Re: [PATCH v1 0/3] KEYS: trusted: Introduce support for NXP CAAM-based trusted keys

From: "Horia Geantă" <horia.geanta@nxp.com>
To: Ahmad Fatoum <a.fatoum@pengutronix.de>,
	Jarkko Sakkinen <jarkko@kernel.org>,
	Mimi Zohar <zohar@linux.ibm.com>,
	Aymen Sghaier <aymen.sghaier@nxp.com>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	"David S. Miller" <davem@davemloft.net>,
	James Bottomley <jejb@linux.ibm.com>
Cc: "kernel@pengutronix.de" <kernel@pengutronix.de>,
	David Howells <dhowells@redhat.com>,
	James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Steffen Trumtrar <s.trumtrar@pengutronix.de>,
	Udit Agarwal <udit.agarwal@nxp.com>,
	Jan Luebbe <j.luebbe@penutronix.de>,
	David Gstir <david@sigma-star.at>,
	Franck Lenormand <franck.lenormand@nxp.com>,
	Sumit Garg <sumit.garg@linaro.org>,
	"linux-integrity@vger.kernel.org"
	<linux-integrity@vger.kernel.org>,
	"keyrings@vger.kernel.org" <keyrings@vger.kernel.org>,
	"linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-security-module@vger.kernel.org" 
	<linux-security-module@vger.kernel.org>
Subject: Re: [PATCH v1 0/3] KEYS: trusted: Introduce support for NXP CAAM-based trusted keys
Date: Sun, 21 Mar 2021 22:01:10 +0200	[thread overview]
Message-ID: <f0f43b30-3dfb-c2a0-7f69-6e5488f871cd@nxp.com> (raw)
In-Reply-To: <cover.56fff82362af6228372ea82e6bd7e586e23f0966.1615914058.git-series.a.fatoum@pengutronix.de>

On 3/16/2021 7:02 PM, Ahmad Fatoum wrote:
> The Cryptographic Acceleration and Assurance Module (CAAM) is an IP core
> built into many newer i.MX and QorIQ SoCs by NXP.
> 
> Its blob mechanism can AES encrypt/decrypt user data using a unique
> never-disclosed device-specific key. There has been multiple
> discussions on how to represent this within the kernel:
> 
>  - [RFC] crypto: caam - add red blobifier
>    Steffen implemented[1] a PoC sysfs driver to start a discussion on how to
>    best integrate the blob mechanism.
>    Mimi suggested that it could be used to implement trusted keys.
>    Trusted keys back then were a TPM-only feature.
> 
>  - security/keys/secure_key: Adds the secure key support based on CAAM.
>    Udit added[2] a new "secure" key type with the CAAM as backend. The key
>    material stays within the kernel only.
>    Mimi and James agreed that this needs a generic interface, not specific
>    to CAAM. Mimi suggested trusted keys. Jan noted that this could serve as
>    basis for TEE-backed keys.
> 
>  - [RFC] drivers: crypto: caam: key: Add caam_tk key type
>    Franck added[3] a new "caam_tk" key type based on Udit's work. The key
>    material stays within the kernel only, but can optionally be user-set
>    instead of coming from RNG. James voiced the opinion that there should
>    be just one user-facing generic wrap/unwrap key type with multiple
>    possible handlers. David suggested trusted keys.
> 
The whole point was to use caam "black blobs", with the main advantage of
keys being kept encrypted in memory after "unsealing" the blobs.
(Keys in blobs are encrypted with a persistent BKEK - blob KEK, derived from
fuse-based OTPMK. OTOH black keys are keys encrypted with an ephemeral, random
KEK that is stored in an internal caam register. When a black blob is unsealed,
the key is practically rekeyed, the random key replacing the BKEK; key is never
exposed in plaintext, rekeying happens in caam).

Current implementation uses "red blobs", which means keys are left unprotected
in memory after blobs are unsealed.

>  - Introduce TEE based Trusted Keys support
>    Sumit reworked[4] trusted keys to support multiple possible backends with
>    one chosen at boot time and added a new TEE backend along with TPM.
>    This now sits in Jarkko's master branch to be sent out for v5.13
> 
> This patch series builds on top of Sumit's rework to have the CAAM as yet another
> trusted key backend.
> 
Shouldn't the description under TRUSTED_KEYS (in security/keys/Kconfig)
be updated to reflect the availability of multiple backends?

Thanks,
Horia