linux-kernel - Re: [PATCH] x86: NX protection for kernel data

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Date:	Sun, 19 Jul 2009 20:15:07 -0400
From:	Siarhei Liakh <sliakh.lkml@...il.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ingo Molnar <mingo@...e.hu>, 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@...s.com,
	Roland Dreier <rdreier@...co.com>
Subject: Re: [PATCH] x86: NX protection for kernel data

On Sun, Jul 19, 2009 at 4:18 PM, Arjan van de Ven<arjan@...radead.org> wrote:
> On Sun, 19 Jul 2009 15:43:06 -0400
> Siarhei Liakh <sliakh.lkml@...il.com> wrote:
>
>> This patch expands functionality of CONFIG_DEBUG_RODATA to set main
>> (static) kernel data area as NX.
>> The following steps are taken to achieve this:
>> 1. Linker scripts are adjusted so .text always starts and end on a
>> page boundary 2. Linker scripts are adjusted so .rodata and .data
>> always starts and end on a page boundary
>> 3. void mark_nxdata_nx(void) added to arch/x86/mm/init_64.c and
>> arch/x86/mm/init_32.c with actual functionality: NX is set for all
>> pages from _etext through _edata
>> 4. mark_nxdata_nx() called from init_post(void) in init/main.c
>>
>> The patch have been developed for Linux 2.6.30 x86 by Siarhei Liakh
>> <sliakh.lkml@...il.com> and Xuxian Jiang <jiang@...ncsu.edu>.
>
> I like the idea, and am happy to see the lack of ifdefs ;)

I was thinking about ifdefs, but could not find a place to put them in ;)

> I wonder if we should have a testcase for this though similar to
> how stackprotector and rodata get tested already....

We probably should. In addition, after looking at the code for a
while, it seems to me that the proper place to enable protection would
be kernel_physical_mapping_init(). This way the kernel could enjoy
protection from the very beginning of init, instead of turning it on
at the end.
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