[RFC PATCH v3 3/5] KVM: x86: Add notifications for Heki policy configuration and violation

["Mickaël Salaün" <mic@digikod.net>]

Add an interface for user space to be notified about guests' Heki policy
and related violations.

Extend the KVM_ENABLE_CAP IOCTL with KVM_CAP_HEKI_CONFIGURE and
KVM_CAP_HEKI_DENIAL. Each one takes a bitmask as first argument that can
contains KVM_HEKI_EXIT_REASON_CR0 and KVM_HEKI_EXIT_REASON_CR4. The
returned value is the bitmask of known Heki exit reasons, for now:
KVM_HEKI_EXIT_REASON_CR0 and KVM_HEKI_EXIT_REASON_CR4.

If KVM_CAP_HEKI_CONFIGURE is set, a VM exit will be triggered for each
KVM_HC_LOCK_CR_UPDATE hypercalls according to the requested control
register. This enables to enlighten the VMM with the guest
auto-restrictions.

If KVM_CAP_HEKI_DENIAL is set, a VM exit will be triggered for each
pinned CR violation. This enables the VMM to react to a policy
violation.

Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20240503131910.307630-4-mic@digikod.net
---

Changes since v1:
* New patch. Making user space aware of Heki properties was requested by
  Sean Christopherson.
---
 arch/x86/kvm/vmx/vmx.c   |   5 +-
 arch/x86/kvm/x86.c       | 114 +++++++++++++++++++++++++++++++++++----
 arch/x86/kvm/x86.h       |   7 +--
 include/linux/kvm_host.h |   2 +
 include/uapi/linux/kvm.h |  22 ++++++++
 5 files changed, 136 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 7ba970b525f7..5869a1ed7866 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5445,6 +5445,7 @@ static int handle_cr(struct kvm_vcpu *vcpu)
 	int reg;
 	int err;
 	int ret;
+	bool exit = false;
 
 	exit_qualification = vmx_get_exit_qual(vcpu);
 	cr = exit_qualification & 15;
@@ -5454,8 +5455,8 @@ static int handle_cr(struct kvm_vcpu *vcpu)
 		val = kvm_register_read(vcpu, reg);
 		trace_kvm_cr_write(cr, val);
 
-		ret = heki_check_cr(vcpu, cr, val);
-		if (ret)
+		ret = heki_check_cr(vcpu, cr, val, &exit);
+		if (exit)
 			return ret;
 
 		switch (cr) {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a5f47be59abc..865e88f2b0fc 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -119,6 +119,10 @@ static u64 __read_mostly cr4_reserved_bits = CR4_RESERVED_BITS;
 
 #define KVM_CAP_PMU_VALID_MASK KVM_PMU_CAP_DISABLE
 
+#define KVM_HEKI_EXIT_REASON_VALID_MASK ( \
+	KVM_HEKI_EXIT_REASON_CR0 | \
+	KVM_HEKI_EXIT_REASON_CR4)
+
 #define KVM_X2APIC_API_VALID_FLAGS (KVM_X2APIC_API_USE_32BIT_IDS | \
                                     KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK)
 
@@ -4836,6 +4840,10 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 		if (kvm_is_vm_type_supported(KVM_X86_SW_PROTECTED_VM))
 			r |= BIT(KVM_X86_SW_PROTECTED_VM);
 		break;
+	case KVM_CAP_HEKI_CONFIGURE:
+	case KVM_CAP_HEKI_DENIAL:
+		r = KVM_HEKI_EXIT_REASON_VALID_MASK;
+		break;
 	default:
 		break;
 	}
@@ -6729,6 +6737,22 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 		}
 		mutex_unlock(&kvm->lock);
 		break;
+#ifdef CONFIG_HEKI
+	case KVM_CAP_HEKI_CONFIGURE:
+		r = -EINVAL;
+		if (cap->args[0] & ~KVM_HEKI_EXIT_REASON_VALID_MASK)
+			break;
+		kvm->heki_configure_exit_reason = cap->args[0];
+		r = 0;
+		break;
+	case KVM_CAP_HEKI_DENIAL:
+		r = -EINVAL;
+		if (cap->args[0] & ~KVM_HEKI_EXIT_REASON_VALID_MASK)
+			break;
+		kvm->heki_denial_exit_reason = cap->args[0];
+		r = 0;
+		break;
+#endif
 	default:
 		r = -EINVAL;
 		break;
@@ -8283,11 +8307,60 @@ static unsigned long emulator_get_cr(struct x86_emulate_ctxt *ctxt, int cr)
 
 #ifdef CONFIG_HEKI
 
+static int complete_heki_configure_exit(struct kvm_vcpu *const vcpu)
+{
+	kvm_rax_write(vcpu, 0);
+	++vcpu->stat.hypercalls;
+	return kvm_skip_emulated_instruction(vcpu);
+}
+
+static int complete_heki_denial_exit(struct kvm_vcpu *const vcpu)
+{
+	kvm_inject_gp(vcpu, 0);
+	return 1;
+}
+
+/* Returns true if the @exit_reason is handled by @vcpu->kvm. */
+static bool heki_exit_cr(struct kvm_vcpu *const vcpu, const __u32 exit_reason,
+			 const u64 heki_reason, unsigned long value)
+{
+	switch (exit_reason) {
+	case KVM_EXIT_HEKI_CONFIGURE:
+		if (!(vcpu->kvm->heki_configure_exit_reason & heki_reason))
+			return false;
+
+		vcpu->run->heki_configure.reason = heki_reason;
+		memset(vcpu->run->heki_configure.reserved, 0,
+		       sizeof(vcpu->run->heki_configure.reserved));
+		vcpu->run->heki_configure.cr_pinned = value;
+		vcpu->arch.complete_userspace_io = complete_heki_configure_exit;
+		break;
+	case KVM_EXIT_HEKI_DENIAL:
+		if (!(vcpu->kvm->heki_denial_exit_reason & heki_reason))
+			return false;
+
+		vcpu->run->heki_denial.reason = heki_reason;
+		memset(vcpu->run->heki_denial.reserved, 0,
+		       sizeof(vcpu->run->heki_denial.reserved));
+		vcpu->run->heki_denial.cr_value = value;
+		vcpu->arch.complete_userspace_io = complete_heki_denial_exit;
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		return false;
+	}
+
+	vcpu->run->exit_reason = exit_reason;
+	return true;
+}
+
 #define HEKI_ABI_VERSION 1
 
 static int heki_lock_cr(struct kvm_vcpu *const vcpu, const unsigned long cr,
-			unsigned long pin, unsigned long flags)
+			unsigned long pin, unsigned long flags, bool *exit)
 {
+	*exit = false;
+
 	if (flags) {
 		if ((flags == KVM_LOCK_CR_UPDATE_VERSION) && !cr && !pin)
 			return HEKI_ABI_VERSION;
@@ -8307,6 +8380,8 @@ static int heki_lock_cr(struct kvm_vcpu *const vcpu, const unsigned long cr,
 			return -KVM_EINVAL;
 
 		atomic_long_or(pin, &vcpu->kvm->heki_pinned_cr0);
+		*exit = heki_exit_cr(vcpu, KVM_EXIT_HEKI_CONFIGURE,
+				     KVM_HEKI_EXIT_REASON_CR0, pin);
 		return 0;
 	case 4:
 		/* Checks for irrelevant bits. */
@@ -8316,24 +8391,37 @@ static int heki_lock_cr(struct kvm_vcpu *const vcpu, const unsigned long cr,
 		/* Ignores bits not present in host. */
 		pin &= __read_cr4();
 		atomic_long_or(pin, &vcpu->kvm->heki_pinned_cr4);
+		*exit = heki_exit_cr(vcpu, KVM_EXIT_HEKI_CONFIGURE,
+				     KVM_HEKI_EXIT_REASON_CR4, pin);
 		return 0;
 	}
 	return -KVM_EINVAL;
 }
 
+/*
+ * Sets @exit to true if the caller must exit (i.e. denied access) with the
+ * returned value:
+ * - 0 when kvm_run is configured;
+ * - 1 when there is no user space handler.
+ */
 int heki_check_cr(struct kvm_vcpu *const vcpu, const unsigned long cr,
-		  const unsigned long val)
+		  const unsigned long val, bool *exit)
 {
 	unsigned long pinned;
 
+	*exit = false;
+
 	switch (cr) {
 	case 0:
 		pinned = atomic_long_read(&vcpu->kvm->heki_pinned_cr0);
 		if ((val & pinned) != pinned) {
 			pr_warn_ratelimited(
 				"heki: Blocked CR0 update: 0x%lx\n", val);
-			kvm_inject_gp(vcpu, 0);
-			return 1;
+			*exit = true;
+			if (heki_exit_cr(vcpu, KVM_EXIT_HEKI_DENIAL,
+					 KVM_HEKI_EXIT_REASON_CR0, val))
+				return 0;
+			return complete_heki_denial_exit(vcpu);
 		}
 		return 0;
 	case 4:
@@ -8341,8 +8429,11 @@ int heki_check_cr(struct kvm_vcpu *const vcpu, const unsigned long cr,
 		if ((val & pinned) != pinned) {
 			pr_warn_ratelimited(
 				"heki: Blocked CR4 update: 0x%lx\n", val);
-			kvm_inject_gp(vcpu, 0);
-			return 1;
+			*exit = true;
+			if (heki_exit_cr(vcpu, KVM_EXIT_HEKI_DENIAL,
+					 KVM_HEKI_EXIT_REASON_CR4, val))
+				return 0;
+			return complete_heki_denial_exit(vcpu);
 		}
 		return 0;
 	}
@@ -8356,9 +8447,10 @@ static int emulator_set_cr(struct x86_emulate_ctxt *ctxt, int cr, ulong val)
 {
 	struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
 	int res = 0;
+	bool exit = false;
 
-	res = heki_check_cr(vcpu, cr, val);
-	if (res)
+	res = heki_check_cr(vcpu, cr, val, &exit);
+	if (exit)
 		return res;
 
 	switch (cr) {
@@ -10222,7 +10314,11 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
 		if (a0 > U32_MAX) {
 			ret = -KVM_EINVAL;
 		} else {
-			ret = heki_lock_cr(vcpu, a0, a1, a2);
+			bool exit = false;
+
+			ret = heki_lock_cr(vcpu, a0, a1, a2, &exit);
+			if (exit)
+				return ret;
 		}
 		break;
 #endif /* CONFIG_HEKI */
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index ade7d68ddaff..2740b74ab583 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -292,18 +292,19 @@ static inline bool kvm_check_has_quirk(struct kvm *kvm, u64 quirk)
 
 #ifdef CONFIG_HEKI
 
-int heki_check_cr(struct kvm_vcpu *vcpu, unsigned long cr, unsigned long val);
+int heki_check_cr(struct kvm_vcpu *vcpu, unsigned long cr, unsigned long val,
+		  bool *exit);
 
 #else /* CONFIG_HEKI */
 
 static inline int heki_check_cr(struct kvm_vcpu *vcpu, unsigned long cr,
-				unsigned long val)
+				unsigned long val, bool *exit)
 {
 	return 0;
 }
 
 static inline int heki_lock_cr(struct kvm_vcpu *const vcpu, unsigned long cr,
-			       unsigned long pin)
+			       unsigned long pin, bool *exit)
 {
 	return 0;
 }
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 6ff13937929a..cf8e271d47aa 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -839,6 +839,8 @@ struct kvm {
 #ifdef CONFIG_HEKI
 	atomic_long_t heki_pinned_cr0;
 	atomic_long_t heki_pinned_cr4;
+	u64 heki_configure_exit_reason;
+	u64 heki_denial_exit_reason;
 #endif /* CONFIG_HEKI */
 
 #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 2190adbe3002..1051c2f817ba 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -178,6 +178,8 @@ struct kvm_xen_exit {
 #define KVM_EXIT_NOTIFY           37
 #define KVM_EXIT_LOONGARCH_IOCSR  38
 #define KVM_EXIT_MEMORY_FAULT     39
+#define KVM_EXIT_HEKI_CONFIGURE   40
+#define KVM_EXIT_HEKI_DENIAL      41
 
 /* For KVM_EXIT_INTERNAL_ERROR */
 /* Emulate instruction failed. */
@@ -433,6 +435,24 @@ struct kvm_run {
 			__u64 gpa;
 			__u64 size;
 		} memory_fault;
+		/* KVM_EXIT_HEKI_CONFIGURE */
+		struct {
+#define KVM_HEKI_EXIT_REASON_CR0	(1ULL << 0)
+#define KVM_HEKI_EXIT_REASON_CR4	(1ULL << 1)
+			__u64 reason;
+			union {
+				__u64 cr_pinned;
+				__u64 reserved[7]; /* ignored */
+			};
+		} heki_configure;
+		/* KVM_EXIT_HEKI_DENIAL */
+		struct {
+			__u64 reason;
+			union {
+				__u64 cr_value;
+				__u64 reserved[7]; /* ignored */
+			};
+		} heki_denial;
 		/* Fix the size of the union. */
 		char padding[256];
 	};
@@ -917,6 +937,8 @@ struct kvm_enable_cap {
 #define KVM_CAP_MEMORY_ATTRIBUTES 233
 #define KVM_CAP_GUEST_MEMFD 234
 #define KVM_CAP_VM_TYPES 235
+#define KVM_CAP_HEKI_CONFIGURE 236
+#define KVM_CAP_HEKI_DENIAL 237
 
 struct kvm_irq_routing_irqchip {
 	__u32 irqchip;
-- 
2.45.0