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Formal Methods at Microsoft: A Tool-Oriented View
0:00:06 Introduction: The speaker thanks the audience and welcomes questions, emphasizing the use of formal methods.
0:01:01 Formal Methods Pipeline: Formal methods are used throughout a software pipeline, from design to diagnosis. The speaker will cover several tools, including some that work besides TLA+.
0:01:30 Talk Roadmap: The talk will provide a tool-oriented view of formal methods, focusing on their scientific heritage, target use, impact, and "North Stars" (goals).
0:02:23 Tool Categories: Tools are categorized into two groups: those using logic as the calculus of computation and those taking a "tomographic" view (observational inferences).
0:03:18 Logic as Calculus of Computation: The speaker references the idea that logic is the primary calculus for reasoning about computation, as opposed to, for instance, the differential and integral calculus that apply to physical systems.
0:04:18 Z3 SMT Solver: The Z3 SMT solver, developed since 2006, is highlighted. Originally targeted at software systems, it's now used in various domains, including network verification, verified crypto libraries, and security risk detection.
0:05:13 Shared Technologies: SMT solvers share technologies with and draw inspiration from SAT solvers, mixed integer programming, and constraint programming.
0:06:50 Z3 Online Guide: A website offers an online guide and tutorial for using Z3, including the SMT-LIB input format.
0:07:18 Symbolic Model Checking: Tools like SLAM, Yogi, and Coral are discussed, focusing on their use in driver verification. Constrained Horn Clauses are introduced as a way to encode symbolic model checking problems as logical formulas.
0:09:01 Seahorn: Seahorn, a tool developed outside Microsoft Research, uses Horn Clauses and Z3's Spacer solver for program verification.
0:09:57 Constrained Horn Clause Example: The McCarthy 91 function is used to demonstrate how program logic and partial correctness conditions can be encoded as Horn Clauses.
0:11:01 Model-Based Testing: Tools like Spec Explorer, Bosi, Ivy, and Sen are discussed. These tools originated from abstract state machine research and are now primarily used in testing.
0:12:33 Bosi and Sen: Bosi is a programming language for high-integrity contracts. Sen is a .NET library for writing contracts using expression languages.
0:13:35 Bosi Example: Bosi code is shown, highlighting its use of regular expressions and refinement types in the type system.
0:14:56 Systems Code Verification: Various verification tools, including those based on the Boogie verification condition generator and those using functional programming/type theory (e.g., F*), are presented.
0:18:38 F:* F* is a language for logical foundations of programs and proofs. It has different targets (OCaml, WebAssembly, C, Assembly) and use-cases (concurrent systems, verified parsers).
0:20:52 EverParse: EverParse generates verified parsers, used in the Hyper-V hypervisor to eliminate parsing-related vulnerabilities.
0:23:06 Cryptography: Verification of assembly code. The EverCrypt project provides a set of verified cryptographic primitives.
0:24:52 Rust Verification. Verification of systems-level code.
0:28:55 Tomography of Computation: This section introduces tools that observe and analyze computations, such as concurrency testing tools.
0:29:51 Concurrency Testing Tools: Tools like Torch and Coyote, derived from explicit state and stateless model checking, are used to control schedulers and explore diverse execution states.
0:31:27 Coyote: Coyote is an open-source tool used in Azure services for concurrency testing.
0:32:24 Torch: Torch infers synchronization primitives and causality relations for effective state space exploration, injecting faults for wider testing.
0:33:11 Fuzzing: Fuzzing tools, starting with DART and CUTE, are discussed, including Pex, Sage, RESTler, and Hyper-Fuzzer.
0:34:14 RESTler: An open-source, stateful fuzzer that uses OpenAPI specifications for web service testing.
0:35:58 Hyper-Fuzzer: A hybrid symbolic/random execution fuzzer for hypervisors, which has found high-value bugs.
0:37:39 Network Verification: The concept of "correct by construction" networks and intent-based networking is introduced.
0:38:51 Example: Router Verification: The talk describes verifying that routers in data centers use shortest paths and have redundant paths for load balancing and congestion avoidance.
0:41:14 Spark and Sen in Network Verification: Spark provides a language for interacting with network topology and devices. Sen allows writing concise checkers for network properties.
0:44:27 Network Change Verification System (NCVS): NCVS is a system used before deploying large network changes, employing simulation, emulation, and verification tools to prevent outages.
0:45:22 Sen Guru: Is built on top of Sen. Used for customer network verification.
0:47:25 Summary: The speaker provides a summary of the covered topics, including symbolic model checking, model-based testing, verification, concurrency, fuzzing, and network verification.
0:47:43 Q&A: TLA+ is discussed in the question, and there's mention of a colleague who used it to find a design bug in a networking system called "Sleeper".
0:48:44 Operational Overhead of NCVS: The speakers describes that those that use NCVS sit near the developers.
0:51:07 Question on the impact of AI-assisted programming (e.g., Copilot) on formal methods: The speaker views AI as an opportunity, a "fast cache of good hints," potentially narrowing the search space for automated reasoning.
0:52:49 Network Latency: The speaker does not have first hand experience verifying probabilities such as network latency.
0:53:54 How can formal methods protect against non-expert software? The speaker suggests that there may be a way to employ some of the techniques to help with low-skill software. The suggestion is made to check for common properties across different policies, which is the analogy of the code.