[PATCH 1/4] KVM: VMX: Refuse to load kvm_intel if EPT and NX are disabled

From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 1/4] KVM: VMX: Refuse to load kvm_intel if EPT and NX are disabled
Date: Tue, 15 Jun 2021 09:45:32 -0700	[thread overview]
Message-ID: <20210615164535.2146172-2-seanjc@google.com> (raw)
In-Reply-To: <20210615164535.2146172-1-seanjc@google.com>

Refuse to load KVM if NX support is not available and EPT is not enabled.
Shadow paging has assumed NX support since commit 9167ab799362 ("KVM:
vmx, svm: always run with EFER.NXE=1 when shadow paging is active"), so
for all intents and purposes this has been a de facto requirement for
over a year.

Do not require NX support if EPT is enabled purely because Intel CPUs let
firmware disable NX support via MSR_IA32_MISC_ENABLES.  If not for that,
VMX (and KVM as a whole) could require NX support with minimal risk to
breaking userspace.

Fixes: 9167ab799362 ("KVM: vmx, svm: always run with EFER.NXE=1 when shadow paging is active")
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/vmx.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 68a72c80bd3f..889e83f71235 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7723,6 +7723,12 @@ static __init int hardware_setup(void)
 	    !cpu_has_vmx_invept_global())
 		enable_ept = 0;
 
+	/* NX support is required for shadow paging. */
+	if (!enable_ept && !boot_cpu_has(X86_FEATURE_NX)) {
+		pr_err_ratelimited("kvm: NX (Execute Disable) not supported\n");
+		return -EOPNOTSUPP;
+	}
+
 	if (!cpu_has_vmx_ept_ad_bits() || !enable_ept)
 		enable_ept_ad_bits = 0;
 
-- 
2.32.0.272.g935e593368-goog

