SoK: On the Effectiveness of Control-Flow Integrity in Practice

Complex programs written in memory-unsafe languages tend to contain memory corruption bugs. Adversaries commonly employ code-reuse attacks to exploit these bugs. Control-flow Integrity (CFI) enforcement schemes try to prevent such attacks from achieving arbitrary code execution. Developers can apply these schemes to existing code bases by setting compiler flags, requiring less effort than rewriting code in memory-safe languages. Although many works propose CFI schemes and attacks against them, they paid little attention to schemes deployed to end-users. We provide a systematic categorization and overview of actively used CFI solutions. We then conduct a large-scale binary analysis on 33 Android images of seven vendors and two Windows builds for different hardware architectures to study CFI utilization in practice. We analyzed over 77,000 files on the Android images. We found that depending on the variant, up to 94% of binaries and 93% of libraries are unprotected. All analyzed binaries depend on unprotected libraries, therefore rendering CFI enforcement ineffective. Further, we look at the development of CFI coverage over time on Android and find it stagnating. CFI roll-out is closer to complete on the Windows builds, but not all files are protected yet (2.63% unprotected). Consequently, our results show that the adoption of CFI protection is lacking, putting devices at risk. Additionally, our results highlight a large gap between the state of the art in research and the reality of deployed systems.