Statistical Reconstruction of Class Hierarchies in Binaries

We address a fundamental problem in reverse engineering of object-oriented code: the reconstruction of a program's class hierarchy from its stripped binary. Existing approaches rely heavily on structural information that is not always available, e.g., calls to parent constructors. As a result, these approaches often leave gaps in the hierarchies they construct, or fail to construct them altogether. Our main insight is that behavioral information can be used to infer subclass/superclass relations, supplementing any missing structural information. Thus, we propose the first statistical approach for static reconstruction of class hierarchies based on behavioral similarity. We capture the behavior of each type using a statistical language model (SLM), define a metric for pairwise similarity between types based on the Kullback-Leibler divergence between their SLMs, and lift it to determine the most likely class hierarchy. We implemented our approach in a tool called ROCK and used it to automatically reconstruct the class hierarchies of several real-world stripped C++ binaries. Our results demonstrate that ROCK obtained significantly more accurate class hierarchies than those obtained using structural analysis alone.