linux-kernel - Re: [PATCH -mm] vmscan: make mapped executable pages the first class citizen

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Date:	Sun, 10 May 2009 15:17:21 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"riel@...hat.com" <riel@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tytso@....edu" <tytso@....edu>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"elladan@...imo.com" <elladan@...imo.com>,
	"npiggin@...e.de" <npiggin@...e.de>,
	"cl@...ux-foundation.org" <cl@...ux-foundation.org>,
	"minchan.kim@...il.com" <minchan.kim@...il.com>
Subject: Re: [PATCH -mm] vmscan: make mapped executable pages the first
 class  citizen

On Sun, 2009-05-10 at 21:39 +0900, KOSAKI Motohiro wrote:
> >> > They always use mmap(PROT_READ | PROT_WRITE | PROT_EXEC) for anycase.
> >> > Please google it. you can find various example.
> >>
> >> How widely is PROT_EXEC abused? Would you share some of your google results?
> >
> > That's a security bug right there and should be fixed regardless of our
> > heuristics.
> 
> Yes, should be. but it's not security issue. it doesn't make any security hole.
> Plus, this claim doesn't help to solve end-user problems.

Having more stuff executable than absolutely needed is always a security
issue.

> I think the basic concept of the patch is right.
>   - executable mapping is important for good latency
>   - executable file is relatively small
> 
> The last problem is, The patch assume executable mappings is rare, but
> it isn't guranteed.
> How do we separate truth executable mapping and mis-used PROT_EXEC usage?

One could possibly limit the size, but I don't think it pays to bother
about this until we really run into it, again as Andrew already said,
there's more ways to screw reclaim if you really want to.



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