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From: Andy Lutomirski <luto@kernel.org>
Date: Wed, 13 Dec 2017 10:31:17 -0800
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Subject: Re: [patch 05/16] mm: Allow special mappings with user access cleared
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
        Dave Hansen <dave.hansen@intel.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
        Borislav Petkov <bpetkov@suse.de>,
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        Juergen Gross <jgross@suse.com>,
        David Laight <David.Laight@aculab.com>,
        Eduardo Valentin <eduval@amazon.com>,
        "Liguori, Anthony" <aliguori@amazon.com>,
        Will Deacon <will.deacon@arm.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        "Aneesh Kumar K. V" <aneesh.kumar@linux.vnet.ibm.com>
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On Wed, Dec 13, 2017 at 10:08 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Wed, Dec 13, 2017 at 7:54 AM, Peter Zijlstra <peterz@infradead.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.