1 // SPDX-License-Identifier: GPL-2.0-only 2 #define pr_fmt(fmt) "SMP alternatives: " fmt 3 4 #include <linux/module.h> 5 #include <linux/sched.h> 6 #include <linux/mutex.h> 7 #include <linux/list.h> 8 #include <linux/stringify.h> 9 #include <linux/mm.h> 10 #include <linux/vmalloc.h> 11 #include <linux/memory.h> 12 #include <linux/stop_machine.h> 13 #include <linux/slab.h> 14 #include <linux/kdebug.h> 15 #include <linux/kprobes.h> 16 #include <linux/mmu_context.h> 17 #include <linux/bsearch.h> 18 #include <asm/text-patching.h> 19 #include <asm/alternative.h> 20 #include <asm/sections.h> 21 #include <asm/pgtable.h> 22 #include <asm/mce.h> 23 #include <asm/nmi.h> 24 #include <asm/cacheflush.h> 25 #include <asm/tlbflush.h> 26 #include <asm/insn.h> 27 #include <asm/io.h> 28 #include <asm/fixmap.h> 29 30 int __read_mostly alternatives_patched; 31 32 EXPORT_SYMBOL_GPL(alternatives_patched); 33 34 #define MAX_PATCH_LEN (255-1) 35 36 static int __initdata_or_module debug_alternative; 37 38 static int __init debug_alt(char *str) 39 { 40 debug_alternative = 1; 41 return 1; 42 } 43 __setup("debug-alternative", debug_alt); 44 45 static int noreplace_smp; 46 47 static int __init setup_noreplace_smp(char *str) 48 { 49 noreplace_smp = 1; 50 return 1; 51 } 52 __setup("noreplace-smp", setup_noreplace_smp); 53 54 #define DPRINTK(fmt, args...) \ 55 do { \ 56 if (debug_alternative) \ 57 printk(KERN_DEBUG "%s: " fmt "\n", __func__, ##args); \ 58 } while (0) 59 60 #define DUMP_BYTES(buf, len, fmt, args...) \ 61 do { \ 62 if (unlikely(debug_alternative)) { \ 63 int j; \ 64 \ 65 if (!(len)) \ 66 break; \ 67 \ 68 printk(KERN_DEBUG fmt, ##args); \ 69 for (j = 0; j < (len) - 1; j++) \ 70 printk(KERN_CONT "%02hhx ", buf[j]); \ 71 printk(KERN_CONT "%02hhx\n", buf[j]); \ 72 } \ 73 } while (0) 74 75 /* 76 * Each GENERIC_NOPX is of X bytes, and defined as an array of bytes 77 * that correspond to that nop. Getting from one nop to the next, we 78 * add to the array the offset that is equal to the sum of all sizes of 79 * nops preceding the one we are after. 80 * 81 * Note: The GENERIC_NOP5_ATOMIC is at the end, as it breaks the 82 * nice symmetry of sizes of the previous nops. 83 */ 84 #if defined(GENERIC_NOP1) && !defined(CONFIG_X86_64) 85 static const unsigned char intelnops[] = 86 { 87 GENERIC_NOP1, 88 GENERIC_NOP2, 89 GENERIC_NOP3, 90 GENERIC_NOP4, 91 GENERIC_NOP5, 92 GENERIC_NOP6, 93 GENERIC_NOP7, 94 GENERIC_NOP8, 95 GENERIC_NOP5_ATOMIC 96 }; 97 static const unsigned char * const intel_nops[ASM_NOP_MAX+2] = 98 { 99 NULL, 100 intelnops, 101 intelnops + 1, 102 intelnops + 1 + 2, 103 intelnops + 1 + 2 + 3, 104 intelnops + 1 + 2 + 3 + 4, 105 intelnops + 1 + 2 + 3 + 4 + 5, 106 intelnops + 1 + 2 + 3 + 4 + 5 + 6, 107 intelnops + 1 + 2 + 3 + 4 + 5 + 6 + 7, 108 intelnops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8, 109 }; 110 #endif 111 112 #ifdef K8_NOP1 113 static const unsigned char k8nops[] = 114 { 115 K8_NOP1, 116 K8_NOP2, 117 K8_NOP3, 118 K8_NOP4, 119 K8_NOP5, 120 K8_NOP6, 121 K8_NOP7, 122 K8_NOP8, 123 K8_NOP5_ATOMIC 124 }; 125 static const unsigned char * const k8_nops[ASM_NOP_MAX+2] = 126 { 127 NULL, 128 k8nops, 129 k8nops + 1, 130 k8nops + 1 + 2, 131 k8nops + 1 + 2 + 3, 132 k8nops + 1 + 2 + 3 + 4, 133 k8nops + 1 + 2 + 3 + 4 + 5, 134 k8nops + 1 + 2 + 3 + 4 + 5 + 6, 135 k8nops + 1 + 2 + 3 + 4 + 5 + 6 + 7, 136 k8nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8, 137 }; 138 #endif 139 140 #if defined(K7_NOP1) && !defined(CONFIG_X86_64) 141 static const unsigned char k7nops[] = 142 { 143 K7_NOP1, 144 K7_NOP2, 145 K7_NOP3, 146 K7_NOP4, 147 K7_NOP5, 148 K7_NOP6, 149 K7_NOP7, 150 K7_NOP8, 151 K7_NOP5_ATOMIC 152 }; 153 static const unsigned char * const k7_nops[ASM_NOP_MAX+2] = 154 { 155 NULL, 156 k7nops, 157 k7nops + 1, 158 k7nops + 1 + 2, 159 k7nops + 1 + 2 + 3, 160 k7nops + 1 + 2 + 3 + 4, 161 k7nops + 1 + 2 + 3 + 4 + 5, 162 k7nops + 1 + 2 + 3 + 4 + 5 + 6, 163 k7nops + 1 + 2 + 3 + 4 + 5 + 6 + 7, 164 k7nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8, 165 }; 166 #endif 167 168 #ifdef P6_NOP1 169 static const unsigned char p6nops[] = 170 { 171 P6_NOP1, 172 P6_NOP2, 173 P6_NOP3, 174 P6_NOP4, 175 P6_NOP5, 176 P6_NOP6, 177 P6_NOP7, 178 P6_NOP8, 179 P6_NOP5_ATOMIC 180 }; 181 static const unsigned char * const p6_nops[ASM_NOP_MAX+2] = 182 { 183 NULL, 184 p6nops, 185 p6nops + 1, 186 p6nops + 1 + 2, 187 p6nops + 1 + 2 + 3, 188 p6nops + 1 + 2 + 3 + 4, 189 p6nops + 1 + 2 + 3 + 4 + 5, 190 p6nops + 1 + 2 + 3 + 4 + 5 + 6, 191 p6nops + 1 + 2 + 3 + 4 + 5 + 6 + 7, 192 p6nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8, 193 }; 194 #endif 195 196 /* Initialize these to a safe default */ 197 #ifdef CONFIG_X86_64 198 const unsigned char * const *ideal_nops = p6_nops; 199 #else 200 const unsigned char * const *ideal_nops = intel_nops; 201 #endif 202 203 void __init arch_init_ideal_nops(void) 204 { 205 switch (boot_cpu_data.x86_vendor) { 206 case X86_VENDOR_INTEL: 207 /* 208 * Due to a decoder implementation quirk, some 209 * specific Intel CPUs actually perform better with 210 * the "k8_nops" than with the SDM-recommended NOPs. 211 */ 212 if (boot_cpu_data.x86 == 6 && 213 boot_cpu_data.x86_model >= 0x0f && 214 boot_cpu_data.x86_model != 0x1c && 215 boot_cpu_data.x86_model != 0x26 && 216 boot_cpu_data.x86_model != 0x27 && 217 boot_cpu_data.x86_model < 0x30) { 218 ideal_nops = k8_nops; 219 } else if (boot_cpu_has(X86_FEATURE_NOPL)) { 220 ideal_nops = p6_nops; 221 } else { 222 #ifdef CONFIG_X86_64 223 ideal_nops = k8_nops; 224 #else 225 ideal_nops = intel_nops; 226 #endif 227 } 228 break; 229 230 case X86_VENDOR_HYGON: 231 ideal_nops = p6_nops; 232 return; 233 234 case X86_VENDOR_AMD: 235 if (boot_cpu_data.x86 > 0xf) { 236 ideal_nops = p6_nops; 237 return; 238 } 239 240 /* fall through */ 241 242 default: 243 #ifdef CONFIG_X86_64 244 ideal_nops = k8_nops; 245 #else 246 if (boot_cpu_has(X86_FEATURE_K8)) 247 ideal_nops = k8_nops; 248 else if (boot_cpu_has(X86_FEATURE_K7)) 249 ideal_nops = k7_nops; 250 else 251 ideal_nops = intel_nops; 252 #endif 253 } 254 } 255 256 /* Use this to add nops to a buffer, then text_poke the whole buffer. */ 257 static void __init_or_module add_nops(void *insns, unsigned int len) 258 { 259 while (len > 0) { 260 unsigned int noplen = len; 261 if (noplen > ASM_NOP_MAX) 262 noplen = ASM_NOP_MAX; 263 memcpy(insns, ideal_nops[noplen], noplen); 264 insns += noplen; 265 len -= noplen; 266 } 267 } 268 269 extern struct alt_instr __alt_instructions[], __alt_instructions_end[]; 270 extern s32 __smp_locks[], __smp_locks_end[]; 271 void text_poke_early(void *addr, const void *opcode, size_t len); 272 273 /* 274 * Are we looking at a near JMP with a 1 or 4-byte displacement. 275 */ 276 static inline bool is_jmp(const u8 opcode) 277 { 278 return opcode == 0xeb || opcode == 0xe9; 279 } 280 281 static void __init_or_module 282 recompute_jump(struct alt_instr *a, u8 *orig_insn, u8 *repl_insn, u8 *insn_buff) 283 { 284 u8 *next_rip, *tgt_rip; 285 s32 n_dspl, o_dspl; 286 int repl_len; 287 288 if (a->replacementlen != 5) 289 return; 290 291 o_dspl = *(s32 *)(insn_buff + 1); 292 293 /* next_rip of the replacement JMP */ 294 next_rip = repl_insn + a->replacementlen; 295 /* target rip of the replacement JMP */ 296 tgt_rip = next_rip + o_dspl; 297 n_dspl = tgt_rip - orig_insn; 298 299 DPRINTK("target RIP: %px, new_displ: 0x%x", tgt_rip, n_dspl); 300 301 if (tgt_rip - orig_insn >= 0) { 302 if (n_dspl - 2 <= 127) 303 goto two_byte_jmp; 304 else 305 goto five_byte_jmp; 306 /* negative offset */ 307 } else { 308 if (((n_dspl - 2) & 0xff) == (n_dspl - 2)) 309 goto two_byte_jmp; 310 else 311 goto five_byte_jmp; 312 } 313 314 two_byte_jmp: 315 n_dspl -= 2; 316 317 insn_buff[0] = 0xeb; 318 insn_buff[1] = (s8)n_dspl; 319 add_nops(insn_buff + 2, 3); 320 321 repl_len = 2; 322 goto done; 323 324 five_byte_jmp: 325 n_dspl -= 5; 326 327 insn_buff[0] = 0xe9; 328 *(s32 *)&insn_buff[1] = n_dspl; 329 330 repl_len = 5; 331 332 done: 333 334 DPRINTK("final displ: 0x%08x, JMP 0x%lx", 335 n_dspl, (unsigned long)orig_insn + n_dspl + repl_len); 336 } 337 338 /* 339 * "noinline" to cause control flow change and thus invalidate I$ and 340 * cause refetch after modification. 341 */ 342 static void __init_or_module noinline optimize_nops(struct alt_instr *a, u8 *instr) 343 { 344 unsigned long flags; 345 int i; 346 347 for (i = 0; i < a->padlen; i++) { 348 if (instr[i] != 0x90) 349 return; 350 } 351 352 local_irq_save(flags); 353 add_nops(instr + (a->instrlen - a->padlen), a->padlen); 354 local_irq_restore(flags); 355 356 DUMP_BYTES(instr, a->instrlen, "%px: [%d:%d) optimized NOPs: ", 357 instr, a->instrlen - a->padlen, a->padlen); 358 } 359 360 /* 361 * Replace instructions with better alternatives for this CPU type. This runs 362 * before SMP is initialized to avoid SMP problems with self modifying code. 363 * This implies that asymmetric systems where APs have less capabilities than 364 * the boot processor are not handled. Tough. Make sure you disable such 365 * features by hand. 366 * 367 * Marked "noinline" to cause control flow change and thus insn cache 368 * to refetch changed I$ lines. 369 */ 370 void __init_or_module noinline apply_alternatives(struct alt_instr *start, 371 struct alt_instr *end) 372 { 373 struct alt_instr *a; 374 u8 *instr, *replacement; 375 u8 insn_buff[MAX_PATCH_LEN]; 376 377 DPRINTK("alt table %px, -> %px", start, end); 378 /* 379 * The scan order should be from start to end. A later scanned 380 * alternative code can overwrite previously scanned alternative code. 381 * Some kernel functions (e.g. memcpy, memset, etc) use this order to 382 * patch code. 383 * 384 * So be careful if you want to change the scan order to any other 385 * order. 386 */ 387 for (a = start; a < end; a++) { 388 int insn_buff_sz = 0; 389 390 instr = (u8 *)&a->instr_offset + a->instr_offset; 391 replacement = (u8 *)&a->repl_offset + a->repl_offset; 392 BUG_ON(a->instrlen > sizeof(insn_buff)); 393 BUG_ON(a->cpuid >= (NCAPINTS + NBUGINTS) * 32); 394 if (!boot_cpu_has(a->cpuid)) { 395 if (a->padlen > 1) 396 optimize_nops(a, instr); 397 398 continue; 399 } 400 401 DPRINTK("feat: %d*32+%d, old: (%pS (%px) len: %d), repl: (%px, len: %d), pad: %d", 402 a->cpuid >> 5, 403 a->cpuid & 0x1f, 404 instr, instr, a->instrlen, 405 replacement, a->replacementlen, a->padlen); 406 407 DUMP_BYTES(instr, a->instrlen, "%px: old_insn: ", instr); 408 DUMP_BYTES(replacement, a->replacementlen, "%px: rpl_insn: ", replacement); 409 410 memcpy(insn_buff, replacement, a->replacementlen); 411 insn_buff_sz = a->replacementlen; 412 413 /* 414 * 0xe8 is a relative jump; fix the offset. 415 * 416 * Instruction length is checked before the opcode to avoid 417 * accessing uninitialized bytes for zero-length replacements. 418 */ 419 if (a->replacementlen == 5 && *insn_buff == 0xe8) { 420 *(s32 *)(insn_buff + 1) += replacement - instr; 421 DPRINTK("Fix CALL offset: 0x%x, CALL 0x%lx", 422 *(s32 *)(insn_buff + 1), 423 (unsigned long)instr + *(s32 *)(insn_buff + 1) + 5); 424 } 425 426 if (a->replacementlen && is_jmp(replacement[0])) 427 recompute_jump(a, instr, replacement, insn_buff); 428 429 if (a->instrlen > a->replacementlen) { 430 add_nops(insn_buff + a->replacementlen, 431 a->instrlen - a->replacementlen); 432 insn_buff_sz += a->instrlen - a->replacementlen; 433 } 434 DUMP_BYTES(insn_buff, insn_buff_sz, "%px: final_insn: ", instr); 435 436 text_poke_early(instr, insn_buff, insn_buff_sz); 437 } 438 } 439 440 #ifdef CONFIG_SMP 441 static void alternatives_smp_lock(const s32 *start, const s32 *end, 442 u8 *text, u8 *text_end) 443 { 444 const s32 *poff; 445 446 for (poff = start; poff < end; poff++) { 447 u8 *ptr = (u8 *)poff + *poff; 448 449 if (!*poff || ptr < text || ptr >= text_end) 450 continue; 451 /* turn DS segment override prefix into lock prefix */ 452 if (*ptr == 0x3e) 453 text_poke(ptr, ((unsigned char []){0xf0}), 1); 454 } 455 } 456 457 static void alternatives_smp_unlock(const s32 *start, const s32 *end, 458 u8 *text, u8 *text_end) 459 { 460 const s32 *poff; 461 462 for (poff = start; poff < end; poff++) { 463 u8 *ptr = (u8 *)poff + *poff; 464 465 if (!*poff || ptr < text || ptr >= text_end) 466 continue; 467 /* turn lock prefix into DS segment override prefix */ 468 if (*ptr == 0xf0) 469 text_poke(ptr, ((unsigned char []){0x3E}), 1); 470 } 471 } 472 473 struct smp_alt_module { 474 /* what is this ??? */ 475 struct module *mod; 476 char *name; 477 478 /* ptrs to lock prefixes */ 479 const s32 *locks; 480 const s32 *locks_end; 481 482 /* .text segment, needed to avoid patching init code ;) */ 483 u8 *text; 484 u8 *text_end; 485 486 struct list_head next; 487 }; 488 static LIST_HEAD(smp_alt_modules); 489 static bool uniproc_patched = false; /* protected by text_mutex */ 490 491 void __init_or_module alternatives_smp_module_add(struct module *mod, 492 char *name, 493 void *locks, void *locks_end, 494 void *text, void *text_end) 495 { 496 struct smp_alt_module *smp; 497 498 mutex_lock(&text_mutex); 499 if (!uniproc_patched) 500 goto unlock; 501 502 if (num_possible_cpus() == 1) 503 /* Don't bother remembering, we'll never have to undo it. */ 504 goto smp_unlock; 505 506 smp = kzalloc(sizeof(*smp), GFP_KERNEL); 507 if (NULL == smp) 508 /* we'll run the (safe but slow) SMP code then ... */ 509 goto unlock; 510 511 smp->mod = mod; 512 smp->name = name; 513 smp->locks = locks; 514 smp->locks_end = locks_end; 515 smp->text = text; 516 smp->text_end = text_end; 517 DPRINTK("locks %p -> %p, text %p -> %p, name %s\n", 518 smp->locks, smp->locks_end, 519 smp->text, smp->text_end, smp->name); 520 521 list_add_tail(&smp->next, &smp_alt_modules); 522 smp_unlock: 523 alternatives_smp_unlock(locks, locks_end, text, text_end); 524 unlock: 525 mutex_unlock(&text_mutex); 526 } 527 528 void __init_or_module alternatives_smp_module_del(struct module *mod) 529 { 530 struct smp_alt_module *item; 531 532 mutex_lock(&text_mutex); 533 list_for_each_entry(item, &smp_alt_modules, next) { 534 if (mod != item->mod) 535 continue; 536 list_del(&item->next); 537 kfree(item); 538 break; 539 } 540 mutex_unlock(&text_mutex); 541 } 542 543 void alternatives_enable_smp(void) 544 { 545 struct smp_alt_module *mod; 546 547 /* Why bother if there are no other CPUs? */ 548 BUG_ON(num_possible_cpus() == 1); 549 550 mutex_lock(&text_mutex); 551 552 if (uniproc_patched) { 553 pr_info("switching to SMP code\n"); 554 BUG_ON(num_online_cpus() != 1); 555 clear_cpu_cap(&boot_cpu_data, X86_FEATURE_UP); 556 clear_cpu_cap(&cpu_data(0), X86_FEATURE_UP); 557 list_for_each_entry(mod, &smp_alt_modules, next) 558 alternatives_smp_lock(mod->locks, mod->locks_end, 559 mod->text, mod->text_end); 560 uniproc_patched = false; 561 } 562 mutex_unlock(&text_mutex); 563 } 564 565 /* 566 * Return 1 if the address range is reserved for SMP-alternatives. 567 * Must hold text_mutex. 568 */ 569 int alternatives_text_reserved(void *start, void *end) 570 { 571 struct smp_alt_module *mod; 572 const s32 *poff; 573 u8 *text_start = start; 574 u8 *text_end = end; 575 576 lockdep_assert_held(&text_mutex); 577 578 list_for_each_entry(mod, &smp_alt_modules, next) { 579 if (mod->text > text_end || mod->text_end < text_start) 580 continue; 581 for (poff = mod->locks; poff < mod->locks_end; poff++) { 582 const u8 *ptr = (const u8 *)poff + *poff; 583 584 if (text_start <= ptr && text_end > ptr) 585 return 1; 586 } 587 } 588 589 return 0; 590 } 591 #endif /* CONFIG_SMP */ 592 593 #ifdef CONFIG_PARAVIRT 594 void __init_or_module apply_paravirt(struct paravirt_patch_site *start, 595 struct paravirt_patch_site *end) 596 { 597 struct paravirt_patch_site *p; 598 char insn_buff[MAX_PATCH_LEN]; 599 600 for (p = start; p < end; p++) { 601 unsigned int used; 602 603 BUG_ON(p->len > MAX_PATCH_LEN); 604 /* prep the buffer with the original instructions */ 605 memcpy(insn_buff, p->instr, p->len); 606 used = pv_ops.init.patch(p->type, insn_buff, (unsigned long)p->instr, p->len); 607 608 BUG_ON(used > p->len); 609 610 /* Pad the rest with nops */ 611 add_nops(insn_buff + used, p->len - used); 612 text_poke_early(p->instr, insn_buff, p->len); 613 } 614 } 615 extern struct paravirt_patch_site __start_parainstructions[], 616 __stop_parainstructions[]; 617 #endif /* CONFIG_PARAVIRT */ 618 619 /* 620 * Self-test for the INT3 based CALL emulation code. 621 * 622 * This exercises int3_emulate_call() to make sure INT3 pt_regs are set up 623 * properly and that there is a stack gap between the INT3 frame and the 624 * previous context. Without this gap doing a virtual PUSH on the interrupted 625 * stack would corrupt the INT3 IRET frame. 626 * 627 * See entry_{32,64}.S for more details. 628 */ 629 630 /* 631 * We define the int3_magic() function in assembly to control the calling 632 * convention such that we can 'call' it from assembly. 633 */ 634 635 extern void int3_magic(unsigned int *ptr); /* defined in asm */ 636 637 asm ( 638 " .pushsection .init.text, \"ax\", @progbits\n" 639 " .type int3_magic, @function\n" 640 "int3_magic:\n" 641 " movl $1, (%" _ASM_ARG1 ")\n" 642 " ret\n" 643 " .size int3_magic, .-int3_magic\n" 644 " .popsection\n" 645 ); 646 647 extern __initdata unsigned long int3_selftest_ip; /* defined in asm below */ 648 649 static int __init 650 int3_exception_notify(struct notifier_block *self, unsigned long val, void *data) 651 { 652 struct die_args *args = data; 653 struct pt_regs *regs = args->regs; 654 655 if (!regs || user_mode(regs)) 656 return NOTIFY_DONE; 657 658 if (val != DIE_INT3) 659 return NOTIFY_DONE; 660 661 if (regs->ip - INT3_INSN_SIZE != int3_selftest_ip) 662 return NOTIFY_DONE; 663 664 int3_emulate_call(regs, (unsigned long)&int3_magic); 665 return NOTIFY_STOP; 666 } 667 668 static void __init int3_selftest(void) 669 { 670 static __initdata struct notifier_block int3_exception_nb = { 671 .notifier_call = int3_exception_notify, 672 .priority = INT_MAX-1, /* last */ 673 }; 674 unsigned int val = 0; 675 676 BUG_ON(register_die_notifier(&int3_exception_nb)); 677 678 /* 679 * Basically: int3_magic(&val); but really complicated :-) 680 * 681 * Stick the address of the INT3 instruction into int3_selftest_ip, 682 * then trigger the INT3, padded with NOPs to match a CALL instruction 683 * length. 684 */ 685 asm volatile ("1: int3; nop; nop; nop; nop\n\t" 686 ".pushsection .init.data,\"aw\"\n\t" 687 ".align " __ASM_SEL(4, 8) "\n\t" 688 ".type int3_selftest_ip, @object\n\t" 689 ".size int3_selftest_ip, " __ASM_SEL(4, 8) "\n\t" 690 "int3_selftest_ip:\n\t" 691 __ASM_SEL(.long, .quad) " 1b\n\t" 692 ".popsection\n\t" 693 : ASM_CALL_CONSTRAINT 694 : __ASM_SEL_RAW(a, D) (&val) 695 : "memory"); 696 697 BUG_ON(val != 1); 698 699 unregister_die_notifier(&int3_exception_nb); 700 } 701 702 void __init alternative_instructions(void) 703 { 704 int3_selftest(); 705 706 /* 707 * The patching is not fully atomic, so try to avoid local 708 * interruptions that might execute the to be patched code. 709 * Other CPUs are not running. 710 */ 711 stop_nmi(); 712 713 /* 714 * Don't stop machine check exceptions while patching. 715 * MCEs only happen when something got corrupted and in this 716 * case we must do something about the corruption. 717 * Ignoring it is worse than an unlikely patching race. 718 * Also machine checks tend to be broadcast and if one CPU 719 * goes into machine check the others follow quickly, so we don't 720 * expect a machine check to cause undue problems during to code 721 * patching. 722 */ 723 724 apply_alternatives(__alt_instructions, __alt_instructions_end); 725 726 #ifdef CONFIG_SMP 727 /* Patch to UP if other cpus not imminent. */ 728 if (!noreplace_smp && (num_present_cpus() == 1 || setup_max_cpus <= 1)) { 729 uniproc_patched = true; 730 alternatives_smp_module_add(NULL, "core kernel", 731 __smp_locks, __smp_locks_end, 732 _text, _etext); 733 } 734 735 if (!uniproc_patched || num_possible_cpus() == 1) { 736 free_init_pages("SMP alternatives", 737 (unsigned long)__smp_locks, 738 (unsigned long)__smp_locks_end); 739 } 740 #endif 741 742 apply_paravirt(__parainstructions, __parainstructions_end); 743 744 restart_nmi(); 745 alternatives_patched = 1; 746 } 747 748 /** 749 * text_poke_early - Update instructions on a live kernel at boot time 750 * @addr: address to modify 751 * @opcode: source of the copy 752 * @len: length to copy 753 * 754 * When you use this code to patch more than one byte of an instruction 755 * you need to make sure that other CPUs cannot execute this code in parallel. 756 * Also no thread must be currently preempted in the middle of these 757 * instructions. And on the local CPU you need to be protected against NMI or 758 * MCE handlers seeing an inconsistent instruction while you patch. 759 */ 760 void __init_or_module text_poke_early(void *addr, const void *opcode, 761 size_t len) 762 { 763 unsigned long flags; 764 765 if (boot_cpu_has(X86_FEATURE_NX) && 766 is_module_text_address((unsigned long)addr)) { 767 /* 768 * Modules text is marked initially as non-executable, so the 769 * code cannot be running and speculative code-fetches are 770 * prevented. Just change the code. 771 */ 772 memcpy(addr, opcode, len); 773 } else { 774 local_irq_save(flags); 775 memcpy(addr, opcode, len); 776 local_irq_restore(flags); 777 sync_core(); 778 779 /* 780 * Could also do a CLFLUSH here to speed up CPU recovery; but 781 * that causes hangs on some VIA CPUs. 782 */ 783 } 784 } 785 786 __ro_after_init struct mm_struct *poking_mm; 787 __ro_after_init unsigned long poking_addr; 788 789 static void *__text_poke(void *addr, const void *opcode, size_t len) 790 { 791 bool cross_page_boundary = offset_in_page(addr) + len > PAGE_SIZE; 792 struct page *pages[2] = {NULL}; 793 temp_mm_state_t prev; 794 unsigned long flags; 795 pte_t pte, *ptep; 796 spinlock_t *ptl; 797 pgprot_t pgprot; 798 799 /* 800 * While boot memory allocator is running we cannot use struct pages as 801 * they are not yet initialized. There is no way to recover. 802 */ 803 BUG_ON(!after_bootmem); 804 805 if (!core_kernel_text((unsigned long)addr)) { 806 pages[0] = vmalloc_to_page(addr); 807 if (cross_page_boundary) 808 pages[1] = vmalloc_to_page(addr + PAGE_SIZE); 809 } else { 810 pages[0] = virt_to_page(addr); 811 WARN_ON(!PageReserved(pages[0])); 812 if (cross_page_boundary) 813 pages[1] = virt_to_page(addr + PAGE_SIZE); 814 } 815 /* 816 * If something went wrong, crash and burn since recovery paths are not 817 * implemented. 818 */ 819 BUG_ON(!pages[0] || (cross_page_boundary && !pages[1])); 820 821 local_irq_save(flags); 822 823 /* 824 * Map the page without the global bit, as TLB flushing is done with 825 * flush_tlb_mm_range(), which is intended for non-global PTEs. 826 */ 827 pgprot = __pgprot(pgprot_val(PAGE_KERNEL) & ~_PAGE_GLOBAL); 828 829 /* 830 * The lock is not really needed, but this allows to avoid open-coding. 831 */ 832 ptep = get_locked_pte(poking_mm, poking_addr, &ptl); 833 834 /* 835 * This must not fail; preallocated in poking_init(). 836 */ 837 VM_BUG_ON(!ptep); 838 839 pte = mk_pte(pages[0], pgprot); 840 set_pte_at(poking_mm, poking_addr, ptep, pte); 841 842 if (cross_page_boundary) { 843 pte = mk_pte(pages[1], pgprot); 844 set_pte_at(poking_mm, poking_addr + PAGE_SIZE, ptep + 1, pte); 845 } 846 847 /* 848 * Loading the temporary mm behaves as a compiler barrier, which 849 * guarantees that the PTE will be set at the time memcpy() is done. 850 */ 851 prev = use_temporary_mm(poking_mm); 852 853 kasan_disable_current(); 854 memcpy((u8 *)poking_addr + offset_in_page(addr), opcode, len); 855 kasan_enable_current(); 856 857 /* 858 * Ensure that the PTE is only cleared after the instructions of memcpy 859 * were issued by using a compiler barrier. 860 */ 861 barrier(); 862 863 pte_clear(poking_mm, poking_addr, ptep); 864 if (cross_page_boundary) 865 pte_clear(poking_mm, poking_addr + PAGE_SIZE, ptep + 1); 866 867 /* 868 * Loading the previous page-table hierarchy requires a serializing 869 * instruction that already allows the core to see the updated version. 870 * Xen-PV is assumed to serialize execution in a similar manner. 871 */ 872 unuse_temporary_mm(prev); 873 874 /* 875 * Flushing the TLB might involve IPIs, which would require enabled 876 * IRQs, but not if the mm is not used, as it is in this point. 877 */ 878 flush_tlb_mm_range(poking_mm, poking_addr, poking_addr + 879 (cross_page_boundary ? 2 : 1) * PAGE_SIZE, 880 PAGE_SHIFT, false); 881 882 /* 883 * If the text does not match what we just wrote then something is 884 * fundamentally screwy; there's nothing we can really do about that. 885 */ 886 BUG_ON(memcmp(addr, opcode, len)); 887 888 pte_unmap_unlock(ptep, ptl); 889 local_irq_restore(flags); 890 return addr; 891 } 892 893 /** 894 * text_poke - Update instructions on a live kernel 895 * @addr: address to modify 896 * @opcode: source of the copy 897 * @len: length to copy 898 * 899 * Only atomic text poke/set should be allowed when not doing early patching. 900 * It means the size must be writable atomically and the address must be aligned 901 * in a way that permits an atomic write. It also makes sure we fit on a single 902 * page. 903 * 904 * Note that the caller must ensure that if the modified code is part of a 905 * module, the module would not be removed during poking. This can be achieved 906 * by registering a module notifier, and ordering module removal and patching 907 * trough a mutex. 908 */ 909 void *text_poke(void *addr, const void *opcode, size_t len) 910 { 911 lockdep_assert_held(&text_mutex); 912 913 return __text_poke(addr, opcode, len); 914 } 915 916 /** 917 * text_poke_kgdb - Update instructions on a live kernel by kgdb 918 * @addr: address to modify 919 * @opcode: source of the copy 920 * @len: length to copy 921 * 922 * Only atomic text poke/set should be allowed when not doing early patching. 923 * It means the size must be writable atomically and the address must be aligned 924 * in a way that permits an atomic write. It also makes sure we fit on a single 925 * page. 926 * 927 * Context: should only be used by kgdb, which ensures no other core is running, 928 * despite the fact it does not hold the text_mutex. 929 */ 930 void *text_poke_kgdb(void *addr, const void *opcode, size_t len) 931 { 932 return __text_poke(addr, opcode, len); 933 } 934 935 static void do_sync_core(void *info) 936 { 937 sync_core(); 938 } 939 940 void text_poke_sync(void) 941 { 942 on_each_cpu(do_sync_core, NULL, 1); 943 } 944 945 struct text_poke_loc { 946 s32 rel_addr; /* addr := _stext + rel_addr */ 947 s32 rel32; 948 u8 opcode; 949 const u8 text[POKE_MAX_OPCODE_SIZE]; 950 }; 951 952 struct bp_patching_desc { 953 struct text_poke_loc *vec; 954 int nr_entries; 955 atomic_t refs; 956 }; 957 958 static struct bp_patching_desc *bp_desc; 959 960 static inline struct bp_patching_desc *try_get_desc(struct bp_patching_desc **descp) 961 { 962 struct bp_patching_desc *desc = READ_ONCE(*descp); /* rcu_dereference */ 963 964 if (!desc || !atomic_inc_not_zero(&desc->refs)) 965 return NULL; 966 967 return desc; 968 } 969 970 static inline void put_desc(struct bp_patching_desc *desc) 971 { 972 smp_mb__before_atomic(); 973 atomic_dec(&desc->refs); 974 } 975 976 static inline void *text_poke_addr(struct text_poke_loc *tp) 977 { 978 return _stext + tp->rel_addr; 979 } 980 981 static int notrace patch_cmp(const void *key, const void *elt) 982 { 983 struct text_poke_loc *tp = (struct text_poke_loc *) elt; 984 985 if (key < text_poke_addr(tp)) 986 return -1; 987 if (key > text_poke_addr(tp)) 988 return 1; 989 return 0; 990 } 991 NOKPROBE_SYMBOL(patch_cmp); 992 993 int notrace poke_int3_handler(struct pt_regs *regs) 994 { 995 struct bp_patching_desc *desc; 996 struct text_poke_loc *tp; 997 int len, ret = 0; 998 void *ip; 999 1000 if (user_mode(regs)) 1001 return 0; 1002 1003 /* 1004 * Having observed our INT3 instruction, we now must observe 1005 * bp_desc: 1006 * 1007 * bp_desc = desc INT3 1008 * WMB RMB 1009 * write INT3 if (desc) 1010 */ 1011 smp_rmb(); 1012 1013 desc = try_get_desc(&bp_desc); 1014 if (!desc) 1015 return 0; 1016 1017 /* 1018 * Discount the INT3. See text_poke_bp_batch(). 1019 */ 1020 ip = (void *) regs->ip - INT3_INSN_SIZE; 1021 1022 /* 1023 * Skip the binary search if there is a single member in the vector. 1024 */ 1025 if (unlikely(desc->nr_entries > 1)) { 1026 tp = bsearch(ip, desc->vec, desc->nr_entries, 1027 sizeof(struct text_poke_loc), 1028 patch_cmp); 1029 if (!tp) 1030 goto out_put; 1031 } else { 1032 tp = desc->vec; 1033 if (text_poke_addr(tp) != ip) 1034 goto out_put; 1035 } 1036 1037 len = text_opcode_size(tp->opcode); 1038 ip += len; 1039 1040 switch (tp->opcode) { 1041 case INT3_INSN_OPCODE: 1042 /* 1043 * Someone poked an explicit INT3, they'll want to handle it, 1044 * do not consume. 1045 */ 1046 goto out_put; 1047 1048 case CALL_INSN_OPCODE: 1049 int3_emulate_call(regs, (long)ip + tp->rel32); 1050 break; 1051 1052 case JMP32_INSN_OPCODE: 1053 case JMP8_INSN_OPCODE: 1054 int3_emulate_jmp(regs, (long)ip + tp->rel32); 1055 break; 1056 1057 default: 1058 BUG(); 1059 } 1060 1061 ret = 1; 1062 1063 out_put: 1064 put_desc(desc); 1065 return ret; 1066 } 1067 NOKPROBE_SYMBOL(poke_int3_handler); 1068 1069 #define TP_VEC_MAX (PAGE_SIZE / sizeof(struct text_poke_loc)) 1070 static struct text_poke_loc tp_vec[TP_VEC_MAX]; 1071 static int tp_vec_nr; 1072 1073 /** 1074 * text_poke_bp_batch() -- update instructions on live kernel on SMP 1075 * @tp: vector of instructions to patch 1076 * @nr_entries: number of entries in the vector 1077 * 1078 * Modify multi-byte instruction by using int3 breakpoint on SMP. 1079 * We completely avoid stop_machine() here, and achieve the 1080 * synchronization using int3 breakpoint. 1081 * 1082 * The way it is done: 1083 * - For each entry in the vector: 1084 * - add a int3 trap to the address that will be patched 1085 * - sync cores 1086 * - For each entry in the vector: 1087 * - update all but the first byte of the patched range 1088 * - sync cores 1089 * - For each entry in the vector: 1090 * - replace the first byte (int3) by the first byte of 1091 * replacing opcode 1092 * - sync cores 1093 */ 1094 static void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries) 1095 { 1096 struct bp_patching_desc desc = { 1097 .vec = tp, 1098 .nr_entries = nr_entries, 1099 .refs = ATOMIC_INIT(1), 1100 }; 1101 unsigned char int3 = INT3_INSN_OPCODE; 1102 unsigned int i; 1103 int do_sync; 1104 1105 lockdep_assert_held(&text_mutex); 1106 1107 smp_store_release(&bp_desc, &desc); /* rcu_assign_pointer */ 1108 1109 /* 1110 * Corresponding read barrier in int3 notifier for making sure the 1111 * nr_entries and handler are correctly ordered wrt. patching. 1112 */ 1113 smp_wmb(); 1114 1115 /* 1116 * First step: add a int3 trap to the address that will be patched. 1117 */ 1118 for (i = 0; i < nr_entries; i++) 1119 text_poke(text_poke_addr(&tp[i]), &int3, INT3_INSN_SIZE); 1120 1121 text_poke_sync(); 1122 1123 /* 1124 * Second step: update all but the first byte of the patched range. 1125 */ 1126 for (do_sync = 0, i = 0; i < nr_entries; i++) { 1127 int len = text_opcode_size(tp[i].opcode); 1128 1129 if (len - INT3_INSN_SIZE > 0) { 1130 text_poke(text_poke_addr(&tp[i]) + INT3_INSN_SIZE, 1131 (const char *)tp[i].text + INT3_INSN_SIZE, 1132 len - INT3_INSN_SIZE); 1133 do_sync++; 1134 } 1135 } 1136 1137 if (do_sync) { 1138 /* 1139 * According to Intel, this core syncing is very likely 1140 * not necessary and we'd be safe even without it. But 1141 * better safe than sorry (plus there's not only Intel). 1142 */ 1143 text_poke_sync(); 1144 } 1145 1146 /* 1147 * Third step: replace the first byte (int3) by the first byte of 1148 * replacing opcode. 1149 */ 1150 for (do_sync = 0, i = 0; i < nr_entries; i++) { 1151 if (tp[i].text[0] == INT3_INSN_OPCODE) 1152 continue; 1153 1154 text_poke(text_poke_addr(&tp[i]), tp[i].text, INT3_INSN_SIZE); 1155 do_sync++; 1156 } 1157 1158 if (do_sync) 1159 text_poke_sync(); 1160 1161 /* 1162 * Remove and synchronize_rcu(), except we have a very primitive 1163 * refcount based completion. 1164 */ 1165 WRITE_ONCE(bp_desc, NULL); /* RCU_INIT_POINTER */ 1166 if (!atomic_dec_and_test(&desc.refs)) 1167 atomic_cond_read_acquire(&desc.refs, !VAL); 1168 } 1169 1170 void text_poke_loc_init(struct text_poke_loc *tp, void *addr, 1171 const void *opcode, size_t len, const void *emulate) 1172 { 1173 struct insn insn; 1174 1175 memcpy((void *)tp->text, opcode, len); 1176 if (!emulate) 1177 emulate = opcode; 1178 1179 kernel_insn_init(&insn, emulate, MAX_INSN_SIZE); 1180 insn_get_length(&insn); 1181 1182 BUG_ON(!insn_complete(&insn)); 1183 BUG_ON(len != insn.length); 1184 1185 tp->rel_addr = addr - (void *)_stext; 1186 tp->opcode = insn.opcode.bytes[0]; 1187 1188 switch (tp->opcode) { 1189 case INT3_INSN_OPCODE: 1190 break; 1191 1192 case CALL_INSN_OPCODE: 1193 case JMP32_INSN_OPCODE: 1194 case JMP8_INSN_OPCODE: 1195 tp->rel32 = insn.immediate.value; 1196 break; 1197 1198 default: /* assume NOP */ 1199 switch (len) { 1200 case 2: /* NOP2 -- emulate as JMP8+0 */ 1201 BUG_ON(memcmp(emulate, ideal_nops[len], len)); 1202 tp->opcode = JMP8_INSN_OPCODE; 1203 tp->rel32 = 0; 1204 break; 1205 1206 case 5: /* NOP5 -- emulate as JMP32+0 */ 1207 BUG_ON(memcmp(emulate, ideal_nops[NOP_ATOMIC5], len)); 1208 tp->opcode = JMP32_INSN_OPCODE; 1209 tp->rel32 = 0; 1210 break; 1211 1212 default: /* unknown instruction */ 1213 BUG(); 1214 } 1215 break; 1216 } 1217 } 1218 1219 /* 1220 * We hard rely on the tp_vec being ordered; ensure this is so by flushing 1221 * early if needed. 1222 */ 1223 static bool tp_order_fail(void *addr) 1224 { 1225 struct text_poke_loc *tp; 1226 1227 if (!tp_vec_nr) 1228 return false; 1229 1230 if (!addr) /* force */ 1231 return true; 1232 1233 tp = &tp_vec[tp_vec_nr - 1]; 1234 if ((unsigned long)text_poke_addr(tp) > (unsigned long)addr) 1235 return true; 1236 1237 return false; 1238 } 1239 1240 static void text_poke_flush(void *addr) 1241 { 1242 if (tp_vec_nr == TP_VEC_MAX || tp_order_fail(addr)) { 1243 text_poke_bp_batch(tp_vec, tp_vec_nr); 1244 tp_vec_nr = 0; 1245 } 1246 } 1247 1248 void text_poke_finish(void) 1249 { 1250 text_poke_flush(NULL); 1251 } 1252 1253 void __ref text_poke_queue(void *addr, const void *opcode, size_t len, const void *emulate) 1254 { 1255 struct text_poke_loc *tp; 1256 1257 if (unlikely(system_state == SYSTEM_BOOTING)) { 1258 text_poke_early(addr, opcode, len); 1259 return; 1260 } 1261 1262 text_poke_flush(addr); 1263 1264 tp = &tp_vec[tp_vec_nr++]; 1265 text_poke_loc_init(tp, addr, opcode, len, emulate); 1266 } 1267 1268 /** 1269 * text_poke_bp() -- update instructions on live kernel on SMP 1270 * @addr: address to patch 1271 * @opcode: opcode of new instruction 1272 * @len: length to copy 1273 * @handler: address to jump to when the temporary breakpoint is hit 1274 * 1275 * Update a single instruction with the vector in the stack, avoiding 1276 * dynamically allocated memory. This function should be used when it is 1277 * not possible to allocate memory. 1278 */ 1279 void __ref text_poke_bp(void *addr, const void *opcode, size_t len, const void *emulate) 1280 { 1281 struct text_poke_loc tp; 1282 1283 if (unlikely(system_state == SYSTEM_BOOTING)) { 1284 text_poke_early(addr, opcode, len); 1285 return; 1286 } 1287 1288 text_poke_loc_init(&tp, addr, opcode, len, emulate); 1289 text_poke_bp_batch(&tp, 1); 1290 } 1291