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authorVlastimil Babka <vbabka@suse.cz>2023-07-11 12:24:59 +0200
committerVlastimil Babka <vbabka@suse.cz>2023-07-14 09:52:37 +0200
commitb06952cdbc7f01a761eb95e8b899633f4ae9334e (patch)
treeb4a31c4d7c168305329caedc893b0d3e4054b9a5 /mm/slub.c
parentmm/slub: refactor freelist to use custom type (diff)
downloadlinux-b06952cdbc7f01a761eb95e8b899633f4ae9334e.tar.xz
linux-b06952cdbc7f01a761eb95e8b899633f4ae9334e.zip
mm/slub: remove redundant kasan_reset_tag() from freelist_ptr calculations
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@suse.cz> Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com> Acked-by: Kees Cook <keescook@chromium.org>
Diffstat (limited to 'mm/slub.c')
-rw-r--r--mm/slub.c22
1 files 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