linux-kernel - Re: [RFC][PATCH] Randomize kernel base address on boot

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Message-ID: <20110527131313.GB8053@redhat.com>
Date:	Fri, 27 May 2011 09:13:13 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Dan Rosenberg <drosenberg@...curity.com>
Cc:	Tony Luck <tony.luck@...il.com>, linux-kernel@...r.kernel.org,
	davej@...hat.com, kees.cook@...onical.com, davem@...emloft.net,
	eranian@...gle.com, torvalds@...ux-foundation.org,
	adobriyan@...il.com, penberg@...nel.org, hpa@...or.com,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Valdis.Kletnieks@...edu, Ingo Molnar <mingo@...e.hu>,
	pageexec@...email.hu
Subject: Re: [RFC][PATCH] Randomize kernel base address on boot

On Thu, May 26, 2011 at 04:44:34PM -0400, Dan Rosenberg wrote:
> On Thu, 2011-05-26 at 16:40 -0400, Vivek Goyal wrote:
> > On Thu, May 26, 2011 at 04:35:02PM -0400, Vivek Goyal wrote:
> > > On Tue, May 24, 2011 at 04:31:45PM -0400, Dan Rosenberg wrote:
> > > > This introduces CONFIG_RANDOMIZE_BASE, which randomizes the address at
> > > > which the kernel is decompressed at boot as a security feature that
> > > > deters exploit attempts relying on knowledge of the location of kernel
> > > > internals.  The default values of the kptr_restrict and dmesg_restrict
> > > > sysctls are set to (1) when this is enabled, since hiding kernel
> > > > pointers is necessary to preserve the secrecy of the randomized base
> > > > address.
> > > 
> > > What happens to /proc/iomem interface which gives us the physical memory
> > > location where kernel is loaded. kexec-tools relies on that interface
> > > heavily so we can not take it away. And if we can not take it away then
> > > I think somebody should be easibly be able to calculate this randomized
> > > base address.
> 
> Is it common to run kexec-tools as non-root?  It may be necessary to
> restrict this interface to root when randomization is used (keep in mind
> nobody's going to force you to turn this on by default, at least for the
> foreseeable future).

Dan, 

I had a stupid question. /proc/kallsyms is also readable by root only. So
if we are doing this so that non-root user can not know kernel virtual and
physical address that should be already covered as non-root users can't
read /proc/kallsysm or /boot/System.map.

And if this randomization is also to protect information from root user
then /proc/iomem exporting the physical address of kernel is still a
valid question in that context.

Thanks
Vivek
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