[PATCH v3 0/2] kasan: fixes for 5.11-rc

[PATCH v3 0/2] kasan: fixes for 5.11-rc

[Andrey Konovalov]

Changes v2->v3:
- Fix up kernel pointer tag in do_tag_check_fault() instead of
  report_tag_fault().

Andrey Konovalov (2):
  kasan, mm: fix conflicts with init_on_alloc/free
  kasan, arm64: fix pointer tags in KASAN reports

 arch/arm64/mm/fault.c | 7 ++++---
 mm/slub.c             | 7 ++++---
 2 files changed, 8 insertions(+), 6 deletions(-)

-- 
2.30.0.284.gd98b1dd5eaa7-goog

[PATCH v3 1/2] kasan, mm: fix conflicts with init_on_alloc/free

[Andrey Konovalov]

A few places where SLUB accesses object's data or metadata were missed in
a previous patch. This leads to false positives with hardware tag-based
KASAN when bulk allocations are used with init_on_alloc/free.

Fix the false-positives by resetting pointer tags during these accesses.

(The kasan_reset_tag call is removed from slab_alloc_node, as it's added
 into maybe_wipe_obj_freeptr.)

Link: https://linux-review.googlesource.com/id/I50dd32838a666e173fe06c3c5c766f2c36aae901
Fixes: aa1ef4d7b3f67 ("kasan, mm: reset tags when accessing metadata")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 mm/slub.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index dc5b42e700b8..75fb097d990d 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2791,7 +2791,8 @@ static __always_inline void maybe_wipe_obj_freeptr(struct kmem_cache *s,
 						   void *obj)
 {
 	if (unlikely(slab_want_init_on_free(s)) && obj)
-		memset((void *)((char *)obj + s->offset), 0, sizeof(void *));
+		memset((void *)((char *)kasan_reset_tag(obj) + s->offset),
+			0, sizeof(void *));
 }
 
 /*
@@ -2883,7 +2884,7 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s,
 		stat(s, ALLOC_FASTPATH);
 	}
 
-	maybe_wipe_obj_freeptr(s, kasan_reset_tag(object));
+	maybe_wipe_obj_freeptr(s, object);
 
 	if (unlikely(slab_want_init_on_alloc(gfpflags, s)) && object)
 		memset(kasan_reset_tag(object), 0, s->object_size);
@@ -3329,7 +3330,7 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
 		int j;
 
 		for (j = 0; j < i; j++)
-			memset(p[j], 0, s->object_size);
+			memset(kasan_reset_tag(p[j]), 0, s->object_size);
 	}
 
 	/* memcg and kmem_cache debug support */
-- 
2.30.0.284.gd98b1dd5eaa7-goog

[PATCH v3 2/2] kasan, arm64: fix pointer tags in KASAN reports

[Andrey Konovalov]

As of the "arm64: expose FAR_EL1 tag bits in siginfo" patch, the address
that is passed to report_tag_fault has pointer tags in the format of 0x0X,
while KASAN uses 0xFX format (note the difference in the top 4 bits).

Fix up the pointer tag for kernel pointers in do_tag_check_fault by
setting them to the same value as bit 55. Explicitly use __untagged_addr()
instead of untagged_addr(), as the latter doesn't affect TTBR1 addresses.

Link: https://linux-review.googlesource.com/id/I9ced973866036d8679e8f4ae325de547eb969649
Fixes: dceec3ff7807 ("arm64: expose FAR_EL1 tag bits in siginfo")
Fixes: 4291e9ee6189 ("kasan, arm64: print report from tag fault handler")
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 arch/arm64/mm/fault.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 3c40da479899..35d75c60e2b8 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -709,10 +709,11 @@ static int do_tag_check_fault(unsigned long far, unsigned int esr,
 			      struct pt_regs *regs)
 {
 	/*
-	 * The architecture specifies that bits 63:60 of FAR_EL1 are UNKNOWN for tag
-	 * check faults. Mask them out now so that userspace doesn't see them.
+	 * The architecture specifies that bits 63:60 of FAR_EL1 are UNKNOWN
+	 * for tag check faults. Set them to corresponding bits in the untagged
+	 * address.
 	 */
-	far &= (1UL << 60) - 1;
+	far = (__untagged_addr(far) & ~MTE_TAG_MASK) | (far & MTE_TAG_MASK);
 	do_bad_area(far, esr, regs);
 	return 0;
 }
-- 
2.30.0.284.gd98b1dd5eaa7-goog

Re: [PATCH v3 2/2] kasan, arm64: fix pointer tags in KASAN reports

[Catalin Marinas]

On Fri, Jan 15, 2021 at 06:41:53PM +0100, Andrey Konovalov wrote:
> As of the "arm64: expose FAR_EL1 tag bits in siginfo" patch, the address
> that is passed to report_tag_fault has pointer tags in the format of 0x0X,
> while KASAN uses 0xFX format (note the difference in the top 4 bits).
> 
> Fix up the pointer tag for kernel pointers in do_tag_check_fault by
> setting them to the same value as bit 55. Explicitly use __untagged_addr()
> instead of untagged_addr(), as the latter doesn't affect TTBR1 addresses.
> 
> Link: https://linux-review.googlesource.com/id/I9ced973866036d8679e8f4ae325de547eb969649

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

Unless there are other comments, I'll queue this for -rc5 through the
arm64 tree (I already finalised the arm64 for-next/fixes branch for this
week).

-- 
Catalin

Re: [PATCH v3 2/2] kasan, arm64: fix pointer tags in KASAN reports

[Vincenzo Frascino]

On 1/15/21 5:41 PM, Andrey Konovalov wrote:
> As of the "arm64: expose FAR_EL1 tag bits in siginfo" patch, the address
> that is passed to report_tag_fault has pointer tags in the format of 0x0X,
> while KASAN uses 0xFX format (note the difference in the top 4 bits).
> 
> Fix up the pointer tag for kernel pointers in do_tag_check_fault by
> setting them to the same value as bit 55. Explicitly use __untagged_addr()
> instead of untagged_addr(), as the latter doesn't affect TTBR1 addresses.
> 
> Link: https://linux-review.googlesource.com/id/I9ced973866036d8679e8f4ae325de547eb969649
> Fixes: dceec3ff7807 ("arm64: expose FAR_EL1 tag bits in siginfo")
> Fixes: 4291e9ee6189 ("kasan, arm64: print report from tag fault handler")
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>

> ---
>  arch/arm64/mm/fault.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 3c40da479899..35d75c60e2b8 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -709,10 +709,11 @@ static int do_tag_check_fault(unsigned long far, unsigned int esr,
>  			      struct pt_regs *regs)
>  {
>  	/*
> -	 * The architecture specifies that bits 63:60 of FAR_EL1 are UNKNOWN for tag
> -	 * check faults. Mask them out now so that userspace doesn't see them.
> +	 * The architecture specifies that bits 63:60 of FAR_EL1 are UNKNOWN
> +	 * for tag check faults. Set them to corresponding bits in the untagged
> +	 * address.
>  	 */
> -	far &= (1UL << 60) - 1;
> +	far = (__untagged_addr(far) & ~MTE_TAG_MASK) | (far & MTE_TAG_MASK);
>  	do_bad_area(far, esr, regs);
>  	return 0;
>  }
> 

-- 
Regards,
Vincenzo

Re: [PATCH v3 2/2] kasan, arm64: fix pointer tags in KASAN reports

[Andrey Konovalov]

On Fri, Jan 15, 2021 at 6:59 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
>
> On Fri, Jan 15, 2021 at 06:41:53PM +0100, Andrey Konovalov wrote:
> > As of the "arm64: expose FAR_EL1 tag bits in siginfo" patch, the address
> > that is passed to report_tag_fault has pointer tags in the format of 0x0X,
> > while KASAN uses 0xFX format (note the difference in the top 4 bits).
> >
> > Fix up the pointer tag for kernel pointers in do_tag_check_fault by
> > setting them to the same value as bit 55. Explicitly use __untagged_addr()
> > instead of untagged_addr(), as the latter doesn't affect TTBR1 addresses.
> >
> > Link: https://linux-review.googlesource.com/id/I9ced973866036d8679e8f4ae325de547eb969649
>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
>
> Unless there are other comments, I'll queue this for -rc5 through the
> arm64 tree (I already finalised the arm64 for-next/fixes branch for this
> week).

Sounds good, thank you!

Re: [PATCH v3 0/2] kasan: fixes for 5.11-rc

[Catalin Marinas]

On Fri, 15 Jan 2021 18:41:51 +0100, Andrey Konovalov wrote:
> Changes v2->v3:
> - Fix up kernel pointer tag in do_tag_check_fault() instead of
>   report_tag_fault().
> 
> Andrey Konovalov (2):
>   kasan, mm: fix conflicts with init_on_alloc/free
>   kasan, arm64: fix pointer tags in KASAN reports
> 
> [...]

Applied to arm64 (for-next/fixes), thanks!

[2/2] kasan, arm64: fix pointer tags in KASAN reports
      https://git.kernel.org/arm64/c/3ed86b9a7140

-- 
Catalin