linux-kernel - Re: [PATCH v11 net-next 12/12] bpf: mini eBPF library, test stubs and verifier testsuite

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Message-ID: <CAMEtUuzEQu30WiYprRcDBogJxxrDeNhvn=kF+z8cVvhR-vjTQg@mail.gmail.com>
Date:	Wed, 10 Sep 2014 11:08:40 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Daniel Borkmann <dborkman@...hat.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...uxfoundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Chema Gonzalez <chema@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...uxfoundation.org>,
	Kees Cook <keescook@...omium.org>,
	Linux API <linux-api@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v11 net-next 12/12] bpf: mini eBPF library, test stubs and
 verifier testsuite

On Wed, Sep 10, 2014 at 4:35 AM, Daniel Borkmann <dborkman@...hat.com> wrote:
>
> Since we already have an extensive BPF test suite, that is, lib/test_bpf.c,
> which currently also does sanity checks for the classic BPF verifier, is
> there a reason these verifier test cases cannot be extended/integrated there
> as well but have to go to kernel/bpf/test_stub.c resp.
> samples/bpf/test_verifier.c ?
> I don't like that we put testing code into kernel/bpf/ whereas we already
> have a BPF test infrastructure in the kernel elsewhere.

yes. there is a reason. Verifier needs to be tested from user space,
since it works on fds. Process local map_fd are part of the eBPF
programs. Therefore one is testing things from kernel and
another from userspace. We definitely need both.
Currently there is no use case to call verifier from inside
the kernel. I'm not sure there will be one. Verifier's main
purpose is to check user supplied programs and provide
humans an understandable error messages of what
is 'unsafe' in particular program.
Eventually we will integrate this verifier messages with
program compilation. Like, the user would write a program
in C then invoke a wrapper of compiler and verifier, which
will point to lines in C code which are doing something
wrong like loops or out of bounds access. Currently verifier
complains about particular 'unsafe' instruction, but
humans have hard time correlating asm to C.
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