linux-kernel - Re: [PATCH] KVM: SVM: Do not terminate SEV-ES guests on GHCB validation failure

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Message-ID: <CAMkAt6qJqTvM0PX+ja3rLP3toY-Rr4pSUbiFKL1GwzYZPG6f8g@mail.gmail.com>
Date:   Fri, 14 May 2021 17:06:11 -0600
From:   Peter Gonda <pgonda@...gle.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     kvm list <kvm@...r.kernel.org>, linux-kernel@...r.kernel.org,
        x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH] KVM: SVM: Do not terminate SEV-ES guests on GHCB
 validation failure

On Fri, May 14, 2021 at 1:22 PM Tom Lendacky <thomas.lendacky@....com> wrote:
>
> Currently, an SEV-ES guest is terminated if the validation of the VMGEXIT
> exit code and parameters fail. Since the VMGEXIT instruction can be issued
> from userspace, even though userspace (likely) can't update the GHCB,
> don't allow userspace to be able to kill the guest.
>
> Return a #GP request through the GHCB when validation fails, rather than
> terminating the guest.

Is this a gap in the spec? I don't see anything that details what
should happen if the correct fields for NAE are not set in the first
couple paragraphs of section 4 'GHCB Protocol'.