Re: general protection fault in __apic_accept_irq

[Wanpeng Li]

On Thu, 5 Sep 2019 at 21:11, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote:
>
> Wanpeng Li <kernellwp@xxxxxxxxx> writes:
>
> > On Thu, 5 Sep 2019 at 16:53, syzbot
> > <syzbot+dff25ee91f0c7d5c1695@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> >>
> >> Hello,
> >>
> >> syzbot found the following crash on:
> >>
> >> HEAD commit:    3b47fd5c Merge tag 'nfs-for-5.3-4' of git://git.linux-nfs...
> >> git tree:       upstream
> >> console output: https://syzkaller.appspot.com/x/log.txt?x=124af12a600000
> >> kernel config:  https://syzkaller.appspot.com/x/.config?x=144488c6c6c6d2b6
> >> dashboard link: https://syzkaller.appspot.com/bug?extid=dff25ee91f0c7d5c1695
> >> compiler:       clang version 9.0.0 (/home/glider/llvm/clang
> >> 80fee25776c2fb61e74c1ecb1a523375c2500b69)
> >> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10954676600000
> >> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1752fe0a600000
> >>
> >> The bug was bisected to:
> >>
> >> commit 0aa67255f54df192d29aec7ac6abb1249d45bda7
> >> Author: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> >> Date:   Mon Nov 26 15:47:29 2018 +0000
> >>
> >>      x86/hyper-v: move synic/stimer control structures definitions to
> >> hyperv-tlfs.h
> >>
> >> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=156128c1600000
> >> console output: https://syzkaller.appspot.com/x/log.txt?x=136128c1600000
> >>
> >> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> >> Reported-by: syzbot+dff25ee91f0c7d5c1695@xxxxxxxxxxxxxxxxxxxxxxxxx
> >> Fixes: 0aa67255f54d ("x86/hyper-v: move synic/stimer control structures
> >> definitions to hyperv-tlfs.h")
> >>
> >> kvm [9347]: vcpu0, guest rIP: 0xcc Hyper-V uhandled wrmsr: 0x40000004 data
> >> 0x94
> >> kvm [9347]: vcpu0, guest rIP: 0xcc Hyper-V uhandled wrmsr: 0x40000004 data
> >> 0x48c
> >> kvm [9347]: vcpu0, guest rIP: 0xcc Hyper-V uhandled wrmsr: 0x40000004 data
> >> 0x4ac
> >> kvm [9347]: vcpu0, guest rIP: 0xcc Hyper-V uhandled wrmsr: 0x40000005 data
> >> 0x1520
> >> kvm [9347]: vcpu0, guest rIP: 0xcc Hyper-V uhandled wrmsr: 0x40000006 data
> >> 0x15d4
> >> kvm [9347]: vcpu0, guest rIP: 0xcc Hyper-V uhandled wrmsr: 0x40000007 data
> >> 0x15c4
> >> kasan: CONFIG_KASAN_INLINE enabled
> >> kasan: GPF could be caused by NULL-ptr deref or user memory access
> >> general protection fault: 0000 [#1] PREEMPT SMP KASAN
> >> CPU: 0 PID: 9347 Comm: syz-executor665 Not tainted 5.3.0-rc7+ #0
> >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> >> Google 01/01/2011
> >> RIP: 0010:__apic_accept_irq+0x46/0x740 arch/x86/kvm/lapic.c:1029
> >
> > Thanks for the report, I found the root cause, will send a patch soon.
> >
>
> I'm really interested in how any issue can be caused by 0aa67255f54d as
> we just moved some definitions from a c file to a common header... (ok,
> we did more than that, some structures gained '__packed' but it all
> still seems legitimate to me and I can't recall any problems with
> genuine Hyper-V...)

Yes, the bisect is false positive, we can focus on fixing the bug.

         Wanpeng