[PATCH v2 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 <andreyk...@google.com>
---
 mm/slub.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index f5a451c49190..a7e7c7f719f9 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1075,6 +1075,16 @@ static void setup_object_debug(struct kmem_cache *s, 
struct page *page,
        init_tracking(s, object);
 }
 
+static void setup_page_debug(struct kmem_cache *s, void *addr, int order)
+{
+       if (!(s->flags & SLAB_POISON))
+               return;
+
+       metadata_access_enable();
+       memset(addr, POISON_INUSE, PAGE_SIZE << order);
+       metadata_access_disable();
+}
+
 static inline int alloc_consistency_checks(struct kmem_cache *s,
                                        struct page *page,
                                        void *object, unsigned long addr)
@@ -1330,6 +1340,8 @@ slab_flags_t kmem_cache_flags(unsigned int object_size,
 #else /* !CONFIG_SLUB_DEBUG */
 static inline void setup_object_debug(struct kmem_cache *s,
                        struct page *page, void *object) {}
+static inline void setup_page_debug(struct kmem_cache *s,
+                       void *addr, int order) {}
 
 static inline int alloc_debug_processing(struct kmem_cache *s,
        struct page *page, void *object, unsigned long addr) { return 0; }
@@ -1643,12 +1655,11 @@ static struct page *allocate_slab(struct kmem_cache *s, 
gfp_t flags, int node)
        if (page_is_pfmemalloc(page))
                SetPageSlabPfmemalloc(page);
 
-       start = page_address(page);
+       kasan_poison_slab(page);
 
-       if (unlikely(s->flags & SLAB_POISON))
-               memset(start, POISON_INUSE, PAGE_SIZE << order);
+       start = page_address(page);
 
-       kasan_poison_slab(page);
+       setup_page_debug(s, start, order);
 
        shuffle = shuffle_freelist(s, page);
 
-- 
2.20.1.791.gb4d0f1c61a-goog