arch/x86/kernel/alternative.c

   1 #define pr_fmt(fmt) "SMP alternatives: " fmt
   2
   3 #include <linux/module.h>
   4 #include <linux/sched.h>
   5 #include <linux/mutex.h>
   6 #include <linux/list.h>
   7 #include <linux/stringify.h>
   8 #include <linux/mm.h>
   9 #include <linux/vmalloc.h>
  10 #include <linux/memory.h>
  11 #include <linux/stop_machine.h>
  12 #include <linux/slab.h>
  13 #include <linux/kdebug.h>
  14 #include <asm/text-patching.h>
  15 #include <asm/alternative.h>
  16 #include <asm/sections.h>
  17 #include <asm/pgtable.h>
  18 #include <asm/mce.h>
  19 #include <asm/nmi.h>
  20 #include <asm/cacheflush.h>
  21 #include <asm/tlbflush.h>
  22 #include <asm/io.h>
  23 #include <asm/fixmap.h>
  24
  25 int __read_mostly alternatives_patched;
  26
  27 EXPORT_SYMBOL_GPL(alternatives_patched);
  28
  29 #define MAX_PATCH_LEN (255-1)
  30
  31 static int __initdata_or_module debug_alternative;
  32
  33 static int __init debug_alt(char *str)
  34 {
  35         debug_alternative = 1;
  36         return 1;
  37 }
  38 __setup("debug-alternative", debug_alt);
  39
  40 static int noreplace_smp;
  41
  42 static int __init setup_noreplace_smp(char *str)
  43 {
  44         noreplace_smp = 1;
  45         return 1;
  46 }
  47 __setup("noreplace-smp", setup_noreplace_smp);
  48
  49 #define DPRINTK(fmt, args...)                                           \
  50 do {                                                                    \
  51         if (debug_alternative)                                          \
  52                 printk(KERN_DEBUG "%s: " fmt "\n", __func__, ##args);   \
  53 } while (0)
  54
  55 #define DUMP_BYTES(buf, len, fmt, args...)                              \
  56 do {                                                                    \
  57         if (unlikely(debug_alternative)) {                              \
  58                 int j;                                                  \
  59                                                                         \
  60                 if (!(len))                                             \
  61                         break;                                          \
  62                                                                         \
  63                 printk(KERN_DEBUG fmt, ##args);                         \
  64                 for (j = 0; j < (len) - 1; j++)                         \
  65                         printk(KERN_CONT "%02hhx ", buf[j]);            \
  66                 printk(KERN_CONT "%02hhx\n", buf[j]);                   \
  67         }                                                               \
  68 } while (0)
  69
  70 /*
  71  * Each GENERIC_NOPX is of X bytes, and defined as an array of bytes
  72  * that correspond to that nop. Getting from one nop to the next, we
  73  * add to the array the offset that is equal to the sum of all sizes of
  74  * nops preceding the one we are after.
  75  *
  76  * Note: The GENERIC_NOP5_ATOMIC is at the end, as it breaks the
  77  * nice symmetry of sizes of the previous nops.
  78  */
  79 #if defined(GENERIC_NOP1) && !defined(CONFIG_X86_64)
  80 static const unsigned char intelnops[] =
  81 {
  82         GENERIC_NOP1,
  83         GENERIC_NOP2,
  84         GENERIC_NOP3,
  85         GENERIC_NOP4,
  86         GENERIC_NOP5,
  87         GENERIC_NOP6,
  88         GENERIC_NOP7,
  89         GENERIC_NOP8,
  90         GENERIC_NOP5_ATOMIC
  91 };
  92 static const unsigned char * const intel_nops[ASM_NOP_MAX+2] =
  93 {
  94         NULL,
  95         intelnops,
  96         intelnops + 1,
  97         intelnops + 1 + 2,
  98         intelnops + 1 + 2 + 3,
  99         intelnops + 1 + 2 + 3 + 4,
 100         intelnops + 1 + 2 + 3 + 4 + 5,
 101         intelnops + 1 + 2 + 3 + 4 + 5 + 6,
 102         intelnops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
 103         intelnops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8,
 104 };
 105 #endif
 106
 107 #ifdef K8_NOP1
 108 static const unsigned char k8nops[] =
 109 {
 110         K8_NOP1,
 111         K8_NOP2,
 112         K8_NOP3,
 113         K8_NOP4,
 114         K8_NOP5,
 115         K8_NOP6,
 116         K8_NOP7,
 117         K8_NOP8,
 118         K8_NOP5_ATOMIC
 119 };
 120 static const unsigned char * const k8_nops[ASM_NOP_MAX+2] =
 121 {
 122         NULL,
 123         k8nops,
 124         k8nops + 1,
 125         k8nops + 1 + 2,
 126         k8nops + 1 + 2 + 3,
 127         k8nops + 1 + 2 + 3 + 4,
 128         k8nops + 1 + 2 + 3 + 4 + 5,
 129         k8nops + 1 + 2 + 3 + 4 + 5 + 6,
 130         k8nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
 131         k8nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8,
 132 };
 133 #endif
 134
 135 #if defined(K7_NOP1) && !defined(CONFIG_X86_64)
 136 static const unsigned char k7nops[] =
 137 {
 138         K7_NOP1,
 139         K7_NOP2,
 140         K7_NOP3,
 141         K7_NOP4,
 142         K7_NOP5,
 143         K7_NOP6,
 144         K7_NOP7,
 145         K7_NOP8,
 146         K7_NOP5_ATOMIC
 147 };
 148 static const unsigned char * const k7_nops[ASM_NOP_MAX+2] =
 149 {
 150         NULL,
 151         k7nops,
 152         k7nops + 1,
 153         k7nops + 1 + 2,
 154         k7nops + 1 + 2 + 3,
 155         k7nops + 1 + 2 + 3 + 4,
 156         k7nops + 1 + 2 + 3 + 4 + 5,
 157         k7nops + 1 + 2 + 3 + 4 + 5 + 6,
 158         k7nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
 159         k7nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8,
 160 };
 161 #endif
 162
 163 #ifdef P6_NOP1
 164 static const unsigned char p6nops[] =
 165 {
 166         P6_NOP1,
 167         P6_NOP2,
 168         P6_NOP3,
 169         P6_NOP4,
 170         P6_NOP5,
 171         P6_NOP6,
 172         P6_NOP7,
 173         P6_NOP8,
 174         P6_NOP5_ATOMIC
 175 };
 176 static const unsigned char * const p6_nops[ASM_NOP_MAX+2] =
 177 {
 178         NULL,
 179         p6nops,
 180         p6nops + 1,
 181         p6nops + 1 + 2,
 182         p6nops + 1 + 2 + 3,
 183         p6nops + 1 + 2 + 3 + 4,
 184         p6nops + 1 + 2 + 3 + 4 + 5,
 185         p6nops + 1 + 2 + 3 + 4 + 5 + 6,
 186         p6nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
 187         p6nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8,
 188 };
 189 #endif
 190
 191 /* Initialize these to a safe default */
 192 #ifdef CONFIG_X86_64
 193 const unsigned char * const *ideal_nops = p6_nops;
 194 #else
 195 const unsigned char * const *ideal_nops = intel_nops;
 196 #endif
 197
 198 void __init arch_init_ideal_nops(void)
 199 {
 200         switch (boot_cpu_data.x86_vendor) {
 201         case X86_VENDOR_INTEL:
 202                 /*
 203                  * Due to a decoder implementation quirk, some
 204                  * specific Intel CPUs actually perform better with
 205                  * the "k8_nops" than with the SDM-recommended NOPs.
 206                  */
 207                 if (boot_cpu_data.x86 == 6 &&
 208                     boot_cpu_data.x86_model >= 0x0f &&
 209                     boot_cpu_data.x86_model != 0x1c &&
 210                     boot_cpu_data.x86_model != 0x26 &&
 211                     boot_cpu_data.x86_model != 0x27 &&
 212                     boot_cpu_data.x86_model < 0x30) {
 213                         ideal_nops = k8_nops;
 214                 } else if (boot_cpu_has(X86_FEATURE_NOPL)) {
 215                            ideal_nops = p6_nops;
 216                 } else {
 217 #ifdef CONFIG_X86_64
 218                         ideal_nops = k8_nops;
 219 #else
 220                         ideal_nops = intel_nops;
 221 #endif
 222                 }
 223                 break;
 224
 225         case X86_VENDOR_HYGON:
 226                 ideal_nops = p6_nops;
 227                 return;
 228
 229         case X86_VENDOR_AMD:
 230                 if (boot_cpu_data.x86 > 0xf) {
 231                         ideal_nops = p6_nops;
 232                         return;
 233                 }
 234
 235                 /* fall through */
 236
 237         default:
 238 #ifdef CONFIG_X86_64
 239                 ideal_nops = k8_nops;
 240 #else
 241                 if (boot_cpu_has(X86_FEATURE_K8))
 242                         ideal_nops = k8_nops;
 243                 else if (boot_cpu_has(X86_FEATURE_K7))
 244                         ideal_nops = k7_nops;
 245                 else
 246                         ideal_nops = intel_nops;
 247 #endif
 248         }
 249 }
 250
 251 /* Use this to add nops to a buffer, then text_poke the whole buffer. */
 252 static void __init_or_module add_nops(void *insns, unsigned int len)
 253 {
 254         while (len > 0) {
 255                 unsigned int noplen = len;
 256                 if (noplen > ASM_NOP_MAX)
 257                         noplen = ASM_NOP_MAX;
 258                 memcpy(insns, ideal_nops[noplen], noplen);
 259                 insns += noplen;
 260                 len -= noplen;
 261         }
 262 }
 263
 264 extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
 265 extern s32 __smp_locks[], __smp_locks_end[];
 266 void *text_poke_early(void *addr, const void *opcode, size_t len);
 267
 268 /*
 269  * Are we looking at a near JMP with a 1 or 4-byte displacement.
 270  */
 271 static inline bool is_jmp(const u8 opcode)
 272 {
 273         return opcode == 0xeb || opcode == 0xe9;
 274 }
 275
 276 static void __init_or_module
 277 recompute_jump(struct alt_instr *a, u8 *orig_insn, u8 *repl_insn, u8 *insnbuf)
 278 {
 279         u8 *next_rip, *tgt_rip;
 280         s32 n_dspl, o_dspl;
 281         int repl_len;
 282
 283         if (a->replacementlen != 5)
 284                 return;
 285
 286         o_dspl = *(s32 *)(insnbuf + 1);
 287
 288         /* next_rip of the replacement JMP */
 289         next_rip = repl_insn + a->replacementlen;
 290         /* target rip of the replacement JMP */
 291         tgt_rip  = next_rip + o_dspl;
 292         n_dspl = tgt_rip - orig_insn;
 293
 294         DPRINTK("target RIP: %px, new_displ: 0x%x", tgt_rip, n_dspl);
 295
 296         if (tgt_rip - orig_insn >= 0) {
 297                 if (n_dspl - 2 <= 127)
 298                         goto two_byte_jmp;
 299                 else
 300                         goto five_byte_jmp;
 301         /* negative offset */
 302         } else {
 303                 if (((n_dspl - 2) & 0xff) == (n_dspl - 2))
 304                         goto two_byte_jmp;
 305                 else
 306                         goto five_byte_jmp;
 307         }
 308
 309 two_byte_jmp:
 310         n_dspl -= 2;
 311
 312         insnbuf[0] = 0xeb;
 313         insnbuf[1] = (s8)n_dspl;
 314         add_nops(insnbuf + 2, 3);
 315
 316         repl_len = 2;
 317         goto done;
 318
 319 five_byte_jmp:
 320         n_dspl -= 5;
 321
 322         insnbuf[0] = 0xe9;
 323         *(s32 *)&insnbuf[1] = n_dspl;
 324
 325         repl_len = 5;
 326
 327 done:
 328
 329         DPRINTK("final displ: 0x%08x, JMP 0x%lx",
 330                 n_dspl, (unsigned long)orig_insn + n_dspl + repl_len);
 331 }
 332
 333 /*
 334  * "noinline" to cause control flow change and thus invalidate I$ and
 335  * cause refetch after modification.
 336  */
 337 static void __init_or_module noinline optimize_nops(struct alt_instr *a, u8 *instr)
 338 {
 339         unsigned long flags;
 340         int i;
 341
 342         for (i = 0; i < a->padlen; i++) {
 343                 if (instr[i] != 0x90)
 344                         return;
 345         }
 346
 347         local_irq_save(flags);
 348         add_nops(instr + (a->instrlen - a->padlen), a->padlen);
 349         local_irq_restore(flags);
 350
 351         DUMP_BYTES(instr, a->instrlen, "%px: [%d:%d) optimized NOPs: ",
 352                    instr, a->instrlen - a->padlen, a->padlen);
 353 }
 354
 355 /*
 356  * Replace instructions with better alternatives for this CPU type. This runs
 357  * before SMP is initialized to avoid SMP problems with self modifying code.
 358  * This implies that asymmetric systems where APs have less capabilities than
 359  * the boot processor are not handled. Tough. Make sure you disable such
 360  * features by hand.
 361  *
 362  * Marked "noinline" to cause control flow change and thus insn cache
 363  * to refetch changed I$ lines.
 364  */
 365 void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 366                                                   struct alt_instr *end)
 367 {
 368         struct alt_instr *a;
 369         u8 *instr, *replacement;
 370         u8 insnbuf[MAX_PATCH_LEN];
 371
 372         DPRINTK("alt table %px, -> %px", start, end);
 373         /*
 374          * The scan order should be from start to end. A later scanned
 375          * alternative code can overwrite previously scanned alternative code.
 376          * Some kernel functions (e.g. memcpy, memset, etc) use this order to
 377          * patch code.
 378          *
 379          * So be careful if you want to change the scan order to any other
 380          * order.
 381          */
 382         for (a = start; a < end; a++) {
 383                 int insnbuf_sz = 0;
 384
 385                 instr = (u8 *)&a->instr_offset + a->instr_offset;
 386                 replacement = (u8 *)&a->repl_offset + a->repl_offset;
 387                 BUG_ON(a->instrlen > sizeof(insnbuf));
 388                 BUG_ON(a->cpuid >= (NCAPINTS + NBUGINTS) * 32);
 389                 if (!boot_cpu_has(a->cpuid)) {
 390                         if (a->padlen > 1)
 391                                 optimize_nops(a, instr);
 392
 393                         continue;
 394                 }
 395
 396                 DPRINTK("feat: %d*32+%d, old: (%px len: %d), repl: (%px, len: %d), pad: %d",
 397                         a->cpuid >> 5,
 398                         a->cpuid & 0x1f,
 399                         instr, a->instrlen,
 400                         replacement, a->replacementlen, a->padlen);
 401
 402                 DUMP_BYTES(instr, a->instrlen, "%px: old_insn: ", instr);
 403                 DUMP_BYTES(replacement, a->replacementlen, "%px: rpl_insn: ", replacement);
 404
 405                 memcpy(insnbuf, replacement, a->replacementlen);
 406                 insnbuf_sz = a->replacementlen;
 407
 408                 /*
 409                  * 0xe8 is a relative jump; fix the offset.
 410                  *
 411                  * Instruction length is checked before the opcode to avoid
 412                  * accessing uninitialized bytes for zero-length replacements.
 413                  */
 414                 if (a->replacementlen == 5 && *insnbuf == 0xe8) {
 415                         *(s32 *)(insnbuf + 1) += replacement - instr;
 416                         DPRINTK("Fix CALL offset: 0x%x, CALL 0x%lx",
 417                                 *(s32 *)(insnbuf + 1),
 418                                 (unsigned long)instr + *(s32 *)(insnbuf + 1) + 5);
 419                 }
 420
 421                 if (a->replacementlen && is_jmp(replacement[0]))
 422                         recompute_jump(a, instr, replacement, insnbuf);
 423
 424                 if (a->instrlen > a->replacementlen) {
 425                         add_nops(insnbuf + a->replacementlen,
 426                                  a->instrlen - a->replacementlen);
 427                         insnbuf_sz += a->instrlen - a->replacementlen;
 428                 }
 429                 DUMP_BYTES(insnbuf, insnbuf_sz, "%px: final_insn: ", instr);
 430
 431                 text_poke_early(instr, insnbuf, insnbuf_sz);
 432         }
 433 }
 434
 435 #ifdef CONFIG_SMP
 436 static void alternatives_smp_lock(const s32 *start, const s32 *end,
 437                                   u8 *text, u8 *text_end)
 438 {
 439         const s32 *poff;
 440
 441         for (poff = start; poff < end; poff++) {
 442                 u8 *ptr = (u8 *)poff + *poff;
 443
 444                 if (!*poff || ptr < text || ptr >= text_end)
 445                         continue;
 446                 /* turn DS segment override prefix into lock prefix */
 447                 if (*ptr == 0x3e)
 448                         text_poke(ptr, ((unsigned char []){0xf0}), 1);
 449         }
 450 }
 451
 452 static void alternatives_smp_unlock(const s32 *start, const s32 *end,
 453                                     u8 *text, u8 *text_end)
 454 {
 455         const s32 *poff;
 456
 457         for (poff = start; poff < end; poff++) {
 458                 u8 *ptr = (u8 *)poff + *poff;
 459
 460                 if (!*poff || ptr < text || ptr >= text_end)
 461                         continue;
 462                 /* turn lock prefix into DS segment override prefix */
 463                 if (*ptr == 0xf0)
 464                         text_poke(ptr, ((unsigned char []){0x3E}), 1);
 465         }
 466 }
 467
 468 struct smp_alt_module {
 469         /* what is this ??? */
 470         struct module   *mod;
 471         char            *name;
 472
 473         /* ptrs to lock prefixes */
 474         const s32       *locks;
 475         const s32       *locks_end;
 476
 477         /* .text segment, needed to avoid patching init code ;) */
 478         u8              *text;
 479         u8              *text_end;
 480
 481         struct list_head next;
 482 };
 483 static LIST_HEAD(smp_alt_modules);
 484 static bool uniproc_patched = false;    /* protected by text_mutex */
 485
 486 void __init_or_module alternatives_smp_module_add(struct module *mod,
 487                                                   char *name,
 488                                                   void *locks, void *locks_end,
 489                                                   void *text,  void *text_end)
 490 {
 491         struct smp_alt_module *smp;
 492
 493         mutex_lock(&text_mutex);
 494         if (!uniproc_patched)
 495                 goto unlock;
 496
 497         if (num_possible_cpus() == 1)
 498                 /* Don't bother remembering, we'll never have to undo it. */
 499                 goto smp_unlock;
 500
 501         smp = kzalloc(sizeof(*smp), GFP_KERNEL);
 502         if (NULL == smp)
 503                 /* we'll run the (safe but slow) SMP code then ... */
 504                 goto unlock;
 505
 506         smp->mod        = mod;
 507         smp->name       = name;
 508         smp->locks      = locks;
 509         smp->locks_end  = locks_end;
 510         smp->text       = text;
 511         smp->text_end   = text_end;
 512         DPRINTK("locks %p -> %p, text %p -> %p, name %s\n",
 513                 smp->locks, smp->locks_end,
 514                 smp->text, smp->text_end, smp->name);
 515
 516         list_add_tail(&smp->next, &smp_alt_modules);
 517 smp_unlock:
 518         alternatives_smp_unlock(locks, locks_end, text, text_end);
 519 unlock:
 520         mutex_unlock(&text_mutex);
 521 }
 522
 523 void __init_or_module alternatives_smp_module_del(struct module *mod)
 524 {
 525         struct smp_alt_module *item;
 526
 527         mutex_lock(&text_mutex);
 528         list_for_each_entry(item, &smp_alt_modules, next) {
 529                 if (mod != item->mod)
 530                         continue;
 531                 list_del(&item->next);
 532                 kfree(item);
 533                 break;
 534         }
 535         mutex_unlock(&text_mutex);
 536 }
 537
 538 void alternatives_enable_smp(void)
 539 {
 540         struct smp_alt_module *mod;
 541
 542         /* Why bother if there are no other CPUs? */
 543         BUG_ON(num_possible_cpus() == 1);
 544
 545         mutex_lock(&text_mutex);
 546
 547         if (uniproc_patched) {
 548                 pr_info("switching to SMP code\n");
 549                 BUG_ON(num_online_cpus() != 1);
 550                 clear_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
 551                 clear_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
 552                 list_for_each_entry(mod, &smp_alt_modules, next)
 553                         alternatives_smp_lock(mod->locks, mod->locks_end,
 554                                               mod->text, mod->text_end);
 555                 uniproc_patched = false;
 556         }
 557         mutex_unlock(&text_mutex);
 558 }
 559
 560 /*
 561  * Return 1 if the address range is reserved for SMP-alternatives.
 562  * Must hold text_mutex.
 563  */
 564 int alternatives_text_reserved(void *start, void *end)
 565 {
 566         struct smp_alt_module *mod;
 567         const s32 *poff;
 568         u8 *text_start = start;
 569         u8 *text_end = end;
 570
 571         lockdep_assert_held(&text_mutex);
 572
 573         list_for_each_entry(mod, &smp_alt_modules, next) {
 574                 if (mod->text > text_end || mod->text_end < text_start)
 575                         continue;
 576                 for (poff = mod->locks; poff < mod->locks_end; poff++) {
 577                         const u8 *ptr = (const u8 *)poff + *poff;
 578
 579                         if (text_start <= ptr && text_end > ptr)
 580                                 return 1;
 581                 }
 582         }
 583
 584         return 0;
 585 }
 586 #endif /* CONFIG_SMP */
 587
 588 #ifdef CONFIG_PARAVIRT
 589 void __init_or_module apply_paravirt(struct paravirt_patch_site *start,
 590                                      struct paravirt_patch_site *end)
 591 {
 592         struct paravirt_patch_site *p;
 593         char insnbuf[MAX_PATCH_LEN];
 594
 595         for (p = start; p < end; p++) {
 596                 unsigned int used;
 597
 598                 BUG_ON(p->len > MAX_PATCH_LEN);
 599                 /* prep the buffer with the original instructions */
 600                 memcpy(insnbuf, p->instr, p->len);
 601                 used = pv_ops.init.patch(p->instrtype, insnbuf,
 602                                          (unsigned long)p->instr, p->len);
 603
 604                 BUG_ON(used > p->len);
 605
 606                 /* Pad the rest with nops */
 607                 add_nops(insnbuf + used, p->len - used);
 608                 text_poke_early(p->instr, insnbuf, p->len);
 609         }
 610 }
 611 extern struct paravirt_patch_site __start_parainstructions[],
 612         __stop_parainstructions[];
 613 #endif  /* CONFIG_PARAVIRT */
 614
 615 void __init alternative_instructions(void)
 616 {
 617         /* The patching is not fully atomic, so try to avoid local interruptions
 618            that might execute the to be patched code.
 619            Other CPUs are not running. */
 620         stop_nmi();
 621
 622         /*
 623          * Don't stop machine check exceptions while patching.
 624          * MCEs only happen when something got corrupted and in this
 625          * case we must do something about the corruption.
 626          * Ignoring it is worse than a unlikely patching race.
 627          * Also machine checks tend to be broadcast and if one CPU
 628          * goes into machine check the others follow quickly, so we don't
 629          * expect a machine check to cause undue problems during to code
 630          * patching.
 631          */
 632
 633         apply_alternatives(__alt_instructions, __alt_instructions_end);
 634
 635 #ifdef CONFIG_SMP
 636         /* Patch to UP if other cpus not imminent. */
 637         if (!noreplace_smp && (num_present_cpus() == 1 || setup_max_cpus <= 1)) {
 638                 uniproc_patched = true;
 639                 alternatives_smp_module_add(NULL, "core kernel",
 640                                             __smp_locks, __smp_locks_end,
 641                                             _text, _etext);
 642         }
 643
 644         if (!uniproc_patched || num_possible_cpus() == 1)
 645                 free_init_pages("SMP alternatives",
 646                                 (unsigned long)__smp_locks,
 647                                 (unsigned long)__smp_locks_end);
 648 #endif
 649
 650         apply_paravirt(__parainstructions, __parainstructions_end);
 651
 652         restart_nmi();
 653         alternatives_patched = 1;
 654 }
 655
 656 /**
 657  * text_poke_early - Update instructions on a live kernel at boot time
 658  * @addr: address to modify
 659  * @opcode: source of the copy
 660  * @len: length to copy
 661  *
 662  * When you use this code to patch more than one byte of an instruction
 663  * you need to make sure that other CPUs cannot execute this code in parallel.
 664  * Also no thread must be currently preempted in the middle of these
 665  * instructions. And on the local CPU you need to be protected again NMI or MCE
 666  * handlers seeing an inconsistent instruction while you patch.
 667  */
 668 void *__init_or_module text_poke_early(void *addr, const void *opcode,
 669                                               size_t len)
 670 {
 671         unsigned long flags;
 672         local_irq_save(flags);
 673         memcpy(addr, opcode, len);
 674         local_irq_restore(flags);
 675         sync_core();
 676         /* Could also do a CLFLUSH here to speed up CPU recovery; but
 677            that causes hangs on some VIA CPUs. */
 678         return addr;
 679 }
 680
 681 /**
 682  * text_poke - Update instructions on a live kernel
 683  * @addr: address to modify
 684  * @opcode: source of the copy
 685  * @len: length to copy
 686  *
 687  * Only atomic text poke/set should be allowed when not doing early patching.
 688  * It means the size must be writable atomically and the address must be aligned
 689  * in a way that permits an atomic write. It also makes sure we fit on a single
 690  * page.
 691  */
 692 void *text_poke(void *addr, const void *opcode, size_t len)
 693 {
 694         unsigned long flags;
 695         char *vaddr;
 696         struct page *pages[2];
 697         int i;
 698
 699         /*
 700          * While boot memory allocator is runnig we cannot use struct
 701          * pages as they are not yet initialized.
 702          */
 703         BUG_ON(!after_bootmem);
 704
 705         lockdep_assert_held(&text_mutex);
 706
 707         if (!core_kernel_text((unsigned long)addr)) {
 708                 pages[0] = vmalloc_to_page(addr);
 709                 pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
 710         } else {
 711                 pages[0] = virt_to_page(addr);
 712                 WARN_ON(!PageReserved(pages[0]));
 713                 pages[1] = virt_to_page(addr + PAGE_SIZE);
 714         }
 715         BUG_ON(!pages[0]);
 716         local_irq_save(flags);
 717         set_fixmap(FIX_TEXT_POKE0, page_to_phys(pages[0]));
 718         if (pages[1])
 719                 set_fixmap(FIX_TEXT_POKE1, page_to_phys(pages[1]));
 720         vaddr = (char *)fix_to_virt(FIX_TEXT_POKE0);
 721         memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
 722         clear_fixmap(FIX_TEXT_POKE0);
 723         if (pages[1])
 724                 clear_fixmap(FIX_TEXT_POKE1);
 725         local_flush_tlb();
 726         sync_core();
 727         /* Could also do a CLFLUSH here to speed up CPU recovery; but
 728            that causes hangs on some VIA CPUs. */
 729         for (i = 0; i < len; i++)
 730                 BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]);
 731         local_irq_restore(flags);
 732         return addr;
 733 }
 734
 735 static void do_sync_core(void *info)
 736 {
 737         sync_core();
 738 }
 739
 740 static bool bp_patching_in_progress;
 741 static void *bp_int3_handler, *bp_int3_addr;
 742
 743 int poke_int3_handler(struct pt_regs *regs)
 744 {
 745         /*
 746          * Having observed our INT3 instruction, we now must observe
 747          * bp_patching_in_progress.
 748          *
 749          *      in_progress = TRUE              INT3
 750          *      WMB                             RMB
 751          *      write INT3                      if (in_progress)
 752          *
 753          * Idem for bp_int3_handler.
 754          */
 755         smp_rmb();
 756
 757         if (likely(!bp_patching_in_progress))
 758                 return 0;
 759
 760         if (user_mode(regs) || regs->ip != (unsigned long)bp_int3_addr)
 761                 return 0;
 762
 763         /* set up the specified breakpoint handler */
 764         regs->ip = (unsigned long) bp_int3_handler;
 765
 766         return 1;
 767
 768 }
 769
 770 /**
 771  * text_poke_bp() -- update instructions on live kernel on SMP
 772  * @addr:       address to patch
 773  * @opcode:     opcode of new instruction
 774  * @len:        length to copy
 775  * @handler:    address to jump to when the temporary breakpoint is hit
 776  *
 777  * Modify multi-byte instruction by using int3 breakpoint on SMP.
 778  * We completely avoid stop_machine() here, and achieve the
 779  * synchronization using int3 breakpoint.
 780  *
 781  * The way it is done:
 782  *      - add a int3 trap to the address that will be patched
 783  *      - sync cores
 784  *      - update all but the first byte of the patched range
 785  *      - sync cores
 786  *      - replace the first byte (int3) by the first byte of
 787  *        replacing opcode
 788  *      - sync cores
 789  */
 790 void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
 791 {
 792         unsigned char int3 = 0xcc;
 793
 794         bp_int3_handler = handler;
 795         bp_int3_addr = (u8 *)addr + sizeof(int3);
 796         bp_patching_in_progress = true;
 797
 798         lockdep_assert_held(&text_mutex);
 799
 800         /*
 801          * Corresponding read barrier in int3 notifier for making sure the
 802          * in_progress and handler are correctly ordered wrt. patching.
 803          */
 804         smp_wmb();
 805
 806         text_poke(addr, &int3, sizeof(int3));
 807
 808         on_each_cpu(do_sync_core, NULL, 1);
 809
 810         if (len - sizeof(int3) > 0) {
 811                 /* patch all but the first byte */
 812                 text_poke((char *)addr + sizeof(int3),
 813                           (const char *) opcode + sizeof(int3),
 814                           len - sizeof(int3));
 815                 /*
 816                  * According to Intel, this core syncing is very likely
 817                  * not necessary and we'd be safe even without it. But
 818                  * better safe than sorry (plus there's not only Intel).
 819                  */
 820                 on_each_cpu(do_sync_core, NULL, 1);
 821         }
 822
 823         /* patch the first byte */
 824         text_poke(addr, opcode, sizeof(int3));
 825
 826         on_each_cpu(do_sync_core, NULL, 1);
 827         /*
 828          * sync_core() implies an smp_mb() and orders this store against
 829          * the writing of the new instruction.
 830          */
 831         bp_patching_in_progress = false;
 832
 833         return addr;
 834 }
 835