A flaw was found in the Linux kernel before version 4.12 in the way the KVM module processed the trap flag(TF) bit in EFLAGS during emulation of the syscall instruction, which leads to a debug exception(#DB) being raised in the guest stack. A user/process inside a guest could use this flaw to potentially escalate their privileges inside the guest. Linux guests are not affected by this. Andy Lutomirski discovered that the KVM implementation in the Linux kernel was vulnerable to a debug exception error when single-stepping through a syscall. A local attacker in a non-Linux guest vm could possibly use this to gain administrative privileges in the guest vm.