linux-kernel - Re: [PATCH v8] RO/NX protection for loadable kernel modules

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Date:	Mon, 8 Feb 2010 12:15:31 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Siarhei Liakh <sliakh.lkml@...il.com>,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-next@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.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>, Ingo Molnar <mingo@...e.hu>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Dave Jones <davej@...hat.com>
Subject: Re: [PATCH v8] RO/NX protection for loadable kernel modules

On Wed, 3 Feb 2010 09:35:39 am Andi Kleen wrote:
> Siarhei Liakh <sliakh.lkml@...il.com> writes:
> 
> > 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:
> 
> My current kernel has 52 modules loaded, most of them very small. 
> Assuming the additional alignment of the data section cost two more
> pages on average (I think that's a good assumption), that's roughly
> 424KB of additional memory, plus associated runtime costs in increased
> TLB usage.
> 
> What would I get for that if I applied the patch and enabled the option? 

Strict RO/NX protection.  But without the option enabled, the patch gives
best-effort protection, which is nice (for no additional space).

Cheers,
Rusty.
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