[PATCH v3 mm 00/13] kasan: optimizations and fixes for HW_TAGS

[PATCH v3 mm 00/13] kasan: optimizations and fixes for HW_TAGS

[Andrey Konovalov]

This patchset makes the HW_TAGS mode more efficient, mostly by reworking
poisoning approaches and simplifying/inlining some internal helpers.

With this change, the overhead of HW_TAGS annotations excluding setting
and checking memory tags is ~3%. The performance impact caused by tags
will be unknown until we have hardware that supports MTE.

As a side-effect, this patchset speeds up generic KASAN by ~15%.

Changes v2->v3:
- Rebased onto mm.
- Add documentation update patch.

Changes v1->v2:
- Use EXPORT_SYMBOL_GPL() for arm64 symbols.
- Rename kmalloc bool flag argument to is_kmalloc.
- Make empty mte_set_mem_tag_range() return void.
- Fix build warning in 32-bit systems by using unsigned long instead
  of u64 in WARN_ON() checks.
- Minor changes in comments and commit descriptions.
- Use kfence_ksize() before __ksize() to avoid crashes with KFENCE.
- Use inline instead of __always_inline.

Andrey Konovalov (13):
  kasan, mm: don't save alloc stacks twice
  kasan, mm: optimize kmalloc poisoning
  kasan: optimize large kmalloc poisoning
  kasan: clean up setting free info in kasan_slab_free
  kasan: unify large kfree checks
  kasan: rework krealloc tests
  kasan, mm: fail krealloc on freed objects
  kasan, mm: optimize krealloc poisoning
  kasan: ensure poisoning size alignment
  arm64: kasan: simplify and inline MTE functions
  kasan: inline HW_TAGS helper functions
  arm64: kasan: export MTE symbols for KASAN tests
  kasan: clarify that only first bug is reported in HW_TAGS

 Documentation/dev-tools/kasan.rst  |   8 +-
 arch/arm64/include/asm/cache.h     |   1 -
 arch/arm64/include/asm/kasan.h     |   1 +
 arch/arm64/include/asm/mte-def.h   |   2 +
 arch/arm64/include/asm/mte-kasan.h |  65 ++++++++--
 arch/arm64/include/asm/mte.h       |   2 -
 arch/arm64/kernel/mte.c            |  48 +-------
 arch/arm64/lib/mte.S               |  16 ---
 include/linux/kasan.h              |  25 ++--
 lib/test_kasan.c                   | 111 +++++++++++++++--
 mm/kasan/common.c                  | 187 ++++++++++++++++++++---------
 mm/kasan/hw_tags.c                 |   2 +-
 mm/kasan/kasan.h                   |  72 +++++++++--
 mm/kasan/shadow.c                  |  53 ++++----
 mm/slab_common.c                   |  18 ++-
 mm/slub.c                          |   3 +-
 16 files changed, 425 insertions(+), 189 deletions(-)

-- 
2.30.0.365.g02bc693789-goog

[PATCH v3 mm 01/13] kasan, mm: don't save alloc stacks twice

[Andrey Konovalov]

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.

Reviewed-by: Marco Elver <elver@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 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 1011e4f30284..e6ed969e74b3 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..bfdf5464f4ef 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 is_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 && !is_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 is_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, is_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, is_kmalloc);
 
 	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

[PATCH v3 mm 02/13] kasan, mm: optimize kmalloc poisoning

[Andrey Konovalov]

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).

Reviewed-by: Marco Elver <elver@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 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 bfdf5464f4ef..00edbc3eb32e 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 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)
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 4fb8106f8e31..d0a3516e0909 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -355,12 +355,51 @@ 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
+
 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

[PATCH v3 mm 03/13] kasan: optimize large kmalloc poisoning

[Andrey Konovalov]

Similarly to kasan_kmalloc(), kasan_kmalloc_large() doesn't need
to unpoison the object as it as already unpoisoned by alloc_pages()
(or by ksize() for krealloc()).

This patch changes kasan_kmalloc_large() to only poison the redzone.

Reviewed-by: Marco Elver <elver@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 mm/kasan/common.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 00edbc3eb32e..f2a6bae13053 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -494,7 +494,6 @@ EXPORT_SYMBOL(__kasan_kmalloc);
 void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size,
 						gfp_t flags)
 {
-	struct page *page;
 	unsigned long redzone_start;
 	unsigned long redzone_end;
 
@@ -504,12 +503,23 @@ void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size,
 	if (unlikely(ptr == NULL))
 		return NULL;
 
-	page = virt_to_page(ptr);
+	/*
+	 * The object has already been unpoisoned by kasan_alloc_pages() for
+	 * alloc_pages() 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(ptr, size);
+
+	/* Poison the aligned part of the redzone. */
 	redzone_start = round_up((unsigned long)(ptr + size),
 				KASAN_GRANULE_SIZE);
-	redzone_end = (unsigned long)ptr + page_size(page);
-
-	kasan_unpoison(ptr, size);
+	redzone_end = (unsigned long)ptr + page_size(virt_to_page(ptr));
 	kasan_poison((void *)redzone_start, redzone_end - redzone_start,
 		     KASAN_PAGE_REDZONE);
 
-- 
2.30.0.365.g02bc693789-goog

[PATCH v3 mm 04/13] kasan: clean up setting free info in kasan_slab_free

[Andrey Konovalov]

Put kasan_stack_collection_enabled() check and kasan_set_free_info()
calls next to each other.

The way this was previously implemented was a minor optimization that
relied of the the fact that kasan_stack_collection_enabled() is always
true for generic KASAN. The confusion that this brings outweights saving
a few instructions.

Reviewed-by: Marco Elver <elver@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 mm/kasan/common.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index f2a6bae13053..da24b144d46c 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -350,13 +350,11 @@ static bool ____kasan_slab_free(struct kmem_cache *cache, void *object,
 
 	kasan_poison(object, cache->object_size, KASAN_KMALLOC_FREE);
 
-	if (!kasan_stack_collection_enabled())
-		return false;
-
 	if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine))
 		return false;
 
-	kasan_set_free_info(cache, object, tag);
+	if (kasan_stack_collection_enabled())
+		kasan_set_free_info(cache, object, tag);
 
 	return kasan_quarantine_put(cache, object);
 }
-- 
2.30.0.365.g02bc693789-goog

[PATCH v3 mm 05/13] kasan: unify large kfree checks

[Andrey Konovalov]

Unify checks in kasan_kfree_large() and in kasan_slab_free_mempool()
for large allocations as it's done for small kfree() allocations.

With this change, kasan_slab_free_mempool() starts checking that the
first byte of the memory that's being freed is accessible.

Reviewed-by: Marco Elver <elver@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 include/linux/kasan.h | 16 ++++++++--------
 mm/kasan/common.c     | 36 ++++++++++++++++++++++++++----------
 2 files changed, 34 insertions(+), 18 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index e6ed969e74b3..14f72ec96492 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -200,6 +200,13 @@ static __always_inline bool kasan_slab_free(struct kmem_cache *s, void *object)
 	return false;
 }
 
+void __kasan_kfree_large(void *ptr, unsigned long ip);
+static __always_inline void kasan_kfree_large(void *ptr)
+{
+	if (kasan_enabled())
+		__kasan_kfree_large(ptr, _RET_IP_);
+}
+
 void __kasan_slab_free_mempool(void *ptr, unsigned long ip);
 static __always_inline void kasan_slab_free_mempool(void *ptr)
 {
@@ -247,13 +254,6 @@ static __always_inline void * __must_check kasan_krealloc(const void *object,
 	return (void *)object;
 }
 
-void __kasan_kfree_large(void *ptr, unsigned long ip);
-static __always_inline void kasan_kfree_large(void *ptr)
-{
-	if (kasan_enabled())
-		__kasan_kfree_large(ptr, _RET_IP_);
-}
-
 /*
  * Unlike kasan_check_read/write(), kasan_check_byte() is performed even for
  * the hardware tag-based mode that doesn't rely on compiler instrumentation.
@@ -302,6 +302,7 @@ static inline bool kasan_slab_free(struct kmem_cache *s, void *object)
 {
 	return false;
 }
+static inline void kasan_kfree_large(void *ptr) {}
 static inline void kasan_slab_free_mempool(void *ptr) {}
 static inline void *kasan_slab_alloc(struct kmem_cache *s, void *object,
 				   gfp_t flags)
@@ -322,7 +323,6 @@ static inline void *kasan_krealloc(const void *object, size_t new_size,
 {
 	return (void *)object;
 }
-static inline void kasan_kfree_large(void *ptr) {}
 static inline bool kasan_check_byte(const void *address)
 {
 	return true;
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index da24b144d46c..7ea643f7e69c 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -364,6 +364,31 @@ bool __kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
 	return ____kasan_slab_free(cache, object, ip, true);
 }
 
+static bool ____kasan_kfree_large(void *ptr, unsigned long ip)
+{
+	if (ptr != page_address(virt_to_head_page(ptr))) {
+		kasan_report_invalid_free(ptr, ip);
+		return true;
+	}
+
+	if (!kasan_byte_accessible(ptr)) {
+		kasan_report_invalid_free(ptr, ip);
+		return true;
+	}
+
+	/*
+	 * The object will be poisoned by kasan_free_pages() or
+	 * kasan_slab_free_mempool().
+	 */
+
+	return false;
+}
+
+void __kasan_kfree_large(void *ptr, unsigned long ip)
+{
+	____kasan_kfree_large(ptr, ip);
+}
+
 void __kasan_slab_free_mempool(void *ptr, unsigned long ip)
 {
 	struct page *page;
@@ -377,10 +402,8 @@ void __kasan_slab_free_mempool(void *ptr, unsigned long ip)
 	 * KMALLOC_MAX_SIZE, and kmalloc falls back onto page_alloc.
 	 */
 	if (unlikely(!PageSlab(page))) {
-		if (ptr != page_address(page)) {
-			kasan_report_invalid_free(ptr, ip);
+		if (____kasan_kfree_large(ptr, ip))
 			return;
-		}
 		kasan_poison(ptr, page_size(page), KASAN_FREE_PAGE);
 	} else {
 		____kasan_slab_free(page->slab_cache, ptr, ip, false);
@@ -539,13 +562,6 @@ void * __must_check __kasan_krealloc(const void *object, size_t size, gfp_t flag
 		return ____kasan_kmalloc(page->slab_cache, object, size, flags);
 }
 
-void __kasan_kfree_large(void *ptr, unsigned long ip)
-{
-	if (ptr != page_address(virt_to_head_page(ptr)))
-		kasan_report_invalid_free(ptr, ip);
-	/* The object will be poisoned by kasan_free_pages(). */
-}
-
 bool __kasan_check_byte(const void *address, unsigned long ip)
 {
 	if (!kasan_byte_accessible(address)) {
-- 
2.30.0.365.g02bc693789-goog

[PATCH v3 mm 06/13] kasan: rework krealloc tests

[Andrey Konovalov]

This patch reworks KASAN-KUnit tests for krealloc() to:

1. Check both slab and page_alloc based krealloc() implementations.
2. Allow at least one full granule to fit between old and new sizes for
   each KASAN mode, and check accesses to that granule accordingly.

Reviewed-by: Marco Elver <elver@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 lib/test_kasan.c | 91 ++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 81 insertions(+), 10 deletions(-)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index d16ec9e66806..ffebad2f0e6e 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -252,11 +252,14 @@ static void kmalloc_large_oob_right(struct kunit *test)
 	kfree(ptr);
 }
 
-static void kmalloc_oob_krealloc_more(struct kunit *test)
+static void krealloc_more_oob_helper(struct kunit *test,
+					size_t size1, size_t size2)
 {
 	char *ptr1, *ptr2;
-	size_t size1 = 17;
-	size_t size2 = 19;
+	size_t middle;
+
+	KUNIT_ASSERT_LT(test, size1, size2);
+	middle = size1 + (size2 - size1) / 2;
 
 	ptr1 = kmalloc(size1, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr1);
@@ -264,15 +267,31 @@ static void kmalloc_oob_krealloc_more(struct kunit *test)
 	ptr2 = krealloc(ptr1, size2, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr2);
 
-	KUNIT_EXPECT_KASAN_FAIL(test, ptr2[size2 + OOB_TAG_OFF] = 'x');
+	/* All offsets up to size2 must be accessible. */
+	ptr2[size1 - 1] = 'x';
+	ptr2[size1] = 'x';
+	ptr2[middle] = 'x';
+	ptr2[size2 - 1] = 'x';
+
+	/* Generic mode is precise, so unaligned size2 must be inaccessible. */
+	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
+		KUNIT_EXPECT_KASAN_FAIL(test, ptr2[size2] = 'x');
+
+	/* For all modes first aligned offset after size2 must be inaccessible. */
+	KUNIT_EXPECT_KASAN_FAIL(test,
+		ptr2[round_up(size2, KASAN_GRANULE_SIZE)] = 'x');
+
 	kfree(ptr2);
 }
 
-static void kmalloc_oob_krealloc_less(struct kunit *test)
+static void krealloc_less_oob_helper(struct kunit *test,
+					size_t size1, size_t size2)
 {
 	char *ptr1, *ptr2;
-	size_t size1 = 17;
-	size_t size2 = 15;
+	size_t middle;
+
+	KUNIT_ASSERT_LT(test, size2, size1);
+	middle = size2 + (size1 - size2) / 2;
 
 	ptr1 = kmalloc(size1, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr1);
@@ -280,10 +299,60 @@ static void kmalloc_oob_krealloc_less(struct kunit *test)
 	ptr2 = krealloc(ptr1, size2, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr2);
 
-	KUNIT_EXPECT_KASAN_FAIL(test, ptr2[size2 + OOB_TAG_OFF] = 'x');
+	/* Must be accessible for all modes. */
+	ptr2[size2 - 1] = 'x';
+
+	/* Generic mode is precise, so unaligned size2 must be inaccessible. */
+	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
+		KUNIT_EXPECT_KASAN_FAIL(test, ptr2[size2] = 'x');
+
+	/* For all modes first aligned offset after size2 must be inaccessible. */
+	KUNIT_EXPECT_KASAN_FAIL(test,
+		ptr2[round_up(size2, KASAN_GRANULE_SIZE)] = 'x');
+
+	/*
+	 * For all modes all size2, middle, and size1 should land in separate
+	 * granules and thus the latter two offsets should be inaccessible.
+	 */
+	KUNIT_EXPECT_LE(test, round_up(size2, KASAN_GRANULE_SIZE),
+				round_down(middle, KASAN_GRANULE_SIZE));
+	KUNIT_EXPECT_LE(test, round_up(middle, KASAN_GRANULE_SIZE),
+				round_down(size1, KASAN_GRANULE_SIZE));
+	KUNIT_EXPECT_KASAN_FAIL(test, ptr2[middle] = 'x');
+	KUNIT_EXPECT_KASAN_FAIL(test, ptr2[size1 - 1] = 'x');
+	KUNIT_EXPECT_KASAN_FAIL(test, ptr2[size1] = 'x');
+
 	kfree(ptr2);
 }
 
+static void krealloc_more_oob(struct kunit *test)
+{
+	krealloc_more_oob_helper(test, 201, 235);
+}
+
+static void krealloc_less_oob(struct kunit *test)
+{
+	krealloc_less_oob_helper(test, 235, 201);
+}
+
+static void krealloc_pagealloc_more_oob(struct kunit *test)
+{
+	/* page_alloc fallback in only implemented for SLUB. */
+	KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_SLUB);
+
+	krealloc_more_oob_helper(test, KMALLOC_MAX_CACHE_SIZE + 201,
+					KMALLOC_MAX_CACHE_SIZE + 235);
+}
+
+static void krealloc_pagealloc_less_oob(struct kunit *test)
+{
+	/* page_alloc fallback in only implemented for SLUB. */
+	KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_SLUB);
+
+	krealloc_less_oob_helper(test, KMALLOC_MAX_CACHE_SIZE + 235,
+					KMALLOC_MAX_CACHE_SIZE + 201);
+}
+
 static void kmalloc_oob_16(struct kunit *test)
 {
 	struct {
@@ -977,8 +1046,10 @@ static struct kunit_case kasan_kunit_test_cases[] = {
 	KUNIT_CASE(pagealloc_oob_right),
 	KUNIT_CASE(pagealloc_uaf),
 	KUNIT_CASE(kmalloc_large_oob_right),
-	KUNIT_CASE(kmalloc_oob_krealloc_more),
-	KUNIT_CASE(kmalloc_oob_krealloc_less),
+	KUNIT_CASE(krealloc_more_oob),
+	KUNIT_CASE(krealloc_less_oob),
+	KUNIT_CASE(krealloc_pagealloc_more_oob),
+	KUNIT_CASE(krealloc_pagealloc_less_oob),
 	KUNIT_CASE(kmalloc_oob_16),
 	KUNIT_CASE(kmalloc_uaf_16),
 	KUNIT_CASE(kmalloc_oob_in_memset),
-- 
2.30.0.365.g02bc693789-goog

[PATCH v3 mm 07/13] kasan, mm: fail krealloc on freed objects

[Andrey Konovalov]

Currently, if krealloc() is called on a freed object with KASAN enabled,
it allocates and returns a new object, but doesn't copy any memory from
the old one as ksize() returns 0. This makes the caller believe that
krealloc() succeeded (KASAN report is printed though).

This patch adds an accessibility check into __do_krealloc(). If the check
fails, krealloc() returns NULL. This check duplicates the one in ksize();
this is fixed in the following patch.

This patch also adds a KASAN-KUnit test to check krealloc() behaviour
when it's called on a freed object.

Reviewed-by: Marco Elver <elver@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 lib/test_kasan.c | 20 ++++++++++++++++++++
 mm/slab_common.c |  3 +++
 2 files changed, 23 insertions(+)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index ffebad2f0e6e..1328c468fdb5 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -353,6 +353,25 @@ static void krealloc_pagealloc_less_oob(struct kunit *test)
 					KMALLOC_MAX_CACHE_SIZE + 201);
 }
 
+/*
+ * Check that krealloc() detects a use-after-free, returns NULL,
+ * and doesn't unpoison the freed object.
+ */
+static void krealloc_uaf(struct kunit *test)
+{
+	char *ptr1, *ptr2;
+	int size1 = 201;
+	int size2 = 235;
+
+	ptr1 = kmalloc(size1, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr1);
+	kfree(ptr1);
+
+	KUNIT_EXPECT_KASAN_FAIL(test, ptr2 = krealloc(ptr1, size2, GFP_KERNEL));
+	KUNIT_ASSERT_PTR_EQ(test, (void *)ptr2, NULL);
+	KUNIT_EXPECT_KASAN_FAIL(test, *(volatile char *)ptr1);
+}
+
 static void kmalloc_oob_16(struct kunit *test)
 {
 	struct {
@@ -1050,6 +1069,7 @@ static struct kunit_case kasan_kunit_test_cases[] = {
 	KUNIT_CASE(krealloc_less_oob),
 	KUNIT_CASE(krealloc_pagealloc_more_oob),
 	KUNIT_CASE(krealloc_pagealloc_less_oob),
+	KUNIT_CASE(krealloc_uaf),
 	KUNIT_CASE(kmalloc_oob_16),
 	KUNIT_CASE(kmalloc_uaf_16),
 	KUNIT_CASE(kmalloc_oob_in_memset),
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 39d1a8ff9bb8..dad70239b54c 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1140,6 +1140,9 @@ static __always_inline void *__do_krealloc(const void *p, size_t new_size,
 	void *ret;
 	size_t ks;
 
+	if (likely(!ZERO_OR_NULL_PTR(p)) && !kasan_check_byte(p))
+		return NULL;
+
 	ks = ksize(p);
 
 	if (ks >= new_size) {
-- 
2.30.0.365.g02bc693789-goog

[PATCH v3 mm 08/13] kasan, mm: optimize krealloc poisoning

[Andrey Konovalov]

Currently, krealloc() always calls ksize(), which unpoisons the whole
object including the redzone. This is inefficient, as kasan_krealloc()
repoisons the redzone for objects that fit into the same buffer.

This patch changes krealloc() instrumentation to use uninstrumented
__ksize() that doesn't unpoison the memory. Instead, kasan_kreallos()
is changed to unpoison the memory excluding the redzone.

For objects that don't fit into the old allocation, this patch disables
KASAN accessibility checks when copying memory into a new object instead
of unpoisoning it.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 mm/kasan/common.c | 12 ++++++++++--
 mm/slab_common.c  | 20 ++++++++++++++------
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 7ea643f7e69c..a8a67dca5e55 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -476,7 +476,7 @@ static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
 
 	/*
 	 * The object has already been unpoisoned by kasan_slab_alloc() for
-	 * kmalloc() or by ksize() for krealloc().
+	 * kmalloc() or by kasan_krealloc() for krealloc().
 	 */
 
 	/*
@@ -526,7 +526,7 @@ void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size,
 
 	/*
 	 * The object has already been unpoisoned by kasan_alloc_pages() for
-	 * alloc_pages() or by ksize() for krealloc().
+	 * alloc_pages() or by kasan_krealloc() for krealloc().
 	 */
 
 	/*
@@ -554,8 +554,16 @@ void * __must_check __kasan_krealloc(const void *object, size_t size, gfp_t flag
 	if (unlikely(object == ZERO_SIZE_PTR))
 		return (void *)object;
 
+	/*
+	 * Unpoison the object's data.
+	 * Part of it might already have been unpoisoned, but it's unknown
+	 * how big that part is.
+	 */
+	kasan_unpoison(object, size);
+
 	page = virt_to_head_page(object);
 
+	/* Piggy-back on kmalloc() instrumentation to poison the redzone. */
 	if (unlikely(!PageSlab(page)))
 		return __kasan_kmalloc_large(object, size, flags);
 	else
diff --git a/mm/slab_common.c b/mm/slab_common.c
index dad70239b54c..60a2f49df6ce 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1140,19 +1140,27 @@ static __always_inline void *__do_krealloc(const void *p, size_t new_size,
 	void *ret;
 	size_t ks;
 
-	if (likely(!ZERO_OR_NULL_PTR(p)) && !kasan_check_byte(p))
-		return NULL;
-
-	ks = ksize(p);
+	/* Don't use instrumented ksize to allow precise KASAN poisoning. */
+	if (likely(!ZERO_OR_NULL_PTR(p))) {
+		if (!kasan_check_byte(p))
+			return NULL;
+		ks = kfence_ksize(p) ?: __ksize(p);
+	} else
+		ks = 0;
 
+	/* If the object still fits, repoison it precisely. */
 	if (ks >= new_size) {
 		p = kasan_krealloc((void *)p, new_size, flags);
 		return (void *)p;
 	}
 
 	ret = kmalloc_track_caller(new_size, flags);
-	if (ret && p)
-		memcpy(ret, p, ks);
+	if (ret && p) {
+		/* Disable KASAN checks as the object's redzone is accessed. */
+		kasan_disable_current();
+		memcpy(ret, kasan_reset_tag(p), ks);
+		kasan_enable_current();
+	}
 
 	return ret;
 }
-- 
2.30.0.365.g02bc693789-goog

[PATCH v3 mm 09/13] kasan: ensure poisoning size alignment

[Andrey Konovalov]

A previous changes d99f6a10c161 ("kasan: don't round_up too much")
attempted to simplify the code by adding a round_up(size) call into
kasan_poison(). While this allows to have less round_up() calls around
the code, this results in round_up() being called multiple times.

This patch removes round_up() of size from kasan_poison() and ensures
that all callers round_up() the size explicitly. This patch also adds
WARN_ON() alignment checks for address and size to kasan_poison() and
kasan_unpoison().

Reviewed-by: Marco Elver <elver@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 mm/kasan/common.c |  9 ++++++---
 mm/kasan/kasan.h  | 33 ++++++++++++++++++++-------------
 mm/kasan/shadow.c | 37 ++++++++++++++++++++++---------------
 3 files changed, 48 insertions(+), 31 deletions(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index a8a67dca5e55..7ffb1e6de2ef 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -261,7 +261,8 @@ void __kasan_unpoison_object_data(struct kmem_cache *cache, void *object)
 
 void __kasan_poison_object_data(struct kmem_cache *cache, void *object)
 {
-	kasan_poison(object, cache->object_size, KASAN_KMALLOC_REDZONE);
+	kasan_poison(object, round_up(cache->object_size, KASAN_GRANULE_SIZE),
+			KASAN_KMALLOC_REDZONE);
 }
 
 /*
@@ -348,7 +349,8 @@ static bool ____kasan_slab_free(struct kmem_cache *cache, void *object,
 		return true;
 	}
 
-	kasan_poison(object, cache->object_size, KASAN_KMALLOC_FREE);
+	kasan_poison(object, round_up(cache->object_size, KASAN_GRANULE_SIZE),
+			KASAN_KMALLOC_FREE);
 
 	if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine))
 		return false;
@@ -490,7 +492,8 @@ static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
 	/* Poison the aligned part of the redzone. */
 	redzone_start = round_up((unsigned long)(object + size),
 				KASAN_GRANULE_SIZE);
-	redzone_end = (unsigned long)object + cache->object_size;
+	redzone_end = round_up((unsigned long)(object + cache->object_size),
+				KASAN_GRANULE_SIZE);
 	kasan_poison((void *)redzone_start, redzone_end - redzone_start,
 			   KASAN_KMALLOC_REDZONE);
 
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index d0a3516e0909..cc787ba47e1b 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -318,30 +318,37 @@ static inline u8 kasan_random_tag(void) { return 0; }
 
 #ifdef CONFIG_KASAN_HW_TAGS
 
-static inline void kasan_poison(const void *address, size_t size, u8 value)
+static inline void kasan_poison(const void *addr, size_t size, u8 value)
 {
-	address = kasan_reset_tag(address);
+	addr = kasan_reset_tag(addr);
 
 	/* Skip KFENCE memory if called explicitly outside of sl*b. */
-	if (is_kfence_address(address))
+	if (is_kfence_address(addr))
 		return;
 
-	hw_set_mem_tag_range((void *)address,
-			round_up(size, KASAN_GRANULE_SIZE), value);
+	if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK))
+		return;
+	if (WARN_ON(size & KASAN_GRANULE_MASK))
+		return;
+
+	hw_set_mem_tag_range((void *)addr, size, value);
 }
 
-static inline void kasan_unpoison(const void *address, size_t size)
+static inline void kasan_unpoison(const void *addr, size_t size)
 {
-	u8 tag = get_tag(address);
+	u8 tag = get_tag(addr);
 
-	address = kasan_reset_tag(address);
+	addr = kasan_reset_tag(addr);
 
 	/* Skip KFENCE memory if called explicitly outside of sl*b. */
-	if (is_kfence_address(address))
+	if (is_kfence_address(addr))
 		return;
 
-	hw_set_mem_tag_range((void *)address,
-			round_up(size, KASAN_GRANULE_SIZE), tag);
+	if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK))
+		return;
+	size = round_up(size, KASAN_GRANULE_SIZE);
+
+	hw_set_mem_tag_range((void *)addr, size, tag);
 }
 
 static inline bool kasan_byte_accessible(const void *addr)
@@ -358,7 +365,7 @@ static inline bool kasan_byte_accessible(const void *addr)
 /**
  * kasan_poison - mark the memory range as unaccessible
  * @addr - range start address, must be aligned to KASAN_GRANULE_SIZE
- * @size - range size
+ * @size - range size, must be aligned to KASAN_GRANULE_SIZE
  * @value - value that's written to metadata for the range
  *
  * The size gets aligned to KASAN_GRANULE_SIZE before marking the range.
@@ -368,7 +375,7 @@ 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
+ * @size - range size, can be unaligned
  *
  * For the tag-based modes, the @size gets aligned to KASAN_GRANULE_SIZE before
  * marking the range.
diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
index 1ed7817e4ee6..63f43443f5d7 100644
--- a/mm/kasan/shadow.c
+++ b/mm/kasan/shadow.c
@@ -69,7 +69,7 @@ void *memcpy(void *dest, const void *src, size_t len)
 	return __memcpy(dest, src, len);
 }
 
-void kasan_poison(const void *address, size_t size, u8 value)
+void kasan_poison(const void *addr, size_t size, u8 value)
 {
 	void *shadow_start, *shadow_end;
 
@@ -78,55 +78,62 @@ void kasan_poison(const void *address, size_t size, u8 value)
 	 * some of the callers (e.g. kasan_poison_object_data) pass tagged
 	 * addresses to this function.
 	 */
-	address = kasan_reset_tag(address);
+	addr = kasan_reset_tag(addr);
 
 	/* Skip KFENCE memory if called explicitly outside of sl*b. */
-	if (is_kfence_address(address))
+	if (is_kfence_address(addr))
 		return;
 
-	size = round_up(size, KASAN_GRANULE_SIZE);
-	shadow_start = kasan_mem_to_shadow(address);
-	shadow_end = kasan_mem_to_shadow(address + size);
+	if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK))
+		return;
+	if (WARN_ON(size & KASAN_GRANULE_MASK))
+		return;
+
+	shadow_start = kasan_mem_to_shadow(addr);
+	shadow_end = kasan_mem_to_shadow(addr + size);
 
 	__memset(shadow_start, value, shadow_end - shadow_start);
 }
 EXPORT_SYMBOL(kasan_poison);
 
 #ifdef CONFIG_KASAN_GENERIC
-void kasan_poison_last_granule(const void *address, size_t size)
+void kasan_poison_last_granule(const void *addr, size_t size)
 {
 	if (size & KASAN_GRANULE_MASK) {
-		u8 *shadow = (u8 *)kasan_mem_to_shadow(address + size);
+		u8 *shadow = (u8 *)kasan_mem_to_shadow(addr + size);
 		*shadow = size & KASAN_GRANULE_MASK;
 	}
 }
 #endif
 
-void kasan_unpoison(const void *address, size_t size)
+void kasan_unpoison(const void *addr, size_t size)
 {
-	u8 tag = get_tag(address);
+	u8 tag = get_tag(addr);
 
 	/*
 	 * Perform shadow offset calculation based on untagged address, as
 	 * some of the callers (e.g. kasan_unpoison_object_data) pass tagged
 	 * addresses to this function.
 	 */
-	address = kasan_reset_tag(address);
+	addr = kasan_reset_tag(addr);
 
 	/*
 	 * Skip KFENCE memory if called explicitly outside of sl*b. Also note
 	 * that calls to ksize(), where size is not a multiple of machine-word
 	 * size, would otherwise poison the invalid portion of the word.
 	 */
-	if (is_kfence_address(address))
+	if (is_kfence_address(addr))
+		return;
+
+	if (WARN_ON((unsigned long)addr & KASAN_GRANULE_MASK))
 		return;
 
-	/* Unpoison round_up(size, KASAN_GRANULE_SIZE) bytes. */
-	kasan_poison(address, size, tag);
+	/* Unpoison all granules that cover the object. */
+	kasan_poison(addr, round_up(size, KASAN_GRANULE_SIZE), tag);
 
 	/* Partially poison the last granule for the generic mode. */
 	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
-		kasan_poison_last_granule(address, size);
+		kasan_poison_last_granule(addr, size);
 }
 
 #ifdef CONFIG_MEMORY_HOTPLUG
-- 
2.30.0.365.g02bc693789-goog

[PATCH v3 mm 10/13] arm64: kasan: simplify and inline MTE functions

[Andrey Konovalov]

This change provides a simpler implementation of mte_get_mem_tag(),
mte_get_random_tag(), and mte_set_mem_tag_range().

Simplifications include removing system_supports_mte() checks as these
functions are onlye called from KASAN runtime that had already checked
system_supports_mte(). Besides that, size and address alignment checks
are removed from mte_set_mem_tag_range(), as KASAN now does those.

This change also moves these functions into the asm/mte-kasan.h header
and implements mte_set_mem_tag_range() via inline assembly to avoid
unnecessary functions calls.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Co-developed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 arch/arm64/include/asm/cache.h     |  1 -
 arch/arm64/include/asm/kasan.h     |  1 +
 arch/arm64/include/asm/mte-def.h   |  2 +
 arch/arm64/include/asm/mte-kasan.h | 65 ++++++++++++++++++++++++++----
 arch/arm64/include/asm/mte.h       |  2 -
 arch/arm64/kernel/mte.c            | 46 ---------------------
 arch/arm64/lib/mte.S               | 16 --------
 7 files changed, 60 insertions(+), 73 deletions(-)

diff --git a/arch/arm64/include/asm/cache.h b/arch/arm64/include/asm/cache.h
index 77cbbe3625f2..a074459f8f2f 100644
--- a/arch/arm64/include/asm/cache.h
+++ b/arch/arm64/include/asm/cache.h
@@ -6,7 +6,6 @@
 #define __ASM_CACHE_H
 
 #include <asm/cputype.h>
-#include <asm/mte-kasan.h>
 
 #define CTR_L1IP_SHIFT		14
 #define CTR_L1IP_MASK		3
diff --git a/arch/arm64/include/asm/kasan.h b/arch/arm64/include/asm/kasan.h
index 0aaf9044cd6a..12d5f47f7dbe 100644
--- a/arch/arm64/include/asm/kasan.h
+++ b/arch/arm64/include/asm/kasan.h
@@ -6,6 +6,7 @@
 
 #include <linux/linkage.h>
 #include <asm/memory.h>
+#include <asm/mte-kasan.h>
 #include <asm/pgtable-types.h>
 
 #define arch_kasan_set_tag(addr, tag)	__tag_set(addr, tag)
diff --git a/arch/arm64/include/asm/mte-def.h b/arch/arm64/include/asm/mte-def.h
index 2d73a1612f09..cf241b0f0a42 100644
--- a/arch/arm64/include/asm/mte-def.h
+++ b/arch/arm64/include/asm/mte-def.h
@@ -11,4 +11,6 @@
 #define MTE_TAG_SIZE		4
 #define MTE_TAG_MASK		GENMASK((MTE_TAG_SHIFT + (MTE_TAG_SIZE - 1)), MTE_TAG_SHIFT)
 
+#define __MTE_PREAMBLE		ARM64_ASM_PREAMBLE ".arch_extension memtag\n"
+
 #endif /* __ASM_MTE_DEF_H  */
diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h
index 3748d5bb88c0..3d58489228c0 100644
--- a/arch/arm64/include/asm/mte-kasan.h
+++ b/arch/arm64/include/asm/mte-kasan.h
@@ -11,11 +11,14 @@
 
 #include <linux/types.h>
 
+#ifdef CONFIG_ARM64_MTE
+
 /*
- * The functions below are meant to be used only for the
- * KASAN_HW_TAGS interface defined in asm/memory.h.
+ * These functions are meant to be only used from KASAN runtime through
+ * the arch_*() interface defined in asm/memory.h.
+ * These functions don't include system_supports_mte() checks,
+ * as KASAN only calls them when MTE is supported and enabled.
  */
-#ifdef CONFIG_ARM64_MTE
 
 static inline u8 mte_get_ptr_tag(void *ptr)
 {
@@ -25,9 +28,54 @@ static inline u8 mte_get_ptr_tag(void *ptr)
 	return tag;
 }
 
-u8 mte_get_mem_tag(void *addr);
-u8 mte_get_random_tag(void);
-void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag);
+/* Get allocation tag for the address. */
+static inline u8 mte_get_mem_tag(void *addr)
+{
+	asm(__MTE_PREAMBLE "ldg %0, [%0]"
+		: "+r" (addr));
+
+	return mte_get_ptr_tag(addr);
+}
+
+/* Generate a random tag. */
+static inline u8 mte_get_random_tag(void)
+{
+	void *addr;
+
+	asm(__MTE_PREAMBLE "irg %0, %0"
+		: "+r" (addr));
+
+	return mte_get_ptr_tag(addr);
+}
+
+/*
+ * Assign allocation tags for a region of memory based on the pointer tag.
+ * Note: The address must be non-NULL and MTE_GRANULE_SIZE aligned and
+ * size must be non-zero and MTE_GRANULE_SIZE aligned.
+ */
+static inline void mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
+{
+	u64 curr, end;
+
+	if (!size)
+		return;
+
+	curr = (u64)__tag_set(addr, tag);
+	end = curr + size;
+
+	do {
+		/*
+		 * 'asm volatile' is required to prevent the compiler to move
+		 * the statement outside of the loop.
+		 */
+		asm volatile(__MTE_PREAMBLE "stg %0, [%0]"
+			     :
+			     : "r" (curr)
+			     : "memory");
+
+		curr += MTE_GRANULE_SIZE;
+	} while (curr != end);
+}
 
 void mte_enable_kernel(void);
 void mte_init_tags(u64 max_tag);
@@ -46,13 +94,14 @@ static inline u8 mte_get_mem_tag(void *addr)
 {
 	return 0xFF;
 }
+
 static inline u8 mte_get_random_tag(void)
 {
 	return 0xFF;
 }
-static inline void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
+
+static inline void mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
 {
-	return addr;
 }
 
 static inline void mte_enable_kernel(void)
diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index d02aff9f493d..9b557a457f24 100644
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h
@@ -8,8 +8,6 @@
 #include <asm/compiler.h>
 #include <asm/mte-def.h>
 
-#define __MTE_PREAMBLE		ARM64_ASM_PREAMBLE ".arch_extension memtag\n"
-
 #ifndef __ASSEMBLY__
 
 #include <linux/bitfield.h>
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index c63b3d7a3cd9..203108d51d40 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -19,7 +19,6 @@
 #include <asm/barrier.h>
 #include <asm/cpufeature.h>
 #include <asm/mte.h>
-#include <asm/mte-kasan.h>
 #include <asm/ptrace.h>
 #include <asm/sysreg.h>
 
@@ -88,51 +87,6 @@ int memcmp_pages(struct page *page1, struct page *page2)
 	return ret;
 }
 
-u8 mte_get_mem_tag(void *addr)
-{
-	if (!system_supports_mte())
-		return 0xFF;
-
-	asm(__MTE_PREAMBLE "ldg %0, [%0]"
-	    : "+r" (addr));
-
-	return mte_get_ptr_tag(addr);
-}
-
-u8 mte_get_random_tag(void)
-{
-	void *addr;
-
-	if (!system_supports_mte())
-		return 0xFF;
-
-	asm(__MTE_PREAMBLE "irg %0, %0"
-	    : "+r" (addr));
-
-	return mte_get_ptr_tag(addr);
-}
-
-void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
-{
-	void *ptr = addr;
-
-	if ((!system_supports_mte()) || (size == 0))
-		return addr;
-
-	/* Make sure that size is MTE granule aligned. */
-	WARN_ON(size & (MTE_GRANULE_SIZE - 1));
-
-	/* Make sure that the address is MTE granule aligned. */
-	WARN_ON((u64)addr & (MTE_GRANULE_SIZE - 1));
-
-	tag = 0xF0 | tag;
-	ptr = (void *)__tag_set(ptr, tag);
-
-	mte_assign_mem_tag_range(ptr, size);
-
-	return ptr;
-}
-
 void mte_init_tags(u64 max_tag)
 {
 	static bool gcr_kernel_excl_initialized;
diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S
index 9e1a12e10053..351537c12f36 100644
--- a/arch/arm64/lib/mte.S
+++ b/arch/arm64/lib/mte.S
@@ -149,19 +149,3 @@ SYM_FUNC_START(mte_restore_page_tags)
 
 	ret
 SYM_FUNC_END(mte_restore_page_tags)
-
-/*
- * Assign allocation tags for a region of memory based on the pointer tag
- *   x0 - source pointer
- *   x1 - size
- *
- * Note: The address must be non-NULL and MTE_GRANULE_SIZE aligned and
- * size must be non-zero and MTE_GRANULE_SIZE aligned.
- */
-SYM_FUNC_START(mte_assign_mem_tag_range)
-1:	stg	x0, [x0]
-	add	x0, x0, #MTE_GRANULE_SIZE
-	subs	x1, x1, #MTE_GRANULE_SIZE
-	b.gt	1b
-	ret
-SYM_FUNC_END(mte_assign_mem_tag_range)
-- 
2.30.0.365.g02bc693789-goog

[PATCH v3 mm 11/13] kasan: inline HW_TAGS helper functions

[Andrey Konovalov]

Mark all static functions in common.c and kasan.h that are used for
hardware tag-based KASAN as inline to avoid unnecessary function calls.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 mm/kasan/common.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 7ffb1e6de2ef..7b53291dafa1 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -279,7 +279,8 @@ 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)
+static inline u8 assign_tag(struct kmem_cache *cache,
+					const void *object, bool init)
 {
 	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
 		return 0xff;
@@ -321,8 +322,8 @@ void * __must_check __kasan_init_slab_obj(struct kmem_cache *cache,
 	return (void *)object;
 }
 
-static bool ____kasan_slab_free(struct kmem_cache *cache, void *object,
-			      unsigned long ip, bool quarantine)
+static inline bool ____kasan_slab_free(struct kmem_cache *cache,
+				void *object, unsigned long ip, bool quarantine)
 {
 	u8 tag;
 	void *tagged_object;
@@ -366,7 +367,7 @@ bool __kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
 	return ____kasan_slab_free(cache, object, ip, true);
 }
 
-static bool ____kasan_kfree_large(void *ptr, unsigned long ip)
+static inline bool ____kasan_kfree_large(void *ptr, unsigned long ip)
 {
 	if (ptr != page_address(virt_to_head_page(ptr))) {
 		kasan_report_invalid_free(ptr, ip);
@@ -461,8 +462,8 @@ void * __must_check __kasan_slab_alloc(struct kmem_cache *cache,
 	return tagged_object;
 }
 
-static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
-					size_t size, gfp_t flags)
+static inline void *____kasan_kmalloc(struct kmem_cache *cache,
+				const void *object, size_t size, gfp_t flags)
 {
 	unsigned long redzone_start;
 	unsigned long redzone_end;
-- 
2.30.0.365.g02bc693789-goog

[PATCH v3 mm 12/13] arm64: kasan: export MTE symbols for KASAN tests

[Andrey Konovalov]

Export mte_enable_kernel() and mte_set_report_once() to fix:

ERROR: modpost: "mte_enable_kernel" [lib/test_kasan.ko] undefined!
ERROR: modpost: "mte_set_report_once" [lib/test_kasan.ko] undefined!

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 arch/arm64/kernel/mte.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index 203108d51d40..a66c2806fc4d 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -113,11 +113,13 @@ void mte_enable_kernel(void)
 	sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
 	isb();
 }
+EXPORT_SYMBOL_GPL(mte_enable_kernel);
 
 void mte_set_report_once(bool state)
 {
 	WRITE_ONCE(report_fault_once, state);
 }
+EXPORT_SYMBOL_GPL(mte_set_report_once);
 
 bool mte_report_once(void)
 {
-- 
2.30.0.365.g02bc693789-goog

[PATCH v3 mm 13/13] kasan: clarify that only first bug is reported in HW_TAGS

[Andrey Konovalov]

Hwardware tag-based KASAN only reports the first found bug. After that MTE
tag checking gets disabled. Clarify this in comments and documentation.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 Documentation/dev-tools/kasan.rst | 8 ++++++--
 mm/kasan/hw_tags.c                | 2 +-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index e022b7506e37..1faabbe23e09 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -155,7 +155,7 @@ Boot parameters
 ~~~~~~~~~~~~~~~
 
 Hardware tag-based KASAN mode (see the section about various modes below) is
-intended for use in production as a security mitigation. Therefore it supports
+intended for use in production as a security mitigation. Therefore, it supports
 boot parameters that allow to disable KASAN competely or otherwise control
 particular KASAN features.
 
@@ -166,7 +166,8 @@ particular KASAN features.
   ``off``).
 
 - ``kasan.fault=report`` or ``=panic`` controls whether to only print a KASAN
-  report or also panic the kernel (default: ``report``).
+  report or also panic the kernel (default: ``report``). Note, that tag
+  checking gets disabled after the first reported bug.
 
 For developers
 ~~~~~~~~~~~~~~
@@ -296,6 +297,9 @@ Note, that enabling CONFIG_KASAN_HW_TAGS always results in in-kernel TBI being
 enabled. Even when kasan.mode=off is provided, or when the hardware doesn't
 support MTE (but supports TBI).
 
+Hardware tag-based KASAN only reports the first found bug. After that MTE tag
+checking gets disabled.
+
 What memory accesses are sanitised by KASAN?
 --------------------------------------------
 
diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index e529428e7a11..6c9285c906b8 100644
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c
@@ -48,7 +48,7 @@ EXPORT_SYMBOL(kasan_flag_enabled);
 /* Whether to collect alloc/free stack traces. */
 DEFINE_STATIC_KEY_FALSE(kasan_flag_stacktrace);
 
-/* Whether panic or disable tag checking on fault. */
+/* Whether to panic or print a report and disable tag checking on fault. */
 bool kasan_flag_panic __ro_after_init;
 
 /* kasan=off/on */
-- 
2.30.0.365.g02bc693789-goog

Re: [PATCH v3 mm 08/13] kasan, mm: optimize krealloc poisoning

[Marco Elver]

On Fri, Feb 05, 2021 at 06:34PM +0100, Andrey Konovalov wrote:
> Currently, krealloc() always calls ksize(), which unpoisons the whole
> object including the redzone. This is inefficient, as kasan_krealloc()
> repoisons the redzone for objects that fit into the same buffer.
> 
> This patch changes krealloc() instrumentation to use uninstrumented
> __ksize() that doesn't unpoison the memory. Instead, kasan_kreallos()
> is changed to unpoison the memory excluding the redzone.
> 
> For objects that don't fit into the old allocation, this patch disables
> KASAN accessibility checks when copying memory into a new object instead
> of unpoisoning it.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

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

Clarification below.

> ---
>  mm/kasan/common.c | 12 ++++++++++--
>  mm/slab_common.c  | 20 ++++++++++++++------
>  2 files changed, 24 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 7ea643f7e69c..a8a67dca5e55 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -476,7 +476,7 @@ static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
>  
>  	/*
>  	 * The object has already been unpoisoned by kasan_slab_alloc() for
> -	 * kmalloc() or by ksize() for krealloc().
> +	 * kmalloc() or by kasan_krealloc() for krealloc().
>  	 */
>  
>  	/*
> @@ -526,7 +526,7 @@ void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size,
>  
>  	/*
>  	 * The object has already been unpoisoned by kasan_alloc_pages() for
> -	 * alloc_pages() or by ksize() for krealloc().
> +	 * alloc_pages() or by kasan_krealloc() for krealloc().
>  	 */
>  
>  	/*
> @@ -554,8 +554,16 @@ void * __must_check __kasan_krealloc(const void *object, size_t size, gfp_t flag
>  	if (unlikely(object == ZERO_SIZE_PTR))
>  		return (void *)object;
>  
> +	/*
> +	 * Unpoison the object's data.
> +	 * Part of it might already have been unpoisoned, but it's unknown
> +	 * how big that part is.
> +	 */
> +	kasan_unpoison(object, size);
> +
>  	page = virt_to_head_page(object);
>  
> +	/* Piggy-back on kmalloc() instrumentation to poison the redzone. */
>  	if (unlikely(!PageSlab(page)))
>  		return __kasan_kmalloc_large(object, size, flags);
>  	else
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index dad70239b54c..60a2f49df6ce 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1140,19 +1140,27 @@ static __always_inline void *__do_krealloc(const void *p, size_t new_size,
>  	void *ret;
>  	size_t ks;
>  
> -	if (likely(!ZERO_OR_NULL_PTR(p)) && !kasan_check_byte(p))
> -		return NULL;
> -
> -	ks = ksize(p);
> +	/* Don't use instrumented ksize to allow precise KASAN poisoning. */
> +	if (likely(!ZERO_OR_NULL_PTR(p))) {
> +		if (!kasan_check_byte(p))
> +			return NULL;

Just checking: Check byte returns true if the object is not tracked by KASAN, right? I.e. if it's a KFENCE object, kasan_check_byte() always returns true.

> +		ks = kfence_ksize(p) ?: __ksize(p);
> +	} else
> +		ks = 0;
>  
> +	/* If the object still fits, repoison it precisely. */
>  	if (ks >= new_size) {
>  		p = kasan_krealloc((void *)p, new_size, flags);
>  		return (void *)p;
>  	}
>  
>  	ret = kmalloc_track_caller(new_size, flags);
> -	if (ret && p)
> -		memcpy(ret, p, ks);
> +	if (ret && p) {
> +		/* Disable KASAN checks as the object's redzone is accessed. */
> +		kasan_disable_current();
> +		memcpy(ret, kasan_reset_tag(p), ks);
> +		kasan_enable_current();
> +	}
>  
>  	return ret;
>  }
> -- 
> 2.30.0.365.g02bc693789-goog
> 

Re: [PATCH v3 mm 11/13] kasan: inline HW_TAGS helper functions

[Marco Elver]

On Fri, Feb 05, 2021 at 06:34PM +0100, Andrey Konovalov wrote:
> Mark all static functions in common.c and kasan.h that are used for
> hardware tag-based KASAN as inline to avoid unnecessary function calls.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

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

> ---
>  mm/kasan/common.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 7ffb1e6de2ef..7b53291dafa1 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -279,7 +279,8 @@ 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)
> +static inline u8 assign_tag(struct kmem_cache *cache,
> +					const void *object, bool init)
>  {
>  	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
>  		return 0xff;
> @@ -321,8 +322,8 @@ void * __must_check __kasan_init_slab_obj(struct kmem_cache *cache,
>  	return (void *)object;
>  }
>  
> -static bool ____kasan_slab_free(struct kmem_cache *cache, void *object,
> -			      unsigned long ip, bool quarantine)
> +static inline bool ____kasan_slab_free(struct kmem_cache *cache,
> +				void *object, unsigned long ip, bool quarantine)
>  {
>  	u8 tag;
>  	void *tagged_object;
> @@ -366,7 +367,7 @@ bool __kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
>  	return ____kasan_slab_free(cache, object, ip, true);
>  }
>  
> -static bool ____kasan_kfree_large(void *ptr, unsigned long ip)
> +static inline bool ____kasan_kfree_large(void *ptr, unsigned long ip)
>  {
>  	if (ptr != page_address(virt_to_head_page(ptr))) {
>  		kasan_report_invalid_free(ptr, ip);
> @@ -461,8 +462,8 @@ void * __must_check __kasan_slab_alloc(struct kmem_cache *cache,
>  	return tagged_object;
>  }
>  
> -static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
> -					size_t size, gfp_t flags)
> +static inline void *____kasan_kmalloc(struct kmem_cache *cache,
> +				const void *object, size_t size, gfp_t flags)
>  {
>  	unsigned long redzone_start;
>  	unsigned long redzone_end;
> -- 
> 2.30.0.365.g02bc693789-goog
> 

Re: [PATCH v3 mm 13/13] kasan: clarify that only first bug is reported in HW_TAGS

[Marco Elver]

On Fri, Feb 05, 2021 at 06:34PM +0100, Andrey Konovalov wrote:
> Hwardware tag-based KASAN only reports the first found bug. After that MTE
> tag checking gets disabled. Clarify this in comments and documentation.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

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

> ---
>  Documentation/dev-tools/kasan.rst | 8 ++++++--
>  mm/kasan/hw_tags.c                | 2 +-
>  2 files changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
> index e022b7506e37..1faabbe23e09 100644
> --- a/Documentation/dev-tools/kasan.rst
> +++ b/Documentation/dev-tools/kasan.rst
> @@ -155,7 +155,7 @@ Boot parameters
>  ~~~~~~~~~~~~~~~
>  
>  Hardware tag-based KASAN mode (see the section about various modes below) is
> -intended for use in production as a security mitigation. Therefore it supports
> +intended for use in production as a security mitigation. Therefore, it supports
>  boot parameters that allow to disable KASAN competely or otherwise control
>  particular KASAN features.
>  
> @@ -166,7 +166,8 @@ particular KASAN features.
>    ``off``).
>  
>  - ``kasan.fault=report`` or ``=panic`` controls whether to only print a KASAN
> -  report or also panic the kernel (default: ``report``).
> +  report or also panic the kernel (default: ``report``). Note, that tag
> +  checking gets disabled after the first reported bug.
>  
>  For developers
>  ~~~~~~~~~~~~~~
> @@ -296,6 +297,9 @@ Note, that enabling CONFIG_KASAN_HW_TAGS always results in in-kernel TBI being
>  enabled. Even when kasan.mode=off is provided, or when the hardware doesn't
>  support MTE (but supports TBI).
>  
> +Hardware tag-based KASAN only reports the first found bug. After that MTE tag
> +checking gets disabled.
> +
>  What memory accesses are sanitised by KASAN?
>  --------------------------------------------
>  
> diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
> index e529428e7a11..6c9285c906b8 100644
> --- a/mm/kasan/hw_tags.c
> +++ b/mm/kasan/hw_tags.c
> @@ -48,7 +48,7 @@ EXPORT_SYMBOL(kasan_flag_enabled);
>  /* Whether to collect alloc/free stack traces. */
>  DEFINE_STATIC_KEY_FALSE(kasan_flag_stacktrace);
>  
> -/* Whether panic or disable tag checking on fault. */
> +/* Whether to panic or print a report and disable tag checking on fault. */
>  bool kasan_flag_panic __ro_after_init;
>  
>  /* kasan=off/on */
> -- 
> 2.30.0.365.g02bc693789-goog
> 

Re: [PATCH v3 mm 08/13] kasan, mm: optimize krealloc poisoning

[Andrey Konovalov]

On Mon, Feb 8, 2021 at 11:48 AM Marco Elver <elver@google.com> wrote:
>
> On Fri, Feb 05, 2021 at 06:34PM +0100, Andrey Konovalov wrote:
> > Currently, krealloc() always calls ksize(), which unpoisons the whole
> > object including the redzone. This is inefficient, as kasan_krealloc()
> > repoisons the redzone for objects that fit into the same buffer.
> >
> > This patch changes krealloc() instrumentation to use uninstrumented
> > __ksize() that doesn't unpoison the memory. Instead, kasan_kreallos()
> > is changed to unpoison the memory excluding the redzone.
> >
> > For objects that don't fit into the old allocation, this patch disables
> > KASAN accessibility checks when copying memory into a new object instead
> > of unpoisoning it.
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
>
> Reviewed-by: Marco Elver <elver@google.com>
>
> Clarification below.
>
> > ---
> >  mm/kasan/common.c | 12 ++++++++++--
> >  mm/slab_common.c  | 20 ++++++++++++++------
> >  2 files changed, 24 insertions(+), 8 deletions(-)
> >
> > diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> > index 7ea643f7e69c..a8a67dca5e55 100644
> > --- a/mm/kasan/common.c
> > +++ b/mm/kasan/common.c
> > @@ -476,7 +476,7 @@ static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
> >
> >       /*
> >        * The object has already been unpoisoned by kasan_slab_alloc() for
> > -      * kmalloc() or by ksize() for krealloc().
> > +      * kmalloc() or by kasan_krealloc() for krealloc().
> >        */
> >
> >       /*
> > @@ -526,7 +526,7 @@ void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size,
> >
> >       /*
> >        * The object has already been unpoisoned by kasan_alloc_pages() for
> > -      * alloc_pages() or by ksize() for krealloc().
> > +      * alloc_pages() or by kasan_krealloc() for krealloc().
> >        */
> >
> >       /*
> > @@ -554,8 +554,16 @@ void * __must_check __kasan_krealloc(const void *object, size_t size, gfp_t flag
> >       if (unlikely(object == ZERO_SIZE_PTR))
> >               return (void *)object;
> >
> > +     /*
> > +      * Unpoison the object's data.
> > +      * Part of it might already have been unpoisoned, but it's unknown
> > +      * how big that part is.
> > +      */
> > +     kasan_unpoison(object, size);
> > +
> >       page = virt_to_head_page(object);
> >
> > +     /* Piggy-back on kmalloc() instrumentation to poison the redzone. */
> >       if (unlikely(!PageSlab(page)))
> >               return __kasan_kmalloc_large(object, size, flags);
> >       else
> > diff --git a/mm/slab_common.c b/mm/slab_common.c
> > index dad70239b54c..60a2f49df6ce 100644
> > --- a/mm/slab_common.c
> > +++ b/mm/slab_common.c
> > @@ -1140,19 +1140,27 @@ static __always_inline void *__do_krealloc(const void *p, size_t new_size,
> >       void *ret;
> >       size_t ks;
> >
> > -     if (likely(!ZERO_OR_NULL_PTR(p)) && !kasan_check_byte(p))
> > -             return NULL;
> > -
> > -     ks = ksize(p);
> > +     /* Don't use instrumented ksize to allow precise KASAN poisoning. */
> > +     if (likely(!ZERO_OR_NULL_PTR(p))) {
> > +             if (!kasan_check_byte(p))
> > +                     return NULL;
>
> Just checking: Check byte returns true if the object is not tracked by KASAN, right? I.e. if it's a KFENCE object, kasan_check_byte() always returns true.

kasan_check_byte() still performs the check, but since KFENCE objects
are never poisoned, the check always passes.

Thanks!