linux-kernel - Re: [PATCH v2] RO/NX protection for loadable kernel modules

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Message-ID: <20090629195410.GE31577@elte.hu>
Date:	Mon, 29 Jun 2009 21:54:10 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Siarhei Liakh <sliakh.lkml@...il.com>,
	James Morris <jmorris@...ei.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, Andi Kleen <ak@....de>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2] RO/NX protection for loadable kernel modules


* Arjan van de Ven <arjan@...radead.org> wrote:

> On Mon, 29 Jun 2009 11:16:40 -0400
> Siarhei Liakh <sliakh.lkml@...il.com> wrote:
> 
> > This patch is a logical extension of the protection provided by
> > CONFIG_DEBUG_RODATA to LKMs. The protection is provided by splitting
> > module_core and module_init into three logical parts each and setting
> > appropriate page access permissions for each individual section:
> > 
> >   1. Code: RO+X
> >   2. RO data: RO+NX
> >   3. RW data: RW+NX
> > 
> > In order to achieve proper protection, layout_sections() have been
> > modified to align each of the three parts mentioned above onto page
> > boundary. Next, the corresponding page access permissions are set
> > right before successful exit from load_module(). Further,
> > module_free() have been modified to set module_core or module_init as
> > RW+NX right before calling vfree(). Functionality of this patch is
> > enabled only when CONFIG_DEBUG_RODATA defined at compile time.
> > 
> > This is the second revision of the patch: it have been re-written to
> > reduce the number of #ifdefs and to make it architecture-agnostic.
> > Code formatting have been corrected also.
> > 
> 
> you can still go one step further....
> there is no downside to doing NX at all for modules, except for the 3
> sections now each being page aligned thing. So in principle NX should
> just not be part of any ifdef, only the alignment has any justification
> for being so.
> What you can do in the !CONFIG_OPTION case, is treating the "overlap"
> pages as "most permissive goes"..... if you do that you should have 1
> ifdef in total.
> 
> (and one can still argue that making this an option is not even 
> worth that, and just always do it unconditional)

agreed.

	Ingo
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