linux-kernel - Re: [v5.15] WARNING in kvm_arch_vcpu_ioctl

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Message-ID: <6ba2-64ecbc00-5-39397d40@6469447>
Date:   Mon, 28 Aug 2023 16:23:26 +0100
From:   "Muhammad Usama Anjum" <usama.anjum@...labora.com>
To:     "Sean Christopherson" <seanjc@...gle.com>
Cc:     "syzbot" <syzbot+412c9ae97b4338c5187e@...kaller.appspotmail.com>,
        syzkaller-lts-bugs@...glegroups.com,
        "syzbot" <syzbot+b000b7d21f93fc69de32@...kaller.appspotmail.com>,
        "Paolo Bonzini" <pbonzini@...hat.com>,
        "Vitaly Kuznetsov" <vkuznets@...hat.com>,
        "Wanpeng Li" <wanpengli@...cent.com>,
        "Jim Mattson" <jmattson@...gle.com>,
        "Joerg Roedel" <joro@...tes.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        H. Peter Anvin <hpa@...or.com>,
        "Jarkko Sakkinen" <jarkko@...nel.org>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org, x86@...nel.org,
        linux-sgx@...r.kernel.org
Subject: Re: [v5.15] WARNING in 
 kvm_arch_vcpu_ioctl_run

On Monday, August 28, 2023 08:11 PM PKT, Sean Christopherson <seanjc@...gle.com> wrote:

> On Mon, Aug 28, 2023, Muhammad Usama Anjum wrote:
> > On 5/5/23 1:28 PM, syzbot wrote:
> > > syzbot has found a reproducer for the following issue on:
> > > 
> > > HEAD commit: 8a7f2a5c5aa1 Linux 5.15.110
> > This same warning has also been found on  6.1.21.
> > 
> > > git tree: linux-5.15.y
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=15f12318280000
> > > kernel config: https://syzkaller.appspot.com/x/.config?x=ba8d5c9d6c5289f
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=412c9ae97b4338c5187e
> > > compiler: Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2
> > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10e13c84280000
> > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=149d9470280000
> > I've tried all the C and syz reproducers. I've also tried syz-crash which
> > launched multiple instances of VMs and ran syz reproducer. But the issue
> > didn't get reproduced.
> > 
> > I don't have kvm skills. Can someone have a look at the the warning
> > (probably by static analysis)?
> > 
> > > 
> > > Downloadable assets:
> > > disk image: https://storage.googleapis.com/syzbot-assets/fc04f54c047f/disk-8a7f2a5c.raw.xz
> > > vmlinux: https://storage.googleapis.com/syzbot-assets/6b4ba4cb1191/vmlinux-8a7f2a5c.xz
> > > kernel image: https://storage.googleapis.com/syzbot-assets/d927dc3f9670/bzImage-8a7f2a5c.xz
> > > 
> > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > Reported-by: syzbot+412c9ae97b4338c5187e@...kaller.appspotmail.com
> > > 
> > > ------------[ cut here ]------------
> > > WARNING: CPU: 0 PID: 3502 at arch/x86/kvm/x86.c:10310 kvm_arch_vcpu_ioctl_run+0x1d63/0x1f80
> 
> "Fixed" by https://lore.kernel.org/all/20230808232057.2498287-1-seanjc@google.com,
> in quotes because sadly the fix was to simply delete the sanity check :-(

Thank you so much Sean. Thank you so much Sean. Syzbot has been finding the issue in LTS kernels. I'm not sure if we should backport a patch which is just removing a false warning. 

#syz fix: KVM: x86: Remove WARN sanity check on hypervisor timer vs. UNINITIALIZED vCPU