Orchestra: A User Space Multi-Variant Execution Environment

In a Multi-Variant Execution Environment (MVEE), several slightly different versions of the same program are executed in lockstep. While this is done, the environment compares the behavior of each version at certain synchronization points with the aim of increasing resilience against attacks. Traditionally, the monitoring component of MVEEs has been implemented as an OS kernel extension, which monitors the behavior of the different instances of the application from inside the kernel. As a result, the monitor becomes a part of the trusted code base for the entire system, greatly increasing the potential repercussions of vulnerabilities in the monitor itself. We describe a MVEE architecture in which the monitor is implemented entirely in user space, eliminating the need for kernel modifications. We have implemented a fully functioning MVEE based on the proposed architecture and benchmark numbers show that the performance penalty of the MVEE on a dual-core system averages about 20% relative to unprotected execution without the MVEE.