On Mon, Feb 01, 2021 at 08:43PM +0100, Andrey Konovalov wrote:
> Currently KASAN saves allocation stacks in both kasan_slab_alloc() and
> kasan_kmalloc() annotations. This patch changes KASAN to save allocation
> stacks for slab objects from kmalloc caches in kasan_kmalloc() only,
> and stacks for other slab objects in kasan_slab_alloc() only.
>
> This change requires ____kasan_kmalloc() knowing whether the object
> belongs to a kmalloc cache. This is implemented by adding a flag field
> to the kasan_info structure. That flag is only set for kmalloc caches
> via a new kasan_cache_create_kmalloc() annotation.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Reviewed-by: Marco Elver <elver@xxxxxxxxxx>
> ---
> include/linux/kasan.h | 9 +++++++++
> mm/kasan/common.c | 18 ++++++++++++++----
> mm/slab_common.c | 1 +
> 3 files changed, 24 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 6d8f3227c264..2d5de4092185 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -83,6 +83,7 @@ static inline void kasan_disable_current(void) {}
> struct kasan_cache {
> int alloc_meta_offset;
> int free_meta_offset;
> + bool is_kmalloc;
> };
>
> #ifdef CONFIG_KASAN_HW_TAGS
> @@ -143,6 +144,13 @@ static __always_inline void kasan_cache_create(struct kmem_cache *cache,
> __kasan_cache_create(cache, size, flags);
> }
>
> +void __kasan_cache_create_kmalloc(struct kmem_cache *cache);
> +static __always_inline void kasan_cache_create_kmalloc(struct kmem_cache *cache)
> +{
> + if (kasan_enabled())
> + __kasan_cache_create_kmalloc(cache);
> +}
> +
> size_t __kasan_metadata_size(struct kmem_cache *cache);
> static __always_inline size_t kasan_metadata_size(struct kmem_cache *cache)
> {
> @@ -278,6 +286,7 @@ static inline void kasan_free_pages(struct page *page, unsigned int order) {}
> static inline void kasan_cache_create(struct kmem_cache *cache,
> unsigned int *size,
> slab_flags_t *flags) {}
> +static inline void kasan_cache_create_kmalloc(struct kmem_cache *cache) {}
> static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
> static inline void kasan_poison_slab(struct page *page) {}
> static inline void kasan_unpoison_object_data(struct kmem_cache *cache,
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index fe852f3cfa42..374049564ea3 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -210,6 +210,11 @@ void __kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
> *size = optimal_size;
> }
>
> +void __kasan_cache_create_kmalloc(struct kmem_cache *cache)
> +{
> + cache->kasan_info.is_kmalloc = true;
> +}
> +
> size_t __kasan_metadata_size(struct kmem_cache *cache)
> {
> if (!kasan_stack_collection_enabled())
> @@ -394,17 +399,22 @@ void __kasan_slab_free_mempool(void *ptr, unsigned long ip)
> }
> }
>
> -static void set_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
> +static void set_alloc_info(struct kmem_cache *cache, void *object,
> + gfp_t flags, bool kmalloc)
> {
> struct kasan_alloc_meta *alloc_meta;
>
> + /* Don't save alloc info for kmalloc caches in kasan_slab_alloc(). */
> + if (cache->kasan_info.is_kmalloc && !kmalloc)
> + return;
> +
> alloc_meta = kasan_get_alloc_meta(cache, object);
> if (alloc_meta)
> kasan_set_track(&alloc_meta->alloc_track, flags);
> }
>
> static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
> - size_t size, gfp_t flags, bool keep_tag)
> + size_t size, gfp_t flags, bool kmalloc)
> {
> unsigned long redzone_start;
> unsigned long redzone_end;
> @@ -423,7 +433,7 @@ static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
> KASAN_GRANULE_SIZE);
> redzone_end = round_up((unsigned long)object + cache->object_size,
> KASAN_GRANULE_SIZE);
> - tag = assign_tag(cache, object, false, keep_tag);
> + tag = assign_tag(cache, object, false, kmalloc);
>
> /* Tag is ignored in set_tag without CONFIG_KASAN_SW/HW_TAGS */
> kasan_unpoison(set_tag(object, tag), size);
> @@ -431,7 +441,7 @@ static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
> KASAN_KMALLOC_REDZONE);
>
> if (kasan_stack_collection_enabled())
> - set_alloc_info(cache, (void *)object, flags);
> + set_alloc_info(cache, (void *)object, flags, kmalloc);
It doesn't bother me too much, but: 'bool kmalloc' shadows function
'kmalloc' so this is technically fine, but using 'kmalloc' as the
variable name here might be confusing and there is a small chance it
might cause problems in a future refactor.
> return set_tag(object, tag);
> }
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 9aa3d2fe4c55..39d1a8ff9bb8 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -647,6 +647,7 @@ struct kmem_cache *__init create_kmalloc_cache(const char *name,
> panic("Out of memory when creating slab %s\n", name);
>
> create_boot_cache(s, name, size, flags, useroffset, usersize);
> + kasan_cache_create_kmalloc(s);
> list_add(&s->list, &slab_caches);
> s->refcount = 1;
> return s;
> --
> 2.30.0.365.g02bc693789-goog
>
