CVE-2021-28698

long running loops in grant table handling In order to properly monitor
resource use, Xen maintains information on the grant mappings a domain may
create to map grants offered by other domains. In the process of carrying
out certain actions, Xen would iterate over all such entries, including
ones which aren’t in use anymore and some which may have been created but
never used. If the number of entries for a given domain is large enough,
this iterating of the entire table may tie up a CPU for too long, starving
other domains or causing issues in the hypervisor itself. Note that a
domain may map its own grants, i.e. there is no need for multiple domains
to be involved here. A pair of “cooperating” guests may, however, cause the
effects to be more severe.

Notes