Re: [PATCH v8 5/6] doc: trusted-encrypted: describe new CAAM trust source

[Jarkko Sakkinen]

On Thu, Apr 28, 2022 at 04:01:44PM +0200, Ahmad Fatoum wrote:
> 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@xxxxxxx>
> Signed-off-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>
> ---
> 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@xxxxxxx>
> To: David Howells <dhowells@xxxxxxxxxx>
> To: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> To: James Bottomley <jejb@xxxxxxxxxxxxx>
> To: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> Cc: James Morris <jmorris@xxxxxxxxx>
> Cc: "Serge E. Hallyn" <serge@xxxxxxxxxx>
> Cc: "Horia Geantă" <horia.geanta@xxxxxxx>
> Cc: Pankaj Gupta <pankaj.gupta@xxxxxxx>
> Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Eric Biggers <ebiggers@xxxxxxxxxx>
> Cc: Jan Luebbe <j.luebbe@xxxxxxxxxxxxxx>
> Cc: David Gstir <david@xxxxxxxxxxxxx>
> Cc: Richard Weinberger <richard@xxxxxx>
> Cc: Franck LENORMAND <franck.lenormand@xxxxxxx>
> Cc: Matthias Schiffer <matthias.schiffer@xxxxxxxxxxxxxxx>
> Cc: Sumit Garg <sumit.garg@xxxxxxxxxx>
> Cc: keyrings@xxxxxxxxxxxxxxx
> Cc: linux-crypto@xxxxxxxxxxxxxxx
> Cc: linux-doc@xxxxxxxxxxxxxxx
> Cc: linux-integrity@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-security-module@xxxxxxxxxxxxxxx
> ---
>  .../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
> 

Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>

BR, Jarkko