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Date: Wed, 29 Mar 2017 14:35:16 -0700
From: Andy Lutomirski <luto@...capital.net>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Kees Cook <keescook@...omium.org>, "H. Peter Anvin" <hpa@...or.com>, 
	LKML <linux-kernel@...r.kernel.org>, Rik van Riel <riel@...hat.com>, 
	Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	"x86@...nel.org" <x86@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>, 
	Radim Krčmář <rkrcmar@...hat.com>, 
	Peter Zijlstra <peterz@...radead.org>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Yu-cheng Yu <yu-cheng.yu@...el.com>, Masahiro Yamada <yamada.masahiro@...ionext.com>, 
	Borislav Petkov <bp@...e.de>, Christian Borntraeger <borntraeger@...ibm.com>, 
	Thomas Garnier <thgarnie@...gle.com>, Brian Gerst <brgerst@...il.com>, 
	He Chen <he.chen@...ux.intel.com>, Mathias Krause <minipli@...glemail.com>, 
	Fenghua Yu <fenghua.yu@...el.com>, Piotr Luc <piotr.luc@...el.com>, Kyle Huey <me@...ehuey.com>, 
	Len Brown <len.brown@...el.com>, KVM <kvm@...r.kernel.org>, 
	"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH] x86/fpu: move FPU state into separate cache

On Wed, Mar 29, 2017 at 2:30 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Wed, Mar 29, 2017 at 2:09 PM, Kees Cook <keescook@...omium.org> wrote:
>>
>> They're adjacent already, which poses a problem for the struct layout
>> randomization plugin, since adjacency may no longer be true (after
>> layout randomization). T
>
> What?
>
> The layout randomization can't change anything, if you just make the
> adjacency be done explicitly instead of by having the thing be a fixed
> member.
>
> The trivial model might be to just declare the fpu part as an unsized
> array at the end:
>
>         /* Floating point and extended processor state */
>         struct fpu              fpu[];
>
> because there is no way in hell that any randomization code can move
> those kinds of unsized arrays around. If it does, the gcc plugin is
> such unbelievable garbage that it would be insane to depend on such
> shit in the first place.
>

Randomization also needs to leave thread_info at the beginning.  Can it do that?

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