// SPDX-License-Identifier: GPL-2.0 /* * Copyright (C) 1994 Linus Torvalds * * Cyrix stuff, June 1998 by: * - Rafael R. Reilova (moved everything from head.S), * * - Channing Corn (tests & fixes), * - Andrew D. Balsa (code cleanup). */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include "cpu.h" static void __init spectre_v1_select_mitigation(void); static void __init spectre_v2_select_mitigation(void); static void __init ssb_select_mitigation(void); static void __init l1tf_select_mitigation(void); static void __init mds_select_mitigation(void); static void __init md_clear_update_mitigation(void); static void __init md_clear_select_mitigation(void); static void __init taa_select_mitigation(void); static void __init mmio_select_mitigation(void); static void __init srbds_select_mitigation(void); /* The base value of the SPEC_CTRL MSR that always has to be preserved. */ u64 x86_spec_ctrl_base; EXPORT_SYMBOL_GPL(x86_spec_ctrl_base); static DEFINE_MUTEX(spec_ctrl_mutex); /* * The vendor and possibly platform specific bits which can be modified in * x86_spec_ctrl_base. */ static u64 __ro_after_init x86_spec_ctrl_mask = SPEC_CTRL_IBRS; /* * AMD specific MSR info for Speculative Store Bypass control. * x86_amd_ls_cfg_ssbd_mask is initialized in identify_boot_cpu(). */ u64 __ro_after_init x86_amd_ls_cfg_base; u64 __ro_after_init x86_amd_ls_cfg_ssbd_mask; /* Control conditional STIBP in switch_to() */ DEFINE_STATIC_KEY_FALSE(switch_to_cond_stibp); /* Control conditional IBPB in switch_mm() */ DEFINE_STATIC_KEY_FALSE(switch_mm_cond_ibpb); /* Control unconditional IBPB in switch_mm() */ DEFINE_STATIC_KEY_FALSE(switch_mm_always_ibpb); /* Control MDS CPU buffer clear before returning to user space */ DEFINE_STATIC_KEY_FALSE(mds_user_clear); EXPORT_SYMBOL_GPL(mds_user_clear); /* Control MDS CPU buffer clear before idling (halt, mwait) */ DEFINE_STATIC_KEY_FALSE(mds_idle_clear); EXPORT_SYMBOL_GPL(mds_idle_clear); /* Controls CPU Fill buffer clear before KVM guest MMIO accesses */ DEFINE_STATIC_KEY_FALSE(mmio_stale_data_clear); EXPORT_SYMBOL_GPL(mmio_stale_data_clear); void __init check_bugs(void) { identify_boot_cpu(); /* * identify_boot_cpu() initialized SMT support information, let the * core code know. */ cpu_smt_check_topology(); if (!IS_ENABLED(CONFIG_SMP)) { pr_info("CPU: "); print_cpu_info(&boot_cpu_data); } /* * Read the SPEC_CTRL MSR to account for reserved bits which may * have unknown values. AMD64_LS_CFG MSR is cached in the early AMD * init code as it is not enumerated and depends on the family. */ if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL)) rdmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base); /* Allow STIBP in MSR_SPEC_CTRL if supported */ if (boot_cpu_has(X86_FEATURE_STIBP)) x86_spec_ctrl_mask |= SPEC_CTRL_STIBP; /* Select the proper CPU mitigations before patching alternatives: */ spectre_v1_select_mitigation(); spectre_v2_select_mitigation(); ssb_select_mitigation(); l1tf_select_mitigation(); md_clear_select_mitigation(); srbds_select_mitigation(); arch_smt_update(); #ifdef CONFIG_X86_32 /* * Check whether we are able to run this kernel safely on SMP. * * - i386 is no longer supported. * - In order to run on anything without a TSC, we need to be * compiled for a i486. */ if (boot_cpu_data.x86 < 4) panic("Kernel requires i486+ for 'invlpg' and other features"); init_utsname()->machine[1] = '0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86); alternative_instructions(); fpu__init_check_bugs(); #else /* CONFIG_X86_64 */ alternative_instructions(); /* * Make sure the first 2MB area is not mapped by huge pages * There are typically fixed size MTRRs in there and overlapping * MTRRs into large pages causes slow downs. * * Right now we don't do that with gbpages because there seems * very little benefit for that case. */ if (!direct_gbpages) set_memory_4k((unsigned long)__va(0), 1); #endif } void x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest) { u64 msrval, guestval, hostval = x86_spec_ctrl_base; struct thread_info *ti = current_thread_info(); /* Is MSR_SPEC_CTRL implemented ? */ if (static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL)) { /* * Restrict guest_spec_ctrl to supported values. Clear the * modifiable bits in the host base value and or the * modifiable bits from the guest value. */ guestval = hostval & ~x86_spec_ctrl_mask; guestval |= guest_spec_ctrl & x86_spec_ctrl_mask; /* SSBD controlled in MSR_SPEC_CTRL */ if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) || static_cpu_has(X86_FEATURE_AMD_SSBD)) hostval |= ssbd_tif_to_spec_ctrl(ti->flags); /* Conditional STIBP enabled? */ if (static_branch_unlikely(&switch_to_cond_stibp)) hostval |= stibp_tif_to_spec_ctrl(ti->flags); if (hostval != guestval) { msrval = setguest ? guestval : hostval; wrmsrl(MSR_IA32_SPEC_CTRL, msrval); } } /* * If SSBD is not handled in MSR_SPEC_CTRL on AMD, update * MSR_AMD64_L2_CFG or MSR_VIRT_SPEC_CTRL if supported. */ if (!static_cpu_has(X86_FEATURE_LS_CFG_SSBD) && !static_cpu_has(X86_FEATURE_VIRT_SSBD)) return; /* * If the host has SSBD mitigation enabled, force it in the host's * virtual MSR value. If its not permanently enabled, evaluate * current's TIF_SSBD thread flag. */ if (static_cpu_has(X86_FEATURE_SPEC_STORE_BYPASS_DISABLE)) hostval = SPEC_CTRL_SSBD; else hostval = ssbd_tif_to_spec_ctrl(ti->flags); /* Sanitize the guest value */ guestval = guest_virt_spec_ctrl & SPEC_CTRL_SSBD; if (hostval != guestval) { unsigned long tif; tif = setguest ? ssbd_spec_ctrl_to_tif(guestval) : ssbd_spec_ctrl_to_tif(hostval); speculation_ctrl_update(tif); } } EXPORT_SYMBOL_GPL(x86_virt_spec_ctrl); static void x86_amd_ssb_disable(void) { u64 msrval = x86_amd_ls_cfg_base | x86_amd_ls_cfg_ssbd_mask; if (boot_cpu_has(X86_FEATURE_VIRT_SSBD)) wrmsrl(MSR_AMD64_VIRT_SPEC_CTRL, SPEC_CTRL_SSBD); else if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD)) wrmsrl(MSR_AMD64_LS_CFG, msrval); } #undef pr_fmt #define pr_fmt(fmt) "MDS: " fmt /* Default mitigation for MDS-affected CPUs */ static enum mds_mitigations mds_mitigation __ro_after_init = MDS_MITIGATION_FULL; static bool mds_nosmt __ro_after_init = false; static const char * const mds_strings[] = { [MDS_MITIGATION_OFF] = "Vulnerable", [MDS_MITIGATION_FULL] = "Mitigation: Clear CPU buffers", [MDS_MITIGATION_VMWERV] = "Vulnerable: Clear CPU buffers attempted, no microcode", }; static void __init mds_select_mitigation(void) { if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_mitigations_off()) { mds_mitigation = MDS_MITIGATION_OFF; return; } if (mds_mitigation == MDS_MITIGATION_FULL) { if (!boot_cpu_has(X86_FEATURE_MD_CLEAR)) mds_mitigation = MDS_MITIGATION_VMWERV; static_branch_enable(&mds_user_clear); if (!boot_cpu_has(X86_BUG_MSBDS_ONLY) && (mds_nosmt || cpu_mitigations_auto_nosmt())) cpu_smt_disable(false); } } static int __init mds_cmdline(char *str) { if (!boot_cpu_has_bug(X86_BUG_MDS)) return 0; if (!str) return -EINVAL; if (!strcmp(str, "off")) mds_mitigation = MDS_MITIGATION_OFF; else if (!strcmp(str, "full")) mds_mitigation = MDS_MITIGATION_FULL; else if (!strcmp(str, "full,nosmt")) { mds_mitigation = MDS_MITIGATION_FULL; mds_nosmt = true; } return 0; } early_param("mds", mds_cmdline); #undef pr_fmt #define pr_fmt(fmt) "TAA: " fmt /* Default mitigation for TAA-affected CPUs */ static enum taa_mitigations taa_mitigation __ro_after_init = TAA_MITIGATION_VERW; static bool taa_nosmt __ro_after_init; static const char * const taa_strings[] = { [TAA_MITIGATION_OFF] = "Vulnerable", [TAA_MITIGATION_UCODE_NEEDED] = "Vulnerable: Clear CPU buffers attempted, no microcode", [TAA_MITIGATION_VERW] = "Mitigation: Clear CPU buffers", [TAA_MITIGATION_TSX_DISABLED] = "Mitigation: TSX disabled", }; static void __init taa_select_mitigation(void) { u64 ia32_cap; if (!boot_cpu_has_bug(X86_BUG_TAA)) { taa_mitigation = TAA_MITIGATION_OFF; return; } /* TSX previously disabled by tsx=off */ if (!boot_cpu_has(X86_FEATURE_RTM)) { taa_mitigation = TAA_MITIGATION_TSX_DISABLED; return; } if (cpu_mitigations_off()) { taa_mitigation = TAA_MITIGATION_OFF; return; } /* * TAA mitigation via VERW is turned off if both * tsx_async_abort=off and mds=off are specified. */ if (taa_mitigation == TAA_MITIGATION_OFF && mds_mitigation == MDS_MITIGATION_OFF) return; if (boot_cpu_has(X86_FEATURE_MD_CLEAR)) taa_mitigation = TAA_MITIGATION_VERW; else taa_mitigation = TAA_MITIGATION_UCODE_NEEDED; /* * VERW doesn't clear the CPU buffers when MD_CLEAR=1 and MDS_NO=1. * A microcode update fixes this behavior to clear CPU buffers. It also * adds support for MSR_IA32_TSX_CTRL which is enumerated by the * ARCH_CAP_TSX_CTRL_MSR bit. * * On MDS_NO=1 CPUs if ARCH_CAP_TSX_CTRL_MSR is not set, microcode * update is required. */ ia32_cap = x86_read_arch_cap_msr(); if ( (ia32_cap & ARCH_CAP_MDS_NO) && !(ia32_cap & ARCH_CAP_TSX_CTRL_MSR)) taa_mitigation = TAA_MITIGATION_UCODE_NEEDED; /* * TSX is enabled, select alternate mitigation for TAA which is * the same as MDS. Enable MDS static branch to clear CPU buffers. * * For guests that can't determine whether the correct microcode is * present on host, enable the mitigation for UCODE_NEEDED as well. */ static_branch_enable(&mds_user_clear); if (taa_nosmt || cpu_mitigations_auto_nosmt()) cpu_smt_disable(false); } static int __init tsx_async_abort_parse_cmdline(char *str) { if (!boot_cpu_has_bug(X86_BUG_TAA)) return 0; if (!str) return -EINVAL; if (!strcmp(str, "off")) { taa_mitigation = TAA_MITIGATION_OFF; } else if (!strcmp(str, "full")) { taa_mitigation = TAA_MITIGATION_VERW; } else if (!strcmp(str, "full,nosmt")) { taa_mitigation = TAA_MITIGATION_VERW; taa_nosmt = true; } return 0; } early_param("tsx_async_abort", tsx_async_abort_parse_cmdline); #undef pr_fmt #define pr_fmt(fmt) "MMIO Stale Data: " fmt enum mmio_mitigations { MMIO_MITIGATION_OFF, MMIO_MITIGATION_UCODE_NEEDED, MMIO_MITIGATION_VERW, }; /* Default mitigation for Processor MMIO Stale Data vulnerabilities */ static enum mmio_mitigations mmio_mitigation __ro_after_init = MMIO_MITIGATION_VERW; static bool mmio_nosmt __ro_after_init = false; static const char * const mmio_strings[] = { [MMIO_MITIGATION_OFF] = "Vulnerable", [MMIO_MITIGATION_UCODE_NEEDED] = "Vulnerable: Clear CPU buffers attempted, no microcode", [MMIO_MITIGATION_VERW] = "Mitigation: Clear CPU buffers", }; static void __init mmio_select_mitigation(void) { u64 ia32_cap; if (!boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA) || boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN) || cpu_mitigations_off()) { mmio_mitigation = MMIO_MITIGATION_OFF; return; } if (mmio_mitigation == MMIO_MITIGATION_OFF) return; ia32_cap = x86_read_arch_cap_msr(); /* * Enable CPU buffer clear mitigation for host and VMM, if also affected * by MDS or TAA. Otherwise, enable mitigation for VMM only. */ if (boot_cpu_has_bug(X86_BUG_MDS) || (boot_cpu_has_bug(X86_BUG_TAA) && boot_cpu_has(X86_FEATURE_RTM))) static_branch_enable(&mds_user_clear); else static_branch_enable(&mmio_stale_data_clear); /* * If Processor-MMIO-Stale-Data bug is present and Fill Buffer data can * be propagated to uncore buffers, clearing the Fill buffers on idle * is required irrespective of SMT state. */ if (!(ia32_cap & ARCH_CAP_FBSDP_NO)) static_branch_enable(&mds_idle_clear); /* * Check if the system has the right microcode. * * CPU Fill buffer clear mitigation is enumerated by either an explicit * FB_CLEAR or by the presence of both MD_CLEAR and L1D_FLUSH on MDS * affected systems. */ if ((ia32_cap & ARCH_CAP_FB_CLEAR) || (boot_cpu_has(X86_FEATURE_MD_CLEAR) && boot_cpu_has(X86_FEATURE_FLUSH_L1D) && !(ia32_cap & ARCH_CAP_MDS_NO))) mmio_mitigation = MMIO_MITIGATION_VERW; else mmio_mitigation = MMIO_MITIGATION_UCODE_NEEDED; if (mmio_nosmt || cpu_mitigations_auto_nosmt()) cpu_smt_disable(false); } static int __init mmio_stale_data_parse_cmdline(char *str) { if (!boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA)) return 0; if (!str) return -EINVAL; if (!strcmp(str, "off")) { mmio_mitigation = MMIO_MITIGATION_OFF; } else if (!strcmp(str, "full")) { mmio_mitigation = MMIO_MITIGATION_VERW; } else if (!strcmp(str, "full,nosmt")) { mmio_mitigation = MMIO_MITIGATION_VERW; mmio_nosmt = true; } return 0; } early_param("mmio_stale_data", mmio_stale_data_parse_cmdline); #undef pr_fmt #define pr_fmt(fmt) "" fmt static void __init md_clear_update_mitigation(void) { if (cpu_mitigations_off()) return; if (!static_key_enabled(&mds_user_clear)) goto out; /* * mds_user_clear is now enabled. Update MDS, TAA and MMIO Stale Data * mitigation, if necessary. */ if (mds_mitigation == MDS_MITIGATION_OFF && boot_cpu_has_bug(X86_BUG_MDS)) { mds_mitigation = MDS_MITIGATION_FULL; mds_select_mitigation(); } if (taa_mitigation == TAA_MITIGATION_OFF && boot_cpu_has_bug(X86_BUG_TAA)) { taa_mitigation = TAA_MITIGATION_VERW; taa_select_mitigation(); } if (mmio_mitigation == MMIO_MITIGATION_OFF && boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA)) { mmio_mitigation = MMIO_MITIGATION_VERW; mmio_select_mitigation(); } out: if (boot_cpu_has_bug(X86_BUG_MDS)) pr_info("MDS: %s\n", mds_strings[mds_mitigation]); if (boot_cpu_has_bug(X86_BUG_TAA)) pr_info("TAA: %s\n", taa_strings[taa_mitigation]); if (boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA)) pr_info("MMIO Stale Data: %s\n", mmio_strings[mmio_mitigation]); else if (boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN)) pr_info("MMIO Stale Data: Unknown: No mitigations\n"); } static void __init md_clear_select_mitigation(void) { mds_select_mitigation(); taa_select_mitigation(); mmio_select_mitigation(); /* * As MDS, TAA and MMIO Stale Data mitigations are inter-related, update * and print their mitigation after MDS, TAA and MMIO Stale Data * mitigation selection is done. */ md_clear_update_mitigation(); } #undef pr_fmt #define pr_fmt(fmt) "SRBDS: " fmt enum srbds_mitigations { SRBDS_MITIGATION_OFF, SRBDS_MITIGATION_UCODE_NEEDED, SRBDS_MITIGATION_FULL, SRBDS_MITIGATION_TSX_OFF, SRBDS_MITIGATION_HYPERVISOR, }; static enum srbds_mitigations srbds_mitigation __ro_after_init = SRBDS_MITIGATION_FULL; static const char * const srbds_strings[] = { [SRBDS_MITIGATION_OFF] = "Vulnerable", [SRBDS_MITIGATION_UCODE_NEEDED] = "Vulnerable: No microcode", [SRBDS_MITIGATION_FULL] = "Mitigation: Microcode", [SRBDS_MITIGATION_TSX_OFF] = "Mitigation: TSX disabled", [SRBDS_MITIGATION_HYPERVISOR] = "Unknown: Dependent on hypervisor status", }; static bool srbds_off; void update_srbds_msr(void) { u64 mcu_ctrl; if (!boot_cpu_has_bug(X86_BUG_SRBDS)) return; if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) return; if (srbds_mitigation == SRBDS_MITIGATION_UCODE_NEEDED) return; rdmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_ctrl); switch (srbds_mitigation) { case SRBDS_MITIGATION_OFF: case SRBDS_MITIGATION_TSX_OFF: mcu_ctrl |= RNGDS_MITG_DIS; break; case SRBDS_MITIGATION_FULL: mcu_ctrl &= ~RNGDS_MITG_DIS; break; default: break; } wrmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_ctrl); } static void __init srbds_select_mitigation(void) { u64 ia32_cap; if (!boot_cpu_has_bug(X86_BUG_SRBDS)) return; /* * Check to see if this is one of the MDS_NO systems supporting TSX that * are only exposed to SRBDS when TSX is enabled or when CPU is affected * by Processor MMIO Stale Data vulnerability. */ ia32_cap = x86_read_arch_cap_msr(); if ((ia32_cap & ARCH_CAP_MDS_NO) && !boot_cpu_has(X86_FEATURE_RTM) && !boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA)) srbds_mitigation = SRBDS_MITIGATION_TSX_OFF; else if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) srbds_mitigation = SRBDS_MITIGATION_HYPERVISOR; else if (!boot_cpu_has(X86_FEATURE_SRBDS_CTRL)) srbds_mitigation = SRBDS_MITIGATION_UCODE_NEEDED; else if (cpu_mitigations_off() || srbds_off) srbds_mitigation = SRBDS_MITIGATION_OFF; update_srbds_msr(); pr_info("%s\n", srbds_strings[srbds_mitigation]); } static int __init srbds_parse_cmdline(char *str) { if (!str) return -EINVAL; if (!boot_cpu_has_bug(X86_BUG_SRBDS)) return 0; srbds_off = !strcmp(str, "off"); return 0; } early_param("srbds", srbds_parse_cmdline); #undef pr_fmt #define pr_fmt(fmt) "Spectre V1 : " fmt enum spectre_v1_mitigation { SPECTRE_V1_MITIGATION_NONE, SPECTRE_V1_MITIGATION_AUTO, }; static enum spectre_v1_mitigation spectre_v1_mitigation __ro_after_init = SPECTRE_V1_MITIGATION_AUTO; static const char * const spectre_v1_strings[] = { [SPECTRE_V1_MITIGATION_NONE] = "Vulnerable: __user pointer sanitization and usercopy barriers only; no swapgs barriers", [SPECTRE_V1_MITIGATION_AUTO] = "Mitigation: usercopy/swapgs barriers and __user pointer sanitization", }; /* * Does SMAP provide full mitigation against speculative kernel access to * userspace? */ static bool smap_works_speculatively(void) { if (!boot_cpu_has(X86_FEATURE_SMAP)) return false; /* * On CPUs which are vulnerable to Meltdown, SMAP does not * prevent speculative access to user data in the L1 cache. * Consider SMAP to be non-functional as a mitigation on these * CPUs. */ if (boot_cpu_has(X86_BUG_CPU_MELTDOWN)) return false; return true; } static void __init spectre_v1_select_mitigation(void) { if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V1) || cpu_mitigations_off()) { spectre_v1_mitigation = SPECTRE_V1_MITIGATION_NONE; return; } if (spectre_v1_mitigation == SPECTRE_V1_MITIGATION_AUTO) { /* * With Spectre v1, a user can speculatively control either * path of a conditional swapgs with a user-controlled GS * value. The mitigation is to add lfences to both code paths. * * If FSGSBASE is enabled, the user can put a kernel address in * GS, in which case SMAP provides no protection. * * [ NOTE: Don't check for X86_FEATURE_FSGSBASE until the * FSGSBASE enablement patches have been merged. ] * * If FSGSBASE is disabled, the user can only put a user space * address in GS. That makes an attack harder, but still * possible if there's no SMAP protection. */ if (!smap_works_speculatively()) { /* * Mitigation can be provided from SWAPGS itself or * PTI as the CR3 write in the Meltdown mitigation * is serializing. * * If neither is there, mitigate with an LFENCE to * stop speculation through swapgs. */ if (boot_cpu_has_bug(X86_BUG_SWAPGS) && !boot_cpu_has(X86_FEATURE_PTI)) setup_force_cpu_cap(X86_FEATURE_FENCE_SWAPGS_USER); /* * Enable lfences in the kernel entry (non-swapgs) * paths, to prevent user entry from speculatively * skipping swapgs. */ setup_force_cpu_cap(X86_FEATURE_FENCE_SWAPGS_KERNEL); } } pr_info("%s\n", spectre_v1_strings[spectre_v1_mitigation]); } static int __init nospectre_v1_cmdline(char *str) { spectre_v1_mitigation = SPECTRE_V1_MITIGATION_NONE; return 0; } early_param("nospectre_v1", nospectre_v1_cmdline); #undef pr_fmt #define pr_fmt(fmt) "Spectre V2 : " fmt static enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init = SPECTRE_V2_NONE; static enum spectre_v2_user_mitigation spectre_v2_user_stibp __ro_after_init = SPECTRE_V2_USER_NONE; static enum spectre_v2_user_mitigation spectre_v2_user_ibpb __ro_after_init = SPECTRE_V2_USER_NONE; #ifdef CONFIG_RETPOLINE static bool spectre_v2_bad_module; bool retpoline_module_ok(bool has_retpoline) { if (spectre_v2_enabled == SPECTRE_V2_NONE || has_retpoline) return true; pr_err("System may be vulnerable to spectre v2\n"); spectre_v2_bad_module = true; return false; } static inline const char *spectre_v2_module_string(void) { return spectre_v2_bad_module ? " - vulnerable module loaded" : ""; } #else static inline const char *spectre_v2_module_string(void) { return ""; } #endif #define SPECTRE_V2_LFENCE_MSG "WARNING: LFENCE mitigation is not recommended for this CPU, data leaks possible!\n" #define SPECTRE_V2_EIBRS_EBPF_MSG "WARNING: Unprivileged eBPF is enabled with eIBRS on, data leaks possible via Spectre v2 BHB attacks!\n" #define SPECTRE_V2_EIBRS_LFENCE_EBPF_SMT_MSG "WARNING: Unprivileged eBPF is enabled with eIBRS+LFENCE mitigation and SMT, data leaks possible via Spectre v2 BHB attacks!\n" #ifdef CONFIG_BPF_SYSCALL void unpriv_ebpf_notify(int new_state) { if (new_state) return; /* Unprivileged eBPF is enabled */ switch (spectre_v2_enabled) { case SPECTRE_V2_EIBRS: pr_err(SPECTRE_V2_EIBRS_EBPF_MSG); break; case SPECTRE_V2_EIBRS_LFENCE: if (sched_smt_active()) pr_err(SPECTRE_V2_EIBRS_LFENCE_EBPF_SMT_MSG); break; default: break; } } #endif static inline bool match_option(const char *arg, int arglen, const char *opt) { int len = strlen(opt); return len == arglen && !strncmp(arg, opt, len); } /* The kernel command line selection for spectre v2 */ enum spectre_v2_mitigation_cmd { SPECTRE_V2_CMD_NONE, SPECTRE_V2_CMD_AUTO, SPECTRE_V2_CMD_FORCE, SPECTRE_V2_CMD_RETPOLINE, SPECTRE_V2_CMD_RETPOLINE_GENERIC, SPECTRE_V2_CMD_RETPOLINE_LFENCE, SPECTRE_V2_CMD_EIBRS, SPECTRE_V2_CMD_EIBRS_RETPOLINE, SPECTRE_V2_CMD_EIBRS_LFENCE, }; enum spectre_v2_user_cmd { SPECTRE_V2_USER_CMD_NONE, SPECTRE_V2_USER_CMD_AUTO, SPECTRE_V2_USER_CMD_FORCE, SPECTRE_V2_USER_CMD_PRCTL, SPECTRE_V2_USER_CMD_PRCTL_IBPB, SPECTRE_V2_USER_CMD_SECCOMP, SPECTRE_V2_USER_CMD_SECCOMP_IBPB, }; static const char * const spectre_v2_user_strings[] = { [SPECTRE_V2_USER_NONE] = "User space: Vulnerable", [SPECTRE_V2_USER_STRICT] = "User space: Mitigation: STIBP protection", [SPECTRE_V2_USER_STRICT_PREFERRED] = "User space: Mitigation: STIBP always-on protection", [SPECTRE_V2_USER_PRCTL] = "User space: Mitigation: STIBP via prctl", [SPECTRE_V2_USER_SECCOMP] = "User space: Mitigation: STIBP via seccomp and prctl", }; static const struct { const char *option; enum spectre_v2_user_cmd cmd; bool secure; } v2_user_options[] __initconst = { { "auto", SPECTRE_V2_USER_CMD_AUTO, false }, { "off", SPECTRE_V2_USER_CMD_NONE, false }, { "on", SPECTRE_V2_USER_CMD_FORCE, true }, { "prctl", SPECTRE_V2_USER_CMD_PRCTL, false }, { "prctl,ibpb", SPECTRE_V2_USER_CMD_PRCTL_IBPB, false }, { "seccomp", SPECTRE_V2_USER_CMD_SECCOMP, false }, { "seccomp,ibpb", SPECTRE_V2_USER_CMD_SECCOMP_IBPB, false }, }; static void __init spec_v2_user_print_cond(const char *reason, bool secure) { if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2) != secure) pr_info("spectre_v2_user=%s forced on command line.\n", reason); } static enum spectre_v2_user_cmd __init spectre_v2_parse_user_cmdline(enum spectre_v2_mitigation_cmd v2_cmd) { char arg[20]; int ret, i; switch (v2_cmd) { case SPECTRE_V2_CMD_NONE: return SPECTRE_V2_USER_CMD_NONE; case SPECTRE_V2_CMD_FORCE: return SPECTRE_V2_USER_CMD_FORCE; default: break; } ret = cmdline_find_option(boot_command_line, "spectre_v2_user", arg, sizeof(arg)); if (ret < 0) return SPECTRE_V2_USER_CMD_AUTO; for (i = 0; i < ARRAY_SIZE(v2_user_options); i++) { if (match_option(arg, ret, v2_user_options[i].option)) { spec_v2_user_print_cond(v2_user_options[i].option, v2_user_options[i].secure); return v2_user_options[i].cmd; } } pr_err("Unknown user space protection option (%s). Switching to AUTO select\n", arg); return SPECTRE_V2_USER_CMD_AUTO; } static inline bool spectre_v2_in_eibrs_mode(enum spectre_v2_mitigation mode) { return (mode == SPECTRE_V2_EIBRS || mode == SPECTRE_V2_EIBRS_RETPOLINE || mode == SPECTRE_V2_EIBRS_LFENCE); } static void __init spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd) { enum spectre_v2_user_mitigation mode = SPECTRE_V2_USER_NONE; bool smt_possible = IS_ENABLED(CONFIG_SMP); enum spectre_v2_user_cmd cmd; if (!boot_cpu_has(X86_FEATURE_IBPB) && !boot_cpu_has(X86_FEATURE_STIBP)) return; if (cpu_smt_control == CPU_SMT_FORCE_DISABLED || cpu_smt_control == CPU_SMT_NOT_SUPPORTED) smt_possible = false; cmd = spectre_v2_parse_user_cmdline(v2_cmd); switch (cmd) { case SPECTRE_V2_USER_CMD_NONE: goto set_mode; case SPECTRE_V2_USER_CMD_FORCE: mode = SPECTRE_V2_USER_STRICT; break; case SPECTRE_V2_USER_CMD_PRCTL: case SPECTRE_V2_USER_CMD_PRCTL_IBPB: mode = SPECTRE_V2_USER_PRCTL; break; case SPECTRE_V2_USER_CMD_AUTO: case SPECTRE_V2_USER_CMD_SECCOMP: case SPECTRE_V2_USER_CMD_SECCOMP_IBPB: if (IS_ENABLED(CONFIG_SECCOMP)) mode = SPECTRE_V2_USER_SECCOMP; else mode = SPECTRE_V2_USER_PRCTL; break; } /* Initialize Indirect Branch Prediction Barrier */ if (boot_cpu_has(X86_FEATURE_IBPB)) { setup_force_cpu_cap(X86_FEATURE_USE_IBPB); spectre_v2_user_ibpb = mode; switch (cmd) { case SPECTRE_V2_USER_CMD_FORCE: case SPECTRE_V2_USER_CMD_PRCTL_IBPB: case SPECTRE_V2_USER_CMD_SECCOMP_IBPB: static_branch_enable(&switch_mm_always_ibpb); spectre_v2_user_ibpb = SPECTRE_V2_USER_STRICT; break; case SPECTRE_V2_USER_CMD_PRCTL: case SPECTRE_V2_USER_CMD_AUTO: case SPECTRE_V2_USER_CMD_SECCOMP: static_branch_enable(&switch_mm_cond_ibpb); break; default: break; } pr_info("mitigation: Enabling %s Indirect Branch Prediction Barrier\n", static_key_enabled(&switch_mm_always_ibpb) ? "always-on" : "conditional"); } /* * If no STIBP, enhanced IBRS is enabled or SMT impossible, STIBP is not * required. */ if (!boot_cpu_has(X86_FEATURE_STIBP) || !smt_possible || spectre_v2_in_eibrs_mode(spectre_v2_enabled)) return; /* * At this point, an STIBP mode other than "off" has been set. * If STIBP support is not being forced, check if STIBP always-on * is preferred. */ if (mode != SPECTRE_V2_USER_STRICT && boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON)) mode = SPECTRE_V2_USER_STRICT_PREFERRED; spectre_v2_user_stibp = mode; set_mode: pr_info("%s\n", spectre_v2_user_strings[mode]); } static const char * const spectre_v2_strings[] = { [SPECTRE_V2_NONE] = "Vulnerable", [SPECTRE_V2_RETPOLINE] = "Mitigation: Retpolines", [SPECTRE_V2_LFENCE] = "Mitigation: LFENCE", [SPECTRE_V2_EIBRS] = "Mitigation: Enhanced IBRS", [SPECTRE_V2_EIBRS_LFENCE] = "Mitigation: Enhanced IBRS + LFENCE", [SPECTRE_V2_EIBRS_RETPOLINE] = "Mitigation: Enhanced IBRS + Retpolines", }; static const struct { const char *option; enum spectre_v2_mitigation_cmd cmd; bool secure; } mitigation_options[] __initconst = { { "off", SPECTRE_V2_CMD_NONE, false }, { "on", SPECTRE_V2_CMD_FORCE, true }, { "retpoline", SPECTRE_V2_CMD_RETPOLINE, false }, { "retpoline,amd", SPECTRE_V2_CMD_RETPOLINE_LFENCE, false }, { "retpoline,lfence", SPECTRE_V2_CMD_RETPOLINE_LFENCE, false }, { "retpoline,generic", SPECTRE_V2_CMD_RETPOLINE_GENERIC, false }, { "eibrs", SPECTRE_V2_CMD_EIBRS, false }, { "eibrs,lfence", SPECTRE_V2_CMD_EIBRS_LFENCE, false }, { "eibrs,retpoline", SPECTRE_V2_CMD_EIBRS_RETPOLINE, false }, { "auto", SPECTRE_V2_CMD_AUTO, false }, }; static void __init spec_v2_print_cond(const char *reason, bool secure) { if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2) != secure) pr_info("%s selected on command line.\n", reason); } static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void) { enum spectre_v2_mitigation_cmd cmd = SPECTRE_V2_CMD_AUTO; char arg[20]; int ret, i; if (cmdline_find_option_bool(boot_command_line, "nospectre_v2") || cpu_mitigations_off()) return SPECTRE_V2_CMD_NONE; ret = cmdline_find_option(boot_command_line, "spectre_v2", arg, sizeof(arg)); if (ret < 0) return SPECTRE_V2_CMD_AUTO; for (i = 0; i < ARRAY_SIZE(mitigation_options); i++) { if (!match_option(arg, ret, mitigation_options[i].option)) continue; cmd = mitigation_options[i].cmd; break; } if (i >= ARRAY_SIZE(mitigation_options)) { pr_err("unknown option (%s). Switching to AUTO select\n", arg); return SPECTRE_V2_CMD_AUTO; } if ((cmd == SPECTRE_V2_CMD_RETPOLINE || cmd == SPECTRE_V2_CMD_RETPOLINE_LFENCE || cmd == SPECTRE_V2_CMD_RETPOLINE_GENERIC || cmd == SPECTRE_V2_CMD_EIBRS_LFENCE || cmd == SPECTRE_V2_CMD_EIBRS_RETPOLINE) && !IS_ENABLED(CONFIG_RETPOLINE)) { pr_err("%s selected but not compiled in. Switching to AUTO select\n", mitigation_options[i].option); return SPECTRE_V2_CMD_AUTO; } if ((cmd == SPECTRE_V2_CMD_EIBRS || cmd == SPECTRE_V2_CMD_EIBRS_LFENCE || cmd == SPECTRE_V2_CMD_EIBRS_RETPOLINE) && !boot_cpu_has(X86_FEATURE_IBRS_ENHANCED)) { pr_err("%s selected but CPU doesn't have eIBRS. Switching to AUTO select\n", mitigation_options[i].option); return SPECTRE_V2_CMD_AUTO; } if ((cmd == SPECTRE_V2_CMD_RETPOLINE_LFENCE || cmd == SPECTRE_V2_CMD_EIBRS_LFENCE) && !boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) { pr_err("%s selected, but CPU doesn't have a serializing LFENCE. Switching to AUTO select\n", mitigation_options[i].option); return SPECTRE_V2_CMD_AUTO; } spec_v2_print_cond(mitigation_options[i].option, mitigation_options[i].secure); return cmd; } static enum spectre_v2_mitigation __init spectre_v2_select_retpoline(void) { if (!IS_ENABLED(CONFIG_RETPOLINE)) { pr_err("Kernel not compiled with retpoline; no mitigation available!"); return SPECTRE_V2_NONE; } return SPECTRE_V2_RETPOLINE; } static void __init spectre_v2_determine_rsb_fill_type_at_vmexit(enum spectre_v2_mitigation mode) { /* * Similar to context switches, there are two types of RSB attacks * after VM exit: * * 1) RSB underflow * * 2) Poisoned RSB entry * * When retpoline is enabled, both are mitigated by filling/clearing * the RSB. * * When IBRS is enabled, while #1 would be mitigated by the IBRS branch * prediction isolation protections, RSB still needs to be cleared * because of #2. Note that SMEP provides no protection here, unlike * user-space-poisoned RSB entries. * * eIBRS should protect against RSB poisoning, but if the EIBRS_PBRSB * bug is present then a LITE version of RSB protection is required, * just a single call needs to retire before a RET is executed. */ switch (mode) { case SPECTRE_V2_NONE: /* These modes already fill RSB at vmexit */ case SPECTRE_V2_LFENCE: case SPECTRE_V2_RETPOLINE: case SPECTRE_V2_EIBRS_RETPOLINE: return; case SPECTRE_V2_EIBRS_LFENCE: case SPECTRE_V2_EIBRS: if (boot_cpu_has_bug(X86_BUG_EIBRS_PBRSB)) { setup_force_cpu_cap(X86_FEATURE_RSB_VMEXIT_LITE); pr_info("Spectre v2 / PBRSB-eIBRS: Retire a single CALL on VMEXIT\n"); } return; } pr_warn_once("Unknown Spectre v2 mode, disabling RSB mitigation at VM exit"); dump_stack(); } 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_EIBRS; break; } mode = spectre_v2_select_retpoline(); break; case SPECTRE_V2_CMD_RETPOLINE_LFENCE: pr_err(SPECTRE_V2_LFENCE_MSG); mode = SPECTRE_V2_LFENCE; break; case SPECTRE_V2_CMD_RETPOLINE_GENERIC: mode = SPECTRE_V2_RETPOLINE; break; case SPECTRE_V2_CMD_RETPOLINE: mode = spectre_v2_select_retpoline(); break; case SPECTRE_V2_CMD_EIBRS: mode = SPECTRE_V2_EIBRS; break; case SPECTRE_V2_CMD_EIBRS_LFENCE: mode = SPECTRE_V2_EIBRS_LFENCE; break; case SPECTRE_V2_CMD_EIBRS_RETPOLINE: mode = SPECTRE_V2_EIBRS_RETPOLINE; break; } if (mode == SPECTRE_V2_EIBRS && unprivileged_ebpf_enabled()) pr_err(SPECTRE_V2_EIBRS_EBPF_MSG); if (spectre_v2_in_eibrs_mode(mode)) { /* Force it so VMEXIT will restore correctly */ x86_spec_ctrl_base |= SPEC_CTRL_IBRS; wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base); } switch (mode) { case SPECTRE_V2_NONE: case SPECTRE_V2_EIBRS: break; case SPECTRE_V2_LFENCE: case SPECTRE_V2_EIBRS_LFENCE: setup_force_cpu_cap(X86_FEATURE_RETPOLINE_LFENCE); fallthrough; case SPECTRE_V2_RETPOLINE: case SPECTRE_V2_EIBRS_RETPOLINE: setup_force_cpu_cap(X86_FEATURE_RETPOLINE); break; } 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"); spectre_v2_determine_rsb_fill_type_at_vmexit(mode); /* * 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) && !spectre_v2_in_eibrs_mode(mode)) { setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW); pr_info("Enabling Restricted Speculation for firmware calls\n"); } /* Set up IBPB and STIBP depending on the general spectre V2 command */ spectre_v2_user_select_mitigation(cmd); } static void update_stibp_msr(void * __unused) { wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base); } /* Update x86_spec_ctrl_base in case SMT state changed. */ static void update_stibp_strict(void) { u64 mask = x86_spec_ctrl_base & ~SPEC_CTRL_STIBP; if (sched_smt_active()) mask |= SPEC_CTRL_STIBP; if (mask == x86_spec_ctrl_base) return; pr_info("Update user space SMT mitigation: STIBP %s\n", mask & SPEC_CTRL_STIBP ? "always-on" : "off"); x86_spec_ctrl_base = mask; on_each_cpu(update_stibp_msr, NULL, 1); } /* Update the static key controlling the evaluation of TIF_SPEC_IB */ static void update_indir_branch_cond(void) { if (sched_smt_active()) static_branch_enable(&switch_to_cond_stibp); else static_branch_disable(&switch_to_cond_stibp); } #undef pr_fmt #define pr_fmt(fmt) fmt /* Update the static key controlling the MDS CPU buffer clear in idle */ static void update_mds_branch_idle(void) { u64 ia32_cap = x86_read_arch_cap_msr(); /* * Enable the idle clearing if SMT is active on CPUs which are * affected only by MSBDS and not any other MDS variant. * * The other variants cannot be mitigated when SMT is enabled, so * clearing the buffers on idle just to prevent the Store Buffer * repartitioning leak would be a window dressing exercise. */ if (!boot_cpu_has_bug(X86_BUG_MSBDS_ONLY)) return; if (sched_smt_active()) { static_branch_enable(&mds_idle_clear); } else if (mmio_mitigation == MMIO_MITIGATION_OFF || (ia32_cap & ARCH_CAP_FBSDP_NO)) { static_branch_disable(&mds_idle_clear); } } #define MDS_MSG_SMT "MDS CPU bug present and SMT on, data leak possible. See https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/mds.html for more details.\n" #define TAA_MSG_SMT "TAA CPU bug present and SMT on, data leak possible. See https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/tsx_async_abort.html for more details.\n" #define MMIO_MSG_SMT "MMIO Stale Data CPU bug present and SMT on, data leak possible. See https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/processor_mmio_stale_data.html for more details.\n" void cpu_bugs_smt_update(void) { mutex_lock(&spec_ctrl_mutex); if (sched_smt_active() && unprivileged_ebpf_enabled() && spectre_v2_enabled == SPECTRE_V2_EIBRS_LFENCE) pr_warn_once(SPECTRE_V2_EIBRS_LFENCE_EBPF_SMT_MSG); switch (spectre_v2_user_stibp) { case SPECTRE_V2_USER_NONE: break; case SPECTRE_V2_USER_STRICT: case SPECTRE_V2_USER_STRICT_PREFERRED: update_stibp_strict(); break; case SPECTRE_V2_USER_PRCTL: case SPECTRE_V2_USER_SECCOMP: update_indir_branch_cond(); break; } switch (mds_mitigation) { case MDS_MITIGATION_FULL: case MDS_MITIGATION_VMWERV: if (sched_smt_active() && !boot_cpu_has(X86_BUG_MSBDS_ONLY)) pr_warn_once(MDS_MSG_SMT); update_mds_branch_idle(); break; case MDS_MITIGATION_OFF: break; } switch (taa_mitigation) { case TAA_MITIGATION_VERW: case TAA_MITIGATION_UCODE_NEEDED: if (sched_smt_active()) pr_warn_once(TAA_MSG_SMT); break; case TAA_MITIGATION_TSX_DISABLED: case TAA_MITIGATION_OFF: break; } switch (mmio_mitigation) { case MMIO_MITIGATION_VERW: case MMIO_MITIGATION_UCODE_NEEDED: if (sched_smt_active()) pr_warn_once(MMIO_MSG_SMT); break; case MMIO_MITIGATION_OFF: break; } mutex_unlock(&spec_ctrl_mutex); } #undef pr_fmt #define pr_fmt(fmt) "Speculative Store Bypass: " fmt static enum ssb_mitigation ssb_mode __ro_after_init = SPEC_STORE_BYPASS_NONE; /* The kernel command line selection */ enum ssb_mitigation_cmd { SPEC_STORE_BYPASS_CMD_NONE, SPEC_STORE_BYPASS_CMD_AUTO, SPEC_STORE_BYPASS_CMD_ON, SPEC_STORE_BYPASS_CMD_PRCTL, SPEC_STORE_BYPASS_CMD_SECCOMP, }; static const char * const ssb_strings[] = { [SPEC_STORE_BYPASS_NONE] = "Vulnerable", [SPEC_STORE_BYPASS_DISABLE] = "Mitigation: Speculative Store Bypass disabled", [SPEC_STORE_BYPASS_PRCTL] = "Mitigation: Speculative Store Bypass disabled via prctl", [SPEC_STORE_BYPASS_SECCOMP] = "Mitigation: Speculative Store Bypass disabled via prctl and seccomp", }; static const struct { const char *option; enum ssb_mitigation_cmd cmd; } ssb_mitigation_options[] __initconst = { { "auto", SPEC_STORE_BYPASS_CMD_AUTO }, /* Platform decides */ { "on", SPEC_STORE_BYPASS_CMD_ON }, /* Disable Speculative Store Bypass */ { "off", SPEC_STORE_BYPASS_CMD_NONE }, /* Don't touch Speculative Store Bypass */ { "prctl", SPEC_STORE_BYPASS_CMD_PRCTL }, /* Disable Speculative Store Bypass via prctl */ { "seccomp", SPEC_STORE_BYPASS_CMD_SECCOMP }, /* Disable Speculative Store Bypass via prctl and seccomp */ }; static enum ssb_mitigation_cmd __init ssb_parse_cmdline(void) { enum ssb_mitigation_cmd cmd = SPEC_STORE_BYPASS_CMD_AUTO; char arg[20]; int ret, i; if (cmdline_find_option_bool(boot_command_line, "nospec_store_bypass_disable") || cpu_mitigations_off()) { return SPEC_STORE_BYPASS_CMD_NONE; } else { ret = cmdline_find_option(boot_command_line, "spec_store_bypass_disable", arg, sizeof(arg)); if (ret < 0) return SPEC_STORE_BYPASS_CMD_AUTO; for (i = 0; i < ARRAY_SIZE(ssb_mitigation_options); i++) { if (!match_option(arg, ret, ssb_mitigation_options[i].option)) continue; cmd = ssb_mitigation_options[i].cmd; break; } if (i >= ARRAY_SIZE(ssb_mitigation_options)) { pr_err("unknown option (%s). Switching to AUTO select\n", arg); return SPEC_STORE_BYPASS_CMD_AUTO; } } return cmd; } static enum ssb_mitigation __init __ssb_select_mitigation(void) { enum ssb_mitigation mode = SPEC_STORE_BYPASS_NONE; enum ssb_mitigation_cmd cmd; if (!boot_cpu_has(X86_FEATURE_SSBD)) return mode; cmd = ssb_parse_cmdline(); if (!boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS) && (cmd == SPEC_STORE_BYPASS_CMD_NONE || cmd == SPEC_STORE_BYPASS_CMD_AUTO)) return mode; switch (cmd) { case SPEC_STORE_BYPASS_CMD_AUTO: case SPEC_STORE_BYPASS_CMD_SECCOMP: /* * Choose prctl+seccomp as the default mode if seccomp is * enabled. */ if (IS_ENABLED(CONFIG_SECCOMP)) mode = SPEC_STORE_BYPASS_SECCOMP; else mode = SPEC_STORE_BYPASS_PRCTL; break; case SPEC_STORE_BYPASS_CMD_ON: mode = SPEC_STORE_BYPASS_DISABLE; break; case SPEC_STORE_BYPASS_CMD_PRCTL: mode = SPEC_STORE_BYPASS_PRCTL; break; case SPEC_STORE_BYPASS_CMD_NONE: break; } /* * If SSBD is controlled by the SPEC_CTRL MSR, then set the proper * bit in the mask to allow guests to use the mitigation even in the * case where the host does not enable it. */ if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) || static_cpu_has(X86_FEATURE_AMD_SSBD)) { x86_spec_ctrl_mask |= SPEC_CTRL_SSBD; } /* * We have three CPU feature flags that are in play here: * - X86_BUG_SPEC_STORE_BYPASS - CPU is susceptible. * - X86_FEATURE_SSBD - CPU is able to turn off speculative store bypass * - X86_FEATURE_SPEC_STORE_BYPASS_DISABLE - engage the mitigation */ if (mode == SPEC_STORE_BYPASS_DISABLE) { setup_force_cpu_cap(X86_FEATURE_SPEC_STORE_BYPASS_DISABLE); /* * Intel uses the SPEC CTRL MSR Bit(2) for this, while AMD may * use a completely different MSR and bit dependent on family. */ if (!static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) && !static_cpu_has(X86_FEATURE_AMD_SSBD)) { x86_amd_ssb_disable(); } else { x86_spec_ctrl_base |= SPEC_CTRL_SSBD; wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base); } } return mode; } static void ssb_select_mitigation(void) { ssb_mode = __ssb_select_mitigation(); if (boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS)) pr_info("%s\n", ssb_strings[ssb_mode]); } #undef pr_fmt #define pr_fmt(fmt) "Speculation prctl: " fmt static void task_update_spec_tif(struct task_struct *tsk) { /* Force the update of the real TIF bits */ set_tsk_thread_flag(tsk, TIF_SPEC_FORCE_UPDATE); /* * Immediately update the speculation control MSRs for the current * task, but for a non-current task delay setting the CPU * mitigation until it is scheduled next. * * This can only happen for SECCOMP mitigation. For PRCTL it's * always the current task. */ if (tsk == current) speculation_ctrl_update_current(); } static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl) { if (ssb_mode != SPEC_STORE_BYPASS_PRCTL && ssb_mode != SPEC_STORE_BYPASS_SECCOMP) return -ENXIO; switch (ctrl) { case PR_SPEC_ENABLE: /* If speculation is force disabled, enable is not allowed */ if (task_spec_ssb_force_disable(task)) return -EPERM; task_clear_spec_ssb_disable(task); task_clear_spec_ssb_noexec(task); task_update_spec_tif(task); break; case PR_SPEC_DISABLE: task_set_spec_ssb_disable(task); task_clear_spec_ssb_noexec(task); task_update_spec_tif(task); break; case PR_SPEC_FORCE_DISABLE: task_set_spec_ssb_disable(task); task_set_spec_ssb_force_disable(task); task_clear_spec_ssb_noexec(task); task_update_spec_tif(task); break; case PR_SPEC_DISABLE_NOEXEC: if (task_spec_ssb_force_disable(task)) return -EPERM; task_set_spec_ssb_disable(task); task_set_spec_ssb_noexec(task); task_update_spec_tif(task); break; default: return -ERANGE; } return 0; } static bool is_spec_ib_user_controlled(void) { return spectre_v2_user_ibpb == SPECTRE_V2_USER_PRCTL || spectre_v2_user_ibpb == SPECTRE_V2_USER_SECCOMP || spectre_v2_user_stibp == SPECTRE_V2_USER_PRCTL || spectre_v2_user_stibp == SPECTRE_V2_USER_SECCOMP; } static int ib_prctl_set(struct task_struct *task, unsigned long ctrl) { switch (ctrl) { case PR_SPEC_ENABLE: if (spectre_v2_user_ibpb == SPECTRE_V2_USER_NONE && spectre_v2_user_stibp == SPECTRE_V2_USER_NONE) return 0; /* * With strict mode for both IBPB and STIBP, the instruction * code paths avoid checking this task flag and instead, * unconditionally run the instruction. However, STIBP and IBPB * are independent and either can be set to conditionally * enabled regardless of the mode of the other. * * If either is set to conditional, allow the task flag to be * updated, unless it was force-disabled by a previous prctl * call. Currently, this is possible on an AMD CPU which has the * feature X86_FEATURE_AMD_STIBP_ALWAYS_ON. In this case, if the * kernel is booted with 'spectre_v2_user=seccomp', then * spectre_v2_user_ibpb == SPECTRE_V2_USER_SECCOMP and * spectre_v2_user_stibp == SPECTRE_V2_USER_STRICT_PREFERRED. */ if (!is_spec_ib_user_controlled() || task_spec_ib_force_disable(task)) return -EPERM; task_clear_spec_ib_disable(task); task_update_spec_tif(task); break; case PR_SPEC_DISABLE: case PR_SPEC_FORCE_DISABLE: /* * Indirect branch speculation is always allowed when * mitigation is force disabled. */ if (spectre_v2_user_ibpb == SPECTRE_V2_USER_NONE && spectre_v2_user_stibp == SPECTRE_V2_USER_NONE) return -EPERM; if (!is_spec_ib_user_controlled()) return 0; task_set_spec_ib_disable(task); if (ctrl == PR_SPEC_FORCE_DISABLE) task_set_spec_ib_force_disable(task); task_update_spec_tif(task); break; default: return -ERANGE; } return 0; } int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which, unsigned long ctrl) { switch (which) { case PR_SPEC_STORE_BYPASS: return ssb_prctl_set(task, ctrl); case PR_SPEC_INDIRECT_BRANCH: return ib_prctl_set(task, ctrl); default: return -ENODEV; } } #ifdef CONFIG_SECCOMP void arch_seccomp_spec_mitigate(struct task_struct *task) { if (ssb_mode == SPEC_STORE_BYPASS_SECCOMP) ssb_prctl_set(task, PR_SPEC_FORCE_DISABLE); if (spectre_v2_user_ibpb == SPECTRE_V2_USER_SECCOMP || spectre_v2_user_stibp == SPECTRE_V2_USER_SECCOMP) ib_prctl_set(task, PR_SPEC_FORCE_DISABLE); } #endif static int ssb_prctl_get(struct task_struct *task) { switch (ssb_mode) { case SPEC_STORE_BYPASS_DISABLE: return PR_SPEC_DISABLE; case SPEC_STORE_BYPASS_SECCOMP: case SPEC_STORE_BYPASS_PRCTL: if (task_spec_ssb_force_disable(task)) return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE; if (task_spec_ssb_noexec(task)) return PR_SPEC_PRCTL | PR_SPEC_DISABLE_NOEXEC; if (task_spec_ssb_disable(task)) return PR_SPEC_PRCTL | PR_SPEC_DISABLE; return PR_SPEC_PRCTL | PR_SPEC_ENABLE; default: if (boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS)) return PR_SPEC_ENABLE; return PR_SPEC_NOT_AFFECTED; } } static int ib_prctl_get(struct task_struct *task) { if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2)) return PR_SPEC_NOT_AFFECTED; if (spectre_v2_user_ibpb == SPECTRE_V2_USER_NONE && spectre_v2_user_stibp == SPECTRE_V2_USER_NONE) return PR_SPEC_ENABLE; else if (is_spec_ib_user_controlled()) { if (task_spec_ib_force_disable(task)) return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE; if (task_spec_ib_disable(task)) return PR_SPEC_PRCTL | PR_SPEC_DISABLE; return PR_SPEC_PRCTL | PR_SPEC_ENABLE; } else if (spectre_v2_user_ibpb == SPECTRE_V2_USER_STRICT || spectre_v2_user_stibp == SPECTRE_V2_USER_STRICT || spectre_v2_user_stibp == SPECTRE_V2_USER_STRICT_PREFERRED) return PR_SPEC_DISABLE; else return PR_SPEC_NOT_AFFECTED; } int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which) { switch (which) { case PR_SPEC_STORE_BYPASS: return ssb_prctl_get(task); case PR_SPEC_INDIRECT_BRANCH: return ib_prctl_get(task); default: return -ENODEV; } } void x86_spec_ctrl_setup_ap(void) { if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL)) wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base); if (ssb_mode == SPEC_STORE_BYPASS_DISABLE) x86_amd_ssb_disable(); } bool itlb_multihit_kvm_mitigation; EXPORT_SYMBOL_GPL(itlb_multihit_kvm_mitigation); #undef pr_fmt #define pr_fmt(fmt) "L1TF: " fmt /* Default mitigation for L1TF-affected CPUs */ enum l1tf_mitigations l1tf_mitigation __ro_after_init = L1TF_MITIGATION_FLUSH; #if IS_ENABLED(CONFIG_KVM_INTEL) EXPORT_SYMBOL_GPL(l1tf_mitigation); #endif enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO; EXPORT_SYMBOL_GPL(l1tf_vmx_mitigation); /* * These CPUs all support 44bits physical address space internally in the * cache but CPUID can report a smaller number of physical address bits. * * The L1TF mitigation uses the top most address bit for the inversion of * non present PTEs. When the installed memory reaches into the top most * address bit due to memory holes, which has been observed on machines * which report 36bits physical address bits and have 32G RAM installed, * then the mitigation range check in l1tf_select_mitigation() triggers. * This is a false positive because the mitigation is still possible due to * the fact that the cache uses 44bit internally. Use the cache bits * instead of the reported physical bits and adjust them on the affected * machines to 44bit if the reported bits are less than 44. */ static void override_cache_bits(struct cpuinfo_x86 *c) { if (c->x86 != 6) return; switch (c->x86_model) { case INTEL_FAM6_NEHALEM: case INTEL_FAM6_WESTMERE: case INTEL_FAM6_SANDYBRIDGE: case INTEL_FAM6_IVYBRIDGE: case INTEL_FAM6_HASWELL: case INTEL_FAM6_HASWELL_L: case INTEL_FAM6_HASWELL_G: case INTEL_FAM6_BROADWELL: case INTEL_FAM6_BROADWELL_G: case INTEL_FAM6_SKYLAKE_L: case INTEL_FAM6_SKYLAKE: case INTEL_FAM6_KABYLAKE_L: case INTEL_FAM6_KABYLAKE: if (c->x86_cache_bits < 44) c->x86_cache_bits = 44; break; } } static void __init l1tf_select_mitigation(void) { u64 half_pa; if (!boot_cpu_has_bug(X86_BUG_L1TF)) return; if (cpu_mitigations_off()) l1tf_mitigation = L1TF_MITIGATION_OFF; else if (cpu_mitigations_auto_nosmt()) l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOSMT; override_cache_bits(&boot_cpu_data); switch (l1tf_mitigation) { case L1TF_MITIGATION_OFF: case L1TF_MITIGATION_FLUSH_NOWARN: case L1TF_MITIGATION_FLUSH: break; case L1TF_MITIGATION_FLUSH_NOSMT: case L1TF_MITIGATION_FULL: cpu_smt_disable(false); break; case L1TF_MITIGATION_FULL_FORCE: cpu_smt_disable(true); break; } #if CONFIG_PGTABLE_LEVELS == 2 pr_warn("Kernel not compiled for PAE. No mitigation for L1TF\n"); return; #endif half_pa = (u64)l1tf_pfn_limit() << PAGE_SHIFT; if (l1tf_mitigation != L1TF_MITIGATION_OFF && e820__mapped_any(half_pa, ULLONG_MAX - half_pa, E820_TYPE_RAM)) { pr_warn("System has more than MAX_PA/2 memory. L1TF mitigation not effective.\n"); pr_info("You may make it effective by booting the kernel with mem=%llu parameter.\n", half_pa); pr_info("However, doing so will make a part of your RAM unusable.\n"); pr_info("Reading https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/l1tf.html might help you decide.\n"); return; } setup_force_cpu_cap(X86_FEATURE_L1TF_PTEINV); } static int __init l1tf_cmdline(char *str) { if (!boot_cpu_has_bug(X86_BUG_L1TF)) return 0; if (!str) return -EINVAL; if (!strcmp(str, "off")) l1tf_mitigation = L1TF_MITIGATION_OFF; else if (!strcmp(str, "flush,nowarn")) l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOWARN; else if (!strcmp(str, "flush")) l1tf_mitigation = L1TF_MITIGATION_FLUSH; else if (!strcmp(str, "flush,nosmt")) l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOSMT; else if (!strcmp(str, "full")) l1tf_mitigation = L1TF_MITIGATION_FULL; else if (!strcmp(str, "full,force")) l1tf_mitigation = L1TF_MITIGATION_FULL_FORCE; return 0; } early_param("l1tf", l1tf_cmdline); #undef pr_fmt #define pr_fmt(fmt) fmt #ifdef CONFIG_SYSFS #define L1TF_DEFAULT_MSG "Mitigation: PTE Inversion" #if IS_ENABLED(CONFIG_KVM_INTEL) static const char * const l1tf_vmx_states[] = { [VMENTER_L1D_FLUSH_AUTO] = "auto", [VMENTER_L1D_FLUSH_NEVER] = "vulnerable", [VMENTER_L1D_FLUSH_COND] = "conditional cache flushes", [VMENTER_L1D_FLUSH_ALWAYS] = "cache flushes", [VMENTER_L1D_FLUSH_EPT_DISABLED] = "EPT disabled", [VMENTER_L1D_FLUSH_NOT_REQUIRED] = "flush not necessary" }; static ssize_t l1tf_show_state(char *buf) { if (l1tf_vmx_mitigation == VMENTER_L1D_FLUSH_AUTO) return sprintf(buf, "%s\n", L1TF_DEFAULT_MSG); if (l1tf_vmx_mitigation == VMENTER_L1D_FLUSH_EPT_DISABLED || (l1tf_vmx_mitigation == VMENTER_L1D_FLUSH_NEVER && sched_smt_active())) { return sprintf(buf, "%s; VMX: %s\n", L1TF_DEFAULT_MSG, l1tf_vmx_states[l1tf_vmx_mitigation]); } return sprintf(buf, "%s; VMX: %s, SMT %s\n", L1TF_DEFAULT_MSG, l1tf_vmx_states[l1tf_vmx_mitigation], sched_smt_active() ? "vulnerable" : "disabled"); } static ssize_t itlb_multihit_show_state(char *buf) { if (itlb_multihit_kvm_mitigation) return sprintf(buf, "KVM: Mitigation: Split huge pages\n"); else return sprintf(buf, "KVM: Vulnerable\n"); } #else static ssize_t l1tf_show_state(char *buf) { return sprintf(buf, "%s\n", L1TF_DEFAULT_MSG); } static ssize_t itlb_multihit_show_state(char *buf) { return sprintf(buf, "Processor vulnerable\n"); } #endif static ssize_t mds_show_state(char *buf) { if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) { return sprintf(buf, "%s; SMT Host state unknown\n", mds_strings[mds_mitigation]); } if (boot_cpu_has(X86_BUG_MSBDS_ONLY)) { return sprintf(buf, "%s; SMT %s\n", mds_strings[mds_mitigation], (mds_mitigation == MDS_MITIGATION_OFF ? "vulnerable" : sched_smt_active() ? "mitigated" : "disabled")); } return sprintf(buf, "%s; SMT %s\n", mds_strings[mds_mitigation], sched_smt_active() ? "vulnerable" : "disabled"); } static ssize_t tsx_async_abort_show_state(char *buf) { if ((taa_mitigation == TAA_MITIGATION_TSX_DISABLED) || (taa_mitigation == TAA_MITIGATION_OFF)) return sprintf(buf, "%s\n", taa_strings[taa_mitigation]); if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) { return sprintf(buf, "%s; SMT Host state unknown\n", taa_strings[taa_mitigation]); } return sprintf(buf, "%s; SMT %s\n", taa_strings[taa_mitigation], sched_smt_active() ? "vulnerable" : "disabled"); } static ssize_t mmio_stale_data_show_state(char *buf) { if (boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN)) return sysfs_emit(buf, "Unknown: No mitigations\n"); if (mmio_mitigation == MMIO_MITIGATION_OFF) return sysfs_emit(buf, "%s\n", mmio_strings[mmio_mitigation]); if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) { return sysfs_emit(buf, "%s; SMT Host state unknown\n", mmio_strings[mmio_mitigation]); } return sysfs_emit(buf, "%s; SMT %s\n", mmio_strings[mmio_mitigation], sched_smt_active() ? "vulnerable" : "disabled"); } static char *stibp_state(void) { if (spectre_v2_in_eibrs_mode(spectre_v2_enabled)) return ""; switch (spectre_v2_user_stibp) { case SPECTRE_V2_USER_NONE: return ", STIBP: disabled"; case SPECTRE_V2_USER_STRICT: return ", STIBP: forced"; case SPECTRE_V2_USER_STRICT_PREFERRED: return ", STIBP: always-on"; case SPECTRE_V2_USER_PRCTL: case SPECTRE_V2_USER_SECCOMP: if (static_key_enabled(&switch_to_cond_stibp)) return ", STIBP: conditional"; } return ""; } static char *ibpb_state(void) { if (boot_cpu_has(X86_FEATURE_IBPB)) { if (static_key_enabled(&switch_mm_always_ibpb)) return ", IBPB: always-on"; if (static_key_enabled(&switch_mm_cond_ibpb)) return ", IBPB: conditional"; return ", IBPB: disabled"; } return ""; } static char *pbrsb_eibrs_state(void) { if (boot_cpu_has_bug(X86_BUG_EIBRS_PBRSB)) { if (boot_cpu_has(X86_FEATURE_RSB_VMEXIT_LITE) || boot_cpu_has(X86_FEATURE_RETPOLINE)) return ", PBRSB-eIBRS: SW sequence"; else return ", PBRSB-eIBRS: Vulnerable"; } else { return ", PBRSB-eIBRS: Not affected"; } } static ssize_t spectre_v2_show_state(char *buf) { if (spectre_v2_enabled == SPECTRE_V2_LFENCE) return sprintf(buf, "Vulnerable: LFENCE\n"); if (spectre_v2_enabled == SPECTRE_V2_EIBRS && unprivileged_ebpf_enabled()) return sprintf(buf, "Vulnerable: eIBRS with unprivileged eBPF\n"); if (sched_smt_active() && unprivileged_ebpf_enabled() && spectre_v2_enabled == SPECTRE_V2_EIBRS_LFENCE) return sprintf(buf, "Vulnerable: eIBRS+LFENCE with unprivileged eBPF and SMT\n"); return sprintf(buf, "%s%s%s%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled], ibpb_state(), boot_cpu_has(X86_FEATURE_USE_IBRS_FW) ? ", IBRS_FW" : "", stibp_state(), boot_cpu_has(X86_FEATURE_RSB_CTXSW) ? ", RSB filling" : "", pbrsb_eibrs_state(), spectre_v2_module_string()); } static ssize_t srbds_show_state(char *buf) { return sprintf(buf, "%s\n", srbds_strings[srbds_mitigation]); } static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr, char *buf, unsigned int bug) { if (!boot_cpu_has_bug(bug)) return sprintf(buf, "Not affected\n"); switch (bug) { case X86_BUG_CPU_MELTDOWN: if (boot_cpu_has(X86_FEATURE_PTI)) return sprintf(buf, "Mitigation: PTI\n"); if (hypervisor_is_type(X86_HYPER_XEN_PV)) return sprintf(buf, "Unknown (XEN PV detected, hypervisor mitigation required)\n"); break; case X86_BUG_SPECTRE_V1: return sprintf(buf, "%s\n", spectre_v1_strings[spectre_v1_mitigation]); case X86_BUG_SPECTRE_V2: return spectre_v2_show_state(buf); case X86_BUG_SPEC_STORE_BYPASS: return sprintf(buf, "%s\n", ssb_strings[ssb_mode]); case X86_BUG_L1TF: if (boot_cpu_has(X86_FEATURE_L1TF_PTEINV)) return l1tf_show_state(buf); break; case X86_BUG_MDS: return mds_show_state(buf); case X86_BUG_TAA: return tsx_async_abort_show_state(buf); case X86_BUG_ITLB_MULTIHIT: return itlb_multihit_show_state(buf); case X86_BUG_SRBDS: return srbds_show_state(buf); case X86_BUG_MMIO_STALE_DATA: case X86_BUG_MMIO_UNKNOWN: return mmio_stale_data_show_state(buf); default: break; } return sprintf(buf, "Vulnerable\n"); } ssize_t cpu_show_meltdown(struct device *dev, struct device_attribute *attr, char *buf) { return cpu_show_common(dev, attr, buf, X86_BUG_CPU_MELTDOWN); } ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr, char *buf) { return cpu_show_common(dev, attr, buf, X86_BUG_SPECTRE_V1); } ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, char *buf) { return cpu_show_common(dev, attr, buf, X86_BUG_SPECTRE_V2); } ssize_t cpu_show_spec_store_bypass(struct device *dev, struct device_attribute *attr, char *buf) { return cpu_show_common(dev, attr, buf, X86_BUG_SPEC_STORE_BYPASS); } ssize_t cpu_show_l1tf(struct device *dev, struct device_attribute *attr, char *buf) { return cpu_show_common(dev, attr, buf, X86_BUG_L1TF); } ssize_t cpu_show_mds(struct device *dev, struct device_attribute *attr, char *buf) { return cpu_show_common(dev, attr, buf, X86_BUG_MDS); } ssize_t cpu_show_tsx_async_abort(struct device *dev, struct device_attribute *attr, char *buf) { return cpu_show_common(dev, attr, buf, X86_BUG_TAA); } ssize_t cpu_show_itlb_multihit(struct device *dev, struct device_attribute *attr, char *buf) { return cpu_show_common(dev, attr, buf, X86_BUG_ITLB_MULTIHIT); } ssize_t cpu_show_srbds(struct device *dev, struct device_attribute *attr, char *buf) { return cpu_show_common(dev, attr, buf, X86_BUG_SRBDS); } ssize_t cpu_show_mmio_stale_data(struct device *dev, struct device_attribute *attr, char *buf) { if (boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN)) return cpu_show_common(dev, attr, buf, X86_BUG_MMIO_UNKNOWN); else return cpu_show_common(dev, attr, buf, X86_BUG_MMIO_STALE_DATA); } #endif