The (1) ioport_read and (2) ioport_write functions in Xen, when qemu is used as a device model within Xen, might allow local x86 HVM guest OS administrators to gain qemu process privileges via vectors involving an out-of-range ioport access.
http://rhn.redhat.com/errata/RHSA-2016-2963.html
https://lists.debian.org/debian-lts-announce/2018/02/msg00005.html
https://security.gentoo.org/glsa/201612-56
https://support.citrix.com/article/CTX219136