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    SubjectRe: [EXT] Re: [PATCH v8 6/6] docs: trusted-encrypted: add DCP as new trust source
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    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
    > >
    > > Caution: This is an external email. Please take care when clicking links or
    > > opening attachments. When in doubt, report the message using the 'Report
    > > this email' button
    > >
    > >
    > > 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

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