[RFC PATCH v2 07/33] KVM: SVM: Prevent debugging under SEV-ES

[Tom Lendacky]

From: Tom Lendacky <thomas.lendacky@xxxxxxx>

Since the guest register state of an SEV-ES guest is encrypted, debugging
is not supported. Update the code to prevent guest debugging when the
guest has protected state.

Additionally, an SEV-ES guest must only and always intercept DR7 reads and
writes. Update set_dr_intercepts() and clr_dr_intercepts() to account for
this.

Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
---
 arch/x86/kvm/svm/svm.c |  9 +++++
 arch/x86/kvm/svm/svm.h | 81 +++++++++++++++++++++++-------------------
 arch/x86/kvm/x86.c     |  3 ++
 3 files changed, 57 insertions(+), 36 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index fb0e8a0881f8..5270735bbdd8 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1817,6 +1817,9 @@ static void svm_set_dr6(struct vcpu_svm *svm, unsigned long value)
 {
 	struct vmcb *vmcb = svm->vmcb;
 
+	if (svm->vcpu.arch.guest_state_protected)
+		return;
+
 	if (unlikely(value != vmcb->save.dr6)) {
 		vmcb->save.dr6 = value;
 		vmcb_mark_dirty(vmcb, VMCB_DR);
@@ -1827,6 +1830,9 @@ static void svm_sync_dirty_debug_regs(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
+	if (vcpu->arch.guest_state_protected)
+		return;
+
 	get_debugreg(vcpu->arch.db[0], 0);
 	get_debugreg(vcpu->arch.db[1], 1);
 	get_debugreg(vcpu->arch.db[2], 2);
@@ -1845,6 +1851,9 @@ static void svm_set_dr7(struct kvm_vcpu *vcpu, unsigned long value)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
+	if (vcpu->arch.guest_state_protected)
+		return;
+
 	svm->vmcb->save.dr7 = value;
 	vmcb_mark_dirty(svm->vmcb, VMCB_DR);
 }
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 09e78487e5d0..e6900c62f164 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -196,6 +196,28 @@ static inline struct kvm_svm *to_kvm_svm(struct kvm *kvm)
 	return container_of(kvm, struct kvm_svm, kvm);
 }
 
+static inline bool sev_guest(struct kvm *kvm)
+{
+#ifdef CONFIG_KVM_AMD_SEV
+	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
+
+	return sev->active;
+#else
+	return false;
+#endif
+}
+
+static inline bool sev_es_guest(struct kvm *kvm)
+{
+#ifdef CONFIG_KVM_AMD_SEV
+	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
+
+	return sev_guest(kvm) && sev->es_active;
+#else
+	return false;
+#endif
+}
+
 static inline void vmcb_mark_all_dirty(struct vmcb *vmcb)
 {
 	vmcb->control.clean = 0;
@@ -247,21 +269,24 @@ static inline void set_dr_intercepts(struct vcpu_svm *svm)
 {
 	struct vmcb *vmcb = get_host_vmcb(svm);
 
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR0_READ);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR1_READ);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR2_READ);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR3_READ);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR4_READ);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR5_READ);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR6_READ);
+	if (!sev_es_guest(svm->vcpu.kvm)) {
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR0_READ);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR1_READ);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR2_READ);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR3_READ);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR4_READ);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR5_READ);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR6_READ);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR0_WRITE);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR1_WRITE);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR2_WRITE);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR3_WRITE);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR4_WRITE);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR5_WRITE);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR6_WRITE);
+	}
+
 	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_READ);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR0_WRITE);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR1_WRITE);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR2_WRITE);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR3_WRITE);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR4_WRITE);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR5_WRITE);
-	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR6_WRITE);
 	vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_WRITE);
 
 	recalc_intercepts(svm);
@@ -273,6 +298,12 @@ static inline void clr_dr_intercepts(struct vcpu_svm *svm)
 
 	vmcb->control.intercepts[INTERCEPT_DR] = 0;
 
+	/* DR7 access must remain intercepted for an SEV-ES guest */
+	if (sev_es_guest(svm->vcpu.kvm)) {
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_READ);
+		vmcb_set_intercept(&vmcb->control, INTERCEPT_DR7_WRITE);
+	}
+
 	recalc_intercepts(svm);
 }
 
@@ -472,28 +503,6 @@ void svm_vcpu_unblocking(struct kvm_vcpu *vcpu);
 
 extern unsigned int max_sev_asid;
 
-static inline bool sev_guest(struct kvm *kvm)
-{
-#ifdef CONFIG_KVM_AMD_SEV
-	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
-
-	return sev->active;
-#else
-	return false;
-#endif
-}
-
-static inline bool sev_es_guest(struct kvm *kvm)
-{
-#ifdef CONFIG_KVM_AMD_SEV
-	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
-
-	return sev_guest(kvm) && sev->es_active;
-#else
-	return false;
-#endif
-}
-
 static inline bool svm_sev_enabled(void)
 {
 	return IS_ENABLED(CONFIG_KVM_AMD_SEV) ? max_sev_asid : 0;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 08812eb0b73e..6b9125f49ddc 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9550,6 +9550,9 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
 	unsigned long rflags;
 	int i, r;
 
+	if (vcpu->arch.guest_state_protected)
+		return -EINVAL;
+
 	vcpu_load(vcpu);
 
 	if (dbg->control & (KVM_GUESTDBG_INJECT_DB | KVM_GUESTDBG_INJECT_BP)) {
-- 
2.28.0