linux-kernel - Re: [PATCH 0/3][RFC] x86: Catch stray non-kprobe breakpoints

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Date:	Tue, 29 Jan 2008 14:29:41 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Abhishek Sagar <sagar.abhishek@...il.com>
CC:	ananth@...ibm.com, LKML <linux-kernel@...r.kernel.org>,
	jkenisto@...ibm.com, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 0/3][RFC] x86: Catch stray non-kprobe breakpoints

Abhishek Sagar wrote:
> On 1/29/08, Masami Hiramatsu <mhiramat@...hat.com> wrote:
>> In that case, why don't you just reduce the priority of kprobe_exceptions_nb?
>> Then, the execution path becomes very simple.
> 
> Ananth mentioned that the kprobe notifier has to be the first to run.

(Hmm.. I think he has just explained current implementation:))
IMHO, since kprobes itself can not know what the external debugger
wants to do, the highest priority should be reserved for those external tools.

> It still wouldnt allow us to notice breakpoints on places like do_int3
> etc.

If you'd like to do that, my recommendation is to modify IDT directly.

>> I also like to use a debugger for debugging kprobes. that will help us.
> 
> Hmm...It would increase the code-path leading upto kprobe_handler.
> That's more territory to be guarded from kprobes.

Sure, all functions of the debugger should be marked __kprobes.
Thus it will be guarded from kprobes.

Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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