arch/s390/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, 2006
  19  *
  20  * s390 port, used ppc64 as template. Mike Grundy <grundym@us.ibm.com>
  21  */
  22
  23 #include <linux/config.h>
  24 #include <linux/kprobes.h>
  25 #include <linux/ptrace.h>
  26 #include <linux/preempt.h>
  27 #include <linux/stop_machine.h>
  28 #include <asm/cacheflush.h>
  29 #include <asm/kdebug.h>
  30 #include <asm/sections.h>
  31 #include <asm/uaccess.h>
  32 #include <linux/module.h>
  33
  34 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  35 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  36
  37 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  38 {
  39         /* Make sure the probe isn't going on a difficult instruction */
  40         if (is_prohibited_opcode((kprobe_opcode_t *) p->addr))
  41                 return -EINVAL;
  42
  43         if ((unsigned long)p->addr & 0x01) {
  44                 printk("Attempt to register kprobe at an unaligned address\n");
  45                 return -EINVAL;
  46                 }
  47
  48         /* Use the get_insn_slot() facility for correctness */
  49         if (!(p->ainsn.insn = get_insn_slot()))
  50                 return -ENOMEM;
  51
  52         memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
  53
  54         get_instruction_type(&p->ainsn);
  55         p->opcode = *p->addr;
  56         return 0;
  57 }
  58
  59 int __kprobes is_prohibited_opcode(kprobe_opcode_t *instruction)
  60 {
  61         switch (*(__u8 *) instruction) {
  62         case 0x0c:      /* bassm */
  63         case 0x0b:      /* bsm   */
  64         case 0x83:      /* diag  */
  65         case 0x44:      /* ex    */
  66                 return -EINVAL;
  67         }
  68         switch (*(__u16 *) instruction) {
  69         case 0x0101:    /* pr    */
  70         case 0xb25a:    /* bsa   */
  71         case 0xb240:    /* bakr  */
  72         case 0xb258:    /* bsg   */
  73         case 0xb218:    /* pc    */
  74         case 0xb228:    /* pt    */
  75                 return -EINVAL;
  76         }
  77         return 0;
  78 }
  79
  80 void __kprobes get_instruction_type(struct arch_specific_insn *ainsn)
  81 {
  82         /* default fixup method */
  83         ainsn->fixup = FIXUP_PSW_NORMAL;
  84
  85         /* save r1 operand */
  86         ainsn->reg = (*ainsn->insn & 0xf0) >> 4;
  87
  88         /* save the instruction length (pop 5-5) in bytes */
  89         switch (*(__u8 *) (ainsn->insn) >> 4) {
  90         case 0:
  91                 ainsn->ilen = 2;
  92                 break;
  93         case 1:
  94         case 2:
  95                 ainsn->ilen = 4;
  96                 break;
  97         case 3:
  98                 ainsn->ilen = 6;
  99                 break;
 100         }
 101
 102         switch (*(__u8 *) ainsn->insn) {
 103         case 0x05:      /* balr */
 104         case 0x0d:      /* basr */
 105                 ainsn->fixup = FIXUP_RETURN_REGISTER;
 106                 /* if r2 = 0, no branch will be taken */
 107                 if ((*ainsn->insn & 0x0f) == 0)
 108                         ainsn->fixup |= FIXUP_BRANCH_NOT_TAKEN;
 109                 break;
 110         case 0x06:      /* bctr */
 111         case 0x07:      /* bcr  */
 112                 ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
 113                 break;
 114         case 0x45:      /* bal  */
 115         case 0x4d:      /* bas  */
 116                 ainsn->fixup = FIXUP_RETURN_REGISTER;
 117                 break;
 118         case 0x47:      /* bc   */
 119         case 0x46:      /* bct  */
 120         case 0x86:      /* bxh  */
 121         case 0x87:      /* bxle */
 122                 ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
 123                 break;
 124         case 0x82:      /* lpsw */
 125                 ainsn->fixup = FIXUP_NOT_REQUIRED;
 126                 break;
 127         case 0xb2:      /* lpswe */
 128                 if (*(((__u8 *) ainsn->insn) + 1) == 0xb2) {
 129                         ainsn->fixup = FIXUP_NOT_REQUIRED;
 130                 }
 131                 break;
 132         case 0xa7:      /* bras */
 133                 if ((*ainsn->insn & 0x0f) == 0x05) {
 134                         ainsn->fixup |= FIXUP_RETURN_REGISTER;
 135                 }
 136                 break;
 137         case 0xc0:
 138                 if ((*ainsn->insn & 0x0f) == 0x00  /* larl  */
 139                         || (*ainsn->insn & 0x0f) == 0x05) /* brasl */
 140                 ainsn->fixup |= FIXUP_RETURN_REGISTER;
 141                 break;
 142         case 0xeb:
 143                 if (*(((__u8 *) ainsn->insn) + 5 ) == 0x44 ||   /* bxhg  */
 144                         *(((__u8 *) ainsn->insn) + 5) == 0x45) {/* bxleg */
 145                         ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
 146                 }
 147                 break;
 148         case 0xe3:      /* bctg */
 149                 if (*(((__u8 *) ainsn->insn) + 5) == 0x46) {
 150                         ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
 151                 }
 152                 break;
 153         }
 154 }
 155
 156 static int __kprobes swap_instruction(void *aref)
 157 {
 158         struct ins_replace_args *args = aref;
 159         int err = -EFAULT;
 160
 161         asm volatile(
 162                 "0: mvc  0(2,%2),0(%3)\n"
 163                 "1: la   %0,0\n"
 164                 "2:\n"
 165                 EX_TABLE(0b,2b)
 166                 : "+d" (err), "=m" (*args->ptr)
 167                 : "a" (args->ptr), "a" (&args->new), "m" (args->new));
 168         return err;
 169 }
 170
 171 void __kprobes arch_arm_kprobe(struct kprobe *p)
 172 {
 173         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 174         unsigned long status = kcb->kprobe_status;
 175         struct ins_replace_args args;
 176
 177         args.ptr = p->addr;
 178         args.old = p->opcode;
 179         args.new = BREAKPOINT_INSTRUCTION;
 180
 181         kcb->kprobe_status = KPROBE_SWAP_INST;
 182         stop_machine_run(swap_instruction, &args, NR_CPUS);
 183         kcb->kprobe_status = status;
 184 }
 185
 186 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 187 {
 188         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 189         unsigned long status = kcb->kprobe_status;
 190         struct ins_replace_args args;
 191
 192         args.ptr = p->addr;
 193         args.old = BREAKPOINT_INSTRUCTION;
 194         args.new = p->opcode;
 195
 196         kcb->kprobe_status = KPROBE_SWAP_INST;
 197         stop_machine_run(swap_instruction, &args, NR_CPUS);
 198         kcb->kprobe_status = status;
 199 }
 200
 201 void __kprobes arch_remove_kprobe(struct kprobe *p)
 202 {
 203         mutex_lock(&kprobe_mutex);
 204         free_insn_slot(p->ainsn.insn);
 205         mutex_unlock(&kprobe_mutex);
 206 }
 207
 208 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 209 {
 210         per_cr_bits kprobe_per_regs[1];
 211
 212         memset(kprobe_per_regs, 0, sizeof(per_cr_bits));
 213         regs->psw.addr = (unsigned long)p->ainsn.insn | PSW_ADDR_AMODE;
 214
 215         /* Set up the per control reg info, will pass to lctl */
 216         kprobe_per_regs[0].em_instruction_fetch = 1;
 217         kprobe_per_regs[0].starting_addr = (unsigned long)p->ainsn.insn;
 218         kprobe_per_regs[0].ending_addr = (unsigned long)p->ainsn.insn + 1;
 219
 220         /* Set the PER control regs, turns on single step for this address */
 221         __ctl_load(kprobe_per_regs, 9, 11);
 222         regs->psw.mask |= PSW_MASK_PER;
 223         regs->psw.mask &= ~(PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
 224 }
 225
 226 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 227 {
 228         kcb->prev_kprobe.kp = kprobe_running();
 229         kcb->prev_kprobe.status = kcb->kprobe_status;
 230         kcb->prev_kprobe.kprobe_saved_imask = kcb->kprobe_saved_imask;
 231         memcpy(kcb->prev_kprobe.kprobe_saved_ctl, kcb->kprobe_saved_ctl,
 232                                         sizeof(kcb->kprobe_saved_ctl));
 233 }
 234
 235 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 236 {
 237         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
 238         kcb->kprobe_status = kcb->prev_kprobe.status;
 239         kcb->kprobe_saved_imask = kcb->prev_kprobe.kprobe_saved_imask;
 240         memcpy(kcb->kprobe_saved_ctl, kcb->prev_kprobe.kprobe_saved_ctl,
 241                                         sizeof(kcb->kprobe_saved_ctl));
 242 }
 243
 244 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
 245                                                 struct kprobe_ctlblk *kcb)
 246 {
 247         __get_cpu_var(current_kprobe) = p;
 248         /* Save the interrupt and per flags */
 249         kcb->kprobe_saved_imask = regs->psw.mask &
 250             (PSW_MASK_PER | PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
 251         /* Save the control regs that govern PER */
 252         __ctl_store(kcb->kprobe_saved_ctl, 9, 11);
 253 }
 254
 255 /* Called with kretprobe_lock held */
 256 void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
 257                                         struct pt_regs *regs)
 258 {
 259         struct kretprobe_instance *ri;
 260
 261         if ((ri = get_free_rp_inst(rp)) != NULL) {
 262                 ri->rp = rp;
 263                 ri->task = current;
 264                 ri->ret_addr = (kprobe_opcode_t *) regs->gprs[14];
 265
 266                 /* Replace the return addr with trampoline addr */
 267                 regs->gprs[14] = (unsigned long)&kretprobe_trampoline;
 268
 269                 add_rp_inst(ri);
 270         } else {
 271                 rp->nmissed++;
 272         }
 273 }
 274
 275 static int __kprobes kprobe_handler(struct pt_regs *regs)
 276 {
 277         struct kprobe *p;
 278         int ret = 0;
 279         unsigned long *addr = (unsigned long *)
 280                 ((regs->psw.addr & PSW_ADDR_INSN) - 2);
 281         struct kprobe_ctlblk *kcb;
 282
 283         /*
 284          * We don't want to be preempted for the entire
 285          * duration of kprobe processing
 286          */
 287         preempt_disable();
 288         kcb = get_kprobe_ctlblk();
 289
 290         /* Check we're not actually recursing */
 291         if (kprobe_running()) {
 292                 p = get_kprobe(addr);
 293                 if (p) {
 294                         if (kcb->kprobe_status == KPROBE_HIT_SS &&
 295                             *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
 296                                 regs->psw.mask &= ~PSW_MASK_PER;
 297                                 regs->psw.mask |= kcb->kprobe_saved_imask;
 298                                 goto no_kprobe;
 299                         }
 300                         /* We have reentered the kprobe_handler(), since
 301                          * another probe was hit while within the handler.
 302                          * We here save the original kprobes variables and
 303                          * just single step on the instruction of the new probe
 304                          * without calling any user handlers.
 305                          */
 306                         save_previous_kprobe(kcb);
 307                         set_current_kprobe(p, regs, kcb);
 308                         kprobes_inc_nmissed_count(p);
 309                         prepare_singlestep(p, regs);
 310                         kcb->kprobe_status = KPROBE_REENTER;
 311                         return 1;
 312                 } else {
 313                         p = __get_cpu_var(current_kprobe);
 314                         if (p->break_handler && p->break_handler(p, regs)) {
 315                                 goto ss_probe;
 316                         }
 317                 }
 318                 goto no_kprobe;
 319         }
 320
 321         p = get_kprobe(addr);
 322         if (!p) {
 323                 if (*addr != BREAKPOINT_INSTRUCTION) {
 324                         /*
 325                          * The breakpoint instruction was removed right
 326                          * after we hit it.  Another cpu has removed
 327                          * either a probepoint or a debugger breakpoint
 328                          * at this address.  In either case, no further
 329                          * handling of this interrupt is appropriate.
 330                          *
 331                          */
 332                         ret = 1;
 333                 }
 334                 /* Not one of ours: let kernel handle it */
 335                 goto no_kprobe;
 336         }
 337
 338         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 339         set_current_kprobe(p, regs, kcb);
 340         if (p->pre_handler && p->pre_handler(p, regs))
 341                 /* handler has already set things up, so skip ss setup */
 342                 return 1;
 343
 344 ss_probe:
 345         prepare_singlestep(p, regs);
 346         kcb->kprobe_status = KPROBE_HIT_SS;
 347         return 1;
 348
 349 no_kprobe:
 350         preempt_enable_no_resched();
 351         return ret;
 352 }
 353
 354 /*
 355  * Function return probe trampoline:
 356  *      - init_kprobes() establishes a probepoint here
 357  *      - When the probed function returns, this probe
 358  *              causes the handlers to fire
 359  */
 360 void __kprobes kretprobe_trampoline_holder(void)
 361 {
 362         asm volatile(".global kretprobe_trampoline\n"
 363                      "kretprobe_trampoline: bcr 0,0\n");
 364 }
 365
 366 /*
 367  * Called when the probe at kretprobe trampoline is hit
 368  */
 369 int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
 370 {
 371         struct kretprobe_instance *ri = NULL;
 372         struct hlist_head *head;
 373         struct hlist_node *node, *tmp;
 374         unsigned long flags, orig_ret_address = 0;
 375         unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
 376
 377         spin_lock_irqsave(&kretprobe_lock, flags);
 378         head = kretprobe_inst_table_head(current);
 379
 380         /*
 381          * It is possible to have multiple instances associated with a given
 382          * task either because an multiple functions in the call path
 383          * have a return probe installed on them, and/or more then one return
 384          * return probe was registered for a target function.
 385          *
 386          * We can handle this because:
 387          *     - instances are always inserted at the head of the list
 388          *     - when multiple return probes are registered for the same
 389          *       function, the first instance's ret_addr will point to the
 390          *       real return address, and all the rest will point to
 391          *       kretprobe_trampoline
 392          */
 393         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
 394                 if (ri->task != current)
 395                         /* another task is sharing our hash bucket */
 396                         continue;
 397
 398                 if (ri->rp && ri->rp->handler)
 399                         ri->rp->handler(ri, regs);
 400
 401                 orig_ret_address = (unsigned long)ri->ret_addr;
 402                 recycle_rp_inst(ri);
 403
 404                 if (orig_ret_address != trampoline_address) {
 405                         /*
 406                          * This is the real return address. Any other
 407                          * instances associated with this task are for
 408                          * other calls deeper on the call stack
 409                          */
 410                         break;
 411                 }
 412         }
 413         BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
 414         regs->psw.addr = orig_ret_address | PSW_ADDR_AMODE;
 415
 416         reset_current_kprobe();
 417         spin_unlock_irqrestore(&kretprobe_lock, flags);
 418         preempt_enable_no_resched();
 419
 420         /*
 421          * By returning a non-zero value, we are telling
 422          * kprobe_handler() that we don't want the post_handler
 423          * to run (and have re-enabled preemption)
 424          */
 425         return 1;
 426 }
 427
 428 /*
 429  * Called after single-stepping.  p->addr is the address of the
 430  * instruction whose first byte has been replaced by the "breakpoint"
 431  * instruction.  To avoid the SMP problems that can occur when we
 432  * temporarily put back the original opcode to single-step, we
 433  * single-stepped a copy of the instruction.  The address of this
 434  * copy is p->ainsn.insn.
 435  */
 436 static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
 437 {
 438         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 439
 440         regs->psw.addr &= PSW_ADDR_INSN;
 441
 442         if (p->ainsn.fixup & FIXUP_PSW_NORMAL)
 443                 regs->psw.addr = (unsigned long)p->addr +
 444                                 ((unsigned long)regs->psw.addr -
 445                                  (unsigned long)p->ainsn.insn);
 446
 447         if (p->ainsn.fixup & FIXUP_BRANCH_NOT_TAKEN)
 448                 if ((unsigned long)regs->psw.addr -
 449                     (unsigned long)p->ainsn.insn == p->ainsn.ilen)
 450                         regs->psw.addr = (unsigned long)p->addr + p->ainsn.ilen;
 451
 452         if (p->ainsn.fixup & FIXUP_RETURN_REGISTER)
 453                 regs->gprs[p->ainsn.reg] = ((unsigned long)p->addr +
 454                                                 (regs->gprs[p->ainsn.reg] -
 455                                                 (unsigned long)p->ainsn.insn))
 456                                                 | PSW_ADDR_AMODE;
 457
 458         regs->psw.addr |= PSW_ADDR_AMODE;
 459         /* turn off PER mode */
 460         regs->psw.mask &= ~PSW_MASK_PER;
 461         /* Restore the original per control regs */
 462         __ctl_load(kcb->kprobe_saved_ctl, 9, 11);
 463         regs->psw.mask |= kcb->kprobe_saved_imask;
 464 }
 465
 466 static int __kprobes post_kprobe_handler(struct pt_regs *regs)
 467 {
 468         struct kprobe *cur = kprobe_running();
 469         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 470
 471         if (!cur)
 472                 return 0;
 473
 474         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
 475                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
 476                 cur->post_handler(cur, regs, 0);
 477         }
 478
 479         resume_execution(cur, regs);
 480
 481         /*Restore back the original saved kprobes variables and continue. */
 482         if (kcb->kprobe_status == KPROBE_REENTER) {
 483                 restore_previous_kprobe(kcb);
 484                 goto out;
 485         }
 486         reset_current_kprobe();
 487 out:
 488         preempt_enable_no_resched();
 489
 490         /*
 491          * if somebody else is singlestepping across a probe point, psw mask
 492          * will have PER set, in which case, continue the remaining processing
 493          * of do_single_step, as if this is not a probe hit.
 494          */
 495         if (regs->psw.mask & PSW_MASK_PER) {
 496                 return 0;
 497         }
 498
 499         return 1;
 500 }
 501
 502 static int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 503 {
 504         struct kprobe *cur = kprobe_running();
 505         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 506         const struct exception_table_entry *entry;
 507
 508         switch(kcb->kprobe_status) {
 509         case KPROBE_SWAP_INST:
 510                 /* We are here because the instruction replacement failed */
 511                 return 0;
 512         case KPROBE_HIT_SS:
 513         case KPROBE_REENTER:
 514                 /*
 515                  * We are here because the instruction being single
 516                  * stepped caused a page fault. We reset the current
 517                  * kprobe and the nip points back to the probe address
 518                  * and allow the page fault handler to continue as a
 519                  * normal page fault.
 520                  */
 521                 regs->psw.addr = (unsigned long)cur->addr | PSW_ADDR_AMODE;
 522                 regs->psw.mask &= ~PSW_MASK_PER;
 523                 regs->psw.mask |= kcb->kprobe_saved_imask;
 524                 if (kcb->kprobe_status == KPROBE_REENTER)
 525                         restore_previous_kprobe(kcb);
 526                 else
 527                         reset_current_kprobe();
 528                 preempt_enable_no_resched();
 529                 break;
 530         case KPROBE_HIT_ACTIVE:
 531         case KPROBE_HIT_SSDONE:
 532                 /*
 533                  * We increment the nmissed count for accounting,
 534                  * we can also use npre/npostfault count for accouting
 535                  * these specific fault cases.
 536                  */
 537                 kprobes_inc_nmissed_count(cur);
 538
 539                 /*
 540                  * We come here because instructions in the pre/post
 541                  * handler caused the page_fault, this could happen
 542                  * if handler tries to access user space by
 543                  * copy_from_user(), get_user() etc. Let the
 544                  * user-specified handler try to fix it first.
 545                  */
 546                 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
 547                         return 1;
 548
 549                 /*
 550                  * In case the user-specified fault handler returned
 551                  * zero, try to fix up.
 552                  */
 553                 entry = search_exception_tables(regs->psw.addr & PSW_ADDR_INSN);
 554                 if (entry) {
 555                         regs->psw.addr = entry->fixup | PSW_ADDR_AMODE;
 556                         return 1;
 557                 }
 558
 559                 /*
 560                  * fixup_exception() could not handle it,
 561                  * Let do_page_fault() fix it.
 562                  */
 563                 break;
 564         default:
 565                 break;
 566         }
 567         return 0;
 568 }
 569
 570 /*
 571  * Wrapper routine to for handling exceptions.
 572  */
 573 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 574                                        unsigned long val, void *data)
 575 {
 576         struct die_args *args = (struct die_args *)data;
 577         int ret = NOTIFY_DONE;
 578
 579         switch (val) {
 580         case DIE_BPT:
 581                 if (kprobe_handler(args->regs))
 582                         ret = NOTIFY_STOP;
 583                 break;
 584         case DIE_SSTEP:
 585                 if (post_kprobe_handler(args->regs))
 586                         ret = NOTIFY_STOP;
 587                 break;
 588         case DIE_TRAP:
 589         case DIE_PAGE_FAULT:
 590                 /* kprobe_running() needs smp_processor_id() */
 591                 preempt_disable();
 592                 if (kprobe_running() &&
 593                     kprobe_fault_handler(args->regs, args->trapnr))
 594                         ret = NOTIFY_STOP;
 595                 preempt_enable();
 596                 break;
 597         default:
 598                 break;
 599         }
 600         return ret;
 601 }
 602
 603 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 604 {
 605         struct jprobe *jp = container_of(p, struct jprobe, kp);
 606         unsigned long addr;
 607         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 608
 609         memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));
 610
 611         /* setup return addr to the jprobe handler routine */
 612         regs->psw.addr = (unsigned long)(jp->entry) | PSW_ADDR_AMODE;
 613
 614         /* r14 is the function return address */
 615         kcb->jprobe_saved_r14 = (unsigned long)regs->gprs[14];
 616         /* r15 is the stack pointer */
 617         kcb->jprobe_saved_r15 = (unsigned long)regs->gprs[15];
 618         addr = (unsigned long)kcb->jprobe_saved_r15;
 619
 620         memcpy(kcb->jprobes_stack, (kprobe_opcode_t *) addr,
 621                MIN_STACK_SIZE(addr));
 622         return 1;
 623 }
 624
 625 void __kprobes jprobe_return(void)
 626 {
 627         asm volatile(".word 0x0002");
 628 }
 629
 630 void __kprobes jprobe_return_end(void)
 631 {
 632         asm volatile("bcr 0,0");
 633 }
 634
 635 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 636 {
 637         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 638         unsigned long stack_addr = (unsigned long)(kcb->jprobe_saved_r15);
 639
 640         /* Put the regs back */
 641         memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
 642         /* put the stack back */
 643         memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
 644                MIN_STACK_SIZE(stack_addr));
 645         preempt_enable_no_resched();
 646         return 1;
 647 }
 648
 649 static struct kprobe trampoline_p = {
 650         .addr = (kprobe_opcode_t *) & kretprobe_trampoline,
 651         .pre_handler = trampoline_probe_handler
 652 };
 653
 654 int __init arch_init_kprobes(void)
 655 {
 656         return register_kprobe(&trampoline_p);
 657 }