linux-kernel - Re: [PATCH v1 3/3] KEYS: trusted: Introduce support for NXP CAAM-based trusted keys

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Message-ID: <CAFA6WYOw_mQwOUN=onhzb7zCTyYDBrcx0E7C3LRk6nPLAVCWEQ@mail.gmail.com>
Date:   Wed, 24 Mar 2021 16:17:21 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     Ahmad Fatoum <a.fatoum@...gutronix.de>
Cc:     Mimi Zohar <zohar@...ux.ibm.com>,
        Horia Geantă <horia.geanta@....com>,
        Jonathan Corbet <corbet@....net>,
        David Howells <dhowells@...hat.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        James Bottomley <jejb@...ux.ibm.com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Aymen Sghaier <aymen.sghaier@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Udit Agarwal <udit.agarwal@....com>,
        Jan Luebbe <j.luebbe@...gutronix.de>,
        David Gstir <david@...ma-star.at>,
        Franck Lenormand <franck.lenormand@....com>,
        "keyrings@...r.kernel.org" <keyrings@...r.kernel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v1 3/3] KEYS: trusted: Introduce support for NXP
 CAAM-based trusted keys

On Wed, 24 Mar 2021 at 14:56, Ahmad Fatoum <a.fatoum@...gutronix.de> wrote:
>
> Hello Mimi,
>
> On 23.03.21 19:07, Mimi Zohar wrote:
> > On Tue, 2021-03-23 at 17:35 +0100, Ahmad Fatoum wrote:
> >> On 21.03.21 21:48, Horia Geantă wrote:
> >>> caam has random number generation capabilities, so it's worth using that
> >>> by implementing .get_random.
> >>
> >> If the CAAM HWRNG is already seeding the kernel RNG, why not use the kernel's?
> >>
> >> Makes for less code duplication IMO.
> >
> > Using kernel RNG, in general, for trusted keys has been discussed
> > before.   Please refer to Dave Safford's detailed explanation for not
> > using it [1].
>
> The argument seems to boil down to:
>
>  - TPM RNG are known to be of good quality
>  - Trusted keys always used it so far
>
> Both are fine by me for TPMs, but the CAAM backend is new code and neither point
> really applies.
>
> get_random_bytes_wait is already used for generating key material elsewhere.
> Why shouldn't new trusted key backends be able to do the same thing?
>

Please refer to documented trusted keys behaviour here [1]. New
trusted key backends should align to this behaviour and in your case
CAAM offers HWRNG so we should be better using that.

Also, do update documentation corresponding to CAAM as a trusted keys backend.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd.git/tree/Documentation/security/keys/trusted-encrypted.rst#n87

-Sumit

> Cheers,
> Ahmad
>
> >
> > thanks,
> >
> > Mimi
> >
> > [1]
> > https://lore.kernel.org/linux-integrity/BCA04D5D9A3B764C9B7405BBA4D4A3C035F2A38B@ALPMBAPA12.e2k.ad.ge.com/
> >
> >
> >
>
> --
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