On Wed, Oct 16, 2019 at 01:09:08PM -0300, Jason Gunthorpe wrote: > On Wed, Oct 16, 2019 at 01:43:22PM +0300, Jarkko Sakkinen wrote: > > On Wed, Oct 16, 2019 at 01:38:05PM +0300, Jarkko Sakkinen wrote: > > > 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. > > > > But I hear you anyway. > > > > I think for trusted keys the best strategy would be to do > > exactly this: > > > > 1. Generate one random value with get_random_bytes_arch() > > 2. Generate another with backend specific technology (we > > have now two TPM and TEE) if an RNG available. > > 3. Xor the values together. > > Feels like something the random core should handle - maybe some way to > say 'my trust model requires trust in this RNG' and then the random > core can more heavily weight data from that RNG Yeah, I think. I'll study these emails threads and RNG implementation a bit when I have more time. Now I think I lack some knowledge to say anything educated so better to take a step back and go back to the drawing board. Thank you for the suggestion. /Jarkko
