linux-kernel - Re: [PATCH v13 net-next 07/11] bpf: verifier (add ability to receive verification log)

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Message-ID: <541B1624.80302@redhat.com>
Date:	Thu, 18 Sep 2014 19:28:04 +0200
From:	Daniel Borkmann <dborkman@...hat.com>
To:	Alexei Starovoitov <ast@...mgrid.com>
CC:	"David S. Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	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@...ux-foundation.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 v13 net-next 07/11] bpf: verifier (add ability to receive
 verification log)

On 09/18/2014 05:24 PM, Alexei Starovoitov wrote:
...
> solve or not. If we decide to solve it, we need to have
> a plan to solve it all the way. Partial fix for size of bpf_attr
> is not a plan. It's something that is not addressing the problem
> completely. Little bit of help is not useful for userspace. It
> would need to deal with new types, verifier differences and
> other things that I mentioned earlier.

Hm, I don't think it would be a strict requirement to solve it
all the way, and I think that perf_event_open() with perf_copy_attr()
is not trying to do so either. It, however, is trying on a ``best
effort basis'' to still load something if new features are unused
by the binary (I guess you saw the comment in perf_copy_attr()).

Iff, e.g. due to new types we fail at the verifier stage, sure,
that's life since we only have backwards-compatible guarantee,
but in case we tried to use features we support, we're still able
to load the eBPF program while right now, we're rejecting it right
up-front. That's just my $0.02 ...
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