Re: [PATCH v5 3/4] mm: kasan: Add free_meta size info in struct kasan_cache

[Andrey Konovalov <andreyknvl@gmail.com>]

On Wed, Sep 7, 2022 at 9:11 AM Feng Tang <feng.tang@intel.com> wrote:
>
> When kasan is enabled for slab/slub, it may save kasan' free_meta
> data in the former part of slab object data area in slab object
> free path, which works fine.
>
> There is ongoing effort to extend slub's debug function which will
> redzone the latter part of kmalloc object area, and when both of
> the debug are enabled, there is possible conflict, especially when
> the kmalloc object has small size, as caught by 0Day bot [1]
>
> For better information for slab/slub, add free_meta's data size
> into 'struct kasan_cache', so that its users can take right action
> to avoid data conflict.
>
> [1]. https://lore.kernel.org/lkml/YuYm3dWwpZwH58Hu@xsang-OptiPlex-9020/
> Reported-by: kernel test robot <oliver.sang@intel.com>
> Signed-off-by: Feng Tang <feng.tang@intel.com>
> Acked-by: Dmitry Vyukov <dvyukov@google.com>
> ---
>  include/linux/kasan.h | 2 ++
>  mm/kasan/common.c     | 2 ++
>  2 files changed, 4 insertions(+)
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index b092277bf48d..293bdaa0ba09 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -100,6 +100,8 @@ static inline bool kasan_has_integrated_init(void)
>  struct kasan_cache {
>         int alloc_meta_offset;
>         int free_meta_offset;
> +       /* size of free_meta data saved in object's data area */
> +       int free_meta_size_in_object;

I thinks calling this field free_meta_size is clear enough. Thanks!

>         bool is_kmalloc;
>  };
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 69f583855c8b..762ae7a7793e 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -201,6 +201,8 @@ void __kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
>                         cache->kasan_info.free_meta_offset = KASAN_NO_FREE_META;
>                         *size = ok_size;
>                 }
> +       } else {
> +               cache->kasan_info.free_meta_size_in_object = sizeof(struct kasan_free_meta);
>         }
>
>         /* Calculate size with optimal redzone. */
> --
> 2.34.1
>
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