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 19:38:06 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     Ahmad Fatoum <a.fatoum@...gutronix.de>,
        James Bottomley <jejb@...ux.ibm.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        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

On Tue, May 17, 2022 at 11:52:55AM -0400, Mimi Zohar wrote:
> On Fri, 2022-05-13 at 16:57 +0200, Ahmad Fatoum wrote:
> >  static int __init init_trusted(void)
> >  {
> > +       int (*get_random)(unsigned char *key, size_t key_len);
> >         int i, ret = 0;
> >  
> >         for (i = 0; i < ARRAY_SIZE(trusted_key_sources); i++) {
> > @@ -322,6 +333,28 @@ static int __init init_trusted(void)
> >                             strlen(trusted_key_sources[i].name)))
> >                         continue;
> >  
> > +               /*
> > +                * We always support trusted.rng="kernel" and "default" as
> > +                * well as trusted.rng=$trusted.source if the trust source
> > +                * defines its own get_random callback.
> > +                */
>  
> While TEE trusted keys support was upstreamed, there was a lot of
> discussion about using kernel RNG.  One of the concerns was lack of or
> insuffiencent entropy during early boot on embedded devices.  This
> concern needs to be clearly documented in both Documentation/admin-
> guide/kernel-parameters.txt and Documentation/security/keys/trusted-
> encrypted.rst.

Sounds like FUD. Use `get_random_bytes_wait()`, and you'll be fine.

Jason