We present Xenon, a solver-aided, interactive method for formally verifying that Verilog hardware executes in constant-time. Xenon scales to realistic hardware designs by drastically reducing the effort needed to localize the root cause of verification failures via a new notion of constant-time counterexamples, which Xenon uses to synthesize a minimal set of secrecy assumptions in an interactive verification loop. To reduce verification time Xenon exploits modularity in Verilog code via module summaries, thereby avoiding duplicate work across multiple module instantiations. We show how Xenon's assumption synthesis and summaries enable us to verify different kinds of circuits, including a highly modular AES- 256 implementation where modularity cuts verification from six hours to under three seconds, and the ScarVside-channel hardened RISC-V micro-controller whose size exceeds previously verified designs by an order of magnitude. In a small study, we also find that Xenon helps non-expert users complete verification tasks correctly and faster than previous state-of-art tools.

We introduce Blade, a new approach to automatically and efficiently eliminate speculative leaks from cryptographic code. Blade is built on the insight that to stop leaks via speculative execution, it suffices to cut the dataflow from expressions that speculatively introduce secrets ( sources ) to those that leak them through the cache ( sinks ), rather than prohibit speculation altogether. We formalize this insight in a static type system that (1) types each expression as either transient , i.e., possibly containing speculative secrets or as being stable , and (2) prohibits speculative leaks by requiring that all sink expressions are stable. Blade relies on a new abstract primitive, protect , to halt speculation at fine granularity. We formalize and implement protect using existing architectural mechanisms, and show how Blade’s type system can automatically synthesize a minimal number of protect s to provably eliminate speculative leaks. We implement Blade in the Cranelift WebAssembly compiler and evaluate our approach by repairing several verified, yet vulnerable WebAssembly implementations of cryptographic primitives. We find that Blade can fix existing programs that leak via speculation automatically , without user intervention, and efficiently even when using fences to implement protect .

We present pretend synchrony , a new approach to verifying distributed systems, based on the observation that while distributed programs must execute asynchronously, we can often soundly treat them as if they were synchronous when verifying their correctness. To do so, we compute a synchronization , a semantically equivalent program where all sends, receives, and message buffers, have been replaced by simple assignments, yielding a program that can be verified using Floyd-Hoare style Verification Conditions and SMT. We implement our approach as a framework for writing verified distributed programs in Go and evaluate it with four challenging case studies— the classic two-phase commit protocol, the Raft leader election protocol, single-decree Paxos protocol, and a Multi-Paxos based distributed key-value store. We find that pretend synchrony allows us to develop performant systems while making verification of functional correctness simpler by reducing manually specified invariants by a factor of 6, and faster , by reducing checking time by three orders of magnitude.

We introduce canonical sequentialization, a new approach to verifying unbounded, asynchronous, message-passing programs at compile-time. Our approach builds upon the following observation: due the combinatorial explosion in complexity, programmers do not reason about their systems by case-splitting over all the possible execution orders. Instead, correct programs tend to be well-structured so that the programmer can reason about a small number of representative executions, which we call the program’s canonical sequentialization. We have implemented our approach in a tool called Brisk that synthesizes canonical sequentializations for programs written in Haskell, and evaluated it on a wide variety of distributed systems including benchmarks from the literature and implementations of MapReduce, two-phase commit, and a version of the Disco distributed file-system. We show that unlike model checking, which gets prohibitively slow with just 10 processes Brisk verifies the unbounded versions of the benchmarks in tens of milliseconds, yielding the first concurrency verification tool that is fast enough to be integrated into a design-implement-check cycle.