[PATCH] rockchip: board: Increase rng-seed size to make it sufficient for modern Linux

[Dragan Simic]

On 2024-10-14 12:52, Marek Vasut wrote:
> On 10/14/24 12:37 PM, Dragan Simic wrote:
>> On 2024-10-14 12:35, Marek Vasut wrote:
>>> On 10/14/24 12:32 PM, Dragan Simic wrote:
>>>> On 2024-10-14 12:26, Alex ThreeD wrote:
>>>>> On Mon, Oct 14, 2024 at 12:10 AM Marek Vasut <marex at denx.de> wrote:
>>>>>> Let's make this override-able via environment variable, because 
>>>>>> this
>>>>>> might be growing in the future again. Does this work ?
>>>>>> 
>>>>>> size_t len = env_get_ulong("kaslrseed_size", 10, 32);
>>>>> 
>>>>> Maybe `env_get_hex("rng_seed_size", 32)` would be better? As most 
>>>>> other env are
>>>>> hexadecimal.
>>>>> 
>>>>> Actually it seems that entropy required to init pool early has 
>>>>> decreased in
>>>>> Linux 5.19 from 64 bytes (2 * CHACHA_KEY_SIZE) to 32 bytes
>>>>> (BLAKE2S_HASH_SIZE)
>>>>> https://elixir.bootlin.com/linux/v5.18/source/drivers/char/ 
>>>>> random.c#L236
>>>>> https://elixir.bootlin.com/linux/v5.19/source/drivers/char/ 
>>>>> random.c#L551
>>>>> Anyway config knob should not harm.
>>>> 
>>>> I think that the value received from the new environment variable
>>>> should be accepted only if it's greater than some hardcoded value,
>>>> in this case 32.  That way, someone won't be able to misconfigure
>>>> their board environment and cause the early random pool 
>>>> initialization
>>>> to be postponed.
>>> 
>>> Using low number could be useful for testing. Print a WARNING if the
>>> number is too low perhaps?
>> 
>> Yes, testing with low values has also crossed my mind.  Priting such
>> warnings would be a viable option.
> 
> Sounds good then, thanks!

Thank you. :)  My early thoughts were like "wow, someone can break
their early random pool initialization this way", but right after
that something like "well, breaking many other things is already
possible in the same way" crossed my mind. :)

So, yes, just printing such warnings is perfectly fine.