From 6fa57d78aa7f212fd7c0de70f5756e18513dcdcf Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Thu, 17 Nov 2022 19:51:59 -0800 Subject: [PATCH] slab: Remove special-casing of const 0 size allocations Passing a constant-0 size allocation into kmalloc() or kmalloc_node() does not need to be a fast-path operation, so the static return value can be removed entirely. This makes sure that all paths through the inlines result in a full extern function call, where __alloc_size() hints will actually be seen[1] by GCC. (A constant return value of 0 means the "0" allocation size won't be propagated by the inline.) [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96503 Cc: Vlastimil Babka Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Andrew Morton Cc: Roman Gushchin Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com> Cc: linux-mm@kvack.org Signed-off-by: Kees Cook Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> Signed-off-by: Vlastimil Babka --- include/linux/slab.h | 12 ++---------- 1 file changed, 2 insertions(+), 10 deletions(-) diff --git a/include/linux/slab.h b/include/linux/slab.h index 8a25d1b..134cc05 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -539,17 +539,13 @@ void *kmalloc_large_node(size_t size, gfp_t flags, int node) __assume_page_align #ifndef CONFIG_SLOB static __always_inline __alloc_size(1) void *kmalloc(size_t size, gfp_t flags) { - if (__builtin_constant_p(size)) { + if (__builtin_constant_p(size) && size) { unsigned int index; if (size > KMALLOC_MAX_CACHE_SIZE) return kmalloc_large(size, flags); index = kmalloc_index(size); - - if (!index) - return ZERO_SIZE_PTR; - return kmalloc_trace( kmalloc_caches[kmalloc_type(flags)][index], flags, size); @@ -569,17 +565,13 @@ static __always_inline __alloc_size(1) void *kmalloc(size_t size, gfp_t flags) #ifndef CONFIG_SLOB static __always_inline __alloc_size(1) void *kmalloc_node(size_t size, gfp_t flags, int node) { - if (__builtin_constant_p(size)) { + if (__builtin_constant_p(size) && size) { unsigned int index; if (size > KMALLOC_MAX_CACHE_SIZE) return kmalloc_large_node(size, flags, node); index = kmalloc_index(size); - - if (!index) - return ZERO_SIZE_PTR; - return kmalloc_node_trace( kmalloc_caches[kmalloc_type(flags)][index], flags, node, size); -- 2.7.4