Modular Control-Flow Integrity

Control-Flow Integrity (CFI) is a software-hardening technique. It inlines checks into a program so that its execution always follows a predetermined Control-Flow Graph (CFG). As a result, CFI is ef-fective at preventing control-flow hijacking attacks. However, past fine-grained CFI implementations do not support separate compi-lation, which hinders its adoption. We present Modular Control-Flow Integrity (MCFI), a new CFI technique that supports separate compilation. MCFI allows mod-ules to be independently instrumented and linked statically or dy-namically. The combined module enforces a CFG that is a combi-nation of the individual modules ’ CFGs. One challenge in support-ing dynamic linking in multithreaded code is how to ensure a safe transition from the old CFG to the new CFG when libraries are dy-namically linked. The key technique we use is to have the CFG rep-resented in a runtime data structure and have reads and updates of the data structure wrapped in transactions to ensure thread safety. Our evaluation on SPECCPU2006 benchmarks shows that MCFI supports separate compilation, incurs low overhead of around 5%, and enhances security