linux-kernel - Re: [PATCH][RESEND] PIE randomization

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Date:	Thu, 05 Jul 2007 16:57:12 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Chuck Ebbert <cebbert@...hat.com>
CC:	Jiri Kosina <jkosina@...e.cz>, Jakub Jelinek <jakub@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kratochvil <honza@...os.cz>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, Ernie Petrides <petrides@...hat.com>
Subject: Re: [PATCH][RESEND] PIE randomization

Chuck Ebbert wrote:
> On 07/04/2007 01:35 PM, Jiri Kosina wrote:
>> On Wed, 4 Jul 2007, Jakub Jelinek wrote:
>>
>>> The above highlighted changes are the cause of random segfaults of PIE 
>>> binaries.  See 
>>> https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=246623 
>> Thanks a lot for pointing this out. Andrew, could this be folded into 
>> pie-randomization.patch please?
>>
>>
>> From: Jiri Kosina <jkosina@...e.cz>
>>
>> pie randomization: fix BAD_ADDR macro
>>
>> pie-randomization.patch makes the load_addr in load_elf_interp() the load 
>> bias of ld.so (difference between the actual load base address and first 
>> PT_LOAD segment's p_vaddr). If the difference equals (on x86) to 
>> 0xfffff000 (which is valid [1]), SIGSEGV is incorrectly sent.
>>
>> This patch changes the BAD_ADDR so that it catches the mappings to the 
>> error-area properly.
> 
> But what about this patch that made the opposite change:
> 
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=ce51059be56f63762089412b3ece348067afda85

Ohhh, interesting.

So the original patch has:

#define BAD_ADDR(x) ((unsigned long)(x) >= TASK_SIZE)

For some reason(?) it got changed to the clearly buggy:

#define BAD_ADDR(x) ((unsigned long)(x) >= PAGE_MASK)

Jiri's patch undoes that second buggy define, which is very
different from the original that was sent in by you and Ernie.

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