Keeping Safe Rust safe with Galeed
December 6, 2021
Rust is a programming language that simultaneously offers high performance and strong security guarantees. Safe Rust (i.e., Rust code that does not use the unsafe keyword) is memory and type safe. However, these guarantees are violated when safe Rust interacts with unsafe code, most notably code written in other programming languages, including in legacy C/C++ applications that are incrementally deploying Rust. This is a significant problem as major applications such as Firefox, Chrome, AWS, Windows, and Linux have either deployed Rust or are exploring doing so. It is important to emphasize that unsafe code is not only unsafe itself, but also it breaks the safety guarantees of ‘safe’ Rust; e.g., a dangling pointer in a linked C/C++ library can access and overwrite memory allocated to Rust even when the Rust code is fully safe. This paper presents Galeed, a technique to keep safe Rust safe from interference from unsafe code. Galeed has two components: a runtime defense to prevent unintended interactions between safe Rust and unsafe code and a sanitizer to secure intended interactions. The runtime component works by isolating Rust’s heap from any external access and is enforced using Intel Memory Protection Key (MPK) technology. The sanitizer uses a smart data structure that we call pseudo-pointer along with automated code transformation to avoid passing raw pointers across safe/unsafe boundaries during intended interactions (e.g., when Rust and C++ code exchange data). We implement and evaluate the effectiveness and performance of Galeed via micro- and macro-benchmarking, and use it to secure a widely used component of Firefox.