linux-kernel - Re: [Linux-ima-user] Initramfs and IMA Appraisal

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Message-ID: <1419908780.14143.75.camel@dhcp-9-2-203-236.watson.ibm.com>
Date:	Mon, 29 Dec 2014 22:06:20 -0500
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	David Lang <david@...g.hm>
Cc:	Rob Landley <rob@...dley.net>, Christophe Fillot <cf@....fr>,
	linux-ima-user@...ts.sourceforge.net,
	linux-security-module <linux-security-module@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [Linux-ima-user] Initramfs and IMA Appraisal

On Mon, 2014-12-29 at 18:25 -0800, David Lang wrote: 
> On Mon, 29 Dec 2014, Mimi Zohar wrote:
> 
> > Thanks Rob for the explanation.  The problem is that ramfs does not
> > support extended attributes, while tmpfs does.  The boot loader could
> > "measure" (trusted boot) the initramfs, but as the initramfs is
> > generated on the target system, the initramfs is not signed, preventing
> > it from being appraised (secure Boot). To close the initramfs integrity
> > appraisal gap requires verifying the individual initramfs file
> > signatures, which are stored as extended attributes.
> 
> what's the point of checking the files on the filesystem against signatures 
> stored on the same filesystem? If someone could alter the file contents they can 
> alter the signatures as well.

It's all about limiting which public keys can be used to verify the file
signatures.  As of 3.17, only keys signed by a "trusted" key on the
system keyring may be added to the IMA keyring.

Mimi 

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