Messages in this thread | | | Date | Tue, 22 Aug 2023 14:59:01 -0700 | From | Josh Poimboeuf <> | Subject | Re: [PATCH 04/22] x86/srso: Fix SBPB enablement for spec_rstack_overflow=off |
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On Tue, Aug 22, 2023 at 08:07:06AM +0200, Borislav Petkov wrote: > On Tue, Aug 22, 2023 at 07:54:52AM +0200, Borislav Petkov wrote: > > If you goto pred_cmd, you will overwrite it with PRED_CMD_SBPB here. > > Looking at this more: > > "If SRSO mitigation is not required or is disabled, software may use > SBPB on context/virtual machine switch to help protect against > vulnerabilities like Spectre v2." > > I think we actually want this overwrite to happen.
Yeah, I had seen that. The combination of spectre_v2_user=on with srso=off doesn't make a whole lot of sense, but... give the user what they want and all. Which would presumably be IBPB *without* the SRSO mitigation (aka SBPB).
> But then if retbleed=ibpb, entry_ibpb() will do bit 0 unconditionally... > > Hmm, lemme talk to people.
I don't think we need to worry about that, SBPB is >= fam19 but retbleed is <= fam17. So either way (0x17 or 0x19) entry_ibpb() should do IBPB.
-- Josh
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