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Date: Wed, 29 Mar 2017 13:45:32 -0700
From: "H. Peter Anvin" <>
To: Kees Cook <>,
Cc: Rik van Riel <>, Andy Lutomirski <>,
        Thomas Gleixner <>, Ingo Molnar <>,, Paolo Bonzini <>,
        Radim Krčmář <>,
        Peter Zijlstra <>,
        Dave Hansen <>,
        Yu-cheng Yu <>,
        Masahiro Yamada <>,
        Borislav Petkov
        Christian Borntraeger <>,
        Thomas Garnier <>, Brian Gerst <>,
        He Chen <>,
        Mathias Krause <>,
        Fenghua Yu <>, Piotr Luc <>,
        Kyle Huey <>, Len Brown <>,,
Subject: Re: [PATCH] x86/fpu: move FPU state into separate cache

On 03/29/17 13:39, Kees Cook wrote:
> This removes ARCH_WANTS_DYNAMIC_TASK_STRUCT from x86, leaving only s390
> still defining this config.
> In order to support future structure layout randomization of the
> task_struct, none of the structure fields are allowed to have a specific
> position or dynamic size. To enable randomization of task_struct on
> x86, the FPU state must be moved to its own dynamically sized cache,
> and dereferenced from the task_struct.
> This change is nearly identical to what was done in grsecurity to support
> structure layout randomization. Hopefully I found all the needed changes.
> This passes allyesconfig, and boot tests.

Is this really what we want to happen?  It seems much more sane to
simply make them adjacent; they don't need to be part of the same
structure (in practice, there are three objects: thread_info,
task_struct, and the FPU state.)


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