// 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 static void __init spectre_v2_select_mitigation(void); void __init check_bugs(void) { identify_boot_cpu(); if (!IS_ENABLED(CONFIG_SMP)) { pr_info("CPU: "); print_cpu_info(&boot_cpu_data); } /* Select the proper spectre mitigation before patching alternatives */ spectre_v2_select_mitigation(); #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 } /* The kernel command line selection */ 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_AMD, }; static const char *spectre_v2_strings[] = { [SPECTRE_V2_NONE] = "Vulnerable", [SPECTRE_V2_RETPOLINE_MINIMAL] = "Vulnerable: Minimal generic ASM retpoline", [SPECTRE_V2_RETPOLINE_MINIMAL_AMD] = "Vulnerable: Minimal AMD ASM retpoline", [SPECTRE_V2_RETPOLINE_GENERIC] = "Mitigation: Full generic retpoline", [SPECTRE_V2_RETPOLINE_AMD] = "Mitigation: Full AMD retpoline", }; #undef pr_fmt #define pr_fmt(fmt) "Spectre V2 mitigation: " fmt static enum spectre_v2_mitigation spectre_v2_enabled = SPECTRE_V2_NONE; static bool spectre_v2_bad_module; #ifdef RETPOLINE bool retpoline_module_ok(bool has_retpoline) { if (spectre_v2_enabled == SPECTRE_V2_NONE || has_retpoline) return true; pr_err("System may be vunerable to spectre v2\n"); spectre_v2_bad_module = true; return false; } #endif static void __init spec2_print_if_insecure(const char *reason) { if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2)) pr_info("%s\n", reason); } static void __init spec2_print_if_secure(const char *reason) { if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2)) pr_info("%s\n", reason); } static inline bool retp_compiler(void) { return __is_defined(RETPOLINE); } static inline bool match_option(const char *arg, int arglen, const char *opt) { int len = strlen(opt); return len == arglen && !strncmp(arg, opt, len); } static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void) { char arg[20]; int ret; ret = cmdline_find_option(boot_command_line, "spectre_v2", arg, sizeof(arg)); if (ret > 0) { if (match_option(arg, ret, "off")) { goto disable; } else if (match_option(arg, ret, "on")) { spec2_print_if_secure("force enabled on command line."); return SPECTRE_V2_CMD_FORCE; } else if (match_option(arg, ret, "retpoline")) { spec2_print_if_insecure("retpoline selected on command line."); return SPECTRE_V2_CMD_RETPOLINE; } else if (match_option(arg, ret, "retpoline,amd")) { if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD) { pr_err("retpoline,amd selected but CPU is not AMD. Switching to AUTO select\n"); return SPECTRE_V2_CMD_AUTO; } spec2_print_if_insecure("AMD retpoline selected on command line."); return SPECTRE_V2_CMD_RETPOLINE_AMD; } else if (match_option(arg, ret, "retpoline,generic")) { spec2_print_if_insecure("generic retpoline selected on command line."); return SPECTRE_V2_CMD_RETPOLINE_GENERIC; } else if (match_option(arg, ret, "auto")) { return SPECTRE_V2_CMD_AUTO; } } if (!cmdline_find_option_bool(boot_command_line, "nospectre_v2")) return SPECTRE_V2_CMD_AUTO; disable: spec2_print_if_insecure("disabled on command line."); return SPECTRE_V2_CMD_NONE; } /* Check for Skylake-like CPUs (for RSB handling) */ static bool __init is_skylake_era(void) { if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL && boot_cpu_data.x86 == 6) { switch (boot_cpu_data.x86_model) { case INTEL_FAM6_SKYLAKE_MOBILE: case INTEL_FAM6_SKYLAKE_DESKTOP: case INTEL_FAM6_SKYLAKE_X: case INTEL_FAM6_KABYLAKE_MOBILE: case INTEL_FAM6_KABYLAKE_DESKTOP: return true; } } return false; } 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]); /* * If neither SMEP or KPTI are available, there is a risk of * hitting userspace addresses in the RSB after a context switch * from a shallow call stack to a deeper one. To prevent this fill * the entire RSB, even when using IBRS. * * Skylake era CPUs have a separate issue with *underflow* of the * RSB, when they will predict 'ret' targets from the generic BTB. * The proper mitigation for this is IBRS. If IBRS is not supported * or deactivated in favour of retpolines the RSB fill on context * switch is required. */ if ((!boot_cpu_has(X86_FEATURE_PTI) && !boot_cpu_has(X86_FEATURE_SMEP)) || is_skylake_era()) { setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW); pr_info("Filling RSB on context switch\n"); } } #undef pr_fmt #ifdef CONFIG_SYSFS ssize_t cpu_show_meltdown(struct device *dev, struct device_attribute *attr, char *buf) { if (!boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN)) return sprintf(buf, "Not affected\n"); if (boot_cpu_has(X86_FEATURE_PTI)) return sprintf(buf, "Mitigation: PTI\n"); return sprintf(buf, "Vulnerable\n"); } ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr, char *buf) { if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V1)) return sprintf(buf, "Not affected\n"); return sprintf(buf, "Vulnerable\n"); } ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, char *buf) { if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2)) return sprintf(buf, "Not affected\n"); return sprintf(buf, "%s%s\n", spectre_v2_strings[spectre_v2_enabled], spectre_v2_bad_module ? " - vulnerable module loaded" : ""); } #endif