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

[Kshitiz Varshney]

Hi Jarkko,


> -----Original Message-----
> From: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> Sent: Wednesday, April 3, 2024 9:18 PM
> To: David Gstir <david@xxxxxxxxxxxxx>; Mimi Zohar <zohar@xxxxxxxxxxxxx>;
> James Bottomley <jejb@xxxxxxxxxxxxx>; Herbert Xu
> <herbert@xxxxxxxxxxxxxxxxxxx>; David S. Miller <davem@xxxxxxxxxxxxx>
> Cc: Shawn Guo <shawnguo@xxxxxxxxxx>; Jonathan Corbet
> <corbet@xxxxxxx>; Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>; Pengutronix
> Kernel Team <kernel@xxxxxxxxxxxxxx>; Fabio Estevam
> <festevam@xxxxxxxxx>; dl-linux-imx <linux-imx@xxxxxxx>; Ahmad Fatoum
> <a.fatoum@xxxxxxxxxxxxxx>; sigma star Kernel Team
> <upstream+dcp@xxxxxxxxxxxxx>; David Howells <dhowells@xxxxxxxxxx>; Li
> Yang <leoyang.li@xxxxxxx>; Paul Moore <paul@xxxxxxxxxxxxxx>; James
> Morris <jmorris@xxxxxxxxx>; Serge E. Hallyn <serge@xxxxxxxxxx>; Paul E.
> McKenney <paulmck@xxxxxxxxxx>; Randy Dunlap <rdunlap@xxxxxxxxxxxxx>;
> Catalin Marinas <catalin.marinas@xxxxxxx>; Rafael J. Wysocki
> <rafael.j.wysocki@xxxxxxxxx>; Tejun Heo <tj@xxxxxxxxxx>; Steven Rostedt
> (Google) <rostedt@xxxxxxxxxxx>; linux-doc@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; linux-integrity@xxxxxxxxxxxxxxx;
> keyrings@xxxxxxxxxxxxxxx; linux-crypto@xxxxxxxxxxxxxxx; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx; linux-security-
> module@xxxxxxxxxxxxxxx; Richard Weinberger <richard@xxxxxx>; David
> Oberhollenzer <david.oberhollenzer@xxxxxxxxxxxxx>
> 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@xxxxxx>
> > Signed-off-by: Richard Weinberger <richard@xxxxxx>
> > Co-developed-by: David Oberhollenzer
> > <david.oberhollenzer@xxxxxxxxxxxxx>
> > Signed-off-by: David Oberhollenzer <david.oberhollenzer@xxxxxxxxxxxxx>
> > Signed-off-by: David Gstir <david@xxxxxxxxxxxxx>
> > ---
> >  .../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@xxxxxxxxxx>
> 
> 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
> BR, Jarkko