• Qian Cai's avatar
    page_poison: play nicely with KASAN · d49efeb1
    Qian Cai authored
    [ 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.pwSigned-off-by: 's avatarQian Cai <cai@lca.pw>
    Acked-by: 's avatarAndrey Ryabinin <aryabinin@virtuozzo.com>
    Signed-off-by: 's avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: 's avatarLinus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: 's avatarSasha Levin <sashal@kernel.org>
    d49efeb1
page_alloc.c 211 KB