The grant-table feature in Xen through 4.8.x mishandles a GNTMAP_device_map and GNTMAP_host_map mapping, when followed by only a GNTMAP_host_map unmapping, which allows guest OS users to cause a denial of service (count mismanagement and memory corruption) or obtain privileged host OS access, aka XSA-224 bug 1.
https://xenbits.xen.org/xsa/advisory-224.html
https://security.gentoo.org/glsa/201710-17
https://security.gentoo.org/glsa/201708-03