static void __init spectre_v2_select_mitigation(void) { enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline(); enum spectre_v2_mitigation mode = SPECTRE_V2_NONE; /* * If the CPU is not affected and the command line mode is NONE or AUTO * then nothing to do. */ if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2) && (cmd == SPECTRE_V2_CMD_NONE || cmd == SPECTRE_V2_CMD_AUTO)) return; switch (cmd) { case SPECTRE_V2_CMD_NONE: return; case SPECTRE_V2_CMD_FORCE: /* FALLTRHU */ case SPECTRE_V2_CMD_AUTO: goto retpoline_auto; case SPECTRE_V2_CMD_RETPOLINE_AMD: if (IS_ENABLED(CONFIG_RETPOLINE)) goto retpoline_amd; break; case SPECTRE_V2_CMD_RETPOLINE_GENERIC: if (IS_ENABLED(CONFIG_RETPOLINE)) goto retpoline_generic; break; case SPECTRE_V2_CMD_RETPOLINE: if (IS_ENABLED(CONFIG_RETPOLINE)) goto retpoline_auto; break; } pr_err("kernel not compiled with retpoline; no mitigation available!"); return; retpoline_auto: if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) { retpoline_amd: if (!boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) { pr_err("LFENCE not serializing. Switching to generic retpoline\n"); goto retpoline_generic; } mode = retp_compiler() ? SPECTRE_V2_RETPOLINE_AMD : SPECTRE_V2_RETPOLINE_MINIMAL_AMD; setup_force_cpu_cap(X86_FEATURE_RETPOLINE_AMD); setup_force_cpu_cap(X86_FEATURE_RETPOLINE); } else { retpoline_generic: mode = retp_compiler() ? SPECTRE_V2_RETPOLINE_GENERIC : SPECTRE_V2_RETPOLINE_MINIMAL; setup_force_cpu_cap(X86_FEATURE_RETPOLINE); } spectre_v2_enabled = mode; pr_info("%s\n", spectre_v2_strings[mode]); }
static void __init spectre_v2_select_mitigation(void) { enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline(); enum spectre_v2_mitigation mode = SPECTRE_V2_NONE; /* * If the CPU is not affected and the command line mode is NONE or AUTO * then nothing to do. */ if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2) && (cmd == SPECTRE_V2_CMD_NONE || cmd == SPECTRE_V2_CMD_AUTO)) return; switch (cmd) { case SPECTRE_V2_CMD_NONE: return; case SPECTRE_V2_CMD_FORCE: case SPECTRE_V2_CMD_AUTO: if (boot_cpu_has(X86_FEATURE_IBRS_ENHANCED)) { mode = SPECTRE_V2_IBRS_ENHANCED; /* Force it so VMEXIT will restore correctly */ x86_spec_ctrl_base |= SPEC_CTRL_IBRS; wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base); goto specv2_set_mode; } if (IS_ENABLED(CONFIG_RETPOLINE)) goto retpoline_auto; break; case SPECTRE_V2_CMD_RETPOLINE_AMD: if (IS_ENABLED(CONFIG_RETPOLINE)) goto retpoline_amd; break; case SPECTRE_V2_CMD_RETPOLINE_GENERIC: if (IS_ENABLED(CONFIG_RETPOLINE)) goto retpoline_generic; break; case SPECTRE_V2_CMD_RETPOLINE: if (IS_ENABLED(CONFIG_RETPOLINE)) goto retpoline_auto; break; } pr_err("Spectre mitigation: kernel not compiled with retpoline; no mitigation available!"); return; retpoline_auto: if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) { retpoline_amd: if (!boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) { pr_err("Spectre mitigation: LFENCE not serializing, switching to generic retpoline\n"); goto retpoline_generic; } mode = retp_compiler() ? SPECTRE_V2_RETPOLINE_AMD : SPECTRE_V2_RETPOLINE_MINIMAL_AMD; setup_force_cpu_cap(X86_FEATURE_RETPOLINE_AMD); setup_force_cpu_cap(X86_FEATURE_RETPOLINE); } else { retpoline_generic: mode = retp_compiler() ? SPECTRE_V2_RETPOLINE_GENERIC : SPECTRE_V2_RETPOLINE_MINIMAL; setup_force_cpu_cap(X86_FEATURE_RETPOLINE); } specv2_set_mode: spectre_v2_enabled = mode; pr_info("%s\n", spectre_v2_strings[mode]); /* * If spectre v2 protection has been enabled, unconditionally fill * RSB during a context switch; this protects against two independent * issues: * * - RSB underflow (and switch to BTB) on Skylake+ * - SpectreRSB variant of spectre v2 on X86_BUG_SPECTRE_V2 CPUs */ setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW); pr_info("Spectre v2 / SpectreRSB mitigation: Filling RSB on context switch\n"); /* Initialize Indirect Branch Prediction Barrier if supported */ if (boot_cpu_has(X86_FEATURE_IBPB)) { setup_force_cpu_cap(X86_FEATURE_USE_IBPB); pr_info("Spectre v2 mitigation: Enabling Indirect Branch Prediction Barrier\n"); } /* * Retpoline means the kernel is safe because it has no indirect * branches. Enhanced IBRS protects firmware too, so, enable restricted * speculation around firmware calls only when Enhanced IBRS isn't * supported. * * Use "mode" to check Enhanced IBRS instead of boot_cpu_has(), because * the user might select retpoline on the kernel command line and if * the CPU supports Enhanced IBRS, kernel might un-intentionally not * enable IBRS around firmware calls. */ if (boot_cpu_has(X86_FEATURE_IBRS) && mode != SPECTRE_V2_IBRS_ENHANCED) { setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW); pr_info("Enabling Restricted Speculation for firmware calls\n"); } }