[PATCH v4 08/13] mm: slub: introduce metadata_access_enable()/metadata_access_disable()

[Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx>]

Wrap access to object's metadata in external functions with
metadata_access_enable()/metadata_access_disable() function calls.

This hooks separates payload accesses from metadata accesses
which might be useful for different checkers (e.g. KASan).

Signed-off-by: Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx>
---
 mm/slub.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/mm/slub.c b/mm/slub.c
index 82282f5..9b1f75c 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -467,13 +467,23 @@ static int slub_debug;
 static char *slub_debug_slabs;
 static int disable_higher_order_debug;
 
+static inline void metadata_access_enable(void)
+{
+}
+
+static inline void metadata_access_disable(void)
+{
+}
+
 /*
  * Object debugging
  */
 static void print_section(char *text, u8 *addr, unsigned int length)
 {
+	metadata_access_enable();
 	print_hex_dump(KERN_ERR, text, DUMP_PREFIX_ADDRESS, 16, 1, addr,
 			length, 1);
+	metadata_access_disable();
 }
 
 static struct track *get_track(struct kmem_cache *s, void *object,
@@ -503,7 +513,9 @@ static void set_track(struct kmem_cache *s, void *object,
 		trace.max_entries = TRACK_ADDRS_COUNT;
 		trace.entries = p->addrs;
 		trace.skip = 3;
+		metadata_access_enable();
 		save_stack_trace(&trace);
+		metadata_access_disable();
 
 		/* See rant in lockdep.c */
 		if (trace.nr_entries != 0 &&
@@ -677,7 +689,9 @@ static int check_bytes_and_report(struct kmem_cache *s, struct page *page,
 	u8 *fault;
 	u8 *end;
 
+	metadata_access_enable();
 	fault = memchr_inv(start, value, bytes);
+	metadata_access_disable();
 	if (!fault)
 		return 1;
 
@@ -770,7 +784,9 @@ static int slab_pad_check(struct kmem_cache *s, struct page *page)
 	if (!remainder)
 		return 1;
 
+	metadata_access_enable();
 	fault = memchr_inv(end - remainder, POISON_INUSE, remainder);
+	metadata_access_disable();
 	if (!fault)
 		return 1;
 	while (end > fault && end[-1] == POISON_INUSE)
-- 
2.1.2

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