linux-kernel - Re: Re: WARNING in x86_emulate

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Date:   Sat, 9 Dec 2017 13:44:02 +0800
From:   "Lan, Tianyu" <tianyu.lan@...el.com>
To:     Wanpeng Li <kernellwp@...il.com>,
        Tianyu Lan <lantianyu1986@...il.com>
Cc:     Jim Mattson <jmattson@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot 
        <bot+75375385991b4f8c599704a10849863c586ea284@...kaller.appspotmail.com>,
        "H. Peter Anvin" <hpa@...or.com>, kvm <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        syzkaller-bugs@...glegroups.com,
        Thomas Gleixner <tglx@...utronix.de>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: Re: WARNING in x86_emulate_insn


On 12/8/2017 5:27 PM, Wanpeng Li wrote:
> 2017-12-08 16:28 GMT+08:00 Tianyu Lan <lantianyu1986@...il.com>:
>> Hi Jim&Wanpeng:
>>           Thanks for your help.
>>
>> 2017-12-08 5:25 GMT+08:00 Jim Mattson <jmattson@...gle.com>:
>>> Try disabling the module parameter, "unrestricted_guest." Make sure
>>> that the module parameter, "emulate_invalid_guest_state" is enabled.
>>> This combination allows userspace to feed invalid guest state into the
>>> in-kernel emulator.
>>
>> Yes, you are right. I need to disable unrestricted_guest to reproduce the issue.
> 
> I can observe ctxt->exception.vector == 0xff which triggers Dmitry's
> report. Do you figure out the reason?
> 

Yes, this is caused by that emulation callback returns error code while
not emulate exception and not set exception vector.
ctxt->exception.vector is default to be 0xff in emulate instruction code
path.