linux-kernel - Re: [PATCH 2/6] KVM: nSVM: Check that VM_HSAVE

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Date:   Wed, 07 Jul 2021 13:28:25 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Cathy Avery <cavery@...hat.com>,
        Emanuele Giuseppe Esposito <eesposit@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Michael Roth <mdroth@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] KVM: nSVM: Check that VM_HSAVE_PA MSR was set
 before VMRUN

On Mon, 2021-06-28 at 12:44 +0200, Vitaly Kuznetsov wrote:
> APM states that "The address written to the VM_HSAVE_PA MSR, which holds
> the address of the page used to save the host state on a VMRUN, must point
> to a hypervisor-owned page. If this check fails, the WRMSR will fail with
> a #GP(0) exception. Note that a value of 0 is not considered valid for the
> VM_HSAVE_PA MSR and a VMRUN that is attempted while the HSAVE_PA is 0 will
> fail with a #GP(0) exception."
> 
> svm_set_msr() already checks that the supplied address is valid, so only
> check for '0' is missing. Add it to nested_svm_vmrun().
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/svm/nested.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 21d03e3a5dfd..1c6b0698b52e 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -618,6 +618,11 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
>  	struct kvm_host_map map;
>  	u64 vmcb12_gpa;
>  
> +	if (!svm->nested.hsave_msr) {
> +		kvm_inject_gp(vcpu, 0);
> +		return 1;
> +	}
> +
>  	if (is_smm(vcpu)) {
>  		kvm_queue_exception(vcpu, UD_VECTOR);
>  		return 1;

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky