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

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Date:   Thu, 1 Apr 2021 02:31:46 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     David Gstir <david@...ma-star.at>,
        Sumit Garg <sumit.garg@...aro.org>,
        Ahmad Fatoum <a.fatoum@...gutronix.de>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Horia Geantă <horia.geanta@....com>,
        Jonathan Corbet <corbet@....net>,
        David Howells <dhowells@...hat.com>,
        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>,
        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 Tue, Mar 30, 2021 at 02:47:18PM -0700, Eric Biggers wrote:
> On Sun, Mar 28, 2021 at 11:37:23PM +0300, Jarkko Sakkinen wrote:
> > 
> > Unfortunately, TPM trusted keys started this bad security practice, and
> > obviously it cannot be fixed without breaking uapi backwards compatibility.
> > 
> 
> The whole point of a randomness source is that it is random.  So userspace can't
> be depending on any particular output, and the randomness source can be changed
> without breaking backwards compatibility.
> 
> So IMO, trusted keys should simply be fixed to use get_random_bytes().
> 
> - Eric

It's a bummer but uapi is the god in the end. Since TPM does not do it
today, that behaviour must be supported forever. That's why a boot option
AND a warning would be the best compromise.

/Jarkko