Message-ID: <4AF9991B.20400@zytor.com>
Date: Tue, 10 Nov 2009 08:47:23 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Kees Cook <kees.cook@canonical.com>
CC: Arjan van de Ven <arjan@infradead.org>,
       Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
       x86@kernel.org, Pekka Enberg <penberg@cs.helsinki.fi>,
       Jan Beulich <jbeulich@novell.com>, Vegard Nossum <vegardno@ifi.uio.no>,
       Yinghai Lu <yinghai@kernel.org>,
       Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] [x86] detect and report lack of NX protections
References: <4ADD1E03.4070200@zytor.com> <20091020045513.GU5394@outflux.net> <20091109221015.GB5129@outflux.net> <4AF8A2C0.5080700@zytor.com> <20091110154956.GF5129@outflux.net>
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On 11/10/2009 07:49 AM, Kees Cook wrote:
>>
>> The second clause can only get executed if CONFIG_X86_PAE is unset,
>> which in turn means _PAGE_NX == 0... so that piece of code is meaningless.
> 
> CONFIG_X86_PAE is unset for x86_64, where _PAGE_NX is valid.  (This was
> the main situation I was trying to address.)  So that chunk runs for
> non-pae 32bit, and all 64bit:
> 

In reality, X86_PAE really should have been defined for 64 bits, since
64 bits really is PAE in most aspects.

Anyway, for the 64-bit case it looks like the proper place for any of
this is in check_efer() just below, not in this null routine.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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