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>
Signed-off-by: Andrey Konovalov <andreyknvl@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
