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Date: Thu, 5 Jan 2017 15:05:34 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Andy Lutomirski <luto@...nel.org>
Cc: Thomas Garnier <thgarnie@...gle.com>, Arjan van de Ven <arjan@...ux.intel.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, 
	Kees Cook <keescook@...omium.org>, Borislav Petkov <bp@...en8.de>, Dave Hansen <dave@...1.net>, 
	Chen Yucong <slaoub@...il.com>, Paul Gortmaker <paul.gortmaker@...driver.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Masahiro Yamada <yamada.masahiro@...ionext.com>, 
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Anna-Maria Gleixner <anna-maria@...utronix.de>, 
	Boris Ostrovsky <boris.ostrovsky@...cle.com>, Rasmus Villemoes <linux@...musvillemoes.dk>, 
	Michael Ellerman <mpe@...erman.id.au>, Juergen Gross <jgross@...e.com>, 
	Richard Weinberger <richard@....at>, X86 ML <x86@...nel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location

On Thu, Jan 5, 2017 at 12:18 PM, Andy Lutomirski <luto@...nel.org> wrote:
>
> Hmm.  I bet that if we preset the accessed bits in all the segments
> then we don't need it to be writable in general.

I'm not sure that this is architecturally safe.

IIRC, we do mark the IDT read-only - but that one we started doing due
to the f00f bug, so we knew it was ok. I'm not sure you can do the
same with the GDT/LDT.

                   Linus

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