[PATCH 4/4] crypto/fsl: add RNG support

[Michael Walle <michael@walle.cc>]

Hi Horia, Hi Heinrich,

Am 2020-06-04 10:05, schrieb Horia Geant?:
> On 6/4/2020 5:31 AM, Heinrich Schuchardt wrote:
>> On 6/3/20 12:05 AM, Michael Walle wrote:
>>> Register the random number generator with the rng subsystem in 
>>> u-boot.
>>> This way it can be used by EFI as well as for the 'rng' command.
>>> 
>>> Signed-off-by: Michael Walle <michael@walle.cc>
>>> ---
>>>  drivers/crypto/fsl/Kconfig   | 11 +++++
>>>  drivers/crypto/fsl/Makefile  |  1 +
>>>  drivers/crypto/fsl/jobdesc.c |  9 ++++
>>>  drivers/crypto/fsl/jobdesc.h |  3 ++
>>>  drivers/crypto/fsl/jr.c      |  9 ++++
>>>  drivers/crypto/fsl/rng.c     | 84 
>>> ++++++++++++++++++++++++++++++++++++
>>>  6 files changed, 117 insertions(+)
>>>  create mode 100644 drivers/crypto/fsl/rng.c
>>> 
>>> diff --git a/drivers/crypto/fsl/Kconfig b/drivers/crypto/fsl/Kconfig
>>> index 181a1e5e99..5936b77494 100644
>>> --- a/drivers/crypto/fsl/Kconfig
>>> +++ b/drivers/crypto/fsl/Kconfig
>>> @@ -45,3 +45,14 @@ config SYS_FSL_SEC_COMPAT
>>> 
>>>  config SYS_FSL_SEC_LE
>>>  	bool "Little-endian access to Freescale Secure Boot"
>>> +
>>> +if FSL_CAAM
>>> +
>>> +config FSL_CAAM_RNG
>>> +	bool "Enable Random Number Generator support"
>>> +	depends on DM_RNG
>>> +	default y
>>> +	help
>>> +	  Enable support for the random number generator module of the 
>>> CAAM.
>> 
>> Hello Michael,
>> 
>> when typing CAAM into Google I got a lot of answers but "Cryptographic
>> Accelerator and Assurance Module" was not under the first 50 hits.
>> 
>> If this is a hardware RNG I think we should put this into the text.
>> 
> Totally agree.

Well I was under the impression that UCLASS_RNG is just for hardware
RNGs.

config DM_RNG
         bool "Driver support for Random Number Generator devices"

Whatever "device" means in that context. But I can certainly add
that this is a h/w rng.

> Besides other cryptographic services, CAAM offers:
> -a hardware RNG / TRNG
> -a PRNG / DRBG (SP800-90A compliant DRBG_Hash) - which is seeded
> from the TRNG

Together with that.

> Both are accessible by SW, so clarifying what the driver does
> would be useful (unless DM_RNG / UCLASS_RNG already implies
> one or the other).
> 
> From what I see, driver added by Michael is using the PRNG / DRBG
> and not the TRNG. Is this acceptable?

Well there is no, expectation from UCLASS_RNG. EFI "blindly" uses
the first RNG device.. so it is just a "better than nothing".

RNG is also used for the BLOB protocol. Will it interfere this if
I instantiate the RNG with PR?

> Conceptually this is similar to choosing between
> RDSEED vs. RDRDAND x86 instructions:
> https://software.intel.com/content/www/us/en/develop/blogs/the-difference-between-rdrand-and-rdseed.html
> 
>> So how about:
>> 
>> "Enable support the hardware random number generator of Freescale SOCs
>> using the Cryptographic Accelerator and Assurance Module (CAAM)."
>> 
> The CAAM acronym is expanded at the top of the same file,
> under FSL_CAAM's help:
> <<Enables the Freescale's Cryptographic Accelerator and Assurance
> Module (CAAM), also known as the SEC version 4 (SEC4). The driver uses
> Job Ring as interface to communicate with CAAM.>>

This isn't apparent from the patch. But please note that the new kconfig
option is "if FSL_CAAM", where CAAM is explained.

-michael