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.
Link: https://linux-review.googlesource.com/id/I50dd32838a666e173fe06c3c5c766f2c36aae901
Fixes: aa1ef4d7b3f67 ("kasan, mm: reset tags when accessing metadata")
Reported-by: Dmitry Vyukov <[email protected]>
Signed-off-by: Andrey Konovalov <[email protected]>
---
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
On 1/13/21 5:03 PM, Andrey Konovalov wrote:
> 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.
>
> Link: https://linux-review.googlesource.com/id/I50dd32838a666e173fe06c3c5c766f2c36aae901
> Fixes: aa1ef4d7b3f67 ("kasan, mm: reset tags when accessing metadata")
> Reported-by: Dmitry Vyukov <[email protected]>
> Signed-off-by: Andrey Konovalov <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
> ---
> 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);
And in that case the reset was unnecessary, right. (commit log only mentions
adding missing resets).
> 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 */
>
On Wed, Jan 13, 2021 at 6:25 PM Vlastimil Babka <[email protected]> wrote:
>
> On 1/13/21 5:03 PM, Andrey Konovalov wrote:
> > 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.
> >
> > Link: https://linux-review.googlesource.com/id/I50dd32838a666e173fe06c3c5c766f2c36aae901
> > Fixes: aa1ef4d7b3f67 ("kasan, mm: reset tags when accessing metadata")
> > Reported-by: Dmitry Vyukov <[email protected]>
> > Signed-off-by: Andrey Konovalov <[email protected]>
>
> Acked-by: Vlastimil Babka <[email protected]>
>
> > ---
> > 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);
>
> And in that case the reset was unnecessary, right. (commit log only mentions
> adding missing resets).
The reset has been moved into maybe_wipe_obj_freeptr(). I'll mention
it in the changelog in v2.
Thanks!