linux-kernel - Re: [PATCH v2] binfmt_elf: Fix PIE execution with randomization disabled (was Re: [RFC PATCH] binfmt_elf: Fix PIE execution with randomization disabled)

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Message-ID: <alpine.LNX.2.00.1110090033561.14901@pobox.suse.cz>
Date:	Sun, 9 Oct 2011 00:35:38 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Andrew Morton <akpm00@...il.com>
Cc:	Josh Boyer <jwboyer@...hat.com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Ingo Molnar <mingo@...e.hu>, hongjiu.lu@...el.com,
	linux-kernel@...r.kernel.org, Russell King <rmk@....linux.org.uk>
Subject: Re: [PATCH v2] binfmt_elf: Fix PIE execution with randomization
 disabled (was Re: [RFC PATCH] binfmt_elf: Fix PIE execution with randomization
 disabled)

On Mon, 3 Oct 2011, Andrew Morton wrote:

> > Signed-off-by: Jiri Kosina <jkosina@...e.cz>
> > ---
> >  fs/binfmt_elf.c |    5 ++++-
> >  1 files changed, 4 insertions(+), 1 deletions(-)
> > 
> > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> > index dd0fdfc..bb11fe4 100644
> > --- a/fs/binfmt_elf.c
> > +++ b/fs/binfmt_elf.c
> > @@ -795,7 +795,10 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs)
> >  			 * might try to exec.  This is because the brk will
> >  			 * follow the loader, and is not movable.  */
> >  #if defined(CONFIG_X86) || defined(CONFIG_ARM)
> > -			load_bias = 0;
> > +			if (current->flags & PF_RANDOMIZE)
> > +				load_bias = 0;
> > +			else
> > +				load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
> >  #else
> >  			load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
> >  #endif
> 
> Guys, it took several people several days and 10+ emails to work out
> what's happening in there, and the first attempt to fix it was buggy. 
> This is all a huuuuge signal that the code is unobvious, hard to
> understand, hard to maintain.
> 
> Please, let's get a good code comment in there while it's fresh in your
> minds.  So the next person who comes along doesn't have the same amount
> of difficulty?

BTW, after thinking about this a little bit more, maybe the patch below 
would be worthwile and could save some mis-routed e-mails and bugreports 
in the future ...


From: Jiri Kosina <jkosina@...e.cz>
Subject: [PATCH] MAINTAINERS: add ASLR maintainer

Since achieving the full ASLR by merging the PIE randomization in commit 
cc503c1b43 ("x86: PIE executable randomization"), I have been dealing with 
most (if not all) of the bugreports reported against userspace address 
space randomization, so it might be a good idea to provide a decent 
contact point in MAINTAINERS.

Signed-off-by: Jiri Kosina <jkosina@...e.cz>
---
 MAINTAINERS |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/MAINTAINERS b/MAINTAINERS
index ace8f9c..c362845 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -317,6 +317,10 @@ W:	http://wiki.analog.com/AD7879
 S:	Supported
 F:	drivers/input/touchscreen/ad7879.c
 
+ADDRESS SPACE LAYOUT RANDOMIZATION (ASLR)
+M:	Jiri Kosina <jkosina@...e.cz>
+S:	Maintained
+
 ADM1025 HARDWARE MONITOR DRIVER
 M:	Jean Delvare <khali@...ux-fr.org>
 L:	lm-sensors@...sensors.org
-- 
1.7.3.1

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