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    SubjectRe: [PATCH AUTOSEL 4.14 22/33] kasan, slab: make freelist stored without tags
    On Wed, Mar 13, 2019 at 8:16 PM Sasha Levin <sashal@kernel.org> wrote:
    >
    > From: Andrey Konovalov <andreyknvl@google.com>
    >
    > [ Upstream commit 51dedad06b5f6c3eea7ec1069631b1ef7796912a ]

    Hi Sasha,

    None of the 4.9, 4.14, 4.19 or 4.20 have tag-based KASAN, so
    backporting these 3 KASAN related patches doesn't make much sense.

    Thanks!


    >
    > Similarly to "kasan, slub: move kasan_poison_slab hook before
    > page_address", move kasan_poison_slab() before alloc_slabmgmt(), which
    > calls page_address(), to make page_address() return value to be
    > non-tagged. This, combined with calling kasan_reset_tag() for off-slab
    > slab management object, leads to freelist being stored non-tagged.
    >
    > Link: http://lkml.kernel.org/r/dfb53b44a4d00de3879a05a9f04c1f55e584f7a1.1550602886.git.andreyknvl@google.com
    > Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
    > Tested-by: Qian Cai <cai@lca.pw>
    > Cc: Alexander Potapenko <glider@google.com>
    > Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
    > Cc: Catalin Marinas <catalin.marinas@arm.com>
    > Cc: Dmitry Vyukov <dvyukov@google.com>
    > Cc: Evgeniy Stepanov <eugenis@google.com>
    > Cc: Kostya Serebryany <kcc@google.com>
    > Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
    > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    > Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    > Signed-off-by: Sasha Levin <sashal@kernel.org>
    > ---
    > mm/slab.c | 9 ++++++++-
    > 1 file changed, 8 insertions(+), 1 deletion(-)
    >
    > diff --git a/mm/slab.c b/mm/slab.c
    > index 409631e49295..766043dd3f8e 100644
    > --- a/mm/slab.c
    > +++ b/mm/slab.c
    > @@ -2378,6 +2378,7 @@ static void *alloc_slabmgmt(struct kmem_cache *cachep,
    > /* Slab management obj is off-slab. */
    > freelist = kmem_cache_alloc_node(cachep->freelist_cache,
    > local_flags, nodeid);
    > + freelist = kasan_reset_tag(freelist);
    > if (!freelist)
    > return NULL;
    > } else {
    > @@ -2690,6 +2691,13 @@ static struct page *cache_grow_begin(struct kmem_cache *cachep,
    >
    > offset *= cachep->colour_off;
    >
    > + /*
    > + * Call kasan_poison_slab() before calling alloc_slabmgmt(), so
    > + * page_address() in the latter returns a non-tagged pointer,
    > + * as it should be for slab pages.
    > + */
    > + kasan_poison_slab(page);
    > +
    > /* Get slab management. */
    > freelist = alloc_slabmgmt(cachep, page, offset,
    > local_flags & ~GFP_CONSTRAINT_MASK, page_node);
    > @@ -2698,7 +2706,6 @@ static struct page *cache_grow_begin(struct kmem_cache *cachep,
    >
    > slab_map_pages(cachep, page, freelist);
    >
    > - kasan_poison_slab(page);
    > cache_init_objs(cachep, page);
    >
    > if (gfpflags_allow_blocking(local_flags))
    > --
    > 2.19.1
    >

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