linux-kernel - Re: [PATCH v2 7/11] Uprobes Implementation

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Date:	Thu, 13 May 2010 12:59:23 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Oleg Nesterov <oleg@...hat.com>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Roland McGrath <roland@...hat.com>, Mel Gorman <mel@....ul.ie>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH v2 7/11] Uprobes Implementation



On Thu, 13 May 2010, Oleg Nesterov wrote:
> 
> But I still think this doesn't actually matter, replace_page() shouldn't
> preserve the mapping, it should always install the anonymous page. I can
> be wrong, of course.

Well, if I reasd the patches right, uprobes will use "copy_to_user()" for 
the self-probing case. So that would definitely just modify a shared 
mapping.

Of course, arguably, who really cares? As long as it's not a security 
issue (and it isn't - since the person could just have written to the 
thing directly instead), I guess it doesn't much matter. But it's a bit 
sad when a probing feature either

 - changes a global mapping that may be executed by other non-related 
   processes that the prober isn't even _aware_ of.

 - changes semantics by creating a non-coherent private page

so arguably it would be good to just make the rule be that you cannot 
probe a shared mapping. Because whatever you do, it's always the wrong 
thing.

			Linus
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