linux-kernel - Re: [PATCH v3 02/37] KVM: nVMX: Validate the EPTP when emulating INVEPT(EXTENT

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Date:   Mon, 23 Mar 2020 15:51:17 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ben Gardon <bgardon@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Liran Alon <liran.alon@...cle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        John Haxby <john.haxby@...cle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH v3 02/37] KVM: nVMX: Validate the EPTP when emulating INVEPT(EXTENT_CONTEXT)

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> Signal VM-Fail for the single-context variant of INVEPT if the specified
> EPTP is invalid.  Per the INEVPT pseudocode in Intel's SDM, it's subject
> to the standard EPT checks:
>
>   If VM entry with the "enable EPT" VM execution control set to 1 would
>   fail due to the EPTP value then VMfail(Invalid operand to INVEPT/INVVPID);
>
> Fixes: bfd0a56b90005 ("nEPT: Nested INVEPT")
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/vmx/nested.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 8578513907d7..f3774cef4fd4 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -5156,8 +5156,12 @@ static int handle_invept(struct kvm_vcpu *vcpu)
>  	}
>  
>  	switch (type) {
> -	case VMX_EPT_EXTENT_GLOBAL:
>  	case VMX_EPT_EXTENT_CONTEXT:
> +		if (!nested_vmx_check_eptp(vcpu, operand.eptp))
> +			return nested_vmx_failValid(vcpu,
> +				VMXERR_INVALID_OPERAND_TO_INVEPT_INVVPID);

I was going to ask "and we don't seem to check that current nested VMPTR
is valid, how can we know that nested_vmx_failValid() is the right
VMfail() to use" but then I checked our nested_vmx_failValid() and there
is a fallback there:

	if (vmx->nested.current_vmptr == -1ull && !vmx->nested.hv_evmcs)
		return nested_vmx_failInvalid(vcpu);

so this is a non-issue. My question, however, transforms into "would it
make sense to introduce nested_vmx_fail() implementing the logic from
SDM:

VMfail(ErrorNumber):
	IF VMCS pointer is valid
		THEN VMfailValid(ErrorNumber);
	ELSE VMfailInvalid;
	FI;

to assist an innocent reader of the code?"

> +		fallthrough;
> +	case VMX_EPT_EXTENT_GLOBAL:
>  	/*
>  	 * TODO: Sync the necessary shadow EPT roots here, rather than
>  	 * at the next emulated VM-entry.

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly