On 8/14/19 6:24 PM, Pavel Machek wrote: > On Wed 2019-08-14 21:17:41, Lendacky, Thomas wrote: >> From: Tom Lendacky <thomas.lenda...@amd.com> >> >> There have been reports of RDRAND issues after resuming from suspend on >> some AMD family 15h and family 16h systems. This issue stems from BIOS >> not performing the proper steps during resume to ensure RDRAND continues >> to function properly. > > Burn it with fire! > > I mean... people were afraid RDRAND would be backdoored, and you now > confirm ... it indeed _is_ backdoored? /., here's news for you! > > So what is the impact? Does it give random-looking but predictable > numbers after resume? Does it give all zeros? Something else?
See this article: https://www.phoronix.com/scan.php?page=news_item&px=AMD-CPUs-RdRand-Suspend Thanks, Tom > >> >> + rdrand_force [X86] >> + On certain AMD processors, the advertisement of the >> + RDRAND instruction has been disabled by the kernel >> + because of buggy BIOS support, specifically around the >> + suspend/resume path. This option allows for overriding >> + that decision if it is known that the BIOS support for >> + RDRAND is not buggy on the system. > > But this is not how we normally deal with buggy BIOSes. We don't want > user to have to decide this... > > Should we introduce black-list or white-list of BIOS versions? > > Hmm. Actually. > > You are the CPU vendor. Surely you can tell us how to init RDRAND in > kernel if BIOS failed to do that... can you? > > Pavel >