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 <vbabka@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: linux-mm@kvack.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 8a25d1b2e420329b063ea6e835e0deab59746b9c..134cc05e57453e4bf1dab2eb8788c9671b4e8ae0 100644 (file)
--- 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);