mm/kasan: Don't store metadata inside kmalloc object when slub_debug_orig_size is on

For a kmalloc object, when both kasan and slub redzone sanity check
are enabled, they could both manipulate its data space like storing
kasan free meta data and setting up kmalloc redzone, and may affect
accuracy of that object's 'orig_size'.

As an accurate 'orig_size' will be needed by some function like
krealloc() soon, save kasan's free meta data in slub's metadata area
instead of inside object when 'orig_size' is enabled.

This will make it easier to maintain/understand the code. Size wise,
when these two options are both enabled, the slub meta data space is
already huge, and this just slightly increase the overall size.

Signed-off-by: Feng Tang <feng.tang@intel.com>
Acked-by: Andrey Konovalov <andreyknvl@gmail.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

1 files changed, 0 insertions, 17 deletions

diff --git a/mm/slub.c b/mm/slub.c
index 5b832512044e..83579b637578 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -230,12 +230,6 @@ static inline bool kmem_cache_debug(struct kmem_cache *s)
 	return kmem_cache_debug_flags(s, SLAB_DEBUG_FLAGS);
 }
 
-static inline bool slub_debug_orig_size(struct kmem_cache *s)
-{
-	return (kmem_cache_debug_flags(s, SLAB_STORE_USER) &&
-			(s->flags & SLAB_KMALLOC));
-}
-
 void *fixup_red_left(struct kmem_cache *s, void *p)
 {
 	if (kmem_cache_debug_flags(s, SLAB_RED_ZONE))
@@ -760,21 +754,10 @@ static inline void set_orig_size(struct kmem_cache *s,
 				void *object, unsigned int orig_size)
 {
 	void *p = kasan_reset_tag(object);
-	unsigned int kasan_meta_size;
 
 	if (!slub_debug_orig_size(s))
 		return;
 
-	/*
-	 * KASAN can save its free meta data inside of the object at offset 0.
-	 * If this meta data size is larger than 'orig_size', it will overlap
-	 * the data redzone in [orig_size+1, object_size]. Thus, we adjust
-	 * 'orig_size' to be as at least as big as KASAN's meta data.
-	 */
-	kasan_meta_size = kasan_metadata_size(s, true);
-	if (kasan_meta_size > orig_size)
-		orig_size = kasan_meta_size;
-
 	p += get_info_end(s);
 	p += sizeof(struct track) * 2;