netdev - Re: [PATCH RFC net-next 07/14] bpf: expand BPF syscall with program load/unload

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Date:	Fri, 27 Jun 2014 23:28:01 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Chema Gonzalez <chema@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Linux API <linux-api@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC net-next 07/14] bpf: expand BPF syscall with program load/unload

On Fri, Jun 27, 2014 at 11:12 PM, Alexei Starovoitov <ast@...mgrid.com> wrote:
> On Fri, Jun 27, 2014 at 5:19 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> On Fri, Jun 27, 2014 at 5:05 PM, Alexei Starovoitov <ast@...mgrid.com> wrote:
>>> eBPF programs are safe run-to-completion functions with load/unload
>>> methods from userspace similar to kernel modules.
>>>
>>> User space API:
>>>
>>> - load eBPF program
>>>   prog_id = bpf_prog_load(int prog_id, bpf_prog_type, struct nlattr *prog, int len)
>>>
>>>   where 'prog' is a sequence of sections (currently TEXT and LICENSE)
>>>   TEXT - array of eBPF instructions
>>>   LICENSE - GPL compatible
>>> +
>>> +       err = -EINVAL;
>>> +       /* look for mandatory license string */
>>> +       if (!tb[BPF_PROG_LICENSE])
>>> +               goto free_attr;
>>> +
>>> +       /* eBPF programs must be GPL compatible */
>>> +       if (!license_is_gpl_compatible(nla_data(tb[BPF_PROG_LICENSE])))
>>> +               goto free_attr;
>>
>> Seriously?  My mind boggles.
>
> Yes. Quite a bit of logic can fit into one eBPF program. I don't think it's wise
> to leave this door open for abuse. This check makes it clear that if you
> write a program in C, the source code must be available.
> If program is written in assembler than this check is nop anyway.
>

I can see this seriously annoying lots of users.  For example,
Chromium might object.

If you want to add GPL-only functions in the future, that would be one
thing.  But if someone writes a nice eBPF compiler, and someone else
writes a little program that filters on network packets, I see no
reason to claim that the little program is a derivative work of the
kernel and therefore must be GPL.

> btw this patch doesn't include debugfs access to all loaded eBPF programs.
> Similarly to kernel modules I'm planning to have a way to list all loaded
> programs with optional assembler dump of instructions.

Users can also dump running programs with ptrace.  That doesn't mean
that all loaded programs need to be GPL.

--Andy
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