KVM: x86: Validate guest writes to MSR_IA32_APICBASE

Check for invalid state transitions on guest-initiated updates of
MSR_IA32_APICBASE. This address both enabling of the x2APIC when it is
not supported and all invalid transitions as described in SDM section
10.12.5. It also checks that no reserved bit is set in APICBASE by the
guest.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
[Use cpuid_maxphyaddr instead of guest_cpuid_get_phys_bits. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 25 insertions, 7 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index dc11b4f9857..34d0d610aa8 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -257,10 +257,26 @@ u64 kvm_get_apic_base(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_get_apic_base);
 
-void kvm_set_apic_base(struct kvm_vcpu *vcpu, u64 data)
-{
-	/* TODO: reserve bits check */
-	kvm_lapic_set_base(vcpu, data);
+int kvm_set_apic_base(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
+{
+	u64 old_state = vcpu->arch.apic_base &
+		(MSR_IA32_APICBASE_ENABLE | X2APIC_ENABLE);
+	u64 new_state = msr_info->data &
+		(MSR_IA32_APICBASE_ENABLE | X2APIC_ENABLE);
+	u64 reserved_bits = ((~0ULL) << cpuid_maxphyaddr(vcpu)) |
+		0x2ff | (guest_cpuid_has_x2apic(vcpu) ? 0 : X2APIC_ENABLE);
+
+	if (!msr_info->host_initiated &&
+	    ((msr_info->data & reserved_bits) != 0 ||
+	     new_state == X2APIC_ENABLE ||
+	     (new_state == MSR_IA32_APICBASE_ENABLE &&
+	      old_state == (MSR_IA32_APICBASE_ENABLE | X2APIC_ENABLE)) ||
+	     (new_state == (MSR_IA32_APICBASE_ENABLE | X2APIC_ENABLE) &&
+	      old_state == 0)))
+		return 1;
+
+	kvm_lapic_set_base(vcpu, msr_info->data);
+	return 0;
 }
 EXPORT_SYMBOL_GPL(kvm_set_apic_base);
 
@@ -2009,8 +2025,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case 0x200 ... 0x2ff:
 		return set_msr_mtrr(vcpu, msr, data);
 	case MSR_IA32_APICBASE:
-		kvm_set_apic_base(vcpu, data);
-		break;
+		return kvm_set_apic_base(vcpu, msr_info);
 	case APIC_BASE_MSR ... APIC_BASE_MSR + 0x3ff:
 		return kvm_x2apic_msr_write(vcpu, msr, data);
 	case MSR_IA32_TSCDEADLINE:
@@ -6412,6 +6427,7 @@ EXPORT_SYMBOL_GPL(kvm_task_switch);
 int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
 				  struct kvm_sregs *sregs)
 {
+	struct msr_data apic_base_msr;
 	int mmu_reset_needed = 0;
 	int pending_vec, max_bits, idx;
 	struct desc_ptr dt;
@@ -6435,7 +6451,9 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
 
 	mmu_reset_needed |= vcpu->arch.efer != sregs->efer;
 	kvm_x86_ops->set_efer(vcpu, sregs->efer);
-	kvm_set_apic_base(vcpu, sregs->apic_base);
+	apic_base_msr.data = sregs->apic_base;
+	apic_base_msr.host_initiated = true;
+	kvm_set_apic_base(vcpu, &apic_base_msr);
 
 	mmu_reset_needed |= kvm_read_cr0(vcpu) != sregs->cr0;
 	kvm_x86_ops->set_cr0(vcpu, sregs->cr0);