linux-kernel - Re: [PATCH v14 28/22] [SQUASH] KVM: SEV: Provide support for SNP_EXTENDED_GUEST

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Date: Wed, 24 Apr 2024 00:36:18 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Michael Roth" <michael.roth@....com>, <kvm@...r.kernel.org>
Cc: <linux-coco@...ts.linux.dev>, <linux-mm@...ck.org>,
 <linux-crypto@...r.kernel.org>, <x86@...nel.org>,
 <linux-kernel@...r.kernel.org>, <tglx@...utronix.de>, <mingo@...hat.com>,
 <jroedel@...e.de>, <thomas.lendacky@....com>, <hpa@...or.com>,
 <ardb@...nel.org>, <pbonzini@...hat.com>, <seanjc@...gle.com>,
 <vkuznets@...hat.com>, <jmattson@...gle.com>, <luto@...nel.org>,
 <dave.hansen@...ux.intel.com>, <slp@...hat.com>, <pgonda@...gle.com>,
 <peterz@...radead.org>, <srinivas.pandruvada@...ux.intel.com>,
 <rientjes@...gle.com>, <dovmurik@...ux.ibm.com>, <tobin@....com>,
 <bp@...en8.de>, <vbabka@...e.cz>, <kirill@...temov.name>,
 <ak@...ux.intel.com>, <tony.luck@...el.com>,
 <sathyanarayanan.kuppuswamy@...ux.intel.com>, <alpergun@...gle.com>,
 <ashish.kalra@....com>, <nikunj.dadhania@....com>, <pankaj.gupta@....com>,
 <liam.merwick@...cle.com>
Subject: Re: [PATCH v14 28/22] [SQUASH] KVM: SEV: Provide support for
 SNP_EXTENDED_GUEST_REQUEST NAE event

On Tue Apr 23, 2024 at 7:21 PM EEST, Michael Roth wrote:
> Ensure an error is returned if a non-SNP guest attempts to issue an
> Extended Guest Request. Also add input validation for RAX/RBX.
>
> Signed-off-by: Michael Roth <michael.roth@....com>
> ---
>  arch/x86/kvm/svm/sev.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 2b30b3b0eec8..ff64ed8df301 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -3297,6 +3297,11 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
>  			goto vmgexit_err;
>  		break;
>  	case SVM_VMGEXIT_EXT_GUEST_REQUEST:
> +		if (!sev_snp_guest(vcpu->kvm))
> +			goto vmgexit_err;
> +		if (!kvm_ghcb_rax_is_valid(svm) ||
> +		    !kvm_ghcb_rbx_is_valid(svm))
> +			goto vmgexit_err;

Hmm... maybe I'm ignoring something but why this is not just:

	if (!sev_snp_guest(vcpu->kvm) ||
	    !kvm_ghcb_rax_is_valid(svm) ||
	    !kvm_ghcb_rbx_is_valid(svm)))

since they branch to the same location.

BR, Jarkko