linux-kernel - Re: [PATCH v5] RO/NX protection for loadable kernel modules

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Date:	Sun, 12 Jul 2009 08:32:27 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Ingo Molnar <mingo@...e.hu>, Siarhei Liakh <sliakh.lkml@...il.com>,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	James Morris <jmorris@...ei.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@....de>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, linux-cris-kernel@...s.com
Subject: Re: [PATCH v5] RO/NX protection for loadable kernel modules

On Sun, 12 Jul 2009 19:28:27 +0930
Rusty Russell <rusty@...tcorp.com.au> wrote:

> On Sun, 12 Jul 2009 05:15:24 pm Arjan van de Ven wrote:
> > Rusty Russell <rusty@...tcorp.com.au> wrote:
> > > (I like the idea of trying kmalloc and falling back, simply
> > > because it reduces TLB pressure, but that's probably best done
> > > after unification).
> >
> > or using a non-power-of-two get_free_pages() thing...
> >
> > some architectures will need to know that memory needs to be
> > executable at allocation time so that it can be put in an
> > executable address range etc...
> 
> Yes, maybe that's better than kmalloc.  On my laptop I have 105
> modules loaded, with 3778464 total length: I'm wasting 206944 bytes
> on unused tails of pages.  But that's only 0.06% of my memory.
>

105 is also a sign that you picked a somewhat suboptimal config...
that's of course your choice but it's a choice that has a small price,
if you don't want to pay that price, changing the config to not be
entirely insane is a good answer as well ;-)



-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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