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Date:   Wed, 25 Oct 2023 20:49:24 +0300
From:   "Jarkko Sakkinen" <jarkko@...nel.org>
To:     "David Gstir" <david@...ma-star.at>,
        "Mimi Zohar" <zohar@...ux.ibm.com>,
        "James Bottomley" <jejb@...ux.ibm.com>,
        "Herbert Xu" <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>
Cc:     "Shawn Guo" <shawnguo@...nel.org>,
        "Jonathan Corbet" <corbet@....net>,
        "Sascha Hauer" <s.hauer@...gutronix.de>,
        "Pengutronix Kernel Team" <kernel@...gutronix.de>,
        "Fabio Estevam" <festevam@...il.com>,
        "NXP Linux Team" <linux-imx@....com>,
        "Ahmad Fatoum" <a.fatoum@...gutronix.de>,
        "sigma star Kernel Team" <upstream+dcp@...ma-star.at>,
        "David Howells" <dhowells@...hat.com>,
        "Li Yang" <leoyang.li@....com>, "Paul Moore" <paul@...l-moore.com>,
        "James Morris" <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        "Randy Dunlap" <rdunlap@...radead.org>,
        "Catalin Marinas" <catalin.marinas@....com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        "Tejun Heo" <tj@...nel.org>,
        "Steven Rostedt (Google)" <rostedt@...dmis.org>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-integrity@...r.kernel.org>, <keyrings@...r.kernel.org>,
        <linux-crypto@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linuxppc-dev@...ts.ozlabs.org>,
        <linux-security-module@...r.kernel.org>,
        "Richard Weinberger" <richard@....at>,
        "David Oberhollenzer" <david.oberhollenzer@...ma-star.at>
Subject: Re: [PATCH v4 2/5] KEYS: trusted: Introduce NXP DCP-backed trusted
 keys

On Tue Oct 24, 2023 at 7:20 PM EEST, David Gstir wrote:
> DCP (Data Co-Processor) is the little brother of NXP's CAAM IP.
> Beside of accelerated crypto operations, it also offers support for
> hardware-bound keys. Using this feature it is possible to implement a blob
> mechanism similar to what CAAM offers. Unlike on CAAM, constructing and
> parsing the blob has to happen in software (i.e. the kernel).
>
> The software-based blob format used by DCP trusted keys encrypts
> the payload using AES-128-GCM with a freshly generated random key and nonce.
> The random key itself is AES-128-ECB encrypted using the DCP unique
> or OTP key.
>
> The DCP trusted key blob format is:
> /*
>  * struct dcp_blob_fmt - DCP BLOB format.
>  *
>  * @fmt_version: Format version, currently being %1
>  * @blob_key: Random AES 128 key which is used to encrypt @payload,
>  *            @blob_key itself is encrypted with OTP or UNIQUE device key in
>  *            AES-128-ECB mode by DCP.
>  * @nonce: Random nonce used for @payload encryption.
>  * @payload_len: Length of the plain text @payload.
>  * @payload: The payload itself, encrypted using AES-128-GCM and @blob_key,
>  *           GCM auth tag of size AES_BLOCK_SIZE is attached at the end of it.
>  *
>  * The total size of a DCP BLOB is sizeof(struct dcp_blob_fmt) + @payload_len +
>  * AES_BLOCK_SIZE.
>  */
> struct dcp_blob_fmt {
> 	__u8 fmt_version;
> 	__u8 blob_key[AES_KEYSIZE_128];
> 	__u8 nonce[AES_KEYSIZE_128];
> 	__le32 payload_len;
> 	__u8 payload[];
> } __packed;
>
> By default the unique key is used. It is also possible to use the
> OTP key. While the unique key should be unique it is not documented how
> this key is derived. Therefore selection the OTP key is supported as
> well via the use_otp_key module parameter.
>
> Co-developed-by: Richard Weinberger <richard@....at>
> Signed-off-by: Richard Weinberger <richard@....at>
> Co-developed-by: David Oberhollenzer <david.oberhollenzer@...ma-star.at>
> Signed-off-by: David Oberhollenzer <david.oberhollenzer@...ma-star.at>
> Signed-off-by: David Gstir <david@...ma-star.at>
> ---
>  include/keys/trusted_dcp.h                |  11 +
>  security/keys/trusted-keys/Kconfig        |   9 +-
>  security/keys/trusted-keys/Makefile       |   2 +
>  security/keys/trusted-keys/trusted_core.c |   6 +-
>  security/keys/trusted-keys/trusted_dcp.c  | 311 ++++++++++++++++++++++
>  5 files changed, 337 insertions(+), 2 deletions(-)
>  create mode 100644 include/keys/trusted_dcp.h
>  create mode 100644 security/keys/trusted-keys/trusted_dcp.c
>
> diff --git a/include/keys/trusted_dcp.h b/include/keys/trusted_dcp.h
> new file mode 100644
> index 000000000000..9aaa42075b40
> --- /dev/null
> +++ b/include/keys/trusted_dcp.h
> @@ -0,0 +1,11 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2021 sigma star gmbh
> + */
> +
> +#ifndef TRUSTED_DCP_H
> +#define TRUSTED_DCP_H
> +
> +extern struct trusted_key_ops dcp_trusted_key_ops;
> +
> +#endif
> diff --git a/security/keys/trusted-keys/Kconfig b/security/keys/trusted-keys/Kconfig
> index dbfdd8536468..c6b80b7e5c78 100644
> --- a/security/keys/trusted-keys/Kconfig
> +++ b/security/keys/trusted-keys/Kconfig
> @@ -33,6 +33,13 @@ config TRUSTED_KEYS_CAAM
>  	  Enable use of NXP's Cryptographic Accelerator and Assurance Module
>  	  (CAAM) as trusted key backend.
>  
> -if !TRUSTED_KEYS_TPM && !TRUSTED_KEYS_TEE && !TRUSTED_KEYS_CAAM
> +config TRUSTED_KEYS_DCP
> +	bool "DCP-based trusted keys"
> +	depends on CRYPTO_DEV_MXS_DCP >= TRUSTED_KEYS
> +	default y
> +	help
> +	  Enable use of NXP's DCP (Data Co-Processor) as trusted key backend.
> +
> +if !TRUSTED_KEYS_TPM && !TRUSTED_KEYS_TEE && !TRUSTED_KEYS_CAAM && !TRUSTED_KEYS_DCP

This does not scale tbh.

I'd suggest to add additional patch before adding the new key type,
which clears this up a little bit.

First:

config HAVE_TRUSTED_KEYS
	bool

And then following this pattern to all trusted key types:

config TRUSTED_KEYS_DCP
	bool "DCP-based trusted keys"
	depends on CRYPTO_DEV_MXS_DCP >= TRUSTED_KEYS
	default y
	select HAVE_TRUSTED_KEYS
	help
	  Enable use of NXP's DCP (Data Co-Processor) as trusted key backend.

And finally:

if !HAVE_TRUSTED_KEYS
	comment "No trust source selected!"
endif

BR, Jarkko

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