linux-kernel - Re: BUG: unable to handle kernel paging request in __switch

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Date:   Fri, 15 Dec 2017 17:44:58 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Wanpeng Li <kernellwp@...il.com>,
        David Hildenbrand <david@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        syzbot 
        <bot+1f445b1009b8eeededa30fe62ccf685f2ec9d155@...kaller.appspotmail.com>,
        Borislav Petkov <bp@...e.de>,
        Dmitry Safonov <dsafonov@...tuozzo.com>,
        Peter Anvin <hpa@...or.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kyle Huey <me@...ehuey.com>, Ingo Molnar <mingo@...hat.com>,
        syzkaller-bugs@...glegroups.com,
        the arch/x86 maintainers <x86@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        KVM list <kvm@...r.kernel.org>,
        "Lan, Tianyu" <tianyu.lan@...el.com>,
        James Mattson <jmattson@...gle.com>
Subject: Re: BUG: unable to handle kernel paging request in __switch_to


* Andy Lutomirski <luto@...nel.org> wrote:

> On Fri, Dec 15, 2017 at 2:02 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> > On Fri, Dec 15, 2017 at 10:58 AM, Wanpeng Li <kernellwp@...il.com> wrote:
> >> 2017-12-15 17:51 GMT+08:00 David Hildenbrand <david@...hat.com>:
> >>>
> >>>> int main()
> >>>> {
> >>>>   int fd = open("/dev/kvm", 0x80102ul);
> >>>>   int vm = ioctl(fd, KVM_CREATE_VM, 0);
> >>>>   int  cpu = ioctl(vm, KVM_CREATE_VCPU, 4);
> >>>
> >>> Not even a memory region :) So maybe the first memory access directly
> >>> triggers a fault?
> >>>
> >>>>   ioctl(cpu, KVM_RUN, 0);
> >>>>   return 0;
> >>>> }
> >>>>
> >>>> And, yes, this in fact triggers instant reboot of kernel (running in qemu).
> >>>> Am I missing something here?
> >>>>
> >>>> +kvm maintainers, you can see full thread here:
> >>>> https://groups.google.com/forum/#!topic/syzkaller-bugs/_oveOKGm3jw
> >>
> >> I didn't see any issue after running the test.
> >
> > Yes, it's strange. But I can reproduce it. There must be something
> > different in our setups.
> > Here is how to build exact same kernel:
> > https://groups.google.com/d/msg/syzkaller-bugs/_oveOKGm3jw/vc1tXvsbCgAJ
> >
> > Here is how I start qemu:
> >
> > qemu-system-x86_64 -hda wheezy.img -net
> > user,host=10.0.2.10,hostfwd=tcp::10022-:22 -net nic -nographic -kernel
> > arch/x86/boot/bzImage -append "kvm-intel.nested=1
> > kvm-intel.unrestricted_guest=1 kvm-intel.ept=1
> > kvm-intel.flexpriority=1 kvm-intel.vpid=1
> > kvm-intel.emulate_invalid_guest_state=1 kvm-intel.eptad=1
> > kvm-intel.enable_shadow_vmcs=1 kvm-intel.pml=1
> > kvm-intel.enable_apicv=1 console=ttyS0 root=/dev/sda
> > earlyprintk=serial slub_debug=UZ vsyscall=native rodata=n oops=panic
> > panic_on_warn=1 panic=86400" -enable-kvm -pidfile vm_pid -m 2G -smp 4
> > -cpu host -usb -usbdevice mouse -usbdevice tablet -soundhw all
> >
> > The image is here:
> > https://github.com/google/syzkaller/blob/master/docs/syzbot.md#crash-does-not-reproduce
> >
> > Host cpu is Intel(R) Xeon(R) CPU E5-2690 v3
> 
> Looking more closely, you seem to be testing this:
> 
> commit d127129e85a020879f334154300ddd3f7ec21c1e (HEAD, tag: next-20171129)
> Author: Stephen Rothwell <s...@...b.auug.org.au>
> Date:   Wed Nov 29 14:09:56 2017 +1100
>     Add linux-next specific files for 20171129
> 
> which is almost certainly missing this fix:
> 
> https://lkml.kernel.org/r/bc7296f4c8d86af71c31a17588c79d89c0890edc.1512109321.git.luto@kernel.org
> 
> on account of the fix being sent the day after the tag.
> 
> The symptoms you're seeing are definitely consistent with a screwed up
> TSS after VM exit.

Note that this should all be fixed in WIP.x86/pti.

If you have:

  5ed1fcd523b9: x86/entry: Fix assumptions that the HW TSS is at the beginning of cpu_tss

then you should be fine.

Thanks,

	Ingo