Message-ID: <1351276649.18115.217.camel@falcor>
Subject: Re: Kdump with signed images
From: Mimi Zohar <zohar@linux.vnet.ibm.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Matthew Garrett <mjg@redhat.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Khalid Aziz <khalid@gonehiking.org>, kexec@lists.infradead.org,
        horms@verge.net.au, Dave Young <dyoung@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        linux kernel mailing list <linux-kernel@vger.kernel.org>,
        Dmitry Kasatkin <dmitry.kasatkin@intel.com>,
        Roberto Sassu <roberto.sassu@polito.it>,
        Kees Cook <keescook@chromium.org>
Date: Fri, 26 Oct 2012 14:37:29 -0400
In-Reply-To: <20121026170609.GB24687@redhat.com>
References: <20121023131854.GA16496@redhat.com>
	 <20121023145920.GD16496@redhat.com> <87fw552mb4.fsf_-_@xmission.com>
	 <20121024173651.GE1821@redhat.com> <1351145401.18115.78.camel@falcor>
	 <20121025141048.GD9377@redhat.com> <1351190421.18115.92.camel@falcor>
	 <20121025185520.GA17995@redhat.com> <1351214158.18115.186.camel@falcor>
	 <20121026023916.GA16762@srcf.ucam.org> <20121026170609.GB24687@redhat.com>
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On Fri, 2012-10-26 at 13:06 -0400, Vivek Goyal wrote:
> On Fri, Oct 26, 2012 at 03:39:16AM +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. 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, and it must be impossible for anything other than 
> > /sbin/kexec to make the kexec system call.
> 
> I am kind of lost now so just trying to summarize whatever I have
> learned so far from this thread.

Thanks for summarizing.

> - So say we can sign /sbin/kexec at build time and distros can do that.
> - Verify the signature at exec time using kernel keyring and if
>   verification happens successfully, say process gains extra capability.
> - Use this new capability to determine whether kexec_load() will be
>   successful or not.
> 
> Even if we can do all this, it still has the issue of being able to
> stop the process in user space and replace the code at run time
> and be able to launch unsigned kernel.
> 
> So until and unless we have a good solution to verify application's
> integrity/authneticity at the time of kexec_load() system call we
> still have the problem. And I don't think we have come up with a
> solution for that yet (until and unless I missed something).
>   
> Thanks
> Vivek
> 

Agreed, you need a new LSM/integrity hook.

thanks,

Mimi

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