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doc: trusted-encrypted: describe new CAAM trust source

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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>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
This commit is contained in:
Ahmad Fatoum 2022-05-13 16:57:04 +02:00 committed by Jarkko Sakkinen
parent e9c5048c2d
commit 5002426e42
1 changed files with 39 additions and 1 deletions
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40
Documentation/security/keys/trusted-encrypted.rst
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@ -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
--------------------