From: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Subject: kasan, mm: optimize kmalloc poisoning 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). Link: https://lkml.kernel.org/r/7e3961cb52be380bc412860332063f5f7ce10d13.1612546384.git.andreyknvl@xxxxxxxxxx Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Reviewed-by: Marco Elver <elver@xxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> Cc: Branislav Rankov <Branislav.Rankov@xxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Evgenii Stepanov <eugenis@xxxxxxxxxx> Cc: Kevin Brodsky <kevin.brodsky@xxxxxxx> Cc: Peter Collingbourne <pcc@xxxxxxxxxx> Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> Cc: Will Deacon <will.deacon@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- 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(-) --- a/mm/kasan/common.c~kasan-mm-optimize-kmalloc-poisoning +++ a/mm/kasan/common.c @@ -278,22 +278,12 @@ void __kasan_poison_object_data(struct k * 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_ob } /* 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_c 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 is_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 km 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, is_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, is_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(con 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) --- a/mm/kasan/kasan.h~kasan-mm-optimize-kmalloc-poisoning +++ a/mm/kasan/kasan.h @@ -367,12 +367,51 @@ static inline bool kasan_byte_accessible #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. --- a/mm/kasan/shadow.c~kasan-mm-optimize-kmalloc-poisoning +++ a/mm/kasan/shadow.c @@ -69,10 +69,6 @@ void *memcpy(void *dest, const void *src 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, s * 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, s } 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 + void kasan_unpoison(const void *address, size_t size) { u8 tag = get_tag(address); @@ -115,16 +121,12 @@ void kasan_unpoison(const void *address, 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 --- a/mm/slub.c~kasan-mm-optimize-kmalloc-poisoning +++ a/mm/slub.c @@ -3579,8 +3579,7 @@ static void early_kmem_cache_node_alloc( 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; _
