kasan: introduce kasan_init_object_meta

Add a kasan_init_object_meta() helper that initializes metadata for a slab
object and use it in the common code.

For now, the implementations of this helper are the same for the Generic
and tag-based modes, but they will diverge later in the series.

This change hides references to alloc_meta from the common code.  This is
desired as only the Generic mode will be using per-object metadata after
this series.

Link: https://lkml.kernel.org/r/47c12938fc7f8105e7aaa592527c0e9d3c81fc37.1662411799.git.andreyknvl@google.comSigned-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Peter Collingbourne <pcc@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/kasan/common.c

@@ -313,13 +313,9 @@ static inline u8 assign_tag(struct kmem_cache *cache,
 void * __must_check __kasan_init_slab_obj(struct kmem_cache *cache,
 						const void *object)
 {
-	struct kasan_alloc_meta *alloc_meta;
-
-	if (kasan_stack_collection_enabled()) {
-		alloc_meta = kasan_get_alloc_meta(cache, object);
-		if (alloc_meta)
-			__memset(alloc_meta, 0, sizeof(*alloc_meta));
-	}
+	/* Initialize per-object metadata if it is present. */
+	if (kasan_stack_collection_enabled())
+		kasan_init_object_meta(cache, object);
 
 	/* Tag is ignored in set_tag() without CONFIG_KASAN_SW/HW_TAGS */
 	object = set_tag(object, assign_tag(cache, object, true));

mm/kasan/generic.c

@@ -328,6 +328,15 @@ DEFINE_ASAN_SET_SHADOW(f3);
 DEFINE_ASAN_SET_SHADOW(f5);
 DEFINE_ASAN_SET_SHADOW(f8);
 
+void kasan_init_object_meta(struct kmem_cache *cache, const void *object)
+{
+	struct kasan_alloc_meta *alloc_meta;
+
+	alloc_meta = kasan_get_alloc_meta(cache, object);
+	if (alloc_meta)
+		__memset(alloc_meta, 0, sizeof(*alloc_meta));
+}
+
 static void __kasan_record_aux_stack(void *addr, bool can_alloc)
 {
 	struct slab *slab = kasan_addr_to_slab(addr);

mm/kasan/kasan.h

@@ -279,6 +279,8 @@ void kasan_report_invalid_free(void *object, unsigned long ip, enum kasan_report
 struct page *kasan_addr_to_page(const void *addr);
 struct slab *kasan_addr_to_slab(const void *addr);
 
+void kasan_init_object_meta(struct kmem_cache *cache, const void *object);
+
 depot_stack_handle_t kasan_save_stack(gfp_t flags, bool can_alloc);
 void kasan_set_track(struct kasan_track *track, gfp_t flags);
 void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags);

mm/kasan/tags.c

@@ -17,6 +17,15 @@
 
 #include "kasan.h"
 
+void kasan_init_object_meta(struct kmem_cache *cache, const void *object)
+{
+	struct kasan_alloc_meta *alloc_meta;
+
+	alloc_meta = kasan_get_alloc_meta(cache, object);
+	if (alloc_meta)
+		__memset(alloc_meta, 0, sizeof(*alloc_meta));
+}
+
 void kasan_save_alloc_info(struct kmem_cache *cache, void *object, gfp_t flags)
 {
 	struct kasan_alloc_meta *alloc_meta;