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Just-in-time (JIT) compilers make JavaScript run efficiently by replacing slow JavaScript interpreter code with fast machine code. However, this efficiency comes at a cost: bugs in JIT compilers can completely subvert all language-based (memory) safety guarantees, and thereby introduce catastrophic exploitable vulnerabilities. We present Icarus: a new framework for implementing JIT compilers that are automatically, formally verified to be safe, and which can then be converted to C++ that can be linked into browser runtimes. Crucially, we show how to build a JIT with Icarus such that verifying the JIT implementation statically ensures the security of all possible programs that the JIT could ever generate at run-time, via a novel technique called symbolic meta-execution that encodes the behaviors of all possible JIT-generated programs as a single Boogie meta-program which can be efficiently verified by SMT solvers. We evaluate Icarus by using it to re-implement components of Firefox's JavaScript JIT. We show that Icarus can scale up to expressing complex JITs, quickly detects real-world JIT bugs and verifies fixed versions, and yields C++ code that is as fast as hand-written code. 

Web applications often handle large amounts of sensitive user data. Modern secure web frameworks protect this data by (1) using declarative languages to specify security policies alongside database schemas and (2) automatically enforcing these policies at runtime. Unfortunately, these frameworks do not handle the very common situation in which the schemas or the policies need to evolve over time—and updates to schemas and policies need to be performed in a carefully coordinated way. Mistakes during schema or policy migrations can unintentionally leak sensitive data or introduce privilege escalation bugs. In this work, we present a domain-specific language (Scooter) for expressing schema and policy migrations, and an associated SMT-based verifier (Sidecar) which ensures that migrations are secure as the application evolves. We describe the design of Scooter and Sidecar and show that our framework can be used to express realistic schemas, policies, and migrations, without giving up on runtime or verification performance. 

We present VeRA, a system for verifying the range analysis pass in browser just-in-time (JIT) compilers. Browser developers write range analysis routines in a subset of C++, and verification developers write infrastructure to verify custom analysis properties. Then, VeRA automatically verifies the range analysis routines, which browser developers can integrate directly into the JIT. We use VeRA to translate and verify Firefox range analysis routines, and it detects a new, confirmed bug that has existed in the browser for six years.