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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id u18-20020a170902e5d200b00186748fe6ccsm2276693plf.214.2022.11.17.19.52.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 17 Nov 2022 19:52:01 -0800 (PST) From: Kees Cook To: Vlastimil Babka Cc: Kees Cook , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH v2 2/2] slab: Remove special-casing of const 0 size allocations Date: Thu, 17 Nov 2022 19:51:59 -0800 Message-Id: <20221118035200.1269184-2-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20221118034713.gonna.754-kees@kernel.org> References: <20221118034713.gonna.754-kees@kernel.org> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2371; h=from:subject; bh=roYcJKurZ1Ad0yqcM7lIDF6nN9ThBNp448RHSIPN1YQ=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBjdwFfZxDK7dz/ZV+GaTBVSw8vUtlA5Z9lYg4dYZxh Ty2FDZaJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCY3cBXwAKCRCJcvTf3G3AJqB3D/ 92I8BImb3l8xp7T7C/K708vzPl/8cg+RmpOK6O8J9tqppE4B5M+SHEFIwWoiPjeSunOrFQ1DwDx9iZ u69XcPWH0rvSq6XgAS4hKKx3hUEvm7SfHhU/tMqqLMduePCXfFRifcSHXyzlATJyq8Wouii8HIaWo4 wpwfW8/jeErjZCLwxoOQFfOGSdrPISOLAvnII7IHQyoHd/w0i9HLKgRHtB8xe4z9u/B0X33zioYBJN J62lW7fZXdQJey/y170LtBc8LAW/Tw7fwE8hxD0AsbzzOxgYShr8FnHhwwcu0EC4j4GnYBuTey8frV EySb8ats1/DK6YD0YCsS5AQB+/IUERCstiwsPOzLUZgZd8bdSusAxZhGH4iBRRof6wHWXGNrjAVwhn 3Snjp2O9GaBhJWiCAuNsthWjbSRE5KabMfNcSbunYrPfQXvBCXcdsUNxPVAILnJG2RgVexDJXdP1+S 95JSp0z6rrSxXhOefnmqdca5dura/qA18ttumMHL/6w2vykG0fx4VLfMizyQgi3/yTu9ykaTsw77+6 /VGws3PmhsMC0P+WacnTRQRezboPQxcBN65EO5en1ch1MUhYl6E+/yKf9e6POwUMv6e8aO56MI3us9 C/kaUdRHt4xCbf/FUTiy6plT2ZYVnNHudbi4m84b46NIo/ancm1AFn8JpH1A== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 is in preparation for making 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 --- 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 9033937c758e..84be05208418 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -561,17 +561,13 @@ 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); @@ -591,17 +587,13 @@ 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); -- 2.34.1