Messages in this thread | | | Date | Mon, 18 Jul 2022 23:17:17 +0100 | From | Ken Moffat <> | Subject | Re: Retbleed, Zen2 and STIBP |
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On Mon, Jul 18, 2022 at 09:19:01AM +0100, Ken Moffat wrote:
Replying to myself to close this speculative misunderstanding.
> > While ibpb might be available (and slow), on my Renoir with > microcode level (0860106h) there were no newer microcode versions > available when I last looked (a few weeks ago) but note 7 at the > bottom of > https://www.amd.com/system/files/documents/technical-guidance-for-mitigating-branch-type-confusion_v > 7_20220712.pdf > implies that the relevant bit is only set on Renoir in 0860109h and > later. > > Some of the text in that pdf implies that at least one of the > options could be set if not already set from the microcode, but the > amount of detail leaves me totally lost. >
Now that I've tried the options, I can see that ibpb *is* available on this zen2 desktop machine (and no, I have no desire to use it, having seen how much things slow down). The default (auto) on this zen2 is the same as 'unret', i.e.
Mitigation: untrained return thunk; SMT enabled with STIBP protection
ĸen -- It is very easy to get ridiculously confused about the tenses of time travel, but most things can be resolved by a sufficiently large ego. -- The Last Continent
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