From: Muchun Song <songmuchun@bytedance.com>
To: akpm@linux-foundation.org
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Muchun Song <songmuchun@bytedance.com>,
Xiongchun duan <duanxiongchun@bytedance.com>
Subject: [PATCH] mm/ksm: Fix kernel NULL pointer dereference at 0000000000000040
Date: Tue, 14 Apr 2020 14:20:50 +0800 [thread overview]
Message-ID: <20200414062050.66644-1-songmuchun@bytedance.com> (raw)
The find_mergeable_vma can return NULL. In this case, it leads
to crash when we access vma->vm_mm(which's offset is 0x40) in
write_protect_page. And this case did happen on our server. The
following calltrace is captured in kernel 4.19 with ksm enabled.
So add a vma check to fix it.
--------------------------------------------------------------------------
BUG: unable to handle kernel NULL pointer dereference at 0000000000000040
PGD 0 P4D 0
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
--------------------------------------------------------------------------
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Xiongchun duan <duanxiongchun@bytedance.com>
---
mm/ksm.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/mm/ksm.c b/mm/ksm.c
index a558da9e71770..69b2f85e22d5b 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2112,8 +2112,11 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
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));
+ else
+ err = -EFAULT;
up_read(&mm->mmap_sem);
/*
* In case of failure, the page was not really empty, so we
--
2.11.0
next reply other threads:[~2020-04-14 6:21 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-14 6:20 Muchun Song [this message]
2020-04-14 11:48 ` [PATCH] mm/ksm: Fix kernel NULL pointer dereference at 0000000000000040 David Hildenbrand
2020-04-14 12:09 ` [External] " Muchun Song
2020-04-14 12:23 ` David Hildenbrand
2020-04-14 13:01 ` Muchun Song
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200414062050.66644-1-songmuchun@bytedance.com \
--to=songmuchun@bytedance.com \
--cc=akpm@linux-foundation.org \
--cc=duanxiongchun@bytedance.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).