On Thu, Jul 14, 2022 at 12:52:35PM -0700, Daniel Sneddon wrote: > Branch History Injection (BHI) attacks can be mitigated using the > BHI_DIS_S indirect predictor control bit located in MSR_IA32_SPEC_CTRL > register. Set BHI_DIS in MSR_IA32_SPC_CTRL to prevent predicted > targets of indirect branches executed in CPL0, CPL1, or CPL2 from > being selected based on branch history from branches executed in CPL3. > Support for this feature is enumerated by CPUID.7.2.EDX[BHI_CTRL] (bit 4). What actual hardware will have this? > Users wanting BHI protection can specify spectre_v2=eibrs,bhi_dis to > enable hardware BHI protections. On platforms where BHI protections > are not available in the hardware revert to eibrs,retpoline > mitigations. AFAICT this doesn't get auto-selected; how bad is performance for this to not be so?
