arch/powerpc/kernel/kprobes.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  *  Kernel Probes (KProbes)
   4  *
   5  * Copyright (C) IBM Corporation, 2002, 2004
   6  *
   7  * 2002-Oct     Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
   8  *              Probes initial implementation ( includes contributions from
   9  *              Rusty Russell).
  10  * 2004-July    Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
  11  *              interface to access function arguments.
  12  * 2004-Nov     Ananth N Mavinakayanahalli <ananth@in.ibm.com> kprobes port
  13  *              for PPC64
  14  */
  15
  16 #include <linux/kprobes.h>
  17 #include <linux/ptrace.h>
  18 #include <linux/preempt.h>
  19 #include <linux/extable.h>
  20 #include <linux/kdebug.h>
  21 #include <linux/slab.h>
  22 #include <asm/code-patching.h>
  23 #include <asm/cacheflush.h>
  24 #include <asm/sstep.h>
  25 #include <asm/sections.h>
  26 #include <asm/inst.h>
  27 #include <linux/uaccess.h>
  28
  29 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  30 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  31
  32 struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
  33
  34 bool arch_within_kprobe_blacklist(unsigned long addr)
  35 {
  36         return  (addr >= (unsigned long)__kprobes_text_start &&
  37                  addr < (unsigned long)__kprobes_text_end) ||
  38                 (addr >= (unsigned long)_stext &&
  39                  addr < (unsigned long)__head_end);
  40 }
  41
  42 kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
  43 {
  44         kprobe_opcode_t *addr = NULL;
  45
  46 #ifdef PPC64_ELF_ABI_v2
  47         /* PPC64 ABIv2 needs local entry point */
  48         addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
  49         if (addr && !offset) {
  50 #ifdef CONFIG_KPROBES_ON_FTRACE
  51                 unsigned long faddr;
  52                 /*
  53                  * Per livepatch.h, ftrace location is always within the first
  54                  * 16 bytes of a function on powerpc with -mprofile-kernel.
  55                  */
  56                 faddr = ftrace_location_range((unsigned long)addr,
  57                                               (unsigned long)addr + 16);
  58                 if (faddr)
  59                         addr = (kprobe_opcode_t *)faddr;
  60                 else
  61 #endif
  62                         addr = (kprobe_opcode_t *)ppc_function_entry(addr);
  63         }
  64 #elif defined(PPC64_ELF_ABI_v1)
  65         /*
  66          * 64bit powerpc ABIv1 uses function descriptors:
  67          * - Check for the dot variant of the symbol first.
  68          * - If that fails, try looking up the symbol provided.
  69          *
  70          * This ensures we always get to the actual symbol and not
  71          * the descriptor.
  72          *
  73          * Also handle <module:symbol> format.
  74          */
  75         char dot_name[MODULE_NAME_LEN + 1 + KSYM_NAME_LEN];
  76         bool dot_appended = false;
  77         const char *c;
  78         ssize_t ret = 0;
  79         int len = 0;
  80
  81         if ((c = strnchr(name, MODULE_NAME_LEN, ':')) != NULL) {
  82                 c++;
  83                 len = c - name;
  84                 memcpy(dot_name, name, len);
  85         } else
  86                 c = name;
  87
  88         if (*c != '\0' && *c != '.') {
  89                 dot_name[len++] = '.';
  90                 dot_appended = true;
  91         }
  92         ret = strscpy(dot_name + len, c, KSYM_NAME_LEN);
  93         if (ret > 0)
  94                 addr = (kprobe_opcode_t *)kallsyms_lookup_name(dot_name);
  95
  96         /* Fallback to the original non-dot symbol lookup */
  97         if (!addr && dot_appended)
  98                 addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
  99 #else
 100         addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
 101 #endif
 102
 103         return addr;
 104 }
 105
 106 int arch_prepare_kprobe(struct kprobe *p)
 107 {
 108         int ret = 0;
 109         struct kprobe *prev;
 110         struct ppc_inst insn = ppc_inst_read((struct ppc_inst *)p->addr);
 111
 112         if ((unsigned long)p->addr & 0x03) {
 113                 printk("Attempt to register kprobe at an unaligned address\n");
 114                 ret = -EINVAL;
 115         } else if (IS_MTMSRD(insn) || IS_RFID(insn) || IS_RFI(insn)) {
 116                 printk("Cannot register a kprobe on rfi/rfid or mtmsr[d]\n");
 117                 ret = -EINVAL;
 118         } else if ((unsigned long)p->addr & ~PAGE_MASK &&
 119                    ppc_inst_prefixed(ppc_inst_read((struct ppc_inst *)(p->addr - 1)))) {
 120                 printk("Cannot register a kprobe on the second word of prefixed instruction\n");
 121                 ret = -EINVAL;
 122         }
 123         preempt_disable();
 124         prev = get_kprobe(p->addr - 1);
 125         preempt_enable_no_resched();
 126         if (prev &&
 127             ppc_inst_prefixed(ppc_inst_read((struct ppc_inst *)prev->ainsn.insn))) {
 128                 printk("Cannot register a kprobe on the second word of prefixed instruction\n");
 129                 ret = -EINVAL;
 130         }
 131
 132         /* insn must be on a special executable page on ppc64.  This is
 133          * not explicitly required on ppc32 (right now), but it doesn't hurt */
 134         if (!ret) {
 135                 p->ainsn.insn = get_insn_slot();
 136                 if (!p->ainsn.insn)
 137                         ret = -ENOMEM;
 138         }
 139
 140         if (!ret) {
 141                 patch_instruction((struct ppc_inst *)p->ainsn.insn, insn);
 142                 p->opcode = ppc_inst_val(insn);
 143         }
 144
 145         p->ainsn.boostable = 0;
 146         return ret;
 147 }
 148 NOKPROBE_SYMBOL(arch_prepare_kprobe);
 149
 150 void arch_arm_kprobe(struct kprobe *p)
 151 {
 152         patch_instruction((struct ppc_inst *)p->addr, ppc_inst(BREAKPOINT_INSTRUCTION));
 153 }
 154 NOKPROBE_SYMBOL(arch_arm_kprobe);
 155
 156 void arch_disarm_kprobe(struct kprobe *p)
 157 {
 158         patch_instruction((struct ppc_inst *)p->addr, ppc_inst(p->opcode));
 159 }
 160 NOKPROBE_SYMBOL(arch_disarm_kprobe);
 161
 162 void arch_remove_kprobe(struct kprobe *p)
 163 {
 164         if (p->ainsn.insn) {
 165                 free_insn_slot(p->ainsn.insn, 0);
 166                 p->ainsn.insn = NULL;
 167         }
 168 }
 169 NOKPROBE_SYMBOL(arch_remove_kprobe);
 170
 171 static nokprobe_inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 172 {
 173         enable_single_step(regs);
 174
 175         /*
 176          * On powerpc we should single step on the original
 177          * instruction even if the probed insn is a trap
 178          * variant as values in regs could play a part in
 179          * if the trap is taken or not
 180          */
 181         regs->nip = (unsigned long)p->ainsn.insn;
 182 }
 183
 184 static nokprobe_inline void save_previous_kprobe(struct kprobe_ctlblk *kcb)
 185 {
 186         kcb->prev_kprobe.kp = kprobe_running();
 187         kcb->prev_kprobe.status = kcb->kprobe_status;
 188         kcb->prev_kprobe.saved_msr = kcb->kprobe_saved_msr;
 189 }
 190
 191 static nokprobe_inline void restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 192 {
 193         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 194         kcb->kprobe_status = kcb->prev_kprobe.status;
 195         kcb->kprobe_saved_msr = kcb->prev_kprobe.saved_msr;
 196 }
 197
 198 static nokprobe_inline void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
 199                                 struct kprobe_ctlblk *kcb)
 200 {
 201         __this_cpu_write(current_kprobe, p);
 202         kcb->kprobe_saved_msr = regs->msr;
 203 }
 204
 205 bool arch_kprobe_on_func_entry(unsigned long offset)
 206 {
 207 #ifdef PPC64_ELF_ABI_v2
 208 #ifdef CONFIG_KPROBES_ON_FTRACE
 209         return offset <= 16;
 210 #else
 211         return offset <= 8;
 212 #endif
 213 #else
 214         return !offset;
 215 #endif
 216 }
 217
 218 void arch_prepare_kretprobe(struct kretprobe_instance *ri, struct pt_regs *regs)
 219 {
 220         ri->ret_addr = (kprobe_opcode_t *)regs->link;
 221         ri->fp = NULL;
 222
 223         /* Replace the return addr with trampoline addr */
 224         regs->link = (unsigned long)kretprobe_trampoline;
 225 }
 226 NOKPROBE_SYMBOL(arch_prepare_kretprobe);
 227
 228 static int try_to_emulate(struct kprobe *p, struct pt_regs *regs)
 229 {
 230         int ret;
 231         struct ppc_inst insn = ppc_inst_read((struct ppc_inst *)p->ainsn.insn);
 232
 233         /* regs->nip is also adjusted if emulate_step returns 1 */
 234         ret = emulate_step(regs, insn);
 235         if (ret > 0) {
 236                 /*
 237                  * Once this instruction has been boosted
 238                  * successfully, set the boostable flag
 239                  */
 240                 if (unlikely(p->ainsn.boostable == 0))
 241                         p->ainsn.boostable = 1;
 242         } else if (ret < 0) {
 243                 /*
 244                  * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
 245                  * So, we should never get here... but, its still
 246                  * good to catch them, just in case...
 247                  */
 248                 printk("Can't step on instruction %s\n", ppc_inst_as_str(insn));
 249                 BUG();
 250         } else {
 251                 /*
 252                  * If we haven't previously emulated this instruction, then it
 253                  * can't be boosted. Note it down so we don't try to do so again.
 254                  *
 255                  * If, however, we had emulated this instruction in the past,
 256                  * then this is just an error with the current run (for
 257                  * instance, exceptions due to a load/store). We return 0 so
 258                  * that this is now single-stepped, but continue to try
 259                  * emulating it in subsequent probe hits.
 260                  */
 261                 if (unlikely(p->ainsn.boostable != 1))
 262                         p->ainsn.boostable = -1;
 263         }
 264
 265         return ret;
 266 }
 267 NOKPROBE_SYMBOL(try_to_emulate);
 268
 269 int kprobe_handler(struct pt_regs *regs)
 270 {
 271         struct kprobe *p;
 272         int ret = 0;
 273         unsigned int *addr = (unsigned int *)regs->nip;
 274         struct kprobe_ctlblk *kcb;
 275
 276         if (user_mode(regs))
 277                 return 0;
 278
 279         if (!(regs->msr & MSR_IR) || !(regs->msr & MSR_DR))
 280                 return 0;
 281
 282         /*
 283          * We don't want to be preempted for the entire
 284          * duration of kprobe processing
 285          */
 286         preempt_disable();
 287         kcb = get_kprobe_ctlblk();
 288
 289         p = get_kprobe(addr);
 290         if (!p) {
 291                 unsigned int instr;
 292
 293                 if (get_kernel_nofault(instr, addr))
 294                         goto no_kprobe;
 295
 296                 if (instr != BREAKPOINT_INSTRUCTION) {
 297                         /*
 298                          * PowerPC has multiple variants of the "trap"
 299                          * instruction. If the current instruction is a
 300                          * trap variant, it could belong to someone else
 301                          */
 302                         if (is_trap(instr))
 303                                 goto no_kprobe;
 304                         /*
 305                          * The breakpoint instruction was removed right
 306                          * after we hit it.  Another cpu has removed
 307                          * either a probepoint or a debugger breakpoint
 308                          * at this address.  In either case, no further
 309                          * handling of this interrupt is appropriate.
 310                          */
 311                         ret = 1;
 312                 }
 313                 /* Not one of ours: let kernel handle it */
 314                 goto no_kprobe;
 315         }
 316
 317         /* Check we're not actually recursing */
 318         if (kprobe_running()) {
 319                 kprobe_opcode_t insn = *p->ainsn.insn;
 320                 if (kcb->kprobe_status == KPROBE_HIT_SS && is_trap(insn)) {
 321                         /* Turn off 'trace' bits */
 322                         regs->msr &= ~MSR_SINGLESTEP;
 323                         regs->msr |= kcb->kprobe_saved_msr;
 324                         goto no_kprobe;
 325                 }
 326
 327                 /*
 328                  * We have reentered the kprobe_handler(), since another probe
 329                  * was hit while within the handler. We here save the original
 330                  * kprobes variables and just single step on the instruction of
 331                  * the new probe without calling any user handlers.
 332                  */
 333                 save_previous_kprobe(kcb);
 334                 set_current_kprobe(p, regs, kcb);
 335                 kprobes_inc_nmissed_count(p);
 336                 kcb->kprobe_status = KPROBE_REENTER;
 337                 if (p->ainsn.boostable >= 0) {
 338                         ret = try_to_emulate(p, regs);
 339
 340                         if (ret > 0) {
 341                                 restore_previous_kprobe(kcb);
 342                                 preempt_enable_no_resched();
 343                                 return 1;
 344                         }
 345                 }
 346                 prepare_singlestep(p, regs);
 347                 return 1;
 348         }
 349
 350         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 351         set_current_kprobe(p, regs, kcb);
 352         if (p->pre_handler && p->pre_handler(p, regs)) {
 353                 /* handler changed execution path, so skip ss setup */
 354                 reset_current_kprobe();
 355                 preempt_enable_no_resched();
 356                 return 1;
 357         }
 358
 359         if (p->ainsn.boostable >= 0) {
 360                 ret = try_to_emulate(p, regs);
 361
 362                 if (ret > 0) {
 363                         if (p->post_handler)
 364                                 p->post_handler(p, regs, 0);
 365
 366                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 367                         reset_current_kprobe();
 368                         preempt_enable_no_resched();
 369                         return 1;
 370                 }
 371         }
 372         prepare_singlestep(p, regs);
 373         kcb->kprobe_status = KPROBE_HIT_SS;
 374         return 1;
 375
 376 no_kprobe:
 377         preempt_enable_no_resched();
 378         return ret;
 379 }
 380 NOKPROBE_SYMBOL(kprobe_handler);
 381
 382 /*
 383  * Function return probe trampoline:
 384  *      - init_kprobes() establishes a probepoint here
 385  *      - When the probed function returns, this probe
 386  *              causes the handlers to fire
 387  */
 388 asm(".global kretprobe_trampoline\n"
 389         ".type kretprobe_trampoline, @function\n"
 390         "kretprobe_trampoline:\n"
 391         "nop\n"
 392         "blr\n"
 393         ".size kretprobe_trampoline, .-kretprobe_trampoline\n");
 394
 395 /*
 396  * Called when the probe at kretprobe trampoline is hit
 397  */
 398 static int trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
 399 {
 400         unsigned long orig_ret_address;
 401
 402         orig_ret_address = __kretprobe_trampoline_handler(regs, &kretprobe_trampoline, NULL);
 403         /*
 404          * We get here through one of two paths:
 405          * 1. by taking a trap -> kprobe_handler() -> here
 406          * 2. by optprobe branch -> optimized_callback() -> opt_pre_handler() -> here
 407          *
 408          * When going back through (1), we need regs->nip to be setup properly
 409          * as it is used to determine the return address from the trap.
 410          * For (2), since nip is not honoured with optprobes, we instead setup
 411          * the link register properly so that the subsequent 'blr' in
 412          * kretprobe_trampoline jumps back to the right instruction.
 413          *
 414          * For nip, we should set the address to the previous instruction since
 415          * we end up emulating it in kprobe_handler(), which increments the nip
 416          * again.
 417          */
 418         regs->nip = orig_ret_address - 4;
 419         regs->link = orig_ret_address;
 420
 421         return 0;
 422 }
 423 NOKPROBE_SYMBOL(trampoline_probe_handler);
 424
 425 /*
 426  * Called after single-stepping.  p->addr is the address of the
 427  * instruction whose first byte has been replaced by the "breakpoint"
 428  * instruction.  To avoid the SMP problems that can occur when we
 429  * temporarily put back the original opcode to single-step, we
 430  * single-stepped a copy of the instruction.  The address of this
 431  * copy is p->ainsn.insn.
 432  */
 433 int kprobe_post_handler(struct pt_regs *regs)
 434 {
 435         int len;
 436         struct kprobe *cur = kprobe_running();
 437         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 438
 439         if (!cur || user_mode(regs))
 440                 return 0;
 441
 442         len = ppc_inst_len(ppc_inst_read((struct ppc_inst *)cur->ainsn.insn));
 443         /* make sure we got here for instruction we have a kprobe on */
 444         if (((unsigned long)cur->ainsn.insn + len) != regs->nip)
 445                 return 0;
 446
 447         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
 448                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
 449                 cur->post_handler(cur, regs, 0);
 450         }
 451
 452         /* Adjust nip to after the single-stepped instruction */
 453         regs->nip = (unsigned long)cur->addr + len;
 454         regs->msr |= kcb->kprobe_saved_msr;
 455
 456         /*Restore back the original saved kprobes variables and continue. */
 457         if (kcb->kprobe_status == KPROBE_REENTER) {
 458                 restore_previous_kprobe(kcb);
 459                 goto out;
 460         }
 461         reset_current_kprobe();
 462 out:
 463         preempt_enable_no_resched();
 464
 465         /*
 466          * if somebody else is singlestepping across a probe point, msr
 467          * will have DE/SE set, in which case, continue the remaining processing
 468          * of do_debug, as if this is not a probe hit.
 469          */
 470         if (regs->msr & MSR_SINGLESTEP)
 471                 return 0;
 472
 473         return 1;
 474 }
 475 NOKPROBE_SYMBOL(kprobe_post_handler);
 476
 477 int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 478 {
 479         struct kprobe *cur = kprobe_running();
 480         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 481         const struct exception_table_entry *entry;
 482
 483         switch(kcb->kprobe_status) {
 484         case KPROBE_HIT_SS:
 485         case KPROBE_REENTER:
 486                 /*
 487                  * We are here because the instruction being single
 488                  * stepped caused a page fault. We reset the current
 489                  * kprobe and the nip points back to the probe address
 490                  * and allow the page fault handler to continue as a
 491                  * normal page fault.
 492                  */
 493                 regs->nip = (unsigned long)cur->addr;
 494                 regs->msr &= ~MSR_SINGLESTEP; /* Turn off 'trace' bits */
 495                 regs->msr |= kcb->kprobe_saved_msr;
 496                 if (kcb->kprobe_status == KPROBE_REENTER)
 497                         restore_previous_kprobe(kcb);
 498                 else
 499                         reset_current_kprobe();
 500                 preempt_enable_no_resched();
 501                 break;
 502         case KPROBE_HIT_ACTIVE:
 503         case KPROBE_HIT_SSDONE:
 504                 /*
 505                  * We increment the nmissed count for accounting,
 506                  * we can also use npre/npostfault count for accounting
 507                  * these specific fault cases.
 508                  */
 509                 kprobes_inc_nmissed_count(cur);
 510
 511                 /*
 512                  * We come here because instructions in the pre/post
 513                  * handler caused the page_fault, this could happen
 514                  * if handler tries to access user space by
 515                  * copy_from_user(), get_user() etc. Let the
 516                  * user-specified handler try to fix it first.
 517                  */
 518                 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
 519                         return 1;
 520
 521                 /*
 522                  * In case the user-specified fault handler returned
 523                  * zero, try to fix up.
 524                  */
 525                 if ((entry = search_exception_tables(regs->nip)) != NULL) {
 526                         regs->nip = extable_fixup(entry);
 527                         return 1;
 528                 }
 529
 530                 /*
 531                  * fixup_exception() could not handle it,
 532                  * Let do_page_fault() fix it.
 533                  */
 534                 break;
 535         default:
 536                 break;
 537         }
 538         return 0;
 539 }
 540 NOKPROBE_SYMBOL(kprobe_fault_handler);
 541
 542 unsigned long arch_deref_entry_point(void *entry)
 543 {
 544 #ifdef PPC64_ELF_ABI_v1
 545         if (!kernel_text_address((unsigned long)entry))
 546                 return ppc_global_function_entry(entry);
 547         else
 548 #endif
 549                 return (unsigned long)entry;
 550 }
 551 NOKPROBE_SYMBOL(arch_deref_entry_point);
 552
 553 static struct kprobe trampoline_p = {
 554         .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
 555         .pre_handler = trampoline_probe_handler
 556 };
 557
 558 int __init arch_init_kprobes(void)
 559 {
 560         return register_kprobe(&trampoline_p);
 561 }
 562
 563 int arch_trampoline_kprobe(struct kprobe *p)
 564 {
 565         if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
 566                 return 1;
 567
 568         return 0;
 569 }
 570 NOKPROBE_SYMBOL(arch_trampoline_kprobe);