unofficial mirror of libc-alpha@sourceware.org
 help / color / mirror / Atom feed
From: Rich Felker <dalias@libc.org>
To: Florian Weimer <fweimer@redhat.com>
Cc: GNU C Library <libc-alpha@sourceware.org>, GCC <gcc@gcc.gnu.org>,
	Binutils <binutils@sourceware.org>
Subject: Re: Run (some?) ELF constructors after applying RELRO protection
Date: Mon, 11 Jun 2018 10:50:13 -0400	[thread overview]
Message-ID: <20180611145013.GG1392@brightrain.aerifal.cx> (raw)
In-Reply-To: <255b0226-8eb1-93f1-280d-ed004e52ca0e@redhat.com>

On Tue, Feb 27, 2018 at 11:01:23AM +0100, Florian Weimer wrote:
> I think it would be a nice addition to the toolchain if it were
> possible to programatically initialize data in the RELRO section.
> We do this in glibc, but I don't think this is currently supported
> for general use.
> 
> One important application is to allocate a memory region with mmap,
> on which protection flags can be changed as needed.  This way, the
> application can have a read-only path to its own configuration data,
> for example.
> 
> Do you think this would be worthwhile to implement?  Any suggestions
> how we should do it, without needing binutils/GCC/glibc updates?

This weakens protection of the actual relro section (because there's a
window where it's writable but application code is running; in the
case of thread creation from ctors, or dlopen in a multithreaded
program, this is a nontrivial window) and has no benefit, except
saving a page of memory, over the application just calling mprotect
itself. If the application already has to annotate that the data is
going to be read-only after ctors, it can just page-align/page-pad the
data itself and call mprotect with minimal additional effort, and no
complex interaction between application code and relro (which is about
RELocations not arbitrary data protection).

Rich

  reply	other threads:[~2018-06-11 14:50 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-27 10:01 Run (some?) ELF constructors after applying RELRO protection Florian Weimer
2018-06-11 14:50 ` Rich Felker [this message]
2018-06-11 17:50   ` Florian Weimer
2018-06-11 18:59     ` Rich Felker
2018-07-05 19:49       ` Florian Weimer

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: https://www.gnu.org/software/libc/involved.html

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180611145013.GG1392@brightrain.aerifal.cx \
    --to=dalias@libc.org \
    --cc=binutils@sourceware.org \
    --cc=fweimer@redhat.com \
    --cc=gcc@gcc.gnu.org \
    --cc=libc-alpha@sourceware.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).