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

[Jason A. Donenfeld]

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