[PATCH v2 0/2] kasan: fixes for 5.11-rc

[PATCH v2 0/2] kasan: fixes for 5.11-rc

[Andrey Konovalov]

Changes v1->v2:
- Update changelog of patch #1.

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 | 2 ++
 mm/slub.c             | 7 ++++---
 2 files changed, 6 insertions(+), 3 deletions(-)

-- 
2.30.0.284.gd98b1dd5eaa7-goog

[PATCH v2 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 v2 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 before calling kasan_report.

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 | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 3c40da479899..a218f6f2fdc8 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -304,6 +304,8 @@ static void report_tag_fault(unsigned long addr, unsigned int esr,
 {
 	bool is_write  = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
 
+	/* The format of KASAN tags is 0xF<x>. */
+	addr |= (0xF0UL << MTE_TAG_SHIFT);
 	/*
 	 * SAS bits aren't set for all faults reported in EL1, so we can't
 	 * find out access size.
-- 
2.30.0.284.gd98b1dd5eaa7-goog

Re: [PATCH v2 2/2] kasan, arm64: fix pointer tags in KASAN reports

[Catalin Marinas]

On Thu, Jan 14, 2021 at 08:33:57PM +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 before calling kasan_report.
> 
> 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 | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 3c40da479899..a218f6f2fdc8 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -304,6 +304,8 @@ static void report_tag_fault(unsigned long addr, unsigned int esr,
>  {
>  	bool is_write  = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
>  
> +	/* The format of KASAN tags is 0xF<x>. */
> +	addr |= (0xF0UL << MTE_TAG_SHIFT);
>  	/*
>  	 * SAS bits aren't set for all faults reported in EL1, so we can't
>  	 * find out access size.

I already replied here but I don't see any change in v2:

https://lore.kernel.org/linux-arm-kernel/20210113165441.GC27045@gaia/

-- 
Catalin

Re: [PATCH v2 2/2] kasan, arm64: fix pointer tags in KASAN reports

[Andrey Konovalov]

On Fri, Jan 15, 2021 at 11:49 AM Catalin Marinas
<catalin.marinas@arm.com> wrote:
>
> On Thu, Jan 14, 2021 at 08:33:57PM +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 before calling kasan_report.
> >
> > 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 | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > index 3c40da479899..a218f6f2fdc8 100644
> > --- a/arch/arm64/mm/fault.c
> > +++ b/arch/arm64/mm/fault.c
> > @@ -304,6 +304,8 @@ static void report_tag_fault(unsigned long addr, unsigned int esr,
> >  {
> >       bool is_write  = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
> >
> > +     /* The format of KASAN tags is 0xF<x>. */
> > +     addr |= (0xF0UL << MTE_TAG_SHIFT);
> >       /*
> >        * SAS bits aren't set for all faults reported in EL1, so we can't
> >        * find out access size.
>
> I already replied here but I don't see any change in v2:
>
> https://lore.kernel.org/linux-arm-kernel/20210113165441.GC27045@gaia/

Hi Catalin,

Sorry, Gmail decided to mark all your emails as spam for some reason,
so I didn't see any of them :(

I'll fix this in v3.

Thanks!