linux-kernel - Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location

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Message-ID: <CAJcbSZGwqMgr79SndxHBVsyPZvefGRRR+bHembgHPXny8k506w@mail.gmail.com>
Date:   Thu, 5 Jan 2017 11:00:20 -0800
From:   Thomas Garnier <thgarnie@...gle.com>
To:     Arjan van de Ven <arjan@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        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>,
        Andy Lutomirski <luto@...nel.org>, 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>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC] x86/mm/KASLR: Remap GDTs at fixed location

On Thu, Jan 5, 2017 at 10:56 AM, Arjan van de Ven <arjan@...ux.intel.com> wrote:
> On 1/5/2017 8:40 AM, Thomas Garnier wrote:
>>
>> Well, it happens only when KASLR memory randomization is enabled. Do
>> you think it should have a separate config option?
>
>
> no I would want it a runtime option.... "sgdt from ring 3" is going away
> with UMIP (and is already possibly gone in virtual machines, see
> https://lwn.net/Articles/694385/) and for those cases it would be a shame
> to lose the randomization
>

That's correct. When UMIP is enabled, we should disable fixed location
for both GDT and IDT. Glad to do that when UMIP support is added.

-- 
Thomas