Abstract This paper describes our experience with symbolic model checking in an industrial setting. We have proved that the initial boot code running in data centers at Amazon Web Services is memory safe, an essential step in establishing the security of any data center. Standard static analysis tools cannot be easily used on boot code without modification owing to issues not commonly found in higher-level code, including memory-mapped device interfaces, byte-level memory access, and linker scripts. This paper describes automated solutions to these issues and their implementation in the C Bounded Model Checker (CBMC). CBMC is now the first source-level static analysis tool to extract the memory layout described in a linker script for use in its analysis.

Abstract This article describes a style of applying symbolic model checking developed over the course of four years at Amazon Web Services (AWS). Lessons learned are drawn from proving properties of numerous C‐based systems, for example, custom hypervisors, encryption code, boot loaders, and an IoT operating system. Using our methodology, we find that we can prove the correctness of industrial low‐level C‐based systems with reasonable effort and predictability. Furthermore, AWS developers are increasingly writing their own formal specifications. As part of this effort, we have developed a CI system that allows integration of the proofs into standard development workflows and extended the proof tools to provide better feedback to users. All proofs discussed in this article are publicly available on GitHub.

We gave CBMC the ability to explore and model check single program paths, as opposed to its default whole-program model-checking behaviour. This means that CBMC, when invoked with the flag, symbolically executes one program path at a time—saving unexplored paths for later—and attempts to prove properties for only that path. By doing this repeatedly for each path that CBMC encounters, CBMC can detect property violations in a scalable and incremental way. Implementing single-path exploration raises the question of which order the paths should be explored in. Our implementation makes it easy for researchers to implement and investigate alternative path exploration strategies. Our competition contribution uses a breadth-first strategy, where diverging paths are each pushed onto a queue at program decision points, and the path to explore next is gotten by dequeueing the oldest path to have been added.

This paper describes our experience with symbolic model checking in an industrial setting. We have proved that the initial boot code running in data centers at Amazon Web Services is memory safe, an essential step in establishing the security of any data center. Standard static analysis tools cannot be easily used on boot code without modification owing to issues not commonly found in higher-level code, including memory-mapped device interfaces, byte-level memory access, and linker scripts. This paper describes automated solutions to these issues and their implementation in the C Bounded Model Checker (CBMC). CBMC is now the first source-level static analysis tool to extract the memory layout described in a linker script for use in its analysis. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Software typically outlives the platform that it was originally written for. To smooth the transition to new tools and platforms, programs should depend on the underlying platform as little as possible. In practice, however, software build processes are highly sensitive to their build platform, notably the implementation of the compiler and standard library. This makes it difficult to port existing, mature software to emerging platforms---web based runtimes like WebAssembly, resource-constrained environments for Internet-of-Things devices, or innovative new operating systems like Fuchsia.