[PATCH 4/5] kasan, slub: move kasan_poison_slab hook before page_address

[Andrey Konovalov]

With tag based KASAN page_address() looks at the page flags to see
whether the resulting pointer needs to have a tag set. Since we don't
want to set a tag when page_address() is called on SLAB pages, we call
page_kasan_tag_reset() in kasan_poison_slab(). However in allocate_slab()
page_address() is called before kasan_poison_slab(). Fix it by changing
the order.

Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
---
 mm/slub.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 4a3d7686902f..ce874a5c9ee7 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1642,12 +1642,15 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
 	if (page_is_pfmemalloc(page))
 		SetPageSlabPfmemalloc(page);
 
+	kasan_poison_slab(page);
+
 	start = page_address(page);
 
-	if (unlikely(s->flags & SLAB_POISON))
+	if (unlikely(s->flags & SLAB_POISON)) {
+		metadata_access_enable();
 		memset(start, POISON_INUSE, PAGE_SIZE << order);
-
-	kasan_poison_slab(page);
+		metadata_access_disable();
+	}
 
 	shuffle = shuffle_freelist(s, page);
 
-- 
2.20.1.791.gb4d0f1c61a-goog