arm: various unimplemented hypercalls log without rate limiting

ISSUE DESCRIPTION

The HYPERVISOR_physdev_op hypercall and most suboperations of the HYPERVISOR_hvm_op hypercall are not currently implemented by Xen on ARM and when called will log the use to the hypervisor console. However these guest accessible log messages are not rate-limited.

IMPACT

A malicious guest could cause repeated logging to the hypervisor console, leading to a Denial of Service attack.

VULNERABLE SYSTEMS

Xen 4.4 and later systems running on ARM hardware are vulnerable.
x86 systems are not affected.