Subject: Re: [RFC][PATCH] Randomize kernel base address on boot
From: Dan Rosenberg <drosenberg@vsecurity.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Tony Luck <tony.luck@gmail.com>, linux-kernel@vger.kernel.org,
        davej@redhat.com, kees.cook@canonical.com, davem@davemloft.net,
        eranian@google.com, torvalds@linux-foundation.org, adobriyan@gmail.com,
        penberg@kernel.org, hpa@zytor.com,
        Arjan van de Ven <arjan@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>, Valdis.Kletnieks@vt.edu,
        Ingo Molnar <mingo@elte.hu>, pageexec@freemail.hu
In-Reply-To: <20110526204030.GL29496@redhat.com>
References: <1306269105.21443.20.camel@dan>
	 <20110526203502.GK29496@redhat.com>  <20110526204030.GL29496@redhat.com>
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Date: Thu, 26 May 2011 16:44:34 -0400
Message-ID: <1306442674.2279.29.camel@dan>
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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

> 
> Thanks
> Vivek


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