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

Mimi Zohar
2022-05-17T18:22:17Z

On Tue, 2022-05-17 at 19:38 +0200, Jason A. Donenfeld wrote:
> 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.

As per the original discussion, there's also certification requirements
[1].

Mimi

[1] https://lkml.org/lkml/2019/10/9/53