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

Jason A. Donenfeld
2022-05-17T17:38:35Z

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