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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@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrey Konovalov 2021-02-25 17:19:59 -08:00 committed by Linus Torvalds
parent 928501344f
commit e2db1a9aa3
4 changed files with 119 additions and 48 deletions
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93
mm/kasan/common.c
View File

@ -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 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 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, 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(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)

43
mm/kasan/kasan.h
View File

@ -367,12 +367,51 @@ 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.

28
mm/kasan/shadow.c
View File

@ -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
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

3
mm/slub.c
View File

@ -3579,8 +3579,7 @@ 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;