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

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Date:   Wed, 31 Mar 2021 23:03:37 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        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>,
        "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 Thu, Apr 01, 2021 at 08:50:05AM +0300, Jarkko Sakkinen wrote:
> On Thu, Apr 01, 2021 at 12:11:32PM +1100, Herbert Xu wrote:
> > On Wed, Mar 31, 2021 at 04:34:29PM -0700, Eric Biggers wrote:
> > > On Thu, Apr 01, 2021 at 02:31:46AM +0300, Jarkko Sakkinen wrote:
> > > > 
> > > > 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.
> > > 
> > > It's not UAPI if there is no way for userspace to tell if it changed.
> > 
> > Exactly.  UAPI is only an issue if something *breaks*.
> 
> If there's even one user that comes shouting that he has a user space
> configuration, where e.g. rng entropy is consumed constantly and the
> code assumes that trusted keys does not add to that, then something
> would break.
> 
> It would be a crap user space yes, but I don't want to go on reverting
> because of that. I think there is small but still existing chance that
> something could break.

random.c no longer provides any interfaces that subtract entropy credits, as
that was never something that made sense.  So "consuming" all the entropy from
random.c isn't a thing anymore.

> 
> Why not just add a boot parameter instead of making brutal enforcing
> changes, indirectly visible to the user space?

Why not just fix this bug instead of providing an option to fix it that everyone
will need to remember to provide?

- Eric