Several access permission issues with IRQs for unprivileged guests

ISSUE DESCRIPTION

Various IRQ related access control operations may not have the intended effect, thus potentially permitting a stub domain to grant its client domain access to an IRQ it doesn’t have access to itself.

IMPACT

Malicious or buggy stub domains kernels can mount a denial of service attack possibly affecting the whole system.

VULNERABLE SYSTEMS

Only Xen systems using stub domains are vulnerable.
Only guests with passed-through IRQs or PCI devices are able to exploit the vulnerability.
It is remotely possible that PV guests with passthrough IRQs or devices may also be able to exploit this vulnerability, although we think this is unlikely.