linux-hardening - Re: [PATCH 3/6] slab: Provide functional __alloc_size() hints to kmalloc

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Date:   Thu, 3 Nov 2022 23:16:53 +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 3/6] slab: Provide functional __alloc_size() hints to
 kmalloc_trace*()

On Tue, Nov 01, 2022 at 03:33:11PM -0700, Kees Cook wrote:
> Since GCC cannot apply the __alloc_size attributes to inlines[1], all
> allocator inlines need to explicitly call into extern functions that
> contain a size argument. Provide these wrappers that end up just
> ignoring the size argument for the actual allocation.
> 
> This allows CONFIG_FORTIFY_SOURCE=y to see all various dynamic allocation
> sizes under GCC 12+ and all supported Clang versions.
> 
> [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 |  8 ++++++--
>  mm/slab_common.c     | 14 ++++++++++++++
>  2 files changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 970e9504949e..051d86ca31a8 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -442,6 +442,8 @@ static_assert(PAGE_SHIFT <= 20);
>  
>  void *__kmalloc(size_t size, gfp_t flags) __assume_kmalloc_alignment __alloc_size(1);
>  void *kmem_cache_alloc(struct kmem_cache *s, gfp_t flags) __assume_slab_alignment __malloc;
> +void *kmem_cache_alloc_sized(struct kmem_cache *s, gfp_t flags, size_t size)
> +			     __assume_slab_alignment __alloc_size(3);
>  void *kmem_cache_alloc_lru(struct kmem_cache *s, struct list_lru *lru,
>  			   gfp_t gfpflags) __assume_slab_alignment __malloc;
>  void kmem_cache_free(struct kmem_cache *s, void *objp);
> @@ -469,6 +471,8 @@ void *__kmalloc_node(size_t size, gfp_t flags, int node) __assume_kmalloc_alignm
>  							 __alloc_size(1);
>  void *kmem_cache_alloc_node(struct kmem_cache *s, gfp_t flags, int node) __assume_slab_alignment
>  									 __malloc;
> +void *kmem_cache_alloc_node_sized(struct kmem_cache *s, gfp_t flags, int node, size_t size)
> +				  __assume_slab_alignment __alloc_size(4);
>  
>  #ifdef CONFIG_TRACING
>  void *kmalloc_trace(struct kmem_cache *s, gfp_t flags, size_t size)
> @@ -482,7 +486,7 @@ void *kmalloc_node_trace(struct kmem_cache *s, gfp_t gfpflags,
>  static __always_inline __alloc_size(3)
>  void *kmalloc_trace(struct kmem_cache *s, gfp_t flags, size_t size)
>  {
> -	void *ret = kmem_cache_alloc(s, flags);
> +	void *ret = kmem_cache_alloc_sized(s, flags, size);
>  
>  	ret = kasan_kmalloc(s, ret, size, flags);
>  	return ret;
> @@ -492,7 +496,7 @@ static __always_inline __alloc_size(4)
>  void *kmalloc_node_trace(struct kmem_cache *s, gfp_t gfpflags,
>  			 int node, size_t size)
>  {
> -	void *ret = kmem_cache_alloc_node(s, gfpflags, node);
> +	void *ret = kmem_cache_alloc_node_sized(s, gfpflags, node, size);
>  
>  	ret = kasan_kmalloc(s, ret, size, gfpflags);
>  	return ret;
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 33b1886b06eb..5fa547539a6a 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1457,6 +1457,20 @@ size_t ksize(const void *objp)
>  }
>  EXPORT_SYMBOL(ksize);
>  
> +/* Wrapper so __alloc_size() can see the actual allocation size. */
> +void *kmem_cache_alloc_sized(struct kmem_cache *s, gfp_t flags, size_t size)
> +{
> +	return kmem_cache_alloc(s, flags);
> +}
> +EXPORT_SYMBOL(kmem_cache_alloc_sized);
> +
> +/* Wrapper so __alloc_size() can see the actual allocation size. */
> +void *kmem_cache_alloc_node_sized(struct kmem_cache *s, gfp_t flags, int node, size_t size)
> +{
> +	return kmem_cache_alloc_node(s, flags, node);
> +}
> +EXPORT_SYMBOL(kmem_cache_alloc_node_sized);

The reason that we have two implementations of kmalloc_trace*
depending on CONFIG_TRACING is to save additional function call when
CONFIG_TRACING is not set.

With this patch there is no reason to keep both.
So let's drop #ifdefs and use single implementation in mm/slab_common.c.

Thanks!

>  /* Tracepoints definitions. */
>  EXPORT_TRACEPOINT_SYMBOL(kmalloc);
>  EXPORT_TRACEPOINT_SYMBOL(kmem_cache_alloc);
> -- 
> 2.34.1
> 

-- 
Hyeonggon