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

[Sumit Garg <sumit.garg@linaro.org>]

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