linux-kernel - for tip-bugfix? Re: [PATCH] NX protection for kernel data : fix xen boot

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Date:	Wed, 2 Feb 2011 15:55:04 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	hpa@...or.com, tglx@...utronix.de, x86@...nel.org
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	linux-security-module@...r.kernel.org,
	Ian Campbell <Ian.Campbell@...citrix.com>,
	Kees Cook <kees.cook@...onical.com>,
	matthieu castet <castet.matthieu@...e.fr>
Subject: for tip-bugfix? Re: [PATCH] NX protection for kernel data : fix
 xen boot

On Thu, Jan 27, 2011 at 11:09:23PM +0100, matthieu castet wrote:
> I think it should be applied before 2.6.38 release, because without
> this patch xen doesn't boot on x86_32 with CONFIG_DEBUG_RODATA.
> 
Hey tglx + hpa,

The title is a bit wrong, the issue here is not with the NX bit
but with setting RW on RO areas in the .bss area.

I was wondering if you guys would be OK picking this up in your
"tip-2.6.38-rc4-bug-fix" branch for Linus? I've done the baremetal tests
on this patch (x86, x86_64) and have not found any regressions with it.


> >From 08f54ec4007ab0df231d81ed436632aa7f605feb Mon Sep 17 00:00:00 2001
> From: Matthieu CASTET <castet.matthieu@...e.fr>
> Date: Thu, 20 Jan 2011 21:11:45 +0100
> Subject: [PATCH] NX protection for kernel data : fix xen boot
> 
> Xen want page table pages read only.
> 
> But the initial page table (from head_*.S) live in .data or .bss.
> 
> That was broken by 64edc8ed5ffae999d8d413ba006850e9e34166cb.
> Revert the problematic part as it is only a protection and
> not really needed.
> 
> Signed-off-by: Matthieu CASTET <castet.matthieu@...e.fr>
> Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
>  arch/x86/mm/pageattr.c |    8 --------
>  1 files changed, 0 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> index 2ad6c48..951eb4a 100644
> --- a/arch/x86/mm/pageattr.c
> +++ b/arch/x86/mm/pageattr.c
> @@ -256,7 +256,6 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long address,
>  				   unsigned long pfn)
>  {
>  	pgprot_t forbidden = __pgprot(0);
> -	pgprot_t required = __pgprot(0);
>  
>  	/*
>  	 * The BIOS area between 640k and 1Mb needs to be executable for
> @@ -286,12 +285,6 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long address,
>  	if (within(pfn, __pa((unsigned long)__start_rodata) >> PAGE_SHIFT,
>  		   __pa((unsigned long)__end_rodata) >> PAGE_SHIFT))
>  		pgprot_val(forbidden) |= _PAGE_RW;
> -	/*
> -	 * .data and .bss should always be writable.
> -	 */
> -	if (within(address, (unsigned long)_sdata, (unsigned long)_edata) ||
> -	    within(address, (unsigned long)__bss_start, (unsigned long)__bss_stop))
> -		pgprot_val(required) |= _PAGE_RW;
>  
>  #if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA)
>  	/*
> @@ -331,7 +324,6 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long address,
>  #endif
>  
>  	prot = __pgprot(pgprot_val(prot) & ~pgprot_val(forbidden));
> -	prot = __pgprot(pgprot_val(prot) | pgprot_val(required));
>  
>  	return prot;
>  }
> -- 
> 1.7.2.3
> 

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