On Fri, 2019-10-04 at 11:33 -0700, Jerry Snitselaar wrote: > On Fri Oct 04 19, James Bottomley wrote: > > 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 > > > > Shouldn't hwrng_fillfn be pulling from it? It should, but the problem seems to be it only polls the "current" hw rng ... it doesn't seem to have a concept that there may be more than one. What happens, according to a brief reading of the code, is when multiple are registered, it determines what the "best" one is and then only pulls from that. What I think it should be doing is filling from all of them using the entropy quality to adjust how many bits we get. James
