On Tue, Oct 01, 2019 at 06:15:02PM +0200, Ahmed S. Darwish wrote: > On Sat, Sep 28, 2019 at 04:53:52PM -0700, Linus Torvalds wrote: > > Ahmed - would you be willing to test this on your problem case (with > > the ext4 optimization re-enabled, of course)? > > > > So I pulled the patch and the revert of the ext4 revert as they're all > now merged in master. It of course made the problem go away... > > To test the quality of the new jitter code, I added a small patch on > top to disable all other sources of randomness except the new jitter > entropy code, [1] and made quick tests on the quality of getrandom(0). > > Using the "ent" tool, [2] also used to test randomness in the Stephen > Müller LRNG paper, on a 500000-byte file, produced the following > results: > > $ ent rand-file > > Entropy = 7.999625 bits per byte. > > Optimum compression would reduce the size of this 500000 byte file > by 0 percent. > > Chi square distribution for 500000 samples is 259.43, and randomly > would exceed this value 41.11 percent of the times. > > Arithmetic mean value of data bytes is 127.4085 (127.5 = random). > > Monte Carlo value for Pi is 3.148476594 (error 0.22 percent). > > Serial correlation coefficient is 0.001740 (totally uncorrelated = 0.0). > > As can be seen above, everything looks random, and almost all of the > statistical randomness tests matched the same kernel without the > "jitter + schedule()" patch added (after getting it un-stuck).
Can you post the patch for [1]? Another test we should do is the multi-boot test. Testing the stream (with ent, or with my dieharder run) is mainly testing the RNG algo. I'd like to see if the first 8 bytes out of the kernel RNG change between multiple boots of the same system. e.g. read the first 8 bytes, for each of 100000 boots, and feed THAT byte "stream" into ent... -- Kees Cook
