The Project

I am trying to build a multi-variant execution environment which runs multiple variants of a single program on different processors/cores and monitors their outputs. Any divergence among the outputs raises an exception and interrupts the execution. The goal of this system is to make programs resilient against malware (viruses, internet worms, etc.).

More specifically we are targeting buffer overflow and similar vulnerabilities such as boundary error, format string, ... that give the opportunity to an attacker to overwrite activation records (return address or frame pointer) on the stack. Overwriting the activation records can lead to malicious code execution.

To fight activation record overwrites, we run two variants of the same program that write the stack in different directions. For example, in x86 stack is written downward and executables generated by compilers conform to this regulation. We have modified a compiler to generate executables that write the stack upward. Running a normal executable along with a reverse-stack executable in a multi-variant environment can disrupt all known buffer overflow exploits. The reason lies behind the fact that all inputs to the program is sent identically to both variants. Therefore, an attacker cannot send different attack vectors to each variant. An attack vector that overwrites activation records on one variant, has different effects on the other one which causes the outputs to diverge. Output divergence is detected by our multi-variant environment and execution is interrupted.