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To: Andi Kleen <andi@firstfloor.org>
Cc: Alexei Starovoitov <ast@plumgrid.com>, Ingo Molnar <mingo@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
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        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Tom Zanussi <tom.zanussi@linux.intel.com>,
        Jovi Zhangwei <jovi.zhangwei@gmail.com>,
        Eric Dumazet <edumazet@google.com>, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH tip 0/5] tracing filters with BPF
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	<87fvq9cwlk.fsf@tassilo.jf.intel.com>
From: fche@redhat.com (Frank Ch. Eigler)
Date: Thu, 05 Dec 2013 11:31:18 -0500
In-Reply-To: <87fvq9cwlk.fsf@tassilo.jf.intel.com> (Andi Kleen's message of "Tue, 03 Dec 2013 16:01:59 -0800")
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Andi Kleen <andi@firstfloor.org> writes:

> [...]  While it sounds interesting, I would strongly advise to make
> this capability only available to root. Traditionally lots of
> complex byte code languages which were designed to be "safe" and
> verifiable weren't really. e.g. i managed to crash things with
> "safe" systemtap multiple times. [...]

Note that systemtap has never been a byte code language, that avenue
being considered lkml-futile at the time, but instead pure C.  Its
safety comes from a mix of compiled-in checks (which you can inspect
via "stap -p3") and script-to-C translation checks (which are
self-explanatory).  Its risks come from bugs in the checks (quite
rare), problems in the runtime library (rare), and problems in
underlying kernel facilities (rare or frequent - consider kprobes).


> So the likelyhood of this having some hole somewhere (either in
> the byte code or in some library function) is high.

Very true!


- FChE