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

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Message-ID: <87lflan2ty.fsf@nanos.tec.linutronix.de>
Date:   Fri, 29 May 2020 18:06:01 +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

Thomas Gleixner <tglx@...utronix.de> writes:
> Dmitry Vyukov <dvyukov@...gle.com> writes:
>> On Fri, May 29, 2020 at 3:14 PM syzbot
>> <syzbot+dc1fa714cb070b184db5@...kaller.appspotmail.com> wrote:
>>
>> 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.

Exactly as I assumed. With KASAN off, no problem, with KASAN on, insta
crash.

This function needs to be excluded from KASAN or any other of those
magic function. I need to walk the dogs first and will look into fixing
it later.

Thanks,

        tglx