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 [off-list ref] wrote:

On Fri, Jun 27, 2014 at 5:19 PM, Andy Lutomirski [off-list ref] wrote:

quoted

On Fri, Jun 27, 2014 at 5:05 PM, Alexei Starovoitov [off-list ref] wrote:

quoted

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