linux-kernel - Re: [PATCH 6/6] x86: kaslr: relocate base offset at boot

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Message-ID: <CAGXu5jJWxHB-oPjGVV5y2jeSNf0At1+3nFgAR0UET8dzxcjB1g@mail.gmail.com>
Date:	Mon, 15 Apr 2013 15:42:59 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Eric Northup <digitaleric@...gle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Jarkko Sakkinen <jarkko.sakkinen@...el.com>,
	Matthew Garrett <mjg@...hat.com>,
	Matt Fleming <matt.fleming@...el.com>,
	Dan Rosenberg <drosenberg@...curity.com>,
	Julien Tinnes <jln@...gle.com>, Will Drewry <wad@...omium.org>
Subject: Re: [PATCH 6/6] x86: kaslr: relocate base offset at boot

On Mon, Apr 15, 2013 at 3:38 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> On Mon, Apr 15, 2013 at 3:07 PM, Kees Cook <keescook@...omium.org> wrote:
>> On Mon, Apr 15, 2013 at 3:00 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>>> also do not overlap with boot_param, command_line, and initrd.
>>>
>>> and need to double check setup_header.init_size to make sure bss and
>>> etc will not
>>> fall into memory hole or reserved area in e820.
>>>
>>> also may need to setup page table for target position as bootloader may only
>>> has ident mapping only for loaded bzImage 64 areas.
>>>
>>> looks you are trying redo the work for bootloader to pick loaded phys addr.
>>
>> aslr.S's select_aslr_address uses z_extract_offset as the upper bound.
>
> so the decompressed image is not moved high?

No, I mean the size of the relocated image is using z_extract_offset
as the end size of the relocated memory. See select_aslr_address. It
takes the chosen aslr offset plus the location of z_extract_offset and
keeps reducing the offset until it's inside the physical end of
memory.

-Kees

--
Kees Cook
Chrome OS Security
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