When SLAB_STORE_USER debug flag is used, any metadata after the original
kmalloc request size (orig_size) is not properly aligned in 64-bit
architectures because its type is unsigned int. When both KASAN and
SLAB_STORE_USER are enabled, kasan_alloc_meta is not properly aligned.

Because not all architectures can handle unaligned memory accesses,
ensure that any metadata (track, orig_size, kasan_{alloc,free}_meta)
in a slab object is word-aligned. struct track, kasan_{alloc,free}_meta
are aligned by adding __aligned(sizeof(unsigned long)).

For orig_size, to avoid confusion that orig_size is an unsigned long,
use ALIGN(sizeof(unsigned int), sizeof(unsigned long)) to indicate that
its size is unsigned int, but it must be aligned to the word boundary.
On 64-bit architectures, this allocates 8 bytes for orig_size, but it's
acceptable since this is for debugging purposes and not for production
use.

Fixes: 6edf2576a6cc ("mm/slub: enable debugging memory wasting of kmalloc")
Signed-off-by: Harry Yoo <harry.yoo@oracle.com>
---

The combination of:
- architectures that cannot handle unaligned memory access
- KASAN
- SLAB_STORE_USER

sounds quite niche, does anyone think it needs to be backported to
-stable?

 mm/kasan/kasan.h |  4 ++--
 mm/slub.c        | 16 +++++++++++-----
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 129178be5e64..d4ea7ecc20c3 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -265,7 +265,7 @@ struct kasan_alloc_meta {
 	struct kasan_track alloc_track;
 	/* Free track is stored in kasan_free_meta. */
 	depot_stack_handle_t aux_stack[2];
-};
+} __aligned(sizeof(unsigned long));
 
 struct qlist_node {
 	struct qlist_node *next;
@@ -289,7 +289,7 @@ struct qlist_node {
 struct kasan_free_meta {
 	struct qlist_node quarantine_link;
 	struct kasan_track free_track;
-};
+} __aligned(sizeof(unsigned long));
 
 #endif /* CONFIG_KASAN_GENERIC */
 
diff --git a/mm/slub.c b/mm/slub.c
index 0ef2ba459ef9..9e91f2016697 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -343,7 +343,7 @@ struct track {
 	int cpu;		/* Was running on cpu */
 	int pid;		/* Pid context */
 	unsigned long when;	/* When did the operation occur */
-};
+} __aligned(sizeof(unsigned long));
 
 enum track_item { TRACK_ALLOC, TRACK_FREE };
 
@@ -1180,7 +1180,7 @@ static void print_trailer(struct kmem_cache *s, struct slab *slab, u8 *p)
 		off += 2 * sizeof(struct track);
 
 	if (slub_debug_orig_size(s))
-		off += sizeof(unsigned int);
+		off += ALIGN(sizeof(unsigned int), sizeof(unsigned long));
 
 	off += kasan_metadata_size(s, false);
 
@@ -1376,7 +1376,8 @@ static int check_pad_bytes(struct kmem_cache *s, struct slab *slab, u8 *p)
 		off += 2 * sizeof(struct track);
 
 		if (s->flags & SLAB_KMALLOC)
-			off += sizeof(unsigned int);
+			off += ALIGN(sizeof(unsigned int),
+				     sizeof(unsigned long));
 	}
 
 	off += kasan_metadata_size(s, false);
@@ -7286,9 +7287,14 @@ static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s)
 		 */
 		size += 2 * sizeof(struct track);
 
-		/* Save the original kmalloc request size */
+		/*
+		 * Save the original kmalloc request size.
+		 * Although the request size is an unsigned int,
+		 * make sure that is aligned to word boundary.
+		 */
 		if (flags & SLAB_KMALLOC)
-			size += sizeof(unsigned int);
+			size += ALIGN(sizeof(unsigned int),
+				      sizeof(unsigned long));
 	}
 #endif
 
-- 
2.43.0