linux-kernel - [PATCH 14/15] KVM: nVMX: WARN if subtly-impossible VMFUNC conditions occur

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Date:   Wed,  9 Jun 2021 16:42:34 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Junaid Shahid <junaids@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Lai Jiangshan <laijs@...ux.alibaba.com>
Subject: [PATCH 14/15] KVM: nVMX: WARN if subtly-impossible VMFUNC conditions occur

WARN and inject #UD when emulating VMFUNC for L2 if the function is
out-of-bounds or if VMFUNC is not enabled in vmcs12.  Neither condition
should occur in practice, as the CPU is supposed to prioritize the #UD
over VM-Exit for out-of-bounds input and KVM is supposed to enable
VMFUNC in vmcs02 if and only if it's enabled in vmcs12, but neither of
those dependencies is obvious.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/nested.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index f686618d9ede..0075d3f0f8fa 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -5494,6 +5494,16 @@ static int handle_vmfunc(struct kvm_vcpu *vcpu)
 	}
 
 	vmcs12 = get_vmcs12(vcpu);
+
+	/*
+	 * #UD on out-of-bounds function has priority over VM-Exit, and VMFUNC
+	 * is enabled in vmcs02 if and only if it's enabled in vmcs12.
+	 */
+	if (WARN_ON_ONCE((function > 63) || !nested_cpu_has_vmfunc(vmcs12))) {
+		kvm_queue_exception(vcpu, UD_VECTOR);
+		return 1;
+	}
+
 	if (!(vmcs12->vm_function_control & BIT_ULL(function)))
 		goto fail;
 
-- 
2.32.0.rc1.229.g3e70b5a671-goog