From: Rusty Russell <rusty@rustcorp.com.au>
To: Andi Kleen <andi@firstfloor.org>
Subject: Re: [PATCH v8] RO/NX protection for loadable kernel modules
Date: Mon, 8 Feb 2010 12:15:31 +1030
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Cc: Siarhei Liakh <sliakh.lkml@gmail.com>, linux-kernel@vger.kernel.org,
       linux-security-module@vger.kernel.org, linux-next@vger.kernel.org,
       Arjan van de Ven <arjan@infradead.org>,
       James Morris <jmorris@namei.org>,
       Andrew Morton <akpm@linux-foundation.org>, Andi Kleen <ak@muc.de>,
       Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
       Ingo Molnar <mingo@elte.hu>, Stephen Rothwell <sfr@canb.auug.org.au>,
       Dave Jones <davej@redhat.com>
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In-Reply-To: <873a1jdyrg.fsf@basil.nowhere.org>
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On Wed, 3 Feb 2010 09:35:39 am Andi Kleen wrote:
> Siarhei Liakh <sliakh.lkml@gmail.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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