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

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Message-ID: <20180109213227.GA13282@1wt.eu>
Date:   Tue, 9 Jan 2018 22:32:27 +0100
From:   Willy Tarreau <w@....eu>
To:     Borislav Petkov <bp@...en8.de>
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 Tue, Jan 09, 2018 at 10:29:40PM +0100, Borislav Petkov wrote:
> On Tue, Jan 09, 2018 at 01:26:57PM -0800, Andy Lutomirski 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.
> 
> Uhh, I like that.
> 
> Maybe also taint the kernel ...

Requiring a reboot just to fix a performance problem you've discovered
the hard way is not the most friendly way to help users I'm afraid.
However, definitely +1 on tainting!

Willy