linux-kernel - Re: [RFC] Tracepoint proposal

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Date:	Tue, 24 Jun 2008 07:55:25 -0400
From:	fche@...hat.com (Frank Ch. Eigler)
To:	"Takashi Nishiie" <t-nishiie@...css.fujitsu.com>
Cc:	"'Masami Hiramatsu'" <mhiramat@...hat.com>,
	"'Alexey Dobriyan'" <adobriyan@...il.com>,
	"'Mathieu Desnoyers'" <mathieu.desnoyers@...ymtl.ca>,
	"'Peter Zijlstra'" <peterz@...radead.org>,
	"'Steven Rostedt'" <rostedt@...dmis.org>,
	"'Ingo Molnar'" <mingo@...e.hu>,
	"'LKML'" <linux-kernel@...r.kernel.org>,
	"'systemtap-ml'" <systemtap@...rces.redhat.com>,
	"'Hideo AOKI'" <haoki@...hat.com>
Subject: Re: [RFC] Tracepoint proposal

"Takashi Nishiie" <t-nishiie@...css.fujitsu.com> writes:

> [...]
> Each kernel sub-system seems to have its own way of dealing with 
> debugging statements. Some of these methods include 'dprintk', 
> 'pr_debug', 'dev_debug', 'DEBUGP'. I think that these functions are
> the tracepoints that has been availably mounted without setting up 
> the tool set of the outside. I think whether mounting that unites 
> these functions can be done if kernel marker and tracepoint are used.

There are efforts underway to collect these various debug methods into
a single run-time-dynamic stream, which may even turn out to connect
to markers.

> By the way, isn't there problem on security?  What kprobe, jprobe,
> and kernel marker, etc. offer looks like what the framework of Linux
> Security Module had offered before.  Gotten kprobe, jprobe, and
> kernel marker, etc. should not be exported to the userland for
> security because it becomes the hotbed of rootkits.

These are all kernel-side facilities with no direct connection to
user-land.

> Users such as kprobe, jprobe, and kernel marker should not be
> Loadable Kernel Module. [...]

That would defeat their usefulness.  Remember, kernel modules run with
no hardware-level restrictions at all, so if an adversary managed to
load up some kernel malware module, the game is over, whether or not
they use kprobes.

- FChE
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