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From: Suren Baghdasaryan <surenb@google.com>
Date: Thu, 11 Jan 2024 20:20:22 +0000
Message-ID: <CAJuCfpG5T71Sc46pB2eGpV7TreMZX2VZ-kDfaNmtn+etP0q9JA@mail.gmail.com>
Subject: Re: [syzbot] [mm?] kernel BUG in move_pages
To: David Hildenbrand <david@redhat.com>
Cc: syzbot <syzbot+705209281e36404998f6@syzkaller.appspotmail.com>, 
	Peter Xu <peterx@redhat.com>, aarcange@redhat.com, akpm@linux-foundation.org, 
	linux-kernel@vger.kernel.org, linux-mm@kvack.org, 
	syzkaller-bugs@googlegroups.com
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On Thu, Jan 11, 2024 at 6:58=E2=80=AFPM David Hildenbrand <david@redhat.com=
> wrote:
>
> On 11.01.24 19:34, Suren Baghdasaryan wrote:
> > On Thu, Jan 11, 2024 at 8:44=E2=80=AFAM Suren Baghdasaryan <surenb@goog=
le.com> wrote:
> >>
> >> On Thu, Jan 11, 2024 at 8:40=E2=80=AFAM Suren Baghdasaryan <surenb@goo=
gle.com> wrote:
> >>>
> >>> On Thu, Jan 11, 2024 at 8:25=E2=80=AFAM syzbot
> >>> <syzbot+705209281e36404998f6@syzkaller.appspotmail.com> wrote:
> >>>>
> >>>> Hello,
> >>>>
> >>>> syzbot found the following issue on:
> >>>>
> >>>> HEAD commit:    e2425464bc87 Add linux-next specific files for 20240=
105
> >>>> git tree:       linux-next
> >>>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=3D14941cde=
e80000
> >>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=3D4056b934=
9f3da8c9
> >>>> dashboard link: https://syzkaller.appspot.com/bug?extid=3D705209281e=
36404998f6
> >>>> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils =
for Debian) 2.40
> >>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=3D125d0a=
09e80000
> >>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=3D15bc7331=
e80000
> >>>>
> >>>> Downloadable assets:
> >>>> disk image: https://storage.googleapis.com/syzbot-assets/2f738185e2c=
f/disk-e2425464.raw.xz
> >>>> vmlinux: https://storage.googleapis.com/syzbot-assets/b248fcf4ea46/v=
mlinux-e2425464.xz
> >>>> kernel image: https://storage.googleapis.com/syzbot-assets/a9945c822=
3f4/bzImage-e2425464.xz
> >>>>
> >>>> The issue was bisected to:
> >>>>
> >>>> commit adef440691bab824e39c1b17382322d195e1fab0
> >>>> Author: Andrea Arcangeli <aarcange@redhat.com>
> >>>> Date:   Wed Dec 6 10:36:56 2023 +0000
> >>>>
> >>>>      userfaultfd: UFFDIO_MOVE uABI
> >>>>
> >>>> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=3D11cb6=
ea9e80000
> >>>> final oops:     https://syzkaller.appspot.com/x/report.txt?x=3D13cb6=
ea9e80000
> >>>> console output: https://syzkaller.appspot.com/x/log.txt?x=3D15cb6ea9=
e80000
> >>>>
> >>>> IMPORTANT: if you fix the issue, please add the following tag to the=
 commit:
> >>>> Reported-by: syzbot+705209281e36404998f6@syzkaller.appspotmail.com
> >>>> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
> >>>>
> >>>>   do_one_initcall+0x128/0x680 init/main.c:1237
> >>>>   do_initcall_level init/main.c:1299 [inline]
> >>>>   do_initcalls init/main.c:1315 [inline]
> >>>>   do_basic_setup init/main.c:1334 [inline]
> >>>>   kernel_init_freeable+0x692/0xc30 init/main.c:1552
> >>>>   kernel_init+0x1c/0x2a0 init/main.c:1442
> >>>>   ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
> >>>>   ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
> >>>> ------------[ cut here ]------------
> >>>> kernel BUG at include/linux/page-flags.h:1035!
> >>>> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> >>>> CPU: 0 PID: 5068 Comm: syz-executor191 Not tainted 6.7.0-rc8-next-20=
240105-syzkaller #0
> >>>> Hardware name: Google Google Compute Engine/Google Compute Engine, B=
IOS Google 11/17/2023
> >>>> RIP: 0010:PageAnonExclusive include/linux/page-flags.h:1035 [inline]
> >>>
> >>>  From a quick look, I think the new ioctl is being used against a
> >>> file-backed page and that's why PageAnonExclusive() throws this error=
.
> >>> I'll confirm if this is indeed the case and will add checks for that
> >>> case. Thanks!
> >>
> >> Hmm. Looking at the reproducer it does not look like a file-backed
> >> memory... Anyways, I'm on it.
> >
> > Looks like the test is trying to move the huge_zero_page. Wonder how
> > we should handle this. Just fail or do something else? Adding David
> > and Peter for feedback.
>
> You'll need some special-casing to handle that. But it should be fairly
> easy.

Ok, so should we treat zeropage the same as PAE and map destination
PTE/PMD to zeropage while clearing source PTE/PMD?

>
> --
> Cheers,
>
> David / dhildenb
>