seL4 is a high-assurance, high-performance operating system microkernel. It is unique because of its comprehensive formal verification, without compromising performance. It is meant to be used as a trustworthy foundation for building safety- and security-critical systems. It is available as open source on GitHub and supported by the seL4 Foundation.
Being a kernel means it is the piece of software that runs at the heart of any software system and controls all accesses to resources. It provides fine-grained access control through capabilities, and controls communication between components of the system. It is the most critical part of the software system, and runs in privileged mode.
Being a microkernel means that it is reduced to a minimal core that is free from policy and therefore can form a dependable base for building arbitrary systems serving many different usage scenarios.
seL4 is a member of the L4 family of microkernels, and is the world's most advanced, most highly assured operating-system kernel.
seL4's formal verification sets it apart from any other operating system. In a nutshell, it provides the highest assurance of isolation between applications running in the system, meaning that a compromise in one part of the system can be contained and prevented from harming other, potentially more critical parts of the system.
Specifically, seL4's implementation is formally (mathematically) proven correct (bug-free) against its specification, has been proved to enforce strong security properties, and if configured correctly its operations have proven safe upper bounds on their worst-case execution times. It was the world's first operating system with such a proof, and is still the only proven operating system featuring fine-grained capability-based security and high performance. It also has the most advanced support for mixed criticality real-time systems.
For detailed explanations of these terms, see our FAQ.
In 2009, the seL4 kernel was a scientific breakthrough result from the Trustworthy Systems group (TS) that showed that high-performance kernels are within the realm of formal verification. Today, seL4 is part of an ecosystem supporting active use in various domains including automotive, aviation, infrastructure, medical, and defence. A key highlight demonstrating its fit for real-world deployment was in the DARPA-funded HACMS program, where seL4 was used to protect an autonomous helicopter against cyber-attacks. TS continues to push the state of the art of operating systems through seL4, in close cooperation with its partners in the seL4 Foundation.
More on TS ongoing and future research about seL4 and trustworthy systems.