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

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Date:   Wed, 27 Sep 2023 08:25:24 +0200
From:   David Gstir <david@...ma-star.at>
To:     Jarkko Sakkinen <jarkko@...nel.org>
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

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.

Thanks,
- David