linux-kernel - Re: [kernel-hardening] [PATCH v7 0/9] x86/mm: memory area address KASLR

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Message-ID: <20160623193358.GL9922@io.lakedaemon.net>
Date:	Thu, 23 Jun 2016 19:33:58 +0000
From:	Jason Cooper <jason@...edaemon.net>
To:	Kees Cook <keescook@...omium.org>
Cc:	Thomas Garnier <thgarnie@...gle.com>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andy Lutomirski <luto@...nel.org>,
	"x86@...nel.org" <x86@...nel.org>, Borislav Petkov <bp@...e.de>,
	Baoquan He <bhe@...hat.com>, Yinghai Lu <yinghai@...nel.org>,
	Juergen Gross <jgross@...e.com>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Toshi Kani <toshi.kani@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Williams <dan.j.williams@...el.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Xiao Guangrong <guangrong.xiao@...ux.intel.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Alexander Kuleshov <kuleshovmail@...il.com>,
	Alexander Popov <alpopov@...ecurity.com>,
	Dave Young <dyoung@...hat.com>, Joerg Roedel <jroedel@...e.de>,
	Lv Zheng <lv.zheng@...el.com>,
	Mark Salter <msalter@...hat.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Jan Beulich <JBeulich@...e.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jonathan Corbet <corbet@....net>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [kernel-hardening] [PATCH v7 0/9] x86/mm: memory area address
 KASLR

Hey Kees, Thomas,

On Wed, Jun 22, 2016 at 10:05:51AM -0700, Kees Cook wrote:
> On Wed, Jun 22, 2016 at 8:59 AM, Thomas Garnier <thgarnie@...gle.com> wrote:
> > On Wed, Jun 22, 2016 at 5:47 AM, Jason Cooper <jason@...edaemon.net> wrote:
> >> Hey Kees,
> >>
> >> On Tue, Jun 21, 2016 at 05:46:57PM -0700, Kees Cook wrote:
> >>> Notable problems that needed solving:
> >> ...
> >>>  - Reasonable entropy is needed early at boot before get_random_bytes()
> >>>    is available.
> >>
> >> This series is targetting x86, which typically has RDRAND/RDSEED
> >> instructions.  Are you referring to other arches?  Older x86?  Also,
> >> isn't this the same requirement for base address KASLR?
> >>
> >> Don't get me wrong, I want more diverse entropy sources available
> >> earlier in the boot process as well. :-)  I'm just wondering what's
> >> different about this series vs base address KASLR wrt early entropy
> >> sources.
> >>
> >
> > I think Kees was referring to the refactor I did to get the similar
> > entropy generation than KASLR module randomization. Our approach was
> > to provide best entropy possible even if you have an older processor
> > or under virtualization without support for these instructions.
> > Unfortunately common on companies with a large number of older
> > machines.
> 
> Right, the memory offset KASLR uses the same routines as the kernel
> base KASLR. The issue is with older x86 systems, which continue to be
> very common.

We have the same issue in embedded. :-(  Compounded by the fact that
there is no rand instruction (at least not on ARM).  So, even if there's
a HW-RNG, you can't access it until the driver is loaded.

This is compounded by the fact that most systems deployed today have
bootloaders a) without hw-rng drivers, b) without dtb editing, and c)
without dtb support at all.

My current thinking is to add a devicetree property
"userspace,random-seed" <address, len>.  This way, existing, deployed
boards can append a dtb to a modern kernel with the property set.
The factory bootloader then only needs to amend its boot scripts to read
random-seed from the fs to the given address.

Modern systems that receive a seed from the bootloader via the
random-seed property (typically from the hw-rng) can mix both sources
for increased resilience.

Unfortunately, I'm not very familiar with the internals of x86
bootstrapping.  Could GRUB be scripted to do a similar task?  How would
the address and size of the seed be passed to the kernel?  command line?

thx,

Jason.