linux-kernel - Re: [RFC PATCH v2 6/6] x86/entry/pti: don't switch PGD on when pti

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Date:   Thu, 11 Jan 2018 20:11:30 +0100
From:   Willy Tarreau <w@....eu>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [RFC PATCH v2 6/6] x86/entry/pti: don't switch PGD on when
 pti_disable is set

On Thu, Jan 11, 2018 at 10:38:07AM -0800, Dave Hansen wrote:
> On 01/11/2018 10:32 AM, Josh Poimboeuf wrote:
> >> hmm. Exposing cr3 to user space will make it trivial for user process
> >> to know whether kpti is active. Not sure how exploitable such
> >> information leak.
> > It's already trivial to detect PTI from user space.
> 
> Do tell.

Probably because meltdown doesn't work anymore ? :-)

Willy