linux-kernel - Re: [patch 05/16] mm: Allow special mappings with user access cleared

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Message-ID: <CA+55aFxjxm3qTaH2cw4o8eOxUjh0AcPW5U6mDc1SS3uRUBFGGA@mail.gmail.com>
Date:   Wed, 13 Dec 2017 10:23:59 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Borislav Petkov <bpetkov@...e.de>,
        Greg KH <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        David Laight <David.Laight@...lab.com>,
        Eduardo Valentin <eduval@...zon.com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        Will Deacon <will.deacon@....com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Aneesh Kumar K. V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [patch 05/16] mm: Allow special mappings with user access cleared

On Wed, Dec 13, 2017 at 10:21 AM, Dave Hansen <dave.hansen@...el.com> wrote:
> On 12/13/2017 10:08 AM, Linus Torvalds wrote:
>> On Wed, Dec 13, 2017 at 7:54 AM, Peter Zijlstr <peterz@...radead.org> wrote:
>>> Which is why get_user_pages() _should_ enforce this.
>>>
>>> What use are protection keys if you can trivially circumvent them?
>> No, we will *not* worry about protection keys in get_user_pages().
>
> We did introduce some support for it here:
>
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=33a709b25a760b91184bb335cf7d7c32b8123013

Ugh. I never realized.

We should revert that, I feel. It's literally extra complexity for no
actual real gain, and there is a real downside: the extra complexity
that will cause people to get things wrong.

This thread about us getting it wrong is just the proof. I vote for
not trying to "fix" this case, let's just remove it.

                  Linus