Enforcing Unique Code Target Property for Control-Flow Integrity

The goal of control-flow integrity (CFI) is to stop control-hijacking attacks by ensuring that each indirect control-flow transfer (ICT) jumps to its legitimate target. However, existing implementations of CFI have fallen short of this goal because their approaches are inaccurate and as a result, the set of allowable targets for an ICT instruction is too large, making illegal jumps possible. In this paper, we propose the Unique Code Target (UCT) property for CFI. Namely, for each invocation of an ICT instruction, there should be one and only one valid target. We develop a prototype called µCFI to enforce this new property. During compilation, µCFI identifies the sensitive instructions that influence ICT and instruments the program to record necessary execution context. At runtime, µCFI monitors the program execution in a different process, and performs points-to analysis by interpreting sensitive instructions using the recorded execution context in a memory safe manner. It checks runtime ICT targets against the analysis results to detect CFI violations. We apply µCFI to SPEC benchmarks and 2 servers (nginx and vsftpd) to evaluate its efficacy of enforcing UCT and its overhead. We also test µCFI against control-hijacking attacks, including 5 real-world exploits, 1 proof of concept COOP attack, and 2 synthesized attacks that bypass existing defenses. The results show that µCFI strictly enforces the UCT property for protected programs, successfully detects all attacks, and introduces less than 10% performance overhead.