linux-kernel - Re: [RFC PATCH v2 2/6] x86/arch_prctl: add ARCH_GET_NOPTI and ARCH_SET

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Date:   Wed, 10 Jan 2018 17:09:22 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Willy Tarreau <w@....eu>
Cc:     Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Kees Cook <keescook@...omium.org>
Subject: Re: [RFC PATCH v2 2/6] x86/arch_prctl: add ARCH_GET_NOPTI and
 ARCH_SET_NOPTI to enable/disable PTI

On Wed, Jan 10, 2018 at 04:39:46PM +0100, Willy Tarreau wrote:
> For production, disabling PTI system-wide when I'm supposed to know what
> performance critical processes should be exempted doesn't appeal me very
> much, especially if it can happen by accident. So in the end I think that
> "pti=off" on the cmdline should be the only way to disable it system-wide
> as it doesn't represent a reasonable production case. Disabling it per
> process should be allowed via a sysctl, which would also be locked disabled
> for safety purposes.

It still might make sense to be able to disable it system-wide without
having to reboot. Imagine a bunch of processes showing performance
regressions and you want to disable PTI completely to rule it out
causing that regression. Then you toggle the master switch.

With the appropriate loud warnings, of course.

Thx.

-- 
Regards/Gruss,
    Boris.

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