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From:   Fuqian Huang <huangfq.daxian@gmail.com>
Date:   Thu, 12 Sep 2019 20:02:20 +0800
Message-ID: <CABXRUiR0YSANWukwij0LNaJK24CiRFy878TE1AqVDAa91R-edg@mail.gmail.com>
Subject: Re: [PATCH] KVM: x86: work around leak of uninitialized stack contents
To:     Vitaly Kuznetsov <vkuznets@redhat.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H . Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        kvm@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Vitaly Kuznetsov <vkuznets@redhat.com> =E6=96=BC 2019=E5=B9=B49=E6=9C=8812=
=E6=97=A5=E9=80=B1=E5=9B=9B =E4=B8=8B=E5=8D=886:53=E5=AF=AB=E9=81=93=EF=BC=
=9A
>
> Fuqian Huang <huangfq.daxian@gmail.com> writes:
>
> > Vitaly Kuznetsov <vkuznets@redhat.com> =E6=96=BC 2019=E5=B9=B49=E6=9C=
=8812=E6=97=A5=E9=80=B1=E5=9B=9B =E4=B8=8B=E5=8D=884:51=E5=AF=AB=E9=81=93=
=EF=BC=9A
> >>
> >> Fuqian Huang <huangfq.daxian@gmail.com> writes:
> >>
> >> > Emulation of VMPTRST can incorrectly inject a page fault
> >> > when passed an operand that points to an MMIO address.
> >> > The page fault will use uninitialized kernel stack memory
> >> > as the CR2 and error code.
> >> >
> >> > The right behavior would be to abort the VM with a KVM_EXIT_INTERNAL=
_ERROR
> >> > exit to userspace;
> >>
> >> Hm, why so? KVM_EXIT_INTERNAL_ERROR is basically an error in KVM, this
> >> is not a proper reaction to a userspace-induced condition (or ever).
> >>
> >> I also looked at VMPTRST's description in Intel's manual and I can't
> >> find and explicit limitation like "this must be normal memory". We're
> >> just supposed to inject #PF "If a page fault occurs in accessing the
> >> memory destination operand."
> >>
> >> In case it seems to be too cumbersome to handle VMPTRST to MMIO and we
> >> think that nobody should be doing that I'd rather prefer injecting #GP=
.
> >>
> >> Please tell me what I'm missing :-)
> >
> > I found it during the code review, and it looks like the problem the
> > commit 353c0956a618 ("KVM: x86: work around leak of uninitialized
> > stack contents (CVE-2019-7222)")
> > mentions. So I fixed it in a similar way.
> >
>
> Oh, yes, I'm not against the fix at all, I was just wondering about why
> you think we need to kill the guest in this case.

I don't know what is the proper way to handle this case, I just initialize =
the
memory to avoid information leakage.
(Actually, I am not an expert on KVM's code)
I will be appreciated if the bug is fixed. :)

>
> --
> Vitaly