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