On the Effectiveness of Multi-Variant Program Execution for Vulnerability Detection and Prevention

Multi-variant program execution is an application of n-version programming, in which several slightly different instances of the same program are executed in lockstep on a multiproces-sor. These variants are created in such a way that they be-have identically under “normal ” operation and diverge when “out of specification ” events occur, which may be indica-tive of attacks. This paper assess the effectiveness of dif-ferent code variation techniques to address different classes of vulnerabilities. In choosing a variant or combination of variants, security demands need to be balanced against run-time overhead. Our study indicates that a good combination of variations when running two variants is to choose one of instruction set randomization, system call number random-ization, and register randomization, and use that together with library entry point randomization. Running more vari-ants simultaneously makes it exponentially more difficult to take over the system. 1