5 files changed, 52 insertions, 20 deletions

diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
index 13bc212cd4bc..e3054e3e46d5 100644
--- a/arch/x86/include/asm/kvm-x86-ops.h
+++ b/arch/x86/include/asm/kvm-x86-ops.h
@@ -37,6 +37,7 @@ KVM_X86_OP(get_segment)
 KVM_X86_OP(get_cpl)
 KVM_X86_OP(set_segment)
 KVM_X86_OP(get_cs_db_l_bits)
+KVM_X86_OP(is_valid_cr0)
 KVM_X86_OP(set_cr0)
 KVM_X86_OP_OPTIONAL(post_set_cr3)
 KVM_X86_OP(is_valid_cr4)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 28bd38303d70..3bc146dfd38d 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1566,9 +1566,10 @@ struct kvm_x86_ops {
 	void (*set_segment)(struct kvm_vcpu *vcpu,
 			    struct kvm_segment *var, int seg);
 	void (*get_cs_db_l_bits)(struct kvm_vcpu *vcpu, int *db, int *l);
+	bool (*is_valid_cr0)(struct kvm_vcpu *vcpu, unsigned long cr0);
 	void (*set_cr0)(struct kvm_vcpu *vcpu, unsigned long cr0);
 	void (*post_set_cr3)(struct kvm_vcpu *vcpu, unsigned long cr3);
-	bool (*is_valid_cr4)(struct kvm_vcpu *vcpu, unsigned long cr0);
+	bool (*is_valid_cr4)(struct kvm_vcpu *vcpu, unsigned long cr4);
 	void (*set_cr4)(struct kvm_vcpu *vcpu, unsigned long cr4);
 	int (*set_efer)(struct kvm_vcpu *vcpu, u64 efer);
 	void (*get_idt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index cea08e5fa69b..956726d867aa 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1786,6 +1786,11 @@ static void sev_post_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
 	}
 }
 
+static bool svm_is_valid_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
+{
+	return true;
+}
+
 void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -4809,6 +4814,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
 	.set_segment = svm_set_segment,
 	.get_cpl = svm_get_cpl,
 	.get_cs_db_l_bits = svm_get_cs_db_l_bits,
+	.is_valid_cr0 = svm_is_valid_cr0,
 	.set_cr0 = svm_set_cr0,
 	.post_set_cr3 = sev_post_set_cr3,
 	.is_valid_cr4 = svm_is_valid_cr4,
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 0dd4612b0ca2..3d011d62d969 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3047,6 +3047,15 @@ static void enter_rmode(struct kvm_vcpu *vcpu)
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	struct kvm_vmx *kvm_vmx = to_kvm_vmx(vcpu->kvm);
 
+	/*
+	 * KVM should never use VM86 to virtualize Real Mode when L2 is active,
+	 * as using VM86 is unnecessary if unrestricted guest is enabled, and
+	 * if unrestricted guest is disabled, VM-Enter (from L1) with CR0.PG=0
+	 * should VM-Fail and KVM should reject userspace attempts to stuff
+	 * CR0.PG=0 when L2 is active.
+	 */
+	WARN_ON_ONCE(is_guest_mode(vcpu));
+
 	vmx_get_segment(vcpu, &vmx->rmode.segs[VCPU_SREG_TR], VCPU_SREG_TR);
 	vmx_get_segment(vcpu, &vmx->rmode.segs[VCPU_SREG_ES], VCPU_SREG_ES);
 	vmx_get_segment(vcpu, &vmx->rmode.segs[VCPU_SREG_DS], VCPU_SREG_DS);
@@ -3236,6 +3245,17 @@ void ept_save_pdptrs(struct kvm_vcpu *vcpu)
 #define CR3_EXITING_BITS (CPU_BASED_CR3_LOAD_EXITING | \
 			  CPU_BASED_CR3_STORE_EXITING)
 
+static bool vmx_is_valid_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
+{
+	if (is_guest_mode(vcpu))
+		return nested_guest_cr0_valid(vcpu, cr0);
+
+	if (to_vmx(vcpu)->nested.vmxon)
+		return nested_host_cr0_valid(vcpu, cr0);
+
+	return true;
+}
+
 void vmx_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -5375,18 +5395,11 @@ static int handle_set_cr0(struct kvm_vcpu *vcpu, unsigned long val)
 		val = (val & ~vmcs12->cr0_guest_host_mask) |
 			(vmcs12->guest_cr0 & vmcs12->cr0_guest_host_mask);
 
-		if (!nested_guest_cr0_valid(vcpu, val))
-			return 1;
-
 		if (kvm_set_cr0(vcpu, val))
 			return 1;
 		vmcs_writel(CR0_READ_SHADOW, orig_val);
 		return 0;
 	} else {
-		if (to_vmx(vcpu)->nested.vmxon &&
-		    !nested_host_cr0_valid(vcpu, val))
-			return 1;
-
 		return kvm_set_cr0(vcpu, val);
 	}
 }
@@ -8214,6 +8227,7 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
 	.set_segment = vmx_set_segment,
 	.get_cpl = vmx_get_cpl,
 	.get_cs_db_l_bits = vmx_get_cs_db_l_bits,
+	.is_valid_cr0 = vmx_is_valid_cr0,
 	.set_cr0 = vmx_set_cr0,
 	.is_valid_cr4 = vmx_is_valid_cr4,
 	.set_cr4 = vmx_set_cr4,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 27080bd986b5..278dbd37dab2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -906,6 +906,22 @@ int load_pdptrs(struct kvm_vcpu *vcpu, unsigned long cr3)
 }
 EXPORT_SYMBOL_GPL(load_pdptrs);
 
+static bool kvm_is_valid_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
+{
+#ifdef CONFIG_X86_64
+	if (cr0 & 0xffffffff00000000UL)
+		return false;
+#endif
+
+	if ((cr0 & X86_CR0_NW) && !(cr0 & X86_CR0_CD))
+		return false;
+
+	if ((cr0 & X86_CR0_PG) && !(cr0 & X86_CR0_PE))
+		return false;
+
+	return static_call(kvm_x86_is_valid_cr0)(vcpu, cr0);
+}
+
 void kvm_post_set_cr0(struct kvm_vcpu *vcpu, unsigned long old_cr0, unsigned long cr0)
 {
 	/*
@@ -952,20 +968,13 @@ int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 {
 	unsigned long old_cr0 = kvm_read_cr0(vcpu);
 
-	cr0 |= X86_CR0_ET;
-
-#ifdef CONFIG_X86_64
-	if (cr0 & 0xffffffff00000000UL)
+	if (!kvm_is_valid_cr0(vcpu, cr0))
 		return 1;
-#endif
-
-	cr0 &= ~CR0_RESERVED_BITS;
 
-	if ((cr0 & X86_CR0_NW) && !(cr0 & X86_CR0_CD))
-		return 1;
+	cr0 |= X86_CR0_ET;
 
-	if ((cr0 & X86_CR0_PG) && !(cr0 & X86_CR0_PE))
-		return 1;
+	/* Write to CR0 reserved bits are ignored, even on Intel. */
+	cr0 &= ~CR0_RESERVED_BITS;
 
 #ifdef CONFIG_X86_64
 	if ((vcpu->arch.efer & EFER_LME) && !is_paging(vcpu) &&
@@ -11468,7 +11477,8 @@ static bool kvm_is_valid_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
 			return false;
 	}
 
-	return kvm_is_valid_cr4(vcpu, sregs->cr4);
+	return kvm_is_valid_cr4(vcpu, sregs->cr4) &&
+	       kvm_is_valid_cr0(vcpu, sregs->cr0);
 }
 
 static int __set_sregs_common(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs,