GNU bug report logs - #11398
24.0.95; Segfault in unexec on Linux 3.3* with grsecurity/PaX

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Stefan Kangas <stefan <at> marxist.se>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#11398: closed (24.0.95; Segfault in unexec on Linux 3.3* with
 grsecurity/PaX)
Date: Wed, 28 Aug 2019 14:28:02 +0000

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Your message dated Wed, 28 Aug 2019 16:27:19 +0200
with message-id <CADwFkmmzedPEtizCXkKx-wYggOrfAKRuM0sp8U8d9aQ=B5UP2Q <at> mail.gmail.com>
and subject line Re: bug#11398: 24.0.95; Segfault in unexec on Linux 3.3* with grsecurity/PaX
has caused the debbugs.gnu.org bug report #11398,
regarding 24.0.95; Segfault in unexec on Linux 3.3* with grsecurity/PaX
to be marked as done.

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11398: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=11398
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From: Ulrich Mueller <ulm <at> gentoo.org>
To: bug-gnu-emacs <at> gnu.org
Cc: Jan Djärv <jan.h.d <at> swipnet.se>
Subject: 24.0.95; Segfault in unexec on Linux 3.3* with grsecurity/PaX
Date: Thu, 3 May 2012 11:12:00 +0200

Forwarding downstream bug <https://bugs.gentoo.org/411439>.

Emacs 23.4 and 24.0.95 both fail to build on a Gentoo system with a
sys-kernel/hardened-sources-3.3* kernel, i.e. Linux 3.3* with the
grsecurity/PaX patches from <http://grsecurity.net/>
(e.g., grsecurity-2.9-3.3.4-201204272006.patch).

   Dumping under the name emacs
   **************************************************
   Warning: Your system has a gap between BSS and the
   heap (15045480 bytes).  This usually means that exec-shield
   or something similar is in effect.  The dump may
   fail because of this.  See the section about
   exec-shield in etc/PROBLEMS for more information.
   **************************************************
   make[1]: *** [bootstrap-emacs] Segmentation fault
   make[1]: Leaving directory `/var/tmp/portage/app-editors/emacs-23.4-r1/work/emacs-23.4/src'
   make: *** [src] Error 2

Since it still could be successfully built with hardened-sources-3.2*,
we had first reported this problem to grsecurity/PaX upstream.
However, they claim that it is due to a bug in Emacs' unexec code.

Quoting from <https://bugs.gentoo.org/show_bug.cgi?id=411439#c13> and
following comments:

| i've debugged the problem and it's a bug in emacs. it wants to create
| a memory dump of its address space without actually looking at what
| memory ranges are available with what access rights. due to recentish
| changes in PaX the gap between the end of the main executable's data
| section and the start of the brk heap is mapped with PROT_NONE rights,
| so no access is allowed and this is where emacs fails.

| ADDR_NO_RANDOMIZE was added as a workaround to fix userland bugs
| like what emacs has (the first bug is about assuming a particular
| address space layout that no standard has ever guaranteed, the
| second bug is that emacs doesn't use the kernel provided interface
| to discover its own address space layout).

| [...] fundamentally a bug in emacs's memory dumper code, the proper
| fix should be in there.

Could GNU Emacs upstream comment on this, please?

Ulrich

[Message part 3 (message/rfc822, inline)]

From: Stefan Kangas <stefan <at> marxist.se>
To: Ulrich Mueller <ulm <at> gentoo.org>
Cc: Jan Djärv <jan.h.d <at> swipnet.se>, 11398-done <at> debbugs.gnu.org
Subject: Re: bug#11398: 24.0.95;
 Segfault in unexec on Linux 3.3* with grsecurity/PaX
Date: Wed, 28 Aug 2019 16:27:19 +0200

Ulrich Mueller <ulm <at> gentoo.org> writes:

> I'd suggest to close this bug. If there are similar problems with the
> portable dumper, it may be cleaner to open a fresh bug for them.

Thanks; closing.

Best regards,
Stefan Kangas

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