[PATCH v5 0/6] DCP as trusted keys backend

[Paul Moore]

On Fri, Dec 15, 2023 at 6:07 AM David Gstir <david at sigma-star.at> wrote:
>
> This is a revival of the previous patch set submitted by Richard Weinberger:
> https://lore.kernel.org/linux-integrity/20210614201620.30451-1-richard@nod.at/
>
> v4 is here:
> https://lore.kernel.org/keyrings/20231024162024.51260-1-david@sigma-star.at/
>
> v4 -> v5:
> - Make Kconfig for trust source check scalable as suggested by Jarkko Sakkinen
> - Add Acked-By from Herbert Xu to patch #1 - thanks!
> v3 -> v4:
> - Split changes on MAINTAINERS and documentation into dedicated patches
> - Use more concise wording in commit messages as suggested by Jarkko Sakkinen
> v2 -> v3:
> - Addressed review comments from Jarkko Sakkinen
> v1 -> v2:
> - Revive and rebase to latest version
> - Include review comments from Ahmad Fatoum
>
> The Data CoProcessor (DCP) is an IP core built into many NXP SoCs such
> as i.mx6ull.
>
> Similar to the CAAM engine used in more powerful SoCs, DCP can AES-
> encrypt/decrypt user data using a unique, never-disclosed,
> device-specific key. Unlike CAAM though, it cannot directly wrap and
> unwrap blobs in hardware. As DCP offers only the bare minimum feature
> set and a blob mechanism needs aid from software. A blob in this case
> is a piece of sensitive data (e.g. a key) that is encrypted and
> authenticated using the device-specific key so that unwrapping can only
> be done on the hardware where the blob was wrapped.
>
> This patch series adds a DCP based, trusted-key backend and is similar
> in spirit to the one by Ahmad Fatoum [0] that does the same for CAAM.
> It is of interest for similar use cases as the CAAM patch set, but for
> lower end devices, where CAAM is not available.
>
> Because constructing and parsing the blob has to happen in software,
> we needed to decide on a blob format and chose the following:
>
> struct dcp_blob_fmt {
>         __u8 fmt_version;
>         __u8 blob_key[AES_KEYSIZE_128];
>         __u8 nonce[AES_KEYSIZE_128];
>         __le32 payload_len;
>         __u8 payload[];
> } __packed;
>
> The `fmt_version` is currently 1.
>
> The encrypted key is stored in the payload area. It is AES-128-GCM
> encrypted using `blob_key` and `nonce`, GCM auth tag is attached at
> the end of the payload (`payload_len` does not include the size of
> the auth tag).
>
> The `blob_key` itself is encrypted in AES-128-ECB mode by DCP using
> the OTP or UNIQUE device key. A new `blob_key` and `nonce` are generated
> randomly, when sealing/exporting the DCP blob.
>
> This patchset was tested with dm-crypt on an i.MX6ULL board.
>
> [0] https://lore.kernel.org/keyrings/20220513145705.2080323-1-a.fatoum@pengutronix.de/
>
> David Gstir (6):
>   crypto: mxs-dcp: Add support for hardware-bound keys
>   KEYS: trusted: improve scalability of trust source config
>   KEYS: trusted: Introduce NXP DCP-backed trusted keys
>   MAINTAINERS: add entry for DCP-based trusted keys
>   docs: document DCP-backed trusted keys kernel params
>   docs: trusted-encrypted: add DCP as new trust source
>
>  .../admin-guide/kernel-parameters.txt         |  13 +
>  .../security/keys/trusted-encrypted.rst       |  85 +++++
>  MAINTAINERS                                   |   9 +
>  drivers/crypto/mxs-dcp.c                      | 104 +++++-
>  include/keys/trusted_dcp.h                    |  11 +
>  include/soc/fsl/dcp.h                         |  17 +
>  security/keys/trusted-keys/Kconfig            |  18 +-
>  security/keys/trusted-keys/Makefile           |   2 +
>  security/keys/trusted-keys/trusted_core.c     |   6 +-
>  security/keys/trusted-keys/trusted_dcp.c      | 311 ++++++++++++++++++
>  10 files changed, 562 insertions(+), 14 deletions(-)
>  create mode 100644 include/keys/trusted_dcp.h
>  create mode 100644 include/soc/fsl/dcp.h
>  create mode 100644 security/keys/trusted-keys/trusted_dcp.c

Jarkko, Mimi, David - if this patchset isn't already in your review
queue, can you take a look at it from a security/keys perspective?

Thanks.

-- 
paul-moore.com