Linux maintainers attending the Linux Kernel Maintainers Summit have said that Rust in the Linux kernel should no longer be treated as experimental, but rather as a core part of the kernel.

In practical terms, the change to Rust in the kernel no longer being experimental is simply a matter of removing "The Rust experiment" section of the kernel's documentation.

The move to rewrite parts of the Linux kernel began with a discussion in 2019 at the Linux Security Summit that concluded that around two-thirds of Linux kernel vulnerabilities derive from memory safety issues.

By using Rust, which has inherently safer APIs, these vulnerabilities could be overcome. A presentation at the Linux Plumbers Conference in August 2020 by John Baublitz, Nick Desaulniers, Alex Gaynor, Miguel Ojeda, Geoffrey Thomas, Josh Triplett explained progress, and Google stepped in in 2021 to provide financial support to project.

At that point, the project was moved under the auspices of the ISRG's  Prossimo project which aims to coordinate efforts to move the Internet’s critical software infrastructure to memory safe code. While this is an open source project with several contributors, funding from Google meant that from April 2021 Miguel Ojeda, who had been working on Rust for Linux as a side-project, had a contract  to work on it full time for a year. 

In April 2021. Ojeda posted an RFC about Rust support in the Linux kernel in which he pointed out that the project was limited in its aims with:

Please note that the Rust support is intended to enable writing drivers and similar "leaf" modules in Rust, at least for the foreseeable future. In particular, we do not intend to rewrite the kernel core nor the major kernel subsystems (e.g. `kernel/`, `mm/`, `sched/`...). Instead, the Rust support is built on top of those. 

Explaining why Rust should be the language of choice, he noted the following advantages Rust offers over C in the context of the Linux kernel:

• No undefined behavior in the safe subset (when unsafe code is sound), including memory safety and the absence of data races.
• Stricter type system for further reduction of logic errors.
• A clear distinction between safe and `unsafe` code.
• Featureful language: sum types, pattern matching, generics, RAII, lifetimes, shared & exclusive references, modules & visibility, powerful hygienic and procedural macros...
• Extensive freestanding standard library: vocabulary types such as `Result` and `Option`, iterators, formatting, pinning,
  checked/saturating/wrapping integer arithmetic, etc.
• Integrated out of the box tooling: documentation generator, formatter and linter all based on the compiler itself.

Overall, Rust is a language that has successfully leveraged decades of experience from system programming languages as well as functional ones, and added lifetimes and borrow checking on top.

While the early work was in limited areas, an increasing subset of Linux has been ported to Rust, especially drivers and higher-level utilities. 

Following the discussions at the Linux Plumbers Conference, Miguel Ojeda has now told the kernel mailing list that he is comfortable in declaring Rust for the Linux kernel a success, and will drop the "experiment" flag. 

Ojeda told the list that the experiment has just been deemed concluded, continuing:

"Obviously, this does not mean that everything works for every kernel configuration, architecture, toolchain etc., or that there won't be new issues. There is still a ton of work to do in all areas, from the kernel to upstream Rust, GCC and other projects. And, in fact, certain combinations (such as the mixed GCC+LLVM builds and the upcoming GCC support) are still quite experimental but getting there. But the experiment is done, i.e. Rust is here to stay."

More Information

Rust for Linux/linux

Ojeda's Post On Mailing List

Rust For Linux Paper

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