**1. Security by design.** Security is our top priority in the design of KxOS. As such, we adopt the widely acknowledged security best practice of [least privilege principle](https://en.wikipedia.org/wiki/Principle_of_least_privilege) and enforce it in a fashion that leverages the full strengths of Rust. To do so, we partition KxOS into two halves: a _privileged_ OS core and _unprivileged_ OS components. As a result, we can write the OS components almost entirely in _safe_ Rust, while taking extra cautions with the _unsafe_ Rust code in the OS core. Furthermore, we propose the idea of _everything-is-a-capability_, which elevates the status of [capabilities](https://en.wikipedia.org/wiki/Capability-based_security) to the level of a ubiquitous security primitive used throughout the OS. We make novel use of Rust's advanced features (e.g., [type-level programming](https://willcrichton.net/notes/type-level-programming/)) to make capabilities more accessible and efficient. The net result is improved security and uncompromised performance.
**2. Trustworthy OS-level virtualization.** OS-level virtualization mechanisms (like Linux's cgroups and namespaces) enable containers, a more lightweight and arguably more popular alternative to virtual machines (VMs). But there is one problem with containers: they are not as secure as VMs (see [StackExchange](https://security.stackexchange.com/questions/169642/what-makes-docker-more-secure-than-vms-or-bare-metal), [LWN](https://lwn.net/Articles/796700/), and [AWS](https://docs.aws.amazon.com/AmazonECS/latest/bestpracticesguide/security-tasks-containers.html)). There is a real risk that malicious containers may exploit privilege escalation bugs in the OS kernel to attack the host. [A study](https://dl.acm.org/doi/10.1145/3274694.3274720) found that 11 out of 88 kernel exploits are effective in breaking the container sandbox. The seemingly inherent insecurity of OS kernels leads to a new breed of container implementations (e.g., [Kata](https://katacontainers.io/) and [gVisor](https://gvisor.dev/)) that are based on VMs, instead of kernels, for isolation and sandboxing. We argue that this unfortunate retreat from OS-level virtualization to VM-based one is unwarranted---if the OS kernels are secure enough. And this is exactly what we plan to achieve with KxOS. We aim to provide a trustworthy OS-level virtualization mechanism on KxOS.
**3. High-velocity development.** Traditional OS kernels like Linux are hard to develop, test, and debug. Kernel development involves countless rounds of programming, failing, and rebooting on bare-metal or virtual machines. This way of life is unproductive and painful. Such a pain point is also recognized and partially addressed by [research work](https://www.usenix.org/conference/fast21/presentation/miller), but we think we can do more. In this spirit, we design the OS core to provide high-level APIs that are largely independent of the underlying hardware and implement it with two targets: one target is as part of a regular OS in kernel space and the other is as a library OS in user space. This way, all the OS components of KxOS, which are stacked above the OS core, can be developed, tested, and debugged in user space, which is more friendly to developers than kernel space.
**4. High-fidelity Linux ABI.** An OS without usable applications is useless. So we believe it is important for KxOS to fit in an established and thriving ecosystem of software, such as the one around Linux. This is why we conclude that KxOS should aim at implementing high-fidelity Linux ABI, including the system calls, the proc file system, etc.
While there is nothing revolutionary in KxOS, it does explore some new design points in constructing secure Rust OSes. To minimize the risks of the project, we plan to move towards Minimal Viable Product (MVP) in iterations.
- [ ] Iteration 1: Build a minimal OS core runnable in both VMs and user space.
- [ ] Iteration 2: Build a minimal set of OS components to run simple programs
- [ ] Iteration 3: Add the compile-time access control mechanism
- [ ] Iteration 4: Add more system calls to support busybox
- [ ] Iteration 5: Add a minimal set of OS-level virtualization functionalities
