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

[Jarkko Sakkinen]

On Tue Dec 19, 2023 at 2:45 AM EET, Paul Moore wrote:
> 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.

I gave my 5 cents. I had no intention not to review it, somehow just
slipped. I try to do my best but sometimes this still does happen :-) So
please ping me if there is radio silence. 

BR, Jarkko