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SubjectRe: [PATCH 4/5] kasan, slub: move kasan_poison_slab hook before page_address
On Mon, 11 Feb 2019 22:59:53 +0100 Andrey Konovalov <andreyknvl@google.com> wrote:

> 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.
>
> ...
>
> --- 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);

This doesn't compile when CONFIG_SLUB_DEBUG=n. Please review carefully:

--- a/mm/slub.c~kasan-slub-move-kasan_poison_slab-hook-before-page_address-fix
+++ a/mm/slub.c
@@ -1357,6 +1357,14 @@ slab_flags_t kmem_cache_flags(unsigned i

#define disable_higher_order_debug 0

+static inline void metadata_access_enable(void)
+{
+}
+
+static inline void metadata_access_disable(void)
+{
+}
+
static inline unsigned long slabs_node(struct kmem_cache *s, int node)
{ return 0; }
static inline unsigned long node_nr_slabs(struct kmem_cache_node *n)
_
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