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Fri, 18 Nov 2022 03:36:19 -0800 (PST) Date: Fri, 18 Nov 2022 20:36:13 +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, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH v2 2/2] slab: Remove special-casing of const 0 size allocations Message-ID: References: <20221118034713.gonna.754-kees@kernel.org> <20221118035200.1269184-2-keescook@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221118035200.1269184-2-keescook@chromium.org> ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=FSxO4upC; spf=pass (imf03.hostedemail.com: domain of 42.hyeyoo@gmail.com designates 209.85.216.50 as permitted sender) smtp.mailfrom=42.hyeyoo@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Seal: i=1; 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dmarc=pass (policy=none) header.from=gmail.com X-Rspamd-Server: rspam02 X-Rspam-User: X-Stat-Signature: n3zdi9amfm5qp9us8i1so5uhwxbkn3t6 X-Rspamd-Queue-Id: 3F40320009 X-HE-Tag: 1668771381-645046 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 Thu, Nov 17, 2022 at 07:51:59PM -0800, 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 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 Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com> -- Thanks, Hyeonggon