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         /*
 281          * We don't want to be preempted for the entire
 282          * duration of kprobe processing
 283          */
 284         preempt_disable();
 285         kcb = get_kprobe_ctlblk();
 286
 287         /* Check we're not actually recursing */
 288         if (kprobe_running()) {
 289                 p = get_kprobe(addr);
 290                 if (p) {
 291                         kprobe_opcode_t insn = *p->ainsn.insn;
 292                         if (kcb->kprobe_status == KPROBE_HIT_SS &&
 293                                         is_trap(insn)) {
 294                                 /* Turn off 'trace' bits */
 295                                 regs->msr &= ~MSR_SINGLESTEP;
 296                                 regs->msr |= kcb->kprobe_saved_msr;
 297                                 goto no_kprobe;
 298                         }
 299                         /* We have reentered the kprobe_handler(), since
 300                          * another probe was hit while within the handler.
 301                          * We here save the original kprobes variables and
 302                          * just single step on the instruction of the new probe
 303                          * without calling any user handlers.
 304                          */
 305                         save_previous_kprobe(kcb);
 306                         set_current_kprobe(p, regs, kcb);
 307                         kprobes_inc_nmissed_count(p);
 308                         kcb->kprobe_status = KPROBE_REENTER;
 309                         if (p->ainsn.boostable >= 0) {
 310                                 ret = try_to_emulate(p, regs);
 311
 312                                 if (ret > 0) {
 313                                         restore_previous_kprobe(kcb);
 314                                         preempt_enable_no_resched();
 315                                         return 1;
 316                                 }
 317                         }
 318                         prepare_singlestep(p, regs);
 319                         return 1;
 320                 } else if (*addr != BREAKPOINT_INSTRUCTION) {
 321                         /* If trap variant, then it belongs not to us */
 322                         kprobe_opcode_t cur_insn = *addr;
 323
 324                         if (is_trap(cur_insn))
 325                                 goto no_kprobe;
 326                         /* The breakpoint instruction was removed by
 327                          * another cpu right after we hit, no further
 328                          * handling of this interrupt is appropriate
 329                          */
 330                         ret = 1;
 331                 }
 332                 goto no_kprobe;
 333         }
 334
 335         p = get_kprobe(addr);
 336         if (!p) {
 337                 if (*addr != BREAKPOINT_INSTRUCTION) {
 338                         /*
 339                          * PowerPC has multiple variants of the "trap"
 340                          * instruction. If the current instruction is a
 341                          * trap variant, it could belong to someone else
 342                          */
 343                         kprobe_opcode_t cur_insn = *addr;
 344                         if (is_trap(cur_insn))
 345                                 goto no_kprobe;
 346                         /*
 347                          * The breakpoint instruction was removed right
 348                          * after we hit it.  Another cpu has removed
 349                          * either a probepoint or a debugger breakpoint
 350                          * at this address.  In either case, no further
 351                          * handling of this interrupt is appropriate.
 352                          */
 353                         ret = 1;
 354                 }
 355                 /* Not one of ours: let kernel handle it */
 356                 goto no_kprobe;
 357         }
 358
 359         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 360         set_current_kprobe(p, regs, kcb);
 361         if (p->pre_handler && p->pre_handler(p, regs)) {
 362                 /* handler changed execution path, so skip ss setup */
 363                 reset_current_kprobe();
 364                 preempt_enable_no_resched();
 365                 return 1;
 366         }
 367
 368         if (p->ainsn.boostable >= 0) {
 369                 ret = try_to_emulate(p, regs);
 370
 371                 if (ret > 0) {
 372                         if (p->post_handler)
 373                                 p->post_handler(p, regs, 0);
 374
 375                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 376                         reset_current_kprobe();
 377                         preempt_enable_no_resched();
 378                         return 1;
 379                 }
 380         }
 381         prepare_singlestep(p, regs);
 382         kcb->kprobe_status = KPROBE_HIT_SS;
 383         return 1;
 384
 385 no_kprobe:
 386         preempt_enable_no_resched();
 387         return ret;
 388 }
 389 NOKPROBE_SYMBOL(kprobe_handler);
 390
 391 /*
 392  * Function return probe trampoline:
 393  *      - init_kprobes() establishes a probepoint here
 394  *      - When the probed function returns, this probe
 395  *              causes the handlers to fire
 396  */
 397 asm(".global kretprobe_trampoline\n"
 398         ".type kretprobe_trampoline, @function\n"
 399         "kretprobe_trampoline:\n"
 400         "nop\n"
 401         "blr\n"
 402         ".size kretprobe_trampoline, .-kretprobe_trampoline\n");
 403
 404 /*
 405  * Called when the probe at kretprobe trampoline is hit
 406  */
 407 static int trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
 408 {
 409         struct kretprobe_instance *ri = NULL;
 410         struct hlist_head *head, empty_rp;
 411         struct hlist_node *tmp;
 412         unsigned long flags, orig_ret_address = 0;
 413         unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
 414
 415         INIT_HLIST_HEAD(&empty_rp);
 416         kretprobe_hash_lock(current, &head, &flags);
 417
 418         /*
 419          * It is possible to have multiple instances associated with a given
 420          * task either because an multiple functions in the call path
 421          * have a return probe installed on them, and/or more than one return
 422          * return probe was registered for a target function.
 423          *
 424          * We can handle this because:
 425          *     - instances are always inserted at the head of the list
 426          *     - when multiple return probes are registered for the same
 427          *       function, the first instance's ret_addr will point to the
 428          *       real return address, and all the rest will point to
 429          *       kretprobe_trampoline
 430          */
 431         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 432                 if (ri->task != current)
 433                         /* another task is sharing our hash bucket */
 434                         continue;
 435
 436                 if (ri->rp && ri->rp->handler)
 437                         ri->rp->handler(ri, regs);
 438
 439                 orig_ret_address = (unsigned long)ri->ret_addr;
 440                 recycle_rp_inst(ri, &empty_rp);
 441
 442                 if (orig_ret_address != trampoline_address)
 443                         /*
 444                          * This is the real return address. Any other
 445                          * instances associated with this task are for
 446                          * other calls deeper on the call stack
 447                          */
 448                         break;
 449         }
 450
 451         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 452
 453         /*
 454          * We get here through one of two paths:
 455          * 1. by taking a trap -> kprobe_handler() -> here
 456          * 2. by optprobe branch -> optimized_callback() -> opt_pre_handler() -> here
 457          *
 458          * When going back through (1), we need regs->nip to be setup properly
 459          * as it is used to determine the return address from the trap.
 460          * For (2), since nip is not honoured with optprobes, we instead setup
 461          * the link register properly so that the subsequent 'blr' in
 462          * kretprobe_trampoline jumps back to the right instruction.
 463          *
 464          * For nip, we should set the address to the previous instruction since
 465          * we end up emulating it in kprobe_handler(), which increments the nip
 466          * again.
 467          */
 468         regs->nip = orig_ret_address - 4;
 469         regs->link = orig_ret_address;
 470
 471         kretprobe_hash_unlock(current, &flags);
 472
 473         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
 474                 hlist_del(&ri->hlist);
 475                 kfree(ri);
 476         }
 477
 478         return 0;
 479 }
 480 NOKPROBE_SYMBOL(trampoline_probe_handler);
 481
 482 /*
 483  * Called after single-stepping.  p->addr is the address of the
 484  * instruction whose first byte has been replaced by the "breakpoint"
 485  * instruction.  To avoid the SMP problems that can occur when we
 486  * temporarily put back the original opcode to single-step, we
 487  * single-stepped a copy of the instruction.  The address of this
 488  * copy is p->ainsn.insn.
 489  */
 490 int kprobe_post_handler(struct pt_regs *regs)
 491 {
 492         struct kprobe *cur = kprobe_running();
 493         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 494
 495         if (!cur || user_mode(regs))
 496                 return 0;
 497
 498         /* make sure we got here for instruction we have a kprobe on */
 499         if (((unsigned long)cur->ainsn.insn + 4) != regs->nip)
 500                 return 0;
 501
 502         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
 503                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
 504                 cur->post_handler(cur, regs, 0);
 505         }
 506
 507         /* Adjust nip to after the single-stepped instruction */
 508         regs->nip = (unsigned long)cur->addr + 4;
 509         regs->msr |= kcb->kprobe_saved_msr;
 510
 511         /*Restore back the original saved kprobes variables and continue. */
 512         if (kcb->kprobe_status == KPROBE_REENTER) {
 513                 restore_previous_kprobe(kcb);
 514                 goto out;
 515         }
 516         reset_current_kprobe();
 517 out:
 518         preempt_enable_no_resched();
 519
 520         /*
 521          * if somebody else is singlestepping across a probe point, msr
 522          * will have DE/SE set, in which case, continue the remaining processing
 523          * of do_debug, as if this is not a probe hit.
 524          */
 525         if (regs->msr & MSR_SINGLESTEP)
 526                 return 0;
 527
 528         return 1;
 529 }
 530 NOKPROBE_SYMBOL(kprobe_post_handler);
 531
 532 int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 533 {
 534         struct kprobe *cur = kprobe_running();
 535         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 536         const struct exception_table_entry *entry;
 537
 538         switch(kcb->kprobe_status) {
 539         case KPROBE_HIT_SS:
 540         case KPROBE_REENTER:
 541                 /*
 542                  * We are here because the instruction being single
 543                  * stepped caused a page fault. We reset the current
 544                  * kprobe and the nip points back to the probe address
 545                  * and allow the page fault handler to continue as a
 546                  * normal page fault.
 547                  */
 548                 regs->nip = (unsigned long)cur->addr;
 549                 regs->msr &= ~MSR_SINGLESTEP; /* Turn off 'trace' bits */
 550                 regs->msr |= kcb->kprobe_saved_msr;
 551                 if (kcb->kprobe_status == KPROBE_REENTER)
 552                         restore_previous_kprobe(kcb);
 553                 else
 554                         reset_current_kprobe();
 555                 preempt_enable_no_resched();
 556                 break;
 557         case KPROBE_HIT_ACTIVE:
 558         case KPROBE_HIT_SSDONE:
 559                 /*
 560                  * We increment the nmissed count for accounting,
 561                  * we can also use npre/npostfault count for accounting
 562                  * these specific fault cases.
 563                  */
 564                 kprobes_inc_nmissed_count(cur);
 565
 566                 /*
 567                  * We come here because instructions in the pre/post
 568                  * handler caused the page_fault, this could happen
 569                  * if handler tries to access user space by
 570                  * copy_from_user(), get_user() etc. Let the
 571                  * user-specified handler try to fix it first.
 572                  */
 573                 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
 574                         return 1;
 575
 576                 /*
 577                  * In case the user-specified fault handler returned
 578                  * zero, try to fix up.
 579                  */
 580                 if ((entry = search_exception_tables(regs->nip)) != NULL) {
 581                         regs->nip = extable_fixup(entry);
 582                         return 1;
 583                 }
 584
 585                 /*
 586                  * fixup_exception() could not handle it,
 587                  * Let do_page_fault() fix it.
 588                  */
 589                 break;
 590         default:
 591                 break;
 592         }
 593         return 0;
 594 }
 595 NOKPROBE_SYMBOL(kprobe_fault_handler);
 596
 597 unsigned long arch_deref_entry_point(void *entry)
 598 {
 599 #ifdef PPC64_ELF_ABI_v1
 600         if (!kernel_text_address((unsigned long)entry))
 601                 return ppc_global_function_entry(entry);
 602         else
 603 #endif
 604                 return (unsigned long)entry;
 605 }
 606 NOKPROBE_SYMBOL(arch_deref_entry_point);
 607
 608 static struct kprobe trampoline_p = {
 609         .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
 610         .pre_handler = trampoline_probe_handler
 611 };
 612
 613 int __init arch_init_kprobes(void)
 614 {
 615         return register_kprobe(&trampoline_p);
 616 }
 617
 618 int arch_trampoline_kprobe(struct kprobe *p)
 619 {
 620         if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
 621                 return 1;
 622
 623         return 0;
 624 }
 625 NOKPROBE_SYMBOL(arch_trampoline_kprobe);