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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Dmitry Vyukov <dvyukov@google.com>,
        syzbot <syzbot+dc1fa714cb070b184db5@syzkaller.appspotmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        the arch/x86 maintainers <x86@kernel.org>,
        Oleg Nesterov <oleg@redhat.com>
Subject: Re: PANIC: double fault in fixup_bad_iret
In-Reply-To: <87o8q6n38p.fsf@nanos.tec.linutronix.de>
References: <000000000000d2474c05a6c938fe@google.com> <CACT4Y+ajjB8RmG3_H_9r-kaRAZ05ejW02-Py47o7wkkBjwup3Q@mail.gmail.com> <87o8q6n38p.fsf@nanos.tec.linutronix.de>
Date:   Fri, 29 May 2020 18:06:01 +0200
Message-ID: <87lflan2ty.fsf@nanos.tec.linutronix.de>
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Thomas Gleixner <tglx@linutronix.de> writes:
> Dmitry Vyukov <dvyukov@google.com> writes:
>> On Fri, May 29, 2020 at 3:14 PM syzbot
>> <syzbot+dc1fa714cb070b184db5@syzkaller.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