On Fri, 2019-10-04 at 21:22 +0300, Jarkko Sakkinen wrote: > On Thu, Oct 03, 2019 at 04:59:37PM -0700, James Bottomley wrote: > > I think the principle of using multiple RNG sources for strong keys > > is a sound one, so could I propose a compromise: We have a tpm > > subsystem random number generator that, when asked for <n> random > > bytes first extracts <n> bytes from the TPM RNG and places it into > > the kernel entropy pool and then asks for <n> random bytes from the > > kernel RNG? That way, it will always have the entropy to satisfy > > the request and in the worst case, where the kernel has picked up > > no other entropy sources at all it will be equivalent to what we > > have now (single entropy source) but usually it will be a much > > better mixed entropy source. > > I think we should rely the existing architecture where TPM is > contributing to the entropy pool as hwrng. That doesn't seem to work: when I trace what happens I see us inject 32 bytes of entropy at boot time, but never again. I think the problem is the kernel entropy pool is push not pull and we have no triggering event in the TPM to get us to push. I suppose we could set a timer to do this or perhaps there is a pull hook and we haven't wired it up correctly? James
