linux-kernel - Re: [syzbot] WARNING in vmx_queue

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Date:   Mon, 2 May 2022 15:13:11 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     syzbot <syzbot+cfafed3bb76d3e37581b@...kaller.appspotmail.com>
Cc:     bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
        jmattson@...gle.com, joro@...tes.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        pbonzini@...hat.com, syzkaller-bugs@...glegroups.com,
        tglx@...utronix.de, vkuznets@...hat.com, wanpengli@...cent.com,
        x86@...nel.org
Subject: Re: [syzbot] WARNING in vmx_queue_exception (2)

On Mon, May 02, 2022, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    57ae8a492116 Merge tag 'driver-core-5.18-rc5' of git://git..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=16d27d72f00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d21a72f6016e37e8
> dashboard link: https://syzkaller.appspot.com/bug?extid=cfafed3bb76d3e37581b
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1202b25af00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1386a07af00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+cfafed3bb76d3e37581b@...kaller.appspotmail.com
> 
> ------------[ cut here ]------------
> WARNING: CPU: 2 PID: 3674 at arch/x86/kvm/vmx/vmx.c:1628 vmx_queue_exception+0x3e6/0x450 arch/x86/kvm/vmx/vmx.c:1628
> Modules linked in:
> CPU: 2 PID: 3674 Comm: syz-executor352 Not tainted 5.18.0-rc4-syzkaller-00396-g57ae8a492116 #0
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014
> RIP: 0010:vmx_queue_exception+0x3e6/0x450 arch/x86/kvm/vmx/vmx.c:1628

Well this is comically straightforward.  Get to invalid guest state and force an
injected exception from userspace.  KVM only bails on a pending exception, because
it's impossible (barring other bugs) to get to an injected exception, but that
obviously fails to account for userspace intervention.  I'll get a patch posted.