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

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Message-ID: <20090719201330.GA3186@merkur.ravnborg.org>
Date:	Sun, 19 Jul 2009 22:13:30 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Siarhei Liakh <sliakh.lkml@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Arjan van de Ven <arjan@...radead.org>,
	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 03:43:06PM -0400, Siarhei Liakh 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>.


The patch no longer applies.
The file vmlinux_32.lds.S and vmlinux_64.lds.S has been unified
into one file.


> --- a/arch/x86/kernel/vmlinux_32.lds.S
> +++ b/arch/x86/kernel/vmlinux_32.lds.S
> @@ -47,6 +47,7 @@ SECTIONS
>  	IRQENTRY_TEXT
>  	*(.fixup)
>  	*(.gnu.warning)
> +  	. = ALIGN(PAGE_SIZE);	/* .text should occupy whole number of pages */
>    	_etext = .;			/* End of text section */

So _etext cover until page boundary - makes sense.

>    } :text = 0x9090
> 
> @@ -93,6 +94,7 @@ SECTIONS
>  	*(.data.read_mostly)
>  	_edata = .;		/* End of data section */
>    }
> +  . = ALIGN(PAGE_SIZE);		/* needed so we can set NX for .data */

But here _edata does not cover until page boundary.
And alignmnet is located outside the output section
definition.
It would be better/more consistent to follow the style you use for .text here.


	Sam
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