arch/x86/kernel/cpu/bugs.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  Copyright (C) 1994  Linus Torvalds
   4  *
   5  *  Cyrix stuff, June 1998 by:
   6  *      - Rafael R. Reilova (moved everything from head.S),
   7  *        <rreilova@ececs.uc.edu>
   8  *      - Channing Corn (tests & fixes),
   9  *      - Andrew D. Balsa (code cleanup).
  10  */
  11 #include <linux/init.h>
  12 #include <linux/utsname.h>
  13 #include <linux/cpu.h>
  14
  15 #include <asm/nospec-branch.h>
  16 #include <asm/cmdline.h>
  17 #include <asm/bugs.h>
  18 #include <asm/processor.h>
  19 #include <asm/processor-flags.h>
  20 #include <asm/fpu/internal.h>
  21 #include <asm/msr.h>
  22 #include <asm/paravirt.h>
  23 #include <asm/alternative.h>
  24 #include <asm/pgtable.h>
  25 #include <asm/set_memory.h>
  26
  27 static void __init spectre_v2_select_mitigation(void);
  28
  29 void __init check_bugs(void)
  30 {
  31         identify_boot_cpu();
  32
  33         if (!IS_ENABLED(CONFIG_SMP)) {
  34                 pr_info("CPU: ");
  35                 print_cpu_info(&boot_cpu_data);
  36         }
  37
  38         /* Select the proper spectre mitigation before patching alternatives */
  39         spectre_v2_select_mitigation();
  40
  41 #ifdef CONFIG_X86_32
  42         /*
  43          * Check whether we are able to run this kernel safely on SMP.
  44          *
  45          * - i386 is no longer supported.
  46          * - In order to run on anything without a TSC, we need to be
  47          *   compiled for a i486.
  48          */
  49         if (boot_cpu_data.x86 < 4)
  50                 panic("Kernel requires i486+ for 'invlpg' and other features");
  51
  52         init_utsname()->machine[1] =
  53                 '0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
  54         alternative_instructions();
  55
  56         fpu__init_check_bugs();
  57 #else /* CONFIG_X86_64 */
  58         alternative_instructions();
  59
  60         /*
  61          * Make sure the first 2MB area is not mapped by huge pages
  62          * There are typically fixed size MTRRs in there and overlapping
  63          * MTRRs into large pages causes slow downs.
  64          *
  65          * Right now we don't do that with gbpages because there seems
  66          * very little benefit for that case.
  67          */
  68         if (!direct_gbpages)
  69                 set_memory_4k((unsigned long)__va(0), 1);
  70 #endif
  71 }
  72
  73 /* The kernel command line selection */
  74 enum spectre_v2_mitigation_cmd {
  75         SPECTRE_V2_CMD_NONE,
  76         SPECTRE_V2_CMD_AUTO,
  77         SPECTRE_V2_CMD_FORCE,
  78         SPECTRE_V2_CMD_RETPOLINE,
  79         SPECTRE_V2_CMD_RETPOLINE_GENERIC,
  80         SPECTRE_V2_CMD_RETPOLINE_AMD,
  81 };
  82
  83 static const char *spectre_v2_strings[] = {
  84         [SPECTRE_V2_NONE]                       = "Vulnerable",
  85         [SPECTRE_V2_RETPOLINE_MINIMAL]          = "Vulnerable: Minimal generic ASM retpoline",
  86         [SPECTRE_V2_RETPOLINE_MINIMAL_AMD]      = "Vulnerable: Minimal AMD ASM retpoline",
  87         [SPECTRE_V2_RETPOLINE_GENERIC]          = "Mitigation: Full generic retpoline",
  88         [SPECTRE_V2_RETPOLINE_AMD]              = "Mitigation: Full AMD retpoline",
  89 };
  90
  91 #undef pr_fmt
  92 #define pr_fmt(fmt)     "Spectre V2 mitigation: " fmt
  93
  94 static enum spectre_v2_mitigation spectre_v2_enabled = SPECTRE_V2_NONE;
  95
  96 static void __init spec2_print_if_insecure(const char *reason)
  97 {
  98         if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
  99                 pr_info("%s\n", reason);
 100 }
 101
 102 static void __init spec2_print_if_secure(const char *reason)
 103 {
 104         if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
 105                 pr_info("%s\n", reason);
 106 }
 107
 108 static inline bool retp_compiler(void)
 109 {
 110         return __is_defined(RETPOLINE);
 111 }
 112
 113 static inline bool match_option(const char *arg, int arglen, const char *opt)
 114 {
 115         int len = strlen(opt);
 116
 117         return len == arglen && !strncmp(arg, opt, len);
 118 }
 119
 120 static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
 121 {
 122         char arg[20];
 123         int ret;
 124
 125         ret = cmdline_find_option(boot_command_line, "spectre_v2", arg,
 126                                   sizeof(arg));
 127         if (ret > 0)  {
 128                 if (match_option(arg, ret, "off")) {
 129                         goto disable;
 130                 } else if (match_option(arg, ret, "on")) {
 131                         spec2_print_if_secure("force enabled on command line.");
 132                         return SPECTRE_V2_CMD_FORCE;
 133                 } else if (match_option(arg, ret, "retpoline")) {
 134                         spec2_print_if_insecure("retpoline selected on command line.");
 135                         return SPECTRE_V2_CMD_RETPOLINE;
 136                 } else if (match_option(arg, ret, "retpoline,amd")) {
 137                         if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD) {
 138                                 pr_err("retpoline,amd selected but CPU is not AMD. Switching to AUTO select\n");
 139                                 return SPECTRE_V2_CMD_AUTO;
 140                         }
 141                         spec2_print_if_insecure("AMD retpoline selected on command line.");
 142                         return SPECTRE_V2_CMD_RETPOLINE_AMD;
 143                 } else if (match_option(arg, ret, "retpoline,generic")) {
 144                         spec2_print_if_insecure("generic retpoline selected on command line.");
 145                         return SPECTRE_V2_CMD_RETPOLINE_GENERIC;
 146                 } else if (match_option(arg, ret, "auto")) {
 147                         return SPECTRE_V2_CMD_AUTO;
 148                 }
 149         }
 150
 151         if (!cmdline_find_option_bool(boot_command_line, "nospectre_v2"))
 152                 return SPECTRE_V2_CMD_AUTO;
 153 disable:
 154         spec2_print_if_insecure("disabled on command line.");
 155         return SPECTRE_V2_CMD_NONE;
 156 }
 157
 158 static void __init spectre_v2_select_mitigation(void)
 159 {
 160         enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();
 161         enum spectre_v2_mitigation mode = SPECTRE_V2_NONE;
 162
 163         /*
 164          * If the CPU is not affected and the command line mode is NONE or AUTO
 165          * then nothing to do.
 166          */
 167         if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2) &&
 168             (cmd == SPECTRE_V2_CMD_NONE || cmd == SPECTRE_V2_CMD_AUTO))
 169                 return;
 170
 171         switch (cmd) {
 172         case SPECTRE_V2_CMD_NONE:
 173                 return;
 174
 175         case SPECTRE_V2_CMD_FORCE:
 176                 /* FALLTRHU */
 177         case SPECTRE_V2_CMD_AUTO:
 178                 goto retpoline_auto;
 179
 180         case SPECTRE_V2_CMD_RETPOLINE_AMD:
 181                 if (IS_ENABLED(CONFIG_RETPOLINE))
 182                         goto retpoline_amd;
 183                 break;
 184         case SPECTRE_V2_CMD_RETPOLINE_GENERIC:
 185                 if (IS_ENABLED(CONFIG_RETPOLINE))
 186                         goto retpoline_generic;
 187                 break;
 188         case SPECTRE_V2_CMD_RETPOLINE:
 189                 if (IS_ENABLED(CONFIG_RETPOLINE))
 190                         goto retpoline_auto;
 191                 break;
 192         }
 193         pr_err("kernel not compiled with retpoline; no mitigation available!");
 194         return;
 195
 196 retpoline_auto:
 197         if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) {
 198         retpoline_amd:
 199                 if (!boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) {
 200                         pr_err("LFENCE not serializing. Switching to generic retpoline\n");
 201                         goto retpoline_generic;
 202                 }
 203                 mode = retp_compiler() ? SPECTRE_V2_RETPOLINE_AMD :
 204                                          SPECTRE_V2_RETPOLINE_MINIMAL_AMD;
 205                 setup_force_cpu_cap(X86_FEATURE_RETPOLINE_AMD);
 206                 setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
 207         } else {
 208         retpoline_generic:
 209                 mode = retp_compiler() ? SPECTRE_V2_RETPOLINE_GENERIC :
 210                                          SPECTRE_V2_RETPOLINE_MINIMAL;
 211                 setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
 212         }
 213
 214         spectre_v2_enabled = mode;
 215         pr_info("%s\n", spectre_v2_strings[mode]);
 216 }
 217
 218 #undef pr_fmt
 219
 220 #ifdef CONFIG_SYSFS
 221 ssize_t cpu_show_meltdown(struct device *dev,
 222                           struct device_attribute *attr, char *buf)
 223 {
 224         if (!boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN))
 225                 return sprintf(buf, "Not affected\n");
 226         if (boot_cpu_has(X86_FEATURE_PTI))
 227                 return sprintf(buf, "Mitigation: PTI\n");
 228         return sprintf(buf, "Vulnerable\n");
 229 }
 230
 231 ssize_t cpu_show_spectre_v1(struct device *dev,
 232                             struct device_attribute *attr, char *buf)
 233 {
 234         if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V1))
 235                 return sprintf(buf, "Not affected\n");
 236         return sprintf(buf, "Vulnerable\n");
 237 }
 238
 239 ssize_t cpu_show_spectre_v2(struct device *dev,
 240                             struct device_attribute *attr, char *buf)
 241 {
 242         if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
 243                 return sprintf(buf, "Not affected\n");
 244
 245         return sprintf(buf, "%s\n", spectre_v2_strings[spectre_v2_enabled]);
 246 }
 247 #endif