linux-kernel - Re: PANIC: double fault in fixup_bad

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Date:   Fri, 29 May 2020 17:57:10 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot <syzbot+dc1fa714cb070b184db5@...kaller.appspotmail.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        the arch/x86 maintainers <x86@...nel.org>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: PANIC: double fault in fixup_bad_iret

Dmitry,

Dmitry Vyukov <dvyukov@...gle.com> writes:
> On Fri, May 29, 2020 at 3:14 PM syzbot
> <syzbot+dc1fa714cb070b184db5@...kaller.appspotmail.com> wrote:
>>
>> Hello,
>>
>> syzbot found the following crash on:
>>
>> HEAD commit:    7b4cb0a4 Add linux-next specific files for 20200525
>> git tree:       linux-next
>> console output: https://syzkaller.appspot.com/x/log.txt?x=15dc34ba100000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=47b0740d89299c10
>> dashboard link: https://syzkaller.appspot.com/bug?extid=dc1fa714cb070b184db5
>> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14678626100000
>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1017ef06100000
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+dc1fa714cb070b184db5@...kaller.appspotmail.com
>
> From the reproducer it seems to be either x86 related or ptrace
> related.
>
>> RIP: 0010:fixup_bad_iret+0x24/0x170 arch/x86/kernel/traps.c:665

as a quick assumption that's related to KASAN in fixup_bad_iret() which
is a frightenly bad idea. I'm about to verify.

Thanks,

        tglx