linux-kernel - Re: [PATCH] x86/fpu: move FPU state into separate cache

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Message-ID: <94D018AF-07C3-47BE-9C62-4B2923D3E39B@zytor.com>
Date:   Wed, 29 Mar 2017 15:28:58 -0700
From:   hpa@...or.com
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>
CC:     Kees Cook <keescook@...omium.org>,
        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 March 29, 2017 2:41:00 PM PDT, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>On Wed, Mar 29, 2017 at 2:35 PM, Andy Lutomirski <luto@...capital.net>
>wrote:
>>
>> Randomization also needs to leave thread_info at the beginning.  Can
>it do that?
>
>Good point, and good question. No idea if the gcc extension can do,
>but yes, it clearly needs a "you can't move this entry".
>
>I assume it has some such capability already, because it's fairly
>common to have that kind of "beginning of structure if fixed" due to
>unions of structures anyway.
>
>                 Linus

An alternative is to wrap the randomized structure inside a nonrandomized wrapper structure.
-- 
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