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

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Jarkko,

On 17.05.22 20:10, Jarkko Sakkinen wrote:
> On Tue, 2022-05-17 at 19:27 +0200, Jason A. Donenfeld wrote:
>> On Fri, May 13, 2022 at 04:57:00PM +0200, Ahmad Fatoum wrote:
>>> +       trusted.rng=    [KEYS]
>>> +                       Format: <string>
>>> +                       The RNG used to generate key material for trusted keys.
>>> +                       Can be one of:
>>> +                       - "kernel"
>>> +                       - the same value as trusted.source: "tpm" or "tee"
>>> +                       - "default"
>>> +                       If not specified, "default" is used. In this case,
>>> +                       the RNG's choice is left to each individual trust source.
>>> +
>>
>> As a general mechanism, I object to this. The kernel's RNG must be
>> trusted in the first place for key material. That's the whole point of
>> it.
> 
> I would relax this  a bit: kernel's RNG must be implicitly must be
> trusted. If the parameter is used, you make an explicit choice that
> you are aware of the trust.
> 
> If this was opt-out parameter, instead of opt-in, I would get your
> argument.
> 
>> However, it sounds like you're not proposing a general mechanism, but
>> just something particular to this "trusted keys" business. In that case,
>> this should be a module flag, and thus not documented here, but rather
>> some place namespaced to your trusted keys stuff. "trusted_keys.preferred_rng={whatever}"
> 
> However, I think this a good proposal. Let's make it a module parameter
> instead.

It's already a module parameter.

> 
>> Jason
> 
> BR, Jarkko


-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |