linux-kernel - Re: [PATCH] x86/mm/pti: Move user W+X check into pti

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Date:   Thu, 9 Aug 2018 13:26:35 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Kees Cook <keescook@...gle.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        Anthony Liguori <aliguori@...zon.com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        Hugh Dickins <hughd@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, Pavel Machek <pavel@....cz>,
        "David H . Gutteridge" <dhgutteridge@...patico.ca>
Subject: Re: [PATCH] x86/mm/pti: Move user W+X check into pti_finalize()

Hi Kees,

On Wed, Aug 08, 2018 at 01:33:01PM -0700, Kees Cook wrote:
> I'm slightly nervous about complicating this and splitting up the
> check. I have a mild preference that all the checks get moved later,
> so that all architectures have the checks happening at the same time
> during boot. Splitting this up could give us some weird differences
> between architectures, etc.

As fas as I can see the checks are implemented on x86, arm, and arm64. I
agree that it would be better to run the checks at a unified place
across architectures and can send a patch-set for set once the dust
around the 32-bit PTI implementation for x86 has settled.

But currently the call-places are architecture specific and with that in
mind the split-up on x86 is the right thing to do. I'll change that back
when I implement your idea above.

Regards,

	Joerg