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Date: Thu, 3 Nov 2022 23:00:53 +0900 From: Hyeonggon Yoo <42.hyeyoo@...il.com> To: Kees Cook <keescook@...omium.org> Cc: Vlastimil Babka <vbabka@...e.cz>, Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, Andrew Morton <akpm@...ux-foundation.org>, Roman Gushchin <roman.gushchin@...ux.dev>, linux-mm@...ck.org, David Gow <davidgow@...gle.com>, Rasmus Villemoes <rasmus.villemoes@...vas.dk>, Guenter Roeck <linux@...ck-us.net>, Andy Shevchenko <andriy.shevchenko@...el.com>, Paolo Abeni <pabeni@...hat.com>, Geert Uytterhoeven <geert@...ux-m68k.org>, Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org, llvm@...ts.linux.dev Subject: Re: [PATCH 2/6] slab: Remove special-casing of const 0 size allocations 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 <vbabka@...e.cz> > Cc: Christoph Lameter <cl@...ux.com> > Cc: Pekka Enberg <penberg@...nel.org> > Cc: David Rientjes <rientjes@...gle.com> > Cc: Joonsoo Kim <iamjoonsoo.kim@....com> > Cc: Andrew Morton <akpm@...ux-foundation.org> > Cc: Roman Gushchin <roman.gushchin@...ux.dev> > Cc: Hyeonggon Yoo <42.hyeyoo@...il.com> > Cc: linux-mm@...ck.org > Signed-off-by: Kees Cook <keescook@...omium.org> > --- > 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@...il.com> -- Thanks, Hyeonggon
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