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

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Date:   Mon, 9 Aug 2021 09:52:20 +0200
From:   Ahmad Fatoum <a.fatoum@...gutronix.de>
To:     Sumit Garg <sumit.garg@...aro.org>
Cc:     James Bottomley <jejb@...ux.ibm.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        David Howells <dhowells@...hat.com>,
        kernel <kernel@...gutronix.de>, James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Horia Geantă <horia.geanta@....com>,
        Aymen Sghaier <aymen.sghaier@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Udit Agarwal <udit.agarwal@....com>,
        Eric Biggers <ebiggers@...nel.org>,
        Jan Luebbe <j.luebbe@...gutronix.de>,
        David Gstir <david@...ma-star.at>,
        Richard Weinberger <richard@....at>,
        Franck LENORMAND <franck.lenormand@....com>,
        "open list:ASYMMETRIC KEYS" <keyrings@...r.kernel.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:SECURITY SUBSYSTEM" 
        <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH 2/4] KEYS: trusted: allow trust sources to use kernel RNG
 for key material

Hello Sumit,

On 22.07.21 08:31, Sumit Garg wrote:
> On Wed, 21 Jul 2021 at 22:19, Ahmad Fatoum <a.fatoum@...gutronix.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@...gutronix.de>
>> ---
>> To: James Bottomley <jejb@...ux.ibm.com>
>> To: Jarkko Sakkinen <jarkko@...nel.org>
>> To: Mimi Zohar <zohar@...ux.ibm.com>
>> To: David Howells <dhowells@...hat.com>
>> Cc: James Morris <jmorris@...ei.org>
>> Cc: "Serge E. Hallyn" <serge@...lyn.com>
>> Cc: "Horia Geantă" <horia.geanta@....com>
>> Cc: Aymen Sghaier <aymen.sghaier@....com>
>> Cc: Herbert Xu <herbert@...dor.apana.org.au>
>> Cc: "David S. Miller" <davem@...emloft.net>
>> Cc: Udit Agarwal <udit.agarwal@....com>
>> Cc: Eric Biggers <ebiggers@...nel.org>
>> Cc: Jan Luebbe <j.luebbe@...gutronix.de>
>> Cc: David Gstir <david@...ma-star.at>
>> Cc: Richard Weinberger <richard@....at>
>> Cc: Franck LENORMAND <franck.lenormand@....com>
>> Cc: Sumit Garg <sumit.garg@...aro.org>
>> Cc: keyrings@...r.kernel.org
>> Cc: linux-crypto@...r.kernel.org
>> Cc: linux-integrity@...r.kernel.org
>> Cc: linux-kernel@...r.kernel.org
>> Cc: linux-security-module@...r.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@...aro.org>

I don't think it improves readability to split up the conditional.
At least I need to take a second pass over the code to understand
the second conditional.

Cheers,
Ahmad

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


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