| Message ID | 20220517233457.1123309-1-mka@chromium.org (mailing list archive) |
|---|---|
| Headers | show |
| Series | LoadPin: Enable loading from trusted dm-verity devices | expand |
On Tue, May 17, 2022 at 04:34:54PM -0700, Matthias Kaehlcke 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. For the coming v5 (which will fix the 0-day reports), if I can get some Acks from the dm folks, I can carry this with other loadpin changes in my tree. Though I'm fine with this going via the dm tree, too: Acked-by: Kees Cook <keescook@chromium.org>
On Wed, May 18 2022 at 3:23P -0400, Kees Cook <keescook@chromium.org> wrote: > On Tue, May 17, 2022 at 04:34:54PM -0700, Matthias Kaehlcke 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. > > For the coming v5 (which will fix the 0-day reports), if I can get some > Acks from the dm folks, I can carry this with other loadpin changes in > my tree. Though I'm fine with this going via the dm tree, too: > > Acked-by: Kees Cook <keescook@chromium.org> I'll review it once it's posted. But I'm going to reply to v4's 1/3 now.
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 Changes in v4: - a trusted verity device must have a single target of type 'verity' - changed struct trusted_root_digest to have an unsized u8 array instead of a pointer - use shared list of verity digests, deleted dm_verity_loadpin_set_trusted_root_digests() - use newline as separator in digest file instead of comma - after reading an invalid/corrupt digest file deny further attempts of setting up the list of digests - added comment to read_trusted_verity_root_digests() explaining that an invalid digests entry invalidates the entire list of digests - minor refactoring of verity related code in LoadPin Changes in v3: - added securityfs for LoadPin (currently only populated when CONFIG_SECURITY_LOADPIN_VERITY=y) - added uapi include for LoadPin - changed the interface for setting up the list of trusted digests from sysctl to ioctl on securityfs entry - added stub for loadpin_is_fs_trusted() to be used CONFIG_SECURITY_LOADPIN_VERITY is not select - depend on CONFIG_SECURITYFS instead of CONFIG_SYSTCL - updated Kconfig help - minor changes in read_trusted_verity_root_digests() - updated commit message Changes in v2: - userspace now passes the path of the file with the verity digests via systcl, instead of the digests themselves - renamed sysctl file to 'trusted_verity_root_digests_path' - have CONFIG_SECURITY_LOADPIN_VERITY depend on CONFIG_SYSCTL - updated Kconfig doc - updated commit message Matthias Kaehlcke (3): dm: Add verity helpers for LoadPin LoadPin: Enable loading from trusted dm-verity devices dm: verity-loadpin: Use CONFIG_SECURITY_LOADPIN_VERITY for conditional compilation drivers/md/Makefile | 1 + drivers/md/dm-verity-loadpin.c | 74 +++++++++++++ drivers/md/dm-verity-target.c | 33 ++++++ drivers/md/dm-verity.h | 4 + include/linux/dm-verity-loadpin.h | 27 +++++ include/uapi/linux/loadpin.h | 22 ++++ security/loadpin/Kconfig | 16 +++ security/loadpin/loadpin.c | 167 +++++++++++++++++++++++++++++- 8 files changed, 343 insertions(+), 1 deletion(-) create mode 100644 drivers/md/dm-verity-loadpin.c create mode 100644 include/linux/dm-verity-loadpin.h create mode 100644 include/uapi/linux/loadpin.h