How can one build a feature-rich, Rust-based operating system (OS) with a minimal and sound Trusted Computing Base (TCB) for memory safety? Existing Rust-based OSes fall short due to their improper usage of unsafe Rust in kernel development. To address these challenges, we propose a novel framekernel architecture that leverages Rust’s memory safety features to enable intra-kernel privilege separation, ensuring TCB minimality and soundness. We present OSTD, a streamlined framework for safe Rust OS development, and Asterinas, a Linux ABI-compatible framekernel OS implemented entirely in safe Rust using OSTD. Supporting over 180 Linux system calls, Asterinas delivers performance on par with Linux, while maintaining a memory safe TCB of just 10K lines of code—about 17% of its total codebase. These results underscore the practicality and benefits of the framekernel architecture in building safe and efficient OSes