A use after free issue was found in the way Linux kernel's KVM hypervisor emulates a preemption timer for L2 guest when nested(=1) virtualization is enabled. This high resolution timer(hrtimer) runs when L2 guest is active. After VM exit, in sync_vmcs12() timer object is stopped. The use-after-free occurs if the timer object is free'd before calling sync_vmcs12() routine. https://nvd.nist.gov/vuln/detail/CVE-2019-7221
