Re: general protection fault in __apic_accept_irq

[Vitaly Kuznetsov]

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...)

-- 
Vitaly