On Mon, Jun 27 2022 at 11:35P -0400, Matthias Kaehlcke <mka@xxxxxxxxxxxx> wrote: > Extend LoadPin to allow loading of kernel files from trusted dm-verity [1] > devices. > > This change adds the concept of trusted verity devices to LoadPin. 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. > > Background: > > 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) [2] 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 to verify > the integrity of the DLC content. > > [1] https://www.kernel.org/doc/html/latest/admin-guide/device-mapper/verity.html > [2] https://chromium.googlesource.com/chromiumos/platform2/+/HEAD/dlcservice/docs/developer.md > > Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx> > Acked-by: Kees Cook <keescook@xxxxxxxxxxxx> Acked-by: Mike Snitzer <snitzer@xxxxxxxxxx> -- dm-devel mailing list dm-devel@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/dm-devel
