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 <linux/slab.h>
  35 #include <asm/code-patching.h>
  36 #include <asm/cacheflush.h>
  37 #include <asm/sstep.h>
  38 #include <asm/uaccess.h>
  39
  40 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  41 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  42
  43 struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
  44
  45 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  46 {
  47         int ret = 0;
  48         kprobe_opcode_t insn = *p->addr;
  49
  50         if ((unsigned long)p->addr & 0x03) {
  51                 printk("Attempt to register kprobe at an unaligned address\n");
  52                 ret = -EINVAL;
  53         } else if (IS_MTMSRD(insn) || IS_RFID(insn) || IS_RFI(insn)) {
  54                 printk("Cannot register a kprobe on rfi/rfid or mtmsr[d]\n");
  55                 ret = -EINVAL;
  56         }
  57
  58         /* insn must be on a special executable page on ppc64.  This is
  59          * not explicitly required on ppc32 (right now), but it doesn't hurt */
  60         if (!ret) {
  61                 p->ainsn.insn = get_insn_slot();
  62                 if (!p->ainsn.insn)
  63                         ret = -ENOMEM;
  64         }
  65
  66         if (!ret) {
  67                 memcpy(p->ainsn.insn, p->addr,
  68                                 MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
  69                 p->opcode = *p->addr;
  70                 flush_icache_range((unsigned long)p->ainsn.insn,
  71                         (unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
  72         }
  73
  74         p->ainsn.boostable = 0;
  75         return ret;
  76 }
  77
  78 void __kprobes arch_arm_kprobe(struct kprobe *p)
  79 {
  80         *p->addr = BREAKPOINT_INSTRUCTION;
  81         flush_icache_range((unsigned long) p->addr,
  82                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
  83 }
  84
  85 void __kprobes arch_disarm_kprobe(struct kprobe *p)
  86 {
  87         *p->addr = p->opcode;
  88         flush_icache_range((unsigned long) p->addr,
  89                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
  90 }
  91
  92 void __kprobes arch_remove_kprobe(struct kprobe *p)
  93 {
  94         if (p->ainsn.insn) {
  95                 free_insn_slot(p->ainsn.insn, 0);
  96                 p->ainsn.insn = NULL;
  97         }
  98 }
  99
 100 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 101 {
 102         enable_single_step(regs);
 103
 104         /*
 105          * On powerpc we should single step on the original
 106          * instruction even if the probed insn is a trap
 107          * variant as values in regs could play a part in
 108          * if the trap is taken or not
 109          */
 110         regs->nip = (unsigned long)p->ainsn.insn;
 111 }
 112
 113 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 114 {
 115         kcb->prev_kprobe.kp = kprobe_running();
 116         kcb->prev_kprobe.status = kcb->kprobe_status;
 117         kcb->prev_kprobe.saved_msr = kcb->kprobe_saved_msr;
 118 }
 119
 120 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 121 {
 122         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 123         kcb->kprobe_status = kcb->prev_kprobe.status;
 124         kcb->kprobe_saved_msr = kcb->prev_kprobe.saved_msr;
 125 }
 126
 127 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
 128                                 struct kprobe_ctlblk *kcb)
 129 {
 130         __this_cpu_write(current_kprobe, p);
 131         kcb->kprobe_saved_msr = regs->msr;
 132 }
 133
 134 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 135                                       struct pt_regs *regs)
 136 {
 137         ri->ret_addr = (kprobe_opcode_t *)regs->link;
 138
 139         /* Replace the return addr with trampoline addr */
 140         regs->link = (unsigned long)kretprobe_trampoline;
 141 }
 142
 143 static int __kprobes kprobe_handler(struct pt_regs *regs)
 144 {
 145         struct kprobe *p;
 146         int ret = 0;
 147         unsigned int *addr = (unsigned int *)regs->nip;
 148         struct kprobe_ctlblk *kcb;
 149
 150         /*
 151          * We don't want to be preempted for the entire
 152          * duration of kprobe processing
 153          */
 154         preempt_disable();
 155         kcb = get_kprobe_ctlblk();
 156
 157         /* Check we're not actually recursing */
 158         if (kprobe_running()) {
 159                 p = get_kprobe(addr);
 160                 if (p) {
 161                         kprobe_opcode_t insn = *p->ainsn.insn;
 162                         if (kcb->kprobe_status == KPROBE_HIT_SS &&
 163                                         is_trap(insn)) {
 164                                 /* Turn off 'trace' bits */
 165                                 regs->msr &= ~MSR_SINGLESTEP;
 166                                 regs->msr |= kcb->kprobe_saved_msr;
 167                                 goto no_kprobe;
 168                         }
 169                         /* We have reentered the kprobe_handler(), since
 170                          * another probe was hit while within the handler.
 171                          * We here save the original kprobes variables and
 172                          * just single step on the instruction of the new probe
 173                          * without calling any user handlers.
 174                          */
 175                         save_previous_kprobe(kcb);
 176                         set_current_kprobe(p, regs, kcb);
 177                         kcb->kprobe_saved_msr = regs->msr;
 178                         kprobes_inc_nmissed_count(p);
 179                         prepare_singlestep(p, regs);
 180                         kcb->kprobe_status = KPROBE_REENTER;
 181                         return 1;
 182                 } else {
 183                         if (*addr != BREAKPOINT_INSTRUCTION) {
 184                                 /* If trap variant, then it belongs not to us */
 185                                 kprobe_opcode_t cur_insn = *addr;
 186                                 if (is_trap(cur_insn))
 187                                         goto no_kprobe;
 188                                 /* The breakpoint instruction was removed by
 189                                  * another cpu right after we hit, no further
 190                                  * handling of this interrupt is appropriate
 191                                  */
 192                                 ret = 1;
 193                                 goto no_kprobe;
 194                         }
 195                         p = __this_cpu_read(current_kprobe);
 196                         if (p->break_handler && p->break_handler(p, regs)) {
 197                                 goto ss_probe;
 198                         }
 199                 }
 200                 goto no_kprobe;
 201         }
 202
 203         p = get_kprobe(addr);
 204         if (!p) {
 205                 if (*addr != BREAKPOINT_INSTRUCTION) {
 206                         /*
 207                          * PowerPC has multiple variants of the "trap"
 208                          * instruction. If the current instruction is a
 209                          * trap variant, it could belong to someone else
 210                          */
 211                         kprobe_opcode_t cur_insn = *addr;
 212                         if (is_trap(cur_insn))
 213                                 goto no_kprobe;
 214                         /*
 215                          * The breakpoint instruction was removed right
 216                          * after we hit it.  Another cpu has removed
 217                          * either a probepoint or a debugger breakpoint
 218                          * at this address.  In either case, no further
 219                          * handling of this interrupt is appropriate.
 220                          */
 221                         ret = 1;
 222                 }
 223                 /* Not one of ours: let kernel handle it */
 224                 goto no_kprobe;
 225         }
 226
 227         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 228         set_current_kprobe(p, regs, kcb);
 229         if (p->pre_handler && p->pre_handler(p, regs))
 230                 /* handler has already set things up, so skip ss setup */
 231                 return 1;
 232
 233 ss_probe:
 234         if (p->ainsn.boostable >= 0) {
 235                 unsigned int insn = *p->ainsn.insn;
 236
 237                 /* regs->nip is also adjusted if emulate_step returns 1 */
 238                 ret = emulate_step(regs, insn);
 239                 if (ret > 0) {
 240                         /*
 241                          * Once this instruction has been boosted
 242                          * successfully, set the boostable flag
 243                          */
 244                         if (unlikely(p->ainsn.boostable == 0))
 245                                 p->ainsn.boostable = 1;
 246
 247                         if (p->post_handler)
 248                                 p->post_handler(p, regs, 0);
 249
 250                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 251                         reset_current_kprobe();
 252                         preempt_enable_no_resched();
 253                         return 1;
 254                 } else if (ret < 0) {
 255                         /*
 256                          * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
 257                          * So, we should never get here... but, its still
 258                          * good to catch them, just in case...
 259                          */
 260                         printk("Can't step on instruction %x\n", insn);
 261                         BUG();
 262                 } else if (ret == 0)
 263                         /* This instruction can't be boosted */
 264                         p->ainsn.boostable = -1;
 265         }
 266         prepare_singlestep(p, regs);
 267         kcb->kprobe_status = KPROBE_HIT_SS;
 268         return 1;
 269
 270 no_kprobe:
 271         preempt_enable_no_resched();
 272         return ret;
 273 }
 274
 275 /*
 276  * Function return probe trampoline:
 277  *      - init_kprobes() establishes a probepoint here
 278  *      - When the probed function returns, this probe
 279  *              causes the handlers to fire
 280  */
 281 static void __used kretprobe_trampoline_holder(void)
 282 {
 283         asm volatile(".global kretprobe_trampoline\n"
 284                         "kretprobe_trampoline:\n"
 285                         "nop\n");
 286 }
 287
 288 /*
 289  * Called when the probe at kretprobe trampoline is hit
 290  */
 291 static int __kprobes trampoline_probe_handler(struct kprobe *p,
 292                                                 struct pt_regs *regs)
 293 {
 294         struct kretprobe_instance *ri = NULL;
 295         struct hlist_head *head, empty_rp;
 296         struct hlist_node *tmp;
 297         unsigned long flags, orig_ret_address = 0;
 298         unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
 299
 300         INIT_HLIST_HEAD(&empty_rp);
 301         kretprobe_hash_lock(current, &head, &flags);
 302
 303         /*
 304          * It is possible to have multiple instances associated with a given
 305          * task either because an multiple functions in the call path
 306          * have a return probe installed on them, and/or more than one return
 307          * return probe was registered for a target function.
 308          *
 309          * We can handle this because:
 310          *     - instances are always inserted at the head of the list
 311          *     - when multiple return probes are registered for the same
 312          *       function, the first instance's ret_addr will point to the
 313          *       real return address, and all the rest will point to
 314          *       kretprobe_trampoline
 315          */
 316         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 317                 if (ri->task != current)
 318                         /* another task is sharing our hash bucket */
 319                         continue;
 320
 321                 if (ri->rp && ri->rp->handler)
 322                         ri->rp->handler(ri, regs);
 323
 324                 orig_ret_address = (unsigned long)ri->ret_addr;
 325                 recycle_rp_inst(ri, &empty_rp);
 326
 327                 if (orig_ret_address != trampoline_address)
 328                         /*
 329                          * This is the real return address. Any other
 330                          * instances associated with this task are for
 331                          * other calls deeper on the call stack
 332                          */
 333                         break;
 334         }
 335
 336         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 337         regs->nip = orig_ret_address;
 338
 339         reset_current_kprobe();
 340         kretprobe_hash_unlock(current, &flags);
 341         preempt_enable_no_resched();
 342
 343         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
 344                 hlist_del(&ri->hlist);
 345                 kfree(ri);
 346         }
 347         /*
 348          * By returning a non-zero value, we are telling
 349          * kprobe_handler() that we don't want the post_handler
 350          * to run (and have re-enabled preemption)
 351          */
 352         return 1;
 353 }
 354
 355 /*
 356  * Called after single-stepping.  p->addr is the address of the
 357  * instruction whose first byte has been replaced by the "breakpoint"
 358  * instruction.  To avoid the SMP problems that can occur when we
 359  * temporarily put back the original opcode to single-step, we
 360  * single-stepped a copy of the instruction.  The address of this
 361  * copy is p->ainsn.insn.
 362  */
 363 static int __kprobes post_kprobe_handler(struct pt_regs *regs)
 364 {
 365         struct kprobe *cur = kprobe_running();
 366         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 367
 368         if (!cur)
 369                 return 0;
 370
 371         /* make sure we got here for instruction we have a kprobe on */
 372         if (((unsigned long)cur->ainsn.insn + 4) != regs->nip)
 373                 return 0;
 374
 375         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
 376                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
 377                 cur->post_handler(cur, regs, 0);
 378         }
 379
 380         /* Adjust nip to after the single-stepped instruction */
 381         regs->nip = (unsigned long)cur->addr + 4;
 382         regs->msr |= kcb->kprobe_saved_msr;
 383
 384         /*Restore back the original saved kprobes variables and continue. */
 385         if (kcb->kprobe_status == KPROBE_REENTER) {
 386                 restore_previous_kprobe(kcb);
 387                 goto out;
 388         }
 389         reset_current_kprobe();
 390 out:
 391         preempt_enable_no_resched();
 392
 393         /*
 394          * if somebody else is singlestepping across a probe point, msr
 395          * will have DE/SE set, in which case, continue the remaining processing
 396          * of do_debug, as if this is not a probe hit.
 397          */
 398         if (regs->msr & MSR_SINGLESTEP)
 399                 return 0;
 400
 401         return 1;
 402 }
 403
 404 int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 405 {
 406         struct kprobe *cur = kprobe_running();
 407         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 408         const struct exception_table_entry *entry;
 409
 410         switch(kcb->kprobe_status) {
 411         case KPROBE_HIT_SS:
 412         case KPROBE_REENTER:
 413                 /*
 414                  * We are here because the instruction being single
 415                  * stepped caused a page fault. We reset the current
 416                  * kprobe and the nip points back to the probe address
 417                  * and allow the page fault handler to continue as a
 418                  * normal page fault.
 419                  */
 420                 regs->nip = (unsigned long)cur->addr;
 421                 regs->msr &= ~MSR_SINGLESTEP; /* Turn off 'trace' bits */
 422                 regs->msr |= kcb->kprobe_saved_msr;
 423                 if (kcb->kprobe_status == KPROBE_REENTER)
 424                         restore_previous_kprobe(kcb);
 425                 else
 426                         reset_current_kprobe();
 427                 preempt_enable_no_resched();
 428                 break;
 429         case KPROBE_HIT_ACTIVE:
 430         case KPROBE_HIT_SSDONE:
 431                 /*
 432                  * We increment the nmissed count for accounting,
 433                  * we can also use npre/npostfault count for accounting
 434                  * these specific fault cases.
 435                  */
 436                 kprobes_inc_nmissed_count(cur);
 437
 438                 /*
 439                  * We come here because instructions in the pre/post
 440                  * handler caused the page_fault, this could happen
 441                  * if handler tries to access user space by
 442                  * copy_from_user(), get_user() etc. Let the
 443                  * user-specified handler try to fix it first.
 444                  */
 445                 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
 446                         return 1;
 447
 448                 /*
 449                  * In case the user-specified fault handler returned
 450                  * zero, try to fix up.
 451                  */
 452                 if ((entry = search_exception_tables(regs->nip)) != NULL) {
 453                         regs->nip = entry->fixup;
 454                         return 1;
 455                 }
 456
 457                 /*
 458                  * fixup_exception() could not handle it,
 459                  * Let do_page_fault() fix it.
 460                  */
 461                 break;
 462         default:
 463                 break;
 464         }
 465         return 0;
 466 }
 467
 468 /*
 469  * Wrapper routine to for handling exceptions.
 470  */
 471 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 472                                        unsigned long val, void *data)
 473 {
 474         struct die_args *args = (struct die_args *)data;
 475         int ret = NOTIFY_DONE;
 476
 477         if (args->regs && user_mode(args->regs))
 478                 return ret;
 479
 480         switch (val) {
 481         case DIE_BPT:
 482                 if (kprobe_handler(args->regs))
 483                         ret = NOTIFY_STOP;
 484                 break;
 485         case DIE_SSTEP:
 486                 if (post_kprobe_handler(args->regs))
 487                         ret = NOTIFY_STOP;
 488                 break;
 489         default:
 490                 break;
 491         }
 492         return ret;
 493 }
 494
 495 unsigned long arch_deref_entry_point(void *entry)
 496 {
 497         return ppc_global_function_entry(entry);
 498 }
 499
 500 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 501 {
 502         struct jprobe *jp = container_of(p, struct jprobe, kp);
 503         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 504
 505         memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));
 506
 507         /* setup return addr to the jprobe handler routine */
 508         regs->nip = arch_deref_entry_point(jp->entry);
 509 #ifdef CONFIG_PPC64
 510 #if defined(_CALL_ELF) && _CALL_ELF == 2
 511         regs->gpr[12] = (unsigned long)jp->entry;
 512 #else
 513         regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
 514 #endif
 515 #endif
 516
 517         return 1;
 518 }
 519
 520 void __used __kprobes jprobe_return(void)
 521 {
 522         asm volatile("trap" ::: "memory");
 523 }
 524
 525 static void __used __kprobes jprobe_return_end(void)
 526 {
 527 };
 528
 529 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 530 {
 531         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 532
 533         /*
 534          * FIXME - we should ideally be validating that we got here 'cos
 535          * of the "trap" in jprobe_return() above, before restoring the
 536          * saved regs...
 537          */
 538         memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
 539         preempt_enable_no_resched();
 540         return 1;
 541 }
 542
 543 static struct kprobe trampoline_p = {
 544         .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
 545         .pre_handler = trampoline_probe_handler
 546 };
 547
 548 int __init arch_init_kprobes(void)
 549 {
 550         return register_kprobe(&trampoline_p);
 551 }
 552
 553 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 554 {
 555         if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
 556                 return 1;
 557
 558         return 0;
 559 }