Commit d36a63a943e3 ("kasan, slub: fix more conflicts with
CONFIG_SLAB_FREELIST_HARDENED") has introduced kasan_reset_tags() to
freelist_ptr() encoding/decoding when CONFIG_SLAB_FREELIST_HARDENED is
enabled to resolve issues when passing tagged or untagged pointers
inconsistently would lead to incorrect calculations.
Later, commit aa1ef4d7b3f6 ("kasan, mm: reset tags when accessing
metadata") made sure all pointers have tags reset regardless of
CONFIG_SLAB_FREELIST_HARDENED, because there was no other way to access
the freepointer metadata safely with hw tag-based KASAN.
Therefore the kasan_reset_tag() usage in freelist_ptr_encode()/decode()
is now redundant, as all callers use kasan_reset_tag() unconditionally
when constructing ptr_addr. Remove the redundant calls and simplify the
code and remove obsolete comments.
Also in freelist_ptr_encode() introduce an 'encoded' variable to make
the lines shorter and make it similar to the _decode() one.
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
These 2 patches build on top of:
https://lore.kernel.org/all/20230704135834.3884421-1-matteorizzo@xxxxxxxxxx/
mm/slub.c | 22 ++++++----------------
1 file changed, 6 insertions(+), 16 deletions(-)
diff --git a/mm/slub.c b/mm/slub.c
index f8cc47eff742..07edad305512 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -374,22 +374,14 @@ typedef struct { unsigned long v; } freeptr_t;
static inline freeptr_t freelist_ptr_encode(const struct kmem_cache *s,
void *ptr, unsigned long ptr_addr)
{
+ unsigned long encoded;
+
#ifdef CONFIG_SLAB_FREELIST_HARDENED
- /*
- * When CONFIG_KASAN_SW/HW_TAGS is enabled, ptr_addr might be tagged.
- * Normally, this doesn't cause any issues, as both set_freepointer()
- * and get_freepointer() are called with a pointer with the same tag.
- * However, there are some issues with CONFIG_SLUB_DEBUG code. For
- * example, when __free_slub() iterates over objects in a cache, it
- * passes untagged pointers to check_object(). check_object() in turns
- * calls get_freepointer() with an untagged pointer, which causes the
- * freepointer to be restored incorrectly.
- */
- return (freeptr_t){.v = (unsigned long)ptr ^ s->random ^
- swab((unsigned long)kasan_reset_tag((void *)ptr_addr))};
+ encoded = (unsigned long)ptr ^ s->random ^ swab(ptr_addr);
#else
- return (freeptr_t){.v = (unsigned long)ptr};
+ encoded = (unsigned long)ptr;
#endif
+ return (freeptr_t){.v = encoded};
}
static inline void *freelist_ptr_decode(const struct kmem_cache *s,
@@ -398,9 +390,7 @@ static inline void *freelist_ptr_decode(const struct kmem_cache *s,
void *decoded;
#ifdef CONFIG_SLAB_FREELIST_HARDENED
- /* See the comment in freelist_ptr_encode */
- decoded = (void *)(ptr.v ^ s->random ^
- swab((unsigned long)kasan_reset_tag((void *)ptr_addr)));
+ decoded = (void *)(ptr.v ^ s->random ^ swab(ptr_addr));
#else
decoded = (void *)ptr.v;
#endif
--
2.41.0
