* [PATCH v2] mm/ksm: Fix NULL pointer dereference when KSM zero page is enabled
@ 2020-04-14 7:56 Muchun Song
2020-04-14 9:17 ` Markus Elfring
0 siblings, 1 reply; 5+ messages in thread
From: Muchun Song @ 2020-04-14 7:56 UTC (permalink / raw)
To: akpm, Markus.Elfring; +Cc: linux-mm, linux-kernel, Muchun Song, Xiongchun Duan
The 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 KSM zero page
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
--------------------------------------------------------------------------
Fixes: e86c59b1b12d ("mm/ksm: improve deduplication of zero pages with colouring")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Xiongchun Duan <duanxiongchun@bytedance.com>
---
Change in v2:
Update commit message and patch subject.
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
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v2] mm/ksm: Fix NULL pointer dereference when KSM zero page is enabled
2020-04-14 7:56 [PATCH v2] mm/ksm: Fix NULL pointer dereference when KSM zero page is enabled Muchun Song
@ 2020-04-14 9:17 ` Markus Elfring
2020-04-14 9:56 ` [External] " Muchun Song
0 siblings, 1 reply; 5+ messages in thread
From: Markus Elfring @ 2020-04-14 9:17 UTC (permalink / raw)
To: Muchun Song, Xiongchun Duan, linux-mm; +Cc: linux-kernel, Andrew Morton
> to crash when we access vma->vm_mm(its offset is 0x40) later in
Will another fine-tuning become relevant also for this wording?
> following calltrace is captured in kernel 4.19 with KSM zero page
Can the mentioned Linux version trigger any special software
development concerns?
Will any other tags become helpful in such a case?
Regards,
Markus
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [External] Re: [PATCH v2] mm/ksm: Fix NULL pointer dereference when KSM zero page is enabled
2020-04-14 9:17 ` Markus Elfring
@ 2020-04-14 9:56 ` Muchun Song
2020-04-14 14:17 ` [v2] " Markus Elfring
0 siblings, 1 reply; 5+ messages in thread
From: Muchun Song @ 2020-04-14 9:56 UTC (permalink / raw)
To: Markus Elfring; +Cc: Xiongchun Duan, linux-mm, linux-kernel, Andrew Morton
On Tue, Apr 14, 2020 at 5:17 PM Markus Elfring <Markus.Elfring@web.de> wrote:
>
> > to crash when we access vma->vm_mm(its offset is 0x40) later in
>
> Will another fine-tuning become relevant also for this wording?
>
Sorry, I don't understand what this means because of my poor English.
Could you explain it again. Thanks.
>
> > following calltrace is captured in kernel 4.19 with KSM zero page
>
> Can the mentioned Linux version trigger any special software
> development concerns?
>
> Will any other tags become helpful in such a case?
How about changing
"following calltrace is captured in kernel 4.19 with KSM zero page"
to
"The following calltrace is captured with the following patch applied:
e86c59b1b12d ("mm/ksm: improve deduplication of zero pages with
colouring")
"
?
--
Yours,
Muchun
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [v2] mm/ksm: Fix NULL pointer dereference when KSM zero page is enabled
2020-04-14 9:56 ` [External] " Muchun Song
@ 2020-04-14 14:17 ` Markus Elfring
2020-04-14 14:39 ` [External] " Muchun Song
0 siblings, 1 reply; 5+ messages in thread
From: Markus Elfring @ 2020-04-14 14:17 UTC (permalink / raw)
To: Muchun Song, Xiongchun Duan, linux-mm; +Cc: linux-kernel, Andrew Morton
>>> to crash when we access vma->vm_mm(its offset is 0x40) later in
>>
>> Will another fine-tuning become relevant also for this wording?
>
> Sorry, I don't understand what this means because of my poor English.
Our language knowledge can evolve over time.
> Could you explain it again.
You integrated a few of my suggestions into your message selection. - Thanks.
I wonder why you did not like the following small adjustment possibilities
so far.
to a crash … vm_mm (its …
>> Will any other tags become helpful in such a case?
>
> How about changing
> "following calltrace is captured in kernel 4.19 with KSM zero page"
> to
> "The following calltrace is captured with the following patch applied:
> e86c59b1b12d ("mm/ksm: improve deduplication of zero pages with
> colouring")
> "
> ?
I find it unlikely that such a wording alternative would be more appropriate
while I became just curious for related development consequences around
the usage of a longterm kernel version.
Would you like to reuse the term “call trace”?
Regards,
Markus
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [External] Re: [v2] mm/ksm: Fix NULL pointer dereference when KSM zero page is enabled
2020-04-14 14:17 ` [v2] " Markus Elfring
@ 2020-04-14 14:39 ` Muchun Song
0 siblings, 0 replies; 5+ messages in thread
From: Muchun Song @ 2020-04-14 14:39 UTC (permalink / raw)
To: Markus Elfring; +Cc: Xiongchun Duan, linux-mm, linux-kernel, Andrew Morton
On Tue, Apr 14, 2020 at 10:17 PM Markus Elfring <Markus.Elfring@web.de> wrote:
>
> >>> to crash when we access vma->vm_mm(its offset is 0x40) later in
> >>
> >> Will another fine-tuning become relevant also for this wording?
> >
> > Sorry, I don't understand what this means because of my poor English.
>
> Our language knowledge can evolve over time.
>
>
> > Could you explain it again.
>
> You integrated a few of my suggestions into your message selection. - Thanks.
> I wonder why you did not like the following small adjustment possibilities
> so far.
>
> to a crash … vm_mm (its …
>
Thanks a lot. I will fix it.
>
> >> Will any other tags become helpful in such a case?
> >
> > How about changing
> > "following calltrace is captured in kernel 4.19 with KSM zero page"
> > to
> > "The following calltrace is captured with the following patch applied:
> > e86c59b1b12d ("mm/ksm: improve deduplication of zero pages with
> > colouring")
> > "
> > ?
>
> I find it unlikely that such a wording alternative would be more appropriate
> while I became just curious for related development consequences around
> the usage of a longterm kernel version.
>
> Would you like to reuse the term “call trace”?
>
OK, I will reuse the “call trace”. Thanks again.
Anyone else have any suggestions? If not, I will post another v4 version
to fix the commit message that Markus mentioned.
--
Yours,
Muchun
^ permalink raw reply [flat|nested] 5+ messages in thread
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2020-04-14 7:56 [PATCH v2] mm/ksm: Fix NULL pointer dereference when KSM zero page is enabled Muchun Song
2020-04-14 9:17 ` Markus Elfring
2020-04-14 9:56 ` [External] " Muchun Song
2020-04-14 14:17 ` [v2] " Markus Elfring
2020-04-14 14:39 ` [External] " Muchun Song
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