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/module.h>
  33 #include <linux/kdebug.h>
  34 #include <asm/cacheflush.h>
  35 #include <asm/sstep.h>
  36 #include <asm/uaccess.h>
  37 #include <asm/system.h>
  38
  39 #ifdef CONFIG_BOOKE
  40 #define MSR_SINGLESTEP  (MSR_DE)
  41 #else
  42 #define MSR_SINGLESTEP  (MSR_SE)
  43 #endif
  44
  45 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  46 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  47
  48 struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
  49
  50 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  51 {
  52         int ret = 0;
  53         kprobe_opcode_t insn = *p->addr;
  54
  55         if ((unsigned long)p->addr & 0x03) {
  56                 printk("Attempt to register kprobe at an unaligned address\n");
  57                 ret = -EINVAL;
  58         } else if (IS_MTMSRD(insn) || IS_RFID(insn) || IS_RFI(insn)) {
  59                 printk("Cannot register a kprobe on rfi/rfid or mtmsr[d]\n");
  60                 ret = -EINVAL;
  61         }
  62
  63         /* insn must be on a special executable page on ppc64.  This is
  64          * not explicitly required on ppc32 (right now), but it doesn't hurt */
  65         if (!ret) {
  66                 p->ainsn.insn = get_insn_slot();
  67                 if (!p->ainsn.insn)
  68                         ret = -ENOMEM;
  69         }
  70
  71         if (!ret) {
  72                 memcpy(p->ainsn.insn, p->addr,
  73                                 MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
  74                 p->opcode = *p->addr;
  75                 flush_icache_range((unsigned long)p->ainsn.insn,
  76                         (unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
  77         }
  78
  79         p->ainsn.boostable = 0;
  80         return ret;
  81 }
  82
  83 void __kprobes arch_arm_kprobe(struct kprobe *p)
  84 {
  85         *p->addr = BREAKPOINT_INSTRUCTION;
  86         flush_icache_range((unsigned long) p->addr,
  87                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
  88 }
  89
  90 void __kprobes arch_disarm_kprobe(struct kprobe *p)
  91 {
  92         *p->addr = p->opcode;
  93         flush_icache_range((unsigned long) p->addr,
  94                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
  95 }
  96
  97 void __kprobes arch_remove_kprobe(struct kprobe *p)
  98 {
  99         mutex_lock(&kprobe_mutex);
 100         free_insn_slot(p->ainsn.insn, 0);
 101         mutex_unlock(&kprobe_mutex);
 102 }
 103
 104 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 105 {
 106         /* We turn off async exceptions to ensure that the single step will
 107          * be for the instruction we have the kprobe on, if we dont its
 108          * possible we'd get the single step reported for an exception handler
 109          * like Decrementer or External Interrupt */
 110         regs->msr &= ~MSR_EE;
 111         regs->msr |= MSR_SINGLESTEP;
 112 #ifdef CONFIG_BOOKE
 113         regs->msr &= ~MSR_CE;
 114         mtspr(SPRN_DBCR0, mfspr(SPRN_DBCR0) | DBCR0_IC | DBCR0_IDM);
 115 #endif
 116
 117         /*
 118          * On powerpc we should single step on the original
 119          * instruction even if the probed insn is a trap
 120          * variant as values in regs could play a part in
 121          * if the trap is taken or not
 122          */
 123         regs->nip = (unsigned long)p->ainsn.insn;
 124 }
 125
 126 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 127 {
 128         kcb->prev_kprobe.kp = kprobe_running();
 129         kcb->prev_kprobe.status = kcb->kprobe_status;
 130         kcb->prev_kprobe.saved_msr = kcb->kprobe_saved_msr;
 131 }
 132
 133 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 134 {
 135         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
 136         kcb->kprobe_status = kcb->prev_kprobe.status;
 137         kcb->kprobe_saved_msr = kcb->prev_kprobe.saved_msr;
 138 }
 139
 140 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
 141                                 struct kprobe_ctlblk *kcb)
 142 {
 143         __get_cpu_var(current_kprobe) = p;
 144         kcb->kprobe_saved_msr = regs->msr;
 145 }
 146
 147 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 148                                       struct pt_regs *regs)
 149 {
 150         ri->ret_addr = (kprobe_opcode_t *)regs->link;
 151
 152         /* Replace the return addr with trampoline addr */
 153         regs->link = (unsigned long)kretprobe_trampoline;
 154 }
 155
 156 static int __kprobes kprobe_handler(struct pt_regs *regs)
 157 {
 158         struct kprobe *p;
 159         int ret = 0;
 160         unsigned int *addr = (unsigned int *)regs->nip;
 161         struct kprobe_ctlblk *kcb;
 162
 163         /*
 164          * We don't want to be preempted for the entire
 165          * duration of kprobe processing
 166          */
 167         preempt_disable();
 168         kcb = get_kprobe_ctlblk();
 169
 170         /* Check we're not actually recursing */
 171         if (kprobe_running()) {
 172                 p = get_kprobe(addr);
 173                 if (p) {
 174                         kprobe_opcode_t insn = *p->ainsn.insn;
 175                         if (kcb->kprobe_status == KPROBE_HIT_SS &&
 176                                         is_trap(insn)) {
 177                                 /* Turn off 'trace' bits */
 178                                 regs->msr &= ~MSR_SINGLESTEP;
 179                                 regs->msr |= kcb->kprobe_saved_msr;
 180                                 goto no_kprobe;
 181                         }
 182                         /* We have reentered the kprobe_handler(), since
 183                          * another probe was hit while within the handler.
 184                          * We here save the original kprobes variables and
 185                          * just single step on the instruction of the new probe
 186                          * without calling any user handlers.
 187                          */
 188                         save_previous_kprobe(kcb);
 189                         set_current_kprobe(p, regs, kcb);
 190                         kcb->kprobe_saved_msr = regs->msr;
 191                         kprobes_inc_nmissed_count(p);
 192                         prepare_singlestep(p, regs);
 193                         kcb->kprobe_status = KPROBE_REENTER;
 194                         return 1;
 195                 } else {
 196                         if (*addr != BREAKPOINT_INSTRUCTION) {
 197                                 /* If trap variant, then it belongs not to us */
 198                                 kprobe_opcode_t cur_insn = *addr;
 199                                 if (is_trap(cur_insn))
 200                                         goto no_kprobe;
 201                                 /* The breakpoint instruction was removed by
 202                                  * another cpu right after we hit, no further
 203                                  * handling of this interrupt is appropriate
 204                                  */
 205                                 ret = 1;
 206                                 goto no_kprobe;
 207                         }
 208                         p = __get_cpu_var(current_kprobe);
 209                         if (p->break_handler && p->break_handler(p, regs)) {
 210                                 goto ss_probe;
 211                         }
 212                 }
 213                 goto no_kprobe;
 214         }
 215
 216         p = get_kprobe(addr);
 217         if (!p) {
 218                 if (*addr != BREAKPOINT_INSTRUCTION) {
 219                         /*
 220                          * PowerPC has multiple variants of the "trap"
 221                          * instruction. If the current instruction is a
 222                          * trap variant, it could belong to someone else
 223                          */
 224                         kprobe_opcode_t cur_insn = *addr;
 225                         if (is_trap(cur_insn))
 226                                 goto no_kprobe;
 227                         /*
 228                          * The breakpoint instruction was removed right
 229                          * after we hit it.  Another cpu has removed
 230                          * either a probepoint or a debugger breakpoint
 231                          * at this address.  In either case, no further
 232                          * handling of this interrupt is appropriate.
 233                          */
 234                         ret = 1;
 235                 }
 236                 /* Not one of ours: let kernel handle it */
 237                 goto no_kprobe;
 238         }
 239
 240         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 241         set_current_kprobe(p, regs, kcb);
 242         if (p->pre_handler && p->pre_handler(p, regs))
 243                 /* handler has already set things up, so skip ss setup */
 244                 return 1;
 245
 246 ss_probe:
 247         if (p->ainsn.boostable >= 0) {
 248                 unsigned int insn = *p->ainsn.insn;
 249
 250                 /* regs->nip is also adjusted if emulate_step returns 1 */
 251                 ret = emulate_step(regs, insn);
 252                 if (ret > 0) {
 253                         /*
 254                          * Once this instruction has been boosted
 255                          * successfully, set the boostable flag
 256                          */
 257                         if (unlikely(p->ainsn.boostable == 0))
 258                                 p->ainsn.boostable = 1;
 259
 260                         if (p->post_handler)
 261                                 p->post_handler(p, regs, 0);
 262
 263                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 264                         reset_current_kprobe();
 265                         preempt_enable_no_resched();
 266                         return 1;
 267                 } else if (ret < 0) {
 268                         /*
 269                          * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
 270                          * So, we should never get here... but, its still
 271                          * good to catch them, just in case...
 272                          */
 273                         printk("Can't step on instruction %x\n", insn);
 274                         BUG();
 275                 } else if (ret == 0)
 276                         /* This instruction can't be boosted */
 277                         p->ainsn.boostable = -1;
 278         }
 279         prepare_singlestep(p, regs);
 280         kcb->kprobe_status = KPROBE_HIT_SS;
 281         return 1;
 282
 283 no_kprobe:
 284         preempt_enable_no_resched();
 285         return ret;
 286 }
 287
 288 /*
 289  * Function return probe trampoline:
 290  *      - init_kprobes() establishes a probepoint here
 291  *      - When the probed function returns, this probe
 292  *              causes the handlers to fire
 293  */
 294 static void __used kretprobe_trampoline_holder(void)
 295 {
 296         asm volatile(".global kretprobe_trampoline\n"
 297                         "kretprobe_trampoline:\n"
 298                         "nop\n");
 299 }
 300
 301 /*
 302  * Called when the probe at kretprobe trampoline is hit
 303  */
 304 static int __kprobes trampoline_probe_handler(struct kprobe *p,
 305                                                 struct pt_regs *regs)
 306 {
 307         struct kretprobe_instance *ri = NULL;
 308         struct hlist_head *head, empty_rp;
 309         struct hlist_node *node, *tmp;
 310         unsigned long flags, orig_ret_address = 0;
 311         unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
 312
 313         INIT_HLIST_HEAD(&empty_rp);
 314         kretprobe_hash_lock(current, &head, &flags);
 315
 316         /*
 317          * It is possible to have multiple instances associated with a given
 318          * task either because an multiple functions in the call path
 319          * have a return probe installed on them, and/or more than one return
 320          * return probe was registered for a target function.
 321          *
 322          * We can handle this because:
 323          *     - instances are always inserted at the head of the list
 324          *     - when multiple return probes are registered for the same
 325          *       function, the first instance's ret_addr will point to the
 326          *       real return address, and all the rest will point to
 327          *       kretprobe_trampoline
 328          */
 329         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
 330                 if (ri->task != current)
 331                         /* another task is sharing our hash bucket */
 332                         continue;
 333
 334                 if (ri->rp && ri->rp->handler)
 335                         ri->rp->handler(ri, regs);
 336
 337                 orig_ret_address = (unsigned long)ri->ret_addr;
 338                 recycle_rp_inst(ri, &empty_rp);
 339
 340                 if (orig_ret_address != trampoline_address)
 341                         /*
 342                          * This is the real return address. Any other
 343                          * instances associated with this task are for
 344                          * other calls deeper on the call stack
 345                          */
 346                         break;
 347         }
 348
 349         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 350         regs->nip = orig_ret_address;
 351
 352         reset_current_kprobe();
 353         kretprobe_hash_unlock(current, &flags);
 354         preempt_enable_no_resched();
 355
 356         hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
 357                 hlist_del(&ri->hlist);
 358                 kfree(ri);
 359         }
 360         /*
 361          * By returning a non-zero value, we are telling
 362          * kprobe_handler() that we don't want the post_handler
 363          * to run (and have re-enabled preemption)
 364          */
 365         return 1;
 366 }
 367
 368 /*
 369  * Called after single-stepping.  p->addr is the address of the
 370  * instruction whose first byte has been replaced by the "breakpoint"
 371  * instruction.  To avoid the SMP problems that can occur when we
 372  * temporarily put back the original opcode to single-step, we
 373  * single-stepped a copy of the instruction.  The address of this
 374  * copy is p->ainsn.insn.
 375  */
 376 static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
 377 {
 378         int ret;
 379         unsigned int insn = *p->ainsn.insn;
 380
 381         regs->nip = (unsigned long)p->addr;
 382         ret = emulate_step(regs, insn);
 383         if (ret == 0)
 384                 regs->nip = (unsigned long)p->addr + 4;
 385 }
 386
 387 static int __kprobes post_kprobe_handler(struct pt_regs *regs)
 388 {
 389         struct kprobe *cur = kprobe_running();
 390         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 391
 392         if (!cur)
 393                 return 0;
 394
 395         /* make sure we got here for instruction we have a kprobe on */
 396         if (((unsigned long)cur->ainsn.insn + 4) != regs->nip)
 397                 return 0;
 398
 399         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
 400                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
 401                 cur->post_handler(cur, regs, 0);
 402         }
 403
 404         resume_execution(cur, regs);
 405         regs->msr |= kcb->kprobe_saved_msr;
 406
 407         /*Restore back the original saved kprobes variables and continue. */
 408         if (kcb->kprobe_status == KPROBE_REENTER) {
 409                 restore_previous_kprobe(kcb);
 410                 goto out;
 411         }
 412         reset_current_kprobe();
 413 out:
 414         preempt_enable_no_resched();
 415
 416         /*
 417          * if somebody else is singlestepping across a probe point, msr
 418          * will have DE/SE set, in which case, continue the remaining processing
 419          * of do_debug, as if this is not a probe hit.
 420          */
 421         if (regs->msr & MSR_SINGLESTEP)
 422                 return 0;
 423
 424         return 1;
 425 }
 426
 427 int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 428 {
 429         struct kprobe *cur = kprobe_running();
 430         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 431         const struct exception_table_entry *entry;
 432
 433         switch(kcb->kprobe_status) {
 434         case KPROBE_HIT_SS:
 435         case KPROBE_REENTER:
 436                 /*
 437                  * We are here because the instruction being single
 438                  * stepped caused a page fault. We reset the current
 439                  * kprobe and the nip points back to the probe address
 440                  * and allow the page fault handler to continue as a
 441                  * normal page fault.
 442                  */
 443                 regs->nip = (unsigned long)cur->addr;
 444                 regs->msr &= ~MSR_SINGLESTEP; /* Turn off 'trace' bits */
 445                 regs->msr |= kcb->kprobe_saved_msr;
 446                 if (kcb->kprobe_status == KPROBE_REENTER)
 447                         restore_previous_kprobe(kcb);
 448                 else
 449                         reset_current_kprobe();
 450                 preempt_enable_no_resched();
 451                 break;
 452         case KPROBE_HIT_ACTIVE:
 453         case KPROBE_HIT_SSDONE:
 454                 /*
 455                  * We increment the nmissed count for accounting,
 456                  * we can also use npre/npostfault count for accouting
 457                  * these specific fault cases.
 458                  */
 459                 kprobes_inc_nmissed_count(cur);
 460
 461                 /*
 462                  * We come here because instructions in the pre/post
 463                  * handler caused the page_fault, this could happen
 464                  * if handler tries to access user space by
 465                  * copy_from_user(), get_user() etc. Let the
 466                  * user-specified handler try to fix it first.
 467                  */
 468                 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
 469                         return 1;
 470
 471                 /*
 472                  * In case the user-specified fault handler returned
 473                  * zero, try to fix up.
 474                  */
 475                 if ((entry = search_exception_tables(regs->nip)) != NULL) {
 476                         regs->nip = entry->fixup;
 477                         return 1;
 478                 }
 479
 480                 /*
 481                  * fixup_exception() could not handle it,
 482                  * Let do_page_fault() fix it.
 483                  */
 484                 break;
 485         default:
 486                 break;
 487         }
 488         return 0;
 489 }
 490
 491 /*
 492  * Wrapper routine to for handling exceptions.
 493  */
 494 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 495                                        unsigned long val, void *data)
 496 {
 497         struct die_args *args = (struct die_args *)data;
 498         int ret = NOTIFY_DONE;
 499
 500         if (args->regs && user_mode(args->regs))
 501                 return ret;
 502
 503         switch (val) {
 504         case DIE_BPT:
 505                 if (kprobe_handler(args->regs))
 506                         ret = NOTIFY_STOP;
 507                 break;
 508         case DIE_SSTEP:
 509                 if (post_kprobe_handler(args->regs))
 510                         ret = NOTIFY_STOP;
 511                 break;
 512         default:
 513                 break;
 514         }
 515         return ret;
 516 }
 517
 518 #ifdef CONFIG_PPC64
 519 unsigned long arch_deref_entry_point(void *entry)
 520 {
 521         return ((func_descr_t *)entry)->entry;
 522 }
 523 #endif
 524
 525 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 526 {
 527         struct jprobe *jp = container_of(p, struct jprobe, kp);
 528         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 529
 530         memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));
 531
 532         /* setup return addr to the jprobe handler routine */
 533         regs->nip = arch_deref_entry_point(jp->entry);
 534 #ifdef CONFIG_PPC64
 535         regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
 536 #endif
 537
 538         return 1;
 539 }
 540
 541 void __used __kprobes jprobe_return(void)
 542 {
 543         asm volatile("trap" ::: "memory");
 544 }
 545
 546 static void __used __kprobes jprobe_return_end(void)
 547 {
 548 };
 549
 550 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 551 {
 552         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 553
 554         /*
 555          * FIXME - we should ideally be validating that we got here 'cos
 556          * of the "trap" in jprobe_return() above, before restoring the
 557          * saved regs...
 558          */
 559         memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
 560         preempt_enable_no_resched();
 561         return 1;
 562 }
 563
 564 static struct kprobe trampoline_p = {
 565         .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
 566         .pre_handler = trampoline_probe_handler
 567 };
 568
 569 int __init arch_init_kprobes(void)
 570 {
 571         return register_kprobe(&trampoline_p);
 572 }
 573
 574 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 575 {
 576         if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
 577                 return 1;
 578
 579         return 0;
 580 }