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

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Date:	Mon, 15 Apr 2013 15:07:17 -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 3:00 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> On Mon, Apr 15, 2013 at 2:46 PM, H. Peter Anvin <hpa@...or.com> wrote:
>> On 04/15/2013 02:41 PM, Kees Cook wrote:
>
>> Please read what I wrote.
>>
>> The 2 GB limit is for the *virtual* mapping.
>>
>> The *physical* mapping, where it lands in RAM, is completely
>> independent, and if you're going to randomize the latter, there is no
>> reason it has to match the former.  Instead, randomize it freely.
>>
>> That is different from the i386 kernel which runs at its
>> physical-mapping address.
>>
>> Incidentally, for performance reasons please avoid locating the kernel
>> below CONFIG_PHYSICAL_ADDRESS if possible.
>>
>> Also make sure your code works with more than 128 e820 entries.
>
> 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.

-Kees

--
Kees Cook
Chrome OS Security
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