Re: [PATCH] tpm: Salt tpm_get_random() result with get_random_bytes()

[Jarkko Sakkinen]

On Tue, Oct 15, 2019 at 02:04:50PM -0300, Jason Gunthorpe wrote:
> On Tue, Oct 15, 2019 at 03:47:02PM +0300, Jarkko Sakkinen wrote:
> > Salt the result that comes from the TPM RNG with random bytes from the
> > kernel RNG. This will allow to use tpm_get_random() as a substitute for
> > get_random_bytes().  TPM could have a bug (making results predicatable),
> > backdoor or even an inteposer in the bus. Salting gives protections
> > against these concerns.
> 
> Seems like a dangerous use case, why would any kernel user that cared
> about quality of randomness ever call a tpm_* API to get quality
> random data?

This is related to this discussion:

https://lore.kernel.org/linux-integrity/CAE=NcrY3BTvD-L2XP6bsO=9oAJLtSD0wYpUymVkAGAnYObsPzQ@xxxxxxxxxxxxxx/T/#t

I could also move this to the call site.

/Jarkko