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Date: Thu, 13 May 2010 12:59:23 -0700 (PDT)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Oleg Nesterov <oleg@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>,
       Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
       Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>,
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       Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
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       Frederic Weisbecker <fweisbec@gmail.com>,
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       Mel Gorman <mel@csn.ul.ie>,
       "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
       Andrea Arcangeli <aarcange@redhat.com>,
       Hugh Dickins <hugh.dickins@tiscali.co.uk>,
       Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH v2 7/11] Uprobes Implementation
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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