Date:   Wed, 15 Sep 2021 20:21:04 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     davem@...emloft.net
Cc:     daniel@...earbox.net, kuba@...nel.org, andrii@...nel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org, kernel-team@...com
Subject: [PATCH bpf-next] bpf: Document BPF licensing.

From: Alexei Starovoitov <ast@...nel.org>

Document and clarify BPF licensing.

Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Acked-by: Toke Høiland-Jørgensen <toke@...hat.com>
Acked-by: Daniel Borkmann <daniel@...earbox.net>
Acked-by: Joe Stringer <joe@...ium.io>
Acked-by: Lorenz Bauer <lmb@...udflare.com>
Acked-by: Dave Thaler <dthaler@...rosoft.com>
---
 Documentation/bpf/bpf_licensing.rst | 91 +++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)
 create mode 100644 Documentation/bpf/bpf_licensing.rst

diff --git a/Documentation/bpf/bpf_licensing.rst b/Documentation/bpf/bpf_licensing.rst
new file mode 100644
index 000000000000..62391923af07
--- /dev/null
+++ b/Documentation/bpf/bpf_licensing.rst
@@ -0,0 +1,91 @@
+=============
+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:
+https://www.kernel.org/doc/html/latest/process/license-rules.html#id1
+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.
-- 
2.30.2

Powered by blists - more mailing lists