[PATCH] KVM: x86: Forbid the use of kvm_load_host_xsave_state() with guest_state_protected

[PATCH] KVM: x86: Forbid the use of kvm_load_host_xsave_state() with guest_state_protected

[Paolo Bonzini]

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@redhat.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

Re: [PATCH] KVM: x86: Forbid the use of kvm_load_host_xsave_state() with guest_state_protected

[Paolo Bonzini]

On 3/7/25 19:41, Paolo Bonzini wrote:
> 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@redhat.com>

Applied now.

Paolo
> ---
>   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) &&