linux-kernel - Re: [PATCH 0/2] mm: introduce MAP_FIXED

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Date:   Wed, 6 Dec 2017 16:19:52 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Michal Hocko <mhocko@...nel.org>,
        Michael Kerrisk <mtk.manpages@...il.com>
Cc:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
        Michael Ellerman <mpe@...erman.id.au>,
        Linux API <linux-api@...r.kernel.org>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Florian Weimer <fweimer@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Abdul Haleem <abdhalee@...ux.vnet.ibm.com>,
        Joel Stanley <joel@....id.au>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH 0/2] mm: introduce MAP_FIXED_SAFE

On Wed, Dec 6, 2017 at 1:08 AM, Michal Hocko <mhocko@...nel.org> wrote:
> On Wed 06-12-17 08:33:37, Rasmus Villemoes wrote:
>> On 2017-12-06 05:50, Michael Ellerman wrote:
>> > Michal Hocko <mhocko@...nel.org> writes:
>> >
>> >> On Wed 29-11-17 14:25:36, Kees Cook wrote:
>> >> It is safe in a sense it doesn't perform any address space dangerous
>> >> operations. mmap is _inherently_ about the address space so the context
>> >> should be kind of clear.
>> >
>> > So now you have to define what "dangerous" means.
>> >
>> >>> MAP_FIXED_UNIQUE
>> >>> MAP_FIXED_ONCE
>> >>> MAP_FIXED_FRESH
>> >>
>> >> Well, I can open a poll for the best name, but none of those you are
>> >> proposing sound much better to me. Yeah, naming sucks...
>>
>> I also don't like the _SAFE name - MAP_FIXED in itself isn't unsafe [1],
>> but I do agree that having a way to avoid clobbering (parts of) an
>> existing mapping is quite useful. Since we're bikeshedding names, how
>> about MAP_FIXED_EXCL, in analogy with the O_ flag.
>
> I really give up on the name discussion. I will take whatever the
> majority comes up with. I just do not want this (useful) funtionality
> get bikeched to death.

Yup, I really want this to land too. What do people think of Matthew
Wilcox's MAP_REQUIRED ? MAP_EXACT isn't exact, and dropping "FIXED"
out of the middle seems sensible to me.

MIchael, any suggestions with your API hat on?

-Kees

-- 
Kees Cook
Pixel Security