From b06952cdbc7f01a761eb95e8b899633f4ae9334e Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Tue, 11 Jul 2023 12:24:59 +0200 Subject: 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 Reviewed-by: Andrey Konovalov Acked-by: Kees Cook --- 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 -- cgit v1.2.3