Re: [PATCH 01/12] kasan, mm: don't save alloc stacks twice

[Andrey Konovalov <andreyknvl@google.com>]

On Tue, Feb 2, 2021 at 5:06 PM Marco Elver <elver@google.com> wrote:
>
> On Mon, Feb 01, 2021 at 08:43PM +0100, Andrey Konovalov wrote:
> > Currently KASAN saves allocation stacks in both kasan_slab_alloc() and
> > kasan_kmalloc() annotations. This patch changes KASAN to save allocation
> > stacks for slab objects from kmalloc caches in kasan_kmalloc() only,
> > and stacks for other slab objects in kasan_slab_alloc() only.
> >
> > This change requires ____kasan_kmalloc() knowing whether the object
> > belongs to a kmalloc cache. This is implemented by adding a flag field
> > to the kasan_info structure. That flag is only set for kmalloc caches
> > via a new kasan_cache_create_kmalloc() annotation.
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
>
> Reviewed-by: Marco Elver <elver@google.com>
>
> > ---
> >  include/linux/kasan.h |  9 +++++++++
> >  mm/kasan/common.c     | 18 ++++++++++++++----
> >  mm/slab_common.c      |  1 +
> >  3 files changed, 24 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> > index 6d8f3227c264..2d5de4092185 100644
> > --- a/include/linux/kasan.h
> > +++ b/include/linux/kasan.h
> > @@ -83,6 +83,7 @@ static inline void kasan_disable_current(void) {}
> >  struct kasan_cache {
> >       int alloc_meta_offset;
> >       int free_meta_offset;
> > +     bool is_kmalloc;
> >  };
> >
> >  #ifdef CONFIG_KASAN_HW_TAGS
> > @@ -143,6 +144,13 @@ static __always_inline void kasan_cache_create(struct kmem_cache *cache,
> >               __kasan_cache_create(cache, size, flags);
> >  }
> >
> > +void __kasan_cache_create_kmalloc(struct kmem_cache *cache);
> > +static __always_inline void kasan_cache_create_kmalloc(struct kmem_cache *cache)
> > +{
> > +     if (kasan_enabled())
> > +             __kasan_cache_create_kmalloc(cache);
> > +}
> > +
> >  size_t __kasan_metadata_size(struct kmem_cache *cache);
> >  static __always_inline size_t kasan_metadata_size(struct kmem_cache *cache)
> >  {
> > @@ -278,6 +286,7 @@ static inline void kasan_free_pages(struct page *page, unsigned int order) {}
> >  static inline void kasan_cache_create(struct kmem_cache *cache,
> >                                     unsigned int *size,
> >                                     slab_flags_t *flags) {}
> > +static inline void kasan_cache_create_kmalloc(struct kmem_cache *cache) {}
> >  static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
> >  static inline void kasan_poison_slab(struct page *page) {}
> >  static inline void kasan_unpoison_object_data(struct kmem_cache *cache,
> > diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> > index fe852f3cfa42..374049564ea3 100644
> > --- a/mm/kasan/common.c
> > +++ b/mm/kasan/common.c
> > @@ -210,6 +210,11 @@ void __kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
> >               *size = optimal_size;
> >  }
> >
> > +void __kasan_cache_create_kmalloc(struct kmem_cache *cache)
> > +{
> > +     cache->kasan_info.is_kmalloc = true;
> > +}
> > +
> >  size_t __kasan_metadata_size(struct kmem_cache *cache)
> >  {
> >       if (!kasan_stack_collection_enabled())
> > @@ -394,17 +399,22 @@ void __kasan_slab_free_mempool(void *ptr, unsigned long ip)
> >       }
> >  }
> >
> > -static void set_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
> > +static void set_alloc_info(struct kmem_cache *cache, void *object,
> > +                             gfp_t flags, bool kmalloc)
> >  {
> >       struct kasan_alloc_meta *alloc_meta;
> >
> > +     /* Don't save alloc info for kmalloc caches in kasan_slab_alloc(). */
> > +     if (cache->kasan_info.is_kmalloc && !kmalloc)
> > +             return;
> > +
> >       alloc_meta = kasan_get_alloc_meta(cache, object);
> >       if (alloc_meta)
> >               kasan_set_track(&alloc_meta->alloc_track, flags);
> >  }
> >
> >  static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
> > -                             size_t size, gfp_t flags, bool keep_tag)
> > +                             size_t size, gfp_t flags, bool kmalloc)
> >  {
> >       unsigned long redzone_start;
> >       unsigned long redzone_end;
> > @@ -423,7 +433,7 @@ static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
> >                               KASAN_GRANULE_SIZE);
> >       redzone_end = round_up((unsigned long)object + cache->object_size,
> >                               KASAN_GRANULE_SIZE);
> > -     tag = assign_tag(cache, object, false, keep_tag);
> > +     tag = assign_tag(cache, object, false, kmalloc);
> >
> >       /* Tag is ignored in set_tag without CONFIG_KASAN_SW/HW_TAGS */
> >       kasan_unpoison(set_tag(object, tag), size);
> > @@ -431,7 +441,7 @@ static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
> >                          KASAN_KMALLOC_REDZONE);
> >
> >       if (kasan_stack_collection_enabled())
> > -             set_alloc_info(cache, (void *)object, flags);
> > +             set_alloc_info(cache, (void *)object, flags, kmalloc);
>
> It doesn't bother me too much, but: 'bool kmalloc' shadows function
> 'kmalloc' so this is technically fine, but using 'kmalloc' as the
> variable name here might be confusing and there is a small chance it
> might cause problems in a future refactor.

Good point. Does "is_kmalloc" sound good?

Thanks!