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We present IronSync, an automated verification framework for concurrent code with shared memory. IronSync scales to complex systems by splitting system-wide proofs into isolated concerns such that each can be substantially automated. As a starting point, IronSync’s ownership type system allows a developer to straightforwardly prove both data safety and the logical correctness of thread-local operations. IronSync then introduces the concept of a Localized Transition System, which connects the correctness of local actions to the correctness of the entire system. We demonstrate IronSync by verifying two state-of-the-art concurrent systems comprising thousands of lines: a library for black-box replication on NUMA architectures, and a highly concurrent page cache. 

Reasoning about memory aliasing and mutation in software verification is a hard problem. This is especially true for systems using SMT-based automated theorem provers. Memory reasoning in SMT verification typically requires a nontrivial amount of manual effort to specify heap invariants, as well as extensive alias reasoning from the SMT solver. In this paper, we present a hybrid approach that combines linear types with SMT-based verification for memory reasoning. We integrate linear types into Dafny, a verification language with an SMT backend, and show that the two approaches complement each other. By separating memory reasoning from verification conditions, linear types reduce the SMT solving time. At the same time, the expressiveness of SMT queries extends the flexibility of the linear type system. In particular, it allows our linear type system to easily and correctly mix linear and nonlinear data in novel ways, encapsulating linear data inside nonlinear data and vice-versa. We formalize the core of our extensions, prove soundness, and provide algorithms for linear type checking. We evaluate our approach by converting the implementation of a verified storage system (about 24K lines of code and proof) written in Dafny, to use our extended Dafny. The resulting system uses linear types for 91% of the code and SMT-based heap reasoning for the remaining 9%. We show that the converted system has 28% fewer lines of proofs and 30% shorter verification time overall. We discuss the development overhead in the original system due to SMT-based heap reasoning and highlight the improved developer experience when using linear types. 

To verify distributed systems, prior work introduced a methodology for verifying both the code running on individual machines and the correctness of the overall system when those machines interact via an asynchronous distributed environment. The methodology requires neither domain-specific logic nor tooling. However, distributed systems are only one instance of the more general phenomenon of systems code that interacts with an asynchronous environment. We argue that the software of a storage system can (and should!) be viewed similarly. We evaluate this approach in VeriSafeKV, a key-value store based on a state-of-the-art B^ε-tree. In building VeriSafeKV, we introduce new techniques to scale automated verification to larger code bases, still without introducing domain-specific logic or tooling. In particular, we show a discipline that keeps the automated verification development cycle responsive. We also combine linear types with dynamic frames to relieve the programmer from most heap-reasoning obligations while enabling them to break out of the linear type system when needed. VeriSafeKV exhibits similar query performance to unverified databases. Its insertion performance is 15× faster than unverified BerkeleyDB and 6× slower than RocksDB.