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From: Florian Weimer <fweimer@redhat.com>
To: ebiederm@xmission.com (Eric W. Biederman)
Cc: "Andy Lutomirski" <luto@kernel.org>,
	"David Hildenbrand" <david@redhat.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
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Subject: Re: [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE
Date: Thu, 12 Aug 2021 20:15:40 +0200	[thread overview]
Message-ID: <87lf56edgz.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <87lf56bllc.fsf@disp2133> (Eric W. Biederman's message of "Thu, 12 Aug 2021 12:48:31 -0500")

* Eric W. Biederman:

> Given that MAP_PRIVATE for shared libraries is our strategy for handling
> writes to shared libraries perhaps we just need to use MAP_POPULATE or a
> new related flag (perhaps MAP_PRIVATE_NOW) that just makes certain that
> everything mapped from the executable is guaranteed to be visible from
> the time of the mmap, and any changes from the filesystem side after
> that are guaranteed to cause a copy on write.

I think this is called MAP_COPY:

  <https://www.gnu.org/software/hurd/glibc/mmap.html>

If we could get that functionality, we would certainly use it in the
glibc dynamic loader.  And it's not just dynamic loaders that would
benefit.

But I assume there are some rather thorny issues around semantics.  If
the changed areas of the file are in the page cache already, everything
is okay.  But if parts of the file are changed or discarded that are
not, they would have to be read in first, which is rather awkward.

That's why I suggested the signal for all future accesses.  It seems
more tractable and addresses the largest issue (the difficulty of
figuring out why some processes crash occasionally).

Thanks,
Florian


  parent reply	other threads:[~2021-08-12 18:16 UTC|newest]

Thread overview: 86+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-12  8:43 [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE David Hildenbrand
2021-08-12  8:43 ` [PATCH v1 1/7] binfmt: don't use MAP_DENYWRITE when loading shared libraries via uselib() David Hildenbrand
2021-08-12  8:43 ` [PATCH v1 2/7] kernel/fork: factor out atomcially replacing the current MM exe_file David Hildenbrand
2021-08-12  9:17   ` Christian Brauner
2021-08-12  8:43 ` [PATCH v1 3/7] kernel/fork: always deny write access to " David Hildenbrand
2021-08-12 10:05   ` Christian Brauner
2021-08-12 10:13     ` David Hildenbrand
2021-08-12 12:32       ` Christian Brauner
2021-08-12 12:38         ` David Hildenbrand
2021-08-12 16:51   ` Linus Torvalds
2021-08-12 19:38     ` David Hildenbrand
2021-08-12  8:43 ` [PATCH v1 4/7] binfmt: remove in-tree usage of MAP_DENYWRITE David Hildenbrand
2021-08-12  8:43 ` [PATCH v1 5/7] mm: remove VM_DENYWRITE David Hildenbrand
2021-08-12  8:43 ` [PATCH v1 6/7] mm: ignore MAP_DENYWRITE in ksys_mmap_pgoff() David Hildenbrand
2021-08-12  8:43 ` [PATCH v1 7/7] fs: update documentation of get_write_access() and friends David Hildenbrand
2021-08-12 12:20 ` [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE Florian Weimer
2021-08-12 12:47   ` David Hildenbrand
2021-08-12 16:17   ` Eric W. Biederman
2021-08-12 17:32 ` Eric W. Biederman
2021-08-12 17:35   ` Andy Lutomirski
2021-08-12 17:48     ` Eric W. Biederman
2021-08-12 18:01       ` Andy Lutomirski
2021-08-12 18:10       ` Linus Torvalds
2021-08-12 18:47         ` Eric W. Biederman
2021-08-13  9:05           ` David Laight
2021-08-13 20:17             ` Eric W. Biederman
2021-08-13 20:51               ` Florian Weimer
2021-08-14  0:31               ` Linus Torvalds
2021-08-14  0:49                 ` Andy Lutomirski
2021-08-14  0:54                   ` Linus Torvalds
2021-08-14  0:58                     ` Linus Torvalds
2021-08-14  1:57                       ` Al Viro
2021-08-14  2:02                         ` Al Viro
2021-08-14  9:06                           ` David Hildenbrand
2021-08-14  7:53                         ` Christian Brauner
2021-08-14 19:52                     ` David Laight
2021-08-26 17:48                     ` Andy Lutomirski
2021-08-26 21:47                       ` David Hildenbrand
2021-08-26 22:13                         ` Eric W. Biederman
2021-08-27  8:22                           ` David Laight
2021-08-27 15:58                             ` Eric W. Biederman
2021-09-01  8:28                           ` David Hildenbrand
2021-08-27 10:18                         ` Christian Brauner
2021-08-14  3:04                   ` Matthew Wilcox
2021-08-17 16:48                     ` Removing Mandatory Locks Eric W. Biederman
2021-08-17 16:50                       ` David Hildenbrand
2021-08-18  9:34                       ` Rodrigo Campos
2021-08-19 19:18                         ` Jeff Layton
2021-08-19 20:03                           ` Willy Tarreau
2021-08-19 18:39                       ` Jeff Layton
2021-08-19 19:15                         ` Linus Torvalds
2021-08-19 19:55                           ` Eric Biggers
2021-08-19 20:18                           ` Jeff Layton
2021-08-19 20:31                             ` Linus Torvalds
2021-08-19 21:43                               ` Jeff Layton
2021-08-19 22:32                                 ` Linus Torvalds
2021-08-20  8:30                                   ` David Laight
2021-08-23  7:55                                     ` Geert Uytterhoeven
2021-08-23  8:14                                       ` David Laight
2021-08-20 13:43                                   ` Steven Rostedt
2021-08-20 16:06                                     ` Linus Torvalds
2021-08-20  2:10                               ` Matthew Wilcox
2021-08-20  6:36                               ` Amir Goldstein
2021-08-20  7:14                                 ` Amir Goldstein
2021-08-20 12:27                                   ` Jeff Layton
2021-08-20 12:38                                     ` Willy Tarreau
2021-08-20 13:03                                       ` Jeff Layton
2021-08-20 13:11                                         ` Willy Tarreau
2021-08-20 16:30                           ` Kees Cook
2021-08-20 19:17                             ` H. Peter Anvin
2021-08-20 21:29                               ` Jeff Layton
2021-08-20 21:29                                 ` Jeff Layton
2021-08-21 12:45                                 ` Jeff Layton
2021-08-21 12:45                                   ` Jeff Layton
2021-08-23 22:15                                   ` J. Bruce Fields
2021-08-20 22:31                               ` Matthew Wilcox
2021-08-18  7:51                     ` [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE Christian Brauner
2021-08-18 15:42                   ` J. Bruce Fields
2021-08-19 13:56                     ` Eric W. Biederman
2021-08-19 14:33                       ` J. Bruce Fields
2021-08-20 12:54                         ` Jeff Layton
2021-08-20  3:44                     ` NeilBrown
2021-08-20  8:25                       ` David Laight
2021-08-12 19:24         ` David Hildenbrand
2021-08-12 18:15       ` Florian Weimer [this message]
2021-08-12 18:21         ` Linus Torvalds

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