Fuzzer unable to find patterns on some DIMMs about blacksmith HOT 3 CLOSED

Dear @hariv,
Please excuse my late reply. I have been very busy the last few weeks. I hope that my comments are anyway still useful to you. Could you meanwhile find bit flips on that one DIMM?

I assume it is unlikely for these DIMMs to be completely robust to the Rowhammer exploit and exploring the search space further should produce bit flips?

Yes, I would assume that these DIMMs are not completely robust to Rowhammer. Were they produced around the same time as the DIMMs in our test pool (see Appendix B in the Blacksmith paper for their manufacturing date)?

Did you also come across something similar in your experiments?

Yes, there were some DIMMs in our test pool (e.g., manufacturer C, Micron) where Blacksmith took quite long to find bit flips. I think this is because these devices use probabilistic mitigations, so even if you trigger a bit flip with a pattern once then repeating it immediately thereafter may not lead to retriggering the bit flips again.

Do you have any practical advice (perhaps alter the THRESH value defined in GlobalDefines.hpp or run the fuzzer on a particular CPU) so I can produce bit flips on these DIMMs too?

There are a few things you could try:

• The parameter deciding the number of activations in a tREFI (refresh interval) is very important. I noticed that Blacksmith could not find bit flips on some DIMMs if the automatic detection of the parameter's value was wrong. You should make sure that the value is indeed correct and you get a similar value for different runs of Blackmsmith.
• You could try to increase the parameter ranges and then just let it run for an extended time (e.g., a few days).
• You could try to run Blacksmith on that DIMM with a reduced refresh rate (= higher refresh interval (tREFI) and less TRRs) just to see how fast it triggers bit flips and the parameters of the patterns that triggered bit flips.

Please also note that I have recently pushed some fixes to a bug that I have mistakenly introduced before in the public version of Blacksmith. You should make sure that you use the latest version.

I hope this helps and good luck!

from blacksmith.

Hi @hariv

I'm having the same problem, did you solve the above issue by adjusting the parameter or something? Or did you solve the problem by changing the DIMM?

from blacksmith.

Hi @borricha, sorry for the late reply. There were some DIMMs on which we could not find patterns. We just moved on to other DIMMs.

from blacksmith.