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Comment by icebraining | Hacker News Reader

Apparently you can now load non-GPL licensed eBPF programs, but they can't then access certain functions marked as "GPL only". This matches the behavior for kernel modules.

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The first BPF programs (original tcpdump use case) were always proprietary-compatible. If you think about it, there is nothing linux-specific about networking, and any code the user writes to tweak the data that is traversing their machine should be theirs to write, and doesn't taint the kernel. The same can be said for iptables/nft rules (you don't have to GPL your firewall configuration). Therefore, the BPF hooks that deal with packets (XDP, tc, socket) are not GPL-restricted and will remain so in the future.

Where GPL comes in is when you use BPF to introspect the kernel. It is quite possible to use BPF programs with the kprobe hook to extract data about how the kernel itself works, and the opinion of the kernel developers on this is that such use cases are within the realm of GPL protection.

Interesting. @icebraining, do you know where this list exists?

The helpers are in http://elixir.free-electrons.com/linux/v4.15-rc3/source/kern.... See the field gpl_only. For the list of which helpers are available in which hooks, the code needs to be read, to find things like: http://elixir.free-electrons.com/linux/v4.15-rc3/source/net/....

Unfortunately, I don't believe the high level list of which hooks have gpl helpers is published, so reading the code is the best method currently.

This list is under progress. Didn't think about adding licensing information for the helpers, but that's an excellent idea!

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