Re: [PATCH v3 12/39] kasan: hide invalid free check implementation

elver
2020-10-01T17:41:12Z

On Fri, Sep 25, 2020 at 12:50AM +0200, Andrey Konovalov 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@google.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>

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

> ---
> 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) \
> { \
> --
> 2.28.0.681.g6f77f65b4e-goog
>