Ubuntu Security Notice 2515-2 – USN-2515-1 fixed vulnerabilities in the Linux kernel. There was an unrelated regression in the use of the virtual counter (CNTVCT) on arm64 architectures. This update fixes the problem. A flaw was discovered in the Kernel Virtual Machine’s (KVM) emulation of the SYSTENTER instruction when the guest OS does not initialize the SYSENTER MSRs. A guest OS user could exploit this flaw to cause a denial of service of the guest OS (crash) or potentially gain privileges on the guest OS. Various other issues were also addressed.