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

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Date:   Wed, 13 Dec 2017 10:31:17 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...el.com>,
        "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 10:08 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Wed, Dec 13, 2017 at 7:54 AM, Peter Zijlstra <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().
>

Hmm.  If I goof some pointer and pass that bogus pointer to read(2),
and I'm using pkey to protect my mmapped database, I think i'd rather
that read(2) fail.  Sure, pkey is trivially circumventable using
wrpkru or mprotect, but those are obvious dangerous functions.