linux-kernel - Re: [PATCH v3 2.6.39-rc1-tip 12/26] 12: uprobes: slot allocation for uprobes

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Message-Id: <20110421161442.61A532C15B@topped-with-meat.com>
Date:	Thu, 21 Apr 2011 09:14:42 -0700 (PDT)
From:	Roland McGrath <roland@...k.frob.com>
To:	Eric Paris <eparis@...hat.com>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Eric Paris <eparis@...isplace.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	SystemTap <systemtap@...rces.redhat.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>, sds@...ho.nsa.gov
Subject: Re: [PATCH v3 2.6.39-rc1-tip 12/26] 12: uprobes: slot allocation
 for uprobes

> Unrelated note: I'd prefer to see that page be READ+EXEC only once it
> has been mapped into the victim task.  Obviously the portion of the code
> that creates this page and sets up the instructions to run is going to
> need write.  Maybe this isn't feasible.  Maybe this magic pages gets
> written a lot even after it's been mapped in.  But I'd rather, if
> possible, know that my victim tasks didn't have a WRITE+EXEC page
> available......

AIUI the page never really needs to be writable in the page tables.  It's
never written from user mode.  It's only written by kernel code, and that
can use a separate momentary kmap to do its writing.


Thanks,
Roland
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