[PATCH RFC v2 16/21] kasan: optimize poisoning in kmalloc and krealloc

[Andrey Konovalov]

Since kasan_kmalloc() always follows kasan_slab_alloc(), there's no need
to reunpoison the object data, only to poison the redzone.

This requires changing kasan annotation for early SLUB cache to
kasan_slab_alloc(). Otherwise kasan_kmalloc() doesn't untag the object.
This doesn't do any functional changes, as kmem_cache_node->object_size
is equal to sizeof(struct kmem_cache_node).

Similarly for kasan_krealloc(), as it's called after ksize(), which
already unpoisoned the object, there's no need to do it again.

Signed-off-by: Andrey Konovalov <andreyknvl at google.com>
Link: https://linux-review.googlesource.com/id/I4083d3b55605f70fef79bca9b90843c4390296f2
---
 mm/kasan/common.c | 31 +++++++++++++++++++++----------
 mm/slub.c         |  3 +--
 2 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index c5ec60e1a4d2..a581937c2a44 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -360,8 +360,14 @@ static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
 	if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) || IS_ENABLED(CONFIG_KASAN_HW_TAGS))
 		tag = assign_tag(cache, object, false, keep_tag);
 
-	/* Tag is ignored in set_tag without CONFIG_KASAN_SW/HW_TAGS */
-	kasan_unpoison_memory(set_tag(object, tag), size);
+	/*
+	 * Don't unpoison the object when keeping the tag. Tag is kept for:
+	 * 1. krealloc(), and then the memory has already been unpoisoned via ksize();
+	 * 2. kmalloc(), and then the memory has already been unpoisoned by kasan_kmalloc().
+	 * Tag is ignored in set_tag() without CONFIG_KASAN_SW/HW_TAGS.
+	 */
+	if (!keep_tag)
+		kasan_unpoison_memory(set_tag(object, tag), size);
 	kasan_poison_memory((void *)redzone_start, redzone_end - redzone_start,
 		KASAN_KMALLOC_REDZONE);
 
@@ -384,10 +390,9 @@ void * __must_check __kasan_kmalloc(struct kmem_cache *cache, const void *object
 }
 EXPORT_SYMBOL(__kasan_kmalloc);
 
-void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size,
-						gfp_t flags)
+static void * __must_check ____kasan_kmalloc_large(struct page *page, const void *ptr,
+						size_t size, gfp_t flags, bool realloc)
 {
-	struct page *page;
 	unsigned long redzone_start;
 	unsigned long redzone_end;
 
@@ -397,18 +402,24 @@ void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size,
 	if (unlikely(ptr == NULL))
 		return NULL;
 
-	page = virt_to_page(ptr);
-	redzone_start = round_up((unsigned long)(ptr + size),
-				KASAN_GRANULE_SIZE);
+	redzone_start = round_up((unsigned long)(ptr + size), KASAN_GRANULE_SIZE);
 	redzone_end = (unsigned long)ptr + page_size(page);
 
-	kasan_unpoison_memory(ptr, size);
+	/* ksize() in __do_krealloc() already unpoisoned the memory. */
+	if (!realloc)
+		kasan_unpoison_memory(ptr, size);
 	kasan_poison_memory((void *)redzone_start, redzone_end - redzone_start,
 		KASAN_PAGE_REDZONE);
 
 	return (void *)ptr;
 }
 
+void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size,
+						gfp_t flags)
+{
+	return ____kasan_kmalloc_large(virt_to_page(ptr), ptr, size, flags, false);
+}
+
 void * __must_check __kasan_krealloc(const void *object, size_t size, gfp_t flags)
 {
 	struct page *page;
@@ -419,7 +430,7 @@ void * __must_check __kasan_krealloc(const void *object, size_t size, gfp_t flag
 	page = virt_to_head_page(object);
 
 	if (unlikely(!PageSlab(page)))
-		return __kasan_kmalloc_large(object, size, flags);
+		return ____kasan_kmalloc_large(page, object, size, flags, true);
 	else
 		return ____kasan_kmalloc(page->slab_cache, object, size,
 						flags, true);
diff --git a/mm/slub.c b/mm/slub.c
index 1d3f2355df3b..afb035b0bf2d 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3535,8 +3535,7 @@ 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;
-- 
2.29.0.rc1.297.gfa9743e501-goog