linux-kernel - Re: [PATCH] binfmt_elf: fix PIE load with randomization disabled

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Date:	Mon, 09 Dec 2013 15:35:32 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"H.J. Lu" <hjl.tools@...il.com>
CC:	Jiri Kosina <jkosina@...e.cz>, LKML <linux-kernel@...r.kernel.org>,
	Josh Boyer <jwboyer@...hat.com>
Subject: Re: [PATCH] binfmt_elf: fix PIE load with randomization disabled

On 12/09/2013 01:44 PM, H.J. Lu wrote:
> On Mon, Dec 9, 2013 at 1:39 PM, H. Peter Anvin <hpa@...or.com> wrote:
>> On 12/09/2013 01:03 PM, H.J. Lu wrote:
>>>
>>> No, please don't do that.  Normally, PIE has zero load address and kernel
>>> can load it anywhere.  There are multiple reasons why PIE has non-zero
>>> load address.  Saying you need to load a program above 4GB under x86-64,
>>> you can't do that with normal dynamic executable.  PIE with non-zero load
>>> address is the only way to do that on x86-64.
>>>
>>
>> Why does it have to be PIE?
>>
> 
> x86-64 small model is limited to 4GB in size.  You can't build
> a dynamic executable in small model larger than 4GB.
> 
> There are medium and large models.  But they are slower than
> small models as well as small models in PIE.  Also there are
> no glibc run-times for medium and large models.
> 

Compiling for the small PIC model shouldn't automatically mean
generating a PIE (ET_DYN) executable, though (and if those are
inherently linked, that is a fundamental bug IMNSHO.)

	-hpa

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