linux-kernel - [PATCH 07/14] KVM: x86: SVM: add warning for CVE-2021-3656

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Date:   Tue, 14 Sep 2021 18:48:18 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Borislav Petkov <bp@...en8.de>, Bandan Das <bsd@...hat.com>,
        linux-kernel@...r.kernel.org (open list),
        Joerg Roedel <joro@...tes.org>, Ingo Molnar <mingo@...hat.com>,
        Wei Huang <wei.huang2@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kselftest@...r.kernel.org (open list:KERNEL SELFTEST FRAMEWORK),
        Maxim Levitsky <mlevitsk@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Jim Mattson <jmattson@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        Shuah Khan <shuah@...nel.org>,
        Wanpeng Li <wanpengli@...cent.com>
Subject: [PATCH 07/14] KVM: x86: SVM: add warning for CVE-2021-3656

Just in case, add a warning ensuring that on guest entry,
either both VMLOAD and VMSAVE intercept is enabled or
vVMLOAD/VMSAVE is enabled.

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/svm/svm.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 861ac9f74331..deeebd05f682 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3784,6 +3784,12 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
 
 	WARN_ON_ONCE(kvm_apicv_activated(vcpu->kvm) != kvm_vcpu_apicv_active(vcpu));
 
+	/* Check that CVE-2021-3656 can't happen again */
+	if (!svm_is_intercept(svm, INTERCEPT_VMSAVE) ||
+	    !svm_is_intercept(svm, INTERCEPT_VMSAVE))
+		WARN_ON(!(svm->vmcb->control.virt_ext &
+			  VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK));
+
 	sync_lapic_to_cr8(vcpu);
 
 	if (unlikely(svm->asid != svm->vmcb->control.asid)) {
-- 
2.26.3