linux-kernel - [PATCH] KVM: x86: Forbid the use of kvm_load_host_xsave_state() with guest_state

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Message-ID: <20250307184125.2947143-1-pbonzini@redhat.com>
Date: Fri,  7 Mar 2025 13:41:25 -0500
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Subject: [PATCH] KVM: x86: Forbid the use of kvm_load_host_xsave_state() with guest_state_protected

kvm_load_host_xsave_state() uses guest save state that is not accessible
when guest_state_protected is true.  Forbid access to it.

For consistency, do the same for kvm_load_guest_xsave_state().

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/svm/svm.c | 7 +++++--
 arch/x86/kvm/x86.c     | 5 ++---
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 2c291f0e89c7..51cfef44b58d 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4251,7 +4251,9 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu,
 		svm_set_dr6(vcpu, DR6_ACTIVE_LOW);
 
 	clgi();
-	kvm_load_guest_xsave_state(vcpu);
+
+	if (!vcpu->arch.guest_state_protected)
+		kvm_load_guest_xsave_state(vcpu);
 
 	kvm_wait_lapic_expire(vcpu);
 
@@ -4280,7 +4282,8 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu,
 	if (unlikely(svm->vmcb->control.exit_code == SVM_EXIT_NMI))
 		kvm_before_interrupt(vcpu, KVM_HANDLING_NMI);
 
-	kvm_load_host_xsave_state(vcpu);
+	if (!vcpu->arch.guest_state_protected)
+		kvm_load_host_xsave_state(vcpu);
 	stgi();
 
 	/* Any pending NMI will happen here */
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b416eec5c167..03db366e794a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1182,11 +1182,10 @@ EXPORT_SYMBOL_GPL(kvm_lmsw);
 
 void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu)
 {
-	if (vcpu->arch.guest_state_protected)
+	if (WARN_ON_ONCE(vcpu->arch.guest_state_protected))
 		return;
 
 	if (kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE)) {
-
 		if (vcpu->arch.xcr0 != kvm_host.xcr0)
 			xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0);
 
@@ -1205,7 +1204,7 @@ EXPORT_SYMBOL_GPL(kvm_load_guest_xsave_state);
 
 void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu)
 {
-	if (vcpu->arch.guest_state_protected)
+	if (WARN_ON_ONCE(vcpu->arch.guest_state_protected))
 		return;
 
 	if (cpu_feature_enabled(X86_FEATURE_PKU) &&
-- 
2.43.5