[GTALUG] Ryzen 3000 CPUs vs Linux

[D. Hugh Redelmeier]

| From: Christopher Browne via talk <talk at gtalug.org>

| This sure seems to point at rdrand being a scary feature to consider using.

I put the blame squarely on AMD.  They've botched rdrand a couple of
times.  It's not really our job to wonder if instructions aren't
implemented correctly.  Imagine if FDIV didn't work?  Whose problem would 
that be?

| I imagine that it would be better to access /dev/urandom or /dev/random,
| and have those facilities mix rdrand in somewhat, if possible.

In this case, not really.  Read the comments in the code (not the commit):

<https://github.com/systemd/systemd/blob/master/src/basic/random-util.c>

rdrand is suspect for another reason.  We have no way knowing if
rdrand has hidden structure.  Such a compromise would amount to a
backdoor into most crypto.  But systemd folks say that their
application of the output of rdrand doesn't need strong random numbers.