KVM: s390: Reject KVM_SET_GSI_ROUTING on ucontrol VMs

Prevent null pointer dereference when processing
KVM_IRQ_ROUTING_S390_ADAPTER routing entries.
The ioctl cannot be processed for ucontrol VMs.

Fixes: f654706 ("KVM: s390/interrupt: do not pin adapter interrupt pages")
Signed-off-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
Tested-by: Hariharan Mari <hari55@linux.ibm.com>
Reviewed-by: Hariharan Mari <hari55@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Link: https://lore.kernel.org/r/20241216092140.329196-4-schlameuss@linux.ibm.com
Message-ID: <20241216092140.329196-4-schlameuss@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

Documentation/virt/kvm/api.rst

@@ -1914,6 +1914,9 @@ No flags are specified so far, the corresponding field must be set to zero.
   #define KVM_IRQ_ROUTING_HV_SINT 4
   #define KVM_IRQ_ROUTING_XEN_EVTCHN 5
 
+On s390, adding a KVM_IRQ_ROUTING_S390_ADAPTER is rejected on ucontrol VMs with
+error -EINVAL.
+
 flags:
 
 - KVM_MSI_VALID_DEVID: used along with KVM_IRQ_ROUTING_MSI routing entry

arch/s390/kvm/interrupt.c

@@ -2898,6 +2898,8 @@ int kvm_set_routing_entry(struct kvm *kvm,
 	switch (ue->type) {
 	/* we store the userspace addresses instead of the guest addresses */
 	case KVM_IRQ_ROUTING_S390_ADAPTER:
+		if (kvm_is_ucontrol(kvm))
+			return -EINVAL;
 		e->set = set_adapter_int;
 		uaddr =  gmap_translate(kvm->arch.gmap, ue->u.adapter.summary_addr);
 		if (uaddr == -EFAULT)