[PATCH v12 69/77] KVM: introspection: restore the state of MSR interception on unhook

Adalbert Lazăr
2021-10-06T17:31:05Z

From: Nicu?or C??u <nicu.citu at icloud.com>

This commit also ensures that the introspection tool and the userspace
do not disable each other the MSR access VM-exit.

Signed-off-by: Nicu?or C??u <nicu.citu at icloud.com>
Signed-off-by: Adalbert Laz?r <alazar at bitdefender.com>
---
 arch/x86/include/asm/kvmi_host.h |  12 +++
 arch/x86/kvm/kvmi.c              | 124 +++++++++++++++++++++++++++----
 arch/x86/kvm/svm/svm.c           |  10 +++
 arch/x86/kvm/vmx/vmx.c           |  11 +++
 4 files changed, 142 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/kvmi_host.h b/arch/x86/include/asm/kvmi_host.h
index 5a4fc5b80907..8822f0310156 100644
--- a/arch/x86/include/asm/kvmi_host.h
+++ b/arch/x86/include/asm/kvmi_host.h
@@ -26,6 +26,12 @@ struct kvmi_interception {
 			DECLARE_BITMAP(low, KVMI_NUM_MSR);
 			DECLARE_BITMAP(high, KVMI_NUM_MSR);
 		} kvmi_mask;
+		struct {
+			DECLARE_BITMAP(low, KVMI_NUM_MSR);
+			DECLARE_BITMAP(high, KVMI_NUM_MSR);
+		} kvm_mask;
+		bool (*monitor_fct)(struct kvm_vcpu *vcpu, u32 msr,
+				    bool enable);
 	} msrw;
 };

@@ -61,6 +67,8 @@ void kvmi_xsetbv_event(struct kvm_vcpu *vcpu, u8 xcr,
 bool kvmi_monitor_desc_intercept(struct kvm_vcpu *vcpu, bool enable);
 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);

 #else /* CONFIG_KVM_INTROSPECTION */

@@ -82,6 +90,10 @@ static inline bool kvmi_descriptor_event(struct kvm_vcpu
*vcpu, u8 descriptor,
 					 bool write) { return true; }
 static inline bool kvmi_msr_event(struct kvm_vcpu *vcpu, struct msr_data *msr)
 				{ return true; }
+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; }

 #endif /* CONFIG_KVM_INTROSPECTION */

diff --git a/arch/x86/kvm/kvmi.c b/arch/x86/kvm/kvmi.c
index c84a140db451..4e25ffc3d131 100644
--- a/arch/x86/kvm/kvmi.c
+++ b/arch/x86/kvm/kvmi.c
@@ -345,22 +345,25 @@ static void kvmi_arch_disable_desc_intercept(struct
kvm_vcpu *vcpu)
 	vcpu->arch.kvmi->descriptor.kvm_intercepted = false;
 }

-static unsigned long *msr_mask(struct kvm_vcpu *vcpu, unsigned int *msr)
+static unsigned long *msr_mask(struct kvm_vcpu *vcpu, unsigned int *msr,
+			       bool kvmi)
 {
 	switch (*msr) {
 	case 0 ... 0x1fff:
-		return vcpu->arch.kvmi->msrw.kvmi_mask.low;
+		return kvmi ? vcpu->arch.kvmi->msrw.kvmi_mask.low :
+			      vcpu->arch.kvmi->msrw.kvm_mask.low;
 	case 0xc0000000 ... 0xc0001fff:
 		*msr &= 0x1fff;
-		return vcpu->arch.kvmi->msrw.kvmi_mask.high;
+		return kvmi ? vcpu->arch.kvmi->msrw.kvmi_mask.high :
+			      vcpu->arch.kvmi->msrw.kvm_mask.high;
 	}

 	return NULL;
 }

-static bool test_msr_mask(struct kvm_vcpu *vcpu, unsigned int msr)
+static bool test_msr_mask(struct kvm_vcpu *vcpu, unsigned int msr, bool kvmi)
 {
-	unsigned long *mask = msr_mask(vcpu, &msr);
+	unsigned long *mask = msr_mask(vcpu, &msr, kvmi);

 	if (!mask)
 		return false;
@@ -368,9 +371,27 @@ static bool test_msr_mask(struct kvm_vcpu *vcpu, unsigned
int msr)
 	return !!test_bit(msr, mask);
 }

-static bool msr_control(struct kvm_vcpu *vcpu, unsigned int msr, bool enable)
+/*
+ * Returns true if one side (kvm or kvmi) tries to disable the MSR write
+ * interception while the other side is still tracking it.
+ */
+bool kvmi_monitor_msrw_intercept(struct kvm_vcpu *vcpu, u32 msr, bool enable)
+{
+	struct kvmi_interception *arch_vcpui;
+
+	if (!vcpu)
+		return false;
+
+	arch_vcpui = READ_ONCE(vcpu->arch.kvmi);
+
+	return (arch_vcpui && arch_vcpui->msrw.monitor_fct(vcpu, msr,
enable));
+}
+EXPORT_SYMBOL(kvmi_monitor_msrw_intercept);
+
+static bool msr_control(struct kvm_vcpu *vcpu, unsigned int msr, bool enable,
+			bool kvmi)
 {
-	unsigned long *mask = msr_mask(vcpu, &msr);
+	unsigned long *mask = msr_mask(vcpu, &msr, kvmi);

 	if (!mask)
 		return false;
@@ -383,6 +404,63 @@ static bool msr_control(struct kvm_vcpu *vcpu, unsigned int
msr, bool enable)
 	return true;
 }

+static bool msr_intercepted_by_kvmi(struct kvm_vcpu *vcpu, u32 msr)
+{
+	return test_msr_mask(vcpu, msr, true);
+}
+
+static bool msr_intercepted_by_kvm(struct kvm_vcpu *vcpu, u32 msr)
+{
+	return test_msr_mask(vcpu, msr, false);
+}
+
+static void record_msr_intercept_status_for_kvmi(struct kvm_vcpu *vcpu, u32
msr,
+						 bool enable)
+{
+	msr_control(vcpu, msr, enable, true);
+}
+
+static void record_msr_intercept_status_for_kvm(struct kvm_vcpu *vcpu, u32 msr,
+						bool enable)
+{
+	msr_control(vcpu, msr, enable, false);
+}
+
+static bool monitor_msrw_fct_kvmi(struct kvm_vcpu *vcpu, u32 msr, bool enable)
+{
+	bool ret = false;
+
+	if (enable) {
+		if (static_call(kvm_x86_msr_write_intercepted)(vcpu, msr))
+			record_msr_intercept_status_for_kvm(vcpu, msr, true);
+	} else {
+		if (unlikely(!msr_intercepted_by_kvmi(vcpu, msr)))
+			ret = true;
+
+		if (msr_intercepted_by_kvm(vcpu, msr))
+			ret = true;
+	}
+
+	record_msr_intercept_status_for_kvmi(vcpu, msr, enable);
+
+	return ret;
+}
+
+static bool monitor_msrw_fct_kvm(struct kvm_vcpu *vcpu, u32 msr, bool enable)
+{
+	bool ret = false;
+
+	if (!(msr_intercepted_by_kvmi(vcpu, msr)))
+		return false;
+
+	if (!enable)
+		ret = true;
+
+	record_msr_intercept_status_for_kvm(vcpu, msr, enable);
+
+	return ret;
+}
+
 static unsigned int msr_mask_to_base(struct kvm_vcpu *vcpu, unsigned long
*mask)
 {
 	if (mask == vcpu->arch.kvmi->msrw.kvmi_mask.high)
@@ -393,13 +471,14 @@ static unsigned int msr_mask_to_base(struct kvm_vcpu
*vcpu, unsigned long *mask)

 void kvmi_control_msrw_intercept(struct kvm_vcpu *vcpu, u32 msr, bool enable)
 {
+	vcpu->arch.kvmi->msrw.monitor_fct = monitor_msrw_fct_kvmi;
 	static_call(kvm_x86_control_msr_intercept)(vcpu, msr, MSR_TYPE_W,
 						   enable);
-	msr_control(vcpu, msr, enable);
+	vcpu->arch.kvmi->msrw.monitor_fct = monitor_msrw_fct_kvm;
 }

-static void kvmi_arch_disable_msr_intercept(struct kvm_vcpu *vcpu,
-					    unsigned long *mask)
+static void kvmi_arch_disable_msrw_intercept(struct kvm_vcpu *vcpu,
+					     unsigned long *mask)
 {
 	unsigned int msr_base = msr_mask_to_base(vcpu, mask);
 	int offset = -1;
@@ -410,8 +489,7 @@ static void kvmi_arch_disable_msr_intercept(struct kvm_vcpu
*vcpu,
 		if (offset >= KVMI_NUM_MSR)
 			break;

-		static_call(kvm_x86_control_msr_intercept)(vcpu,
-				msr_base + offset, MSR_TYPE_W, false);
+		kvmi_control_msrw_intercept(vcpu, msr_base + offset, false);
 	}

 	bitmap_zero(mask, KVMI_NUM_MSR);
@@ -463,8 +541,8 @@ static void kvmi_arch_restore_interception(struct kvm_vcpu
*vcpu)
 	kvmi_arch_disable_bp_intercept(vcpu);
 	kvmi_arch_disable_cr3w_intercept(vcpu);
 	kvmi_arch_disable_desc_intercept(vcpu);
-	kvmi_arch_disable_msr_intercept(vcpu, arch_vcpui->msrw.kvmi_mask.low);
-	kvmi_arch_disable_msr_intercept(vcpu, arch_vcpui->msrw.kvmi_mask.high);
+	kvmi_arch_disable_msrw_intercept(vcpu, arch_vcpui->msrw.kvmi_mask.low);
+	kvmi_arch_disable_msrw_intercept(vcpu, arch_vcpui->msrw.kvmi_mask.high);
 }

 bool kvmi_arch_clean_up_interception(struct kvm_vcpu *vcpu)
@@ -491,12 +569,14 @@ bool kvmi_arch_vcpu_alloc_interception(struct kvm_vcpu
*vcpu)
 	arch_vcpui->breakpoint.monitor_fct = monitor_bp_fct_kvm;
 	arch_vcpui->cr3w.monitor_fct = monitor_cr3w_fct_kvm;
 	arch_vcpui->descriptor.monitor_fct = monitor_desc_fct_kvm;
+	arch_vcpui->msrw.monitor_fct = monitor_msrw_fct_kvm;

 	/*
 	 * paired with:
 	 *  - kvmi_monitor_bp_intercept()
 	 *  - kvmi_monitor_cr3w_intercept()
 	 *  - kvmi_monitor_desc_intercept()
+	 *  - kvmi_monitor_msrw_intercept()
 	 */
 	smp_wmb();
 	WRITE_ONCE(vcpu->arch.kvmi, arch_vcpui);
@@ -778,6 +858,20 @@ bool kvmi_descriptor_event(struct kvm_vcpu *vcpu, u8
descriptor, bool write)
 }
 EXPORT_SYMBOL(kvmi_descriptor_event);

+bool kvmi_msrw_intercept_originator(struct kvm_vcpu *vcpu)
+{
+	struct kvmi_interception *arch_vcpui;
+
+	if (!vcpu)
+		return false;
+
+	arch_vcpui = READ_ONCE(vcpu->arch.kvmi);
+
+	return (arch_vcpui &&
+		arch_vcpui->msrw.monitor_fct == monitor_msrw_fct_kvmi);
+}
+EXPORT_SYMBOL(kvmi_msrw_intercept_originator);
+
 static bool __kvmi_msr_event(struct kvm_vcpu *vcpu, struct msr_data *msr)
 {
 	struct msr_data old_msr = {
@@ -788,7 +882,7 @@ static bool __kvmi_msr_event(struct kvm_vcpu *vcpu, struct
msr_data *msr)
 	u32 action;
 	bool ret;

-	if (!test_msr_mask(vcpu, msr->index))
+	if (!test_msr_mask(vcpu, msr->index, true))
 		return true;
 	if (static_call(kvm_x86_get_msr)(vcpu, &old_msr))
 		return true;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index d3d061615536..ea2843027671 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -673,6 +673,16 @@ static void set_msr_interception_bitmap(struct kvm_vcpu
*vcpu, u32 *msrpm,
 	unsigned long tmp;
 	u32 offset;

+#ifdef CONFIG_KVM_INTROSPECTION
+	if ((type & MSR_TYPE_W) &&
+	    kvmi_monitor_msrw_intercept(vcpu, msr, !value))
+		type &= ~MSR_TYPE_W;
+
+	/*
+	 * Avoid the below warning for kvmi intercepted msrs.
+	 */
+	if (!kvmi_msrw_intercept_originator(vcpu))
+#endif /* CONFIG_KVM_INTROSPECTION */
 	/*
 	 * If this warning triggers extend the direct_access_msrs list at the
 	 * beginning of the file
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 964840430537..1df0a29d1d8d 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3798,6 +3798,12 @@ void vmx_disable_intercept_for_msr(struct kvm_vcpu *vcpu,
u32 msr, int type)
 	if (!cpu_has_vmx_msr_bitmap())
 		return;

+#ifdef CONFIG_KVM_INTROSPECTION
+	if ((type & MSR_TYPE_W) &&
+	    kvmi_monitor_msrw_intercept(vcpu, msr, false))
+		type &= ~MSR_TYPE_W;
+#endif /* CONFIG_KVM_INTROSPECTION */
+
 	if (static_branch_unlikely(&enable_evmcs))
 		evmcs_touch_msr_bitmap();

@@ -3843,6 +3849,11 @@ void vmx_enable_intercept_for_msr(struct kvm_vcpu *vcpu,
u32 msr, int type)
 	if (!cpu_has_vmx_msr_bitmap())
 		return;

+#ifdef CONFIG_KVM_INTROSPECTION
+	if (type & MSR_TYPE_W)
+		kvmi_monitor_msrw_intercept(vcpu, msr, true);
+#endif /* CONFIG_KVM_INTROSPECTION */
+
 	if (static_branch_unlikely(&enable_evmcs))
 		evmcs_touch_msr_bitmap();