linux-kernel - Re: KASAN: use-after-free Read in do_general

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Message-ID: <CACT4Y+ZdPtSV0pky4j=gAe7U+8PA5jGk3Sm5UB9=m1i=e=FZoA@mail.gmail.com>
Date:   Wed, 20 Jun 2018 09:52:13 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     syzbot <syzbot+a1264132fc103340628f@...kaller.appspotmail.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        KVM list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: KASAN: use-after-free Read in do_general_protection

On Tue, Jun 5, 2018 at 10:16 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Mon, May 28, 2018 at 1:25 PM, Paolo Bonzini <pbonzini@...hat.com> wrote:
>> On 26/05/2018 11:29, Dmitry Vyukov wrote:
>>> KASAN: stack-out-of-bounds Read in do_general_protection
>>> KASAN: slab-out-of-bounds Read in vmx_vcpu_run
>>> KASAN: use-after-scope Read in vmx_vcpu_run
>>> KASAN: stack-out-of-bounds Write in notify_die
>>>
>>> See full info at:
>>> https://syzkaller.appspot.com/bug?extid=a1264132fc103340628f
>>>
>>>
>>> There seems to be 2 problems:
>>>
>>> 1. msr_write_intercepted doing something notoriously bad.
>>
>> The faulting line is
>>
>>         msr_bitmap = to_vmx(vcpu)->loaded_vmcs->msr_bitmap;
>>
>> so I suppose to_vmx(vcpu)->loaded_vmcs is bogus?  That seems like "just"
>> a corruption of the struct kvm_vcpu, because the loaded_vmcs field is
>> pointing elsewhere inside the same struct.
>
> This is reproducible and the reproducer only uses KVM syscalls. So it
> seems that KVM corrupts itself. Perhaps it's KVM_SET_MSRS that messes
> things?

This one looks like the same root cause as here:

KASAN: stack-out-of-bounds Read in unwind_next_frame
https://groups.google.com/d/msg/syzkaller-bugs/MGQ_W8DPYXA/k-xK7sBrBgAJ