linux-kernel - Re: [tip:x86/security] x86: Add NX protection for kernel data

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Date:	Thu, 20 Jan 2011 16:55:56 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	matthieu castet <castet.matthieu@...e.fr>
Cc:	Ian Campbell <Ian.Campbell@...citrix.com>,
	Kees Cook <kees.cook@...onical.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"keir.fraser@...citrix.com" <keir.fraser@...citrix.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"sliakh.lkml@...il.com" <sliakh.lkml@...il.com>,
	"jmorris@...ei.org" <jmorris@...ei.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>,
	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
	"ak@....de" <ak@....de>, "davej@...hat.com" <davej@...hat.com>,
	"jiang@...ncsu.edu" <jiang@...ncsu.edu>,
	"arjan@...radead.org" <arjan@...radead.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
	"mingo@...e.hu" <mingo@...e.hu>,
	Stefan Bader <stefan.bader@...onical.com>
Subject: Re: [tip:x86/security] x86: Add NX protection for kernel data

> -	 * .data and .bss should always be writable.
> +	 * .data and .bss should always be writable, but xen won't like
> +	 * if we make page table rw (that live in .data or .bss)
>  	 */
> +#ifdef CONFIG_X86_32
>  	if (within(address, (unsigned long)_sdata, (unsigned long)_edata) ||
> -	    within(address, (unsigned long)__bss_start, (unsigned long)__bss_stop))
> -		pgprot_val(required) |= _PAGE_RW;
> +	    within(address, (unsigned long)__bss_start, (unsigned long)__bss_stop)) {
> +		unsigned int level;
> +		if (lookup_address(address, &level) && (level != PG_LEVEL_4K))
> +			pgprot_val(forbidden) |= _PAGE_RW;
> +	}
> +#endif
>  
>  #if defined(CONFIG_X86_64) && defined(CONFIG_DEBUG_RODATA)
> 
> fyi, it does make it boot.

Hold it.. ccache is a wonderful tool but I think I've just "rebuilt" the
binaries with the .bss HPAGE_ALIGN aligment by mistake, so this path got never
taken.
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