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Date: Thu, 11 Jan 2024 19:58:00 +0100
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Subject: Re: [syzbot] [mm?] kernel BUG in move_pages
To: Suren Baghdasaryan <surenb@google.com>,
 syzbot <syzbot+705209281e36404998f6@syzkaller.appspotmail.com>,
 Peter Xu <peterx@redhat.com>
Cc: aarcange@redhat.com, akpm@linux-foundation.org,
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 syzkaller-bugs@googlegroups.com
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From: David Hildenbrand <david@redhat.com>
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On 11.01.24 19:34, Suren Baghdasaryan wrote:
> On Thu, Jan 11, 2024 at 8:44 AM Suren Baghdasaryan <surenb@google.com> wrote:
>>
>> On Thu, Jan 11, 2024 at 8:40 AM Suren Baghdasaryan <surenb@google.com> wrote:
>>>
>>> On Thu, Jan 11, 2024 at 8:25 AM syzbot
>>> <syzbot+705209281e36404998f6@syzkaller.appspotmail.com> wrote:
>>>>
>>>> Hello,
>>>>
>>>> syzbot found the following issue on:
>>>>
>>>> HEAD commit:    e2425464bc87 Add linux-next specific files for 20240105
>>>> git tree:       linux-next
>>>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=14941cdee80000
>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=4056b9349f3da8c9
>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=705209281e36404998f6
>>>> 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=125d0a09e80000
>>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15bc7331e80000
>>>>
>>>> Downloadable assets:
>>>> disk image: https://storage.googleapis.com/syzbot-assets/2f738185e2cf/disk-e2425464.raw.xz
>>>> vmlinux: https://storage.googleapis.com/syzbot-assets/b248fcf4ea46/vmlinux-e2425464.xz
>>>> kernel image: https://storage.googleapis.com/syzbot-assets/a9945c8223f4/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=11cb6ea9e80000
>>>> final oops:     https://syzkaller.appspot.com/x/report.txt?x=13cb6ea9e80000
>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=15cb6ea9e80000
>>>>
>>>> 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-20240105-syzkaller #0
>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS 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.

-- 
Cheers,

David / dhildenb