Linux kernel maintainers have already implemented mitigations for VMScape by adding an Indirect Branch Prediction Barrier (IBPB) on each VMEXIT instruction, which occurs when a guest executes a privileged instruction. Researchers found this mitigation introduces only marginal performance overhead in common scenarios.
“Most systems are vulnerable to some vBTI primitives,” the researchers noted. “Since VMScape only affects virtualized environments, systems that never run untrusted code in local VMs are not directly exploitable. Nevertheless, given the widespread use of cloud services, it is likely that you rely on infrastructure running on vulnerable hardware.”
The Xen hypervisor is not affected by this issue, but the impact on other hypervisors that do not rely on KVM, such as Microsoft Hyper-V, VMware, or VirtualBox, remains unclear. The researchers disclosed their findings to AMD, Intel, and the Linux kernel maintainers responsible for KVM.
