An issue was discovered in Xen through 4.11.x allowing x86 PV guest OS users to cause a denial of service or gain privileges because a guest can manipulate its virtualised %cr4 in a way that is incompatible with Linux (and possibly other guest kernels). Upstream issue and patch: https://xenbits.xen.org/xsa/advisory-293.html
Created xen tracking bugs for this issue: Affects: fedora-all [bug 1771445]