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

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Date:	Sun, 10 May 2009 19:44:54 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"peterz@...radead.org" <peterz@...radead.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, May 10, 2009 at 07:39:12PM +0800, KOSAKI Motohiro wrote:
> >> > So if that's what they want, let them have it to their heart's content.
> >> >
> >> > You know it's normal for many users/apps to care only about the result.
> >> > When they want something but cannot get it from the smarter version of
> >> > PROT_EXEC heuristics, they will go on to devise more complicated tricks.
> >> >
> >> > In the end both sides loose.
> >> >
> >> > If the abused case is important enough, then let's introduce a feature
> >> > to explicitly prioritize the pages. But let's leave the PROT_EXEC case
> >> > simple.
> >>
> >> No.
> >> explicit priotize mechanism don't solve problem anyway. application
> >> developer don't know end-user environment.
> >> they can't mark proper page priority.
> >
> > So it's simply wrong for an application to prioritize itself and is
> > not fair gaming and hence should be blamed. I doubt any application
> > aimed for a wide audience will do this insane hack.
> 
> There already are.
> some application don't interest strict PROT_ setting.

> 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?

Thanks,
Fengguang

> 
> > But specific
> > targeted applications are more likely to do all tricks which fits
> > their needs&environment, and likely they are doing so for good reasons
> > and are aware of the consequences.
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