linux-kernel - [PATCH V3 5/5] KVM: SVM: Raise #UD if VMMCALL instruction is not intercepted

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Message-ID: <20260122045755.205203-6-chengkev@google.com>
Date: Thu, 22 Jan 2026 04:57:54 +0000
From: Kevin Cheng <chengkev@...gle.com>
To: seanjc@...gle.com, pbonzini@...hat.com
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, yosry.ahmed@...ux.dev, 
	Kevin Cheng <chengkev@...gle.com>, Manali Shukla <manali.shukla@....com>
Subject: [PATCH V3 5/5] KVM: SVM: Raise #UD if VMMCALL instruction is not intercepted

The AMD APM states that if VMMCALL instruction is not intercepted, the
instruction raises a #UD exception.

Create a vmmcall exit handler that generates a #UD if a VMMCALL exit
from L2 is being handled by L0, which means that L1 did not intercept
the VMMCALL instruction.

Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Kevin Cheng <chengkev@...gle.com>
Reviewed-by: Yosry Ahmed <yosry.ahmed@...ux.dev>
Reviewed-by: Manali Shukla <manali.shukla@....com>
Tested-by: Manali Shukla <manali.shukla@....com>
---
 arch/x86/kvm/svm/svm.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 1888211e20988..9257976ded539 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3194,6 +3194,20 @@ static int bus_lock_exit(struct kvm_vcpu *vcpu)
 	return 0;
 }
 
+static int vmmcall_interception(struct kvm_vcpu *vcpu)
+{
+	/*
+	 * VMMCALL #UDs if it's not intercepted, and KVM reaches this point if
+	 * and only if the VMMCALL intercept is not set in vmcb12.
+	 */
+	if (is_guest_mode(vcpu)) {
+		kvm_queue_exception(vcpu, UD_VECTOR);
+		return 1;
+	}
+
+	return kvm_emulate_hypercall(vcpu);
+}
+
 static int (*const svm_exit_handlers[])(struct kvm_vcpu *vcpu) = {
 	[SVM_EXIT_READ_CR0]			= cr_interception,
 	[SVM_EXIT_READ_CR3]			= cr_interception,
@@ -3244,7 +3258,7 @@ static int (*const svm_exit_handlers[])(struct kvm_vcpu *vcpu) = {
 	[SVM_EXIT_TASK_SWITCH]			= task_switch_interception,
 	[SVM_EXIT_SHUTDOWN]			= shutdown_interception,
 	[SVM_EXIT_VMRUN]			= vmrun_interception,
-	[SVM_EXIT_VMMCALL]			= kvm_emulate_hypercall,
+	[SVM_EXIT_VMMCALL]			= vmmcall_interception,
 	[SVM_EXIT_VMLOAD]			= vmload_interception,
 	[SVM_EXIT_VMSAVE]			= vmsave_interception,
 	[SVM_EXIT_STGI]				= stgi_interception,
-- 
2.52.0.457.g6b5491de43-goog