Spectres, Virtual Ghosts, and Hardware Support

Side-channel attacks, such as Spectre and Meltdown, that leverage speculative execution pose a serious threat to computing systems. Worse yet, such attacks can be perpetrated by compromised operating system (OS) kernels to bypass defenses that protect applications from the OS kernel. This work evaluates the performance impact of three different defenses against in-kernel speculation side-channel attacks within the context of Virtual Ghost, a system that protects user data from compromised OS kernels: Intel MPX bounds checks, which require a memory fence; address bit-masking and testing, which creates a dependence between the bounds check and the load/store; and the use of separate virtual address spaces for applications, the OS kernel, and the Virtual Ghost virtual machine, forcing a speculation boundary. Our results indicate that an instrumentation-based bit-masking approach to protection incurs the least overhead by minimizing speculation boundaries. Our work also highlights possible improvements to Intel MPX that could help mitigate speculation side-channel attacks at a lower cost.