KVM: s390: Sanitize fpc registers for KVM_SET_FPU

(cherry picked from commit 85175587)

commit 7eef87dc (KVM: s390: fix
register setting) added a load of the floating point control register
to the KVM_SET_FPU path. Lets make sure that the fpc is valid.
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

arch/s390/kvm/kvm-s390.c

@@ -418,7 +418,7 @@ int kvm_arch_vcpu_ioctl_get_sregs(struct kvm_vcpu *vcpu,
 int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
 {
 	memcpy(&vcpu->arch.guest_fpregs.fprs, &fpu->fprs, sizeof(fpu->fprs));
-	vcpu->arch.guest_fpregs.fpc = fpu->fpc;
+	vcpu->arch.guest_fpregs.fpc = fpu->fpc & FPC_VALID_MASK;
 	restore_fp_regs(&vcpu->arch.guest_fpregs);
 	return 0;
 }