The seL4 Foundation licenses and accepts contributions for
- the seL4 kernel itself under GPL Version 2,
- user code and proof libraries under the BSD 2 Clause license,
- code and proofs that depend on GPL-code or GPL-proofs under GPL,
- documentation under Creative Commons Attribution-ShareAlike.
Note that, as in the Linux syscall note for the GPL, the seL4 kernel GPL license does not cover user-level code that uses kernel services by normal system calls - this is merely considered normal use of the kernel, and does not fall under the heading of “derived work”. Syscall headers are provided under BSD.
For a longer explanation of how the seL4 license does or does not affect your own code see also this blog post.
The repositories of the seL4 GitHub organisation also contain third-party code
under additional compatible open source licenses. See the individual file
headers for details, or use one of the publicly available SPDX tools to
generate a software bill of materials. The directory
LICENSES/ in each repository
contains the text for all licenses that are mentioned by files in that