linux-kernel - Re: kaslr should avoid setup

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Date:	Fri, 9 May 2014 11:21:43 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: kaslr should avoid setup_data region

On 05/08/14 at 12:31pm, Kees Cook wrote:
> 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.
> 

So will dereference them directly and ignore setup_data which is above 4G.

Thanks
Dave
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