On Wed, 5 Jul 2023 at 14:44, <andrey.konovalov@xxxxxxxxx> wrote:
>
> From: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
>
> Commit 946fa0dbf2d8 ("mm/slub: extend redzone check to extra allocated
> kmalloc space than requested") added precise kmalloc redzone poisoning
> to the slub_debug functionality.
>
> However, this commit didn't account for HW_TAGS KASAN fully initializing
> the object via its built-in memory initialization feature. Even though
> HW_TAGS KASAN memory initialization contains special memory initialization
> handling for when slub_debug is enabled, it does not account for in-object
> slub_debug redzones. As a result, HW_TAGS KASAN can overwrite these
> redzones and cause false-positive slub_debug reports.
>
> To fix the issue, avoid HW_TAGS KASAN memory initialization when slub_debug
> is enabled altogether. Implement this by moving the __slub_debug_enabled
> check to slab_post_alloc_hook. Common slab code seems like a more
> appropriate place for a slub_debug check anyway.
>
> Fixes: 946fa0dbf2d8 ("mm/slub: extend redzone check to extra allocated kmalloc space than requested")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Reported-by: Mark Rutland <mark.rutland@xxxxxxx>
Is it fixing this issue:
https://lore.kernel.org/all/20230628154714.GB22090@willie-the-truck/
Or some other issue?
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Other than the question above, it looks sane:
Acked-by: Marco Elver <elver@xxxxxxxxxx>
> ---
> mm/kasan/kasan.h | 12 ------------
> mm/slab.h | 16 ++++++++++++++--
> 2 files changed, 14 insertions(+), 14 deletions(-)
>
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index b799f11e45dc..2e973b36fe07 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -466,18 +466,6 @@ static inline void kasan_unpoison(const void *addr, size_t size, bool init)
>
> if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK))
> return;
> - /*
> - * Explicitly initialize the memory with the precise object size to
> - * avoid overwriting the slab redzone. This disables initialization in
> - * the arch code and may thus lead to performance penalty. This penalty
> - * does not affect production builds, as slab redzones are not enabled
> - * there.
> - */
> - if (__slub_debug_enabled() &&
> - init && ((unsigned long)size & KASAN_GRANULE_MASK)) {
> - init = false;
> - memzero_explicit((void *)addr, size);
> - }
> size = round_up(size, KASAN_GRANULE_SIZE);
>
> hw_set_mem_tag_range((void *)addr, size, tag, init);
> diff --git a/mm/slab.h b/mm/slab.h
> index 6a5633b25eb5..9c0e09d0f81f 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -723,6 +723,7 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s,
> unsigned int orig_size)
> {
> unsigned int zero_size = s->object_size;
> + bool kasan_init = init;
> size_t i;
>
> flags &= gfp_allowed_mask;
> @@ -739,6 +740,17 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s,
> (s->flags & SLAB_KMALLOC))
> zero_size = orig_size;
>
> + /*
> + * When slub_debug is enabled, avoid memory initialization integrated
> + * into KASAN and instead zero out the memory via the memset below with
> + * the proper size. Otherwise, KASAN might overwrite SLUB redzones and
> + * cause false-positive reports. This does not lead to a performance
> + * penalty on production builds, as slub_debug is not intended to be
> + * enabled there.
> + */
> + if (__slub_debug_enabled())
> + kasan_init = false;
> +
> /*
> * As memory initialization might be integrated into KASAN,
> * kasan_slab_alloc and initialization memset must be
> @@ -747,8 +759,8 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s,
> * As p[i] might get tagged, memset and kmemleak hook come after KASAN.
> */
> for (i = 0; i < size; i++) {
> - p[i] = kasan_slab_alloc(s, p[i], flags, init);
> - if (p[i] && init && !kasan_has_integrated_init())
> + p[i] = kasan_slab_alloc(s, p[i], flags, kasan_init);
> + if (p[i] && init && (!kasan_init || !kasan_has_integrated_init()))
> memset(p[i], 0, zero_size);
> kmemleak_alloc_recursive(p[i], s->object_size, 1,
> s->flags, flags);
> --
> 2.25.1
>
