Exploiting Trust in Deterministic Builds

摘要

Deterministic builds, where the compile and build processes are reproducible, can be used to achieve increased trust in distributed binaries. As the trust can be distributed across a set of builders, where all provide their own signature of a byte-to-byte identical binary, all have to cooperate in order to introduce unwanted code in the binary. On the other hand, if an attacker manages to incorporate malicious code in the source, and make this remain undetected during code reviews, the deterministic build provides additional opportunities to introduce e.g., a backdoor. The impact of such a successful attack would be serious since the actual trust model is exploited. In this paper, the problem of crafting such hidden code that is difficult to detect, both during code reviews of the source code as well as static analysis of the binary executable is addressed. It is shown that the displacement and immediate fields of an instruction can be used the embed hidden code directly from the C programming language.