From: Andrey Konovalov andreyknvl@google.com
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@vger.kernel.org Reported-by: Mark Rutland mark.rutland@arm.com Signed-off-by: Andrey Konovalov andreyknvl@google.com --- 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);