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 <dvyu...@google.com>
> Signed-off-by: Andrey Konovalov <andreyk...@google.com>
Acked-by: Vlastimil Babka <vba...@suse.cz>
> ---
> 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 */
>
