linux-kernel - Re: Kdump with signed images

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Date:	Fri, 26 Oct 2012 13:59:34 -0400
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	Matthew Garrett <mjg@...hat.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Khalid Aziz <khalid@...ehiking.org>, kexec@...ts.infradead.org,
	horms@...ge.net.au, Dave Young <dyoung@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Dmitry Kasatkin <dmitry.kasatkin@...el.com>,
	Roberto Sassu <roberto.sassu@...ito.it>,
	Kees Cook <keescook@...omium.org>
Subject: Re: Kdump with signed images

On Fri, 2012-10-26 at 03:39 +0100, Matthew Garrett wrote:
> On Thu, Oct 25, 2012 at 09:15:58PM -0400, Mimi Zohar wrote:
> 
> > On a running system, the package installer, after verifying the package
> > integrity, would install each file with the associated 'security.ima'
> > extended attribute.  The 'security.evm' digital signature would be
> > installed with an HMAC, calculated using a system unique key. 
> 
> The idea isn't to prevent /sbin/kexec from being modified after 
> installation - it's to prevent it from being possible to install a 
> system that has a modified /sbin/kexec.

Understood.

>  Leaving any part of this up to 
> the package installer means that it doesn't solve the problem we're 
> trying to solve here. It must be impossible for the kernel to launch any 
> /sbin/kexec that hasn't been signed by a trusted key that's been built 
> into the kernel, 

With Dmitry's patch "5e0d1a4 ima: added policy support for security.ima
type", or something similar, we can force 'security.ima' to a specific
type, in this case, a digital signature.  With that patch, this
shouldn't be a problem.

> and it must be impossible for anything other than 
> /sbin/kexec to make the kexec system call.

Permission is a MAC issue. :)

thanks,

Mimi


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