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Date:	Tue, 10 Nov 2009 12:25:39 -0800
From:	"H. Peter Anvin" <>
To:	Kees Cook <>
CC:	Arjan van de Ven <>,
	Thomas Gleixner <>,
	Ingo Molnar <>,,
	Pekka Enberg <>,
	Jan Beulich <>,
	Vegard Nossum <>,
	Yinghai Lu <>,
	Jeremy Fitzhardinge <>,
Subject: Re: [PATCH v4] [x86] detect and report lack of NX protections

The more I stare at the underlying code, the more I'm convinced that the
fundamental problem is that the underlying code is insane, with multiple
levels of detection for what amounts to cpu_has_nx, each effectively
checking what the previous code has done.

check_efer(), for example, screws with EFER, but EFER is simply set in
head_64.S from CPUID (unless Xen does something insane -- but if so, Xen
should clear X86_FEATURE_NX instead.)

The 32-bit startup code also sets NX, but yet on 32 bits we wiggle EFER
as if it had never been.  This code is screaming for cleanup and


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