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    Subject[PATCH AUTOSEL 4.19 034/192] page_poison: play nicely with KASAN
    Date
    From: Qian Cai <cai@lca.pw>

    [ Upstream commit 4117992df66a26fa33908b4969e04801534baab1 ]

    KASAN does not play well with the page poisoning (CONFIG_PAGE_POISONING).
    It triggers false positives in the allocation path:

    BUG: KASAN: use-after-free in memchr_inv+0x2ea/0x330
    Read of size 8 at addr ffff88881f800000 by task swapper/0
    CPU: 0 PID: 0 Comm: swapper Not tainted 5.0.0-rc1+ #54
    Call Trace:
    dump_stack+0xe0/0x19a
    print_address_description.cold.2+0x9/0x28b
    kasan_report.cold.3+0x7a/0xb5
    __asan_report_load8_noabort+0x19/0x20
    memchr_inv+0x2ea/0x330
    kernel_poison_pages+0x103/0x3d5
    get_page_from_freelist+0x15e7/0x4d90

    because KASAN has not yet unpoisoned the shadow page for allocation
    before it checks memchr_inv() but only found a stale poison pattern.

    Also, false positives in free path,

    BUG: KASAN: slab-out-of-bounds in kernel_poison_pages+0x29e/0x3d5
    Write of size 4096 at addr ffff8888112cc000 by task swapper/0/1
    CPU: 5 PID: 1 Comm: swapper/0 Not tainted 5.0.0-rc1+ #55
    Call Trace:
    dump_stack+0xe0/0x19a
    print_address_description.cold.2+0x9/0x28b
    kasan_report.cold.3+0x7a/0xb5
    check_memory_region+0x22d/0x250
    memset+0x28/0x40
    kernel_poison_pages+0x29e/0x3d5
    __free_pages_ok+0x75f/0x13e0

    due to KASAN adds poisoned redzones around slab objects, but the page
    poisoning needs to poison the whole page.

    Link: http://lkml.kernel.org/r/20190114233405.67843-1-cai@lca.pw
    Signed-off-by: Qian Cai <cai@lca.pw>
    Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.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/page_alloc.c | 2 +-
    mm/page_poison.c | 4 ++++
    2 files changed, 5 insertions(+), 1 deletion(-)

    diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    index ef99971c13dd..8e6932a140b8 100644
    --- a/mm/page_alloc.c
    +++ b/mm/page_alloc.c
    @@ -1922,8 +1922,8 @@ inline void post_alloc_hook(struct page *page, unsigned int order,

    arch_alloc_page(page, order);
    kernel_map_pages(page, 1 << order, 1);
    - kernel_poison_pages(page, 1 << order, 1);
    kasan_alloc_pages(page, order);
    + kernel_poison_pages(page, 1 << order, 1);
    set_page_owner(page, order, gfp_flags);
    }

    diff --git a/mm/page_poison.c b/mm/page_poison.c
    index aa2b3d34e8ea..6cfa8e7d7213 100644
    --- a/mm/page_poison.c
    +++ b/mm/page_poison.c
    @@ -6,6 +6,7 @@
    #include <linux/page_ext.h>
    #include <linux/poison.h>
    #include <linux/ratelimit.h>
    +#include <linux/kasan.h>

    static bool want_page_poisoning __read_mostly;

    @@ -34,7 +35,10 @@ static void poison_page(struct page *page)
    {
    void *addr = kmap_atomic(page);

    + /* KASAN still think the page is in-use, so skip it. */
    + kasan_disable_current();
    memset(addr, PAGE_POISON, PAGE_SIZE);
    + kasan_enable_current();
    kunmap_atomic(addr);
    }

    --
    2.19.1
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