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

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Date:	Tue, 23 Jun 2009 12:00:40 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	James Morris <jmorris@...ei.org>
Cc:	Siarhei Liakh <sliakh.lkml@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.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] RO/NX protection for loadable kernel modules


* James Morris <jmorris@...ei.org> wrote:

> On Thu, 18 Jun 2009, Siarhei Liakh 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 looks potentially useful to me, but I'm not an x86 expert 
> (several now added to Cc:).

Pinged a few folks about this already. It looks useful, with the 
main worry being:

 1) the increase in effective module size (probably worth the price)
 2) some uglies in the patch (fixable)

The main ugliness is the excessive use of #ifdefs - those should be 
eliminated. Also, most scripts/checkpatch.pl warnings about this 
patch should be taken seriously.

	Ingo
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