linux-kernel - Re: [PATCH v3 1/3] crypto: mxs-dcp: Add support for hardware provided keys

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Date:   Tue, 03 Oct 2023 01:50:43 +0300
From:   "Jarkko Sakkinen" <jarkko@...nel.org>
To:     "David Gstir" <david@...ma-star.at>
Cc:     "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>,
        "Shawn Guo" <shawnguo@...nel.org>,
        "Jonathan Corbet" <corbet@....net>,
        "Sascha Hauer" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <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-kernel@...r.kernel.org>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "keyrings@...r.kernel.org" <keyrings@...r.kernel.org>,
        "linux-crypto@...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" 
        <linux-security-module@...r.kernel.org>,
        "Richard Weinberger" <richard@....at>,
        "David Oberhollenzer" <david.oberhollenzer@...ma-star.at>
Subject: Re: [PATCH v3 1/3] crypto: mxs-dcp: Add support for hardware
 provided keys

On Wed Sep 27, 2023 at 9:25 AM EEST, David Gstir wrote:
> Jarkko,
>
> > On 25.09.2023, at 17:22, Jarkko Sakkinen <jarkko@...nel.org> wrote:
> > 
> > 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.
> >> 
> >> 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.
> > 
> > Not sure what the action of feeding key into DCP even means if such
> > action does not exists.
> > 
> > What you probably would want to describe here is how keys get created
> > and how they are referenced by the kernel.
> > 
> > For the "use" part please try to avoid academic paper style long
> > expression starting with "we" pronomine.
> > 
> > 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?
> > 
> > When using too much prose there can be surprsingly little digestable
> > information, thus this nitpicking.
>
> Thanks for reviewing that in detail! I’ll rephrase the commit
> messages on all patches to get rid of the academic paper style.
>
>
> > 
> >> 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.
> >> 
> >> 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.
> > 
> > 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.
> > 
> > This description also lacks actions taken by the code changes below,
> > which is really the beef of any commit description.
>
> You’re right. I’ll add that.

Yup, I'm just doing my part of the job, as I'm expected to do it :-)
Thanks for understanding.

> Thanks,
> - David

BR, Jarkko