Re: [PATCH mm] kasan: untag addresses for KFENCE

[Marco Elver <elver@google.com>]

On Fri, 29 Jan 2021 at 19:50, Andrey Konovalov <andreyknvl@google.com> wrote:
>
> KFENCE annotations operate on untagged addresses.
>
> Untag addresses in KASAN runtime where they might be tagged.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

Reviewed-by: Marco Elver <elver@google.com>

Thank you!

> ---
>
> This can be squashed into:
>
> revert kasan-remove-kfence-leftovers
> kfence, kasan: make KFENCE compatible with KASA
>
> ---
>  mm/kasan/common.c |  2 +-
>  mm/kasan/kasan.h  | 12 +++++++++---
>  2 files changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index a390fae9d64b..fe852f3cfa42 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -416,7 +416,7 @@ static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
>         if (unlikely(object == NULL))
>                 return NULL;
>
> -       if (is_kfence_address(object))
> +       if (is_kfence_address(kasan_reset_tag(object)))
>                 return (void *)object;
>
>         redzone_start = round_up((unsigned long)(object + size),
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 11c6e3650468..4fb8106f8e31 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -320,22 +320,28 @@ static inline u8 kasan_random_tag(void) { return 0; }
>
>  static inline void kasan_poison(const void *address, size_t size, u8 value)
>  {
> +       address = kasan_reset_tag(address);
> +
>         /* Skip KFENCE memory if called explicitly outside of sl*b. */
>         if (is_kfence_address(address))
>                 return;
>
> -       hw_set_mem_tag_range(kasan_reset_tag(address),
> +       hw_set_mem_tag_range((void *)address,
>                         round_up(size, KASAN_GRANULE_SIZE), value);
>  }
>
>  static inline void kasan_unpoison(const void *address, size_t size)
>  {
> +       u8 tag = get_tag(address);
> +
> +       address = kasan_reset_tag(address);
> +
>         /* Skip KFENCE memory if called explicitly outside of sl*b. */
>         if (is_kfence_address(address))
>                 return;
>
> -       hw_set_mem_tag_range(kasan_reset_tag(address),
> -                       round_up(size, KASAN_GRANULE_SIZE), get_tag(address));
> +       hw_set_mem_tag_range((void *)address,
> +                       round_up(size, KASAN_GRANULE_SIZE), tag);
>  }
>
>  static inline bool kasan_byte_accessible(const void *addr)
> --
> 2.30.0.365.g02bc693789-goog
>