General Dynamics C4 Systems and NICTA are pleased to announce the open sourcing of seL4, the world’s first operating-system kernel with an end-to-end proof of implementation correctness and security enforcement. It is still the world’s most highly-assured OS.

What’s being released?

It includes all of the kernel’s source code, all the proofs, plus other code and proofs useful for building highly trustworthy systems. All is under standard open-source licensing terms — either GPL version 2, or the 2-clause BSD licence.

via Home | seL4.

Unique about seL4 is its unprecedented degree of assurance, achieved through formal verification. Specifically, the ARM version of seL4 is the first (and still only) general-purpose OS kernel with a full code-level functional correctness proof, meaning a mathematical proof that the implementation (written in C) adheres to its specification. In short, the implementation is proved to be bug-free (see below). This also implies a number of other properties, such as freedom from buffer overflows, null pointer exceptions, use-after-free, etc