KVM: x86: disallow KVM_{SET,GET}_LAPIC without allocated in-kernel lapic

Otherwise kvm might attempt to dereference a NULL pointer.
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/x86.c

@@ -1893,6 +1893,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 
 	switch (ioctl) {
 	case KVM_GET_LAPIC: {
+		r = -EINVAL;
+		if (!vcpu->arch.apic)
+			goto out;
 		lapic = kzalloc(sizeof(struct kvm_lapic_state), GFP_KERNEL);
 
 		r = -ENOMEM;
@@ -1908,6 +1911,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 		break;
 	}
 	case KVM_SET_LAPIC: {
+		r = -EINVAL;
+		if (!vcpu->arch.apic)
+			goto out;
 		lapic = kmalloc(sizeof(struct kvm_lapic_state), GFP_KERNEL);
 		r = -ENOMEM;
 		if (!lapic)