[PATCH v10 6/7] doc: trusted-encrypted: describe new CAAM trust source

Ahmad Fatoum
2022-05-13T14:58:13Z

Update documentation for trusted key use with the Cryptographic
Acceleration and Assurance Module (CAAM), an IP on NXP SoCs.

Reviewed-by: Pankaj Gupta <pankaj.gupta@nxp.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
v9 -> v10:
- no change
v8 -> v9:
- add Jarkko's Reviewed-by
v7 -> v8:
- add Pankaj's Reviewed-by
v6 -> v7:
- docs update split off as new Patch (Jarkko)
- fixed typo in "Trusted Keys usage: CAAM" section

To: Jonathan Corbet <corbet@lwn.net>
To: David Howells <dhowells@redhat.com>
To: Jarkko Sakkinen <jarkko@kernel.org>
To: James Bottomley <jejb@linux.ibm.com>
To: Mimi Zohar <zohar@linux.ibm.com>
Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: "Horia Geantă" <horia.geanta@nxp.com>
Cc: Pankaj Gupta <pankaj.gupta@nxp.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Jan Luebbe <j.luebbe@pengutronix.de>
Cc: David Gstir <david@sigma-star.at>
Cc: Richard Weinberger <richard@nod.at>
Cc: Franck LENORMAND <franck.lenormand@nxp.com>
Cc: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Cc: Michael Walle <michael@walle.cc>
Cc: John Ernberg <john.ernberg@actia.se>
Cc: Sumit Garg <sumit.garg@linaro.org>
Cc: keyrings@vger.kernel.org
Cc: linux-crypto@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-integrity@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-security-module@vger.kernel.org
---
.../security/keys/trusted-encrypted.rst | 40 ++++++++++++++++++-
1 file changed, 39 insertions(+), 1 deletion(-)

diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
index 2fe6fd1a2bbd..0bfb4c339748 100644
--- a/Documentation/security/keys/trusted-encrypted.rst
+++ b/Documentation/security/keys/trusted-encrypted.rst
@@ -35,6 +35,13 @@ safe.
Rooted to Hardware Unique Key (HUK) which is generally burnt in on-chip
fuses and is accessible to TEE only.

+ (3) CAAM (Cryptographic Acceleration and Assurance Module: IP on NXP SoCs)
+
+ When High Assurance Boot (HAB) is enabled and the CAAM is in secure
+ mode, trust is rooted to the OTPMK, a never-disclosed 256-bit key
+ randomly generated and fused into each SoC at manufacturing time.
+ Otherwise, a common fixed test key is used instead.
+
* Execution isolation

(1) TPM
@@ -46,6 +53,10 @@ safe.
Customizable set of operations running in isolated execution
environment verified via Secure/Trusted boot process.

+ (3) CAAM
+
+ Fixed set of operations running in isolated execution environment.
+
* Optional binding to platform integrity state

(1) TPM
@@ -63,6 +74,11 @@ safe.
Relies on Secure/Trusted boot process for platform integrity. It can
be extended with TEE based measured boot process.

+ (3) CAAM
+
+ Relies on the High Assurance Boot (HAB) mechanism of NXP SoCs
+ for platform integrity.
+
* Interfaces and APIs

(1) TPM
@@ -74,10 +90,13 @@ safe.
TEEs have well-documented, standardized client interface and APIs. For
more details refer to ``Documentation/staging/tee.rst``.

+ (3) CAAM
+
+ Interface is specific to silicon vendor.

* Threat model

- The strength and appropriateness of a particular TPM or TEE for a given
+ The strength and appropriateness of a particular trust source for a given
purpose must be assessed when using them to protect security-relevant data.

@@ -104,6 +123,12 @@ selected trust source:
from platform specific hardware RNG or a software based Fortuna CSPRNG
which can be seeded via multiple entropy sources.

+ * CAAM: Kernel RNG
+
+ The normal kernel random number generator is used. To seed it from the
+ CAAM HWRNG, enable CRYPTO_DEV_FSL_CAAM_RNG_API and ensure the device
+ is probed.
+
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.

@@ -193,6 +218,19 @@ Usage::
specific to TEE device implementation. The key length for new keys is always
in bytes. Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).

+Trusted Keys usage: CAAM
+------------------------
+
+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 a
+CAAM-specific format. The key length for new keys is always in bytes.
+Trusted Keys can be 32 - 128 bytes (256 - 1024 bits).
+
Encrypted Keys usage
--------------------

--
2.30.2