1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * Kernel Probes Jump Optimization (Optprobes) 4 * 5 * Copyright (C) IBM Corporation, 2002, 2004 6 * Copyright (C) Hitachi Ltd., 2012 7 */ 8 #include <linux/kprobes.h> 9 #include <linux/perf_event.h> 10 #include <linux/ptrace.h> 11 #include <linux/string.h> 12 #include <linux/slab.h> 13 #include <linux/hardirq.h> 14 #include <linux/preempt.h> 15 #include <linux/extable.h> 16 #include <linux/kdebug.h> 17 #include <linux/kallsyms.h> 18 #include <linux/kgdb.h> 19 #include <linux/ftrace.h> 20 #include <linux/objtool.h> 21 #include <linux/pgtable.h> 22 #include <linux/static_call.h> 23 24 #include <asm/text-patching.h> 25 #include <asm/cacheflush.h> 26 #include <asm/desc.h> 27 #include <linux/uaccess.h> 28 #include <asm/alternative.h> 29 #include <asm/insn.h> 30 #include <asm/debugreg.h> 31 #include <asm/set_memory.h> 32 #include <asm/sections.h> 33 #include <asm/nospec-branch.h> 34 35 #include "common.h" 36 37 unsigned long __recover_optprobed_insn(kprobe_opcode_t *buf, unsigned long addr) 38 { 39 struct optimized_kprobe *op; 40 struct kprobe *kp; 41 long offs; 42 int i; 43 44 for (i = 0; i < JMP32_INSN_SIZE; i++) { 45 kp = get_kprobe((void *)addr - i); 46 /* This function only handles jump-optimized kprobe */ 47 if (kp && kprobe_optimized(kp)) { 48 op = container_of(kp, struct optimized_kprobe, kp); 49 /* If op is optimized or under unoptimizing */ 50 if (list_empty(&op->list) || optprobe_queued_unopt(op)) 51 goto found; 52 } 53 } 54 55 return addr; 56 found: 57 /* 58 * If the kprobe can be optimized, original bytes which can be 59 * overwritten by jump destination address. In this case, original 60 * bytes must be recovered from op->optinsn.copied_insn buffer. 61 */ 62 if (copy_from_kernel_nofault(buf, (void *)addr, 63 MAX_INSN_SIZE * sizeof(kprobe_opcode_t))) 64 return 0UL; 65 66 if (addr == (unsigned long)kp->addr) { 67 buf[0] = kp->opcode; 68 memcpy(buf + 1, op->optinsn.copied_insn, DISP32_SIZE); 69 } else { 70 offs = addr - (unsigned long)kp->addr - 1; 71 memcpy(buf, op->optinsn.copied_insn + offs, DISP32_SIZE - offs); 72 } 73 74 return (unsigned long)buf; 75 } 76 77 static void synthesize_clac(kprobe_opcode_t *addr) 78 { 79 /* 80 * Can't be static_cpu_has() due to how objtool treats this feature bit. 81 * This isn't a fast path anyway. 82 */ 83 if (!boot_cpu_has(X86_FEATURE_SMAP)) 84 return; 85 86 /* Replace the NOP3 with CLAC */ 87 addr[0] = 0x0f; 88 addr[1] = 0x01; 89 addr[2] = 0xca; 90 } 91 92 /* Insert a move instruction which sets a pointer to eax/rdi (1st arg). */ 93 static void synthesize_set_arg1(kprobe_opcode_t *addr, unsigned long val) 94 { 95 #ifdef CONFIG_X86_64 96 *addr++ = 0x48; 97 *addr++ = 0xbf; 98 #else 99 *addr++ = 0xb8; 100 #endif 101 *(unsigned long *)addr = val; 102 } 103 104 asm ( 105 ".pushsection .rodata\n" 106 "optprobe_template_func:\n" 107 ".global optprobe_template_entry\n" 108 "optprobe_template_entry:\n" 109 #ifdef CONFIG_X86_64 110 " pushq $" __stringify(__KERNEL_DS) "\n" 111 /* Save the 'sp - 8', this will be fixed later. */ 112 " pushq %rsp\n" 113 " pushfq\n" 114 ".global optprobe_template_clac\n" 115 "optprobe_template_clac:\n" 116 ASM_NOP3 117 SAVE_REGS_STRING 118 " movq %rsp, %rsi\n" 119 ".global optprobe_template_val\n" 120 "optprobe_template_val:\n" 121 ASM_NOP5 122 ASM_NOP5 123 ".global optprobe_template_call\n" 124 "optprobe_template_call:\n" 125 ASM_NOP5 126 /* Copy 'regs->flags' into 'regs->ss'. */ 127 " movq 18*8(%rsp), %rdx\n" 128 " movq %rdx, 20*8(%rsp)\n" 129 RESTORE_REGS_STRING 130 /* Skip 'regs->flags' and 'regs->sp'. */ 131 " addq $16, %rsp\n" 132 /* And pop flags register from 'regs->ss'. */ 133 " popfq\n" 134 #else /* CONFIG_X86_32 */ 135 " pushl %ss\n" 136 /* Save the 'sp - 4', this will be fixed later. */ 137 " pushl %esp\n" 138 " pushfl\n" 139 ".global optprobe_template_clac\n" 140 "optprobe_template_clac:\n" 141 ASM_NOP3 142 SAVE_REGS_STRING 143 " movl %esp, %edx\n" 144 ".global optprobe_template_val\n" 145 "optprobe_template_val:\n" 146 ASM_NOP5 147 ".global optprobe_template_call\n" 148 "optprobe_template_call:\n" 149 ASM_NOP5 150 /* Copy 'regs->flags' into 'regs->ss'. */ 151 " movl 14*4(%esp), %edx\n" 152 " movl %edx, 16*4(%esp)\n" 153 RESTORE_REGS_STRING 154 /* Skip 'regs->flags' and 'regs->sp'. */ 155 " addl $8, %esp\n" 156 /* And pop flags register from 'regs->ss'. */ 157 " popfl\n" 158 #endif 159 ".global optprobe_template_end\n" 160 "optprobe_template_end:\n" 161 ".popsection\n"); 162 163 void optprobe_template_func(void); 164 STACK_FRAME_NON_STANDARD(optprobe_template_func); 165 166 #define TMPL_CLAC_IDX \ 167 ((long)optprobe_template_clac - (long)optprobe_template_entry) 168 #define TMPL_MOVE_IDX \ 169 ((long)optprobe_template_val - (long)optprobe_template_entry) 170 #define TMPL_CALL_IDX \ 171 ((long)optprobe_template_call - (long)optprobe_template_entry) 172 #define TMPL_END_IDX \ 173 ((long)optprobe_template_end - (long)optprobe_template_entry) 174 175 /* Optimized kprobe call back function: called from optinsn */ 176 static void 177 optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs) 178 { 179 /* This is possible if op is under delayed unoptimizing */ 180 if (kprobe_disabled(&op->kp)) 181 return; 182 183 preempt_disable(); 184 if (kprobe_running()) { 185 kprobes_inc_nmissed_count(&op->kp); 186 } else { 187 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk(); 188 /* Adjust stack pointer */ 189 regs->sp += sizeof(long); 190 /* Save skipped registers */ 191 regs->cs = __KERNEL_CS; 192 #ifdef CONFIG_X86_32 193 regs->gs = 0; 194 #endif 195 regs->ip = (unsigned long)op->kp.addr + INT3_INSN_SIZE; 196 regs->orig_ax = ~0UL; 197 198 __this_cpu_write(current_kprobe, &op->kp); 199 kcb->kprobe_status = KPROBE_HIT_ACTIVE; 200 opt_pre_handler(&op->kp, regs); 201 __this_cpu_write(current_kprobe, NULL); 202 } 203 preempt_enable(); 204 } 205 NOKPROBE_SYMBOL(optimized_callback); 206 207 static int copy_optimized_instructions(u8 *dest, u8 *src, u8 *real) 208 { 209 struct insn insn; 210 int len = 0, ret; 211 212 while (len < JMP32_INSN_SIZE) { 213 ret = __copy_instruction(dest + len, src + len, real + len, &insn); 214 if (!ret || !can_boost(&insn, src + len)) 215 return -EINVAL; 216 len += ret; 217 } 218 /* Check whether the address range is reserved */ 219 if (ftrace_text_reserved(src, src + len - 1) || 220 alternatives_text_reserved(src, src + len - 1) || 221 jump_label_text_reserved(src, src + len - 1) || 222 static_call_text_reserved(src, src + len - 1)) 223 return -EBUSY; 224 225 return len; 226 } 227 228 /* Check whether insn is indirect jump */ 229 static int insn_is_indirect_jump(struct insn *insn) 230 { 231 return ((insn->opcode.bytes[0] == 0xff && 232 (X86_MODRM_REG(insn->modrm.value) & 6) == 4) || /* Jump */ 233 insn->opcode.bytes[0] == 0xea); /* Segment based jump */ 234 } 235 236 /* Check whether insn jumps into specified address range */ 237 static int insn_jump_into_range(struct insn *insn, unsigned long start, int len) 238 { 239 unsigned long target = 0; 240 241 switch (insn->opcode.bytes[0]) { 242 case 0xe0: /* loopne */ 243 case 0xe1: /* loope */ 244 case 0xe2: /* loop */ 245 case 0xe3: /* jcxz */ 246 case 0xe9: /* near relative jump */ 247 case 0xeb: /* short relative jump */ 248 break; 249 case 0x0f: 250 if ((insn->opcode.bytes[1] & 0xf0) == 0x80) /* jcc near */ 251 break; 252 return 0; 253 default: 254 if ((insn->opcode.bytes[0] & 0xf0) == 0x70) /* jcc short */ 255 break; 256 return 0; 257 } 258 target = (unsigned long)insn->next_byte + insn->immediate.value; 259 260 return (start <= target && target <= start + len); 261 } 262 263 /* Decode whole function to ensure any instructions don't jump into target */ 264 static int can_optimize(unsigned long paddr) 265 { 266 unsigned long addr, size = 0, offset = 0; 267 struct insn insn; 268 kprobe_opcode_t buf[MAX_INSN_SIZE]; 269 270 /* Lookup symbol including addr */ 271 if (!kallsyms_lookup_size_offset(paddr, &size, &offset)) 272 return 0; 273 274 /* 275 * Do not optimize in the entry code due to the unstable 276 * stack handling and registers setup. 277 */ 278 if (((paddr >= (unsigned long)__entry_text_start) && 279 (paddr < (unsigned long)__entry_text_end))) 280 return 0; 281 282 /* Check there is enough space for a relative jump. */ 283 if (size - offset < JMP32_INSN_SIZE) 284 return 0; 285 286 /* Decode instructions */ 287 addr = paddr - offset; 288 while (addr < paddr - offset + size) { /* Decode until function end */ 289 unsigned long recovered_insn; 290 int ret; 291 292 if (search_exception_tables(addr)) 293 /* 294 * Since some fixup code will jumps into this function, 295 * we can't optimize kprobe in this function. 296 */ 297 return 0; 298 recovered_insn = recover_probed_instruction(buf, addr); 299 if (!recovered_insn) 300 return 0; 301 302 ret = insn_decode_kernel(&insn, (void *)recovered_insn); 303 if (ret < 0) 304 return 0; 305 #ifdef CONFIG_KGDB 306 /* 307 * If there is a dynamically installed kgdb sw breakpoint, 308 * this function should not be probed. 309 */ 310 if (insn.opcode.bytes[0] == INT3_INSN_OPCODE && 311 kgdb_has_hit_break(addr)) 312 return 0; 313 #endif 314 /* Recover address */ 315 insn.kaddr = (void *)addr; 316 insn.next_byte = (void *)(addr + insn.length); 317 /* 318 * Check any instructions don't jump into target, indirectly or 319 * directly. 320 * 321 * The indirect case is present to handle a code with jump 322 * tables. When the kernel uses retpolines, the check should in 323 * theory additionally look for jumps to indirect thunks. 324 * However, the kernel built with retpolines or IBT has jump 325 * tables disabled so the check can be skipped altogether. 326 */ 327 if (!IS_ENABLED(CONFIG_MITIGATION_RETPOLINE) && 328 !IS_ENABLED(CONFIG_X86_KERNEL_IBT) && 329 insn_is_indirect_jump(&insn)) 330 return 0; 331 if (insn_jump_into_range(&insn, paddr + INT3_INSN_SIZE, 332 DISP32_SIZE)) 333 return 0; 334 addr += insn.length; 335 } 336 337 return 1; 338 } 339 340 /* Check optimized_kprobe can actually be optimized. */ 341 int arch_check_optimized_kprobe(struct optimized_kprobe *op) 342 { 343 int i; 344 struct kprobe *p; 345 346 for (i = 1; i < op->optinsn.size; i++) { 347 p = get_kprobe(op->kp.addr + i); 348 if (p && !kprobe_disarmed(p)) 349 return -EEXIST; 350 } 351 352 return 0; 353 } 354 355 /* Check the addr is within the optimized instructions. */ 356 int arch_within_optimized_kprobe(struct optimized_kprobe *op, 357 kprobe_opcode_t *addr) 358 { 359 return (op->kp.addr <= addr && 360 op->kp.addr + op->optinsn.size > addr); 361 } 362 363 /* Free optimized instruction slot */ 364 static 365 void __arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty) 366 { 367 u8 *slot = op->optinsn.insn; 368 if (slot) { 369 int len = TMPL_END_IDX + op->optinsn.size + JMP32_INSN_SIZE; 370 371 /* Record the perf event before freeing the slot */ 372 if (dirty) 373 perf_event_text_poke(slot, slot, len, NULL, 0); 374 375 free_optinsn_slot(slot, dirty); 376 op->optinsn.insn = NULL; 377 op->optinsn.size = 0; 378 } 379 } 380 381 void arch_remove_optimized_kprobe(struct optimized_kprobe *op) 382 { 383 __arch_remove_optimized_kprobe(op, 1); 384 } 385 386 /* 387 * Copy replacing target instructions 388 * Target instructions MUST be relocatable (checked inside) 389 * This is called when new aggr(opt)probe is allocated or reused. 390 */ 391 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, 392 struct kprobe *__unused) 393 { 394 u8 *buf = NULL, *slot; 395 int ret, len; 396 long rel; 397 398 if (!can_optimize((unsigned long)op->kp.addr)) 399 return -EILSEQ; 400 401 buf = kzalloc(MAX_OPTINSN_SIZE, GFP_KERNEL); 402 if (!buf) 403 return -ENOMEM; 404 405 op->optinsn.insn = slot = get_optinsn_slot(); 406 if (!slot) { 407 ret = -ENOMEM; 408 goto out; 409 } 410 411 /* 412 * Verify if the address gap is in 2GB range, because this uses 413 * a relative jump. 414 */ 415 rel = (long)slot - (long)op->kp.addr + JMP32_INSN_SIZE; 416 if (abs(rel) > 0x7fffffff) { 417 ret = -ERANGE; 418 goto err; 419 } 420 421 /* Copy arch-dep-instance from template */ 422 memcpy(buf, optprobe_template_entry, TMPL_END_IDX); 423 424 /* Copy instructions into the out-of-line buffer */ 425 ret = copy_optimized_instructions(buf + TMPL_END_IDX, op->kp.addr, 426 slot + TMPL_END_IDX); 427 if (ret < 0) 428 goto err; 429 op->optinsn.size = ret; 430 len = TMPL_END_IDX + op->optinsn.size; 431 432 synthesize_clac(buf + TMPL_CLAC_IDX); 433 434 /* Set probe information */ 435 synthesize_set_arg1(buf + TMPL_MOVE_IDX, (unsigned long)op); 436 437 /* Set probe function call */ 438 synthesize_relcall(buf + TMPL_CALL_IDX, 439 slot + TMPL_CALL_IDX, optimized_callback); 440 441 /* Set returning jmp instruction at the tail of out-of-line buffer */ 442 synthesize_reljump(buf + len, slot + len, 443 (u8 *)op->kp.addr + op->optinsn.size); 444 len += JMP32_INSN_SIZE; 445 446 /* 447 * Note len = TMPL_END_IDX + op->optinsn.size + JMP32_INSN_SIZE is also 448 * used in __arch_remove_optimized_kprobe(). 449 */ 450 451 /* We have to use text_poke() for instruction buffer because it is RO */ 452 perf_event_text_poke(slot, NULL, 0, buf, len); 453 text_poke(slot, buf, len); 454 455 ret = 0; 456 out: 457 kfree(buf); 458 return ret; 459 460 err: 461 __arch_remove_optimized_kprobe(op, 0); 462 goto out; 463 } 464 465 /* 466 * Replace breakpoints (INT3) with relative jumps (JMP.d32). 467 * Caller must call with locking kprobe_mutex and text_mutex. 468 * 469 * The caller will have installed a regular kprobe and after that issued 470 * syncrhonize_rcu_tasks(), this ensures that the instruction(s) that live in 471 * the 4 bytes after the INT3 are unused and can now be overwritten. 472 */ 473 void arch_optimize_kprobes(struct list_head *oplist) 474 { 475 struct optimized_kprobe *op, *tmp; 476 u8 insn_buff[JMP32_INSN_SIZE]; 477 478 list_for_each_entry_safe(op, tmp, oplist, list) { 479 s32 rel = (s32)((long)op->optinsn.insn - 480 ((long)op->kp.addr + JMP32_INSN_SIZE)); 481 482 WARN_ON(kprobe_disabled(&op->kp)); 483 484 /* Backup instructions which will be replaced by jump address */ 485 memcpy(op->optinsn.copied_insn, op->kp.addr + INT3_INSN_SIZE, 486 DISP32_SIZE); 487 488 insn_buff[0] = JMP32_INSN_OPCODE; 489 *(s32 *)(&insn_buff[1]) = rel; 490 491 text_poke_bp(op->kp.addr, insn_buff, JMP32_INSN_SIZE, NULL); 492 493 list_del_init(&op->list); 494 } 495 } 496 497 /* 498 * Replace a relative jump (JMP.d32) with a breakpoint (INT3). 499 * 500 * After that, we can restore the 4 bytes after the INT3 to undo what 501 * arch_optimize_kprobes() scribbled. This is safe since those bytes will be 502 * unused once the INT3 lands. 503 */ 504 void arch_unoptimize_kprobe(struct optimized_kprobe *op) 505 { 506 u8 new[JMP32_INSN_SIZE] = { INT3_INSN_OPCODE, }; 507 u8 old[JMP32_INSN_SIZE]; 508 u8 *addr = op->kp.addr; 509 510 memcpy(old, op->kp.addr, JMP32_INSN_SIZE); 511 memcpy(new + INT3_INSN_SIZE, 512 op->optinsn.copied_insn, 513 JMP32_INSN_SIZE - INT3_INSN_SIZE); 514 515 text_poke(addr, new, INT3_INSN_SIZE); 516 text_poke_sync(); 517 text_poke(addr + INT3_INSN_SIZE, 518 new + INT3_INSN_SIZE, 519 JMP32_INSN_SIZE - INT3_INSN_SIZE); 520 text_poke_sync(); 521 522 perf_event_text_poke(op->kp.addr, old, JMP32_INSN_SIZE, new, JMP32_INSN_SIZE); 523 } 524 525 /* 526 * Recover original instructions and breakpoints from relative jumps. 527 * Caller must call with locking kprobe_mutex. 528 */ 529 extern void arch_unoptimize_kprobes(struct list_head *oplist, 530 struct list_head *done_list) 531 { 532 struct optimized_kprobe *op, *tmp; 533 534 list_for_each_entry_safe(op, tmp, oplist, list) { 535 arch_unoptimize_kprobe(op); 536 list_move(&op->list, done_list); 537 } 538 } 539 540 int setup_detour_execution(struct kprobe *p, struct pt_regs *regs, int reenter) 541 { 542 struct optimized_kprobe *op; 543 544 if (p->flags & KPROBE_FLAG_OPTIMIZED) { 545 /* This kprobe is really able to run optimized path. */ 546 op = container_of(p, struct optimized_kprobe, kp); 547 /* Detour through copied instructions */ 548 regs->ip = (unsigned long)op->optinsn.insn + TMPL_END_IDX; 549 if (!reenter) 550 reset_current_kprobe(); 551 return 1; 552 } 553 return 0; 554 } 555 NOKPROBE_SYMBOL(setup_detour_execution); 556