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Filament is a Rust library for static information flow control (IFC) that implements a Denning-style system without requiring compiler modifications. It achieves fine-grained explicit-flow checking using Rust's type inference and enforces implicit flows with a novel `pc_block!` macro for compile-time program counter labeling. Evaluation demonstrates negligible compile-time overhead, modest annotation requirements, and a more permissive programming model compared to prior work like Cocoon.
Rustaceans can now enforce fine-grained information flow control without modifying the compiler, unlocking safer systems programming.
Existing language-based information-flow control (IFC) tools face a fundamental tension: Denning-style systems that track explicit and implicit flows at the variable level typically require compiler modifications, while more coarse-grained approaches, including recent work Cocoon, avoid compiler changes but impose more restrictive programming models. We present Filament, a Denning-style static IFC library for Rust that requires no compiler modifications. Filament addresses three key challenges in building a practical IFC library for Rust. First, it enables fine-grained explicit-flow checking with minimal annotation overhead by leveraging Rust's type inference. Second, it introduces pc_block!, a lightweight construct for enforcing implicit flows via a compile-time program counter label, without requiring compiler support. Third, it provides fcall! and mcall! macros to support seamless and safe interoperability with standard and third-party libraries. Our evaluation shows that Filament incurs negligible compile-time overhead and requires only modest annotations. Moreover, compared to Cocoon, Filament offers a more permissive programming model, reducing the need for frequent escape hatches that bypass security checks.
