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Fine-grained information flow control (IFC) ensures confidentiality and integrity at the programming language level by ensuring that high-secrecy values do not affect low-secrecy values and that low-integrity values do not affect high-integrity values. However, prior support for fine-grained IFC is impractical: It either analyzes programs using whole-program static analysis, detecting false IFC violations; or it extends the language and compiler, thwarting adoption. Recent work called Cocoon demonstrates how to provide fine-grained IFC for Rust programs without modifying the language or compiler, but it is limited to static secrecy labels, and its case studies are limited. This paper introduces an approach called Carapace that employs Cocoon’s core approach and supports both static and dynamic IFC and supports both secrecy and integrity. We demonstrate Carapace using three case studies involving real applications and comprehensive security policies. An evaluation shows that applications can be retrofitted to use Carapace with relatively few changes, while incurring negligible run-time overhead in most cases. Carapace advances the state of the art by being the first hybrid static–dynamic IFC that works with an off-the-shelf language—Rust—and its unmodified compiler 

Information flow control (IFC) provides confidentiality by enforcing noninterference, which ensures that high-secrecy values cannot affect low-secrecy values. Prior work introduces fine-grained IFC approaches that modify the programming language and use non-standard compilation tools, impose run-time overhead, or report false secrecy leaks—all of which hinder adoption. This paper presents Cocoon, a Rust library for static type-based IFC that uses the unmodified Rust language and compiler. The key insight of Cocoon lies in leveraging Rust’s type system and procedural macros to establish an effect system that enforces noninterference. A performance evaluation shows that using Cocoon increases compile time but has no impact on application performance. To demonstrate Cocoon’s utility, we retrofitted two popular Rust programs, the Spotify TUI client and Mozilla’s Servo browser engine, to use Cocoon to enforce limited confidentiality policies