Remix: On-demand Live Randomization

Code randomization is an effective defense against code reuse attacks. It scrambles program code to prevent attackers from locating useful functions or gadgets. The key to secure code randomization is achieving high entropy. A practical approach to boost entropy is on-demand live randomization that works on running processes. However, enabling live randomization is challenging in that it often requires manual efforts to solve ambiguity in identifying function pointers. In this paper, we propose Remix, an efficient and practical live randomization system for both user processes and kernel modules. Remix randomly shuffles basic blocks within their respective functions. By doing so, it avoids the complexity of migrating stale function pointers, and allows mixing randomized and non-randomized code to strike a balance between performance and security. Remix randomizes a running process in two steps: it first randomly reorders its basic blocks, and then comprehensively migrates live pointers to basic blocks. Our experiments show that Remix can significantly increase randomness with low performance overhead on both CPU and I/O intensive benchmarks and kernel modules, even at very short randomization intervals.