arch/powerpc/kernel/kprobes.c

   1 /*
   2  *  Kernel Probes (KProbes)
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  17  *
  18  * Copyright (C) IBM Corporation, 2002, 2004
  19  *
  20  * 2002-Oct     Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
  21  *              Probes initial implementation ( includes contributions from
  22  *              Rusty Russell).
  23  * 2004-July    Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
  24  *              interface to access function arguments.
  25  * 2004-Nov     Ananth N Mavinakayanahalli <ananth@in.ibm.com> kprobes port
  26  *              for PPC64
  27  */
  28
  29 #include <linux/kprobes.h>
  30 #include <linux/ptrace.h>
  31 #include <linux/preempt.h>
  32 #include <linux/extable.h>
  33 #include <linux/kdebug.h>
  34 #include <linux/slab.h>
  35 #include <asm/code-patching.h>
  36 #include <asm/cacheflush.h>
  37 #include <asm/sstep.h>
  38 #include <asm/sections.h>
  39 #include <linux/uaccess.h>
  40
  41 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  42 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  43
  44 struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
  45
  46 bool arch_within_kprobe_blacklist(unsigned long addr)
  47 {
  48         return  (addr >= (unsigned long)__kprobes_text_start &&
  49                  addr < (unsigned long)__kprobes_text_end) ||
  50                 (addr >= (unsigned long)_stext &&
  51                  addr < (unsigned long)__head_end);
  52 }
  53
  54 kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
  55 {
  56         kprobe_opcode_t *addr = NULL;
  57
  58 #ifdef PPC64_ELF_ABI_v2
  59         /* PPC64 ABIv2 needs local entry point */
  60         addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
  61         if (addr && !offset) {
  62 #ifdef CONFIG_KPROBES_ON_FTRACE
  63                 unsigned long faddr;
  64                 /*
  65                  * Per livepatch.h, ftrace location is always within the first
  66                  * 16 bytes of a function on powerpc with -mprofile-kernel.
  67                  */
  68                 faddr = ftrace_location_range((unsigned long)addr,
  69                                               (unsigned long)addr + 16);
  70                 if (faddr)
  71                         addr = (kprobe_opcode_t *)faddr;
  72                 else
  73 #endif
  74                         addr = (kprobe_opcode_t *)ppc_function_entry(addr);
  75         }
  76 #elif defined(PPC64_ELF_ABI_v1)
  77         /*
  78          * 64bit powerpc ABIv1 uses function descriptors:
  79          * - Check for the dot variant of the symbol first.
  80          * - If that fails, try looking up the symbol provided.
  81          *
  82          * This ensures we always get to the actual symbol and not
  83          * the descriptor.
  84          *
  85          * Also handle <module:symbol> format.
  86          */
  87         char dot_name[MODULE_NAME_LEN + 1 + KSYM_NAME_LEN];
  88         bool dot_appended = false;
  89         const char *c;
  90         ssize_t ret = 0;
  91         int len = 0;
  92
  93         if ((c = strnchr(name, MODULE_NAME_LEN, ':')) != NULL) {
  94                 c++;
  95                 len = c - name;
  96                 memcpy(dot_name, name, len);
  97         } else
  98                 c = name;
  99
 100         if (*c != '\0' && *c != '.') {
 101                 dot_name[len++] = '.';
 102                 dot_appended = true;
 103         }
 104         ret = strscpy(dot_name + len, c, KSYM_NAME_LEN);
 105         if (ret > 0)
 106                 addr = (kprobe_opcode_t *)kallsyms_lookup_name(dot_name);
 107
 108         /* Fallback to the original non-dot symbol lookup */
 109         if (!addr && dot_appended)
 110                 addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
 111 #else
 112         addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
 113 #endif
 114
 115         return addr;
 116 }
 117
 118 int arch_prepare_kprobe(struct kprobe *p)
 119 {
 120         int ret = 0;
 121         kprobe_opcode_t insn = *p->addr;
 122
 123         if ((unsigned long)p->addr & 0x03) {
 124                 printk("Attempt to register kprobe at an unaligned address\n");
 125                 ret = -EINVAL;
 126         } else if (IS_MTMSRD(insn) || IS_RFID(insn) || IS_RFI(insn)) {
 127                 printk("Cannot register a kprobe on rfi/rfid or mtmsr[d]\n");
 128                 ret = -EINVAL;
 129         }
 130
 131         /* insn must be on a special executable page on ppc64.  This is
 132          * not explicitly required on ppc32 (right now), but it doesn't hurt */
 133         if (!ret) {
 134                 p->ainsn.insn = get_insn_slot();
 135                 if (!p->ainsn.insn)
 136                         ret = -ENOMEM;
 137         }
 138
 139         if (!ret) {
 140                 memcpy(p->ainsn.insn, p->addr,
 141                                 MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
 142                 p->opcode = *p->addr;
 143                 flush_icache_range((unsigned long)p->ainsn.insn,
 144                         (unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
 145         }
 146
 147         p->ainsn.boostable = 0;
 148         return ret;
 149 }
 150 NOKPROBE_SYMBOL(arch_prepare_kprobe);
 151
 152 void arch_arm_kprobe(struct kprobe *p)
 153 {
 154         patch_instruction(p->addr, BREAKPOINT_INSTRUCTION);
 155 }
 156 NOKPROBE_SYMBOL(arch_arm_kprobe);
 157
 158 void arch_disarm_kprobe(struct kprobe *p)
 159 {
 160         patch_instruction(p->addr, p->opcode);
 161 }
 162 NOKPROBE_SYMBOL(arch_disarm_kprobe);
 163
 164 void arch_remove_kprobe(struct kprobe *p)
 165 {
 166         if (p->ainsn.insn) {
 167                 free_insn_slot(p->ainsn.insn, 0);
 168                 p->ainsn.insn = NULL;
 169         }
 170 }
 171 NOKPROBE_SYMBOL(arch_remove_kprobe);
 172
 173 static nokprobe_inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 174 {
 175         enable_single_step(regs);
 176
 177         /*
 178          * On powerpc we should single step on the original
 179          * instruction even if the probed insn is a trap
 180          * variant as values in regs could play a part in
 181          * if the trap is taken or not
 182          */
 183         regs->nip = (unsigned long)p->ainsn.insn;
 184 }
 185
 186 static nokprobe_inline void save_previous_kprobe(struct kprobe_ctlblk *kcb)
 187 {
 188         kcb->prev_kprobe.kp = kprobe_running();
 189         kcb->prev_kprobe.status = kcb->kprobe_status;
 190         kcb->prev_kprobe.saved_msr = kcb->kprobe_saved_msr;
 191 }
 192
 193 static nokprobe_inline void restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 194 {
 195         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 196         kcb->kprobe_status = kcb->prev_kprobe.status;
 197         kcb->kprobe_saved_msr = kcb->prev_kprobe.saved_msr;
 198 }
 199
 200 static nokprobe_inline void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
 201                                 struct kprobe_ctlblk *kcb)
 202 {
 203         __this_cpu_write(current_kprobe, p);
 204         kcb->kprobe_saved_msr = regs->msr;
 205 }
 206
 207 bool arch_kprobe_on_func_entry(unsigned long offset)
 208 {
 209 #ifdef PPC64_ELF_ABI_v2
 210 #ifdef CONFIG_KPROBES_ON_FTRACE
 211         return offset <= 16;
 212 #else
 213         return offset <= 8;
 214 #endif
 215 #else
 216         return !offset;
 217 #endif
 218 }
 219
 220 void arch_prepare_kretprobe(struct kretprobe_instance *ri, struct pt_regs *regs)
 221 {
 222         ri->ret_addr = (kprobe_opcode_t *)regs->link;
 223
 224         /* Replace the return addr with trampoline addr */
 225         regs->link = (unsigned long)kretprobe_trampoline;
 226 }
 227 NOKPROBE_SYMBOL(arch_prepare_kretprobe);
 228
 229 static int try_to_emulate(struct kprobe *p, struct pt_regs *regs)
 230 {
 231         int ret;
 232         unsigned int insn = *p->ainsn.insn;
 233
 234         /* regs->nip is also adjusted if emulate_step returns 1 */
 235         ret = emulate_step(regs, insn);
 236         if (ret > 0) {
 237                 /*
 238                  * Once this instruction has been boosted
 239                  * successfully, set the boostable flag
 240                  */
 241                 if (unlikely(p->ainsn.boostable == 0))
 242                         p->ainsn.boostable = 1;
 243         } else if (ret < 0) {
 244                 /*
 245                  * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
 246                  * So, we should never get here... but, its still
 247                  * good to catch them, just in case...
 248                  */
 249                 printk("Can't step on instruction %x\n", insn);
 250                 BUG();
 251         } else {
 252                 /*
 253                  * If we haven't previously emulated this instruction, then it
 254                  * can't be boosted. Note it down so we don't try to do so again.
 255                  *
 256                  * If, however, we had emulated this instruction in the past,
 257                  * then this is just an error with the current run (for
 258                  * instance, exceptions due to a load/store). We return 0 so
 259                  * that this is now single-stepped, but continue to try
 260                  * emulating it in subsequent probe hits.
 261                  */
 262                 if (unlikely(p->ainsn.boostable != 1))
 263                         p->ainsn.boostable = -1;
 264         }
 265
 266         return ret;
 267 }
 268 NOKPROBE_SYMBOL(try_to_emulate);
 269
 270 int kprobe_handler(struct pt_regs *regs)
 271 {
 272         struct kprobe *p;
 273         int ret = 0;
 274         unsigned int *addr = (unsigned int *)regs->nip;
 275         struct kprobe_ctlblk *kcb;
 276
 277         if (user_mode(regs))
 278                 return 0;
 279
 280         if (!IS_ENABLED(CONFIG_BOOKE) &&
 281             (!(regs->msr & MSR_IR) || !(regs->msr & MSR_DR)))
 282                 return 0;
 283
 284         /*
 285          * We don't want to be preempted for the entire
 286          * duration of kprobe processing
 287          */
 288         preempt_disable();
 289         kcb = get_kprobe_ctlblk();
 290
 291         /* Check we're not actually recursing */
 292         if (kprobe_running()) {
 293                 p = get_kprobe(addr);
 294                 if (p) {
 295                         kprobe_opcode_t insn = *p->ainsn.insn;
 296                         if (kcb->kprobe_status == KPROBE_HIT_SS &&
 297                                         is_trap(insn)) {
 298                                 /* Turn off 'trace' bits */
 299                                 regs->msr &= ~MSR_SINGLESTEP;
 300                                 regs->msr |= kcb->kprobe_saved_msr;
 301                                 goto no_kprobe;
 302                         }
 303                         /* We have reentered the kprobe_handler(), since
 304                          * another probe was hit while within the handler.
 305                          * We here save the original kprobes variables and
 306                          * just single step on the instruction of the new probe
 307                          * without calling any user handlers.
 308                          */
 309                         save_previous_kprobe(kcb);
 310                         set_current_kprobe(p, regs, kcb);
 311                         kprobes_inc_nmissed_count(p);
 312                         kcb->kprobe_status = KPROBE_REENTER;
 313                         if (p->ainsn.boostable >= 0) {
 314                                 ret = try_to_emulate(p, regs);
 315
 316                                 if (ret > 0) {
 317                                         restore_previous_kprobe(kcb);
 318                                         preempt_enable_no_resched();
 319                                         return 1;
 320                                 }
 321                         }
 322                         prepare_singlestep(p, regs);
 323                         return 1;
 324                 } else if (*addr != BREAKPOINT_INSTRUCTION) {
 325                         /* If trap variant, then it belongs not to us */
 326                         kprobe_opcode_t cur_insn = *addr;
 327
 328                         if (is_trap(cur_insn))
 329                                 goto no_kprobe;
 330                         /* The breakpoint instruction was removed by
 331                          * another cpu right after we hit, no further
 332                          * handling of this interrupt is appropriate
 333                          */
 334                         ret = 1;
 335                 }
 336                 goto no_kprobe;
 337         }
 338
 339         p = get_kprobe(addr);
 340         if (!p) {
 341                 if (*addr != BREAKPOINT_INSTRUCTION) {
 342                         /*
 343                          * PowerPC has multiple variants of the "trap"
 344                          * instruction. If the current instruction is a
 345                          * trap variant, it could belong to someone else
 346                          */
 347                         kprobe_opcode_t cur_insn = *addr;
 348                         if (is_trap(cur_insn))
 349                                 goto no_kprobe;
 350                         /*
 351                          * The breakpoint instruction was removed right
 352                          * after we hit it.  Another cpu has removed
 353                          * either a probepoint or a debugger breakpoint
 354                          * at this address.  In either case, no further
 355                          * handling of this interrupt is appropriate.
 356                          */
 357                         ret = 1;
 358                 }
 359                 /* Not one of ours: let kernel handle it */
 360                 goto no_kprobe;
 361         }
 362
 363         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 364         set_current_kprobe(p, regs, kcb);
 365         if (p->pre_handler && p->pre_handler(p, regs)) {
 366                 /* handler changed execution path, so skip ss setup */
 367                 reset_current_kprobe();
 368                 preempt_enable_no_resched();
 369                 return 1;
 370         }
 371
 372         if (p->ainsn.boostable >= 0) {
 373                 ret = try_to_emulate(p, regs);
 374
 375                 if (ret > 0) {
 376                         if (p->post_handler)
 377                                 p->post_handler(p, regs, 0);
 378
 379                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 380                         reset_current_kprobe();
 381                         preempt_enable_no_resched();
 382                         return 1;
 383                 }
 384         }
 385         prepare_singlestep(p, regs);
 386         kcb->kprobe_status = KPROBE_HIT_SS;
 387         return 1;
 388
 389 no_kprobe:
 390         preempt_enable_no_resched();
 391         return ret;
 392 }
 393 NOKPROBE_SYMBOL(kprobe_handler);
 394
 395 /*
 396  * Function return probe trampoline:
 397  *      - init_kprobes() establishes a probepoint here
 398  *      - When the probed function returns, this probe
 399  *              causes the handlers to fire
 400  */
 401 asm(".global kretprobe_trampoline\n"
 402         ".type kretprobe_trampoline, @function\n"
 403         "kretprobe_trampoline:\n"
 404         "nop\n"
 405         "blr\n"
 406         ".size kretprobe_trampoline, .-kretprobe_trampoline\n");
 407
 408 /*
 409  * Called when the probe at kretprobe trampoline is hit
 410  */
 411 static int trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
 412 {
 413         struct kretprobe_instance *ri = NULL;
 414         struct hlist_head *head, empty_rp;
 415         struct hlist_node *tmp;
 416         unsigned long flags, orig_ret_address = 0;
 417         unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
 418
 419         INIT_HLIST_HEAD(&empty_rp);
 420         kretprobe_hash_lock(current, &head, &flags);
 421
 422         /*
 423          * It is possible to have multiple instances associated with a given
 424          * task either because an multiple functions in the call path
 425          * have a return probe installed on them, and/or more than one return
 426          * return probe was registered for a target function.
 427          *
 428          * We can handle this because:
 429          *     - instances are always inserted at the head of the list
 430          *     - when multiple return probes are registered for the same
 431          *       function, the first instance's ret_addr will point to the
 432          *       real return address, and all the rest will point to
 433          *       kretprobe_trampoline
 434          */
 435         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 436                 if (ri->task != current)
 437                         /* another task is sharing our hash bucket */
 438                         continue;
 439
 440                 if (ri->rp && ri->rp->handler)
 441                         ri->rp->handler(ri, regs);
 442
 443                 orig_ret_address = (unsigned long)ri->ret_addr;
 444                 recycle_rp_inst(ri, &empty_rp);
 445
 446                 if (orig_ret_address != trampoline_address)
 447                         /*
 448                          * This is the real return address. Any other
 449                          * instances associated with this task are for
 450                          * other calls deeper on the call stack
 451                          */
 452                         break;
 453         }
 454
 455         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 456
 457         /*
 458          * We get here through one of two paths:
 459          * 1. by taking a trap -> kprobe_handler() -> here
 460          * 2. by optprobe branch -> optimized_callback() -> opt_pre_handler() -> here
 461          *
 462          * When going back through (1), we need regs->nip to be setup properly
 463          * as it is used to determine the return address from the trap.
 464          * For (2), since nip is not honoured with optprobes, we instead setup
 465          * the link register properly so that the subsequent 'blr' in
 466          * kretprobe_trampoline jumps back to the right instruction.
 467          *
 468          * For nip, we should set the address to the previous instruction since
 469          * we end up emulating it in kprobe_handler(), which increments the nip
 470          * again.
 471          */
 472         regs->nip = orig_ret_address - 4;
 473         regs->link = orig_ret_address;
 474
 475         kretprobe_hash_unlock(current, &flags);
 476
 477         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
 478                 hlist_del(&ri->hlist);
 479                 kfree(ri);
 480         }
 481
 482         return 0;
 483 }
 484 NOKPROBE_SYMBOL(trampoline_probe_handler);
 485
 486 /*
 487  * Called after single-stepping.  p->addr is the address of the
 488  * instruction whose first byte has been replaced by the "breakpoint"
 489  * instruction.  To avoid the SMP problems that can occur when we
 490  * temporarily put back the original opcode to single-step, we
 491  * single-stepped a copy of the instruction.  The address of this
 492  * copy is p->ainsn.insn.
 493  */
 494 int kprobe_post_handler(struct pt_regs *regs)
 495 {
 496         struct kprobe *cur = kprobe_running();
 497         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 498
 499         if (!cur || user_mode(regs))
 500                 return 0;
 501
 502         /* make sure we got here for instruction we have a kprobe on */
 503         if (((unsigned long)cur->ainsn.insn + 4) != regs->nip)
 504                 return 0;
 505
 506         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
 507                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
 508                 cur->post_handler(cur, regs, 0);
 509         }
 510
 511         /* Adjust nip to after the single-stepped instruction */
 512         regs->nip = (unsigned long)cur->addr + 4;
 513         regs->msr |= kcb->kprobe_saved_msr;
 514
 515         /*Restore back the original saved kprobes variables and continue. */
 516         if (kcb->kprobe_status == KPROBE_REENTER) {
 517                 restore_previous_kprobe(kcb);
 518                 goto out;
 519         }
 520         reset_current_kprobe();
 521 out:
 522         preempt_enable_no_resched();
 523
 524         /*
 525          * if somebody else is singlestepping across a probe point, msr
 526          * will have DE/SE set, in which case, continue the remaining processing
 527          * of do_debug, as if this is not a probe hit.
 528          */
 529         if (regs->msr & MSR_SINGLESTEP)
 530                 return 0;
 531
 532         return 1;
 533 }
 534 NOKPROBE_SYMBOL(kprobe_post_handler);
 535
 536 int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 537 {
 538         struct kprobe *cur = kprobe_running();
 539         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 540         const struct exception_table_entry *entry;
 541
 542         switch(kcb->kprobe_status) {
 543         case KPROBE_HIT_SS:
 544         case KPROBE_REENTER:
 545                 /*
 546                  * We are here because the instruction being single
 547                  * stepped caused a page fault. We reset the current
 548                  * kprobe and the nip points back to the probe address
 549                  * and allow the page fault handler to continue as a
 550                  * normal page fault.
 551                  */
 552                 regs->nip = (unsigned long)cur->addr;
 553                 regs->msr &= ~MSR_SINGLESTEP; /* Turn off 'trace' bits */
 554                 regs->msr |= kcb->kprobe_saved_msr;
 555                 if (kcb->kprobe_status == KPROBE_REENTER)
 556                         restore_previous_kprobe(kcb);
 557                 else
 558                         reset_current_kprobe();
 559                 preempt_enable_no_resched();
 560                 break;
 561         case KPROBE_HIT_ACTIVE:
 562         case KPROBE_HIT_SSDONE:
 563                 /*
 564                  * We increment the nmissed count for accounting,
 565                  * we can also use npre/npostfault count for accounting
 566                  * these specific fault cases.
 567                  */
 568                 kprobes_inc_nmissed_count(cur);
 569
 570                 /*
 571                  * We come here because instructions in the pre/post
 572                  * handler caused the page_fault, this could happen
 573                  * if handler tries to access user space by
 574                  * copy_from_user(), get_user() etc. Let the
 575                  * user-specified handler try to fix it first.
 576                  */
 577                 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
 578                         return 1;
 579
 580                 /*
 581                  * In case the user-specified fault handler returned
 582                  * zero, try to fix up.
 583                  */
 584                 if ((entry = search_exception_tables(regs->nip)) != NULL) {
 585                         regs->nip = extable_fixup(entry);
 586                         return 1;
 587                 }
 588
 589                 /*
 590                  * fixup_exception() could not handle it,
 591                  * Let do_page_fault() fix it.
 592                  */
 593                 break;
 594         default:
 595                 break;
 596         }
 597         return 0;
 598 }
 599 NOKPROBE_SYMBOL(kprobe_fault_handler);
 600
 601 unsigned long arch_deref_entry_point(void *entry)
 602 {
 603 #ifdef PPC64_ELF_ABI_v1
 604         if (!kernel_text_address((unsigned long)entry))
 605                 return ppc_global_function_entry(entry);
 606         else
 607 #endif
 608                 return (unsigned long)entry;
 609 }
 610 NOKPROBE_SYMBOL(arch_deref_entry_point);
 611
 612 static struct kprobe trampoline_p = {
 613         .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
 614         .pre_handler = trampoline_probe_handler
 615 };
 616
 617 int __init arch_init_kprobes(void)
 618 {
 619         return register_kprobe(&trampoline_p);
 620 }
 621
 622 int arch_trampoline_kprobe(struct kprobe *p)
 623 {
 624         if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
 625                 return 1;
 626
 627         return 0;
 628 }
 629 NOKPROBE_SYMBOL(arch_trampoline_kprobe);