Re: [PATCH 3/6] slab: Provide functional __alloc_size() hints to kmalloc_trace*()

[Kees Cook]

On Thu, Nov 03, 2022 at 11:16:53PM +0900, Hyeonggon Yoo wrote:
> 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@xxxxxxx>
> > Cc: Christoph Lameter <cl@xxxxxxxxx>
> > Cc: Pekka Enberg <penberg@xxxxxxxxxx>
> > Cc: David Rientjes <rientjes@xxxxxxxxxx>
> > Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
> > Cc: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
> > Cc: linux-mm@xxxxxxxxx
> > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > ---
> >  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.

Okay, I'll respin...

-- 
Kees Cook