Re: Immediate values

Mathieu Desnoyers
2009-09-25T07:40:13Z

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

> >
> > * H. Peter Anvin <hpa@zytor.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

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Mathieu Desnoyers
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