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Date: Mon, 15 Apr 2013 19:34:16 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Yinghai Lu <yinghai@...nel.org>
CC: Kees Cook <keescook@...omium.org>, 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 04/15/2013 03:38 PM, Yinghai Lu 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.
That seems really, really odd.
> so the decompressed image is not moved high?
This really seems wrong in so many ways.
If you relocate pre-decompression the amount of memory you need is given
by init_size:
#define ZO_INIT_SIZE (ZO__end - ZO_startup_32 + ZO_z_extract_offset)
#define VO_INIT_SIZE (VO__end - VO__text)
#if ZO_INIT_SIZE > VO_INIT_SIZE
#define INIT_SIZE ZO_INIT_SIZE
#else
#define INIT_SIZE VO_INIT_SIZE
#endif
init_size: .long INIT_SIZE # kernel initialization size
In real life, VO_INIT_SIZE dominates almost every time.
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
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