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Date: Thu, 5 Jan 2017 15:16:05 -0800
From: Thomas Garnier <>
To: Linus Torvalds <>
Cc: Andy Lutomirski <>, Arjan van de Ven <>, 
	Thomas Gleixner <>, Ingo Molnar <>, "H . Peter Anvin" <>, 
	Kees Cook <>, Borislav Petkov <>, Dave Hansen <>, 
	Chen Yucong <>, Paul Gortmaker <>, 
	Andrew Morton <>, Masahiro Yamada <>, 
	Sebastian Andrzej Siewior <>, Anna-Maria Gleixner <>, 
	Boris Ostrovsky <>, Rasmus Villemoes <>, 
	Michael Ellerman <>, Juergen Gross <>, 
	Richard Weinberger <>, X86 ML <>, 
	"" <>, 
	"" <>
Subject: Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location

On Thu, Jan 5, 2017 at 3:05 PM, Linus Torvalds
<> wrote:
> On Thu, Jan 5, 2017 at 12:18 PM, Andy Lutomirski <> 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.

I started testing a variant that make the GDT remapping read-only by
default and writeable only for LTR. Everything works fine, even
hibernation. I need to do more testing though on different

To be on the safe side, I could separate the read-only part in a
separate patch so we can easily remove it if extended testing show

>                    Linus


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