Messages in this thread | | | Date | Tue, 22 Aug 2023 07:54:52 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH 04/22] x86/srso: Fix SBPB enablement for spec_rstack_overflow=off |
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On Mon, Aug 21, 2023 at 09:36:49AM -0700, Josh Poimboeuf wrote: > Hm? How exactly is this overriding the retbleed IBPB mitigation?
Sorry, clearly -ETOOMANYMITIGATIONS.
I meant the spectre_v2_user thing which does indirect_branch_prediction_barrier() based on X86_FEATURE_USE_IBPB.
indirect_branch_prediction_barrier() uses x86_pred_cmd to select which MSR bits to set and it is initialized by default to PRED_CMD_IBPB.
If you goto pred_cmd, you will overwrite it with PRED_CMD_SBPB here.
I think it should not overwrite it and simply return like before. Meaning: if SRSO mitigation is off but the spectre_v2_user isn't so you get what you want.
If you do mitigations=off - which is what most use cases do when they don't care about mitigations - then it'll work too.
I don't see a sensible use case where user->user spectre_v2 is enabled but SRSO is off. Maybe there is...
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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