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 <linux/uaccess.h>
  27
  28 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  29 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  30
  31 struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
  32
  33 bool arch_within_kprobe_blacklist(unsigned long addr)
  34 {
  35         return  (addr >= (unsigned long)__kprobes_text_start &&
  36                  addr < (unsigned long)__kprobes_text_end) ||
  37                 (addr >= (unsigned long)_stext &&
  38                  addr < (unsigned long)__head_end);
  39 }
  40
  41 kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
  42 {
  43         kprobe_opcode_t *addr = NULL;
  44
  45 #ifdef PPC64_ELF_ABI_v2
  46         /* PPC64 ABIv2 needs local entry point */
  47         addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
  48         if (addr && !offset) {
  49 #ifdef CONFIG_KPROBES_ON_FTRACE
  50                 unsigned long faddr;
  51                 /*
  52                  * Per livepatch.h, ftrace location is always within the first
  53                  * 16 bytes of a function on powerpc with -mprofile-kernel.
  54                  */
  55                 faddr = ftrace_location_range((unsigned long)addr,
  56                                               (unsigned long)addr + 16);
  57                 if (faddr)
  58                         addr = (kprobe_opcode_t *)faddr;
  59                 else
  60 #endif
  61                         addr = (kprobe_opcode_t *)ppc_function_entry(addr);
  62         }
  63 #elif defined(PPC64_ELF_ABI_v1)
  64         /*
  65          * 64bit powerpc ABIv1 uses function descriptors:
  66          * - Check for the dot variant of the symbol first.
  67          * - If that fails, try looking up the symbol provided.
  68          *
  69          * This ensures we always get to the actual symbol and not
  70          * the descriptor.
  71          *
  72          * Also handle <module:symbol> format.
  73          */
  74         char dot_name[MODULE_NAME_LEN + 1 + KSYM_NAME_LEN];
  75         bool dot_appended = false;
  76         const char *c;
  77         ssize_t ret = 0;
  78         int len = 0;
  79
  80         if ((c = strnchr(name, MODULE_NAME_LEN, ':')) != NULL) {
  81                 c++;
  82                 len = c - name;
  83                 memcpy(dot_name, name, len);
  84         } else
  85                 c = name;
  86
  87         if (*c != '\0' && *c != '.') {
  88                 dot_name[len++] = '.';
  89                 dot_appended = true;
  90         }
  91         ret = strscpy(dot_name + len, c, KSYM_NAME_LEN);
  92         if (ret > 0)
  93                 addr = (kprobe_opcode_t *)kallsyms_lookup_name(dot_name);
  94
  95         /* Fallback to the original non-dot symbol lookup */
  96         if (!addr && dot_appended)
  97                 addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
  98 #else
  99         addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
 100 #endif
 101
 102         return addr;
 103 }
 104
 105 int arch_prepare_kprobe(struct kprobe *p)
 106 {
 107         int ret = 0;
 108         kprobe_opcode_t insn = *p->addr;
 109
 110         if ((unsigned long)p->addr & 0x03) {
 111                 printk("Attempt to register kprobe at an unaligned address\n");
 112                 ret = -EINVAL;
 113         } else if (IS_MTMSRD(insn) || IS_RFID(insn) || IS_RFI(insn)) {
 114                 printk("Cannot register a kprobe on rfi/rfid or mtmsr[d]\n");
 115                 ret = -EINVAL;
 116         }
 117
 118         /* insn must be on a special executable page on ppc64.  This is
 119          * not explicitly required on ppc32 (right now), but it doesn't hurt */
 120         if (!ret) {
 121                 p->ainsn.insn = get_insn_slot();
 122                 if (!p->ainsn.insn)
 123                         ret = -ENOMEM;
 124         }
 125
 126         if (!ret) {
 127                 memcpy(p->ainsn.insn, p->addr,
 128                                 MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
 129                 p->opcode = *p->addr;
 130                 flush_icache_range((unsigned long)p->ainsn.insn,
 131                         (unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
 132         }
 133
 134         p->ainsn.boostable = 0;
 135         return ret;
 136 }
 137 NOKPROBE_SYMBOL(arch_prepare_kprobe);
 138
 139 void arch_arm_kprobe(struct kprobe *p)
 140 {
 141         patch_instruction(p->addr, BREAKPOINT_INSTRUCTION);
 142 }
 143 NOKPROBE_SYMBOL(arch_arm_kprobe);
 144
 145 void arch_disarm_kprobe(struct kprobe *p)
 146 {
 147         patch_instruction(p->addr, p->opcode);
 148 }
 149 NOKPROBE_SYMBOL(arch_disarm_kprobe);
 150
 151 void arch_remove_kprobe(struct kprobe *p)
 152 {
 153         if (p->ainsn.insn) {
 154                 free_insn_slot(p->ainsn.insn, 0);
 155                 p->ainsn.insn = NULL;
 156         }
 157 }
 158 NOKPROBE_SYMBOL(arch_remove_kprobe);
 159
 160 static nokprobe_inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 161 {
 162         enable_single_step(regs);
 163
 164         /*
 165          * On powerpc we should single step on the original
 166          * instruction even if the probed insn is a trap
 167          * variant as values in regs could play a part in
 168          * if the trap is taken or not
 169          */
 170         regs->nip = (unsigned long)p->ainsn.insn;
 171 }
 172
 173 static nokprobe_inline void save_previous_kprobe(struct kprobe_ctlblk *kcb)
 174 {
 175         kcb->prev_kprobe.kp = kprobe_running();
 176         kcb->prev_kprobe.status = kcb->kprobe_status;
 177         kcb->prev_kprobe.saved_msr = kcb->kprobe_saved_msr;
 178 }
 179
 180 static nokprobe_inline void restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 181 {
 182         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 183         kcb->kprobe_status = kcb->prev_kprobe.status;
 184         kcb->kprobe_saved_msr = kcb->prev_kprobe.saved_msr;
 185 }
 186
 187 static nokprobe_inline void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
 188                                 struct kprobe_ctlblk *kcb)
 189 {
 190         __this_cpu_write(current_kprobe, p);
 191         kcb->kprobe_saved_msr = regs->msr;
 192 }
 193
 194 bool arch_kprobe_on_func_entry(unsigned long offset)
 195 {
 196 #ifdef PPC64_ELF_ABI_v2
 197 #ifdef CONFIG_KPROBES_ON_FTRACE
 198         return offset <= 16;
 199 #else
 200         return offset <= 8;
 201 #endif
 202 #else
 203         return !offset;
 204 #endif
 205 }
 206
 207 void arch_prepare_kretprobe(struct kretprobe_instance *ri, struct pt_regs *regs)
 208 {
 209         ri->ret_addr = (kprobe_opcode_t *)regs->link;
 210
 211         /* Replace the return addr with trampoline addr */
 212         regs->link = (unsigned long)kretprobe_trampoline;
 213 }
 214 NOKPROBE_SYMBOL(arch_prepare_kretprobe);
 215
 216 static int try_to_emulate(struct kprobe *p, struct pt_regs *regs)
 217 {
 218         int ret;
 219         unsigned int insn = *p->ainsn.insn;
 220
 221         /* regs->nip is also adjusted if emulate_step returns 1 */
 222         ret = emulate_step(regs, insn);
 223         if (ret > 0) {
 224                 /*
 225                  * Once this instruction has been boosted
 226                  * successfully, set the boostable flag
 227                  */
 228                 if (unlikely(p->ainsn.boostable == 0))
 229                         p->ainsn.boostable = 1;
 230         } else if (ret < 0) {
 231                 /*
 232                  * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
 233                  * So, we should never get here... but, its still
 234                  * good to catch them, just in case...
 235                  */
 236                 printk("Can't step on instruction %x\n", insn);
 237                 BUG();
 238         } else {
 239                 /*
 240                  * If we haven't previously emulated this instruction, then it
 241                  * can't be boosted. Note it down so we don't try to do so again.
 242                  *
 243                  * If, however, we had emulated this instruction in the past,
 244                  * then this is just an error with the current run (for
 245                  * instance, exceptions due to a load/store). We return 0 so
 246                  * that this is now single-stepped, but continue to try
 247                  * emulating it in subsequent probe hits.
 248                  */
 249                 if (unlikely(p->ainsn.boostable != 1))
 250                         p->ainsn.boostable = -1;
 251         }
 252
 253         return ret;
 254 }
 255 NOKPROBE_SYMBOL(try_to_emulate);
 256
 257 int kprobe_handler(struct pt_regs *regs)
 258 {
 259         struct kprobe *p;
 260         int ret = 0;
 261         unsigned int *addr = (unsigned int *)regs->nip;
 262         struct kprobe_ctlblk *kcb;
 263
 264         if (user_mode(regs))
 265                 return 0;
 266
 267         /*
 268          * We don't want to be preempted for the entire
 269          * duration of kprobe processing
 270          */
 271         preempt_disable();
 272         kcb = get_kprobe_ctlblk();
 273
 274         /* Check we're not actually recursing */
 275         if (kprobe_running()) {
 276                 p = get_kprobe(addr);
 277                 if (p) {
 278                         kprobe_opcode_t insn = *p->ainsn.insn;
 279                         if (kcb->kprobe_status == KPROBE_HIT_SS &&
 280                                         is_trap(insn)) {
 281                                 /* Turn off 'trace' bits */
 282                                 regs->msr &= ~MSR_SINGLESTEP;
 283                                 regs->msr |= kcb->kprobe_saved_msr;
 284                                 goto no_kprobe;
 285                         }
 286                         /* We have reentered the kprobe_handler(), since
 287                          * another probe was hit while within the handler.
 288                          * We here save the original kprobes variables and
 289                          * just single step on the instruction of the new probe
 290                          * without calling any user handlers.
 291                          */
 292                         save_previous_kprobe(kcb);
 293                         set_current_kprobe(p, regs, kcb);
 294                         kprobes_inc_nmissed_count(p);
 295                         kcb->kprobe_status = KPROBE_REENTER;
 296                         if (p->ainsn.boostable >= 0) {
 297                                 ret = try_to_emulate(p, regs);
 298
 299                                 if (ret > 0) {
 300                                         restore_previous_kprobe(kcb);
 301                                         preempt_enable_no_resched();
 302                                         return 1;
 303                                 }
 304                         }
 305                         prepare_singlestep(p, regs);
 306                         return 1;
 307                 } else if (*addr != BREAKPOINT_INSTRUCTION) {
 308                         /* If trap variant, then it belongs not to us */
 309                         kprobe_opcode_t cur_insn = *addr;
 310
 311                         if (is_trap(cur_insn))
 312                                 goto no_kprobe;
 313                         /* The breakpoint instruction was removed by
 314                          * another cpu right after we hit, no further
 315                          * handling of this interrupt is appropriate
 316                          */
 317                         ret = 1;
 318                 }
 319                 goto no_kprobe;
 320         }
 321
 322         p = get_kprobe(addr);
 323         if (!p) {
 324                 if (*addr != BREAKPOINT_INSTRUCTION) {
 325                         /*
 326                          * PowerPC has multiple variants of the "trap"
 327                          * instruction. If the current instruction is a
 328                          * trap variant, it could belong to someone else
 329                          */
 330                         kprobe_opcode_t cur_insn = *addr;
 331                         if (is_trap(cur_insn))
 332                                 goto no_kprobe;
 333                         /*
 334                          * The breakpoint instruction was removed right
 335                          * after we hit it.  Another cpu has removed
 336                          * either a probepoint or a debugger breakpoint
 337                          * at this address.  In either case, no further
 338                          * handling of this interrupt is appropriate.
 339                          */
 340                         ret = 1;
 341                 }
 342                 /* Not one of ours: let kernel handle it */
 343                 goto no_kprobe;
 344         }
 345
 346         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 347         set_current_kprobe(p, regs, kcb);
 348         if (p->pre_handler && p->pre_handler(p, regs)) {
 349                 /* handler changed execution path, so skip ss setup */
 350                 reset_current_kprobe();
 351                 preempt_enable_no_resched();
 352                 return 1;
 353         }
 354
 355         if (p->ainsn.boostable >= 0) {
 356                 ret = try_to_emulate(p, regs);
 357
 358                 if (ret > 0) {
 359                         if (p->post_handler)
 360                                 p->post_handler(p, regs, 0);
 361
 362                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 363                         reset_current_kprobe();
 364                         preempt_enable_no_resched();
 365                         return 1;
 366                 }
 367         }
 368         prepare_singlestep(p, regs);
 369         kcb->kprobe_status = KPROBE_HIT_SS;
 370         return 1;
 371
 372 no_kprobe:
 373         preempt_enable_no_resched();
 374         return ret;
 375 }
 376 NOKPROBE_SYMBOL(kprobe_handler);
 377
 378 /*
 379  * Function return probe trampoline:
 380  *      - init_kprobes() establishes a probepoint here
 381  *      - When the probed function returns, this probe
 382  *              causes the handlers to fire
 383  */
 384 asm(".global kretprobe_trampoline\n"
 385         ".type kretprobe_trampoline, @function\n"
 386         "kretprobe_trampoline:\n"
 387         "nop\n"
 388         "blr\n"
 389         ".size kretprobe_trampoline, .-kretprobe_trampoline\n");
 390
 391 /*
 392  * Called when the probe at kretprobe trampoline is hit
 393  */
 394 static int trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
 395 {
 396         struct kretprobe_instance *ri = NULL;
 397         struct hlist_head *head, empty_rp;
 398         struct hlist_node *tmp;
 399         unsigned long flags, orig_ret_address = 0;
 400         unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
 401
 402         INIT_HLIST_HEAD(&empty_rp);
 403         kretprobe_hash_lock(current, &head, &flags);
 404
 405         /*
 406          * It is possible to have multiple instances associated with a given
 407          * task either because an multiple functions in the call path
 408          * have a return probe installed on them, and/or more than one return
 409          * return probe was registered for a target function.
 410          *
 411          * We can handle this because:
 412          *     - instances are always inserted at the head of the list
 413          *     - when multiple return probes are registered for the same
 414          *       function, the first instance's ret_addr will point to the
 415          *       real return address, and all the rest will point to
 416          *       kretprobe_trampoline
 417          */
 418         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 419                 if (ri->task != current)
 420                         /* another task is sharing our hash bucket */
 421                         continue;
 422
 423                 if (ri->rp && ri->rp->handler)
 424                         ri->rp->handler(ri, regs);
 425
 426                 orig_ret_address = (unsigned long)ri->ret_addr;
 427                 recycle_rp_inst(ri, &empty_rp);
 428
 429                 if (orig_ret_address != trampoline_address)
 430                         /*
 431                          * This is the real return address. Any other
 432                          * instances associated with this task are for
 433                          * other calls deeper on the call stack
 434                          */
 435                         break;
 436         }
 437
 438         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 439
 440         /*
 441          * We get here through one of two paths:
 442          * 1. by taking a trap -> kprobe_handler() -> here
 443          * 2. by optprobe branch -> optimized_callback() -> opt_pre_handler() -> here
 444          *
 445          * When going back through (1), we need regs->nip to be setup properly
 446          * as it is used to determine the return address from the trap.
 447          * For (2), since nip is not honoured with optprobes, we instead setup
 448          * the link register properly so that the subsequent 'blr' in
 449          * kretprobe_trampoline jumps back to the right instruction.
 450          *
 451          * For nip, we should set the address to the previous instruction since
 452          * we end up emulating it in kprobe_handler(), which increments the nip
 453          * again.
 454          */
 455         regs->nip = orig_ret_address - 4;
 456         regs->link = orig_ret_address;
 457
 458         kretprobe_hash_unlock(current, &flags);
 459
 460         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
 461                 hlist_del(&ri->hlist);
 462                 kfree(ri);
 463         }
 464
 465         return 0;
 466 }
 467 NOKPROBE_SYMBOL(trampoline_probe_handler);
 468
 469 /*
 470  * Called after single-stepping.  p->addr is the address of the
 471  * instruction whose first byte has been replaced by the "breakpoint"
 472  * instruction.  To avoid the SMP problems that can occur when we
 473  * temporarily put back the original opcode to single-step, we
 474  * single-stepped a copy of the instruction.  The address of this
 475  * copy is p->ainsn.insn.
 476  */
 477 int kprobe_post_handler(struct pt_regs *regs)
 478 {
 479         struct kprobe *cur = kprobe_running();
 480         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 481
 482         if (!cur || user_mode(regs))
 483                 return 0;
 484
 485         /* make sure we got here for instruction we have a kprobe on */
 486         if (((unsigned long)cur->ainsn.insn + 4) != regs->nip)
 487                 return 0;
 488
 489         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
 490                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
 491                 cur->post_handler(cur, regs, 0);
 492         }
 493
 494         /* Adjust nip to after the single-stepped instruction */
 495         regs->nip = (unsigned long)cur->addr + 4;
 496         regs->msr |= kcb->kprobe_saved_msr;
 497
 498         /*Restore back the original saved kprobes variables and continue. */
 499         if (kcb->kprobe_status == KPROBE_REENTER) {
 500                 restore_previous_kprobe(kcb);
 501                 goto out;
 502         }
 503         reset_current_kprobe();
 504 out:
 505         preempt_enable_no_resched();
 506
 507         /*
 508          * if somebody else is singlestepping across a probe point, msr
 509          * will have DE/SE set, in which case, continue the remaining processing
 510          * of do_debug, as if this is not a probe hit.
 511          */
 512         if (regs->msr & MSR_SINGLESTEP)
 513                 return 0;
 514
 515         return 1;
 516 }
 517 NOKPROBE_SYMBOL(kprobe_post_handler);
 518
 519 int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 520 {
 521         struct kprobe *cur = kprobe_running();
 522         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 523         const struct exception_table_entry *entry;
 524
 525         switch(kcb->kprobe_status) {
 526         case KPROBE_HIT_SS:
 527         case KPROBE_REENTER:
 528                 /*
 529                  * We are here because the instruction being single
 530                  * stepped caused a page fault. We reset the current
 531                  * kprobe and the nip points back to the probe address
 532                  * and allow the page fault handler to continue as a
 533                  * normal page fault.
 534                  */
 535                 regs->nip = (unsigned long)cur->addr;
 536                 regs->msr &= ~MSR_SINGLESTEP; /* Turn off 'trace' bits */
 537                 regs->msr |= kcb->kprobe_saved_msr;
 538                 if (kcb->kprobe_status == KPROBE_REENTER)
 539                         restore_previous_kprobe(kcb);
 540                 else
 541                         reset_current_kprobe();
 542                 preempt_enable_no_resched();
 543                 break;
 544         case KPROBE_HIT_ACTIVE:
 545         case KPROBE_HIT_SSDONE:
 546                 /*
 547                  * We increment the nmissed count for accounting,
 548                  * we can also use npre/npostfault count for accounting
 549                  * these specific fault cases.
 550                  */
 551                 kprobes_inc_nmissed_count(cur);
 552
 553                 /*
 554                  * We come here because instructions in the pre/post
 555                  * handler caused the page_fault, this could happen
 556                  * if handler tries to access user space by
 557                  * copy_from_user(), get_user() etc. Let the
 558                  * user-specified handler try to fix it first.
 559                  */
 560                 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
 561                         return 1;
 562
 563                 /*
 564                  * In case the user-specified fault handler returned
 565                  * zero, try to fix up.
 566                  */
 567                 if ((entry = search_exception_tables(regs->nip)) != NULL) {
 568                         regs->nip = extable_fixup(entry);
 569                         return 1;
 570                 }
 571
 572                 /*
 573                  * fixup_exception() could not handle it,
 574                  * Let do_page_fault() fix it.
 575                  */
 576                 break;
 577         default:
 578                 break;
 579         }
 580         return 0;
 581 }
 582 NOKPROBE_SYMBOL(kprobe_fault_handler);
 583
 584 unsigned long arch_deref_entry_point(void *entry)
 585 {
 586 #ifdef PPC64_ELF_ABI_v1
 587         if (!kernel_text_address((unsigned long)entry))
 588                 return ppc_global_function_entry(entry);
 589         else
 590 #endif
 591                 return (unsigned long)entry;
 592 }
 593 NOKPROBE_SYMBOL(arch_deref_entry_point);
 594
 595 static struct kprobe trampoline_p = {
 596         .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
 597         .pre_handler = trampoline_probe_handler
 598 };
 599
 600 int __init arch_init_kprobes(void)
 601 {
 602         return register_kprobe(&trampoline_p);
 603 }
 604
 605 int arch_trampoline_kprobe(struct kprobe *p)
 606 {
 607         if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
 608                 return 1;
 609
 610         return 0;
 611 }
 612 NOKPROBE_SYMBOL(arch_trampoline_kprobe);