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

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Date:   Mon, 13 May 2019 14:47:45 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     Arvind Sankar <niveditas98@...il.com>,
        Roberto Sassu <roberto.sassu@...wei.com>,
        Rob Landley <rob@...dley.net>, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-integrity@...r.kernel.org, initramfs@...r.kernel.org
Subject: Re: [PATCH v2 0/3] initramfs: add support for xattrs in the initial
 ram disk

On Mon, May 13, 2019 at 02:36:24PM -0400, Mimi Zohar wrote:
> 
> > > How does this work today then? Is it actually the case that initramfs
> > > just cannot be used on an IMA-enabled system, or it can but it leaves
> > > the initramfs unverified and we're trying to fix that? I had assumed the
> > > latter.
> > Oooh, it's done not by starting IMA appraisal later, but by loading a
> > default policy to ignore initramfs?
> 
> Right, when rootfs is a tmpfs filesystem, it supports xattrs, allowing
> for finer grained policies to be defined.  This patch set would allow
> a builtin IMA appraise policy to be defined which includes tmpfs.
> 
> Mimi
> 
Ok, but wouldn't my idea still work? Leave the default compiled-in
policy set to not appraise initramfs. The embedded /init sets all the
xattrs, changes the policy to appraise tmpfs, and then exec's the real
init? Then everything except the embedded /init and the file with the
xattrs will be appraised, and the embedded /init was verified as part of
the kernel image signature. The only additional kernel change needed
then is to add a config option to the kernel to disallow overwriting the
embedded initramfs (or at least the embedded /init).