A flaw was found in the way Linux kernel KVM hypervisor before 4.18 emulated instructions such as sgdt/sidt/fxsave/fxrstor. It did not check current privilege(CPL) level while emulating unprivileged instructions. An unprivileged guest user/process could use this flaw to potentially escalate privileges inside guest.
https://www.openwall.com/lists/oss-security/2018/09/02/1
https://usn.ubuntu.com/3777-2/
https://usn.ubuntu.com/3777-1/
https://lists.debian.org/debian-lts-announce/2018/07/msg00020.html
https://lists.debian.org/debian-lts-announce/2018/07/msg00016.html
https://lists.debian.org/debian-lts-announce/2018/07/msg00015.html
https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2018-10853
https://access.redhat.com/errata/RHSA-2020:0179
https://access.redhat.com/errata/RHSA-2020:0103
https://access.redhat.com/errata/RHSA-2020:0036
https://access.redhat.com/errata/RHSA-2019:2043
https://access.redhat.com/errata/RHSA-2019:2029
http://lists.opensuse.org/opensuse-security-announce/2019-05/msg00043.html