An issue was discovered in Xen through 4.9.x allowing HVM guest OS users to gain privileges on the host OS, obtain sensitive information, or cause a denial of service (BUG and host OS crash) by leveraging the mishandling of Populate on Demand (PoD) Physical-to-Machine (P2M) errors.
https://xenbits.xen.org/xsa/advisory-247.html
https://support.citrix.com/article/CTX230138
https://security.gentoo.org/glsa/201801-14
https://lists.debian.org/debian-lts-announce/2018/10/msg00021.html
https://lists.debian.org/debian-lts-announce/2018/01/msg00003.html
http://www.securitytracker.com/id/1039879