DMOP map/unmap missing argument checks

ISSUE DESCRIPTION

DMOPs (which were a subgroup of HVMOPs in older releases) allow guests to control and drive other guests. The I/O request server page mapping interface uses range sets to represent I/O resources the emulation of which is provided by a given I/O request server. The internals of the range set implementation require that ranges have a starting value no lower than the ending one. Checks for this fact were missing.

IMPACT

Malicious or buggy stub domain kernels or tool stacks otherwise living outside of Domain0 can mount a denial of service attack which, if successful, can affect the whole system.
Only domains controlling HVM guests can exploit this vulnerability. (This includes domains providing hardware emulation services to HVM guests.)

VULNERABLE SYSTEMS

Xen versions 4.5 and later are vulnerable. Xen versions 4.4 and earlier are not vulnerable.
Only x86 systems are affected. ARM systems are not affected.
This vulnerability is only applicable to Xen systems using stub domains or other forms of disaggregation of control domains for HVM guests.