linux-kernel - Re: 2.6.23-rc3-mm1 - memory layout change? - lost support for MAP_32BIT?

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Date:	Thu, 23 Aug 2007 16:52:01 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Zan Lynx <zlynx@....org>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Roland McGrath <roland@...hat.com>,
	Jakub Jelinek <jakub@...hat.com>
Subject: Re: 2.6.23-rc3-mm1 - memory layout change?  - lost support for
 MAP_32BIT? - mono crashes

On Thu, 23 Aug 2007 11:28:25 +0200 (CEST)
Jiri Kosina <jkosina@...e.cz> wrote:

> Handle MAP_32BIT flags properly in x86_64 flexmmap
> 
> We need to handle MAP_32BIT flags of mmap() properly for 64bit 
> applications with filexible mmap layout.
> 
> This patch introduces x86_64-specific version of 
> arch_get_unmapped_area_topdown() which differs from the generic one in 
> handling of the MAP_32BIT flag -- when this flag is passed to mmap(), we 
> stick back to the legacy layout for this particular mmap, which gives 
> proper 32bit range.
> 

 arch/x86_64/kernel/sys_x86_64.c |   98 ++++++++++++++++++++++++++++++++++++++++
 include/asm-x86_64/pgtable.h    |    1 

well that's another hunk of code for us to maintain and to slow all our
computers down.

It is quite unobvious to me that the whole pie-randomization thing is
worth merging.  Why shouldn't we just drop the lot?


<looks at the changelog>

  This patch is using mmap()'s randomization functionality in such a way
  that it maps the main executable of (specially compiled/linked
  -pie/-fpie) ET_DYN binaries onto a random address (in cases in which
  mmap() is allowed to perform a randomization).

  The code has been extraced from Ingo's exec-shield patch
  http://people.redhat.com/mingo/exec-shield/

that certainly doesn't tell anyone why we should merge this code into Linux.
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