linux-kernel - Re: [PATCH v10 2/7] KEYS: trusted: allow use of kernel RNG for key material

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Date:   Tue, 17 May 2022 20:00:45 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Ahmad Fatoum <a.fatoum@...gutronix.de>
Cc:     James Bottomley <jejb@...ux.ibm.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        David Howells <dhowells@...hat.com>, kernel@...gutronix.de,
        Sumit Garg <sumit.garg@...aro.org>,
        Pankaj Gupta <pankaj.gupta@....com>,
        David Gstir <david@...ma-star.at>,
        Michael Walle <michael@...le.cc>,
        John Ernberg <john.ernberg@...ia.se>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Horia Geantă <horia.geanta@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Jan Luebbe <j.luebbe@...gutronix.de>,
        Eric Biggers <ebiggers@...nel.org>,
        Richard Weinberger <richard@....at>,
        Franck LENORMAND <franck.lenormand@....com>,
        Matthias Schiffer <matthias.schiffer@...tq-group.com>,
        keyrings@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH v10 2/7] KEYS: trusted: allow use of kernel RNG for key
 material

Hi Ahmad,

On Tue, May 17, 2022 at 07:52:51PM +0200, Ahmad Fatoum wrote:
> Hello Jason,
> 
> On 17.05.22 19:27, Jason A. Donenfeld wrote:
> > On Fri, May 13, 2022 at 04:57:00PM +0200, Ahmad Fatoum wrote:
> >> +	trusted.rng=	[KEYS]
> >> +			Format: <string>
> >> +			The RNG used to generate key material for trusted keys.
> >> +			Can be one of:
> >> +			- "kernel"
> >> +			- the same value as trusted.source: "tpm" or "tee"
> >> +			- "default"
> >> +			If not specified, "default" is used. In this case,
> >> +			the RNG's choice is left to each individual trust source.
> >> +
> > 
> > As a general mechanism, I object to this. The kernel's RNG must be
> > trusted in the first place for key material. That's the whole point of
> > it.
> > 
> > However, it sounds like you're not proposing a general mechanism, but
> > just something particular to this "trusted keys" business.
> 
> The two currently upstream trust sources (trusted key backends) each provide
> their own RNG callback. This series adds a third backend that uses kernel RNG
> and additionally provides users of the two existing trust sources the option
> to benefit from kernel RNG as well.
> 
> > this should be a module flag, and thus not documented here, but rather
> > some place namespaced to your trusted keys stuff. "trusted_keys.preferred_rng={whatever}"
> 
> The trusted keys module is trusted.ko and directly before my added lines is
> the trusted.source=  documentation, so I think this is already at the correct place.

My apologies; I should have looked at the file itself instead of just
relying on git line context. You're right, the module itself is called
trusted.ko. This is confusing (shouldn't it be trusted_keys or
something?) , but what you propose sounds consistent from a namespacing
perspective with what's already there.

Jason