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Date: Mon, 6 Apr 2020 21:27:02 -0400
From: Peter Xu <peterx@...hat.com>
To: Randy Dunlap <rdunlap@...radead.org>
Cc: syzbot <syzbot+693dc11fcb53120b5559@...kaller.appspotmail.com>,
akpm@...ux-foundation.org, bgeffon@...gle.com,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
syzkaller-bugs@...glegroups.com, torvalds@...ux-foundation.org
Subject: Re: BUG: unable to handle kernel paging request in
kernel_get_mempolicy
On Mon, Apr 06, 2020 at 06:05:54PM -0700, Randy Dunlap wrote:
> On 4/6/20 5:47 PM, Peter Xu wrote:
> > On Mon, Apr 06, 2020 at 11:16:13AM -0700, syzbot wrote:
> >> Hello,
> >>
> >> syzbot found the following crash on:
> >>
> >> HEAD commit: bef7b2a7 Merge tag 'devicetree-for-5.7' of git://git.kerne..
> >> git tree: upstream
> >> console output: https://syzkaller.appspot.com/x/log.txt?x=13966e8fe00000
> >> kernel config: https://syzkaller.appspot.com/x/.config?x=91b674b8f0368e69
> >> dashboard link: https://syzkaller.appspot.com/bug?extid=693dc11fcb53120b5559
> >> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> >> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1738b02be00000
> >> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17d2c76de00000
> >>
> >> The bug was bisected to:
> >>
> >> commit 4426e945df588f2878affddf88a51259200f7e29
> >> Author: Peter Xu <peterx@...hat.com>
> >> Date: Thu Apr 2 04:08:49 2020 +0000
> >>
> >> mm/gup: allow VM_FAULT_RETRY for multiple times
> >>
> >> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=14ac4a5de00000
> >> final crash: https://syzkaller.appspot.com/x/report.txt?x=16ac4a5de00000
> >> console output: https://syzkaller.appspot.com/x/log.txt?x=12ac4a5de00000
> >>
> >> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> >> Reported-by: syzbot+693dc11fcb53120b5559@...kaller.appspotmail.com
> >> Fixes: 4426e945df58 ("mm/gup: allow VM_FAULT_RETRY for multiple times")
> >>
> >> BUG: unable to handle page fault for address: ffffffff00000000
> >> #PF: supervisor read access in kernel mode
> >> #PF: error_code(0x0000) - not-present page
> >> PGD 987c067 P4D 987c067 PUD 0
> >> Oops: 0000 [#1] PREEMPT SMP KASAN
> >> CPU: 1 PID: 7181 Comm: syz-executor616 Not tainted 5.6.0-syzkaller #0
> >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> >> RIP: 0010:page_to_nid include/linux/mm.h:1245 [inline]
> >> RIP: 0010:lookup_node mm/mempolicy.c:906 [inline]
> >> RIP: 0010:do_get_mempolicy mm/mempolicy.c:970 [inline]
> >> RIP: 0010:kernel_get_mempolicy+0x60e/0xfb0 mm/mempolicy.c:1615
> >> Code: 88 00 07 00 00 e8 b2 35 c5 ff 4c 8b 7c 24 78 48 b8 00 00 00 00 00 fc ff df 4c 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 fb 08 00 00 <49> 8b 1f 48 c7 c7 ff ff ff ff 48 89 de e8 10 37 c5 ff 48 83 fb ff
> >> RSP: 0018:ffffc900018d7de8 EFLAGS: 00010246
> >> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff81adaaf1
> >> RDX: 1fffffffe0000000 RSI: ffffffff81adaafe RDI: 0000000000000005
> >> RBP: 0000000000000000 R08: ffff88808de924c0 R09: ffffed1011bd2499
> >> R10: ffff88808de924c7 R11: ffffed1011bd2498 R12: 0000000000000000
> >> R13: 1ffff9200031afc4 R14: ffffffff89a6df60 R15: ffffffff00000000
> >> FS: 00007f848cd4a700(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
> >> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> CR2: ffffffff00000000 CR3: 00000000a7a8d000 CR4: 00000000001406e0
> >> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> >> Call Trace:
> >> __do_sys_get_mempolicy mm/mempolicy.c:1633 [inline]
> >> __se_sys_get_mempolicy mm/mempolicy.c:1629 [inline]
> >> __x64_sys_get_mempolicy+0xba/0x150 mm/mempolicy.c:1629
> >> do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
> >> entry_SYSCALL_64_after_hwframe+0x49/0xb3
> >> RIP: 0033:0x446719
> >> Code: e8 5c b3 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 0b 08 fc ff c3 66 2e 0f 1f 84 00 00 00 00
> >> RSP: 002b:00007f848cd49db8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ef
> >> RAX: ffffffffffffffda RBX: 00000000006dbc28 RCX: 0000000000446719
> >> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> >> RBP: 00000000006dbc20 R08: 0000000000000003 R09: 0000000000000000
> >> R10: 000000002073b000 R11: 0000000000000246 R12: 00000000006dbc2c
> >> R13: 00007ffcfe6ba66f R14: 00007f848cd4a9c0 R15: 20c49ba5e353f7cf
> >> Modules linked in:
> >> CR2: ffffffff00000000
> >> ---[ end trace 0becf554e06291c3 ]---
> >> RIP: 0010:page_to_nid include/linux/mm.h:1245 [inline]
> >> RIP: 0010:lookup_node mm/mempolicy.c:906 [inline]
> >> RIP: 0010:do_get_mempolicy mm/mempolicy.c:970 [inline]
> >> RIP: 0010:kernel_get_mempolicy+0x60e/0xfb0 mm/mempolicy.c:1615
> >> Code: 88 00 07 00 00 e8 b2 35 c5 ff 4c 8b 7c 24 78 48 b8 00 00 00 00 00 fc ff df 4c 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 fb 08 00 00 <49> 8b 1f 48 c7 c7 ff ff ff ff 48 89 de e8 10 37 c5 ff 48 83 fb ff
> >> RSP: 0018:ffffc900018d7de8 EFLAGS: 00010246
> >> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff81adaaf1
> >> RDX: 1fffffffe0000000 RSI: ffffffff81adaafe RDI: 0000000000000005
> >> RBP: 0000000000000000 R08: ffff88808de924c0 R09: ffffed1011bd2499
> >> R10: ffff88808de924c7 R11: ffffed1011bd2498 R12: 0000000000000000
> >> R13: 1ffff9200031afc4 R14: ffffffff89a6df60 R15: ffffffff00000000
> >> FS: 00007f848cd4a700(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
> >> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> CR2: ffffffff00000000 CR3: 00000000a7a8d000 CR4: 00000000001406e0
> >> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> >
> > Hi, Andrew & all,
> >
> > I can reproduce this locally right after I run the test program, and
> > below patch fixed it for me - the test program can run with quite a
> > few minutes without crashing again.
> >
> > Is there a way I can feed this to the syzbot to re-verify this?
>
> Hi Peter,
>
> Send the patch. At the top of the email, put something like
> #syz test <git repo> <branch>
>
> It's documented here:
> https://github.com/google/syzkaller/blob/master/docs/syzbot.md
Thanks Randy.
#syz test https://github.com/xzpeter/linux.git 23800bff6fa346a4e9b3806dc0cfeb74498df757
>
>
> > Thanks,
> >
> > 8<---------------------------------------------------------------
> > From 23800bff6fa346a4e9b3806dc0cfeb74498df757 Mon Sep 17 00:00:00 2001
> > From: Peter Xu <peterx@...hat.com>
> > Date: Mon, 6 Apr 2020 20:40:13 -0400
> > Subject: [PATCH] mm/mempolicy: Allow lookup_node() to handle fatal signal
> >
> > lookup_node() uses gup to pin the page and get node information. It
> > checks against ret>=0 assuming the page will be filled in. However
> > it's also possible that gup will return zero, for example, when the
> > thread is quickly killed with a fatal signal. Teach lookup_node() to
> > gracefully return an error -EFAULT if it happens.
> >
> > Reported-by: syzbot+693dc11fcb53120b5559@...kaller.appspotmail.com
> > Fixes: 4426e945df58 ("mm/gup: allow VM_FAULT_RETRY for multiple times")
> > Signed-off-by: Peter Xu <peterx@...hat.com>
> > ---
> > mm/mempolicy.c | 5 ++++-
> > 1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> > index 5fb427aed612..1398578db025 100644
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -902,7 +902,10 @@ static int lookup_node(struct mm_struct *mm, unsigned long addr)
> >
> > int locked = 1;
> > err = get_user_pages_locked(addr & PAGE_MASK, 1, 0, &p, &locked);
> > - if (err >= 0) {
> > + if (err == 0) {
> > + /* E.g. GUP interupted by fatal signal */
> > + err = -EFAULT;
> > + } else if (err > 0) {
> > err = page_to_nid(p);
> > put_page(p);
> > }
> >
>
>
>
> --
> ~Randy
> Reported-by: Randy Dunlap <rdunlap@...radead.org>
>
--
Peter Xu
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