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

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Message-ID: <CAGXu5jK5Qd2kQ68h58ThUzJ2t+Tvy754qZuiOWHqLDu0A62eww@mail.gmail.com>
Date:   Tue, 9 Jan 2018 13:34:07 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Willy Tarreau <w@....eu>, Borislav Petkov <bp@...en8.de>,
        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>
Subject: Re: [RFC PATCH v2 2/6] x86/arch_prctl: add ARCH_GET_NOPTI and
 ARCH_SET_NOPTI to enable/disable PTI

On Tue, Jan 9, 2018 at 1:26 PM, Andy Lutomirski <luto@...nel.org> wrote:
> 2.Turning off PTI is, in general, a terrible idea.  It totally breaks
> any semblance of a security model on a Meltdown-affected CPU.  So I
> think we should require CAP_SYS_RAWIO *and* that the system is booted
> with pti=allow_optout or something like that.

Agreed, this shouldn't be default-available. Besides, your most
trusted processes are the ones most likely to be targeted for attack.
:(

-Kees

-- 
Kees Cook
Pixel Security