Bug 1997522 (CVE-2021-28699)

The v2 grant table interface separates grant attributes from grant
status.  That is, when operating in this mode, a guest has two tables.
As a result, guests also need to be able to retrieve the addresses that
the new status tracking table can be accessed through.
For 32-bit guests on x86, translation of requests has to occur because
the interface structure layouts commonly differ between 32- and 64-bit.
The translation of the request to obtain the frame numbers of the
grant status table involves translating the resulting array of frame
numbers.  Since the space used to carry out the translation is limited,
the translation layer tells the core function the capacity of the array
within translation space.  Unfortunately the core function then only
enforces array bounds to be below 8 times the specified value, and would
write past the available space if enough frame numbers needed storing.