linux-kernel - Re: [tip: x86/seves] x86/kvm: Add KVM-specific VMMCALL handling under SEV-ES

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Date:   Fri, 30 Oct 2020 11:23:14 +0100
From:   Joerg Roedel <jroedel@...e.de>
To:     Erdem Aktas <erdemaktas@...gle.com>
Cc:     linux-kernel@...r.kernel.org,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        linux-tip-commits@...r.kernel.org, Borislav Petkov <bp@...e.de>,
        x86 <x86@...nel.org>
Subject: Re: [tip: x86/seves] x86/kvm: Add KVM-specific VMMCALL handling
 under SEV-ES

On Wed, Oct 28, 2020 at 11:03:05AM -0700, Erdem Aktas wrote:
> I might be missing something here but I think what you say is only
> correct for the kvm_hypercall4 cases. All other functions use a
> smaller number of registers. #VC blindly assumes that all those
> registers are used in the vmcall and exposes them.

Right, I think we should fix that in the guest and zero out the unused
registers. VMMCALL can come from userspace after all, and the #VC
handler does not look at the hypercall numbers.

Further, on the host side KVM will unconditionally read out all 4
registers too, which requires us to set them valid in the GHCB.

Regards,

	Joerg