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Thu, 03 Nov 2022 07:01:01 -0700 (PDT) Date: Thu, 3 Nov 2022 23:00:53 +0900 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> To: Kees Cook Cc: Vlastimil Babka , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Roman Gushchin , linux-mm@kvack.org, David Gow , Rasmus Villemoes , Guenter Roeck , Andy Shevchenko , Paolo Abeni , Geert Uytterhoeven , Nathan Chancellor , Nick Desaulniers , Tom Rix , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org, llvm@lists.linux.dev Subject: Re: [PATCH 2/6] slab: Remove special-casing of const 0 size allocations Message-ID: References: <20221101222520.never.109-kees@kernel.org> <20221101223321.1326815-2-keescook@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221101223321.1326815-2-keescook@chromium.org> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1667484063; a=rsa-sha256; cv=none; b=U+6jaT4iqyBEXu560+UHSpl0+Fa1v0jGVmT6Eo1u5nlfHNA4Jfcz+YuZ3oSt1NKpJt2NIk boyBDilEwlxF0gOwy4n9yHv49cJyaV/f3Q8SUQndQyvi/+sIcVjmuFMAujPEQ8wmzn1GfX HUQrpM6TwoPynO/AhlO4/h/CR++g7C4= ARC-Authentication-Results: i=1; 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dkim=pass header.d=gmail.com header.s=20210112 header.b=HSYM5aB4; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf10.hostedemail.com: domain of 42.hyeyoo@gmail.com designates 209.85.216.54 as permitted sender) smtp.mailfrom=42.hyeyoo@gmail.com X-HE-Tag: 1667484063-127809 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Nov 01, 2022 at 03:33:10PM -0700, Kees Cook wrote: > 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 e08fe7978b5c..970e9504949e 100644 > --- a/include/linux/slab.h > +++ b/include/linux/slab.h > @@ -562,17 +562,13 @@ 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); > @@ -592,17 +588,13 @@ 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 Looks good to me. Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> -- Thanks, Hyeonggon