Re: [EXT] Re: [PATCH v8 6/6] docs: trusted-encrypted: add DCP as new trust source

["Jarkko Sakkinen" <jarkko@kernel.org>]

On Tue Apr 9, 2024 at 12:48 PM EEST, Kshitiz Varshney wrote:
> Hi Jarkko,
>
>
> > -----Original Message-----
> > From: Jarkko Sakkinen <jarkko@kernel.org>
> > Sent: Wednesday, April 3, 2024 9:18 PM
> > To: David Gstir <david@sigma-star.at>; Mimi Zohar <zohar@linux.ibm.com>;
> > James Bottomley <jejb@linux.ibm.com>; Herbert Xu
> > <herbert@gondor.apana.org.au>; David S. Miller <davem@davemloft.net>
> > Cc: Shawn Guo <shawnguo@kernel.org>; Jonathan Corbet
> > <corbet@lwn.net>; Sascha Hauer <s.hauer@pengutronix.de>; Pengutronix
> > Kernel Team <kernel@pengutronix.de>; Fabio Estevam
> > <festevam@gmail.com>; dl-linux-imx <linux-imx@nxp.com>; Ahmad Fatoum
> > <a.fatoum@pengutronix.de>; sigma star Kernel Team
> > <upstream+dcp@sigma-star.at>; David Howells <dhowells@redhat.com>; Li
> > Yang <leoyang.li@nxp.com>; Paul Moore <paul@paul-moore.com>; James
> > Morris <jmorris@namei.org>; Serge E. Hallyn <serge@hallyn.com>; Paul E.
> > McKenney <paulmck@kernel.org>; Randy Dunlap <rdunlap@infradead.org>;
> > Catalin Marinas <catalin.marinas@arm.com>; Rafael J. Wysocki
> > <rafael.j.wysocki@intel.com>; Tejun Heo <tj@kernel.org>; Steven Rostedt
> > (Google) <rostedt@goodmis.org>; linux-doc@vger.kernel.org; linux-
> > kernel@vger.kernel.org; linux-integrity@vger.kernel.org;
> > keyrings@vger.kernel.org; linux-crypto@vger.kernel.org; linux-arm-
> > kernel@lists.infradead.org; linuxppc-dev@lists.ozlabs.org; linux-security-
> > module@vger.kernel.org; Richard Weinberger <richard@nod.at>; David
> > Oberhollenzer <david.oberhollenzer@sigma-star.at>
> > Subject: [EXT] Re: [PATCH v8 6/6] docs: trusted-encrypted: add DCP as new
> > trust source
> > 
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> > 
> > 
> > On Wed Apr 3, 2024 at 10:21 AM EEST, David Gstir wrote:
> > > Update the documentation for trusted and encrypted KEYS with DCP as
> > > new trust source:
> > >
> > > - Describe security properties of DCP trust source
> > > - Describe key usage
> > > - Document blob format
> > >
> > > Co-developed-by: Richard Weinberger <richard@nod.at>
> > > Signed-off-by: Richard Weinberger <richard@nod.at>
> > > Co-developed-by: David Oberhollenzer
> > > <david.oberhollenzer@sigma-star.at>
> > > Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>
> > > Signed-off-by: David Gstir <david@sigma-star.at>
> > > ---
> > >  .../security/keys/trusted-encrypted.rst       | 53 +++++++++++++++++++
> > >  security/keys/trusted-keys/trusted_dcp.c      | 19 +++++++
> > >  2 files changed, 72 insertions(+)
> > >
> > > diff --git a/Documentation/security/keys/trusted-encrypted.rst
> > > b/Documentation/security/keys/trusted-encrypted.rst
> > > index e989b9802f92..f4d7e162d5e4 100644
> > > --- a/Documentation/security/keys/trusted-encrypted.rst
> > > +++ b/Documentation/security/keys/trusted-encrypted.rst
> > > @@ -42,6 +42,14 @@ safe.
> > >           randomly generated and fused into each SoC at manufacturing time.
> > >           Otherwise, a common fixed test key is used instead.
> > >
> > > +     (4) DCP (Data Co-Processor: crypto accelerator of various i.MX
> > > + SoCs)
> > > +
> > > +         Rooted to a one-time programmable key (OTP) that is generally
> > burnt
> > > +         in the on-chip fuses and is accessible to the DCP encryption engine
> > only.
> > > +         DCP provides two keys that can be used as root of trust: the OTP
> > key
> > > +         and the UNIQUE key. Default is to use the UNIQUE key, but selecting
> > > +         the OTP key can be done via a module parameter
> > (dcp_use_otp_key).
> > > +
> > >    *  Execution isolation
> > >
> > >       (1) TPM
> > > @@ -57,6 +65,12 @@ safe.
> > >
> > >           Fixed set of operations running in isolated execution environment.
> > >
> > > +     (4) DCP
> > > +
> > > +         Fixed set of cryptographic operations running in isolated execution
> > > +         environment. Only basic blob key encryption is executed there.
> > > +         The actual key sealing/unsealing is done on main processor/kernel
> > space.
> > > +
> > >    * Optional binding to platform integrity state
> > >
> > >       (1) TPM
> > > @@ -79,6 +93,11 @@ safe.
> > >           Relies on the High Assurance Boot (HAB) mechanism of NXP SoCs
> > >           for platform integrity.
> > >
> > > +     (4) DCP
> > > +
> > > +         Relies on Secure/Trusted boot process (called HAB by vendor) for
> > > +         platform integrity.
> > > +
> > >    *  Interfaces and APIs
> > >
> > >       (1) TPM
> > > @@ -94,6 +113,11 @@ safe.
> > >
> > >           Interface is specific to silicon vendor.
> > >
> > > +     (4) DCP
> > > +
> > > +         Vendor-specific API that is implemented as part of the DCP crypto
> > driver in
> > > +         ``drivers/crypto/mxs-dcp.c``.
> > > +
> > >    *  Threat model
> > >
> > >       The strength and appropriateness of a particular trust source
> > > for a given @@ -129,6 +153,13 @@ selected trust source:
> > >       CAAM HWRNG, enable CRYPTO_DEV_FSL_CAAM_RNG_API and ensure
> > the device
> > >       is probed.
> > >
> > > +  *  DCP (Data Co-Processor: crypto accelerator of various i.MX SoCs)
> > > +
> > > +     The DCP hardware device itself does not provide a dedicated RNG
> > interface,
> > > +     so the kernel default RNG is used. SoCs with DCP like the i.MX6ULL do
> > have
> > > +     a dedicated hardware RNG that is independent from DCP which can be
> > enabled
> > > +     to back the kernel RNG.
> > > +
> > >  Users may override this by specifying ``trusted.rng=kernel`` on the
> > > kernel  command-line to override the used RNG with the kernel's random
> > number pool.
> > >
> > > @@ -231,6 +262,19 @@ Usage::
> > >  CAAM-specific format.  The key length for new keys is always in bytes.
> > >  Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).
> > >
> > > +Trusted Keys usage: DCP
> > > +-----------------------
> > > +
> > > +Usage::
> > > +
> > > +    keyctl add trusted name "new keylen" ring
> > > +    keyctl add trusted name "load hex_blob" ring
> > > +    keyctl print keyid
> > > +
> > > +"keyctl print" returns an ASCII hex copy of the sealed key, which is
> > > +in format specific to this DCP key-blob implementation.  The key
> > > +length for new keys is always in bytes. Trusted Keys can be 32 - 128 bytes
> > (256 - 1024 bits).
> > > +
> > >  Encrypted Keys usage
> > >  --------------------
> > >
> > > @@ -426,3 +470,12 @@ string length.
> > >  privkey is the binary representation of TPM2B_PUBLIC excluding the
> > > initial TPM2B header which can be reconstructed from the ASN.1 octed
> > > string length.
> > > +
> > > +DCP Blob Format
> > > +---------------
> > > +
> > > +.. kernel-doc:: security/keys/trusted-keys/trusted_dcp.c
> > > +   :doc: dcp blob format
> > > +
> > > +.. kernel-doc:: security/keys/trusted-keys/trusted_dcp.c
> > > +   :identifiers: struct dcp_blob_fmt
> > > diff --git a/security/keys/trusted-keys/trusted_dcp.c
> > > b/security/keys/trusted-keys/trusted_dcp.c
> > > index 16c44aafeab3..b5f81a05be36 100644
> > > --- a/security/keys/trusted-keys/trusted_dcp.c
> > > +++ b/security/keys/trusted-keys/trusted_dcp.c
> > > @@ -19,6 +19,25 @@
> > >  #define DCP_BLOB_VERSION 1
> > >  #define DCP_BLOB_AUTHLEN 16
> > >
> > > +/**
> > > + * DOC: dcp blob format
> > > + *
> > > + * The Data Co-Processor (DCP) provides hardware-bound AES keys using
> > > +its
> > > + * AES encryption engine only. It does not provide direct key
> > sealing/unsealing.
> > > + * To make DCP hardware encryption keys usable as trust source, we
> > > +define
> > > + * our own custom format that uses a hardware-bound key to secure the
> > > +sealing
> > > + * key stored in the key blob.
> > > + *
> > > + * Whenever a new trusted key using DCP is generated, we generate a
> > > +random 128-bit
> > > + * blob encryption key (BEK) and 128-bit nonce. The BEK and nonce are
> > > +used to
> > > + * encrypt the trusted key payload using AES-128-GCM.
> > > + *
> > > + * The BEK itself is encrypted using the hardware-bound key using the
> > > +DCP's AES
> > > + * encryption engine with AES-128-ECB. The encrypted BEK, generated
> > > +nonce,
> > > + * BEK-encrypted payload and authentication tag make up the blob
> > > +format together
> > > + * with a version number, payload length and authentication tag.
> > > + */
> > > +
> > >  /**
> > >   * struct dcp_blob_fmt - DCP BLOB format.
> > >   *
> > 
> > Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
> > 
> > I can only test that this does not break a machine without the hardware
> > feature.
> > 
> > Is there anyone who could possibly peer test these patches?
> I am already working on testing this patchset on i.MX6 platform.
> Regards,
> Kshitiz

OK great.

BR, Jarkko