linux-kernel - Re: Immediate values

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Message-ID: <20090925073512.GA10346@Krystal>
Date:	Fri, 25 Sep 2009 03:35:13 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Jason Baron <jbaron@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>, Andi Kleen <ak@...e.de>,
	linux-kernel@...r.kernel.org,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Prasanna S Panchamukhi <prasanna@...ibm.com>,
	Rusty Lynch <rusty.lynch@...el.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Vamsi Krishna S <vamsi_krishna@...ibm.com>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Nathan Sidwell <nathan@...esourcery.com>,
	Dominique Toupin <dominique.toupin@...csson.com>,
	Anton Massoud <anton.massoud@...csson.com>,
	Richard J Moore <richardj_moore@...ibm.com>
Subject: Re: Immediate values

* Arjan van de Ven (arjan@...radead.org) wrote:
> On Thu, 24 Sep 2009 21:34:22 +0200
> Ingo Molnar <mingo@...e.hu> wrote:
> 
[context for people CCed: see
http://lkml.org/lkml/2009/9/24/262]

> > 
> > * H. Peter Anvin <hpa@...or.com> wrote:
> > 
> > > I would like to get an official ACK or NAK for this patching
> > > technique from inside Intel, and preferrably from AMD as well.  If
> > > it does work as described it would provide a very clean way to do
> > > one-shot alternative functions, which probably would be higher
> > > value than immediate data values.
> > 
> > Sounds tempting. Things like the CONFIG_SECURITY hookery could use it?
> > 
> > But ... since it's patched under stopmachine, is there any reason why 
> > this wouldnt work?
> > 
> 
> stopmachine is fine.
> 
> more aggressive tricks are rather dicey.
> 
> (cross modifying code that's being executed in ring 0 is ... not
> something CPU designers had in mind)
> 

Then, following your advice, kprobes should be re-designed to do a
stop_machine around the int3 breakpoint insertion ? And gdb
should be stopping all threads of a target process before inserting a
breakpoint. Therefore, I do not seem to be the only one confused about
Intel statement on this issue.

Mathieu

> -- 
> Arjan van de Ven 	Intel Open Source Technology Centre
> For development, discussion and tips for power savings, 
> visit http://www.lesswatts.org

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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