plenty of driver-available interfaces that take
PAGE_KERNEL_* permissions.

Signed-off-by: Dave Hansen <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: [email protected]
Cc: Nadav Amit <[email protected]>
---

b/arch/x86/include/asm/pgtable_types.h | 27 +++++++++++++++------------
b/arch/x86/mm/init.c | 6 ++++++
b/arch/x86/mm/init_32.c | 8 +++++++-
b/arch/x86/mm/init_64.c | 5 +++++
4 files changed, 33 insertions(+), 13 deletions(-)

diff -puN arch/x86/include/asm/pgtable_types.h~KERN-pgprot-default arch/x86/include/asm/pgtable_types.h
--- a/arch/x86/include/asm/pgtable_types.h~KERN-pgprot-default 2018-04-06 10:47:54.732796127 -0700
+++ b/arch/x86/include/asm/pgtable_types.h 2018-04-06 10:47:54.741796127 -0700
@@ -196,19 +196,21 @@ enum page_cache_mode {
#define __PAGE_KERNEL_NOENC (__PAGE_KERNEL)
#define __PAGE_KERNEL_NOENC_WP (__PAGE_KERNEL_WP)

-#define PAGE_KERNEL __pgprot(__PAGE_KERNEL | _PAGE_ENC)
-#define PAGE_KERNEL_NOENC __pgprot(__PAGE_KERNEL)
-#define PAGE_KERNEL_RO __pgprot(__PAGE_KERNEL_RO | _PAGE_ENC)
-#define PAGE_KERNEL_EXEC __pgprot(__PAGE_KERNEL_EXEC | _PAGE_ENC)
-#define PAGE_KERNEL_EXEC_NOENC __pgprot(__PAGE_KERNEL_EXEC)
-#define PAGE_KERNEL_RX __pgprot(__PAGE_KERNEL_RX | _PAGE_ENC)
-#define PAGE_KERNEL_NOCACHE __pgprot(__PAGE_KERNEL_NOCACHE | _PAGE_ENC)
-#define PAGE_KERNEL_LARGE __pgprot(__PAGE_KERNEL_LARGE | _PAGE_ENC)
-#define PAGE_KERNEL_LARGE_EXEC __pgprot(__PAGE_KERNEL_LARGE_EXEC | _PAGE_ENC)
-#define PAGE_KERNEL_VVAR __pgprot(__PAGE_KERNEL_VVAR | _PAGE_ENC)
+#define default_pgprot(x) __pgprot((x) & __default_kernel_pte_mask)

-#define PAGE_KERNEL_IO __pgprot(__PAGE_KERNEL_IO)
-#define PAGE_KERNEL_IO_NOCACHE __pgprot(__PAGE_KERNEL_IO_NOCACHE)
+#define PAGE_KERNEL default_pgprot(__PAGE_KERNEL | _PAGE_ENC)
+#define PAGE_KERNEL_NOENC default_pgprot(__PAGE_KERNEL)
+#define PAGE_KERNEL_RO default_pgprot(__PAGE_KERNEL_RO | _PAGE_ENC)
+#define PAGE_KERNEL_EXEC default_pgprot(__PAGE_KERNEL_EXEC | _PAGE_ENC)
+#define PAGE_KERNEL_EXEC_NOENC default_pgprot(__PAGE_KERNEL_EXEC)
+#define PAGE_KERNEL_RX default_pgprot(__PAGE_KERNEL_RX | _PAGE_ENC)
+#define PAGE_KERNEL_NOCACHE default_pgprot(__PAGE_KERNEL_NOCACHE | _PAGE_ENC)
+#define PAGE_KERNEL_LARGE default_pgprot(__PAGE_KERNEL_LARGE | _PAGE_ENC)
+#define PAGE_KERNEL_LARGE_EXEC default_pgprot(__PAGE_KERNEL_LARGE_EXEC | _PAGE_ENC)
+#define PAGE_KERNEL_VVAR default_pgprot(__PAGE_KERNEL_VVAR | _PAGE_ENC)
+
+#define PAGE_KERNEL_IO default_pgprot(__PAGE_KERNEL_IO)
+#define PAGE_KERNEL_IO_NOCACHE default_pgprot(__PAGE_KERNEL_IO_NOCACHE)

#endif /* __ASSEMBLY__ */

@@ -483,6 +485,7 @@ static inline pgprot_t pgprot_large_2_4k
typedef struct page *pgtable_t;

extern pteval_t __supported_pte_mask;
+extern pteval_t __default_kernel_pte_mask;
extern void set_nx(void);
extern int nx_enabled;

diff -puN arch/x86/mm/init_32.c~KERN-pgprot-default arch/x86/mm/init_32.c
--- a/arch/x86/mm/init_32.c~KERN-pgprot-default 2018-04-06 10:47:54.733796127 -0700
+++ b/arch/x86/mm/init_32.c 2018-04-06 10:47:54.741796127 -0700
@@ -558,8 +558,14 @@ static void __init pagetable_init(void)
permanent_kmaps_init(pgd_base);
}

-pteval_t __supported_pte_mask __read_mostly = ~(_PAGE_NX | _PAGE_GLOBAL);
+#define DEFAULT_PTE_MASK ~(_PAGE_NX | _PAGE_GLOBAL)
+/* Bits supported by the hardware: */
+pteval_t __supported_pte_mask __read_mostly = DEFAULT_PTE_MASK;
+/* Bits allowed in normal kernel mappings: */
+pteval_t __default_kernel_pte_mask __read_mostly = DEFAULT_PTE_MASK;
EXPORT_SYMBOL_GPL(__supported_pte_mask);
+/* Used in PAGE_KERNEL_* macros which are reasonably used out-of-tree: */
+EXPORT_SYMBOL(__default_kernel_pte_mask);

/* user-defined highmem size */
static unsigned int highmem_pages = -1;
diff -puN arch/x86/mm/init_64.c~KERN-pgprot-default arch/x86/mm/init_64.c
--- a/arch/x86/mm/init_64.c~KERN-pgprot-default 2018-04-06 10:47:54.735796127 -0700
+++ b/arch/x86/mm/init_64.c 2018-04-06 10:47:54.742796127 -0700
@@ -65,8 +65,13 @@
* around without checking the pgd every time.
*/

+/* Bits supported by the hardware: */
pteval_t __supported_pte_mask __read_mostly = ~0;
+/* Bits allowed in normal kernel mappings: */
+pteval_t __default_kernel_pte_mask __read_mostly = ~0;
EXPORT_SYMBOL_GPL(__supported_pte_mask);
+/* Used in PAGE_KERNEL_* macros which are reasonably used out-of-tree: */
+EXPORT_SYMBOL(__default_kernel_pte_mask);

int force_personality32;

diff -puN arch/x86/mm/init.c~KERN-pgprot-default arch/x86/mm/init.c
--- a/arch/x86/mm/init.c~KERN-pgprot-default 2018-04-06 10:47:54.737796127 -0700
+++ b/arch/x86/mm/init.c 2018-04-06 10:47:54.742796127 -0700
@@ -190,6 +190,12 @@ static void __init probe_page_size_mask(
enable_global_pages();
}

+ /* By the default is everything supported: */
+ __default_kernel_pte_mask = __supported_pte_mask;
+ /* Except when with PTI where the kernel is mostly non-Global: */
+ if (cpu_feature_enabled(X86_FEATURE_PTI))
+ __default_kernel_pte_mask &= ~_PAGE_GLOBAL;
+
/* Enable 1 GB linear kernel mappings if available: */
if (direct_gbpages && boot_cpu_has(X86_FEATURE_GBPAGES)) {
printk(KERN_INFO "Using GB pages for direct mapping\n");
_

2018-04-06 21:02:03

by Dave Hansen

[permalink] [raw]

Subject: [PATCH 08/11] x86/mm: do not forbid _PAGE_RW before init for __ro_after_init

From: Dave Hansen <[email protected]>

__ro_after_init data gets stuck in the .rodata section. That's normally
fine because the kernel itself manages the R/W properties.

But, if we run __change_page_attr() on an area which is __ro_after_init,
the .rodata checks will trigger and force the area to be immediately
read-only, even if it is early-ish in boot. This caused problems when
trying to clear the _PAGE_GLOBAL bit for these area in the PTI code:
it cleared _PAGE_GLOBAL like I asked, but also took it up on itself
to clear _PAGE_RW. The kernel then oopses the next time it wrote to
a __ro_after_init data structure.

To fix this, add the kernel_set_to_readonly check, just like we have
for kernel text, just a few lines below in this function.

Signed-off-by: Dave Hansen <[email protected]>
Acked-by: Kees Cook <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: [email protected]
Cc: Nadav Amit <[email protected]>
---

b/arch/x86/mm/pageattr.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff -puN arch/x86/mm/pageattr.c~check-kernel_set_to_readonly arch/x86/mm/pageattr.c
--- a/arch/x86/mm/pageattr.c~check-kernel_set_to_readonly 2018-04-06 10:47:57.711796120 -0700
+++ b/arch/x86/mm/pageattr.c 2018-04-06 10:47:57.714796120 -0700
@@ -298,9 +298,11 @@ static inline pgprot_t static_protection

/*
* The .rodata section needs to be read-only. Using the pfn
- * catches all aliases.
+ * catches all aliases. This also includes __ro_after_init,
+ * so do not enforce until kernel_set_to_readonly is true.
*/
- if (within(pfn, __pa_symbol(__start_rodata) >> PAGE_SHIFT,
+ if (kernel_set_to_readonly &&
+ within(pfn, __pa_symbol(__start_rodata) >> PAGE_SHIFT,
__pa_symbol(__end_rodata) >> PAGE_SHIFT))
pgprot_val(forbidden) |= _PAGE_RW;

_

2018-04-06 21:02:23

by Dave Hansen

[permalink] [raw]

Subject: [PATCH 10/11] x86/pti: never implicitly clear _PAGE_GLOBAL for kernel image

From: Dave Hansen <[email protected]>

Summary:

In current kernels, with PTI enabled, no pages are marked Global. This
potentially increases TLB misses. But, the mechanism by which the Global
bit is set and cleared is rather haphazard. This patch makes the process
more explicit. In the end, it leaves us with Global entries in the page
tables for the areas truly shared by userspace and kernel and increases
TLB hit rates.

The place this patch really shines in on systems without PCIDs. In this
case, we are using an lseek microbenchmark[1] to see how a reasonably
non-trivial syscall behaves. Higher is better:

No Global pages (baseline): 6077741 lseeks/sec
88 Global Pages (this set): 7528609 lseeks/sec (+23.9%)

On a modern Skylake desktop with PCIDs, the benefits are tangible, but not
huge for a kernel compile (lower is better):

No Global pages (baseline): 186.951 seconds time elapsed ( +- 0.35% )
28 Global pages (this set): 185.756 seconds time elapsed ( +- 0.09% )
-1.195 seconds (-0.64%)

I also re-checked everything using the lseek1 test[1]:

No Global pages (baseline): 15783951 lseeks/sec
28 Global pages (this set): 16054688 lseeks/sec
+270737 lseeks/sec (+1.71%)

The effect is more visible, but still modest.

Details:

The kernel page tables are inherited from head_64.S which rudely marks
them as _PAGE_GLOBAL. For PTI, we have been relying on the grace of
$DEITY and some insane behavior in pageattr.c to clear _PAGE_GLOBAL.
This patch tries to do better.

First, stop filtering out "unsupported" bits from being cleared in the
pageattr code. It's fine to filter out *setting* these bits but it
is insane to keep us from clearing them.

Then, *explicitly* go clear _PAGE_GLOBAL from the kernel identity map.
Do not rely on pageattr to do it magically.

After this patch, we can see that "GLB" shows up in each copy of the
page tables, that we have the same number of global entries in each
and that they are the *same* entries.

# grep -c GLB /sys/kernel/debug/page_tables/*
/sys/kernel/debug/page_tables/current_kernel:11
/sys/kernel/debug/page_tables/current_user:11
/sys/kernel/debug/page_tables/kernel:11

# for f in `ls /sys/kernel/debug/page_tables/`; do grep GLB /sys/kernel/debug/page_tables/$f > $f.GLB; done
# md5sum *.GLB
9caae8ad6a1fb53aca2407ec037f612d current_kernel.GLB
9caae8ad6a1fb53aca2407ec037f612d current_user.GLB
9caae8ad6a1fb53aca2407ec037f612d kernel.GLB

A quick visual audit also shows that all the entries make sense.
0xfffffe0000000000 is the cpu_entry_area and 0xffffffff81c00000
is the entry/exit text:

# grep -c GLB /sys/kernel/debug/page_tables/current_user
0xfffffe0000000000-0xfffffe0000002000 8K ro GLB NX pte
0xfffffe0000002000-0xfffffe0000003000 4K RW GLB NX pte
0xfffffe0000003000-0xfffffe0000006000 12K ro GLB NX pte
0xfffffe0000006000-0xfffffe0000007000 4K ro GLB x pte
0xfffffe0000007000-0xfffffe000000d000 24K RW GLB NX pte
0xfffffe000002d000-0xfffffe000002e000 4K ro GLB NX pte
0xfffffe000002e000-0xfffffe000002f000 4K RW GLB NX pte
0xfffffe000002f000-0xfffffe0000032000 12K ro GLB NX pte
0xfffffe0000032000-0xfffffe0000033000 4K ro GLB x pte
0xfffffe0000033000-0xfffffe0000039000 24K RW GLB NX pte
0xffffffff81c00000-0xffffffff81e00000 2M ro PSE GLB x pmd

1. https://github.com/antonblanchard/will-it-scale/blob/master/tests/lseek1.c

Signed-off-by: Dave Hansen <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: [email protected]
Cc: Nadav Amit <[email protected]>
---

b/arch/x86/mm/init.c | 8 +-------
b/arch/x86/mm/pageattr.c | 12 +++++++++---
b/arch/x86/mm/pti.c | 25 +++++++++++++++++++++++++
3 files changed, 35 insertions(+), 10 deletions(-)

diff -puN arch/x86/mm/init.c~clear-global-for-pti arch/x86/mm/init.c
--- a/arch/x86/mm/init.c~clear-global-for-pti 2018-04-06 10:47:58.807796117 -0700
+++ b/arch/x86/mm/init.c 2018-04-06 10:47:58.815796117 -0700
@@ -161,12 +161,6 @@ struct map_range {

static int page_size_mask;

-static void enable_global_pages(void)
-{
- if (!static_cpu_has(X86_FEATURE_PTI))
- __supported_pte_mask |= _PAGE_GLOBAL;
-}
-
static void __init probe_page_size_mask(void)
{
/*
@@ -187,7 +181,7 @@ static void __init probe_page_size_mask(
__supported_pte_mask &= ~_PAGE_GLOBAL;
if (boot_cpu_has(X86_FEATURE_PGE)) {
cr4_set_bits_and_update_boot(X86_CR4_PGE);
- enable_global_pages();
+ __supported_pte_mask |= _PAGE_GLOBAL;
}

/* By the default is everything supported: */
diff -puN arch/x86/mm/pageattr.c~clear-global-for-pti arch/x86/mm/pageattr.c
--- a/arch/x86/mm/pageattr.c~clear-global-for-pti 2018-04-06 10:47:58.809796117 -0700
+++ b/arch/x86/mm/pageattr.c 2018-04-06 10:47:58.815796117 -0700
@@ -1411,11 +1411,11 @@ static int change_page_attr_set_clr(unsi
memset(&cpa, 0, sizeof(cpa));

/*
- * Check, if we are requested to change a not supported
- * feature:
+ * Check, if we are requested to set a not supported
+ * feature. Clearing non-supported features is OK.
*/
mask_set = canon_pgprot(mask_set);
- mask_clr = canon_pgprot(mask_clr);
+
if (!pgprot_val(mask_set) && !pgprot_val(mask_clr) && !force_split)
return 0;

@@ -1758,6 +1758,12 @@ int set_memory_4k(unsigned long addr, in
__pgprot(0), 1, 0, NULL);
}

+int set_memory_nonglobal(unsigned long addr, int numpages)
+{
+ return change_page_attr_clear(&addr, numpages,
+ __pgprot(_PAGE_GLOBAL), 0);
+}
+
static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc)
{
struct cpa_data cpa;
diff -puN arch/x86/mm/pti.c~clear-global-for-pti arch/x86/mm/pti.c
--- a/arch/x86/mm/pti.c~clear-global-for-pti 2018-04-06 10:47:58.811796117 -0700
+++ b/arch/x86/mm/pti.c 2018-04-06 10:47:58.816796117 -0700
@@ -373,6 +373,27 @@ static void __init pti_clone_entry_text(
}

/*
+ * This is the only user for it and it is not arch-generic like
+ * the other set_memory.h functions. Just extern it.
+ */
+extern int set_memory_nonglobal(unsigned long addr, int numpages);
+void pti_set_kernel_image_nonglobal(void)
+{
+ /*
+ * The identity map is created with PMDs, regardless of the
+ * actual length of the kernel. We need to clear
+ * _PAGE_GLOBAL up to a PMD boundary, not just to the end
+ * of the image.
+ */
+ unsigned long start = PFN_ALIGN(_text);
+ unsigned long end = ALIGN((unsigned long)_end, PMD_PAGE_SIZE);
+
+ pr_debug("set kernel image non-global\n");
+
+ set_memory_nonglobal(start, (end - start) >> PAGE_SHIFT);
+}
+
+/*
* Initialize kernel page table isolation
*/
void __init pti_init(void)
@@ -383,6 +404,10 @@ void __init pti_init(void)
pr_info("enabled\n");

pti_clone_user_shared();
+
+ /* Undo all global bits from the init pagetables in head_64.S: */
+ pti_set_kernel_image_nonglobal();
+ /* Replace some of the global bits just for shared entry text: */
pti_clone_entry_text();
pti_setup_espfix64();
pti_setup_vsyscall();
_

2018-04-06 21:02:53

by Dave Hansen

[permalink] [raw]

Subject: [PATCH 05/11] x86/mm: do not auto-massage page protections

From: Dave Hansen <[email protected]>

A PTE is constructed from a physical address and a pgprotval_t.
__PAGE_KERNEL, for instance, is a pgprot_t and must be converted
into a pgprotval_t before it can be used to create a PTE. This is
done implicitly within functions like pfn_pte() by massage_pgprot().

However, this makes it very challenging to set bits (and keep them
set) if your bit is being filtered out by massage_pgprot().

This moves the bit filtering out of pfn_pte() and friends. For
users of PAGE_KERNEL*, filtering will be done automatically inside
those macros but for users of __PAGE_KERNEL*, they need to do their
own filtering now.

Note that we also just move pfn_pte/pmd/pud() over to check_pgprot()
instead of massage_pgprot(). This way, we still *look* for
unsupported bits and properly warn about them if we find them. This
might happen if an unfiltered __PAGE_KERNEL* value was passed in,
for instance.

Signed-off-by: Dave Hansen <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: [email protected]
Cc: Nadav Amit <[email protected]>
---

b/arch/x86/boot/compressed/kaslr.c | 3 +++
b/arch/x86/include/asm/pgtable.h | 27 ++++++++++++++++++++++-----
b/arch/x86/kernel/head64.c | 2 ++
b/arch/x86/kernel/ldt.c | 6 +++++-
b/arch/x86/mm/ident_map.c | 3 +++
b/arch/x86/mm/iomap_32.c | 6 ++++++
b/arch/x86/mm/ioremap.c | 3 +++
b/arch/x86/mm/kasan_init_64.c | 14 +++++++++++++-
b/arch/x86/mm/pgtable.c | 3 +++
b/arch/x86/power/hibernate_64.c | 20 +++++++++++++++-----
10 files changed, 75 insertions(+), 12 deletions(-)

diff -puN arch/x86/boot/compressed/kaslr.c~x86-no-auto-massage arch/x86/boot/compressed/kaslr.c
--- a/arch/x86/boot/compressed/kaslr.c~x86-no-auto-massage 2018-04-06 10:47:55.879796124 -0700
+++ b/arch/x86/boot/compressed/kaslr.c 2018-04-06 10:47:55.902796124 -0700
@@ -54,6 +54,9 @@ unsigned int ptrs_per_p4d __ro_after_ini

extern unsigned long get_cmd_line_ptr(void);

+/* Used by PAGE_KERN* macros: */
+pteval_t __default_kernel_pte_mask __read_mostly;
+
/* Simplified build-specific string for starting entropy. */
static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
diff -puN arch/x86/include/asm/pgtable.h~x86-no-auto-massage arch/x86/include/asm/pgtable.h
--- a/arch/x86/include/asm/pgtable.h~x86-no-auto-massage 2018-04-06 10:47:55.881796124 -0700
+++ b/arch/x86/include/asm/pgtable.h 2018-04-06 10:47:55.900796124 -0700
@@ -526,22 +526,39 @@ static inline pgprotval_t massage_pgprot
return protval;
}

+static inline pgprotval_t check_pgprot(pgprot_t pgprot)
+{
+ pgprotval_t massaged_val = massage_pgprot(pgprot);
+
+ /* mmdebug.h can not be included here because of dependencies */
+#ifdef CONFIG_DEBUG_VM
+ WARN_ONCE(pgprot_val(pgprot) != massaged_val,
+ "attempted to set unsupported pgprot: %016lx "
+ "bits: %016lx supported: %016lx\n",
+ pgprot_val(pgprot),
+ pgprot_val(pgprot) ^ massaged_val,
+ __supported_pte_mask);
+#endif
+
+ return massaged_val;
+}
+
static inline pte_t pfn_pte(unsigned long page_nr, pgprot_t pgprot)
{
return __pte(((phys_addr_t)page_nr << PAGE_SHIFT) |
- massage_pgprot(pgprot));
+ check_pgprot(pgprot));
}

static inline pmd_t pfn_pmd(unsigned long page_nr, pgprot_t pgprot)
{
return __pmd(((phys_addr_t)page_nr << PAGE_SHIFT) |
- massage_pgprot(pgprot));
+ check_pgprot(pgprot));
}

static inline pud_t pfn_pud(unsigned long page_nr, pgprot_t pgprot)
{
return __pud(((phys_addr_t)page_nr << PAGE_SHIFT) |
- massage_pgprot(pgprot));
+ check_pgprot(pgprot));
}

static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
@@ -553,7 +570,7 @@ static inline pte_t pte_modify(pte_t pte
* the newprot (if present):
*/
val &= _PAGE_CHG_MASK;
- val |= massage_pgprot(newprot) & ~_PAGE_CHG_MASK;
+ val |= check_pgprot(newprot) & ~_PAGE_CHG_MASK;

return __pte(val);
}
@@ -563,7 +580,7 @@ static inline pmd_t pmd_modify(pmd_t pmd
pmdval_t val = pmd_val(pmd);

val &= _HPAGE_CHG_MASK;
- val |= massage_pgprot(newprot) & ~_HPAGE_CHG_MASK;
+ val |= check_pgprot(newprot) & ~_HPAGE_CHG_MASK;

return __pmd(val);
}
diff -puN arch/x86/kernel/head64.c~x86-no-auto-massage arch/x86/kernel/head64.c
--- a/arch/x86/kernel/head64.c~x86-no-auto-massage 2018-04-06 10:47:55.883796124 -0700
+++ b/arch/x86/kernel/head64.c 2018-04-06 10:47:55.900796124 -0700
@@ -195,6 +195,8 @@ unsigned long __head __startup_64(unsign
pud[i + 1] = (pudval_t)pmd + pgtable_flags;

pmd_entry = __PAGE_KERNEL_LARGE_EXEC & ~_PAGE_GLOBAL;
+ /* Filter out unsupported __PAGE_KERNEL_* bits: */
+ pmd_entry &= __supported_pte_mask;
pmd_entry += sme_get_me_mask();
pmd_entry += physaddr;

diff -puN arch/x86/kernel/ldt.c~x86-no-auto-massage arch/x86/kernel/ldt.c
--- a/arch/x86/kernel/ldt.c~x86-no-auto-massage 2018-04-06 10:47:55.885796124 -0700
+++ b/arch/x86/kernel/ldt.c 2018-04-06 10:47:55.900796124 -0700
@@ -145,6 +145,7 @@ map_ldt_struct(struct mm_struct *mm, str
unsigned long offset = i << PAGE_SHIFT;
const void *src = (char *)ldt->entries + offset;
unsigned long pfn;
+ pgprot_t pte_prot;
pte_t pte, *ptep;

va = (unsigned long)ldt_slot_va(slot) + offset;
@@ -163,7 +164,10 @@ map_ldt_struct(struct mm_struct *mm, str
* target via some kernel interface which misses a
* permission check.
*/
- pte = pfn_pte(pfn, __pgprot(__PAGE_KERNEL_RO & ~_PAGE_GLOBAL));
+ pte_prot = __pgprot(__PAGE_KERNEL_RO & ~_PAGE_GLOBAL);
+ /* Filter out unsuppored __PAGE_KERNEL* bits: */
+ pgprot_val(pte_prot) |= __supported_pte_mask;
+ pte = pfn_pte(pfn, pte_prot);
set_pte_at(mm, va, ptep, pte);
pte_unmap_unlock(ptep, ptl);
}
diff -puN arch/x86/mm/ident_map.c~x86-no-auto-massage arch/x86/mm/ident_map.c
--- a/arch/x86/mm/ident_map.c~x86-no-auto-massage 2018-04-06 10:47:55.887796124 -0700
+++ b/arch/x86/mm/ident_map.c 2018-04-06 10:47:55.901796124 -0700
@@ -98,6 +98,9 @@ int kernel_ident_mapping_init(struct x86
if (!info->kernpg_flag)
info->kernpg_flag = _KERNPG_TABLE;

+ /* Filter out unsupported __PAGE_KERNEL_* bits: */
+ info->kernpg_flag &= __default_kernel_pte_mask;
+
for (; addr < end; addr = next) {
pgd_t *pgd = pgd_page + pgd_index(addr);
p4d_t *p4d;
diff -puN arch/x86/mm/iomap_32.c~x86-no-auto-massage arch/x86/mm/iomap_32.c
--- a/arch/x86/mm/iomap_32.c~x86-no-auto-massage 2018-04-06 10:47:55.888796124 -0700
+++ b/arch/x86/mm/iomap_32.c 2018-04-06 10:47:55.901796124 -0700
@@ -44,6 +44,9 @@ int iomap_create_wc(resource_size_t base
return ret;

*prot = __pgprot(__PAGE_KERNEL | cachemode2protval(pcm));
+ /* Filter out unsupported __PAGE_KERNEL* bits: */
+ pgprot_val(*prot) &= __default_kernel_pte_mask;
+
return 0;
}
EXPORT_SYMBOL_GPL(iomap_create_wc);
@@ -88,6 +91,9 @@ iomap_atomic_prot_pfn(unsigned long pfn,
prot = __pgprot(__PAGE_KERNEL |
cachemode2protval(_PAGE_CACHE_MODE_UC_MINUS));

+ /* Filter out unsupported __PAGE_KERNEL* bits: */
+ pgprot_val(prot) &= __default_kernel_pte_mask;
+
return (void __force __iomem *) kmap_atomic_prot_pfn(pfn, prot);
}
EXPORT_SYMBOL_GPL(iomap_atomic_prot_pfn);
diff -puN arch/x86/mm/ioremap.c~x86-no-auto-massage arch/x86/mm/ioremap.c
--- a/arch/x86/mm/ioremap.c~x86-no-auto-massage 2018-04-06 10:47:55.890796124 -0700
+++ b/arch/x86/mm/ioremap.c 2018-04-06 10:47:55.901796124 -0700
@@ -816,6 +816,9 @@ void __init __early_set_fixmap(enum fixe
}
pte = early_ioremap_pte(addr);

+ /* Sanitize 'prot' against any unsupported bits: */
+ pgprot_val(flags) &= __default_kernel_pte_mask;
+
if (pgprot_val(flags))
set_pte(pte, pfn_pte(phys >> PAGE_SHIFT, flags));
else
diff -puN arch/x86/mm/kasan_init_64.c~x86-no-auto-massage arch/x86/mm/kasan_init_64.c
--- a/arch/x86/mm/kasan_init_64.c~x86-no-auto-massage 2018-04-06 10:47:55.892796124 -0700
+++ b/arch/x86/mm/kasan_init_64.c 2018-04-06 10:47:55.901796124 -0700
@@ -269,6 +269,12 @@ void __init kasan_early_init(void)
pudval_t pud_val = __pa_nodebug(kasan_zero_pmd) | _KERNPG_TABLE;
p4dval_t p4d_val = __pa_nodebug(kasan_zero_pud) | _KERNPG_TABLE;

+ /* Mask out unsupported __PAGE_KERNEL bits: */
+ pte_val &= __default_kernel_pte_mask;
+ pmd_val &= __default_kernel_pte_mask;
+ pud_val &= __default_kernel_pte_mask;
+ p4d_val &= __default_kernel_pte_mask;
+
for (i = 0; i < PTRS_PER_PTE; i++)
kasan_zero_pte[i] = __pte(pte_val);

@@ -371,7 +377,13 @@ void __init kasan_init(void)
*/
memset(kasan_zero_page, 0, PAGE_SIZE);
for (i = 0; i < PTRS_PER_PTE; i++) {
- pte_t pte = __pte(__pa(kasan_zero_page) | __PAGE_KERNEL_RO | _PAGE_ENC);
+ pte_t pte;
+ pgprot_t prot;
+
+ prot = __pgprot(__PAGE_KERNEL_RO | _PAGE_ENC);
+ pgprot_val(prot) &= __default_kernel_pte_mask;
+
+ pte = __pte(__pa(kasan_zero_page) | pgprot_val(prot));
set_pte(&kasan_zero_pte[i], pte);
}
/* Flush TLBs again to be sure that write protection applied. */
diff -puN arch/x86/mm/pgtable.c~x86-no-auto-massage arch/x86/mm/pgtable.c
--- a/arch/x86/mm/pgtable.c~x86-no-auto-massage 2018-04-06 10:47:55.894796124 -0700
+++ b/arch/x86/mm/pgtable.c 2018-04-06 10:47:55.902796124 -0700
@@ -583,6 +583,9 @@ void __native_set_fixmap(enum fixed_addr
void native_set_fixmap(enum fixed_addresses idx, phys_addr_t phys,
pgprot_t flags)
{
+ /* Sanitize 'prot' against any unsupported bits: */
+ pgprot_val(flags) &= __default_kernel_pte_mask;
+
__native_set_fixmap(idx, pfn_pte(phys >> PAGE_SHIFT, flags));
}

diff -puN arch/x86/power/hibernate_64.c~x86-no-auto-massage arch/x86/power/hibernate_64.c
--- a/arch/x86/power/hibernate_64.c~x86-no-auto-massage 2018-04-06 10:47:55.896796124 -0700
+++ b/arch/x86/power/hibernate_64.c 2018-04-06 10:47:55.902796124 -0700
@@ -51,6 +51,12 @@ static int set_up_temporary_text_mapping
pmd_t *pmd;
pud_t *pud;
p4d_t *p4d = NULL;
+ pgprot_t pgtable_prot = __pgprot(_KERNPG_TABLE);
+ pgprot_t pmd_text_prot = __pgprot(__PAGE_KERNEL_LARGE_EXEC);
+
+ /* Filter out unsupported __PAGE_KERNEL* bits: */
+ pgprot_val(pmd_text_prot) &= __default_kernel_pte_mask;
+ pgprot_val(pgtable_prot) &= __default_kernel_pte_mask;

/*
* The new mapping only has to cover the page containing the image
@@ -81,15 +87,19 @@ static int set_up_temporary_text_mapping
return -ENOMEM;

set_pmd(pmd + pmd_index(restore_jump_address),
- __pmd((jump_address_phys & PMD_MASK) | __PAGE_KERNEL_LARGE_EXEC));
+ __pmd((jump_address_phys & PMD_MASK) | pgprot_val(pmd_text_prot)));
set_pud(pud + pud_index(restore_jump_address),
- __pud(__pa(pmd) | _KERNPG_TABLE));
+ __pud(__pa(pmd) | pgprot_val(pgtable_prot)));
if (p4d) {
- set_p4d(p4d + p4d_index(restore_jump_address), __p4d(__pa(pud) | _KERNPG_TABLE));
- set_pgd(pgd + pgd_index(restore_jump_address), __pgd(__pa(p4d) | _KERNPG_TABLE));
+ p4d_t new_p4d = __p4d(__pa(pud) | pgprot_val(pgtable_prot));
+ pgd_t new_pgd = __pgd(__pa(p4d) | pgprot_val(pgtable_prot));
+
+ set_p4d(p4d + p4d_index(restore_jump_address), new_p4d);
+ set_pgd(pgd + pgd_index(restore_jump_address), new_pgd);
} else {
/* No p4d for 4-level paging: point the pgd to the pud page table */
- set_pgd(pgd + pgd_index(restore_jump_address), __pgd(__pa(pud) | _KERNPG_TABLE));
+ pgd_t new_pgd = __pgd(__pa(p4d) | pgprot_val(pgtable_prot));
+ set_pgd(pgd + pgd_index(restore_jump_address), new_pgd);
}

return 0;
_

2018-04-06 21:03:09

by Dave Hansen

[permalink] [raw]

Subject: [PATCH 09/11] x86/pti: enable global pages for shared areas

From: Dave Hansen <[email protected]>

The entry/exit text and cpu_entry_area are mapped into userspace and
the kernel. But, they are not _PAGE_GLOBAL. This creates unnecessary
TLB misses.

Add the _PAGE_GLOBAL flag for these areas.

Signed-off-by: Dave Hansen <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: [email protected]
Cc: Nadav Amit <[email protected]>
---

b/arch/x86/mm/cpu_entry_area.c | 14 +++++++++++++-
b/arch/x86/mm/pti.c | 23 ++++++++++++++++++++++-
2 files changed, 35 insertions(+), 2 deletions(-)

diff -puN arch/x86/mm/cpu_entry_area.c~kpti-why-no-global arch/x86/mm/cpu_entry_area.c
--- a/arch/x86/mm/cpu_entry_area.c~kpti-why-no-global 2018-04-06 10:47:58.246796118 -0700
+++ b/arch/x86/mm/cpu_entry_area.c 2018-04-06 10:47:58.252796118 -0700
@@ -27,8 +27,20 @@ EXPORT_SYMBOL(get_cpu_entry_area);
void cea_set_pte(void *cea_vaddr, phys_addr_t pa, pgprot_t flags)
{
unsigned long va = (unsigned long) cea_vaddr;
+ pte_t pte = pfn_pte(pa >> PAGE_SHIFT, flags);

- set_pte_vaddr(va, pfn_pte(pa >> PAGE_SHIFT, flags));
+ /*
+ * The cpu_entry_area is shared between the user and kernel
+ * page tables. All of its ptes can safely be global.
+ * _PAGE_GLOBAL gets reused to help indicate PROT_NONE for
+ * non-present PTEs, so be careful not to set it in that
+ * case to avoid confusion.
+ */
+ if (boot_cpu_has(X86_FEATURE_PGE) &&
+ (pgprot_val(flags) & _PAGE_PRESENT))
+ pte = pte_set_flags(pte, _PAGE_GLOBAL);
+
+ set_pte_vaddr(va, pte);
}

static void __init
diff -puN arch/x86/mm/pti.c~kpti-why-no-global arch/x86/mm/pti.c
--- a/arch/x86/mm/pti.c~kpti-why-no-global 2018-04-06 10:47:58.248796118 -0700
+++ b/arch/x86/mm/pti.c 2018-04-06 10:47:58.252796118 -0700
@@ -300,6 +300,27 @@ pti_clone_pmds(unsigned long start, unsi
return;

/*
+ * Only clone present PMDs. This ensures only setting
+ * _PAGE_GLOBAL on present PMDs. This should only be
+ * called on well-known addresses anyway, so a non-
+ * present PMD would be a surprise.
+ */
+ if (WARN_ON(!(pmd_flags(*pmd) & _PAGE_PRESENT)))
+ return;
+
+ /*
+ * Setting 'target_pmd' below creates a mapping in both
+ * the user and kernel page tables. It is effectively
+ * global, so set it as global in both copies. Note:
+ * the X86_FEATURE_PGE check is not _required_ because
+ * the CPU ignores _PAGE_GLOBAL when PGE is not
+ * supported. The check keeps consistentency with
+ * code that only set this bit when supported.
+ */
+ if (boot_cpu_has(X86_FEATURE_PGE))
+ *pmd = pmd_set_flags(*pmd, _PAGE_GLOBAL);
+
+ /*
* Copy the PMD. That is, the kernelmode and usermode
* tables will share the last-level page tables of this
* address range
@@ -348,7 +369,7 @@ static void __init pti_clone_entry_text(
{
pti_clone_pmds((unsigned long) __entry_text_start,
(unsigned long) __irqentry_text_end,
- _PAGE_RW | _PAGE_GLOBAL);
+ _PAGE_RW);
}

/*
_

2018-04-06 21:04:00

by Dave Hansen

[permalink] [raw]

Subject: [PATCH 06/11] x86/mm: remove extra filtering in pageattr code

From: Dave Hansen <[email protected]>

The pageattr code has a mode where it can set or clear PTE bits in
existing PTEs, so the page protections of the *new* PTEs come from
one of two places:
1. The set/clear masks: cpa->mask_clr / cpa->mask_set
2. The existing PTE

We filter ->mask_set/clr for supported PTE bits at entry to
__change_page_attr() so we never need to filter them again.

The only other place permissions can come from is an existing PTE
and those already presumably have good bits. We do not need to filter
them again.

Signed-off-by: Dave Hansen <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: [email protected]
Cc: Nadav Amit <[email protected]>

---

b/arch/x86/mm/pageattr.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff -puN arch/x86/mm/pageattr.c~x86-pageattr-dont-filter-global arch/x86/mm/pageattr.c
--- a/arch/x86/mm/pageattr.c~x86-pageattr-dont-filter-global 2018-04-06 10:47:56.635796122 -0700
+++ b/arch/x86/mm/pageattr.c 2018-04-06 10:47:56.639796122 -0700
@@ -598,7 +598,6 @@ try_preserve_large_page(pte_t *kpte, uns
req_prot = pgprot_clear_protnone_bits(req_prot);
if (pgprot_val(req_prot) & _PAGE_PRESENT)
pgprot_val(req_prot) |= _PAGE_PSE;
- req_prot = canon_pgprot(req_prot);

/*
* old_pfn points to the large page base pfn. So we need
@@ -718,7 +717,7 @@ __split_large_page(struct cpa_data *cpa,
*/
pfn = ref_pfn;
for (i = 0; i < PTRS_PER_PTE; i++, pfn += pfninc)
- set_pte(&pbase[i], pfn_pte(pfn, canon_pgprot(ref_prot)));
+ set_pte(&pbase[i], pfn_pte(pfn, ref_prot));

if (virt_addr_valid(address)) {
unsigned long pfn = PFN_DOWN(__pa(address));
@@ -935,7 +934,6 @@ static void populate_pte(struct cpa_data
pte = pte_offset_kernel(pmd, start);

pgprot = pgprot_clear_protnone_bits(pgprot);
- pgprot = canon_pgprot(pgprot);

while (num_pages-- && start < end) {
set_pte(pte, pfn_pte(cpa->pfn, pgprot));
@@ -1234,7 +1232,7 @@ repeat:
* after all we're only going to change it's attributes
* not the memory it points to
*/
- new_pte = pfn_pte(pfn, canon_pgprot(new_prot));
+ new_pte = pfn_pte(pfn, new_prot);
cpa->pfn = pfn;
/*
* Do we really change anything ?
_

2018-04-06 21:04:55

by Dave Hansen

[permalink] [raw]

Subject: [PATCH 07/11] x86/mm: comment _PAGE_GLOBAL mystery

From: Dave Hansen <[email protected]>

I was mystified as to where the _PAGE_GLOBAL in the kernel page tables
for kernel text came from. I audited all the places I could find, but
I missed one: head_64.S.

The page tables that we create in here live for a long time, and they
also have _PAGE_GLOBAL set, despite whether the processor supports it
or not. It's harmless, and we got *lucky* that the pageattr code
accidentally clears it when we wipe it out of __supported_pte_mask and
then later try to mark kernel text read-only.

Comment some of these properties to make it easier to find and
understand in the future.

Signed-off-by: Dave Hansen <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: [email protected]
Cc: Nadav Amit <[email protected]>
---

b/arch/x86/kernel/head_64.S | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff -puN arch/x86/kernel/head_64.S~comment-global-page arch/x86/kernel/head_64.S
--- a/arch/x86/kernel/head_64.S~comment-global-page 2018-04-06 10:47:57.176796121 -0700
+++ b/arch/x86/kernel/head_64.S 2018-04-06 10:47:57.179796121 -0700
@@ -399,8 +399,13 @@ NEXT_PAGE(level3_ident_pgt)
.quad level2_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE_NOENC
.fill 511, 8, 0
NEXT_PAGE(level2_ident_pgt)
- /* Since I easily can, map the first 1G.
+ /*
+ * Since I easily can, map the first 1G.
* Don't set NX because code runs from these pages.
+ *
+ * Note: This sets _PAGE_GLOBAL despite whether
+ * the CPU supports it or it is enabled. But,
+ * the CPU should ignore the bit.
*/
PMDS(0, __PAGE_KERNEL_IDENT_LARGE_EXEC, PTRS_PER_PMD)
#else
@@ -431,6 +436,10 @@ NEXT_PAGE(level2_kernel_pgt)
* (NOTE: at +512MB starts the module area, see MODULES_VADDR.
* If you want to increase this then increase MODULES_VADDR
* too.)
+ *
+ * This table is eventually used by the kernel during normal
+ * runtime. Care must be taken to clear out undesired bits
+ * later, like _PAGE_RW or _PAGE_GLOBAL in some cases.
*/
PMDS(0, __PAGE_KERNEL_LARGE_EXEC,
KERNEL_IMAGE_SIZE/PMD_SIZE)
_

2018-04-06 21:04:55

by Dave Hansen

[permalink] [raw]

Subject: [PATCH 04/11] x86/espfix: document use of _PAGE_GLOBAL

From: Dave Hansen <[email protected]>

The "normal" kernel page table creation mechanisms using
PAGE_KERNEL_* page protections will never set _PAGE_GLOBAL with PTI.
The few places in the kernel that always want _PAGE_GLOBAL must
avoid using PAGE_KERNEL_*.

Document that we want it here and its use is not accidental.

Signed-off-by: Dave Hansen <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: [email protected]
Cc: Nadav Amit <[email protected]>
---

b/arch/x86/kernel/espfix_64.c | 4 ++++
1 file changed, 4 insertions(+)

diff -puN arch/x86/kernel/espfix_64.c~espfix-use-kern-defaults-not-supported arch/x86/kernel/espfix_64.c
--- a/arch/x86/kernel/espfix_64.c~espfix-use-kern-defaults-not-supported 2018-04-06 10:47:55.343796126 -0700
+++ b/arch/x86/kernel/espfix_64.c 2018-04-06 10:47:55.346796126 -0700
@@ -195,6 +195,10 @@ void init_espfix_ap(int cpu)

pte_p = pte_offset_kernel(&pmd, addr);
stack_page = page_address(alloc_pages_node(node, GFP_KERNEL, 0));
+ /*
+ * __PAGE_KERNEL_* includes _PAGE_GLOBAL, which we want since
+ * this is mapped to userspace.
+ */
pte = __pte(__pa(stack_page) | ((__PAGE_KERNEL_RO | _PAGE_ENC) & ptemask));
for (n = 0; n < ESPFIX_PTE_CLONES; n++)
set_pte(&pte_p[n*PTE_STRIDE], pte);
_

2018-04-06 21:05:14

by Dave Hansen

[permalink] [raw]

Subject: [PATCH 02/11] x86/mm: undo double _PAGE_PSE clearing

From: Dave Hansen <[email protected]>

When clearing _PAGE_PRESENT on a huge page, we need to be careful
to also clear _PAGE_PSE, otherwise it might still get confused
for a valid large page table entry.

We do that near the spot where we *set* _PAGE_PSE. That's fine,
but it's unnecessary. pgprot_large_2_4k() already did it.

BTW, I also noticed that pgprot_large_2_4k() and
pgprot_4k_2_large() are not symmetric. pgprot_large_2_4k() clears
_PAGE_PSE (because it is aliased to _PAGE_PAT) but
pgprot_4k_2_large() does not put _PAGE_PSE back. Bummer.

Also, add some comments and change "promote" to "move". "Promote"
seems an odd word to move when we are logically moving a bit to a
lower bit position. Also add an extra line return to make it clear
to which line the comment applies.

Signed-off-by: Dave Hansen <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: [email protected]
Cc: Nadav Amit <[email protected]>
---

b/arch/x86/mm/pageattr.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff -puN arch/x86/mm/pageattr.c~kpti-undo-double-_PAGE_PSE-clear arch/x86/mm/pageattr.c
--- a/arch/x86/mm/pageattr.c~kpti-undo-double-_PAGE_PSE-clear 2018-04-06 10:47:54.193796129 -0700
+++ b/arch/x86/mm/pageattr.c 2018-04-06 10:47:54.197796129 -0700
@@ -583,6 +583,7 @@ try_preserve_large_page(pte_t *kpte, uns
* up accordingly.
*/
old_pte = *kpte;
+ /* Clear PSE (aka _PAGE_PAT) and move PAT bit to correct position */
req_prot = pgprot_large_2_4k(old_prot);

pgprot_val(req_prot) &= ~pgprot_val(cpa->mask_clr);
@@ -597,8 +598,6 @@ try_preserve_large_page(pte_t *kpte, uns
req_prot = pgprot_clear_protnone_bits(req_prot);
if (pgprot_val(req_prot) & _PAGE_PRESENT)
pgprot_val(req_prot) |= _PAGE_PSE;
- else
- pgprot_val(req_prot) &= ~_PAGE_PSE;
req_prot = canon_pgprot(req_prot);

/*
@@ -684,8 +683,12 @@ __split_large_page(struct cpa_data *cpa,
switch (level) {
case PG_LEVEL_2M:
ref_prot = pmd_pgprot(*(pmd_t *)kpte);
- /* clear PSE and promote PAT bit to correct position */
+ /*
+ * Clear PSE (aka _PAGE_PAT) and move
+ * PAT bit to correct position.
+ */
ref_prot = pgprot_large_2_4k(ref_prot);
+
ref_pfn = pmd_pfn(*(pmd_t *)kpte);
break;

_

2018-04-06 21:08:48

by Dave Hansen

[permalink] [raw]

Subject: [PATCH 01/11] x86/mm: factor out pageattr _PAGE_GLOBAL setting

From: Dave Hansen <[email protected]>

The pageattr code has a pattern repeated where it sets _PAGE_GLOBAL
for present PTEs but clears it for non-present PTEs. The intention
is to keep _PAGE_GLOBAL from getting confused with _PAGE_PROTNONE
since _PAGE_GLOBAL is for present PTEs and _PAGE_PROTNONE is for
non-present

But, this pattern makes no sense. Effectively, it says, if you use
the pageattr code, always set _PAGE_GLOBAL when _PAGE_PRESENT.
canon_pgprot() will clear it if unsupported (because it masks the
value with __supported_pte_mask) but we *always* set it. Even if
canon_pgprot() did not filter _PAGE_GLOBAL, it would be OK.
_PAGE_GLOBAL is ignored when CR4.PGE=0 by the hardware.

This unconditional setting of _PAGE_GLOBAL is a problem when we have
PTI and non-PTI and we want some areas to have _PAGE_GLOBAL and some
not.

This updated version of the code says:
1. Clear _PAGE_GLOBAL when !_PAGE_PRESENT
2. Never set _PAGE_GLOBAL implicitly
3. Allow _PAGE_GLOBAL to be in cpa.set_mask
4. Allow _PAGE_GLOBAL to be inherited from previous PTE

Signed-off-by: Dave Hansen <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: [email protected]
Cc: Nadav Amit <[email protected]>
---

b/arch/x86/mm/pageattr.c | 66 ++++++++++++++++-------------------------------
1 file changed, 23 insertions(+), 43 deletions(-)

diff -puN arch/x86/mm/pageattr.c~kpti-centralize-global-setting arch/x86/mm/pageattr.c
--- a/arch/x86/mm/pageattr.c~kpti-centralize-global-setting 2018-04-06 10:47:53.651796130 -0700
+++ b/arch/x86/mm/pageattr.c 2018-04-06 10:47:53.655796130 -0700
@@ -512,6 +512,23 @@ static void __set_pmd_pte(pte_t *kpte, u
#endif
}

+static pgprot_t pgprot_clear_protnone_bits(pgprot_t prot)
+{
+ /*
+ * _PAGE_GLOBAL means "global page" for present PTEs.
+ * But, it is also used to indicate _PAGE_PROTNONE
+ * for non-present PTEs.
+ *
+ * This ensures that a _PAGE_GLOBAL PTE going from
+ * present to non-present is not confused as
+ * _PAGE_PROTNONE.
+ */
+ if (!(pgprot_val(prot) & _PAGE_PRESENT))
+ pgprot_val(prot) &= ~_PAGE_GLOBAL;
+
+ return prot;
+}
+
static int
try_preserve_large_page(pte_t *kpte, unsigned long address,
struct cpa_data *cpa)
@@ -577,18 +594,11 @@ try_preserve_large_page(pte_t *kpte, uns
* different bit positions in the two formats.
*/
req_prot = pgprot_4k_2_large(req_prot);
-
- /*
- * Set the PSE and GLOBAL flags only if the PRESENT flag is
- * set otherwise pmd_present/pmd_huge will return true even on
- * a non present pmd. The canon_pgprot will clear _PAGE_GLOBAL
- * for the ancient hardware that doesn't support it.
- */
+ req_prot = pgprot_clear_protnone_bits(req_prot);
if (pgprot_val(req_prot) & _PAGE_PRESENT)
- pgprot_val(req_prot) |= _PAGE_PSE | _PAGE_GLOBAL;
+ pgprot_val(req_prot) |= _PAGE_PSE;
else
- pgprot_val(req_prot) &= ~(_PAGE_PSE | _PAGE_GLOBAL);
-
+ pgprot_val(req_prot) &= ~_PAGE_PSE;
req_prot = canon_pgprot(req_prot);

/*
@@ -698,16 +708,7 @@ __split_large_page(struct cpa_data *cpa,
return 1;
}

- /*
- * Set the GLOBAL flags only if the PRESENT flag is set
- * otherwise pmd/pte_present will return true even on a non
- * present pmd/pte. The canon_pgprot will clear _PAGE_GLOBAL
- * for the ancient hardware that doesn't support it.
- */
- if (pgprot_val(ref_prot) & _PAGE_PRESENT)
- pgprot_val(ref_prot) |= _PAGE_GLOBAL;
- else
- pgprot_val(ref_prot) &= ~_PAGE_GLOBAL;
+ ref_prot = pgprot_clear_protnone_bits(ref_prot);

/*
* Get the target pfn from the original entry:
@@ -930,18 +931,7 @@ static void populate_pte(struct cpa_data

pte = pte_offset_kernel(pmd, start);

- /*
- * Set the GLOBAL flags only if the PRESENT flag is
- * set otherwise pte_present will return true even on
- * a non present pte. The canon_pgprot will clear
- * _PAGE_GLOBAL for the ancient hardware that doesn't
- * support it.
- */
- if (pgprot_val(pgprot) & _PAGE_PRESENT)
- pgprot_val(pgprot) |= _PAGE_GLOBAL;
- else
- pgprot_val(pgprot) &= ~_PAGE_GLOBAL;
-
+ pgprot = pgprot_clear_protnone_bits(pgprot);
pgprot = canon_pgprot(pgprot);

while (num_pages-- && start < end) {
@@ -1234,17 +1224,7 @@ repeat:

new_prot = static_protections(new_prot, address, pfn);

- /*
- * Set the GLOBAL flags only if the PRESENT flag is
- * set otherwise pte_present will return true even on
- * a non present pte. The canon_pgprot will clear
- * _PAGE_GLOBAL for the ancient hardware that doesn't
- * support it.
- */
- if (pgprot_val(new_prot) & _PAGE_PRESENT)
- pgprot_val(new_prot) |= _PAGE_GLOBAL;
- else
- pgprot_val(new_prot) &= ~_PAGE_GLOBAL;
+ new_prot = pgprot_clear_protnone_bits(new_prot);

/*
* We need to keep the pfn from the existing PTE,
_

2018-04-09 17:17:34

Subject: [PATCH 00/11] [v5] Use global pages with PTI

Subject: [PATCH 11/11] x86/pti: leave kernel text global for !PCID

Subject: [PATCH 03/11] x86/mm: introduce "default" kernel PTE mask

Subject: [PATCH 08/11] x86/mm: do not forbid _PAGE_RW before init for __ro_after_init

Subject: [PATCH 10/11] x86/pti: never implicitly clear _PAGE_GLOBAL for kernel image

Subject: [PATCH 05/11] x86/mm: do not auto-massage page protections

Subject: [PATCH 09/11] x86/pti: enable global pages for shared areas

Subject: [PATCH 06/11] x86/mm: remove extra filtering in pageattr code

Subject: [PATCH 07/11] x86/mm: comment _PAGE_GLOBAL mystery

Subject: [PATCH 04/11] x86/espfix: document use of _PAGE_GLOBAL

Subject: [PATCH 02/11] x86/mm: undo double _PAGE_PSE clearing

Subject: [PATCH 01/11] x86/mm: factor out pageattr _PAGE_GLOBAL setting

Subject: [tip:x86/pti] x86/mm: Factor out pageattr _PAGE_GLOBAL setting

Subject: [tip:x86/pti] x86/mm: Undo double _PAGE_PSE clearing

Subject: [tip:x86/pti] x86/mm: Introduce "default" kernel PTE mask

Subject: [tip:x86/pti] x86/mm: Remove extra filtering in pageattr code

Subject: [tip:x86/pti] x86/mm: Do not forbid _PAGE_RW before init for __ro_after_init

Subject: [tip:x86/pti] x86/espfix: Document use of _PAGE_GLOBAL

Subject: [tip:x86/pti] x86/mm: Do not auto-massage page protections

Subject: [tip:x86/pti] x86/pti: Never implicitly clear _PAGE_GLOBAL for kernel image

Subject: [tip:x86/pti] x86/pti: Leave kernel text global for !PCID

Subject: [tip:x86/pti] x86/pti: Enable global pages for shared areas

Subject: Re: [PATCH 00/11] [v5] Use global pages with PTI

Subject: Re: [PATCH 00/11] [v5] Use global pages with PTI

Subject: Re: [PATCH 00/11] [v5] Use global pages with PTI

Subject: Re: [PATCH 00/11] [v5] Use global pages with PTI

Subject: Re: [PATCH 00/11] [v5] Use global pages with PTI

Subject: [tip:x86/pti] x86/mm: Comment _PAGE_GLOBAL mystery

Subject: [tip:x86/pti] x86/mm: Remove extra filtering in pageattr code

Subject: [tip:x86/pti] x86/mm: Do not auto-massage page protections

Subject: [tip:x86/pti] x86/mm: Comment _PAGE_GLOBAL mystery

Subject: [tip:x86/pti] x86/pti: Enable global pages for shared areas

Subject: [tip:x86/pti] x86/pti: Leave kernel text global for !PCID

Subject: [tip:x86/pti] x86/pti: Never implicitly clear _PAGE_GLOBAL for kernel image

Subject: [tip:x86/pti] x86/mm: Do not forbid _PAGE_RW before init for __ro_after_init

Subject: Re: [PATCH 11/11] x86/pti: leave kernel text global for !PCID

Subject: Re: [PATCH 11/11] x86/pti: leave kernel text global for !PCID

Subject: Re: [PATCH 11/11] x86/pti: leave kernel text global for !PCID