linux-kernel - Re: [PATCH v2 6/6] KEYS: trusted: Introduce support for NXP CAAM-based trusted keys

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Date:   Fri, 2 Jul 2021 14:33:52 +0200
From:   Ahmad Fatoum <a.fatoum@...gutronix.de>
To:     Richard Weinberger <richard@....at>
Cc:     Jonathan Corbet <corbet@....net>,
        David Howells <dhowells@...hat.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        James Bottomley <jejb@...ux.ibm.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        kernel <kernel@...gutronix.de>, James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        horia geanta <horia.geanta@....com>,
        aymen sghaier <aymen.sghaier@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        davem <davem@...emloft.net>, Udit Agarwal <udit.agarwal@....com>,
        Eric Biggers <ebiggers@...nel.org>,
        Jan Luebbe <j.luebbe@...gutronix.de>,
        david <david@...ma-star.at>,
        Franck Lenormand <franck.lenormand@....com>,
        Sumit Garg <sumit.garg@...aro.org>,
        "open list, ASYMMETRIC KEYS" <keyrings@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        LSM <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v2 6/6] KEYS: trusted: Introduce support for NXP
 CAAM-based trusted keys

On 02.07.21 12:53, Richard Weinberger wrote:
> Ahmad,
> 
> ----- Ursprüngliche Mail -----
>> Von: "Ahmad Fatoum" <a.fatoum@...gutronix.de>
>>> I'm still think that hard coding the key modifier is not wise.
>>> As I said[0], there are folks out there that want to provide their own modifier,
>>> so it is not only about being binary compatible with other CAAM blob patches in
>>> the wild.
>>
>> I don't think the characterization as a salt is accurate. AFAIU it's more
>> of a namespace, so blobs being loaded are "type-checked" against the modifier.
> 
> Well, the CAAM programmer's reference manual states that the blob key is a 128 bit modifier
> and has two purposes:
> 1. It can be used as tag to provide separation between blobs to detect accidental replacement of blobs.
> 2. But it can also be treated as secret to provide additional protection. Because the blob encryption
> key derivation includes the key modifier.
> 
> While you have case 1 in mind, I care about case 2. :-)

Ah, using the key modifier as a passphrase didn't occur to me.

>>> I'll happily implement that feature after your patches got merged but IMHO we
>>> should first agree on an interface.
>>> How about allowing another optional parameter to Opt_new and Opt_load
>>
>> Sound good to me. pcrlock for TPM trusted keys has the same interface.
>>
>> I'd prefer the new option to accept strings, not hex though.
> 
> Both is possible. If the string starts with "0x" it needs to be decoded to a
> 128 bit key. Otherwise it has to be a up to 16 byte string.

Fine by me. Looking forward to your patches. :-)


Cheers,
Ahmad

> 
> Thanks,
> //richard
> 

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