linux-kernel - Re: kaslr should avoid setup

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Message-ID: <CAGXu5j+VbEYWH80mvY3wQscqqfkDpKkKv81xQa-qmUz-mqHF2Q@mail.gmail.com>
Date:	Thu, 8 May 2014 12:31:44 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Dave Young <dyoung@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: kaslr should avoid setup_data region

On Thu, May 8, 2014 at 2:46 AM, Dave Young <dyoung@...hat.com> wrote:
> On 04/24/14 at 03:50pm, Kees Cook wrote:
>> On Wed, Apr 23, 2014 at 7:50 PM, Dave Young <dyoung@...hat.com> wrote:
>> > On 04/23/14 at 07:43pm, Kees Cook wrote:
>> >> On Wed, Apr 23, 2014 at 7:35 PM, Dave Young <dyoung@...hat.com> wrote:
>> >> > Hello Kees
>> >> >
>> >> > I'm worrying that setup_data regions could be overwitten by randomize
>> >> > kernel base. Would you like to fix it in kaslr code?
>> >> >
>> >> > One problem is there could be a lot of setup_data regions but current
>> >> > mem_avoid is an fixed array.
>> >>
>> >> Sure, can you give me some examples? Seems like it shouldn't be too
>> >> hard to have the mem_avoid logic walk additional areas.
>> >
>> > Great, To walk through the list just like the function parse_setup_data in
>> > arch/x86/kernel/setup.c
>
> One problem for me is that I am not sure how to read the setup_data memory
> and iterate it, I think early_ioremap is not available that early. BTW the
> setup_data region could be above 4G.
>
> Appreciate for any hints.

Hm, I'm not sure. The kASLR code only deals with memory that has been
set up during the physical/virtual identity mapping.

-Kees

-- 
Kees Cook
Chrome OS Security
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