[patch 070/118] kasan, mm: don't save alloc stacks twice

[Andrew Morton <akpm@linux-foundation.org>]

From: Andrey Konovalov <andreyknvl@google.com>
Subject: kasan, mm: don't save alloc stacks twice

Patch series "kasan: optimizations and fixes for HW_TAGS", v4.

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%.


This patch (of 13):

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.

Link: https://lkml.kernel.org/r/cover.1612546384.git.andreyknvl@google.com
Link: https://lkml.kernel.org/r/7c673ebca8d00f40a7ad6f04ab9a2bddeeae2097.1612546384.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/kasan.h |    9 +++++++++
 mm/kasan/common.c     |   18 ++++++++++++++----
 mm/slab_common.c      |    1 +
 3 files changed, 24 insertions(+), 4 deletions(-)

--- a/include/linux/kasan.h~kasan-mm-dont-save-alloc-stacks-twice
+++ a/include/linux/kasan.h
@@ -83,6 +83,7 @@ static inline void kasan_disable_current
 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_
 		__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(stru
 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,
--- a/mm/kasan/common.c~kasan-mm-dont-save-alloc-stacks-twice
+++ a/mm/kasan/common.c
@@ -210,6 +210,11 @@ void __kasan_cache_create(struct kmem_ca
 		*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
 	}
 }
 
-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 km
 				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 km
 			   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);
 }
--- a/mm/slab_common.c~kasan-mm-dont-save-alloc-stacks-twice
+++ a/mm/slab_common.c
@@ -643,6 +643,7 @@ struct kmem_cache *__init create_kmalloc
 		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;
_