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Subject: Re: [PATCH v3 2/3] KEYS: trusted: Introduce support for NXP DCP-based
 trusted keys
From:   David Gstir <david@sigma-star.at>
In-Reply-To: <CVS3WN3Q04XY.B40S4RBH9QM7@suppilovahvero>
Date:   Wed, 27 Sep 2023 08:33:01 +0200
Cc:     Mimi Zohar <zohar@linux.ibm.com>,
        James Bottomley <jejb@linux.ibm.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Shawn Guo <shawnguo@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        "kernel@pengutronix.de" <kernel@pengutronix.de>,
        Fabio Estevam <festevam@gmail.com>,
        NXP Linux Team <linux-imx@nxp.com>,
        Ahmad Fatoum <a.fatoum@pengutronix.de>,
        sigma star Kernel Team <upstream+dcp@sigma-star.at>,
        David Howells <dhowells@redhat.com>,
        Li Yang <leoyang.li@nxp.com>, Paul Moore <paul@paul-moore.com>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Tejun Heo <tj@kernel.org>,
        "Steven Rostedt (Google)" <rostedt@goodmis.org>,
        linux-doc@vger.kernel.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.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-arm-kernel@lists.infradead.org,
        linuxppc-dev@lists.ozlabs.org,
        "linux-security-module@vger.kernel.org" 
        <linux-security-module@vger.kernel.org>,
        Richard Weinberger <richard@nod.at>,
        David Oberhollenzer <david.oberhollenzer@sigma-star.at>
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Message-Id: <085CABBD-1EA1-44A9-AA9C-C04039A627AB@sigma-star.at>
References: <20230918141826.8139-1-david@sigma-star.at>
 <20230918141826.8139-3-david@sigma-star.at>
 <CVS3WN3Q04XY.B40S4RBH9QM7@suppilovahvero>
To:     Jarkko Sakkinen <jarkko@kernel.org>
Precedence: bulk

Jarkko,

> On 25.09.2023, at 17:34, Jarkko Sakkinen <jarkko@kernel.org> wrote:
>=20
> On Mon Sep 18, 2023 at 5:18 PM EEST, David Gstir wrote:
>> DCP (Data Co-Processor) is the little brother of NXP's CAAM IP.
>>=20
>> Beside of accelerated crypto operations, it also offers support for
>> hardware-bound keys. Using this feature it is possible to implement a =
blob
>> mechanism just like CAAM offers. Unlike on CAAM, constructing and
>> parsing the blob has to happen in software.
>>=20
>> We chose the following format for the blob:
>=20
> Who is we?

The authors of this patch. But I=E2=80=99ll rephrase that to get rid
of the academic paper style.

> And there is no choosing anything if the below structure if hardware
> defined (not software defined):

The below structure is actually software-defined by this patch.
Contrary to CAAM, DCP does not have a key blob feature.
DCP=E2=80=99s hardware-bound UNIQUE or OTP key is used to bind
these key blobs to a specific DCP chip.


>=20
>> /*
>> * 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;
>>=20
>> @payload is the key provided by trusted_key_ops->seal().
>>=20
>> By default the UNIQUE device key is used, it is also possible to use
>> the OTP key. While the UNIQUE device key should be unique it is not
>> entirely clear whether this is the case due to unclear documentation.
>> If someone wants to be sure they can burn their own unique key
>> into the OTP fuse and set the use_otp_key module parameter.
>>=20
>> Co-developed-by: Richard Weinberger <richard@nod.at>
>> Signed-off-by: Richard Weinberger <richard@nod.at>
>> Co-developed-by: David Oberhollenzer =
<david.oberhollenzer@sigma-star.at>
>> Signed-off-by: David Oberhollenzer =
<david.oberhollenzer@sigma-star.at>
>> Signed-off-by: David Gstir <david@sigma-star.at>
>> ---
>> .../admin-guide/kernel-parameters.txt         |  13 +
>=20
> Separate commit for this.
>=20
>> MAINTAINERS                                   |   9 +
>=20
> Ditto (i.e. total two additional patches).

Will do for v4!=20

Thanks,
- David=