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

[Andrey Konovalov <andreyknvl@google.com>]

On Tue, Feb 12, 2019 at 10:12 PM Andrew Morton
<akpm@linux-foundation.org> wrote:
>
> 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:

Sorry, missed this. I think it makes more sense to move this memset
into another function CONFIG_SLUB_DEBUG ifdef, since all other
poisoning code is also there. I'll send a v2.

>
> --- 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)
> _
>