From: Florian Weimer <fweimer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
To: Pavel Machek <pavel-+ZI9xUNit7I@public.gmane.org>,
Michael Ellerman <mpe-Gsx/Oe8HsFggBc27wqDAHg@public.gmane.org>
Cc: Matthew Wilcox <willy-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
Kees Cook <keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>,
Cyril Hrubis <chrubis-AlSwsSmVLrQ@public.gmane.org>,
Michal Hocko <mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
Linux API <linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Khalid Aziz <khalid.aziz-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>,
Andrew Morton
<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
Russell King - ARM Linux
<linux-I+IVW8TIWO2tmTQ+vhA3Yw@public.gmane.org>,
Andrea Arcangeli
<aarcange-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
Linux-MM <linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org>,
LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
linux-arch <linux-arch-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
John Hubbard <jhubbard-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>,
Abdul Haleem
<abdhalee-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>,
Joel Stanley <joel-U3u1mxZcP9KHXe+LvDLADg@public.gmane.org>
Subject: Re: [PATCH 0/2] mm: introduce MAP_FIXED_SAFE
Date: Fri, 8 Dec 2017 21:47:21 +0100 [thread overview]
Message-ID: <289f0cc8-9e24-fc38-cb83-4223f9923940@redhat.com> (raw)
In-Reply-To: <20171208142714.GB7793@amd>
On 12/08/2017 03:27 PM, Pavel Machek wrote:
> On Fri 2017-12-08 22:08:07, Michael Ellerman wrote:
>> If we had a time machine, the right set of flags would be:
>>
>> - MAP_FIXED: don't treat addr as a hint, fail if addr is not free
>> - MAP_REPLACE: replace an existing mapping (or force or clobber)
> Actually, if we had a time machine... would we even provide
> MAP_REPLACE functionality?
Probably yes. ELF loading needs to construct a complex set of mappings
from a single file. munmap (to create a hole) followed by mmap would be
racy because another thread could have reused the gap in the meantime.
The only alternative to overriding existing mappings would be mremap
with MREMAP_FIXED, and that doesn't look like an improvement API-wise.
(The glibc dynamic linker uses an mmap call with an increased length to
reserve address space and then loads additional segments with MAP_FIXED
at the offsets specified in the program header.)
Thanks,
Florian
WARNING: multiple messages have this Message-ID (diff)
From: Florian Weimer <fweimer@redhat.com>
To: Pavel Machek <pavel@ucw.cz>, Michael Ellerman <mpe@ellerman.id.au>
Cc: Matthew Wilcox <willy@infradead.org>,
Kees Cook <keescook@chromium.org>, Cyril Hrubis <chrubis@suse.cz>,
Michal Hocko <mhocko@kernel.org>,
Linux API <linux-api@vger.kernel.org>,
Khalid Aziz <khalid.aziz@oracle.com>,
Andrew Morton <akpm@linux-foundation.org>,
Russell King - ARM Linux <linux@armlinux.org.uk>,
Andrea Arcangeli <aarcange@redhat.com>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-arch <linux-arch@vger.kernel.org>,
John Hubbard <jhubbard@nvidia.com>,
Abdul Haleem <abdhalee@linux.vnet.ibm.com>,
Joel Stanley <joel@jms.id.au>
Subject: Re: [PATCH 0/2] mm: introduce MAP_FIXED_SAFE
Date: Fri, 8 Dec 2017 21:47:21 +0100 [thread overview]
Message-ID: <289f0cc8-9e24-fc38-cb83-4223f9923940@redhat.com> (raw)
Message-ID: <20171208204721.wgk_fN7tG5llFr_4YXlppz6twdfJrWfZmlDW8gBYdnM@z> (raw)
In-Reply-To: <20171208142714.GB7793@amd>
On 12/08/2017 03:27 PM, Pavel Machek wrote:
> On Fri 2017-12-08 22:08:07, Michael Ellerman wrote:
>> If we had a time machine, the right set of flags would be:
>>
>> - MAP_FIXED: don't treat addr as a hint, fail if addr is not free
>> - MAP_REPLACE: replace an existing mapping (or force or clobber)
> Actually, if we had a time machine... would we even provide
> MAP_REPLACE functionality?
Probably yes. ELF loading needs to construct a complex set of mappings
from a single file. munmap (to create a hole) followed by mmap would be
racy because another thread could have reused the gap in the meantime.
The only alternative to overriding existing mappings would be mremap
with MREMAP_FIXED, and that doesn't look like an improvement API-wise.
(The glibc dynamic linker uses an mmap call with an increased length to
reserve address space and then loads additional segments with MAP_FIXED
at the offsets specified in the program header.)
Thanks,
Florian
next prev parent reply other threads:[~2017-12-08 20:47 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-29 14:42 [PATCH 0/2] mm: introduce MAP_FIXED_SAFE Michal Hocko
2017-11-29 14:42 ` Michal Hocko
2017-11-29 14:42 ` [PATCH 1/2] " Michal Hocko
2017-11-29 14:42 ` Michal Hocko
2017-12-06 5:15 ` Michael Ellerman
2017-12-06 5:15 ` Michael Ellerman
2017-12-06 9:27 ` Michal Hocko
2017-12-06 9:27 ` Michal Hocko
2017-12-06 10:02 ` Michal Hocko
2017-12-06 10:02 ` Michal Hocko
2017-12-07 12:07 ` Pavel Machek
2017-11-29 14:42 ` [PATCH 2/2] fs, elf: drop MAP_FIXED usage from elf_map Michal Hocko
2017-11-29 14:42 ` Michal Hocko
2017-11-29 17:45 ` Khalid Aziz
2017-11-29 17:45 ` Khalid Aziz
2017-11-29 14:45 ` [PATCH] mmap.2: document new MAP_FIXED_SAFE flag Michal Hocko
2017-11-30 3:16 ` John Hubbard
2017-11-30 3:16 ` John Hubbard
2017-11-30 8:23 ` Michal Hocko
2017-11-30 8:23 ` Michal Hocko
2017-11-30 8:24 ` [PATCH v2] " Michal Hocko
2017-11-30 8:24 ` Michal Hocko
2017-11-30 18:31 ` John Hubbard
2017-11-30 18:39 ` Michal Hocko
2017-11-30 18:39 ` Michal Hocko
2017-11-29 15:13 ` [PATCH 0/2] mm: introduce MAP_FIXED_SAFE Rasmus Villemoes
2017-11-29 15:13 ` Rasmus Villemoes
[not found] ` <b154b794-7a8b-995e-0954-9234b9446b31-rjjw5hvvQKZaa/9Udqfwiw@public.gmane.org>
2017-11-29 15:50 ` Michal Hocko
2017-11-29 15:50 ` Michal Hocko
2017-11-29 22:15 ` Kees Cook
2017-11-29 22:12 ` Kees Cook
2017-11-29 22:12 ` Kees Cook
2017-11-29 22:25 ` Kees Cook
[not found] ` <CAGXu5jLa=b2HhjWXXTQunaZuz11qUhm5aNXHpS26jVqb=G-gfw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-11-30 6:58 ` Michal Hocko
2017-11-30 6:58 ` Michal Hocko
2017-12-01 15:26 ` Cyril Hrubis
2017-12-01 15:26 ` Cyril Hrubis
2017-12-06 4:51 ` Michael Ellerman
2017-12-06 4:51 ` Michael Ellerman
2017-12-06 4:54 ` Matthew Wilcox
2017-12-06 4:54 ` Matthew Wilcox
2017-12-06 7:03 ` Matthew Wilcox
2017-12-06 7:03 ` Matthew Wilcox
2017-12-06 7:33 ` John Hubbard
2017-12-06 7:33 ` John Hubbard
[not found] ` <5f4fc834-274a-b8f1-bda0-5bcddc5902ed-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
2017-12-06 7:35 ` Florian Weimer
2017-12-06 7:35 ` Florian Weimer
2017-12-06 8:06 ` John Hubbard
2017-12-06 8:06 ` John Hubbard
[not found] ` <27ee1755-76d8-f086-5760-9c973b31108a-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
2017-12-06 8:54 ` Florian Weimer
2017-12-06 8:54 ` Florian Weimer
[not found] ` <20171206070355.GA32044-PfSpb0PWhxZc2C7mugBRk2EX/6BAtgUQ@public.gmane.org>
2017-12-07 5:46 ` Michael Ellerman
2017-12-07 5:46 ` Michael Ellerman
2017-12-07 19:14 ` Kees Cook
2017-12-07 19:14 ` Kees Cook
[not found] ` <CAGXu5jLWRQn6EaXEEvdvXr+4gbiJawwp1EaLMfYisHVfMiqgSA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-12-07 19:57 ` Matthew Wilcox
2017-12-07 19:57 ` Matthew Wilcox
2017-12-08 8:33 ` Michal Hocko
[not found] ` <20171208083315.GR20234-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org>
2017-12-08 20:13 ` Kees Cook
2017-12-08 20:13 ` Kees Cook
[not found] ` <CAGXu5j+VupGmKEEHx-uNXw27Xvndu=0ObsBqMwQiaYPyMGD+vw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-12-08 20:57 ` Matthew Wilcox
2017-12-08 20:57 ` Matthew Wilcox
2017-12-08 11:08 ` Michael Ellerman
2017-12-08 11:08 ` Michael Ellerman
2017-12-08 14:27 ` Pavel Machek
2017-12-08 14:27 ` Pavel Machek
2017-12-08 20:31 ` Cyril Hrubis
2017-12-08 20:31 ` Cyril Hrubis
2017-12-08 20:47 ` Florian Weimer [this message]
2017-12-08 20:47 ` Florian Weimer
2017-12-08 14:33 ` David Laight
2017-12-08 14:33 ` David Laight
2017-12-06 4:50 ` Michael Ellerman
2017-12-06 4:50 ` Michael Ellerman
[not found] ` <87zi6we9z2.fsf-W0DJWXSxmBNbyGPkN3NxC2scP1bn1w/D@public.gmane.org>
2017-12-06 7:33 ` Rasmus Villemoes
2017-12-06 7:33 ` Rasmus Villemoes
[not found] ` <a3b3129a-2626-a65e-59b0-68aada523723-rjjw5hvvQKZaa/9Udqfwiw@public.gmane.org>
2017-12-06 9:08 ` Michal Hocko
2017-12-06 9:08 ` Michal Hocko
2017-12-07 0:19 ` Kees Cook
2017-12-07 0:19 ` Kees Cook
2017-12-07 1:08 ` John Hubbard
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