__arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address,
but it will modify pointer tag into 0xff, so there is a false positive.
When enable tag-based kasan, phys_to_virt() function need to rewrite
its original pointer tag in order to avoid kasan report an incorrect
memory corruption.
BUG: KASAN: double-free or invalid-free in __arm_v7s_unmap+0x720/0xda4
Pointer tag: [ff], memory tag: [c1]
Call trace:
dump_backtrace+0x0/0x1d4
show_stack+0x14/0x1c
dump_stack+0xe8/0x140
print_address_description+0x80/0x2f0
kasan_report_invalid_free+0x58/0x74
__kasan_slab_free+0x1e4/0x220
kasan_slab_free+0xc/0x18
kmem_cache_free+0xfc/0x884
__arm_v7s_unmap+0x720/0xda4
__arm_v7s_map+0xc8/0x774
arm_v7s_map+0x80/0x158
mtk_iommu_map+0xb4/0xe0
iommu_map+0x154/0x450
iommu_map_sg+0xe4/0x150
iommu_dma_map_sg+0x214/0x4ec
__iommu_map_sg_attrs+0xf0/0x110
ion_map_dma_buf+0xe8/0x114
dma_buf_map_attachment+0x4c/0x80
disp_sync_prepare_buf+0x378/0x820
_ioctl_prepare_buffer+0x130/0x870
mtk_disp_mgr_ioctl+0x5c4/0xab0
do_vfs_ioctl+0x8e0/0x15a4
__arm64_sys_ioctl+0x8c/0xb4
el0_svc_common+0xe4/0x1e0
el0_svc_handler+0x30/0x3c
el0_svc+0x8/0xc
Signed-off-by: Walter Wu <[email protected]>
---
arch/arm64/include/asm/kasan.h | 1 -
arch/arm64/include/asm/memory.h | 10 ++++++++++
2 files changed, 10 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/kasan.h b/arch/arm64/include/asm/kasan.h
index b52aacd2c526..59894cafad60 100644
--- a/arch/arm64/include/asm/kasan.h
+++ b/arch/arm64/include/asm/kasan.h
@@ -5,7 +5,6 @@
#ifndef __ASSEMBLY__
#include <linux/linkage.h>
-#include <asm/memory.h>
#include <asm/pgtable-types.h>
#define arch_kasan_set_tag(addr, tag) __tag_set(addr, tag)
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 8ffcf5a512bb..75af5ba9ff22 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -171,6 +171,7 @@
#include <linux/bitops.h>
#include <linux/mmdebug.h>
+#include <asm/kasan.h>
extern s64 memstart_addr;
/* PHYS_OFFSET - the physical address of the start of memory. */
@@ -282,7 +283,16 @@ static inline phys_addr_t virt_to_phys(const volatile void *x)
#define phys_to_virt phys_to_virt
static inline void *phys_to_virt(phys_addr_t x)
{
+#ifdef CONFIG_KASAN_SW_TAGS
+ unsigned long addr = __phys_to_virt(x);
+ u8 *tag = (void *)(addr >> KASAN_SHADOW_SCALE_SHIFT)
+ + KASAN_SHADOW_OFFSET;
+
+ addr = __tag_set(addr, *tag);
+ return (void *)addr;
+#else
return (void *)(__phys_to_virt(x));
+#endif
}
/*
--
2.18.0
On Mon, Aug 19, 2019 at 07:44:20PM +0800, Walter Wu wrote:
> __arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address,
> but it will modify pointer tag into 0xff, so there is a false positive.
>
> When enable tag-based kasan, phys_to_virt() function need to rewrite
> its original pointer tag in order to avoid kasan report an incorrect
> memory corruption.
Hmm. Which tree did you see this on? We've recently queued a load of fixes
in this area, but I /thought/ they were only needed after the support for
52-bit virtual addressing in the kernel.
Will
On Mon, Aug 19, 2019 at 01:56:26PM +0100, Will Deacon wrote:
> On Mon, Aug 19, 2019 at 07:44:20PM +0800, Walter Wu wrote:
> > __arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address,
> > but it will modify pointer tag into 0xff, so there is a false positive.
> >
> > When enable tag-based kasan, phys_to_virt() function need to rewrite
> > its original pointer tag in order to avoid kasan report an incorrect
> > memory corruption.
>
> Hmm. Which tree did you see this on? We've recently queued a load of fixes
> in this area, but I /thought/ they were only needed after the support for
> 52-bit virtual addressing in the kernel.
I'm seeing similar issues in the virtio blk code (splat below), atop of
the arm64 for-next/core branch. I think this is a latent issue, and
people are only just starting to test with KASAN_SW_TAGS.
It looks like the virtio blk code will round-trip a SLUB-allocated pointer from
virt->page->virt, losing the per-object tag in the process.
Our page_to_virt() seems to get a per-page tag, but this only makes
sense if you're dealing with the page allocator, rather than something
like SLUB which carves a page into smaller objects giving each object a
distinct tag.
Any round-trip of a pointer from SLUB is going to lose the per-object
tag.
Thanks,
Mark.
==================================================================
BUG: KASAN: double-free or invalid-free in virtblk_request_done+0x128/0x1d8 drivers/block/virtio_blk.c:215
Pointer tag: [ff], memory tag: [a8]
CPU: 0 PID: 19116 Comm: syz-executor.0 Not tainted 5.3.0-rc3-00075-gcb38552 #1
Hardware name: linux,dummy-virt (DT)
Call trace:
dump_backtrace+0x0/0x3c0 arch/arm64/include/asm/stacktrace.h:166
show_stack+0x24/0x30 arch/arm64/kernel/traps.c:138
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x138/0x1f4 lib/dump_stack.c:113
print_address_description+0x7c/0x328 mm/kasan/report.c:351
kasan_report_invalid_free+0x80/0xe0 mm/kasan/report.c:444
__kasan_slab_free+0x1a8/0x208 mm/kasan/common.c:56
kasan_slab_free+0xc/0x18 mm/kasan/common.c:457
slab_free_hook mm/slub.c:1423 [inline]
slab_free_freelist_hook mm/slub.c:1474 [inline]
slab_free mm/slub.c:3016 [inline]
kfree+0x254/0x9dc mm/slub.c:3957
virtblk_request_done+0x128/0x1d8 drivers/block/virtio_blk.c:215
blk_done_softirq+0x3dc/0x49c block/blk-softirq.c:37
__do_softirq+0xa90/0x1504 kernel/softirq.c:292
do_softirq_own_stack include/linux/interrupt.h:549 [inline]
invoke_softirq kernel/softirq.c:380 [inline]
irq_exit+0x3b0/0x4f8 kernel/softirq.c:413
__handle_domain_irq+0x150/0x250 kernel/irq/irqdesc.c:671
atomic_read include/asm-generic/atomic-instrumented.h:26 [inline]
static_key_count include/linux/jump_label.h:254 [inline]
cpus_have_const_cap arch/arm64/include/asm/cpufeature.h:410 [inline]
gic_read_iar drivers/irqchip/irq-gic-v3.c:152 [inline]
gic_handle_irq+0x244/0x4ac drivers/irqchip/irq-gic-v3.c:490
el1_irq+0xbc/0x140 arch/arm64/kernel/entry.S:670
ktime_add_safe kernel/time/hrtimer.c:321 [inline]
hrtimer_set_expires_range_ns include/linux/hrtimer.h:235 [inline]
hrtimer_nanosleep kernel/time/hrtimer.c:1732 [inline]
__do_sys_nanosleep kernel/time/hrtimer.c:1767 [inline]
__se_sys_nanosleep kernel/time/hrtimer.c:1754 [inline]
__arm64_sys_nanosleep+0x344/0x554 kernel/time/hrtimer.c:1754
__invoke_syscall arch/arm64/kernel/syscall.c:36 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:48 [inline]
el0_svc_common arch/arm64/kernel/syscall.c:114 [inline]
el0_svc_handler+0x300/0x540 arch/arm64/kernel/syscall.c:160
el0_svc+0x8/0xc arch/arm64/kernel/entry.S:1006
Allocated by task 170:
save_stack mm/kasan/common.c:69 [inline]
set_track mm/kasan/common.c:77 [inline]
__kasan_kmalloc+0x114/0x1d0 mm/kasan/common.c:487
kasan_kmalloc+0x10/0x18 mm/kasan/common.c:501
__kmalloc+0x1f0/0x48c mm/slub.c:3811
kmalloc_array include/linux/slab.h:676 [inline]
virtblk_setup_discard_write_zeroes drivers/block/virtio_blk.c:188 [inline]
virtio_queue_rq+0x948/0xe48 drivers/block/virtio_blk.c:322
blk_mq_dispatch_rq_list+0x914/0x16fc block/blk-mq.c:1257
blk_mq_do_dispatch_sched+0x374/0x4d8 block/blk-mq-sched.c:115
blk_mq_sched_dispatch_requests+0x4d0/0x68c block/blk-mq-sched.c:216
__blk_mq_run_hw_queue+0x22c/0x35c block/blk-mq.c:1387
blk_mq_run_work_fn+0x64/0x78 block/blk-mq.c:1620
process_one_work+0x10bc/0x1df0 kernel/workqueue.c:2269
worker_thread+0x1124/0x17bc kernel/workqueue.c:2415
kthread+0x3c0/0x3d0 kernel/kthread.c:255
ret_from_fork+0x10/0x18 arch/arm64/kernel/entry.S:1164
Freed by task 17121:
save_stack mm/kasan/common.c:69 [inline]
set_track mm/kasan/common.c:77 [inline]
__kasan_slab_free+0x138/0x208 mm/kasan/common.c:449
kasan_slab_free+0xc/0x18 mm/kasan/common.c:457
slab_free_hook mm/slub.c:1423 [inline]
slab_free_freelist_hook mm/slub.c:1474 [inline]
slab_free mm/slub.c:3016 [inline]
kfree+0x254/0x9dc mm/slub.c:3957
kvfree+0x54/0x60 mm/util.c:488
__vunmap+0xa3c/0xafc mm/vmalloc.c:2255
__vfree mm/vmalloc.c:2299 [inline]
vfree+0xe4/0x1c4 mm/vmalloc.c:2329
copy_entries_to_user net/ipv6/netfilter/ip6_tables.c:883 [inline]
get_entries net/ipv6/netfilter/ip6_tables.c:1041 [inline]
do_ip6t_get_ctl+0xf78/0x1804 net/ipv6/netfilter/ip6_tables.c:1709
nf_sockopt net/netfilter/nf_sockopt.c:104 [inline]
nf_getsockopt+0x238/0x258 net/netfilter/nf_sockopt.c:122
ipv6_getsockopt+0x3374/0x40c4 net/ipv6/ipv6_sockglue.c:1400
tcp_getsockopt+0x214/0x54e0 net/ipv4/tcp.c:3662
sock_common_getsockopt+0xc8/0xf4 net/core/sock.c:3089
__sys_getsockopt net/socket.c:2129 [inline]
__do_sys_getsockopt net/socket.c:2144 [inline]
__se_sys_getsockopt net/socket.c:2141 [inline]
__arm64_sys_getsockopt+0x240/0x308 net/socket.c:2141
__invoke_syscall arch/arm64/kernel/syscall.c:36 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:48 [inline]
el0_svc_common arch/arm64/kernel/syscall.c:114 [inline]
el0_svc_handler+0x300/0x540 arch/arm64/kernel/syscall.c:160
el0_svc+0x8/0xc arch/arm64/kernel/entry.S:1006
The buggy address belongs to the object at ffff00005338eb80
which belongs to the cache kmalloc-128 of size 128
The buggy address is located 0 bytes inside of
128-byte region [ffff00005338eb80, ffff00005338ec00)
The buggy address belongs to the page:
page:ffffffdffff4ce00 refcount:1 mapcount:0 mapping:e5ff0000576b0480 index:0x29ff000053388f00
flags: 0xffffff000000200(slab)
raw: 0ffffff000000200 ffffffdffff00108 5eff0000576afd40 e5ff0000576b0480
raw: 29ff000053388f00 000000000066005d 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
ffff00005338e900: 34 34 34 34 34 34 34 34 fe fe fe fe fe fe fe fe
ffff00005338ea00: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
>ffff00005338eb00: fe fe fe fe fe fe fe fe a8 fe fe fe fe fe fe fe
^
ffff00005338ec00: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
ffff00005338ed00: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
==================================================================
On Mon, Aug 19, 2019 at 02:23:48PM +0100, Mark Rutland wrote:
> On Mon, Aug 19, 2019 at 01:56:26PM +0100, Will Deacon wrote:
> > On Mon, Aug 19, 2019 at 07:44:20PM +0800, Walter Wu wrote:
> > > __arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address,
> > > but it will modify pointer tag into 0xff, so there is a false positive.
> > >
> > > When enable tag-based kasan, phys_to_virt() function need to rewrite
> > > its original pointer tag in order to avoid kasan report an incorrect
> > > memory corruption.
> >
> > Hmm. Which tree did you see this on? We've recently queued a load of fixes
> > in this area, but I /thought/ they were only needed after the support for
> > 52-bit virtual addressing in the kernel.
>
> I'm seeing similar issues in the virtio blk code (splat below), atop of
> the arm64 for-next/core branch. I think this is a latent issue, and
> people are only just starting to test with KASAN_SW_TAGS.
>
> It looks like the virtio blk code will round-trip a SLUB-allocated pointer from
> virt->page->virt, losing the per-object tag in the process.
>
> Our page_to_virt() seems to get a per-page tag, but this only makes
> sense if you're dealing with the page allocator, rather than something
> like SLUB which carves a page into smaller objects giving each object a
> distinct tag.
>
> Any round-trip of a pointer from SLUB is going to lose the per-object
> tag.
Urgh, I wonder how this is supposed to work?
If we end up having to check the KASAN shadow for *_to_virt(), then why
do we need to store anything in the page flags at all? Andrey?
Will
On Mon, Aug 19, 2019 at 3:34 PM Will Deacon <[email protected]> wrote:
>
> On Mon, Aug 19, 2019 at 02:23:48PM +0100, Mark Rutland wrote:
> > On Mon, Aug 19, 2019 at 01:56:26PM +0100, Will Deacon wrote:
> > > On Mon, Aug 19, 2019 at 07:44:20PM +0800, Walter Wu wrote:
> > > > __arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address,
> > > > but it will modify pointer tag into 0xff, so there is a false positive.
> > > >
> > > > When enable tag-based kasan, phys_to_virt() function need to rewrite
> > > > its original pointer tag in order to avoid kasan report an incorrect
> > > > memory corruption.
> > >
> > > Hmm. Which tree did you see this on? We've recently queued a load of fixes
> > > in this area, but I /thought/ they were only needed after the support for
> > > 52-bit virtual addressing in the kernel.
> >
> > I'm seeing similar issues in the virtio blk code (splat below), atop of
> > the arm64 for-next/core branch. I think this is a latent issue, and
> > people are only just starting to test with KASAN_SW_TAGS.
> >
> > It looks like the virtio blk code will round-trip a SLUB-allocated pointer from
> > virt->page->virt, losing the per-object tag in the process.
> >
> > Our page_to_virt() seems to get a per-page tag, but this only makes
> > sense if you're dealing with the page allocator, rather than something
> > like SLUB which carves a page into smaller objects giving each object a
> > distinct tag.
> >
> > Any round-trip of a pointer from SLUB is going to lose the per-object
> > tag.
>
> Urgh, I wonder how this is supposed to work?
>
> If we end up having to check the KASAN shadow for *_to_virt(), then why
> do we need to store anything in the page flags at all? Andrey?
As per 2813b9c0 ("kasan, mm, arm64: tag non slab memory allocated via
pagealloc") we should only save a non-0xff tag in page flags for non
slab pages.
Could you share your .config so I can reproduce this?
On 8/19/19 4:34 PM, Will Deacon wrote:
> On Mon, Aug 19, 2019 at 02:23:48PM +0100, Mark Rutland wrote:
>> On Mon, Aug 19, 2019 at 01:56:26PM +0100, Will Deacon wrote:
>>> On Mon, Aug 19, 2019 at 07:44:20PM +0800, Walter Wu wrote:
>>>> __arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address,
>>>> but it will modify pointer tag into 0xff, so there is a false positive.
>>>>
>>>> When enable tag-based kasan, phys_to_virt() function need to rewrite
>>>> its original pointer tag in order to avoid kasan report an incorrect
>>>> memory corruption.
>>>
>>> Hmm. Which tree did you see this on? We've recently queued a load of fixes
>>> in this area, but I /thought/ they were only needed after the support for
>>> 52-bit virtual addressing in the kernel.
>>
>> I'm seeing similar issues in the virtio blk code (splat below), atop of
>> the arm64 for-next/core branch. I think this is a latent issue, and
>> people are only just starting to test with KASAN_SW_TAGS.
>>
>> It looks like the virtio blk code will round-trip a SLUB-allocated pointer from
>> virt->page->virt, losing the per-object tag in the process.
>>
>> Our page_to_virt() seems to get a per-page tag, but this only makes
>> sense if you're dealing with the page allocator, rather than something
>> like SLUB which carves a page into smaller objects giving each object a
>> distinct tag.
>>
>> Any round-trip of a pointer from SLUB is going to lose the per-object
>> tag.
>
> Urgh, I wonder how this is supposed to work?
>
We supposed to ignore pointers with 0xff tags. We do ignore them when memory access checked,
but not in kfree() path.
This untested patch should fix the issue:
---
mm/kasan/common.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 895dc5e2b3d5..0a81cc328049 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -407,7 +407,7 @@ static inline bool shadow_invalid(u8 tag, s8 shadow_byte)
return shadow_byte < 0 ||
shadow_byte >= KASAN_SHADOW_SCALE_SIZE;
else
- return tag != (u8)shadow_byte;
+ return (tag != KASAN_TAG_KERNEL) && (tag != (u8)shadow_byte);
}
static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
--
2.21.0
On Mon, 2019-08-19 at 17:06 +0300, Andrey Ryabinin wrote:
>
> On 8/19/19 4:34 PM, Will Deacon wrote:
> > On Mon, Aug 19, 2019 at 02:23:48PM +0100, Mark Rutland wrote:
> >> On Mon, Aug 19, 2019 at 01:56:26PM +0100, Will Deacon wrote:
> >>> On Mon, Aug 19, 2019 at 07:44:20PM +0800, Walter Wu wrote:
> >>>> __arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address,
> >>>> but it will modify pointer tag into 0xff, so there is a false positive.
> >>>>
> >>>> When enable tag-based kasan, phys_to_virt() function need to rewrite
> >>>> its original pointer tag in order to avoid kasan report an incorrect
> >>>> memory corruption.
> >>>
> >>> Hmm. Which tree did you see this on? We've recently queued a load of fixes
> >>> in this area, but I /thought/ they were only needed after the support for
> >>> 52-bit virtual addressing in the kernel.
> >>
> >> I'm seeing similar issues in the virtio blk code (splat below), atop of
> >> the arm64 for-next/core branch. I think this is a latent issue, and
> >> people are only just starting to test with KASAN_SW_TAGS.
> >>
> >> It looks like the virtio blk code will round-trip a SLUB-allocated pointer from
> >> virt->page->virt, losing the per-object tag in the process.
> >>
> >> Our page_to_virt() seems to get a per-page tag, but this only makes
> >> sense if you're dealing with the page allocator, rather than something
> >> like SLUB which carves a page into smaller objects giving each object a
> >> distinct tag.
> >>
> >> Any round-trip of a pointer from SLUB is going to lose the per-object
> >> tag.
> >
> > Urgh, I wonder how this is supposed to work?
> >
>
> We supposed to ignore pointers with 0xff tags. We do ignore them when memory access checked,
> but not in kfree() path.
> This untested patch should fix the issue:
>
>
>
> ---
> mm/kasan/common.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 895dc5e2b3d5..0a81cc328049 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -407,7 +407,7 @@ static inline bool shadow_invalid(u8 tag, s8 shadow_byte)
> return shadow_byte < 0 ||
> shadow_byte >= KASAN_SHADOW_SCALE_SIZE;
> else
> - return tag != (u8)shadow_byte;
> + return (tag != KASAN_TAG_KERNEL) && (tag != (u8)shadow_byte);
> }
>
> static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
Hi, Andrey,
Does it miss the double-free case after ignore pointer tag 0xff ?
and please help review my another patch about memory corruption
identification.
Thanks your respondence
Walter
On Mon, Aug 19, 2019 at 04:05:22PM +0200, Andrey Konovalov wrote:
> On Mon, Aug 19, 2019 at 3:34 PM Will Deacon <[email protected]> wrote:
> >
> > On Mon, Aug 19, 2019 at 02:23:48PM +0100, Mark Rutland wrote:
> > > On Mon, Aug 19, 2019 at 01:56:26PM +0100, Will Deacon wrote:
> > > > On Mon, Aug 19, 2019 at 07:44:20PM +0800, Walter Wu wrote:
> > > > > __arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address,
> > > > > but it will modify pointer tag into 0xff, so there is a false positive.
> > > > >
> > > > > When enable tag-based kasan, phys_to_virt() function need to rewrite
> > > > > its original pointer tag in order to avoid kasan report an incorrect
> > > > > memory corruption.
> > > >
> > > > Hmm. Which tree did you see this on? We've recently queued a load of fixes
> > > > in this area, but I /thought/ they were only needed after the support for
> > > > 52-bit virtual addressing in the kernel.
> > >
> > > I'm seeing similar issues in the virtio blk code (splat below), atop of
> > > the arm64 for-next/core branch. I think this is a latent issue, and
> > > people are only just starting to test with KASAN_SW_TAGS.
> > >
> > > It looks like the virtio blk code will round-trip a SLUB-allocated pointer from
> > > virt->page->virt, losing the per-object tag in the process.
> > >
> > > Our page_to_virt() seems to get a per-page tag, but this only makes
> > > sense if you're dealing with the page allocator, rather than something
> > > like SLUB which carves a page into smaller objects giving each object a
> > > distinct tag.
> > >
> > > Any round-trip of a pointer from SLUB is going to lose the per-object
> > > tag.
> >
> > Urgh, I wonder how this is supposed to work?
> >
> > If we end up having to check the KASAN shadow for *_to_virt(), then why
> > do we need to store anything in the page flags at all? Andrey?
>
> As per 2813b9c0 ("kasan, mm, arm64: tag non slab memory allocated via
> pagealloc") we should only save a non-0xff tag in page flags for non
> slab pages.
Thanks, that makes sense. Hopefully the patch from Andrey R will solve
both of the reported splats, since I'd not realised they were both on the
kfree() path.
> Could you share your .config so I can reproduce this?
This is in the iopgtable code, so it's probably pretty tricky to trigger
at runtime unless you have the write IOMMU hardware, unfortunately.
Will
On 19/08/2019 15:22, Will Deacon wrote:
> On Mon, Aug 19, 2019 at 04:05:22PM +0200, Andrey Konovalov wrote:
>> On Mon, Aug 19, 2019 at 3:34 PM Will Deacon <[email protected]> wrote:
>>>
>>> On Mon, Aug 19, 2019 at 02:23:48PM +0100, Mark Rutland wrote:
>>>> On Mon, Aug 19, 2019 at 01:56:26PM +0100, Will Deacon wrote:
>>>>> On Mon, Aug 19, 2019 at 07:44:20PM +0800, Walter Wu wrote:
>>>>>> __arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address,
>>>>>> but it will modify pointer tag into 0xff, so there is a false positive.
>>>>>>
>>>>>> When enable tag-based kasan, phys_to_virt() function need to rewrite
>>>>>> its original pointer tag in order to avoid kasan report an incorrect
>>>>>> memory corruption.
>>>>>
>>>>> Hmm. Which tree did you see this on? We've recently queued a load of fixes
>>>>> in this area, but I /thought/ they were only needed after the support for
>>>>> 52-bit virtual addressing in the kernel.
>>>>
>>>> I'm seeing similar issues in the virtio blk code (splat below), atop of
>>>> the arm64 for-next/core branch. I think this is a latent issue, and
>>>> people are only just starting to test with KASAN_SW_TAGS.
>>>>
>>>> It looks like the virtio blk code will round-trip a SLUB-allocated pointer from
>>>> virt->page->virt, losing the per-object tag in the process.
>>>>
>>>> Our page_to_virt() seems to get a per-page tag, but this only makes
>>>> sense if you're dealing with the page allocator, rather than something
>>>> like SLUB which carves a page into smaller objects giving each object a
>>>> distinct tag.
>>>>
>>>> Any round-trip of a pointer from SLUB is going to lose the per-object
>>>> tag.
>>>
>>> Urgh, I wonder how this is supposed to work?
>>>
>>> If we end up having to check the KASAN shadow for *_to_virt(), then why
>>> do we need to store anything in the page flags at all? Andrey?
>>
>> As per 2813b9c0 ("kasan, mm, arm64: tag non slab memory allocated via
>> pagealloc") we should only save a non-0xff tag in page flags for non
>> slab pages.
>
> Thanks, that makes sense. Hopefully the patch from Andrey R will solve
> both of the reported splats, since I'd not realised they were both on the
> kfree() path.
>
>> Could you share your .config so I can reproduce this?
>
> This is in the iopgtable code, so it's probably pretty tricky to trigger
> at runtime unless you have the write IOMMU hardware, unfortunately.
If simply freeing any entry from the l2_tables cache is sufficient, then
the short-descriptor selftest should do the job, and that ought to run
on anything (modulo insane RAM layouts).
Robin.
On Mon, Aug 19, 2019 at 03:35:16PM +0100, Robin Murphy wrote:
> On 19/08/2019 15:22, Will Deacon wrote:
> > On Mon, Aug 19, 2019 at 04:05:22PM +0200, Andrey Konovalov wrote:
> > > On Mon, Aug 19, 2019 at 3:34 PM Will Deacon <[email protected]> wrote:
> > > >
> > > > On Mon, Aug 19, 2019 at 02:23:48PM +0100, Mark Rutland wrote:
> > > > > On Mon, Aug 19, 2019 at 01:56:26PM +0100, Will Deacon wrote:
> > > > > > On Mon, Aug 19, 2019 at 07:44:20PM +0800, Walter Wu wrote:
> > > > > > > __arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address,
> > > > > > > but it will modify pointer tag into 0xff, so there is a false positive.
> > > > > > >
> > > > > > > When enable tag-based kasan, phys_to_virt() function need to rewrite
> > > > > > > its original pointer tag in order to avoid kasan report an incorrect
> > > > > > > memory corruption.
> > > > > >
> > > > > > Hmm. Which tree did you see this on? We've recently queued a load of fixes
> > > > > > in this area, but I /thought/ they were only needed after the support for
> > > > > > 52-bit virtual addressing in the kernel.
> > > > >
> > > > > I'm seeing similar issues in the virtio blk code (splat below), atop of
> > > > > the arm64 for-next/core branch. I think this is a latent issue, and
> > > > > people are only just starting to test with KASAN_SW_TAGS.
> > > > >
> > > > > It looks like the virtio blk code will round-trip a SLUB-allocated pointer from
> > > > > virt->page->virt, losing the per-object tag in the process.
> > > > >
> > > > > Our page_to_virt() seems to get a per-page tag, but this only makes
> > > > > sense if you're dealing with the page allocator, rather than something
> > > > > like SLUB which carves a page into smaller objects giving each object a
> > > > > distinct tag.
> > > > >
> > > > > Any round-trip of a pointer from SLUB is going to lose the per-object
> > > > > tag.
> > > >
> > > > Urgh, I wonder how this is supposed to work?
> > > >
> > > > If we end up having to check the KASAN shadow for *_to_virt(), then why
> > > > do we need to store anything in the page flags at all? Andrey?
> > >
> > > As per 2813b9c0 ("kasan, mm, arm64: tag non slab memory allocated via
> > > pagealloc") we should only save a non-0xff tag in page flags for non
> > > slab pages.
> >
> > Thanks, that makes sense. Hopefully the patch from Andrey R will solve
> > both of the reported splats, since I'd not realised they were both on the
> > kfree() path.
> >
> > > Could you share your .config so I can reproduce this?
> >
> > This is in the iopgtable code, so it's probably pretty tricky to trigger
> > at runtime unless you have the write IOMMU hardware, unfortunately.
>
> If simply freeing any entry from the l2_tables cache is sufficient, then the
> short-descriptor selftest should do the job, and that ought to run on
> anything (modulo insane RAM layouts).
Ok, so that would be defconfig + CONFIG_IOMMU_IO_PGTABLE_ARMV7S +
CONFIG_IOMMU_IO_PGTABLE_ARMV7S_SELFTEST + KASAN...
Will
On Mon, Aug 19, 2019 at 04:05:22PM +0200, Andrey Konovalov wrote:
> On Mon, Aug 19, 2019 at 3:34 PM Will Deacon <[email protected]> wrote:
> >
> > On Mon, Aug 19, 2019 at 02:23:48PM +0100, Mark Rutland wrote:
> > > On Mon, Aug 19, 2019 at 01:56:26PM +0100, Will Deacon wrote:
> > > > On Mon, Aug 19, 2019 at 07:44:20PM +0800, Walter Wu wrote:
> > > > > __arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address,
> > > > > but it will modify pointer tag into 0xff, so there is a false positive.
> > > > >
> > > > > When enable tag-based kasan, phys_to_virt() function need to rewrite
> > > > > its original pointer tag in order to avoid kasan report an incorrect
> > > > > memory corruption.
> > > >
> > > > Hmm. Which tree did you see this on? We've recently queued a load of fixes
> > > > in this area, but I /thought/ they were only needed after the support for
> > > > 52-bit virtual addressing in the kernel.
> > >
> > > I'm seeing similar issues in the virtio blk code (splat below), atop of
> > > the arm64 for-next/core branch. I think this is a latent issue, and
> > > people are only just starting to test with KASAN_SW_TAGS.
> > >
> > > It looks like the virtio blk code will round-trip a SLUB-allocated pointer from
> > > virt->page->virt, losing the per-object tag in the process.
> > >
> > > Our page_to_virt() seems to get a per-page tag, but this only makes
> > > sense if you're dealing with the page allocator, rather than something
> > > like SLUB which carves a page into smaller objects giving each object a
> > > distinct tag.
> > >
> > > Any round-trip of a pointer from SLUB is going to lose the per-object
> > > tag.
> >
> > Urgh, I wonder how this is supposed to work?
> >
> > If we end up having to check the KASAN shadow for *_to_virt(), then why
> > do we need to store anything in the page flags at all? Andrey?
>
> As per 2813b9c0 ("kasan, mm, arm64: tag non slab memory allocated via
> pagealloc") we should only save a non-0xff tag in page flags for non
> slab pages.
>
> Could you share your .config so I can reproduce this?
I wrote a test (below) to do so. :)
It fires with arm64 defconfig, + CONFIG_TEST_KASAN=m.
With Andrey Ryabinin's patch it works as expected with no KASAN splats
for the two new test cases.
Thanks,
Mark.
---->8----
From 7e8569b558fca21ad4e80fddae659591bc84ce1f Mon Sep 17 00:00:00 2001
From: Mark Rutland <[email protected]>
Date: Mon, 19 Aug 2019 15:39:32 +0100
Subject: [PATCH] lib/test_kasan: add roundtrip tests
In several places we needs to be able to operate on pointers which have
gone via a roundtrip:
virt -> {phys,page} -> virt
With KASAN_SW_TAGS, we can't preserve the tag for SLUB objects, and the
{phys,page} -> virt conversion will use KASAN_TAG_KERNEL.
This patch adds tests to ensure that this works as expected, without
false positives.
Signed-off-by: Mark Rutland <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Andrey Konovalov <[email protected]>
Cc: Will Deacon <[email protected]>
---
lib/test_kasan.c | 40 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 40 insertions(+)
diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index b63b367a94e8..cf7b93f0d90c 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -19,6 +19,8 @@
#include <linux/string.h>
#include <linux/uaccess.h>
+#include <asm/page.h>
+
/*
* Note: test functions are marked noinline so that their names appear in
* reports.
@@ -337,6 +339,42 @@ static noinline void __init kmalloc_uaf2(void)
kfree(ptr2);
}
+static noinline void __init kfree_via_page(void)
+{
+ char *ptr;
+ size_t size = 8;
+ struct page *page;
+ unsigned long offset;
+
+ pr_info("invalid-free false positive (via page)\n");
+ ptr = kmalloc(size, GFP_KERNEL);
+ if (!ptr) {
+ pr_err("Allocation failed\n");
+ return;
+ }
+
+ page = virt_to_page(ptr);
+ offset = offset_in_page(ptr);
+ kfree(page_address(page) + offset);
+}
+
+static noinline void __init kfree_via_phys(void)
+{
+ char *ptr;
+ size_t size = 8;
+ phys_addr_t phys;
+
+ pr_info("invalid-free false positive (via phys)\n");
+ ptr = kmalloc(size, GFP_KERNEL);
+ if (!ptr) {
+ pr_err("Allocation failed\n");
+ return;
+ }
+
+ phys = virt_to_phys(ptr);
+ kfree(phys_to_virt(phys));
+}
+
static noinline void __init kmem_cache_oob(void)
{
char *p;
@@ -737,6 +775,8 @@ static int __init kmalloc_tests_init(void)
kmalloc_uaf();
kmalloc_uaf_memset();
kmalloc_uaf2();
+ kfree_via_page();
+ kfree_via_phys();
kmem_cache_oob();
memcg_accounted_kmem_cache();
kasan_stack_oob();
--
2.11.0
On Mon, Aug 19, 2019 at 5:03 PM Mark Rutland <[email protected]> wrote:
>
> On Mon, Aug 19, 2019 at 04:05:22PM +0200, Andrey Konovalov wrote:
> > On Mon, Aug 19, 2019 at 3:34 PM Will Deacon <[email protected]> wrote:
> > >
> > > On Mon, Aug 19, 2019 at 02:23:48PM +0100, Mark Rutland wrote:
> > > > On Mon, Aug 19, 2019 at 01:56:26PM +0100, Will Deacon wrote:
> > > > > On Mon, Aug 19, 2019 at 07:44:20PM +0800, Walter Wu wrote:
> > > > > > __arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address,
> > > > > > but it will modify pointer tag into 0xff, so there is a false positive.
> > > > > >
> > > > > > When enable tag-based kasan, phys_to_virt() function need to rewrite
> > > > > > its original pointer tag in order to avoid kasan report an incorrect
> > > > > > memory corruption.
> > > > >
> > > > > Hmm. Which tree did you see this on? We've recently queued a load of fixes
> > > > > in this area, but I /thought/ they were only needed after the support for
> > > > > 52-bit virtual addressing in the kernel.
> > > >
> > > > I'm seeing similar issues in the virtio blk code (splat below), atop of
> > > > the arm64 for-next/core branch. I think this is a latent issue, and
> > > > people are only just starting to test with KASAN_SW_TAGS.
> > > >
> > > > It looks like the virtio blk code will round-trip a SLUB-allocated pointer from
> > > > virt->page->virt, losing the per-object tag in the process.
> > > >
> > > > Our page_to_virt() seems to get a per-page tag, but this only makes
> > > > sense if you're dealing with the page allocator, rather than something
> > > > like SLUB which carves a page into smaller objects giving each object a
> > > > distinct tag.
> > > >
> > > > Any round-trip of a pointer from SLUB is going to lose the per-object
> > > > tag.
> > >
> > > Urgh, I wonder how this is supposed to work?
> > >
> > > If we end up having to check the KASAN shadow for *_to_virt(), then why
> > > do we need to store anything in the page flags at all? Andrey?
> >
> > As per 2813b9c0 ("kasan, mm, arm64: tag non slab memory allocated via
> > pagealloc") we should only save a non-0xff tag in page flags for non
> > slab pages.
> >
> > Could you share your .config so I can reproduce this?
>
> I wrote a test (below) to do so. :)
>
> It fires with arm64 defconfig, + CONFIG_TEST_KASAN=m.
>
> With Andrey Ryabinin's patch it works as expected with no KASAN splats
> for the two new test cases.
OK, Andrey's patch makes sense and fixes both Mark's test patch and
reports from CONFIG_IOMMU_IO_PGTABLE_ARMV7S_SELFTEST.
Tested-by: Andrey Konovalov <[email protected]>
Reviewed-by: Andrey Konovalov <[email protected]>
on both patches.
>
> Thanks,
> Mark.
>
> ---->8----
> From 7e8569b558fca21ad4e80fddae659591bc84ce1f Mon Sep 17 00:00:00 2001
> From: Mark Rutland <[email protected]>
> Date: Mon, 19 Aug 2019 15:39:32 +0100
> Subject: [PATCH] lib/test_kasan: add roundtrip tests
>
> In several places we needs to be able to operate on pointers which have
"needs" => "need"
> gone via a roundtrip:
>
> virt -> {phys,page} -> virt
>
> With KASAN_SW_TAGS, we can't preserve the tag for SLUB objects, and the
> {phys,page} -> virt conversion will use KASAN_TAG_KERNEL.
>
> This patch adds tests to ensure that this works as expected, without
> false positives.
>
> Signed-off-by: Mark Rutland <[email protected]>
> Cc: Andrey Ryabinin <[email protected]>
> Cc: Andrey Konovalov <[email protected]>
> Cc: Will Deacon <[email protected]>
> ---
> lib/test_kasan.c | 40 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 40 insertions(+)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index b63b367a94e8..cf7b93f0d90c 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -19,6 +19,8 @@
> #include <linux/string.h>
> #include <linux/uaccess.h>
>
> +#include <asm/page.h>
> +
> /*
> * Note: test functions are marked noinline so that their names appear in
> * reports.
> @@ -337,6 +339,42 @@ static noinline void __init kmalloc_uaf2(void)
> kfree(ptr2);
> }
>
> +static noinline void __init kfree_via_page(void)
> +{
> + char *ptr;
> + size_t size = 8;
> + struct page *page;
> + unsigned long offset;
> +
> + pr_info("invalid-free false positive (via page)\n");
> + ptr = kmalloc(size, GFP_KERNEL);
> + if (!ptr) {
> + pr_err("Allocation failed\n");
> + return;
> + }
> +
> + page = virt_to_page(ptr);
> + offset = offset_in_page(ptr);
> + kfree(page_address(page) + offset);
> +}
> +
> +static noinline void __init kfree_via_phys(void)
> +{
> + char *ptr;
> + size_t size = 8;
> + phys_addr_t phys;
> +
> + pr_info("invalid-free false positive (via phys)\n");
> + ptr = kmalloc(size, GFP_KERNEL);
> + if (!ptr) {
> + pr_err("Allocation failed\n");
> + return;
> + }
> +
> + phys = virt_to_phys(ptr);
> + kfree(phys_to_virt(phys));
> +}
> +
> static noinline void __init kmem_cache_oob(void)
> {
> char *p;
> @@ -737,6 +775,8 @@ static int __init kmalloc_tests_init(void)
> kmalloc_uaf();
> kmalloc_uaf_memset();
> kmalloc_uaf2();
> + kfree_via_page();
> + kfree_via_phys();
> kmem_cache_oob();
> memcg_accounted_kmem_cache();
> kasan_stack_oob();
> --
> 2.11.0
>
On Mon, Aug 19, 2019 at 05:37:36PM +0200, Andrey Konovalov wrote:
> On Mon, Aug 19, 2019 at 5:03 PM Mark Rutland <[email protected]> wrote:
> >
> > On Mon, Aug 19, 2019 at 04:05:22PM +0200, Andrey Konovalov wrote:
> > > On Mon, Aug 19, 2019 at 3:34 PM Will Deacon <[email protected]> wrote:
> > > >
> > > > On Mon, Aug 19, 2019 at 02:23:48PM +0100, Mark Rutland wrote:
> > > > > On Mon, Aug 19, 2019 at 01:56:26PM +0100, Will Deacon wrote:
> > > > > > On Mon, Aug 19, 2019 at 07:44:20PM +0800, Walter Wu wrote:
> > > > > > > __arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address,
> > > > > > > but it will modify pointer tag into 0xff, so there is a false positive.
> > > > > > >
> > > > > > > When enable tag-based kasan, phys_to_virt() function need to rewrite
> > > > > > > its original pointer tag in order to avoid kasan report an incorrect
> > > > > > > memory corruption.
> > > > > >
> > > > > > Hmm. Which tree did you see this on? We've recently queued a load of fixes
> > > > > > in this area, but I /thought/ they were only needed after the support for
> > > > > > 52-bit virtual addressing in the kernel.
> > > > >
> > > > > I'm seeing similar issues in the virtio blk code (splat below), atop of
> > > > > the arm64 for-next/core branch. I think this is a latent issue, and
> > > > > people are only just starting to test with KASAN_SW_TAGS.
> > > > >
> > > > > It looks like the virtio blk code will round-trip a SLUB-allocated pointer from
> > > > > virt->page->virt, losing the per-object tag in the process.
> > > > >
> > > > > Our page_to_virt() seems to get a per-page tag, but this only makes
> > > > > sense if you're dealing with the page allocator, rather than something
> > > > > like SLUB which carves a page into smaller objects giving each object a
> > > > > distinct tag.
> > > > >
> > > > > Any round-trip of a pointer from SLUB is going to lose the per-object
> > > > > tag.
> > > >
> > > > Urgh, I wonder how this is supposed to work?
> > > >
> > > > If we end up having to check the KASAN shadow for *_to_virt(), then why
> > > > do we need to store anything in the page flags at all? Andrey?
> > >
> > > As per 2813b9c0 ("kasan, mm, arm64: tag non slab memory allocated via
> > > pagealloc") we should only save a non-0xff tag in page flags for non
> > > slab pages.
> > >
> > > Could you share your .config so I can reproduce this?
> >
> > I wrote a test (below) to do so. :)
> >
> > It fires with arm64 defconfig, + CONFIG_TEST_KASAN=m.
> >
> > With Andrey Ryabinin's patch it works as expected with no KASAN splats
> > for the two new test cases.
>
> OK, Andrey's patch makes sense and fixes both Mark's test patch and
> reports from CONFIG_IOMMU_IO_PGTABLE_ARMV7S_SELFTEST.
>
> Tested-by: Andrey Konovalov <[email protected]>
> Reviewed-by: Andrey Konovalov <[email protected]>
>
> on both patches.
>
> >
> > Thanks,
> > Mark.
> >
> > ---->8----
> > From 7e8569b558fca21ad4e80fddae659591bc84ce1f Mon Sep 17 00:00:00 2001
> > From: Mark Rutland <[email protected]>
> > Date: Mon, 19 Aug 2019 15:39:32 +0100
> > Subject: [PATCH] lib/test_kasan: add roundtrip tests
> >
> > In several places we needs to be able to operate on pointers which have
>
> "needs" => "need"
Thanks!
I'll spin a standalone v2 of this with that fixed and your tags folded
in.
Mark.
>
> > gone via a roundtrip:
> >
> > virt -> {phys,page} -> virt
> >
> > With KASAN_SW_TAGS, we can't preserve the tag for SLUB objects, and the
> > {phys,page} -> virt conversion will use KASAN_TAG_KERNEL.
> >
> > This patch adds tests to ensure that this works as expected, without
> > false positives.
> >
> > Signed-off-by: Mark Rutland <[email protected]>
> > Cc: Andrey Ryabinin <[email protected]>
> > Cc: Andrey Konovalov <[email protected]>
> > Cc: Will Deacon <[email protected]>
> > ---
> > lib/test_kasan.c | 40 ++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 40 insertions(+)
> >
> > diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> > index b63b367a94e8..cf7b93f0d90c 100644
> > --- a/lib/test_kasan.c
> > +++ b/lib/test_kasan.c
> > @@ -19,6 +19,8 @@
> > #include <linux/string.h>
> > #include <linux/uaccess.h>
> >
> > +#include <asm/page.h>
> > +
> > /*
> > * Note: test functions are marked noinline so that their names appear in
> > * reports.
> > @@ -337,6 +339,42 @@ static noinline void __init kmalloc_uaf2(void)
> > kfree(ptr2);
> > }
> >
> > +static noinline void __init kfree_via_page(void)
> > +{
> > + char *ptr;
> > + size_t size = 8;
> > + struct page *page;
> > + unsigned long offset;
> > +
> > + pr_info("invalid-free false positive (via page)\n");
> > + ptr = kmalloc(size, GFP_KERNEL);
> > + if (!ptr) {
> > + pr_err("Allocation failed\n");
> > + return;
> > + }
> > +
> > + page = virt_to_page(ptr);
> > + offset = offset_in_page(ptr);
> > + kfree(page_address(page) + offset);
> > +}
> > +
> > +static noinline void __init kfree_via_phys(void)
> > +{
> > + char *ptr;
> > + size_t size = 8;
> > + phys_addr_t phys;
> > +
> > + pr_info("invalid-free false positive (via phys)\n");
> > + ptr = kmalloc(size, GFP_KERNEL);
> > + if (!ptr) {
> > + pr_err("Allocation failed\n");
> > + return;
> > + }
> > +
> > + phys = virt_to_phys(ptr);
> > + kfree(phys_to_virt(phys));
> > +}
> > +
> > static noinline void __init kmem_cache_oob(void)
> > {
> > char *p;
> > @@ -737,6 +775,8 @@ static int __init kmalloc_tests_init(void)
> > kmalloc_uaf();
> > kmalloc_uaf_memset();
> > kmalloc_uaf2();
> > + kfree_via_page();
> > + kfree_via_phys();
> > kmem_cache_oob();
> > memcg_accounted_kmem_cache();
> > kasan_stack_oob();
> > --
> > 2.11.0
> >