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