[PATCH v2 4/5] kasan, slub: move kasan_poison_slab hook before page_address

From: Andrey Konovalov
Date: Wed Feb 13 2019 - 08:58:56 EST


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 | 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