forked from Minki/linux
c86216bc96
Document and clarify BPF licensing. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Reviewed-by: Simon Horman <simon.horman@corigine.com> Acked-by: Toke Høiland-Jørgensen <toke@redhat.com> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Joe Stringer <joe@cilium.io> Acked-by: Lorenz Bauer <lmb@cloudflare.com> Acked-by: Dave Thaler <dthaler@microsoft.com> Acked-by: Stephen Hemminger <stephen@networkplumber.org> Acked-by: Jesper Dangaard Brouer <brouer@redhat.com> Acked-by: KP Singh <kpsingh@kernel.org> Link: https://lore.kernel.org/bpf/20210917230034.51080-1-alexei.starovoitov@gmail.com
93 lines
3.5 KiB
ReStructuredText
93 lines
3.5 KiB
ReStructuredText
=============
|
|
BPF licensing
|
|
=============
|
|
|
|
Background
|
|
==========
|
|
|
|
* Classic BPF was BSD licensed
|
|
|
|
"BPF" was originally introduced as BSD Packet Filter in
|
|
http://www.tcpdump.org/papers/bpf-usenix93.pdf. The corresponding instruction
|
|
set and its implementation came from BSD with BSD license. That original
|
|
instruction set is now known as "classic BPF".
|
|
|
|
However an instruction set is a specification for machine-language interaction,
|
|
similar to a programming language. It is not a code. Therefore, the
|
|
application of a BSD license may be misleading in a certain context, as the
|
|
instruction set may enjoy no copyright protection.
|
|
|
|
* eBPF (extended BPF) instruction set continues to be BSD
|
|
|
|
In 2014, the classic BPF instruction set was significantly extended. We
|
|
typically refer to this instruction set as eBPF to disambiguate it from cBPF.
|
|
The eBPF instruction set is still BSD licensed.
|
|
|
|
Implementations of eBPF
|
|
=======================
|
|
|
|
Using the eBPF instruction set requires implementing code in both kernel space
|
|
and user space.
|
|
|
|
In Linux Kernel
|
|
---------------
|
|
|
|
The reference implementations of the eBPF interpreter and various just-in-time
|
|
compilers are part of Linux and are GPLv2 licensed. The implementation of
|
|
eBPF helper functions is also GPLv2 licensed. Interpreters, JITs, helpers,
|
|
and verifiers are called eBPF runtime.
|
|
|
|
In User Space
|
|
-------------
|
|
|
|
There are also implementations of eBPF runtime (interpreter, JITs, helper
|
|
functions) under
|
|
Apache2 (https://github.com/iovisor/ubpf),
|
|
MIT (https://github.com/qmonnet/rbpf), and
|
|
BSD (https://github.com/DPDK/dpdk/blob/main/lib/librte_bpf).
|
|
|
|
In HW
|
|
-----
|
|
|
|
The HW can choose to execute eBPF instruction natively and provide eBPF runtime
|
|
in HW or via the use of implementing firmware with a proprietary license.
|
|
|
|
In other operating systems
|
|
--------------------------
|
|
|
|
Other kernels or user space implementations of eBPF instruction set and runtime
|
|
can have proprietary licenses.
|
|
|
|
Using BPF programs in the Linux kernel
|
|
======================================
|
|
|
|
Linux Kernel (while being GPLv2) allows linking of proprietary kernel modules
|
|
under these rules:
|
|
Documentation/process/license-rules.rst
|
|
|
|
When a kernel module is loaded, the linux kernel checks which functions it
|
|
intends to use. If any function is marked as "GPL only," the corresponding
|
|
module or program has to have GPL compatible license.
|
|
|
|
Loading BPF program into the Linux kernel is similar to loading a kernel
|
|
module. BPF is loaded at run time and not statically linked to the Linux
|
|
kernel. BPF program loading follows the same license checking rules as kernel
|
|
modules. BPF programs can be proprietary if they don't use "GPL only" BPF
|
|
helper functions.
|
|
|
|
Further, some BPF program types - Linux Security Modules (LSM) and TCP
|
|
Congestion Control (struct_ops), as of Aug 2021 - are required to be GPL
|
|
compatible even if they don't use "GPL only" helper functions directly. The
|
|
registration step of LSM and TCP congestion control modules of the Linux
|
|
kernel is done through EXPORT_SYMBOL_GPL kernel functions. In that sense LSM
|
|
and struct_ops BPF programs are implicitly calling "GPL only" functions.
|
|
The same restriction applies to BPF programs that call kernel functions
|
|
directly via unstable interface also known as "kfunc".
|
|
|
|
Packaging BPF programs with user space applications
|
|
====================================================
|
|
|
|
Generally, proprietary-licensed applications and GPL licensed BPF programs
|
|
written for the Linux kernel in the same package can co-exist because they are
|
|
separate executable processes. This applies to both cBPF and eBPF programs.
|