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/perf_event.h> 7 #include <linux/mutex.h> 8 #include <linux/list.h> 9 #include <linux/stringify.h> 10 #include <linux/highmem.h> 11 #include <linux/mm.h> 12 #include <linux/vmalloc.h> 13 #include <linux/memory.h> 14 #include <linux/stop_machine.h> 15 #include <linux/slab.h> 16 #include <linux/kdebug.h> 17 #include <linux/kprobes.h> 18 #include <linux/mmu_context.h> 19 #include <linux/bsearch.h> 20 #include <linux/sync_core.h> 21 #include <asm/text-patching.h> 22 #include <asm/alternative.h> 23 #include <asm/sections.h> 24 #include <asm/mce.h> 25 #include <asm/nmi.h> 26 #include <asm/cacheflush.h> 27 #include <asm/tlbflush.h> 28 #include <asm/insn.h> 29 #include <asm/io.h> 30 #include <asm/fixmap.h> 31 32 int __read_mostly alternatives_patched; 33 34 EXPORT_SYMBOL_GPL(alternatives_patched); 35 36 #define MAX_PATCH_LEN (255-1) 37 38 static int __initdata_or_module debug_alternative; 39 40 static int __init debug_alt(char *str) 41 { 42 debug_alternative = 1; 43 return 1; 44 } 45 __setup("debug-alternative", debug_alt); 46 47 static int noreplace_smp; 48 49 static int __init setup_noreplace_smp(char *str) 50 { 51 noreplace_smp = 1; 52 return 1; 53 } 54 __setup("noreplace-smp", setup_noreplace_smp); 55 56 #define DPRINTK(fmt, args...) \ 57 do { \ 58 if (debug_alternative) \ 59 printk(KERN_DEBUG pr_fmt(fmt) "\n", ##args); \ 60 } while (0) 61 62 #define DUMP_BYTES(buf, len, fmt, args...) \ 63 do { \ 64 if (unlikely(debug_alternative)) { \ 65 int j; \ 66 \ 67 if (!(len)) \ 68 break; \ 69 \ 70 printk(KERN_DEBUG pr_fmt(fmt), ##args); \ 71 for (j = 0; j < (len) - 1; j++) \ 72 printk(KERN_CONT "%02hhx ", buf[j]); \ 73 printk(KERN_CONT "%02hhx\n", buf[j]); \ 74 } \ 75 } while (0) 76 77 /* 78 * Each GENERIC_NOPX is of X bytes, and defined as an array of bytes 79 * that correspond to that nop. Getting from one nop to the next, we 80 * add to the array the offset that is equal to the sum of all sizes of 81 * nops preceding the one we are after. 82 * 83 * Note: The GENERIC_NOP5_ATOMIC is at the end, as it breaks the 84 * nice symmetry of sizes of the previous nops. 85 */ 86 #if defined(GENERIC_NOP1) && !defined(CONFIG_X86_64) 87 static const unsigned char intelnops[] = 88 { 89 GENERIC_NOP1, 90 GENERIC_NOP2, 91 GENERIC_NOP3, 92 GENERIC_NOP4, 93 GENERIC_NOP5, 94 GENERIC_NOP6, 95 GENERIC_NOP7, 96 GENERIC_NOP8, 97 GENERIC_NOP5_ATOMIC 98 }; 99 static const unsigned char * const intel_nops[ASM_NOP_MAX+2] = 100 { 101 NULL, 102 intelnops, 103 intelnops + 1, 104 intelnops + 1 + 2, 105 intelnops + 1 + 2 + 3, 106 intelnops + 1 + 2 + 3 + 4, 107 intelnops + 1 + 2 + 3 + 4 + 5, 108 intelnops + 1 + 2 + 3 + 4 + 5 + 6, 109 intelnops + 1 + 2 + 3 + 4 + 5 + 6 + 7, 110 intelnops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8, 111 }; 112 #endif 113 114 #ifdef K8_NOP1 115 static const unsigned char k8nops[] = 116 { 117 K8_NOP1, 118 K8_NOP2, 119 K8_NOP3, 120 K8_NOP4, 121 K8_NOP5, 122 K8_NOP6, 123 K8_NOP7, 124 K8_NOP8, 125 K8_NOP5_ATOMIC 126 }; 127 static const unsigned char * const k8_nops[ASM_NOP_MAX+2] = 128 { 129 NULL, 130 k8nops, 131 k8nops + 1, 132 k8nops + 1 + 2, 133 k8nops + 1 + 2 + 3, 134 k8nops + 1 + 2 + 3 + 4, 135 k8nops + 1 + 2 + 3 + 4 + 5, 136 k8nops + 1 + 2 + 3 + 4 + 5 + 6, 137 k8nops + 1 + 2 + 3 + 4 + 5 + 6 + 7, 138 k8nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8, 139 }; 140 #endif 141 142 #if defined(K7_NOP1) && !defined(CONFIG_X86_64) 143 static const unsigned char k7nops[] = 144 { 145 K7_NOP1, 146 K7_NOP2, 147 K7_NOP3, 148 K7_NOP4, 149 K7_NOP5, 150 K7_NOP6, 151 K7_NOP7, 152 K7_NOP8, 153 K7_NOP5_ATOMIC 154 }; 155 static const unsigned char * const k7_nops[ASM_NOP_MAX+2] = 156 { 157 NULL, 158 k7nops, 159 k7nops + 1, 160 k7nops + 1 + 2, 161 k7nops + 1 + 2 + 3, 162 k7nops + 1 + 2 + 3 + 4, 163 k7nops + 1 + 2 + 3 + 4 + 5, 164 k7nops + 1 + 2 + 3 + 4 + 5 + 6, 165 k7nops + 1 + 2 + 3 + 4 + 5 + 6 + 7, 166 k7nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8, 167 }; 168 #endif 169 170 #ifdef P6_NOP1 171 static const unsigned char p6nops[] = 172 { 173 P6_NOP1, 174 P6_NOP2, 175 P6_NOP3, 176 P6_NOP4, 177 P6_NOP5, 178 P6_NOP6, 179 P6_NOP7, 180 P6_NOP8, 181 P6_NOP5_ATOMIC 182 }; 183 static const unsigned char * const p6_nops[ASM_NOP_MAX+2] = 184 { 185 NULL, 186 p6nops, 187 p6nops + 1, 188 p6nops + 1 + 2, 189 p6nops + 1 + 2 + 3, 190 p6nops + 1 + 2 + 3 + 4, 191 p6nops + 1 + 2 + 3 + 4 + 5, 192 p6nops + 1 + 2 + 3 + 4 + 5 + 6, 193 p6nops + 1 + 2 + 3 + 4 + 5 + 6 + 7, 194 p6nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8, 195 }; 196 #endif 197 198 /* Initialize these to a safe default */ 199 #ifdef CONFIG_X86_64 200 const unsigned char * const *ideal_nops = p6_nops; 201 #else 202 const unsigned char * const *ideal_nops = intel_nops; 203 #endif 204 205 void __init arch_init_ideal_nops(void) 206 { 207 switch (boot_cpu_data.x86_vendor) { 208 case X86_VENDOR_INTEL: 209 /* 210 * Due to a decoder implementation quirk, some 211 * specific Intel CPUs actually perform better with 212 * the "k8_nops" than with the SDM-recommended NOPs. 213 */ 214 if (boot_cpu_data.x86 == 6 && 215 boot_cpu_data.x86_model >= 0x0f && 216 boot_cpu_data.x86_model != 0x1c && 217 boot_cpu_data.x86_model != 0x26 && 218 boot_cpu_data.x86_model != 0x27 && 219 boot_cpu_data.x86_model < 0x30) { 220 ideal_nops = k8_nops; 221 } else if (boot_cpu_has(X86_FEATURE_NOPL)) { 222 ideal_nops = p6_nops; 223 } else { 224 #ifdef CONFIG_X86_64 225 ideal_nops = k8_nops; 226 #else 227 ideal_nops = intel_nops; 228 #endif 229 } 230 break; 231 232 case X86_VENDOR_HYGON: 233 ideal_nops = p6_nops; 234 return; 235 236 case X86_VENDOR_AMD: 237 if (boot_cpu_data.x86 > 0xf) { 238 ideal_nops = p6_nops; 239 return; 240 } 241 242 fallthrough; 243 244 default: 245 #ifdef CONFIG_X86_64 246 ideal_nops = k8_nops; 247 #else 248 if (boot_cpu_has(X86_FEATURE_K8)) 249 ideal_nops = k8_nops; 250 else if (boot_cpu_has(X86_FEATURE_K7)) 251 ideal_nops = k7_nops; 252 else 253 ideal_nops = intel_nops; 254 #endif 255 } 256 } 257 258 /* Use this to add nops to a buffer, then text_poke the whole buffer. */ 259 static void __init_or_module add_nops(void *insns, unsigned int len) 260 { 261 while (len > 0) { 262 unsigned int noplen = len; 263 if (noplen > ASM_NOP_MAX) 264 noplen = ASM_NOP_MAX; 265 memcpy(insns, ideal_nops[noplen], noplen); 266 insns += noplen; 267 len -= noplen; 268 } 269 } 270 271 extern struct alt_instr __alt_instructions[], __alt_instructions_end[]; 272 extern s32 __smp_locks[], __smp_locks_end[]; 273 void text_poke_early(void *addr, const void *opcode, size_t len); 274 275 /* 276 * Are we looking at a near JMP with a 1 or 4-byte displacement. 277 */ 278 static inline bool is_jmp(const u8 opcode) 279 { 280 return opcode == 0xeb || opcode == 0xe9; 281 } 282 283 static void __init_or_module 284 recompute_jump(struct alt_instr *a, u8 *orig_insn, u8 *repl_insn, u8 *insn_buff) 285 { 286 u8 *next_rip, *tgt_rip; 287 s32 n_dspl, o_dspl; 288 int repl_len; 289 290 if (a->replacementlen != 5) 291 return; 292 293 o_dspl = *(s32 *)(insn_buff + 1); 294 295 /* next_rip of the replacement JMP */ 296 next_rip = repl_insn + a->replacementlen; 297 /* target rip of the replacement JMP */ 298 tgt_rip = next_rip + o_dspl; 299 n_dspl = tgt_rip - orig_insn; 300 301 DPRINTK("target RIP: %px, new_displ: 0x%x", tgt_rip, n_dspl); 302 303 if (tgt_rip - orig_insn >= 0) { 304 if (n_dspl - 2 <= 127) 305 goto two_byte_jmp; 306 else 307 goto five_byte_jmp; 308 /* negative offset */ 309 } else { 310 if (((n_dspl - 2) & 0xff) == (n_dspl - 2)) 311 goto two_byte_jmp; 312 else 313 goto five_byte_jmp; 314 } 315 316 two_byte_jmp: 317 n_dspl -= 2; 318 319 insn_buff[0] = 0xeb; 320 insn_buff[1] = (s8)n_dspl; 321 add_nops(insn_buff + 2, 3); 322 323 repl_len = 2; 324 goto done; 325 326 five_byte_jmp: 327 n_dspl -= 5; 328 329 insn_buff[0] = 0xe9; 330 *(s32 *)&insn_buff[1] = n_dspl; 331 332 repl_len = 5; 333 334 done: 335 336 DPRINTK("final displ: 0x%08x, JMP 0x%lx", 337 n_dspl, (unsigned long)orig_insn + n_dspl + repl_len); 338 } 339 340 /* 341 * "noinline" to cause control flow change and thus invalidate I$ and 342 * cause refetch after modification. 343 */ 344 static void __init_or_module noinline optimize_nops(struct alt_instr *a, u8 *instr) 345 { 346 unsigned long flags; 347 int i; 348 349 for (i = 0; i < a->padlen; i++) { 350 if (instr[i] != 0x90) 351 return; 352 } 353 354 local_irq_save(flags); 355 add_nops(instr + (a->instrlen - a->padlen), a->padlen); 356 local_irq_restore(flags); 357 358 DUMP_BYTES(instr, a->instrlen, "%px: [%d:%d) optimized NOPs: ", 359 instr, a->instrlen - a->padlen, a->padlen); 360 } 361 362 /* 363 * Replace instructions with better alternatives for this CPU type. This runs 364 * before SMP is initialized to avoid SMP problems with self modifying code. 365 * This implies that asymmetric systems where APs have less capabilities than 366 * the boot processor are not handled. Tough. Make sure you disable such 367 * features by hand. 368 * 369 * Marked "noinline" to cause control flow change and thus insn cache 370 * to refetch changed I$ lines. 371 */ 372 void __init_or_module noinline apply_alternatives(struct alt_instr *start, 373 struct alt_instr *end) 374 { 375 struct alt_instr *a; 376 u8 *instr, *replacement; 377 u8 insn_buff[MAX_PATCH_LEN]; 378 379 DPRINTK("alt table %px, -> %px", start, end); 380 /* 381 * The scan order should be from start to end. A later scanned 382 * alternative code can overwrite previously scanned alternative code. 383 * Some kernel functions (e.g. memcpy, memset, etc) use this order to 384 * patch code. 385 * 386 * So be careful if you want to change the scan order to any other 387 * order. 388 */ 389 for (a = start; a < end; a++) { 390 int insn_buff_sz = 0; 391 392 instr = (u8 *)&a->instr_offset + a->instr_offset; 393 replacement = (u8 *)&a->repl_offset + a->repl_offset; 394 BUG_ON(a->instrlen > sizeof(insn_buff)); 395 BUG_ON(a->cpuid >= (NCAPINTS + NBUGINTS) * 32); 396 if (!boot_cpu_has(a->cpuid)) { 397 if (a->padlen > 1) 398 optimize_nops(a, instr); 399 400 continue; 401 } 402 403 DPRINTK("feat: %d*32+%d, old: (%pS (%px) len: %d), repl: (%px, len: %d), pad: %d", 404 a->cpuid >> 5, 405 a->cpuid & 0x1f, 406 instr, instr, a->instrlen, 407 replacement, a->replacementlen, a->padlen); 408 409 DUMP_BYTES(instr, a->instrlen, "%px: old_insn: ", instr); 410 DUMP_BYTES(replacement, a->replacementlen, "%px: rpl_insn: ", replacement); 411 412 memcpy(insn_buff, replacement, a->replacementlen); 413 insn_buff_sz = a->replacementlen; 414 415 /* 416 * 0xe8 is a relative jump; fix the offset. 417 * 418 * Instruction length is checked before the opcode to avoid 419 * accessing uninitialized bytes for zero-length replacements. 420 */ 421 if (a->replacementlen == 5 && *insn_buff == 0xe8) { 422 *(s32 *)(insn_buff + 1) += replacement - instr; 423 DPRINTK("Fix CALL offset: 0x%x, CALL 0x%lx", 424 *(s32 *)(insn_buff + 1), 425 (unsigned long)instr + *(s32 *)(insn_buff + 1) + 5); 426 } 427 428 if (a->replacementlen && is_jmp(replacement[0])) 429 recompute_jump(a, instr, replacement, insn_buff); 430 431 if (a->instrlen > a->replacementlen) { 432 add_nops(insn_buff + a->replacementlen, 433 a->instrlen - a->replacementlen); 434 insn_buff_sz += a->instrlen - a->replacementlen; 435 } 436 DUMP_BYTES(insn_buff, insn_buff_sz, "%px: final_insn: ", instr); 437 438 text_poke_early(instr, insn_buff, insn_buff_sz); 439 } 440 } 441 442 #ifdef CONFIG_SMP 443 static void alternatives_smp_lock(const s32 *start, const s32 *end, 444 u8 *text, u8 *text_end) 445 { 446 const s32 *poff; 447 448 for (poff = start; poff < end; poff++) { 449 u8 *ptr = (u8 *)poff + *poff; 450 451 if (!*poff || ptr < text || ptr >= text_end) 452 continue; 453 /* turn DS segment override prefix into lock prefix */ 454 if (*ptr == 0x3e) 455 text_poke(ptr, ((unsigned char []){0xf0}), 1); 456 } 457 } 458 459 static void alternatives_smp_unlock(const s32 *start, const s32 *end, 460 u8 *text, u8 *text_end) 461 { 462 const s32 *poff; 463 464 for (poff = start; poff < end; poff++) { 465 u8 *ptr = (u8 *)poff + *poff; 466 467 if (!*poff || ptr < text || ptr >= text_end) 468 continue; 469 /* turn lock prefix into DS segment override prefix */ 470 if (*ptr == 0xf0) 471 text_poke(ptr, ((unsigned char []){0x3E}), 1); 472 } 473 } 474 475 struct smp_alt_module { 476 /* what is this ??? */ 477 struct module *mod; 478 char *name; 479 480 /* ptrs to lock prefixes */ 481 const s32 *locks; 482 const s32 *locks_end; 483 484 /* .text segment, needed to avoid patching init code ;) */ 485 u8 *text; 486 u8 *text_end; 487 488 struct list_head next; 489 }; 490 static LIST_HEAD(smp_alt_modules); 491 static bool uniproc_patched = false; /* protected by text_mutex */ 492 493 void __init_or_module alternatives_smp_module_add(struct module *mod, 494 char *name, 495 void *locks, void *locks_end, 496 void *text, void *text_end) 497 { 498 struct smp_alt_module *smp; 499 500 mutex_lock(&text_mutex); 501 if (!uniproc_patched) 502 goto unlock; 503 504 if (num_possible_cpus() == 1) 505 /* Don't bother remembering, we'll never have to undo it. */ 506 goto smp_unlock; 507 508 smp = kzalloc(sizeof(*smp), GFP_KERNEL); 509 if (NULL == smp) 510 /* we'll run the (safe but slow) SMP code then ... */ 511 goto unlock; 512 513 smp->mod = mod; 514 smp->name = name; 515 smp->locks = locks; 516 smp->locks_end = locks_end; 517 smp->text = text; 518 smp->text_end = text_end; 519 DPRINTK("locks %p -> %p, text %p -> %p, name %s\n", 520 smp->locks, smp->locks_end, 521 smp->text, smp->text_end, smp->name); 522 523 list_add_tail(&smp->next, &smp_alt_modules); 524 smp_unlock: 525 alternatives_smp_unlock(locks, locks_end, text, text_end); 526 unlock: 527 mutex_unlock(&text_mutex); 528 } 529 530 void __init_or_module alternatives_smp_module_del(struct module *mod) 531 { 532 struct smp_alt_module *item; 533 534 mutex_lock(&text_mutex); 535 list_for_each_entry(item, &smp_alt_modules, next) { 536 if (mod != item->mod) 537 continue; 538 list_del(&item->next); 539 kfree(item); 540 break; 541 } 542 mutex_unlock(&text_mutex); 543 } 544 545 void alternatives_enable_smp(void) 546 { 547 struct smp_alt_module *mod; 548 549 /* Why bother if there are no other CPUs? */ 550 BUG_ON(num_possible_cpus() == 1); 551 552 mutex_lock(&text_mutex); 553 554 if (uniproc_patched) { 555 pr_info("switching to SMP code\n"); 556 BUG_ON(num_online_cpus() != 1); 557 clear_cpu_cap(&boot_cpu_data, X86_FEATURE_UP); 558 clear_cpu_cap(&cpu_data(0), X86_FEATURE_UP); 559 list_for_each_entry(mod, &smp_alt_modules, next) 560 alternatives_smp_lock(mod->locks, mod->locks_end, 561 mod->text, mod->text_end); 562 uniproc_patched = false; 563 } 564 mutex_unlock(&text_mutex); 565 } 566 567 /* 568 * Return 1 if the address range is reserved for SMP-alternatives. 569 * Must hold text_mutex. 570 */ 571 int alternatives_text_reserved(void *start, void *end) 572 { 573 struct smp_alt_module *mod; 574 const s32 *poff; 575 u8 *text_start = start; 576 u8 *text_end = end; 577 578 lockdep_assert_held(&text_mutex); 579 580 list_for_each_entry(mod, &smp_alt_modules, next) { 581 if (mod->text > text_end || mod->text_end < text_start) 582 continue; 583 for (poff = mod->locks; poff < mod->locks_end; poff++) { 584 const u8 *ptr = (const u8 *)poff + *poff; 585 586 if (text_start <= ptr && text_end > ptr) 587 return 1; 588 } 589 } 590 591 return 0; 592 } 593 #endif /* CONFIG_SMP */ 594 595 #ifdef CONFIG_PARAVIRT 596 void __init_or_module apply_paravirt(struct paravirt_patch_site *start, 597 struct paravirt_patch_site *end) 598 { 599 struct paravirt_patch_site *p; 600 char insn_buff[MAX_PATCH_LEN]; 601 602 for (p = start; p < end; p++) { 603 unsigned int used; 604 605 BUG_ON(p->len > MAX_PATCH_LEN); 606 /* prep the buffer with the original instructions */ 607 memcpy(insn_buff, p->instr, p->len); 608 used = pv_ops.init.patch(p->type, insn_buff, (unsigned long)p->instr, p->len); 609 610 BUG_ON(used > p->len); 611 612 /* Pad the rest with nops */ 613 add_nops(insn_buff + used, p->len - used); 614 text_poke_early(p->instr, insn_buff, p->len); 615 } 616 } 617 extern struct paravirt_patch_site __start_parainstructions[], 618 __stop_parainstructions[]; 619 #endif /* CONFIG_PARAVIRT */ 620 621 /* 622 * Self-test for the INT3 based CALL emulation code. 623 * 624 * This exercises int3_emulate_call() to make sure INT3 pt_regs are set up 625 * properly and that there is a stack gap between the INT3 frame and the 626 * previous context. Without this gap doing a virtual PUSH on the interrupted 627 * stack would corrupt the INT3 IRET frame. 628 * 629 * See entry_{32,64}.S for more details. 630 */ 631 632 /* 633 * We define the int3_magic() function in assembly to control the calling 634 * convention such that we can 'call' it from assembly. 635 */ 636 637 extern void int3_magic(unsigned int *ptr); /* defined in asm */ 638 639 asm ( 640 " .pushsection .init.text, \"ax\", @progbits\n" 641 " .type int3_magic, @function\n" 642 "int3_magic:\n" 643 " movl $1, (%" _ASM_ARG1 ")\n" 644 " ret\n" 645 " .size int3_magic, .-int3_magic\n" 646 " .popsection\n" 647 ); 648 649 extern __initdata unsigned long int3_selftest_ip; /* defined in asm below */ 650 651 static int __init 652 int3_exception_notify(struct notifier_block *self, unsigned long val, void *data) 653 { 654 struct die_args *args = data; 655 struct pt_regs *regs = args->regs; 656 657 if (!regs || user_mode(regs)) 658 return NOTIFY_DONE; 659 660 if (val != DIE_INT3) 661 return NOTIFY_DONE; 662 663 if (regs->ip - INT3_INSN_SIZE != int3_selftest_ip) 664 return NOTIFY_DONE; 665 666 int3_emulate_call(regs, (unsigned long)&int3_magic); 667 return NOTIFY_STOP; 668 } 669 670 static void __init int3_selftest(void) 671 { 672 static __initdata struct notifier_block int3_exception_nb = { 673 .notifier_call = int3_exception_notify, 674 .priority = INT_MAX-1, /* last */ 675 }; 676 unsigned int val = 0; 677 678 BUG_ON(register_die_notifier(&int3_exception_nb)); 679 680 /* 681 * Basically: int3_magic(&val); but really complicated :-) 682 * 683 * Stick the address of the INT3 instruction into int3_selftest_ip, 684 * then trigger the INT3, padded with NOPs to match a CALL instruction 685 * length. 686 */ 687 asm volatile ("1: int3; nop; nop; nop; nop\n\t" 688 ".pushsection .init.data,\"aw\"\n\t" 689 ".align " __ASM_SEL(4, 8) "\n\t" 690 ".type int3_selftest_ip, @object\n\t" 691 ".size int3_selftest_ip, " __ASM_SEL(4, 8) "\n\t" 692 "int3_selftest_ip:\n\t" 693 __ASM_SEL(.long, .quad) " 1b\n\t" 694 ".popsection\n\t" 695 : ASM_CALL_CONSTRAINT 696 : __ASM_SEL_RAW(a, D) (&val) 697 : "memory"); 698 699 BUG_ON(val != 1); 700 701 unregister_die_notifier(&int3_exception_nb); 702 } 703 704 void __init alternative_instructions(void) 705 { 706 int3_selftest(); 707 708 /* 709 * The patching is not fully atomic, so try to avoid local 710 * interruptions that might execute the to be patched code. 711 * Other CPUs are not running. 712 */ 713 stop_nmi(); 714 715 /* 716 * Don't stop machine check exceptions while patching. 717 * MCEs only happen when something got corrupted and in this 718 * case we must do something about the corruption. 719 * Ignoring it is worse than an unlikely patching race. 720 * Also machine checks tend to be broadcast and if one CPU 721 * goes into machine check the others follow quickly, so we don't 722 * expect a machine check to cause undue problems during to code 723 * patching. 724 */ 725 726 apply_alternatives(__alt_instructions, __alt_instructions_end); 727 728 #ifdef CONFIG_SMP 729 /* Patch to UP if other cpus not imminent. */ 730 if (!noreplace_smp && (num_present_cpus() == 1 || setup_max_cpus <= 1)) { 731 uniproc_patched = true; 732 alternatives_smp_module_add(NULL, "core kernel", 733 __smp_locks, __smp_locks_end, 734 _text, _etext); 735 } 736 737 if (!uniproc_patched || num_possible_cpus() == 1) { 738 free_init_pages("SMP alternatives", 739 (unsigned long)__smp_locks, 740 (unsigned long)__smp_locks_end); 741 } 742 #endif 743 744 apply_paravirt(__parainstructions, __parainstructions_end); 745 746 restart_nmi(); 747 alternatives_patched = 1; 748 } 749 750 /** 751 * text_poke_early - Update instructions on a live kernel at boot time 752 * @addr: address to modify 753 * @opcode: source of the copy 754 * @len: length to copy 755 * 756 * When you use this code to patch more than one byte of an instruction 757 * you need to make sure that other CPUs cannot execute this code in parallel. 758 * Also no thread must be currently preempted in the middle of these 759 * instructions. And on the local CPU you need to be protected against NMI or 760 * MCE handlers seeing an inconsistent instruction while you patch. 761 */ 762 void __init_or_module text_poke_early(void *addr, const void *opcode, 763 size_t len) 764 { 765 unsigned long flags; 766 767 if (boot_cpu_has(X86_FEATURE_NX) && 768 is_module_text_address((unsigned long)addr)) { 769 /* 770 * Modules text is marked initially as non-executable, so the 771 * code cannot be running and speculative code-fetches are 772 * prevented. Just change the code. 773 */ 774 memcpy(addr, opcode, len); 775 } else { 776 local_irq_save(flags); 777 memcpy(addr, opcode, len); 778 local_irq_restore(flags); 779 sync_core(); 780 781 /* 782 * Could also do a CLFLUSH here to speed up CPU recovery; but 783 * that causes hangs on some VIA CPUs. 784 */ 785 } 786 } 787 788 typedef struct { 789 struct mm_struct *mm; 790 } temp_mm_state_t; 791 792 /* 793 * Using a temporary mm allows to set temporary mappings that are not accessible 794 * by other CPUs. Such mappings are needed to perform sensitive memory writes 795 * that override the kernel memory protections (e.g., W^X), without exposing the 796 * temporary page-table mappings that are required for these write operations to 797 * other CPUs. Using a temporary mm also allows to avoid TLB shootdowns when the 798 * mapping is torn down. 799 * 800 * Context: The temporary mm needs to be used exclusively by a single core. To 801 * harden security IRQs must be disabled while the temporary mm is 802 * loaded, thereby preventing interrupt handler bugs from overriding 803 * the kernel memory protection. 804 */ 805 static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm) 806 { 807 temp_mm_state_t temp_state; 808 809 lockdep_assert_irqs_disabled(); 810 811 /* 812 * Make sure not to be in TLB lazy mode, as otherwise we'll end up 813 * with a stale address space WITHOUT being in lazy mode after 814 * restoring the previous mm. 815 */ 816 if (this_cpu_read(cpu_tlbstate.is_lazy)) 817 leave_mm(smp_processor_id()); 818 819 temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm); 820 switch_mm_irqs_off(NULL, mm, current); 821 822 /* 823 * If breakpoints are enabled, disable them while the temporary mm is 824 * used. Userspace might set up watchpoints on addresses that are used 825 * in the temporary mm, which would lead to wrong signals being sent or 826 * crashes. 827 * 828 * Note that breakpoints are not disabled selectively, which also causes 829 * kernel breakpoints (e.g., perf's) to be disabled. This might be 830 * undesirable, but still seems reasonable as the code that runs in the 831 * temporary mm should be short. 832 */ 833 if (hw_breakpoint_active()) 834 hw_breakpoint_disable(); 835 836 return temp_state; 837 } 838 839 static inline void unuse_temporary_mm(temp_mm_state_t prev_state) 840 { 841 lockdep_assert_irqs_disabled(); 842 switch_mm_irqs_off(NULL, prev_state.mm, current); 843 844 /* 845 * Restore the breakpoints if they were disabled before the temporary mm 846 * was loaded. 847 */ 848 if (hw_breakpoint_active()) 849 hw_breakpoint_restore(); 850 } 851 852 __ro_after_init struct mm_struct *poking_mm; 853 __ro_after_init unsigned long poking_addr; 854 855 static void *__text_poke(void *addr, const void *opcode, size_t len) 856 { 857 bool cross_page_boundary = offset_in_page(addr) + len > PAGE_SIZE; 858 struct page *pages[2] = {NULL}; 859 temp_mm_state_t prev; 860 unsigned long flags; 861 pte_t pte, *ptep; 862 spinlock_t *ptl; 863 pgprot_t pgprot; 864 865 /* 866 * While boot memory allocator is running we cannot use struct pages as 867 * they are not yet initialized. There is no way to recover. 868 */ 869 BUG_ON(!after_bootmem); 870 871 if (!core_kernel_text((unsigned long)addr)) { 872 pages[0] = vmalloc_to_page(addr); 873 if (cross_page_boundary) 874 pages[1] = vmalloc_to_page(addr + PAGE_SIZE); 875 } else { 876 pages[0] = virt_to_page(addr); 877 WARN_ON(!PageReserved(pages[0])); 878 if (cross_page_boundary) 879 pages[1] = virt_to_page(addr + PAGE_SIZE); 880 } 881 /* 882 * If something went wrong, crash and burn since recovery paths are not 883 * implemented. 884 */ 885 BUG_ON(!pages[0] || (cross_page_boundary && !pages[1])); 886 887 /* 888 * Map the page without the global bit, as TLB flushing is done with 889 * flush_tlb_mm_range(), which is intended for non-global PTEs. 890 */ 891 pgprot = __pgprot(pgprot_val(PAGE_KERNEL) & ~_PAGE_GLOBAL); 892 893 /* 894 * The lock is not really needed, but this allows to avoid open-coding. 895 */ 896 ptep = get_locked_pte(poking_mm, poking_addr, &ptl); 897 898 /* 899 * This must not fail; preallocated in poking_init(). 900 */ 901 VM_BUG_ON(!ptep); 902 903 local_irq_save(flags); 904 905 pte = mk_pte(pages[0], pgprot); 906 set_pte_at(poking_mm, poking_addr, ptep, pte); 907 908 if (cross_page_boundary) { 909 pte = mk_pte(pages[1], pgprot); 910 set_pte_at(poking_mm, poking_addr + PAGE_SIZE, ptep + 1, pte); 911 } 912 913 /* 914 * Loading the temporary mm behaves as a compiler barrier, which 915 * guarantees that the PTE will be set at the time memcpy() is done. 916 */ 917 prev = use_temporary_mm(poking_mm); 918 919 kasan_disable_current(); 920 memcpy((u8 *)poking_addr + offset_in_page(addr), opcode, len); 921 kasan_enable_current(); 922 923 /* 924 * Ensure that the PTE is only cleared after the instructions of memcpy 925 * were issued by using a compiler barrier. 926 */ 927 barrier(); 928 929 pte_clear(poking_mm, poking_addr, ptep); 930 if (cross_page_boundary) 931 pte_clear(poking_mm, poking_addr + PAGE_SIZE, ptep + 1); 932 933 /* 934 * Loading the previous page-table hierarchy requires a serializing 935 * instruction that already allows the core to see the updated version. 936 * Xen-PV is assumed to serialize execution in a similar manner. 937 */ 938 unuse_temporary_mm(prev); 939 940 /* 941 * Flushing the TLB might involve IPIs, which would require enabled 942 * IRQs, but not if the mm is not used, as it is in this point. 943 */ 944 flush_tlb_mm_range(poking_mm, poking_addr, poking_addr + 945 (cross_page_boundary ? 2 : 1) * PAGE_SIZE, 946 PAGE_SHIFT, false); 947 948 /* 949 * If the text does not match what we just wrote then something is 950 * fundamentally screwy; there's nothing we can really do about that. 951 */ 952 BUG_ON(memcmp(addr, opcode, len)); 953 954 local_irq_restore(flags); 955 pte_unmap_unlock(ptep, ptl); 956 return addr; 957 } 958 959 /** 960 * text_poke - Update instructions on a live kernel 961 * @addr: address to modify 962 * @opcode: source of the copy 963 * @len: length to copy 964 * 965 * Only atomic text poke/set should be allowed when not doing early patching. 966 * It means the size must be writable atomically and the address must be aligned 967 * in a way that permits an atomic write. It also makes sure we fit on a single 968 * page. 969 * 970 * Note that the caller must ensure that if the modified code is part of a 971 * module, the module would not be removed during poking. This can be achieved 972 * by registering a module notifier, and ordering module removal and patching 973 * trough a mutex. 974 */ 975 void *text_poke(void *addr, const void *opcode, size_t len) 976 { 977 lockdep_assert_held(&text_mutex); 978 979 return __text_poke(addr, opcode, len); 980 } 981 982 /** 983 * text_poke_kgdb - Update instructions on a live kernel by kgdb 984 * @addr: address to modify 985 * @opcode: source of the copy 986 * @len: length to copy 987 * 988 * Only atomic text poke/set should be allowed when not doing early patching. 989 * It means the size must be writable atomically and the address must be aligned 990 * in a way that permits an atomic write. It also makes sure we fit on a single 991 * page. 992 * 993 * Context: should only be used by kgdb, which ensures no other core is running, 994 * despite the fact it does not hold the text_mutex. 995 */ 996 void *text_poke_kgdb(void *addr, const void *opcode, size_t len) 997 { 998 return __text_poke(addr, opcode, len); 999 } 1000 1001 static void do_sync_core(void *info) 1002 { 1003 sync_core(); 1004 } 1005 1006 void text_poke_sync(void) 1007 { 1008 on_each_cpu(do_sync_core, NULL, 1); 1009 } 1010 1011 struct text_poke_loc { 1012 s32 rel_addr; /* addr := _stext + rel_addr */ 1013 s32 rel32; 1014 u8 opcode; 1015 const u8 text[POKE_MAX_OPCODE_SIZE]; 1016 u8 old; 1017 }; 1018 1019 struct bp_patching_desc { 1020 struct text_poke_loc *vec; 1021 int nr_entries; 1022 atomic_t refs; 1023 }; 1024 1025 static struct bp_patching_desc *bp_desc; 1026 1027 static __always_inline 1028 struct bp_patching_desc *try_get_desc(struct bp_patching_desc **descp) 1029 { 1030 struct bp_patching_desc *desc = __READ_ONCE(*descp); /* rcu_dereference */ 1031 1032 if (!desc || !arch_atomic_inc_not_zero(&desc->refs)) 1033 return NULL; 1034 1035 return desc; 1036 } 1037 1038 static __always_inline void put_desc(struct bp_patching_desc *desc) 1039 { 1040 smp_mb__before_atomic(); 1041 arch_atomic_dec(&desc->refs); 1042 } 1043 1044 static __always_inline void *text_poke_addr(struct text_poke_loc *tp) 1045 { 1046 return _stext + tp->rel_addr; 1047 } 1048 1049 static __always_inline int patch_cmp(const void *key, const void *elt) 1050 { 1051 struct text_poke_loc *tp = (struct text_poke_loc *) elt; 1052 1053 if (key < text_poke_addr(tp)) 1054 return -1; 1055 if (key > text_poke_addr(tp)) 1056 return 1; 1057 return 0; 1058 } 1059 1060 noinstr int poke_int3_handler(struct pt_regs *regs) 1061 { 1062 struct bp_patching_desc *desc; 1063 struct text_poke_loc *tp; 1064 int len, ret = 0; 1065 void *ip; 1066 1067 if (user_mode(regs)) 1068 return 0; 1069 1070 /* 1071 * Having observed our INT3 instruction, we now must observe 1072 * bp_desc: 1073 * 1074 * bp_desc = desc INT3 1075 * WMB RMB 1076 * write INT3 if (desc) 1077 */ 1078 smp_rmb(); 1079 1080 desc = try_get_desc(&bp_desc); 1081 if (!desc) 1082 return 0; 1083 1084 /* 1085 * Discount the INT3. See text_poke_bp_batch(). 1086 */ 1087 ip = (void *) regs->ip - INT3_INSN_SIZE; 1088 1089 /* 1090 * Skip the binary search if there is a single member in the vector. 1091 */ 1092 if (unlikely(desc->nr_entries > 1)) { 1093 tp = __inline_bsearch(ip, desc->vec, desc->nr_entries, 1094 sizeof(struct text_poke_loc), 1095 patch_cmp); 1096 if (!tp) 1097 goto out_put; 1098 } else { 1099 tp = desc->vec; 1100 if (text_poke_addr(tp) != ip) 1101 goto out_put; 1102 } 1103 1104 len = text_opcode_size(tp->opcode); 1105 ip += len; 1106 1107 switch (tp->opcode) { 1108 case INT3_INSN_OPCODE: 1109 /* 1110 * Someone poked an explicit INT3, they'll want to handle it, 1111 * do not consume. 1112 */ 1113 goto out_put; 1114 1115 case RET_INSN_OPCODE: 1116 int3_emulate_ret(regs); 1117 break; 1118 1119 case CALL_INSN_OPCODE: 1120 int3_emulate_call(regs, (long)ip + tp->rel32); 1121 break; 1122 1123 case JMP32_INSN_OPCODE: 1124 case JMP8_INSN_OPCODE: 1125 int3_emulate_jmp(regs, (long)ip + tp->rel32); 1126 break; 1127 1128 default: 1129 BUG(); 1130 } 1131 1132 ret = 1; 1133 1134 out_put: 1135 put_desc(desc); 1136 return ret; 1137 } 1138 1139 #define TP_VEC_MAX (PAGE_SIZE / sizeof(struct text_poke_loc)) 1140 static struct text_poke_loc tp_vec[TP_VEC_MAX]; 1141 static int tp_vec_nr; 1142 1143 /** 1144 * text_poke_bp_batch() -- update instructions on live kernel on SMP 1145 * @tp: vector of instructions to patch 1146 * @nr_entries: number of entries in the vector 1147 * 1148 * Modify multi-byte instruction by using int3 breakpoint on SMP. 1149 * We completely avoid stop_machine() here, and achieve the 1150 * synchronization using int3 breakpoint. 1151 * 1152 * The way it is done: 1153 * - For each entry in the vector: 1154 * - add a int3 trap to the address that will be patched 1155 * - sync cores 1156 * - For each entry in the vector: 1157 * - update all but the first byte of the patched range 1158 * - sync cores 1159 * - For each entry in the vector: 1160 * - replace the first byte (int3) by the first byte of 1161 * replacing opcode 1162 * - sync cores 1163 */ 1164 static void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries) 1165 { 1166 struct bp_patching_desc desc = { 1167 .vec = tp, 1168 .nr_entries = nr_entries, 1169 .refs = ATOMIC_INIT(1), 1170 }; 1171 unsigned char int3 = INT3_INSN_OPCODE; 1172 unsigned int i; 1173 int do_sync; 1174 1175 lockdep_assert_held(&text_mutex); 1176 1177 smp_store_release(&bp_desc, &desc); /* rcu_assign_pointer */ 1178 1179 /* 1180 * Corresponding read barrier in int3 notifier for making sure the 1181 * nr_entries and handler are correctly ordered wrt. patching. 1182 */ 1183 smp_wmb(); 1184 1185 /* 1186 * First step: add a int3 trap to the address that will be patched. 1187 */ 1188 for (i = 0; i < nr_entries; i++) { 1189 tp[i].old = *(u8 *)text_poke_addr(&tp[i]); 1190 text_poke(text_poke_addr(&tp[i]), &int3, INT3_INSN_SIZE); 1191 } 1192 1193 text_poke_sync(); 1194 1195 /* 1196 * Second step: update all but the first byte of the patched range. 1197 */ 1198 for (do_sync = 0, i = 0; i < nr_entries; i++) { 1199 u8 old[POKE_MAX_OPCODE_SIZE] = { tp[i].old, }; 1200 int len = text_opcode_size(tp[i].opcode); 1201 1202 if (len - INT3_INSN_SIZE > 0) { 1203 memcpy(old + INT3_INSN_SIZE, 1204 text_poke_addr(&tp[i]) + INT3_INSN_SIZE, 1205 len - INT3_INSN_SIZE); 1206 text_poke(text_poke_addr(&tp[i]) + INT3_INSN_SIZE, 1207 (const char *)tp[i].text + INT3_INSN_SIZE, 1208 len - INT3_INSN_SIZE); 1209 do_sync++; 1210 } 1211 1212 /* 1213 * Emit a perf event to record the text poke, primarily to 1214 * support Intel PT decoding which must walk the executable code 1215 * to reconstruct the trace. The flow up to here is: 1216 * - write INT3 byte 1217 * - IPI-SYNC 1218 * - write instruction tail 1219 * At this point the actual control flow will be through the 1220 * INT3 and handler and not hit the old or new instruction. 1221 * Intel PT outputs FUP/TIP packets for the INT3, so the flow 1222 * can still be decoded. Subsequently: 1223 * - emit RECORD_TEXT_POKE with the new instruction 1224 * - IPI-SYNC 1225 * - write first byte 1226 * - IPI-SYNC 1227 * So before the text poke event timestamp, the decoder will see 1228 * either the old instruction flow or FUP/TIP of INT3. After the 1229 * text poke event timestamp, the decoder will see either the 1230 * new instruction flow or FUP/TIP of INT3. Thus decoders can 1231 * use the timestamp as the point at which to modify the 1232 * executable code. 1233 * The old instruction is recorded so that the event can be 1234 * processed forwards or backwards. 1235 */ 1236 perf_event_text_poke(text_poke_addr(&tp[i]), old, len, 1237 tp[i].text, len); 1238 } 1239 1240 if (do_sync) { 1241 /* 1242 * According to Intel, this core syncing is very likely 1243 * not necessary and we'd be safe even without it. But 1244 * better safe than sorry (plus there's not only Intel). 1245 */ 1246 text_poke_sync(); 1247 } 1248 1249 /* 1250 * Third step: replace the first byte (int3) by the first byte of 1251 * replacing opcode. 1252 */ 1253 for (do_sync = 0, i = 0; i < nr_entries; i++) { 1254 if (tp[i].text[0] == INT3_INSN_OPCODE) 1255 continue; 1256 1257 text_poke(text_poke_addr(&tp[i]), tp[i].text, INT3_INSN_SIZE); 1258 do_sync++; 1259 } 1260 1261 if (do_sync) 1262 text_poke_sync(); 1263 1264 /* 1265 * Remove and synchronize_rcu(), except we have a very primitive 1266 * refcount based completion. 1267 */ 1268 WRITE_ONCE(bp_desc, NULL); /* RCU_INIT_POINTER */ 1269 if (!atomic_dec_and_test(&desc.refs)) 1270 atomic_cond_read_acquire(&desc.refs, !VAL); 1271 } 1272 1273 static void text_poke_loc_init(struct text_poke_loc *tp, void *addr, 1274 const void *opcode, size_t len, const void *emulate) 1275 { 1276 struct insn insn; 1277 1278 memcpy((void *)tp->text, opcode, len); 1279 if (!emulate) 1280 emulate = opcode; 1281 1282 kernel_insn_init(&insn, emulate, MAX_INSN_SIZE); 1283 insn_get_length(&insn); 1284 1285 BUG_ON(!insn_complete(&insn)); 1286 BUG_ON(len != insn.length); 1287 1288 tp->rel_addr = addr - (void *)_stext; 1289 tp->opcode = insn.opcode.bytes[0]; 1290 1291 switch (tp->opcode) { 1292 case INT3_INSN_OPCODE: 1293 case RET_INSN_OPCODE: 1294 break; 1295 1296 case CALL_INSN_OPCODE: 1297 case JMP32_INSN_OPCODE: 1298 case JMP8_INSN_OPCODE: 1299 tp->rel32 = insn.immediate.value; 1300 break; 1301 1302 default: /* assume NOP */ 1303 switch (len) { 1304 case 2: /* NOP2 -- emulate as JMP8+0 */ 1305 BUG_ON(memcmp(emulate, ideal_nops[len], len)); 1306 tp->opcode = JMP8_INSN_OPCODE; 1307 tp->rel32 = 0; 1308 break; 1309 1310 case 5: /* NOP5 -- emulate as JMP32+0 */ 1311 BUG_ON(memcmp(emulate, ideal_nops[NOP_ATOMIC5], len)); 1312 tp->opcode = JMP32_INSN_OPCODE; 1313 tp->rel32 = 0; 1314 break; 1315 1316 default: /* unknown instruction */ 1317 BUG(); 1318 } 1319 break; 1320 } 1321 } 1322 1323 /* 1324 * We hard rely on the tp_vec being ordered; ensure this is so by flushing 1325 * early if needed. 1326 */ 1327 static bool tp_order_fail(void *addr) 1328 { 1329 struct text_poke_loc *tp; 1330 1331 if (!tp_vec_nr) 1332 return false; 1333 1334 if (!addr) /* force */ 1335 return true; 1336 1337 tp = &tp_vec[tp_vec_nr - 1]; 1338 if ((unsigned long)text_poke_addr(tp) > (unsigned long)addr) 1339 return true; 1340 1341 return false; 1342 } 1343 1344 static void text_poke_flush(void *addr) 1345 { 1346 if (tp_vec_nr == TP_VEC_MAX || tp_order_fail(addr)) { 1347 text_poke_bp_batch(tp_vec, tp_vec_nr); 1348 tp_vec_nr = 0; 1349 } 1350 } 1351 1352 void text_poke_finish(void) 1353 { 1354 text_poke_flush(NULL); 1355 } 1356 1357 void __ref text_poke_queue(void *addr, const void *opcode, size_t len, const void *emulate) 1358 { 1359 struct text_poke_loc *tp; 1360 1361 if (unlikely(system_state == SYSTEM_BOOTING)) { 1362 text_poke_early(addr, opcode, len); 1363 return; 1364 } 1365 1366 text_poke_flush(addr); 1367 1368 tp = &tp_vec[tp_vec_nr++]; 1369 text_poke_loc_init(tp, addr, opcode, len, emulate); 1370 } 1371 1372 /** 1373 * text_poke_bp() -- update instructions on live kernel on SMP 1374 * @addr: address to patch 1375 * @opcode: opcode of new instruction 1376 * @len: length to copy 1377 * @emulate: instruction to be emulated 1378 * 1379 * Update a single instruction with the vector in the stack, avoiding 1380 * dynamically allocated memory. This function should be used when it is 1381 * not possible to allocate memory. 1382 */ 1383 void __ref text_poke_bp(void *addr, const void *opcode, size_t len, const void *emulate) 1384 { 1385 struct text_poke_loc tp; 1386 1387 if (unlikely(system_state == SYSTEM_BOOTING)) { 1388 text_poke_early(addr, opcode, len); 1389 return; 1390 } 1391 1392 text_poke_loc_init(&tp, addr, opcode, len, emulate); 1393 text_poke_bp_batch(&tp, 1); 1394 } 1395