On Thu, Oct 17, 2019 at 09:04:40PM +0300, Jarkko Sakkinen wrote: > On Wed, Oct 16, 2019 at 03:10:29PM -0400, James Bottomley wrote: > > On Wed, 2019-10-16 at 19:25 +0300, Jarkko Sakkinen wrote: > > > On Wed, Oct 16, 2019 at 08:34:12AM -0400, James Bottomley wrote: > > > > reversible ciphers are generally frowned upon in random number > > > > generation, that's why the krng uses chacha20. In general I think > > > > we shouldn't try to code our own mixing and instead should get the > > > > krng to do it for us using whatever the algorithm du jour that the > > > > crypto guys have blessed is. That's why I proposed adding the TPM > > > > output to the krng as entropy input and then taking the output of > > > > the krng. > > > > > > It is already registered as hwrng. What else? > > > > It only contributes entropy once at start of OS. > > Ok. > > > > Was the issue that it is only used as seed when the rng is init'd > > > first? I haven't at this point gone to the internals of krng. > > > > Basically it was similar to your xor patch except I got the kernel rng > > to do the mixing, so it would use the chacha20 cipher at the moment > > until they decide that's unsafe and change it to something else: > > > > https://lore.kernel.org/linux-crypto/1570227068.17537.4.camel@xxxxxxxxxxxxxxxxxxxxx/ > > > > It uses add_hwgenerator_randomness() to do the mixing. It also has an > > unmixed source so that read of the TPM hwrng device works as expected. > > Thinking that could this potentially racy? I.e. between the calls > something else could eat the entropy added? Also, what is wrong just taking one value from krng and mixing it with a value from TPM RNG where needed? That would be non-racy too. /Jarkko
