Re: [PATCH v6 3/4] mm: kasan: Add free_meta size info in struct kasan_cache

[Andrey Konovalov <andreyknvl@gmail.com>]

On Sun, Sep 25, 2022 at 1:27 PM Feng Tang <feng.tang@intel.com> wrote:
>
> > [1] https://lore.kernel.org/linux-mm/c7b316d30d90e5947eb8280f4dc78856a49298cf.1662411799.git.andreyknvl@google.com/
>
> I noticed this has been merged to -mm tree's 'mm-everything' branch,
> so following is the patch againt that. Thanks!
>
> One thing I'm not very sure is, to check 'in-object' kasan's meta
> size, I didn't check 'alloc_meta_offset', as from the code reading
> the alloc_meta is never put inside slab object data area.

Yes, this is correct.

> Thanks,
> Feng
>
> ---8<---
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index d811b3d7d2a1..96c9d56e5510 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -302,7 +302,7 @@ static inline void kasan_unpoison_task_stack(struct task_struct *task) {}
>
>  #ifdef CONFIG_KASAN_GENERIC
>
> -size_t kasan_metadata_size(struct kmem_cache *cache);
> +size_t kasan_metadata_size(struct kmem_cache *cache, bool in_object);
>  slab_flags_t kasan_never_merge(void);
>  void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
>                         slab_flags_t *flags);
> @@ -315,7 +315,8 @@ void kasan_record_aux_stack_noalloc(void *ptr);
>  #else /* CONFIG_KASAN_GENERIC */
>
>  /* Tag-based KASAN modes do not use per-object metadata. */
> -static inline size_t kasan_metadata_size(struct kmem_cache *cache)
> +static inline size_t kasan_metadata_size(struct kmem_cache *cache,
> +                                               bool in_object)
>  {
>         return 0;
>  }
> diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> index d8b5590f9484..5a806f9b9466 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -450,15 +450,22 @@ void kasan_init_object_meta(struct kmem_cache *cache, const void *object)
>                 __memset(alloc_meta, 0, sizeof(*alloc_meta));
>  }
>
> -size_t kasan_metadata_size(struct kmem_cache *cache)
> +size_t kasan_metadata_size(struct kmem_cache *cache, bool in_object)
>  {
> +       struct kasan_cache *info = &cache->kasan_info ;
> +
>         if (!kasan_requires_meta())
>                 return 0;
> -       return (cache->kasan_info.alloc_meta_offset ?
> -               sizeof(struct kasan_alloc_meta) : 0) +
> -               ((cache->kasan_info.free_meta_offset &&
> -                 cache->kasan_info.free_meta_offset != KASAN_NO_FREE_META) ?
> -                sizeof(struct kasan_free_meta) : 0);
> +
> +       if (in_object)
> +               return (info->free_meta_offset ?
> +                       0 : sizeof(struct kasan_free_meta));
> +       else
> +               return (info->alloc_meta_offset ?
> +                       sizeof(struct kasan_alloc_meta) : 0) +
> +                       ((info->free_meta_offset &&
> +                       info->free_meta_offset != KASAN_NO_FREE_META) ?
> +                       sizeof(struct kasan_free_meta) : 0);
>  }
>
>  static void __kasan_record_aux_stack(void *addr, bool can_alloc)
> diff --git a/mm/slub.c b/mm/slub.c
> index ce8310e131b3..a75c21a0da8b 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -887,7 +887,7 @@ static void print_trailer(struct kmem_cache *s, struct slab *slab, u8 *p)
>         if (s->flags & SLAB_STORE_USER)
>                 off += 2 * sizeof(struct track);
>
> -       off += kasan_metadata_size(s);
> +       off += kasan_metadata_size(s, false);
>
>         if (off != size_from_object(s))
>                 /* Beginning of the filler is the free pointer */
> @@ -1042,7 +1042,7 @@ static int check_pad_bytes(struct kmem_cache *s, struct slab *slab, u8 *p)
>                 /* We also have user information there */
>                 off += 2 * sizeof(struct track);
>
> -       off += kasan_metadata_size(s);
> +       off += kasan_metadata_size(s, false);
>
>         if (size_from_object(s) == off)
>                 return 1;

Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>

Thanks!