Re: [PATCH v9 13/44] kasan: hide invalid free check implementation

[Alexander Potapenko]

On Tue, Nov 10, 2020 at 11:11 PM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
>
> This is a preparatory commit for the upcoming addition of a new hardware
> tag-based (MTE-based) KASAN mode.
>
> For software KASAN modes the check is based on the value in the shadow
> memory. Hardware tag-based KASAN won't be using shadow, so hide the
> implementation of the check in check_invalid_free().
>
> Also simplify the code for software tag-based mode.
>
> No functional changes for software modes.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
> Reviewed-by: Marco Elver <elver@xxxxxxxxxx>
Reviewed-by: Alexander Potapenko <glider@xxxxxxxxxx>

> ---
> Change-Id: I5fae9531c9fc948eb4d4e0c589744032fc5a0789
> ---
>  mm/kasan/common.c  | 19 +------------------
>  mm/kasan/generic.c |  7 +++++++
>  mm/kasan/kasan.h   |  2 ++
>  mm/kasan/sw_tags.c |  9 +++++++++
>  4 files changed, 19 insertions(+), 18 deletions(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 123abfb760d4..543e6bf2168f 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -272,25 +272,9 @@ void * __must_check kasan_init_slab_obj(struct kmem_cache *cache,
>         return (void *)object;
>  }
>
> -static inline bool shadow_invalid(u8 tag, s8 shadow_byte)
> -{
> -       if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> -               return shadow_byte < 0 ||
> -                       shadow_byte >= KASAN_GRANULE_SIZE;
> -
> -       /* else CONFIG_KASAN_SW_TAGS: */
> -       if ((u8)shadow_byte == KASAN_TAG_INVALID)
> -               return true;
> -       if ((tag != KASAN_TAG_KERNEL) && (tag != (u8)shadow_byte))
> -               return true;
> -
> -       return false;
> -}
> -
>  static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
>                               unsigned long ip, bool quarantine)
>  {
> -       s8 shadow_byte;
>         u8 tag;
>         void *tagged_object;
>         unsigned long rounded_up_size;
> @@ -309,8 +293,7 @@ static bool __kasan_slab_free(struct kmem_cache *cache, void *object,
>         if (unlikely(cache->flags & SLAB_TYPESAFE_BY_RCU))
>                 return false;
>
> -       shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
> -       if (shadow_invalid(tag, shadow_byte)) {
> +       if (check_invalid_free(tagged_object)) {
>                 kasan_report_invalid_free(tagged_object, ip);
>                 return true;
>         }
> diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> index ec4417156943..e1af3b6c53b8 100644
> --- a/mm/kasan/generic.c
> +++ b/mm/kasan/generic.c
> @@ -187,6 +187,13 @@ bool check_memory_region(unsigned long addr, size_t size, bool write,
>         return check_memory_region_inline(addr, size, write, ret_ip);
>  }
>
> +bool check_invalid_free(void *addr)
> +{
> +       s8 shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(addr));
> +
> +       return shadow_byte < 0 || shadow_byte >= KASAN_GRANULE_SIZE;
> +}
> +
>  void kasan_cache_shrink(struct kmem_cache *cache)
>  {
>         quarantine_remove_cache(cache);
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 1865bb92d47a..3eff57e71ff5 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -164,6 +164,8 @@ void kasan_poison_memory(const void *address, size_t size, u8 value);
>  bool check_memory_region(unsigned long addr, size_t size, bool write,
>                                 unsigned long ret_ip);
>
> +bool check_invalid_free(void *addr);
> +
>  void *find_first_bad_addr(void *addr, size_t size);
>  const char *get_bug_type(struct kasan_access_info *info);
>
> diff --git a/mm/kasan/sw_tags.c b/mm/kasan/sw_tags.c
> index 4bdd7dbd6647..b2638c2cd58a 100644
> --- a/mm/kasan/sw_tags.c
> +++ b/mm/kasan/sw_tags.c
> @@ -121,6 +121,15 @@ bool check_memory_region(unsigned long addr, size_t size, bool write,
>         return true;
>  }
>
> +bool check_invalid_free(void *addr)
> +{
> +       u8 tag = get_tag(addr);
> +       u8 shadow_byte = READ_ONCE(*(u8 *)kasan_mem_to_shadow(reset_tag(addr)));
> +
> +       return (shadow_byte == KASAN_TAG_INVALID) ||
> +               (tag != KASAN_TAG_KERNEL && tag != shadow_byte);
> +}
> +
>  #define DEFINE_HWASAN_LOAD_STORE(size)                                 \
>         void __hwasan_load##size##_noabort(unsigned long addr)          \
>         {                                                               \
> --
> 2.29.2.222.g5d2a92d10f8-goog
>


-- 
Alexander Potapenko
Software Engineer

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