linux-kernel - [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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Date:	Mon, 3 Oct 2011 17:11:47 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Josh Boyer <jwboyer@...hat.com>
Cc:	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Andrew Morton <akpm00@...il.com>, Ingo Molnar <mingo@...e.hu>,
	hongjiu.lu@...el.com, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Russell King <rmk@....linux.org.uk>
Subject: [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, Josh Boyer wrote:

> > > Perhaps another check here for randomize?  Something like:
> > > 
> > > #if defined(CONFIG_X86) || defined(CONFIG_ARM)
> > > 		if (current->flags & PF_RANDOMIZE)
> > > 			load_bias = 0;
> > > 		else if (vaddr)
> > > 			load_bias = 0;
> > > 		else
> > > 			load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE);
> > > #else
> > > 		load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
> > > #endif
> > > 
> > > If that's stupid, then feel free to tell me.  I won't pretend like I
> > > understand what is going on here yet, but based on the explanation you
> > > provided that might work.
> > 
> > I have just verified my hunch that the original patch from H.J. / Josh 
> > breaks ASLR completely, so Andrew, please drop it for now.
> 
> Yes, please drop the original.

Thanks.

> > I am now looking into how to fix things properly.
> > 
> > Josh, looking at what you are proposing -- do you see any reason to make 
> > the behavior different in #else branch and in !(current->flags & 
> > PF_RANDOMIZE) case?
> 
> I was mostly just trying to adapt H.J.'s patch to account for the
> PF_RANDOMIZE case.  Looking at it a bit more, I'm not sure why they
> would need to be different.  H.J., do you recall why you made that
> change originally?

How about the patch below instead? It survives my testing, and I believe 
it handles both cases properly.

Confirmation from the original bug reporter would obviously be a nice 
bonus too :)




From: Jiri Kosina <jkosina@...e.cz>
Subject: [PATCH] binfmt_elf: fix PIE execution with randomization disabled

The case of address space randomization being disabled in runtime through
randomize_va_space sysctl is not treated properly in load_elf_binary(),
resulting in SIGKILL coming at exec() time for certain PIE-linked binaries
in case the randomization has been disabled at runtime prior to calling
exec().

Handle the randomize_va_space == 0 case the same way as if we were not
supporting .text randomization at all.

Based on original patch by H.J. Lu <hongjiu.lu@...el.com> and
Josh Boyer <jwboyer@...hat.com>

Cc: Ingo Molnar <mingo@...e.hu>
Cc: Jiri Kosina <jkosina@...e.cz>
Cc: Nicolas Pitre <nicolas.pitre@...aro.org>
Cc: Russell King <rmk@....linux.org.uk>
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

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