On Mon, Feb 01, 2021 at 08:43PM +0100, Andrey Konovalov wrote:
> For allocations from kmalloc caches, kasan_kmalloc() always follows
> kasan_slab_alloc(). Currenly, both of them unpoison the whole object,
> which is unnecessary.
>
> This patch provides separate implementations for both annotations:
> kasan_slab_alloc() unpoisons the whole object, and kasan_kmalloc()
> only poisons the redzone.
>
> For generic KASAN, the redzone start might not be aligned to
> KASAN_GRANULE_SIZE. Therefore, the poisoning is split in two parts:
> kasan_poison_last_granule() poisons the unaligned part, and then
> kasan_poison() poisons the rest.
>
> This patch also clarifies alignment guarantees of each of the poisoning
> functions and drops the unnecessary round_up() call for redzone_end.
>
> With this change, the early SLUB cache annotation needs to be changed to
> kasan_slab_alloc(), as kasan_kmalloc() doesn't unpoison objects now.
> The number of poisoned bytes for objects in this cache stays the same, as
> kmem_cache_node->object_size is equal to sizeof(struct kmem_cache_node).
>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> ---
> mm/kasan/common.c | 93 +++++++++++++++++++++++++++++++----------------
> mm/kasan/kasan.h | 43 +++++++++++++++++++++-
> mm/kasan/shadow.c | 28 +++++++-------
> mm/slub.c | 3 +-
> 4 files changed, 119 insertions(+), 48 deletions(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 374049564ea3..128cb330ca73 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -278,21 +278,11 @@ void __kasan_poison_object_data(struct kmem_cache *cache, void *object)
> * based on objects indexes, so that objects that are next to each other
> * get different tags.
> */
> -static u8 assign_tag(struct kmem_cache *cache, const void *object,
> - bool init, bool keep_tag)
> +static u8 assign_tag(struct kmem_cache *cache, const void *object, bool init)
> {
> if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> return 0xff;
>
> - /*
> - * 1. When an object is kmalloc()'ed, two hooks are called:
> - * kasan_slab_alloc() and kasan_kmalloc(). We assign the
> - * tag only in the first one.
> - * 2. We reuse the same tag for krealloc'ed objects.
> - */
> - if (keep_tag)
> - return get_tag(object);
> -
> /*
> * If the cache neither has a constructor nor has SLAB_TYPESAFE_BY_RCU
> * set, assign a tag when the object is being allocated (init == false).
> @@ -325,7 +315,7 @@ void * __must_check __kasan_init_slab_obj(struct kmem_cache *cache,
> }
>
> /* Tag is ignored in set_tag() without CONFIG_KASAN_SW/HW_TAGS */
> - object = set_tag(object, assign_tag(cache, object, true, false));
> + object = set_tag(object, assign_tag(cache, object, true));
>
> return (void *)object;
> }
> @@ -413,12 +403,46 @@ static void set_alloc_info(struct kmem_cache *cache, void *object,
> kasan_set_track(&alloc_meta->alloc_track, flags);
> }
>
> +void * __must_check __kasan_slab_alloc(struct kmem_cache *cache,
> + void *object, gfp_t flags)
> +{
> + u8 tag;
> + void *tagged_object;
> +
> + if (gfpflags_allow_blocking(flags))
> + kasan_quarantine_reduce();
> +
> + if (unlikely(object == NULL))
> + return NULL;
> +
> + if (is_kfence_address(object))
> + return (void *)object;
> +
> + /*
> + * Generate and assign random tag for tag-based modes.
> + * Tag is ignored in set_tag() for the generic mode.
> + */
> + tag = assign_tag(cache, object, false);
> + tagged_object = set_tag(object, tag);
> +
> + /*
> + * Unpoison the whole object.
> + * For kmalloc() allocations, kasan_kmalloc() will do precise poisoning.
> + */
> + kasan_unpoison(tagged_object, cache->object_size);
> +
> + /* Save alloc info (if possible) for non-kmalloc() allocations. */
> + if (kasan_stack_collection_enabled())
> + set_alloc_info(cache, (void *)object, flags, false);
> +
> + return tagged_object;
> +}
> +
> static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
> - size_t size, gfp_t flags, bool kmalloc)
> + size_t size, gfp_t flags)
> {
> unsigned long redzone_start;
> unsigned long redzone_end;
> - u8 tag;
>
> if (gfpflags_allow_blocking(flags))
> kasan_quarantine_reduce();
> @@ -429,33 +453,41 @@ static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
> if (is_kfence_address(kasan_reset_tag(object)))
> return (void *)object;
>
> + /*
> + * The object has already been unpoisoned by kasan_slab_alloc() for
> + * kmalloc() or by ksize() for krealloc().
> + */
> +
> + /*
> + * The redzone has byte-level precision for the generic mode.
> + * Partially poison the last object granule to cover the unaligned
> + * part of the redzone.
> + */
> + if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> + kasan_poison_last_granule((void *)object, size);
> +
> + /* Poison the aligned part of the redzone. */
> redzone_start = round_up((unsigned long)(object + size),
> KASAN_GRANULE_SIZE);
> - redzone_end = round_up((unsigned long)object + cache->object_size,
> - KASAN_GRANULE_SIZE);
> - 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);
> + redzone_end = (unsigned long)object + cache->object_size;
> kasan_poison((void *)redzone_start, redzone_end - redzone_start,
> KASAN_KMALLOC_REDZONE);
>
> + /*
> + * Save alloc info (if possible) for kmalloc() allocations.
> + * This also rewrites the alloc info when called from kasan_krealloc().
> + */
> if (kasan_stack_collection_enabled())
> - set_alloc_info(cache, (void *)object, flags, kmalloc);
> + set_alloc_info(cache, (void *)object, flags, true);
>
> - return set_tag(object, tag);
> -}
> -
> -void * __must_check __kasan_slab_alloc(struct kmem_cache *cache,
> - void *object, gfp_t flags)
> -{
> - return ____kasan_kmalloc(cache, object, cache->object_size, flags, false);
> + /* Keep the tag that was set by kasan_slab_alloc(). */
> + return (void *)object;
> }
>
> void * __must_check __kasan_kmalloc(struct kmem_cache *cache, const void *object,
> size_t size, gfp_t flags)
> {
> - return ____kasan_kmalloc(cache, object, size, flags, true);
> + return ____kasan_kmalloc(cache, object, size, flags);
> }
> EXPORT_SYMBOL(__kasan_kmalloc);
>
> @@ -496,8 +528,7 @@ void * __must_check __kasan_krealloc(const void *object, size_t size, gfp_t flag
> if (unlikely(!PageSlab(page)))
> return __kasan_kmalloc_large(object, size, flags);
> else
> - return ____kasan_kmalloc(page->slab_cache, object, size,
> - flags, true);
> + return ____kasan_kmalloc(page->slab_cache, object, size, flags);
> }
>
> void __kasan_kfree_large(void *ptr, unsigned long ip)
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index dd14e8870023..6a2882997f23 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -358,12 +358,51 @@ static inline bool kasan_byte_accessible(const void *addr)
>
> #else /* CONFIG_KASAN_HW_TAGS */
>
> -void kasan_poison(const void *address, size_t size, u8 value);
> -void kasan_unpoison(const void *address, size_t size);
> +/**
> + * kasan_poison - mark the memory range as unaccessible
> + * @addr - range start address, must be aligned to KASAN_GRANULE_SIZE
> + * @size - range size
> + * @value - value that's written to metadata for the range
> + *
> + * The size gets aligned to KASAN_GRANULE_SIZE before marking the range.
> + */
> +void kasan_poison(const void *addr, size_t size, u8 value);
> +
> +/**
> + * kasan_unpoison - mark the memory range as accessible
> + * @addr - range start address, must be aligned to KASAN_GRANULE_SIZE
> + * @size - range size
> + *
> + * For the tag-based modes, the @size gets aligned to KASAN_GRANULE_SIZE before
> + * marking the range.
> + * For the generic mode, the last granule of the memory range gets partially
> + * unpoisoned based on the @size.
> + */
> +void kasan_unpoison(const void *addr, size_t size);
> +
> bool kasan_byte_accessible(const void *addr);
>
> #endif /* CONFIG_KASAN_HW_TAGS */
>
> +#ifdef CONFIG_KASAN_GENERIC
> +
> +/**
> + * kasan_poison_last_granule - mark the last granule of the memory range as
> + * unaccessible
> + * @addr - range start address, must be aligned to KASAN_GRANULE_SIZE
> + * @size - range size
> + *
> + * This function is only available for the generic mode, as it's the only mode
> + * that has partially poisoned memory granules.
> + */
> +void kasan_poison_last_granule(const void *address, size_t size);
> +
> +#else /* CONFIG_KASAN_GENERIC */
> +
> +static inline void kasan_poison_last_granule(const void *address, size_t size) { }
> +
> +#endif /* CONFIG_KASAN_GENERIC */
> +
> /*
> * Exported functions for interfaces called from assembly or from generated
> * code. Declarations here to avoid warning about missing declarations.
> diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
> index 1372a2fc0ca9..1ed7817e4ee6 100644
> --- a/mm/kasan/shadow.c
> +++ b/mm/kasan/shadow.c
> @@ -69,10 +69,6 @@ void *memcpy(void *dest, const void *src, size_t len)
> return __memcpy(dest, src, len);
> }
>
> -/*
> - * Poisons the shadow memory for 'size' bytes starting from 'addr'.
> - * Memory addresses should be aligned to KASAN_GRANULE_SIZE.
> - */
> void kasan_poison(const void *address, size_t size, u8 value)
> {
> void *shadow_start, *shadow_end;
> @@ -83,12 +79,12 @@ void kasan_poison(const void *address, size_t size, u8 value)
> * addresses to this function.
> */
> address = kasan_reset_tag(address);
> - size = round_up(size, KASAN_GRANULE_SIZE);
>
> /* Skip KFENCE memory if called explicitly outside of sl*b. */
> if (is_kfence_address(address))
> return;
>
> + size = round_up(size, KASAN_GRANULE_SIZE);
> shadow_start = kasan_mem_to_shadow(address);
> shadow_end = kasan_mem_to_shadow(address + size);
>
> @@ -96,6 +92,16 @@ void kasan_poison(const void *address, size_t size, u8 value)
> }
> EXPORT_SYMBOL(kasan_poison);
>
> +#ifdef CONFIG_KASAN_GENERIC
> +void kasan_poison_last_granule(const void *address, size_t size)
> +{
> + if (size & KASAN_GRANULE_MASK) {
> + u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size);
> + *shadow = size & KASAN_GRANULE_MASK;
> + }
> +}
> +#endif
The function declaration still needs to exist in the dead branch if
!IS_ENABLED(CONFIG_KASAN_GENERIC). It appears in that case it's declared
(in kasan.h), but not defined. We shouldn't get linker errors because
the optimizer should remove the dead branch. Nevertheless, is this code
generally acceptable?
> void kasan_unpoison(const void *address, size_t size)
> {
> u8 tag = get_tag(address);
> @@ -115,16 +121,12 @@ void kasan_unpoison(const void *address, size_t size)
> if (is_kfence_address(address))
> return;
>
> + /* Unpoison round_up(size, KASAN_GRANULE_SIZE) bytes. */
> kasan_poison(address, size, tag);
>
> - if (size & KASAN_GRANULE_MASK) {
> - u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size);
> -
> - if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
> - *shadow = tag;
> - else /* CONFIG_KASAN_GENERIC */
> - *shadow = size & KASAN_GRANULE_MASK;
> - }
> + /* Partially poison the last granule for the generic mode. */
> + if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> + kasan_poison_last_granule(address, size);
> }
>
> #ifdef CONFIG_MEMORY_HOTPLUG
> diff --git a/mm/slub.c b/mm/slub.c
> index 176b1cb0d006..e564008c2329 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3565,8 +3565,7 @@ static void early_kmem_cache_node_alloc(int node)
> init_object(kmem_cache_node, n, SLUB_RED_ACTIVE);
> init_tracking(kmem_cache_node, n);
> #endif
> - n = kasan_kmalloc(kmem_cache_node, n, sizeof(struct kmem_cache_node),
> - GFP_KERNEL);
> + n = kasan_slab_alloc(kmem_cache_node, n, GFP_KERNEL);
> page->freelist = get_freepointer(kmem_cache_node, n);
> page->inuse = 1;
> page->frozen = 0;
> --
> 2.30.0.365.g02bc693789-goog
>
