linux-kernel - Re: [PATCH v2 0/3] initramfs: add support for xattrs in the initial ram disk

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Date:   Sun, 12 May 2019 20:02:30 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Dominik Brodowski <linux@...inikbrodowski.net>, hpa@...or.com
Cc:     Roberto Sassu <roberto.sassu@...wei.com>, viro@...iv.linux.org.uk,
        linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org, initramfs@...r.kernel.org,
        linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, zohar@...ux.vnet.ibm.com,
        silviu.vlasceanu@...wei.com, dmitry.kasatkin@...wei.com,
        takondra@...co.com, kamensky@...co.com, arnd@...db.de,
        rob@...dley.net, james.w.mcmechan@...il.com
Subject: Re: [PATCH v2 0/3] initramfs: add support for xattrs in the initial
 ram disk

On Sun, 2019-05-12 at 17:31 +0200, Dominik Brodowski wrote:
> On Sun, May 12, 2019 at 08:52:47AM -0400, Mimi Zohar wrote:


> > It's too late.  The /init itself should be signed and verified.
> 
> Could you elaborate a bit more about the threat model, and why deferring
> this to the initramfs is too late?

The IMA policy defines a number of different methods of identifying
which files to measure, appraise, audit.[1]  Without xattrs, the
granularity of the policy rules is severely limited.  Without xattrs,
a filesystem is either in policy, or not.

With an IMA policy rule requiring rootfs (tmpfs) files to be verified,
then /init needs to be properly labeled, otherwise /init will fail to
execute.

Mimi

[1] Documentation/ABI/testing/ima_policy