Enforcing Forward-Edge Control-Flow Integrity in GCC & LLVM
Constraining dynamic control transfers is a common technique for mitigating software vulnerabilities. This defense has been widely and successfully used to protect return addresses and stack data; hence, current attacks instead typically corrupt vtable and function pointers to subvert a forward edge (an indirect jump or call) in the control-flow graph. Forward edges can be protected using Control-Flow Integrity (CFI) but, to date, CFI implementations have been research prototypes, based on impractical assumptions or ad hoc, heuristic techniques. To be widely adoptable, CFI mechanisms must be integrated into production compilers and be compatible with software-engineering aspects such as incremental compilation and dynamic libraries. This paper presents implementations of fine-grained, forward-edge CFI enforcement and analysis for GCC and LLVM that meet the above requirements. An analysis and evaluation of the security, performance, and resource consumption of these mechanisms applied to the SPEC CPU2006 benchmarks and common benchmarks for the Chromium web browser show the practicality of our approach: these fine-grained CFI mechanisms have significantly lower overhead than recent academic CFI prototypes. Implementing CFI in industrial compiler frameworks has also led to insights into design tradeoffs and practical challenges, such as dynamic loading.