On Wed, 24 Mar 2021 at 14:56, Ahmad Fatoum [off-list ref] wrote:

Hello Mimi,

On 23.03.21 19:07, Mimi Zohar wrote:

quoted

On Tue, 2021-03-23 at 17:35 +0100, Ahmad Fatoum wrote:

quoted

On 21.03.21 21:48, Horia Geantă wrote:

quoted

caam has random number generation capabilities, so it's worth using that
by implementing .get_random.

If the CAAM HWRNG is already seeding the kernel RNG, why not use the kernel's?

Makes for less code duplication IMO.

Using kernel RNG, in general, for trusted keys has been discussed
before.   Please refer to Dave Safford's detailed explanation for not
using it [1].

The argument seems to boil down to:

 - TPM RNG are known to be of good quality
 - Trusted keys always used it so far

Both are fine by me for TPMs, but the CAAM backend is new code and neither point
really applies.

get_random_bytes_wait is already used for generating key material elsewhere.
Why shouldn't new trusted key backends be able to do the same thing?

Please refer to documented trusted keys behaviour here [1]. New
trusted key backends should align to this behaviour and in your case
CAAM offers HWRNG so we should be better using that.

Also, do update documentation corresponding to CAAM as a trusted keys backend.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd.git/tree/Documentation/security/keys/trusted-encrypted.rst#n87

-Sumit

Cheers,
Ahmad

quoted

thanks,

Mimi

[1]
https://lore.kernel.org/linux-integrity/BCA04D5D9A3B764C9B7405BBA4D4A3C035F2A38B@ALPMBAPA12.e2k.ad.ge.com/ (local)

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