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

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Message-ID: <20090713105948.GI12383@axis.com>
Date:	Mon, 13 Jul 2009 12:59:49 +0200
From:	Jesper Nilsson <jesper.nilsson@...s.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Siarhei Liakh <sliakh.lkml@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-security-module@...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 <linux-cris-kernel@...s.com>
Subject: Re: [PATCH v5] RO/NX protection for loadable kernel modules

On Sun, Jul 12, 2009 at 06:40:39AM +0200, Rusty Russell wrote:
> On Sun, 12 Jul 2009 01:19:58 am Arjan van de Ven wrote:
> > Rusty Russell <rusty@...tcorp.com.au> wrote:
> > > I have a question about this patch though: I think it's unsafe in
> > > general to mark the last partial page as NX (we asked for executable
> > > pages, this could remove executable from some unrelated allocation).
> >
> > we vmalloc / g_f_p modules right? so we don't share the last page.
> 
> Historically yes, but I don't think we should be counting on it.  It makes 
> sense to kmalloc for small modules, and it's arch specific code.
> 
> OTOH, a quick grep shows currently only cris does kmalloc, and that's a config
> option.

...which is a not often used debug option.

> It might be time to unify this code.  If we rename MODULE_START to 
> MODULE_VADDR on MIPS, then ignoring CRIS there's only two real variants; 
> vmalloc and __vmalloc.
> 
> (I like the idea of trying kmalloc and falling back, simply because it reduces 
> TLB pressure, but that's probably best done after unification).
> 
> Thoughts?
> Rusty.

/^JN - Jesper Nilsson
-- 
               Jesper Nilsson -- jesper.nilsson@...s.com
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