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Subject: Re: [PATCH v3 1/3] crypto: mxs-dcp: Add support for hardware provided
 keys
From:   David Gstir <david@sigma-star.at>
In-Reply-To: <CVS3NIJ8OO6Y.2C6GJ9OBR6COC@suppilovahvero>
Date:   Wed, 27 Sep 2023 08:25:24 +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>,
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        Jonathan Corbet <corbet@lwn.net>,
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        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>,
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References: <20230918141826.8139-1-david@sigma-star.at>
 <20230918141826.8139-2-david@sigma-star.at>
 <CVS3NIJ8OO6Y.2C6GJ9OBR6COC@suppilovahvero>
To:     Jarkko Sakkinen <jarkko@kernel.org>
Precedence: bulk

Jarkko,

> On 25.09.2023, at 17:22, Jarkko Sakkinen <jarkko@kernel.org> wrote:
>=20
> On Mon Sep 18, 2023 at 5:18 PM EEST, David Gstir wrote:
>> DCP is capable to performing AES with hardware-bound keys.
>> These keys are not stored in main memory and are therefore not =
directly
>> accessible by the operating system.
>>=20
>> So instead of feeding the key into DCP, we need to place a
>> reference to such a key before initiating the crypto operation.
>> Keys are referenced by a one byte identifiers.
>=20
> Not sure what the action of feeding key into DCP even means if such
> action does not exists.
>=20
> What you probably would want to describe here is how keys get created
> and how they are referenced by the kernel.
>=20
> For the "use" part please try to avoid academic paper style long
> expression starting with "we" pronomine.
>=20
> So the above paragraph would normalize into "The keys inside DCP
> are referenced by one byte identifier". Here of course would be
> for the context nice to know what is this set of DCP keys. E.g.
> are total 256 keys or some subset?
>=20
> When using too much prose there can be surprsingly little digestable
> information, thus this nitpicking.

Thanks for reviewing that in detail! I=E2=80=99ll rephrase the commit
messages on all patches to get rid of the academic paper style.


>=20
>> DCP supports 6 different keys: 4 slots in the secure memory area,
>> a one time programmable key which can be burnt via on-chip fuses
>> and an unique device key.
>>=20
>> Using these keys is restricted to in-kernel users that use them as =
building
>> block for other crypto tools such as trusted keys. Allowing userspace
>> (e.g. via AF_ALG) to use these keys to crypt or decrypt data is a =
security
>> risk, because there is no access control mechanism.
>=20
> Unless this patch has anything else than trusted keys this should not
> be an open-ended sentence. You want to say roughly that DCP hardware
> keys are implemented for the sake to implement trusted keys support,
> and exactly and only that.
>=20
> This description also lacks actions taken by the code changes below,
> which is really the beef of any commit description.

You=E2=80=99re right. I=E2=80=99ll add that.

Thanks,
- David