[PATCH v8 80/81] KVM: introspection: emulate a guest page table walk on SPT violations due to A/D bit updates

["Adalbert Lazăr" <alazar@bitdefender.com>]

From: Mihai Donțu <mdontu@bitdefender.com>

On SPT page faults caused by guest page table walks, use the existing
guest page table walk code to make the necessary adjustments to the A/D
bits and return to guest. This effectively bypasses the x86 emulator
who was making the wrong modifications leading one OS (Windows 8.1 x64)
to triple-fault very early in the boot process with the introspection
enabled.

With introspection disabled, these faults are handled by simply removing
the protection from the affected guest page and returning to guest.

Signed-off-by: Mihai Donțu <mdontu@bitdefender.com>
Signed-off-by: Adalbert Lazăr <alazar@bitdefender.com>
---
 arch/x86/include/asm/kvmi_host.h |  2 ++
 arch/x86/kvm/kvmi.c              | 33 ++++++++++++++++++++++++++++++++
 arch/x86/kvm/mmu/mmu.c           | 11 +++++++++--
 include/linux/kvmi_host.h        |  3 +++
 virt/kvm/introspection/kvmi.c    | 26 +++++++++++++++++++++++++
 5 files changed, 73 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kvmi_host.h b/arch/x86/include/asm/kvmi_host.h
index 8d0c3ed3021b..9c9d6a018206 100644
--- a/arch/x86/include/asm/kvmi_host.h
+++ b/arch/x86/include/asm/kvmi_host.h
@@ -61,6 +61,7 @@ bool kvmi_descriptor_event(struct kvm_vcpu *vcpu, u8 descriptor, bool write);
 bool kvmi_msr_event(struct kvm_vcpu *vcpu, struct msr_data *msr);
 bool kvmi_monitor_msrw_intercept(struct kvm_vcpu *vcpu, u32 msr, bool enable);
 bool kvmi_msrw_intercept_originator(struct kvm_vcpu *vcpu);
+bool kvmi_update_ad_flags(struct kvm_vcpu *vcpu);
 
 #else /* CONFIG_KVM_INTROSPECTION */
 
@@ -83,6 +84,7 @@ static inline bool kvmi_monitor_msrw_intercept(struct kvm_vcpu *vcpu, u32 msr,
 					       bool enable) { return false; }
 static inline bool kvmi_msrw_intercept_originator(struct kvm_vcpu *vcpu)
 				{ return false; }
+bool kvmi_update_ad_flags(struct kvm_vcpu *vcpu) { return false; }
 
 #endif /* CONFIG_KVM_INTROSPECTION */
 
diff --git a/arch/x86/kvm/kvmi.c b/arch/x86/kvm/kvmi.c
index d339a879ba0b..f649630b089e 100644
--- a/arch/x86/kvm/kvmi.c
+++ b/arch/x86/kvm/kvmi.c
@@ -1232,3 +1232,36 @@ gpa_t kvmi_arch_cmd_translate_gva(struct kvm_vcpu *vcpu, gva_t gva)
 {
 	return kvm_mmu_gva_to_gpa_system(vcpu, gva, 0, NULL);
 }
+
+bool kvmi_update_ad_flags(struct kvm_vcpu *vcpu)
+{
+	struct kvm_introspection *kvmi;
+	bool ret = false;
+	gva_t gva;
+	gpa_t gpa;
+
+	kvmi = kvmi_get(vcpu->kvm);
+	if (!kvmi)
+		return false;
+
+	gva = kvm_x86_ops->fault_gla(vcpu);
+	if (gva == ~0ull) {
+		kvmi_warn_once(kvmi, "%s: cannot perform translation\n",
+			       __func__);
+		goto out;
+	}
+
+	gpa = kvm_mmu_gva_to_gpa_system(vcpu, gva, PFERR_WRITE_MASK, NULL);
+	if (gpa == UNMAPPED_GVA) {
+		struct x86_exception exception = { };
+
+		gpa = kvm_mmu_gva_to_gpa_system(vcpu, gva, 0, &exception);
+	}
+
+	ret = (gpa != UNMAPPED_GVA);
+
+out:
+	kvmi_put(vcpu->kvm);
+
+	return ret;
+}
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 35be9f2a2fc7..19a61136e1f1 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5574,8 +5574,15 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 error_code,
 	 */
 	if (vcpu->arch.mmu->direct_map &&
 	    (error_code & PFERR_NESTED_GUEST_PAGE) == PFERR_NESTED_GUEST_PAGE) {
-		kvm_mmu_unprotect_page(vcpu->kvm, gpa_to_gfn(cr2_or_gpa));
-		return 1;
+		gfn_t gfn = gpa_to_gfn(cr2_or_gpa);
+
+		if (kvmi_tracked_gfn(vcpu, gfn)) {
+			if (kvmi_update_ad_flags(vcpu))
+				return 1;
+		} else {
+			kvm_mmu_unprotect_page(vcpu->kvm, gfn);
+			return 1;
+		}
 	}
 
 	/*
diff --git a/include/linux/kvmi_host.h b/include/linux/kvmi_host.h
index 58a30c087d63..a301148c8857 100644
--- a/include/linux/kvmi_host.h
+++ b/include/linux/kvmi_host.h
@@ -97,6 +97,7 @@ bool kvmi_enter_guest(struct kvm_vcpu *vcpu);
 bool kvmi_vcpu_running_singlestep(struct kvm_vcpu *vcpu);
 void kvmi_singlestep_done(struct kvm_vcpu *vcpu);
 void kvmi_singlestep_failed(struct kvm_vcpu *vcpu);
+bool kvmi_tracked_gfn(struct kvm_vcpu *vcpu, gfn_t gfn);
 
 #else
 
@@ -117,6 +118,8 @@ static inline bool kvmi_vcpu_running_singlestep(struct kvm_vcpu *vcpu)
 			{ return false; }
 static inline void kvmi_singlestep_done(struct kvm_vcpu *vcpu) { }
 static inline void kvmi_singlestep_failed(struct kvm_vcpu *vcpu) { }
+static inline bool kvmi_tracked_gfn(struct kvm_vcpu *vcpu, gfn_t gfn)
+			{ return false; }
 
 #endif /* CONFIG_KVM_INTROSPECTION */
 
diff --git a/virt/kvm/introspection/kvmi.c b/virt/kvm/introspection/kvmi.c
index 8a73fac287b4..9176ae147d2a 100644
--- a/virt/kvm/introspection/kvmi.c
+++ b/virt/kvm/introspection/kvmi.c
@@ -1381,3 +1381,29 @@ void kvmi_singlestep_failed(struct kvm_vcpu *vcpu)
 	kvmi_handle_singlestep_exit(vcpu, false);
 }
 EXPORT_SYMBOL(kvmi_singlestep_failed);
+
+static bool __kvmi_tracked_gfn(struct kvm_introspection *kvmi, gfn_t gfn)
+{
+	u8 ignored_access;
+
+	if (kvmi_get_gfn_access(kvmi, gfn, &ignored_access))
+		return false;
+
+	return true;
+}
+
+bool kvmi_tracked_gfn(struct kvm_vcpu *vcpu, gfn_t gfn)
+{
+	struct kvm_introspection *kvmi;
+	bool ret;
+
+	kvmi = kvmi_get(vcpu->kvm);
+	if (!kvmi)
+		return false;
+
+	ret = __kvmi_tracked_gfn(kvmi, gfn);
+
+	kvmi_put(vcpu->kvm);
+
+	return ret;
+}