Message-ID: <4AF9B6AD.8020505@zytor.com>
Date: Tue, 10 Nov 2009 10:53:33 -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> <4AF9991B.20400@zytor.com> <20091110165738.GH5129@outflux.net> <4AF99F0C.2050806@zytor.com> <20091110174622.GK5129@outflux.net>
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On 11/10/2009 09:46 AM, Kees Cook wrote:
> 
> The kernel as-is does not set nx_enabled for 64-bit, so this message is
> skipped completely:
> 
>         if (nx_enabled)
>                 printk(KERN_INFO "NX (Execute Disable) protection: active\n");
> 
> The only time this printk is shown is on 32-bit with PAE (with NX).
> There is no "else" currently.
> 

The structure you have is:

	if (nx_enabled)
	else if (cpu_has_pae)

The test for cpu_has_pae is unconditional (you only #ifdef the message)
-- in fact, this should cause a compile-time error on 64 bits:

#undef  cpu_has_pae
#define cpu_has_pae             ___BUG___

	-hpa
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