[2/4] KEYS: trusted: allow trust sources to use kernel RNG for key material

The two existing trusted key sources don't make use of the kernel RNG,
but instead let the hardware that does the sealing/unsealing also
generate the random key material. While a previous change offers users
the choice to use the kernel RNG instead for both, new trust sources
may want to unconditionally use the kernel RNG for generating key
material, like it's done elsewhere in the kernel.

This is especially prudent for hardware that has proven-in-production
HWRNG drivers implemented, as otherwise code would have to be duplicated
only to arrive at a possibly worse result.

Make this possible by turning struct trusted_key_ops::get_random
into an optional member. If a driver leaves it NULL, kernel RNG
will be used instead.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
To: James Bottomley <jejb@linux.ibm.com>
To: Jarkko Sakkinen <jarkko@kernel.org>
To: Mimi Zohar <zohar@linux.ibm.com>
To: David Howells <dhowells@redhat.com>
Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: "Horia Geantă" <horia.geanta@nxp.com>
Cc: Aymen Sghaier <aymen.sghaier@nxp.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Udit Agarwal <udit.agarwal@nxp.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Jan Luebbe <j.luebbe@pengutronix.de>
Cc: David Gstir <david@sigma-star.at>
Cc: Richard Weinberger <richard@nod.at>
Cc: Franck LENORMAND <franck.lenormand@nxp.com>
Cc: Sumit Garg <sumit.garg@linaro.org>
Cc: keyrings@vger.kernel.org
Cc: linux-crypto@vger.kernel.org
Cc: linux-integrity@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-security-module@vger.kernel.org
---
 include/keys/trusted-type.h               | 2 +-
 security/keys/trusted-keys/trusted_core.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

On Wed, 21 Jul 2021 at 22:19, Ahmad Fatoum <a.fatoum@pengutronix.de> wrote:
>
> The two existing trusted key sources don't make use of the kernel RNG,
> but instead let the hardware that does the sealing/unsealing also
> generate the random key material. While a previous change offers users
> the choice to use the kernel RNG instead for both, new trust sources
> may want to unconditionally use the kernel RNG for generating key
> material, like it's done elsewhere in the kernel.
>
> This is especially prudent for hardware that has proven-in-production
> HWRNG drivers implemented, as otherwise code would have to be duplicated
> only to arrive at a possibly worse result.
>
> Make this possible by turning struct trusted_key_ops::get_random
> into an optional member. If a driver leaves it NULL, kernel RNG
> will be used instead.
>
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
> ---
> To: James Bottomley <jejb@linux.ibm.com>
> To: Jarkko Sakkinen <jarkko@kernel.org>
> To: Mimi Zohar <zohar@linux.ibm.com>
> To: David Howells <dhowells@redhat.com>
> Cc: James Morris <jmorris@namei.org>
> Cc: "Serge E. Hallyn" <serge@hallyn.com>
> Cc: "Horia Geantă" <horia.geanta@nxp.com>
> Cc: Aymen Sghaier <aymen.sghaier@nxp.com>
> Cc: Herbert Xu <herbert@gondor.apana.org.au>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Udit Agarwal <udit.agarwal@nxp.com>
> Cc: Eric Biggers <ebiggers@kernel.org>
> Cc: Jan Luebbe <j.luebbe@pengutronix.de>
> Cc: David Gstir <david@sigma-star.at>
> Cc: Richard Weinberger <richard@nod.at>
> Cc: Franck LENORMAND <franck.lenormand@nxp.com>
> Cc: Sumit Garg <sumit.garg@linaro.org>
> Cc: keyrings@vger.kernel.org
> Cc: linux-crypto@vger.kernel.org
> Cc: linux-integrity@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-security-module@vger.kernel.org
> ---
>  include/keys/trusted-type.h               | 2 +-
>  security/keys/trusted-keys/trusted_core.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/keys/trusted-type.h b/include/keys/trusted-type.h
> index d89fa2579ac0..4eb64548a74f 100644
> --- a/include/keys/trusted-type.h
> +++ b/include/keys/trusted-type.h
> @@ -64,7 +64,7 @@ struct trusted_key_ops {
>         /* Unseal a key. */
>         int (*unseal)(struct trusted_key_payload *p, char *datablob);
>
> -       /* Get a randomized key. */
> +       /* Optional: Get a randomized key. */
>         int (*get_random)(unsigned char *key, size_t key_len);
>
>         /* Exit key interface. */
> diff --git a/security/keys/trusted-keys/trusted_core.c b/security/keys/trusted-keys/trusted_core.c
> index 569af9af8df0..d2b7626cde8b 100644
> --- a/security/keys/trusted-keys/trusted_core.c
> +++ b/security/keys/trusted-keys/trusted_core.c
> @@ -334,7 +334,7 @@ static int __init init_trusted(void)
>                         continue;
>
>                 get_random = trusted_key_sources[i].ops->get_random;
> -               if (trusted_kernel_rng)
> +               if (trusted_kernel_rng || !get_random)
>                         get_random = kernel_get_random;
>

For ease of understanding, I would prefer to write it as:

                  get_random = trusted_key_sources[i].ops->get_random ?:
                                         kernel_get_random;
                  if (trusted_kernel_rng)
                        get_random = kernel_get_random;

With that:

Acked-by: Sumit Garg <sumit.garg@linaro.org>

-Sumit

>                 static_call_update(trusted_key_init,
> --
> git-series 0.9.1