The seL4 kernel itself and most of its proof is licensed under GPL Version
2. For full terms and conditions, see the file
in the seL4 repository. As for Linux, the GPL applies to the kernel itself,
not to user-level programs running on top of it.
Various further components, libraries, and tools are released under the
2-clause BSD license. For details see the file
in the respective repositories. See the individual file headers for which
license applies to which file.
Additionally, the release contains 3rd-party open-source software, available under standard open-source licenses such as GPLv2, 3-clause BSD, and MIT/Expat. See the individual file headers for details.
All code is hosted on github, available at https://github.com/seL4.