From: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Reorganize the code to avoid nested if/else checks to improve the
readability.
Also drop the confusing comments about KMALLOC_MAX_SIZE checks: they
are relevant for both SLUB and SLAB (originally, the comments likely
confused KMALLOC_MAX_SIZE with KMALLOC_MAX_CACHE_SIZE).
Fixes: a5989d4ed40c ("kasan: improve free meta storage in Generic KASAN")
Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
---
mm/kasan/generic.c | 67 +++++++++++++++++++++++++++-------------------
1 file changed, 39 insertions(+), 28 deletions(-)
diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
index 54e20b2bc3e1..769e43e05d0b 100644
--- a/mm/kasan/generic.c
+++ b/mm/kasan/generic.c
@@ -381,16 +381,11 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
ok_size = *size;
- /* Add alloc meta into redzone. */
+ /* Add alloc meta into the redzone. */
cache->kasan_info.alloc_meta_offset = *size;
*size += sizeof(struct kasan_alloc_meta);
- /*
- * If alloc meta doesn't fit, don't add it.
- * This can only happen with SLAB, as it has KMALLOC_MAX_SIZE equal
- * to KMALLOC_MAX_CACHE_SIZE and doesn't fall back to page_alloc for
- * larger sizes.
- */
+ /* If alloc meta doesn't fit, don't add it. */
if (*size > KMALLOC_MAX_SIZE) {
cache->kasan_info.alloc_meta_offset = 0;
*size = ok_size;
@@ -401,36 +396,52 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
orig_alloc_meta_offset = cache->kasan_info.alloc_meta_offset;
/*
- * Add free meta into redzone when it's not possible to store
+ * Store free meta in the redzone when it's not possible to store
* it in the object. This is the case when:
* 1. Object is SLAB_TYPESAFE_BY_RCU, which means that it can
* be touched after it was freed, or
* 2. Object has a constructor, which means it's expected to
- * retain its content until the next allocation, or
- * 3. Object is too small and SLUB DEBUG is enabled. Avoid
- * free meta that exceeds the object size corrupts the
- * SLUB DEBUG metadata.
- * Otherwise cache->kasan_info.free_meta_offset = 0 is implied.
- * If the object is smaller than the free meta and SLUB DEBUG
- * is not enabled, it is still possible to store part of the
- * free meta in the object.
+ * retain its content until the next allocation.
*/
if ((cache->flags & SLAB_TYPESAFE_BY_RCU) || cache->ctor) {
cache->kasan_info.free_meta_offset = *size;
*size += sizeof(struct kasan_free_meta);
- } else if (cache->object_size < sizeof(struct kasan_free_meta)) {
- if (__slub_debug_enabled()) {
- cache->kasan_info.free_meta_offset = *size;
- *size += sizeof(struct kasan_free_meta);
- } else {
- rem_free_meta_size = sizeof(struct kasan_free_meta) -
- cache->object_size;
- *size += rem_free_meta_size;
- if (cache->kasan_info.alloc_meta_offset != 0)
- cache->kasan_info.alloc_meta_offset += rem_free_meta_size;
- }
+ goto free_meta_added;
+ }
+
+ /*
+ * Otherwise, if the object is large enough to contain free meta,
+ * store it within the object.
+ */
+ if (sizeof(struct kasan_free_meta) <= cache->object_size) {
+ /* cache->kasan_info.free_meta_offset = 0 is implied. */
+ goto free_meta_added;
}
+ /*
+ * For smaller objects, store the beginning of free meta within the
+ * object and the end in the redzone. And thus shift the location of
+ * alloc meta to free up space for free meta.
+ * This is only possible when slub_debug is disabled, as otherwise
+ * the end of free meta will overlap with slub_debug metadata.
+ */
+ if (!__slub_debug_enabled()) {
+ rem_free_meta_size = sizeof(struct kasan_free_meta) -
+ cache->object_size;
+ *size += rem_free_meta_size;
+ if (cache->kasan_info.alloc_meta_offset != 0)
+ cache->kasan_info.alloc_meta_offset += rem_free_meta_size;
+ goto free_meta_added;
+ }
+
+ /*
+ * If the object is small and slub_debug is enabled, store free meta
+ * in the redzone after alloc meta.
+ */
+ cache->kasan_info.free_meta_offset = *size;
+ *size += sizeof(struct kasan_free_meta);
+
+free_meta_added:
/* If free meta doesn't fit, don't add it. */
if (*size > KMALLOC_MAX_SIZE) {
cache->kasan_info.free_meta_offset = KASAN_NO_FREE_META;
@@ -440,7 +451,7 @@ void kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
/* Calculate size with optimal redzone. */
optimal_size = cache->object_size + optimal_redzone(cache->object_size);
- /* Limit it with KMALLOC_MAX_SIZE (relevant for SLAB only). */
+ /* Limit it with KMALLOC_MAX_SIZE. */
if (optimal_size > KMALLOC_MAX_SIZE)
optimal_size = KMALLOC_MAX_SIZE;
/* Use optimal size if the size with added metas is not large enough. */
--
2.25.1
