KVM: s390: Reject setting flic pfault attributes on ucontrol VMs

Prevent null pointer dereference when processing the
KVM_DEV_FLIC_APF_ENABLE and KVM_DEV_FLIC_APF_DISABLE_WAIT ioctls in the
interrupt controller.

Fixes: 3c038e6be0e2 ("KVM: async_pf: Async page fault support on s390")
Reported-by: Claudio Imbrenda <[e-mail]>
Signed-off-by: Christoph Schlameuss <[e-mail]>
Reviewed-by: Hariharan Mari <[e-mail]>
Reviewed-by: Claudio Imbrenda <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Message-ID: <[e-mail]>
Signed-off-by: Claudio Imbrenda <[e-mail]>

Documentation/virt/kvm/devices/s390_flic.rst

···
     Enables async page faults for the guest. So in case of a major page fault
     the host is allowed to handle this async and continues the guest.
 
+    -EINVAL is returned when called on the FLIC of a ucontrol VM.
+
   KVM_DEV_FLIC_APF_DISABLE_WAIT
     Disables async page faults for the guest and waits until already pending
     async page faults are done. This is necessary to trigger a completion interrupt
     for every init interrupt before migrating the interrupt list.
+
+    -EINVAL is returned when called on the FLIC of a ucontrol VM.
 
   KVM_DEV_FLIC_ADAPTER_REGISTER
     Register an I/O adapter interrupt source. Takes a kvm_s390_io_adapter

arch/s390/kvm/interrupt.c

···
 		kvm_s390_clear_float_irqs(dev->kvm);
 		break;
 	case KVM_DEV_FLIC_APF_ENABLE:
+		if (kvm_is_ucontrol(dev->kvm))
+			return -EINVAL;
 		dev->kvm->arch.gmap->pfault_enabled = 1;
 		break;
 	case KVM_DEV_FLIC_APF_DISABLE_WAIT:
+		if (kvm_is_ucontrol(dev->kvm))
+			return -EINVAL;
 		dev->kvm->arch.gmap->pfault_enabled = 0;
 		/*
 		 * Make sure no async faults are in transition when