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

[Mike Snitzer <snitzer@kernel.org>]

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.

Mike