Re: [dm-devel] [PATCH v7 0/3] LoadPin: Enable loading from trusted dm-verity devices

From: Kees Cook <keescook@chromium.org>
To: Mike Snitzer <snitzer@kernel.org>
Cc: linux-security-module@vger.kernel.org,
	Douglas Anderson <dianders@chromium.org>,
	linux-kernel@vger.kernel.org, James Morris <jmorris@namei.org>,
	linux-raid@vger.kernel.org, Song Liu <song@kernel.org>,
	dm-devel@redhat.com, Matthias Kaehlcke <mka@chromium.org>,
	Milan Broz <gmazyland@gmail.com>,
	Alasdair Kergon <agk@redhat.com>,
	"Serge E . Hallyn" <serge@hallyn.com>
Subject: Re: [dm-devel] [PATCH v7 0/3] LoadPin: Enable loading from trusted dm-verity devices
Date: Wed, 6 Jul 2022 20:58:19 -0700	[thread overview]
Message-ID: <202207062058.49046961A4@keescook> (raw)
In-Reply-To: <YsWmPt7xwTlvTfAf@redhat.com>

On Wed, Jul 06, 2022 at 11:11:58AM -0400, Mike Snitzer wrote:
> On Mon, Jun 27 2022 at 11:35P -0400,
> Matthias Kaehlcke <mka@chromium.org> wrote:
> 
> > As of now LoadPin restricts loading of kernel files to a single pinned
> > filesystem, typically the rootfs. This works for many systems, however it
> > can result in a bloated rootfs (and OTA updates) on platforms where
> > multiple boards with different hardware configurations use the same rootfs
> > image. Especially when 'optional' files are large it may be preferable to
> > download/install them only when they are actually needed by a given board.
> > Chrome OS uses Downloadable Content (DLC) [1] to deploy certain 'packages'
> > at runtime. As an example a DLC package could contain firmware for a
> > peripheral that is not present on all boards. DLCs use dm-verity [2] to
> > verify the integrity of the DLC content.
> > 
> > This series extends LoadPin to allow loading of kernel files from trusted
> > dm-verity devices. LoadPin maintains a list of root digests of verity
> > devices it considers trusted. Userspace can populate this list through an
> > ioctl on the new LoadPin securityfs entry 'dm-verity'. The ioctl receives
> > a file descriptor of a file with verity digests as parameter. Verity reads
> > the digests from this file after confirming that the file is located on the
> > pinned root. The digest file must contain one digest per line. The list of
> > trusted digests can only be set up once, which is typically done at boot
> > time.
> > 
> > When a kernel file is read LoadPin first checks (as usual) whether the file
> > is located on the pinned root, if so the file can be loaded. Otherwise, if
> > the verity extension is enabled, LoadPin determines whether the file is
> > located on a verity backed device and whether the root digest of that
> > device is in the list of trusted digests. The file can be loaded if the
> > verity device has a trusted root digest.
> > 
> > [1] https://chromium.googlesource.com/chromiumos/platform2/+/HEAD/dlcservice/docs/developer.md
> > [2] https://www.kernel.org/doc/html/latest/admin-guide/device-mapper/verity.html
> 
> Hi Kees,
> 
> Please pick this series up, thanks.

Thanks for the Acks! I'll get this into -next shortly.

-- 
Kees Cook

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