On Wed, Apr 15, 2020 at 3:44 PM Kirill Tkhai ktkhai@virtuozzo.com wrote:
On 15.04.2020 04:54, Andrew Morton wrote:
The patch titled Subject: mm/ksm: fix NULL pointer dereference when KSM zero page is enabled has been added to the -mm tree. Its filename is mm-ksm-fix-null-pointer-dereference-when-ksm-zero-page-is-enabled.patch
This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-ksm-fix-null-pointer-dereference... and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-ksm-fix-null-pointer-dereference...
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From: Muchun Song songmuchun@bytedance.com Subject: mm/ksm: fix NULL pointer dereference when KSM zero page is enabled
find_mergeable_vma can return NULL. In this case, it leads to crash when we access vma->vm_mm(its offset is 0x40) later in write_protect_page. And this case did happen on our server. The following calltrace is captured in kernel 4.19 with the following patch applied and KSM zero page enabled on our server.
commit e86c59b1b12d ("mm/ksm: improve deduplication of zero pages with colouring")
So add a vma check to fix it.
BUG: unable to handle kernel NULL pointer dereference at 0000000000000040 Oops: 0000 [#1] SMP NOPTI CPU: 9 PID: 510 Comm: ksmd Kdump: loaded Tainted: G OE 4.19.36.bsk.9-amd64 #4.19.36.bsk.9 Hardware name: FOXCONN R-5111/GROOT, BIOS IC1B111F 08/17/2019 RIP: 0010:try_to_merge_one_page+0xc7/0x760 Code: 24 58 65 48 33 34 25 28 00 00 00 89 e8 0f 85 a3 06 00 00 48 83 c4 60 5b 5d 41 5c 41 5d 41 5e 41 5f c3 48 8b 46 08 a8 01 75 b8 <49> 8b 44 24 40 4c 8d 7c 24 20 b9 07 00 00 00 4c 89 e6 4c 89 ff 48 RSP: 0018:ffffadbdd9fffdb0 EFLAGS: 00010246 RAX: ffffda83ffd4be08 RBX: ffffda83ffd4be40 RCX: 0000002c6e800000 RDX: 0000000000000000 RSI: ffffda83ffd4be40 RDI: 0000000000000000 RBP: ffffa11939f02ec0 R08: 0000000094e1a447 R09: 00000000abe76577 R10: 0000000000000962 R11: 0000000000004e6a R12: 0000000000000000 R13: ffffda83b1e06380 R14: ffffa18f31f072c0 R15: ffffda83ffd4be40 FS: 0000000000000000(0000) GS:ffffa0da43b80000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000040 CR3: 0000002c77c0a003 CR4: 00000000007626e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: ? follow_page_pte+0x36d/0x5e0 ksm_scan_thread+0x115e/0x1960 ? remove_wait_queue+0x60/0x60 kthread+0xf5/0x130 ? try_to_merge_with_ksm_page+0x90/0x90 ? kthread_create_worker_on_cpu+0x70/0x70 ret_from_fork+0x1f/0x30
Link: http://lkml.kernel.org/r/20200414132905.83819-1-songmuchun@bytedance.com Fixes: e86c59b1b12d ("mm/ksm: improve deduplication of zero pages with colouring") Signed-off-by: Muchun Song songmuchun@bytedance.com Co-developed-by: Xiongchun Duan duanxiongchun@bytedance.com Reviewed-by: David Hildenbrand david@redhat.com
Reviewed-by: Kirill Tkhai ktkhai@virtuozzo.com
Cc: Hugh Dickins hughd@google.com Cc: Yang Shi yang.shi@linux.alibaba.com Cc: Claudio Imbrenda imbrenda@linux.vnet.ibm.com Cc: Markus Elfring Markus.Elfring@web.de Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org
mm/ksm.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
--- a/mm/ksm.c~mm-ksm-fix-null-pointer-dereference-when-ksm-zero-page-is-enabled +++ a/mm/ksm.c @@ -2112,8 +2112,11 @@ static void cmp_and_merge_page(struct pa
down_read(&mm->mmap_sem); vma = find_mergeable_vma(mm, rmap_item->address);
err = try_to_merge_one_page(vma, page,ZERO_PAGE(rmap_item->address));
if (vma)err = try_to_merge_one_page(vma, page,ZERO_PAGE(rmap_item->address));elseerr = -EFAULT; up_read(&mm->mmap_sem);In case of vma is out of date, we also may consider to exit this function without calling unstable_tree_search_insert().
Yeah, I agree with you. Should I send another patch to fix this patch or an upgraded version(v4) of this patch.
/* * In case of failure, the page was not really empty, so we_
Patches currently in -mm which might be from songmuchun@bytedance.com are
mm-ksm-fix-null-pointer-dereference-when-ksm-zero-page-is-enabled.patch