linux-kernel - Re: [PATCH -tip v2 3/9] ftrace/x86: Support SAVE

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Date:	Tue, 5 Jun 2012 19:41:33 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	yrl.pp-manager.tt@...achi.com
Subject: Re: [PATCH -tip v2 3/9] ftrace/x86: Support SAVE_REGS feature on i386

Hi -

> > That would be the way for a kprobe to modify variables/values that
> > happen to be in the registers.  In systemtap, for example:
> > # stap -g -e 'probe kernel.function("foo") { $bar = 1 }'
>
> And why would we want to allow this?
> Modifying variables with probes is another way to lead to disaster. [...]
> What real world example leads to external sources modifying internal
> core variables? With the obvious exception of rootkits.

Among others, systemtap has been successfully used for fault injection
for development/testing, as well as band-aids for kernel security
vulnerabilities, where a small change of state can improve the state
of the system.  Obviously, this functionality is restricted to highly
privileged users.

- FChE
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