arch/x86/kernel/cpu/bugs.c

   1 /*
   2  *  Copyright (C) 1994  Linus Torvalds
   3  *
   4  *  Cyrix stuff, June 1998 by:
   5  *      - Rafael R. Reilova (moved everything from head.S),
   6  *        <rreilova@ececs.uc.edu>
   7  *      - Channing Corn (tests & fixes),
   8  *      - Andrew D. Balsa (code cleanup).
   9  */
  10 #include <linux/init.h>
  11 #include <linux/utsname.h>
  12 #include <linux/cpu.h>
  13
  14 #include <asm/nospec-branch.h>
  15 #include <asm/cmdline.h>
  16 #include <asm/bugs.h>
  17 #include <asm/processor.h>
  18 #include <asm/processor-flags.h>
  19 #include <asm/i387.h>
  20 #include <asm/msr.h>
  21 #include <asm/paravirt.h>
  22 #include <asm/alternative.h>
  23 #include <asm/pgtable.h>
  24 #include <asm/cacheflush.h>
  25 #include <asm/intel-family.h>
  26
  27 static void __init spectre_v2_select_mitigation(void);
  28
  29 #ifdef CONFIG_X86_32
  30
  31 static int __init no_halt(char *s)
  32 {
  33         WARN_ONCE(1, "\"no-hlt\" is deprecated, please use \"idle=poll\"\n");
  34         boot_cpu_data.hlt_works_ok = 0;
  35         return 1;
  36 }
  37
  38 __setup("no-hlt", no_halt);
  39
  40 static int __init no_387(char *s)
  41 {
  42         boot_cpu_data.hard_math = 0;
  43         write_cr0(X86_CR0_TS | X86_CR0_EM | X86_CR0_MP | read_cr0());
  44         return 1;
  45 }
  46
  47 __setup("no387", no_387);
  48
  49 static double __initdata x = 4195835.0;
  50 static double __initdata y = 3145727.0;
  51
  52 /*
  53  * This used to check for exceptions..
  54  * However, it turns out that to support that,
  55  * the XMM trap handlers basically had to
  56  * be buggy. So let's have a correct XMM trap
  57  * handler, and forget about printing out
  58  * some status at boot.
  59  *
  60  * We should really only care about bugs here
  61  * anyway. Not features.
  62  */
  63 static void __init check_fpu(void)
  64 {
  65         s32 fdiv_bug;
  66
  67         if (!boot_cpu_data.hard_math) {
  68 #ifndef CONFIG_MATH_EMULATION
  69                 printk(KERN_EMERG "No coprocessor found and no math emulation present.\n");
  70                 printk(KERN_EMERG "Giving up.\n");
  71                 for (;;) ;
  72 #endif
  73                 return;
  74         }
  75
  76         kernel_fpu_begin();
  77
  78         /*
  79          * trap_init() enabled FXSR and company _before_ testing for FP
  80          * problems here.
  81          *
  82          * Test for the divl bug..
  83          */
  84         __asm__("fninit\n\t"
  85                 "fldl %1\n\t"
  86                 "fdivl %2\n\t"
  87                 "fmull %2\n\t"
  88                 "fldl %1\n\t"
  89                 "fsubp %%st,%%st(1)\n\t"
  90                 "fistpl %0\n\t"
  91                 "fwait\n\t"
  92                 "fninit"
  93                 : "=m" (*&fdiv_bug)
  94                 : "m" (*&x), "m" (*&y));
  95
  96         kernel_fpu_end();
  97
  98         boot_cpu_data.fdiv_bug = fdiv_bug;
  99         if (boot_cpu_data.fdiv_bug)
 100                 printk(KERN_WARNING "Hmm, FPU with FDIV bug.\n");
 101 }
 102
 103 static void __init check_hlt(void)
 104 {
 105         if (boot_cpu_data.x86 >= 5 || paravirt_enabled())
 106                 return;
 107
 108         printk(KERN_INFO "Checking 'hlt' instruction... ");
 109         if (!boot_cpu_data.hlt_works_ok) {
 110                 printk("disabled\n");
 111                 return;
 112         }
 113         halt();
 114         halt();
 115         halt();
 116         halt();
 117         printk(KERN_CONT "OK.\n");
 118 }
 119
 120 /*
 121  *      Most 386 processors have a bug where a POPAD can lock the
 122  *      machine even from user space.
 123  */
 124
 125 static void __init check_popad(void)
 126 {
 127 #ifndef CONFIG_X86_POPAD_OK
 128         int res, inp = (int) &res;
 129
 130         printk(KERN_INFO "Checking for popad bug... ");
 131         __asm__ __volatile__(
 132           "movl $12345678,%%eax; movl $0,%%edi; pusha; popa; movl (%%edx,%%edi),%%ecx "
 133           : "=&a" (res)
 134           : "d" (inp)
 135           : "ecx", "edi");
 136         /*
 137          * If this fails, it means that any user program may lock the
 138          * CPU hard. Too bad.
 139          */
 140         if (res != 12345678)
 141                 printk(KERN_CONT "Buggy.\n");
 142         else
 143                 printk(KERN_CONT "OK.\n");
 144 #endif
 145 }
 146
 147 /*
 148  * Check whether we are able to run this kernel safely on SMP.
 149  *
 150  * - In order to run on a i386, we need to be compiled for i386
 151  *   (for due to lack of "invlpg" and working WP on a i386)
 152  * - In order to run on anything without a TSC, we need to be
 153  *   compiled for a i486.
 154  */
 155
 156 static void __init check_config(void)
 157 {
 158 /*
 159  * We'd better not be a i386 if we're configured to use some
 160  * i486+ only features! (WP works in supervisor mode and the
 161  * new "invlpg" and "bswap" instructions)
 162  */
 163 #if defined(CONFIG_X86_WP_WORKS_OK) || defined(CONFIG_X86_INVLPG) || \
 164         defined(CONFIG_X86_BSWAP)
 165         if (boot_cpu_data.x86 == 3)
 166                 panic("Kernel requires i486+ for 'invlpg' and other features");
 167 #endif
 168 }
 169
 170 #endif /* CONFIG_X86_32 */
 171
 172 void __init check_bugs(void)
 173 {
 174 #ifdef CONFIG_X86_32
 175         /*
 176          * Regardless of whether PCID is enumerated, the SDM says
 177          * that it can't be enabled in 32-bit mode.
 178          */
 179         setup_clear_cpu_cap(X86_FEATURE_PCID);
 180 #endif
 181
 182         identify_boot_cpu();
 183
 184         if (!IS_ENABLED(CONFIG_SMP)) {
 185                 pr_info("CPU: ");
 186                 print_cpu_info(&boot_cpu_data);
 187         }
 188
 189         /* Select the proper spectre mitigation before patching alternatives */
 190         spectre_v2_select_mitigation();
 191
 192 #ifdef CONFIG_X86_32
 193         check_config();
 194         check_fpu();
 195         check_hlt();
 196         check_popad();
 197         init_utsname()->machine[1] =
 198                 '0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
 199         alternative_instructions();
 200 #else /* CONFIG_X86_64 */
 201         alternative_instructions();
 202
 203         /*
 204          * Make sure the first 2MB area is not mapped by huge pages
 205          * There are typically fixed size MTRRs in there and overlapping
 206          * MTRRs into large pages causes slow downs.
 207          *
 208          * Right now we don't do that with gbpages because there seems
 209          * very little benefit for that case.
 210          */
 211         if (!direct_gbpages)
 212                 set_memory_4k((unsigned long)__va(0), 1);
 213 #endif
 214 }
 215
 216 /* The kernel command line selection */
 217 enum spectre_v2_mitigation_cmd {
 218         SPECTRE_V2_CMD_NONE,
 219         SPECTRE_V2_CMD_AUTO,
 220         SPECTRE_V2_CMD_FORCE,
 221         SPECTRE_V2_CMD_RETPOLINE,
 222         SPECTRE_V2_CMD_RETPOLINE_GENERIC,
 223         SPECTRE_V2_CMD_RETPOLINE_AMD,
 224 };
 225
 226 static const char *spectre_v2_strings[] = {
 227         [SPECTRE_V2_NONE]                       = "Vulnerable",
 228         [SPECTRE_V2_RETPOLINE_MINIMAL]          = "Vulnerable: Minimal generic ASM retpoline",
 229         [SPECTRE_V2_RETPOLINE_MINIMAL_AMD]      = "Vulnerable: Minimal AMD ASM retpoline",
 230         [SPECTRE_V2_RETPOLINE_GENERIC]          = "Mitigation: Full generic retpoline",
 231         [SPECTRE_V2_RETPOLINE_AMD]              = "Mitigation: Full AMD retpoline",
 232 };
 233
 234 #undef pr_fmt
 235 #define pr_fmt(fmt)     "Spectre V2 mitigation: " fmt
 236
 237 static enum spectre_v2_mitigation spectre_v2_enabled = SPECTRE_V2_NONE;
 238
 239 static void __init spec2_print_if_insecure(const char *reason)
 240 {
 241         if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
 242                 pr_info("%s\n", reason);
 243 }
 244
 245 static void __init spec2_print_if_secure(const char *reason)
 246 {
 247         if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
 248                 pr_info("%s\n", reason);
 249 }
 250
 251 static inline bool retp_compiler(void)
 252 {
 253         return __is_defined(RETPOLINE);
 254 }
 255
 256 static inline bool match_option(const char *arg, int arglen, const char *opt)
 257 {
 258         int len = strlen(opt);
 259
 260         return len == arglen && !strncmp(arg, opt, len);
 261 }
 262
 263 static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
 264 {
 265         char arg[20];
 266         int ret;
 267
 268         ret = cmdline_find_option(boot_command_line, "spectre_v2", arg,
 269                                   sizeof(arg));
 270         if (ret > 0)  {
 271                 if (match_option(arg, ret, "off")) {
 272                         goto disable;
 273                 } else if (match_option(arg, ret, "on")) {
 274                         spec2_print_if_secure("force enabled on command line.");
 275                         return SPECTRE_V2_CMD_FORCE;
 276                 } else if (match_option(arg, ret, "retpoline")) {
 277                         spec2_print_if_insecure("retpoline selected on command line.");
 278                         return SPECTRE_V2_CMD_RETPOLINE;
 279                 } else if (match_option(arg, ret, "retpoline,amd")) {
 280                         if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD) {
 281                                 pr_err("retpoline,amd selected but CPU is not AMD. Switching to AUTO select\n");
 282                                 return SPECTRE_V2_CMD_AUTO;
 283                         }
 284                         spec2_print_if_insecure("AMD retpoline selected on command line.");
 285                         return SPECTRE_V2_CMD_RETPOLINE_AMD;
 286                 } else if (match_option(arg, ret, "retpoline,generic")) {
 287                         spec2_print_if_insecure("generic retpoline selected on command line.");
 288                         return SPECTRE_V2_CMD_RETPOLINE_GENERIC;
 289                 } else if (match_option(arg, ret, "auto")) {
 290                         return SPECTRE_V2_CMD_AUTO;
 291                 }
 292         }
 293
 294         if (!cmdline_find_option_bool(boot_command_line, "nospectre_v2"))
 295                 return SPECTRE_V2_CMD_AUTO;
 296 disable:
 297         spec2_print_if_insecure("disabled on command line.");
 298         return SPECTRE_V2_CMD_NONE;
 299 }
 300
 301 /* Check for Skylake-like CPUs (for RSB handling) */
 302 static bool __init is_skylake_era(void)
 303 {
 304         if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
 305             boot_cpu_data.x86 == 6) {
 306                 switch (boot_cpu_data.x86_model) {
 307                 case INTEL_FAM6_SKYLAKE_MOBILE:
 308                 case INTEL_FAM6_SKYLAKE_DESKTOP:
 309                 case INTEL_FAM6_SKYLAKE_X:
 310                 case INTEL_FAM6_KABYLAKE_MOBILE:
 311                 case INTEL_FAM6_KABYLAKE_DESKTOP:
 312                         return true;
 313                 }
 314         }
 315         return false;
 316 }
 317
 318 static void __init spectre_v2_select_mitigation(void)
 319 {
 320         enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();
 321         enum spectre_v2_mitigation mode = SPECTRE_V2_NONE;
 322
 323         /*
 324          * If the CPU is not affected and the command line mode is NONE or AUTO
 325          * then nothing to do.
 326          */
 327         if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2) &&
 328             (cmd == SPECTRE_V2_CMD_NONE || cmd == SPECTRE_V2_CMD_AUTO))
 329                 return;
 330
 331         switch (cmd) {
 332         case SPECTRE_V2_CMD_NONE:
 333                 return;
 334
 335         case SPECTRE_V2_CMD_FORCE:
 336                 /* FALLTRHU */
 337         case SPECTRE_V2_CMD_AUTO:
 338                 goto retpoline_auto;
 339
 340         case SPECTRE_V2_CMD_RETPOLINE_AMD:
 341                 if (IS_ENABLED(CONFIG_RETPOLINE))
 342                         goto retpoline_amd;
 343                 break;
 344         case SPECTRE_V2_CMD_RETPOLINE_GENERIC:
 345                 if (IS_ENABLED(CONFIG_RETPOLINE))
 346                         goto retpoline_generic;
 347                 break;
 348         case SPECTRE_V2_CMD_RETPOLINE:
 349                 if (IS_ENABLED(CONFIG_RETPOLINE))
 350                         goto retpoline_auto;
 351                 break;
 352         }
 353         pr_err("kernel not compiled with retpoline; no mitigation available!");
 354         return;
 355
 356 retpoline_auto:
 357         if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) {
 358         retpoline_amd:
 359                 if (!boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) {
 360                         pr_err("LFENCE not serializing. Switching to generic retpoline\n");
 361                         goto retpoline_generic;
 362                 }
 363                 mode = retp_compiler() ? SPECTRE_V2_RETPOLINE_AMD :
 364                                          SPECTRE_V2_RETPOLINE_MINIMAL_AMD;
 365                 setup_force_cpu_cap(X86_FEATURE_RETPOLINE_AMD);
 366                 setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
 367         } else {
 368         retpoline_generic:
 369                 mode = retp_compiler() ? SPECTRE_V2_RETPOLINE_GENERIC :
 370                                          SPECTRE_V2_RETPOLINE_MINIMAL;
 371                 setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
 372         }
 373
 374         spectre_v2_enabled = mode;
 375         pr_info("%s\n", spectre_v2_strings[mode]);
 376
 377         /*
 378          * If neither SMEP or KPTI are available, there is a risk of
 379          * hitting userspace addresses in the RSB after a context switch
 380          * from a shallow call stack to a deeper one. To prevent this fill
 381          * the entire RSB, even when using IBRS.
 382          *
 383          * Skylake era CPUs have a separate issue with *underflow* of the
 384          * RSB, when they will predict 'ret' targets from the generic BTB.
 385          * The proper mitigation for this is IBRS. If IBRS is not supported
 386          * or deactivated in favour of retpolines the RSB fill on context
 387          * switch is required.
 388          */
 389         if ((!boot_cpu_has(X86_FEATURE_KAISER) &&
 390              !boot_cpu_has(X86_FEATURE_SMEP)) || is_skylake_era()) {
 391                 setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW);
 392                 pr_info("Filling RSB on context switch\n");
 393         }
 394 }
 395
 396 #undef pr_fmt
 397
 398 #ifdef CONFIG_SYSFS
 399 ssize_t cpu_show_meltdown(struct sysdev_class *dev,
 400                           struct sysdev_class_attribute *attr, char *buf)
 401 {
 402         if (!boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN))
 403                 return sprintf(buf, "Not affected\n");
 404         if (boot_cpu_has(X86_FEATURE_KAISER))
 405                 return sprintf(buf, "Mitigation: PTI\n");
 406         return sprintf(buf, "Vulnerable\n");
 407 }
 408
 409 ssize_t cpu_show_spectre_v1(struct sysdev_class *dev,
 410                             struct sysdev_class_attribute *attr, char *buf)
 411 {
 412         if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V1))
 413                 return sprintf(buf, "Not affected\n");
 414         return sprintf(buf, "Vulnerable\n");
 415 }
 416
 417 ssize_t cpu_show_spectre_v2(struct sysdev_class *dev,
 418                             struct sysdev_class_attribute *attr, char *buf)
 419 {
 420         if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
 421                 return sprintf(buf, "Not affected\n");
 422
 423         return sprintf(buf, "%s\n", spectre_v2_strings[spectre_v2_enabled]);
 424 }
 425 #endif