KVM: s390: Disallow invalid bits in kvm_valid_regs and kvm_dirty_regs

If unknown bits are set in kvm_valid_regs or kvm_dirty_regs, this
clearly indicates that something went wrong in the KVM userspace
application. The x86 variant of KVM already contains a check for
bad bits, so let's do the same on s390x now, too.

Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Link: https://lore.kernel.org/lkml/20190904085200.29021-2-thuth@redhat.com/
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>

arch/s390/include/uapi/asm/kvm.h

@@ -231,6 +231,12 @@ struct kvm_guest_debug_arch {
 #define KVM_SYNC_GSCB   (1UL << 9)
 #define KVM_SYNC_BPBC   (1UL << 10)
 #define KVM_SYNC_ETOKEN (1UL << 11)
+
+#define KVM_SYNC_S390_VALID_FIELDS \
+	(KVM_SYNC_PREFIX | KVM_SYNC_GPRS | KVM_SYNC_ACRS | KVM_SYNC_CRS | \
+	 KVM_SYNC_ARCH0 | KVM_SYNC_PFAULT | KVM_SYNC_VRS | KVM_SYNC_RICCB | \
+	 KVM_SYNC_FPRS | KVM_SYNC_GSCB | KVM_SYNC_BPBC | KVM_SYNC_ETOKEN)
+
 /* length and alignment of the sdnx as a power of two */
 #define SDNXC 8
 #define SDNXL (1UL << SDNXC)

arch/s390/kvm/kvm-s390.c

@@ -4008,6 +4008,10 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 	if (kvm_run->immediate_exit)
 		return -EINTR;
 
+	if (kvm_run->kvm_valid_regs & ~KVM_SYNC_S390_VALID_FIELDS ||
+	    kvm_run->kvm_dirty_regs & ~KVM_SYNC_S390_VALID_FIELDS)
+		return -EINVAL;
+
 	vcpu_load(vcpu);
 
 	if (guestdbg_exit_pending(vcpu)) {