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

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Message-ID: <CACT4Y+Y0d4O3Mgz5fH1nCWdoFOstWPmaRixavb4hfjqOuwhGrg@mail.gmail.com>
Date:   Tue, 5 Jun 2018 10:16:28 +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 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?