arch/i386/kernel/kprobes.c

   1 /*
   2  *  Kernel Probes (KProbes)
   3  *  arch/i386/kernel/kprobes.c
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program; if not, write to the Free Software
  17  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  18  *
  19  * Copyright (C) IBM Corporation, 2002, 2004
  20  *
  21  * 2002-Oct     Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
  22  *              Probes initial implementation ( includes contributions from
  23  *              Rusty Russell).
  24  * 2004-July    Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
  25  *              interface to access function arguments.
  26  * 2005-May     Hien Nguyen <hien@us.ibm.com>, Jim Keniston
  27  *              <jkenisto@us.ibm.com> and Prasanna S Panchamukhi
  28  *              <prasanna@in.ibm.com> added function-return probes.
  29  */
  30
  31 #include <linux/config.h>
  32 #include <linux/kprobes.h>
  33 #include <linux/ptrace.h>
  34 #include <linux/preempt.h>
  35 #include <asm/cacheflush.h>
  36 #include <asm/kdebug.h>
  37 #include <asm/desc.h>
  38
  39 void jprobe_return_end(void);
  40
  41 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  42 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  43
  44 /* insert a jmp code */
  45 static inline void set_jmp_op(void *from, void *to)
  46 {
  47         struct __arch_jmp_op {
  48                 char op;
  49                 long raddr;
  50         } __attribute__((packed)) *jop;
  51         jop = (struct __arch_jmp_op *)from;
  52         jop->raddr = (long)(to) - ((long)(from) + 5);
  53         jop->op = RELATIVEJUMP_INSTRUCTION;
  54 }
  55
  56 /*
  57  * returns non-zero if opcodes can be boosted.
  58  */
  59 static inline int can_boost(kprobe_opcode_t opcode)
  60 {
  61         switch (opcode & 0xf0 ) {
  62         case 0x70:
  63                 return 0; /* can't boost conditional jump */
  64         case 0x90:
  65                 /* can't boost call and pushf */
  66                 return opcode != 0x9a && opcode != 0x9c;
  67         case 0xc0:
  68                 /* can't boost undefined opcodes and soft-interruptions */
  69                 return (0xc1 < opcode && opcode < 0xc6) ||
  70                         (0xc7 < opcode && opcode < 0xcc) || opcode == 0xcf;
  71         case 0xd0:
  72                 /* can boost AA* and XLAT */
  73                 return (opcode == 0xd4 || opcode == 0xd5 || opcode == 0xd7);
  74         case 0xe0:
  75                 /* can boost in/out and (may be) jmps */
  76                 return (0xe3 < opcode && opcode != 0xe8);
  77         case 0xf0:
  78                 /* clear and set flags can be boost */
  79                 return (opcode == 0xf5 || (0xf7 < opcode && opcode < 0xfe));
  80         default:
  81                 /* currently, can't boost 2 bytes opcodes */
  82                 return opcode != 0x0f;
  83         }
  84 }
  85
  86
  87 /*
  88  * returns non-zero if opcode modifies the interrupt flag.
  89  */
  90 static inline int is_IF_modifier(kprobe_opcode_t opcode)
  91 {
  92         switch (opcode) {
  93         case 0xfa:              /* cli */
  94         case 0xfb:              /* sti */
  95         case 0xcf:              /* iret/iretd */
  96         case 0x9d:              /* popf/popfd */
  97                 return 1;
  98         }
  99         return 0;
 100 }
 101
 102 int __kprobes arch_prepare_kprobe(struct kprobe *p)
 103 {
 104         /* insn: must be on special executable page on i386. */
 105         p->ainsn.insn = get_insn_slot();
 106         if (!p->ainsn.insn)
 107                 return -ENOMEM;
 108
 109         memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
 110         p->opcode = *p->addr;
 111         if (can_boost(p->opcode)) {
 112                 p->ainsn.boostable = 0;
 113         } else {
 114                 p->ainsn.boostable = -1;
 115         }
 116         return 0;
 117 }
 118
 119 void __kprobes arch_arm_kprobe(struct kprobe *p)
 120 {
 121         *p->addr = BREAKPOINT_INSTRUCTION;
 122         flush_icache_range((unsigned long) p->addr,
 123                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
 124 }
 125
 126 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 127 {
 128         *p->addr = p->opcode;
 129         flush_icache_range((unsigned long) p->addr,
 130                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
 131 }
 132
 133 void __kprobes arch_remove_kprobe(struct kprobe *p)
 134 {
 135         mutex_lock(&kprobe_mutex);
 136         free_insn_slot(p->ainsn.insn);
 137         mutex_unlock(&kprobe_mutex);
 138 }
 139
 140 static inline void save_previous_kprobe(struct kprobe_ctlblk *kcb)
 141 {
 142         kcb->prev_kprobe.kp = kprobe_running();
 143         kcb->prev_kprobe.status = kcb->kprobe_status;
 144         kcb->prev_kprobe.old_eflags = kcb->kprobe_old_eflags;
 145         kcb->prev_kprobe.saved_eflags = kcb->kprobe_saved_eflags;
 146 }
 147
 148 static inline void restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 149 {
 150         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
 151         kcb->kprobe_status = kcb->prev_kprobe.status;
 152         kcb->kprobe_old_eflags = kcb->prev_kprobe.old_eflags;
 153         kcb->kprobe_saved_eflags = kcb->prev_kprobe.saved_eflags;
 154 }
 155
 156 static inline void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
 157                                 struct kprobe_ctlblk *kcb)
 158 {
 159         __get_cpu_var(current_kprobe) = p;
 160         kcb->kprobe_saved_eflags = kcb->kprobe_old_eflags
 161                 = (regs->eflags & (TF_MASK | IF_MASK));
 162         if (is_IF_modifier(p->opcode))
 163                 kcb->kprobe_saved_eflags &= ~IF_MASK;
 164 }
 165
 166 static inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 167 {
 168         regs->eflags |= TF_MASK;
 169         regs->eflags &= ~IF_MASK;
 170         /*single step inline if the instruction is an int3*/
 171         if (p->opcode == BREAKPOINT_INSTRUCTION)
 172                 regs->eip = (unsigned long)p->addr;
 173         else
 174                 regs->eip = (unsigned long)p->ainsn.insn;
 175 }
 176
 177 /* Called with kretprobe_lock held */
 178 void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
 179                                       struct pt_regs *regs)
 180 {
 181         unsigned long *sara = (unsigned long *)&regs->esp;
 182         struct kretprobe_instance *ri;
 183
 184         if ((ri = get_free_rp_inst(rp)) != NULL) {
 185                 ri->rp = rp;
 186                 ri->task = current;
 187                 ri->ret_addr = (kprobe_opcode_t *) *sara;
 188
 189                 /* Replace the return addr with trampoline addr */
 190                 *sara = (unsigned long) &kretprobe_trampoline;
 191
 192                 add_rp_inst(ri);
 193         } else {
 194                 rp->nmissed++;
 195         }
 196 }
 197
 198 /*
 199  * Interrupts are disabled on entry as trap3 is an interrupt gate and they
 200  * remain disabled thorough out this function.
 201  */
 202 static int __kprobes kprobe_handler(struct pt_regs *regs)
 203 {
 204         struct kprobe *p;
 205         int ret = 0;
 206         kprobe_opcode_t *addr = NULL;
 207         unsigned long *lp;
 208         struct kprobe_ctlblk *kcb;
 209 #ifdef CONFIG_PREEMPT
 210         unsigned pre_preempt_count = preempt_count();
 211 #endif /* CONFIG_PREEMPT */
 212
 213         /*
 214          * We don't want to be preempted for the entire
 215          * duration of kprobe processing
 216          */
 217         preempt_disable();
 218         kcb = get_kprobe_ctlblk();
 219
 220         /* Check if the application is using LDT entry for its code segment and
 221          * calculate the address by reading the base address from the LDT entry.
 222          */
 223         if ((regs->xcs & 4) && (current->mm)) {
 224                 lp = (unsigned long *) ((unsigned long)((regs->xcs >> 3) * 8)
 225                                         + (char *) current->mm->context.ldt);
 226                 addr = (kprobe_opcode_t *) (get_desc_base(lp) + regs->eip -
 227                                                 sizeof(kprobe_opcode_t));
 228         } else {
 229                 addr = (kprobe_opcode_t *)(regs->eip - sizeof(kprobe_opcode_t));
 230         }
 231         /* Check we're not actually recursing */
 232         if (kprobe_running()) {
 233                 p = get_kprobe(addr);
 234                 if (p) {
 235                         if (kcb->kprobe_status == KPROBE_HIT_SS &&
 236                                 *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
 237                                 regs->eflags &= ~TF_MASK;
 238                                 regs->eflags |= kcb->kprobe_saved_eflags;
 239                                 goto no_kprobe;
 240                         }
 241                         /* We have reentered the kprobe_handler(), since
 242                          * another probe was hit while within the handler.
 243                          * We here save the original kprobes variables and
 244                          * just single step on the instruction of the new probe
 245                          * without calling any user handlers.
 246                          */
 247                         save_previous_kprobe(kcb);
 248                         set_current_kprobe(p, regs, kcb);
 249                         kprobes_inc_nmissed_count(p);
 250                         prepare_singlestep(p, regs);
 251                         kcb->kprobe_status = KPROBE_REENTER;
 252                         return 1;
 253                 } else {
 254                         if (regs->eflags & VM_MASK) {
 255                         /* We are in virtual-8086 mode. Return 0 */
 256                                 goto no_kprobe;
 257                         }
 258                         if (*addr != BREAKPOINT_INSTRUCTION) {
 259                         /* The breakpoint instruction was removed by
 260                          * another cpu right after we hit, no further
 261                          * handling of this interrupt is appropriate
 262                          */
 263                                 regs->eip -= sizeof(kprobe_opcode_t);
 264                                 ret = 1;
 265                                 goto no_kprobe;
 266                         }
 267                         p = __get_cpu_var(current_kprobe);
 268                         if (p->break_handler && p->break_handler(p, regs)) {
 269                                 goto ss_probe;
 270                         }
 271                 }
 272                 goto no_kprobe;
 273         }
 274
 275         p = get_kprobe(addr);
 276         if (!p) {
 277                 if (regs->eflags & VM_MASK) {
 278                         /* We are in virtual-8086 mode. Return 0 */
 279                         goto no_kprobe;
 280                 }
 281
 282                 if (*addr != BREAKPOINT_INSTRUCTION) {
 283                         /*
 284                          * The breakpoint instruction was removed right
 285                          * after we hit it.  Another cpu has removed
 286                          * either a probepoint or a debugger breakpoint
 287                          * at this address.  In either case, no further
 288                          * handling of this interrupt is appropriate.
 289                          * Back up over the (now missing) int3 and run
 290                          * the original instruction.
 291                          */
 292                         regs->eip -= sizeof(kprobe_opcode_t);
 293                         ret = 1;
 294                 }
 295                 /* Not one of ours: let kernel handle it */
 296                 goto no_kprobe;
 297         }
 298
 299         set_current_kprobe(p, regs, kcb);
 300         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 301
 302         if (p->pre_handler && p->pre_handler(p, regs))
 303                 /* handler has already set things up, so skip ss setup */
 304                 return 1;
 305
 306         if (p->ainsn.boostable == 1 &&
 307 #ifdef CONFIG_PREEMPT
 308             !(pre_preempt_count) && /*
 309                                        * This enables booster when the direct
 310                                        * execution path aren't preempted.
 311                                        */
 312 #endif /* CONFIG_PREEMPT */
 313             !p->post_handler && !p->break_handler ) {
 314                 /* Boost up -- we can execute copied instructions directly */
 315                 reset_current_kprobe();
 316                 regs->eip = (unsigned long)p->ainsn.insn;
 317                 preempt_enable_no_resched();
 318                 return 1;
 319         }
 320
 321 ss_probe:
 322         prepare_singlestep(p, regs);
 323         kcb->kprobe_status = KPROBE_HIT_SS;
 324         return 1;
 325
 326 no_kprobe:
 327         preempt_enable_no_resched();
 328         return ret;
 329 }
 330
 331 /*
 332  * For function-return probes, init_kprobes() establishes a probepoint
 333  * here. When a retprobed function returns, this probe is hit and
 334  * trampoline_probe_handler() runs, calling the kretprobe's handler.
 335  */
 336  void __kprobes kretprobe_trampoline_holder(void)
 337  {
 338         asm volatile ( ".global kretprobe_trampoline\n"
 339                         "kretprobe_trampoline: \n"
 340                         "       pushf\n"
 341                         /* skip cs, eip, orig_eax, es, ds */
 342                         "       subl $20, %esp\n"
 343                         "       pushl %eax\n"
 344                         "       pushl %ebp\n"
 345                         "       pushl %edi\n"
 346                         "       pushl %esi\n"
 347                         "       pushl %edx\n"
 348                         "       pushl %ecx\n"
 349                         "       pushl %ebx\n"
 350                         "       movl %esp, %eax\n"
 351                         "       call trampoline_handler\n"
 352                         /* move eflags to cs */
 353                         "       movl 48(%esp), %edx\n"
 354                         "       movl %edx, 44(%esp)\n"
 355                         /* save true return address on eflags */
 356                         "       movl %eax, 48(%esp)\n"
 357                         "       popl %ebx\n"
 358                         "       popl %ecx\n"
 359                         "       popl %edx\n"
 360                         "       popl %esi\n"
 361                         "       popl %edi\n"
 362                         "       popl %ebp\n"
 363                         "       popl %eax\n"
 364                         /* skip eip, orig_eax, es, ds */
 365                         "       addl $16, %esp\n"
 366                         "       popf\n"
 367                         "       ret\n");
 368 }
 369
 370 /*
 371  * Called from kretprobe_trampoline
 372  */
 373 fastcall void *__kprobes trampoline_handler(struct pt_regs *regs)
 374 {
 375         struct kretprobe_instance *ri = NULL;
 376         struct hlist_head *head;
 377         struct hlist_node *node, *tmp;
 378         unsigned long flags, orig_ret_address = 0;
 379         unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
 380
 381         spin_lock_irqsave(&kretprobe_lock, flags);
 382         head = kretprobe_inst_table_head(current);
 383
 384         /*
 385          * It is possible to have multiple instances associated with a given
 386          * task either because an multiple functions in the call path
 387          * have a return probe installed on them, and/or more then one return
 388          * return probe was registered for a target function.
 389          *
 390          * We can handle this because:
 391          *     - instances are always inserted at the head of the list
 392          *     - when multiple return probes are registered for the same
 393          *       function, the first instance's ret_addr will point to the
 394          *       real return address, and all the rest will point to
 395          *       kretprobe_trampoline
 396          */
 397         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
 398                 if (ri->task != current)
 399                         /* another task is sharing our hash bucket */
 400                         continue;
 401
 402                 if (ri->rp && ri->rp->handler){
 403                         __get_cpu_var(current_kprobe) = &ri->rp->kp;
 404                         ri->rp->handler(ri, regs);
 405                         __get_cpu_var(current_kprobe) = NULL;
 406                 }
 407
 408                 orig_ret_address = (unsigned long)ri->ret_addr;
 409                 recycle_rp_inst(ri);
 410
 411                 if (orig_ret_address != trampoline_address)
 412                         /*
 413                          * This is the real return address. Any other
 414                          * instances associated with this task are for
 415                          * other calls deeper on the call stack
 416                          */
 417                         break;
 418         }
 419
 420         BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
 421
 422         spin_unlock_irqrestore(&kretprobe_lock, flags);
 423
 424         return (void*)orig_ret_address;
 425 }
 426
 427 /*
 428  * Called after single-stepping.  p->addr is the address of the
 429  * instruction whose first byte has been replaced by the "int 3"
 430  * instruction.  To avoid the SMP problems that can occur when we
 431  * temporarily put back the original opcode to single-step, we
 432  * single-stepped a copy of the instruction.  The address of this
 433  * copy is p->ainsn.insn.
 434  *
 435  * This function prepares to return from the post-single-step
 436  * interrupt.  We have to fix up the stack as follows:
 437  *
 438  * 0) Except in the case of absolute or indirect jump or call instructions,
 439  * the new eip is relative to the copied instruction.  We need to make
 440  * it relative to the original instruction.
 441  *
 442  * 1) If the single-stepped instruction was pushfl, then the TF and IF
 443  * flags are set in the just-pushed eflags, and may need to be cleared.
 444  *
 445  * 2) If the single-stepped instruction was a call, the return address
 446  * that is atop the stack is the address following the copied instruction.
 447  * We need to make it the address following the original instruction.
 448  *
 449  * This function also checks instruction size for preparing direct execution.
 450  */
 451 static void __kprobes resume_execution(struct kprobe *p,
 452                 struct pt_regs *regs, struct kprobe_ctlblk *kcb)
 453 {
 454         unsigned long *tos = (unsigned long *)&regs->esp;
 455         unsigned long copy_eip = (unsigned long)p->ainsn.insn;
 456         unsigned long orig_eip = (unsigned long)p->addr;
 457
 458         regs->eflags &= ~TF_MASK;
 459         switch (p->ainsn.insn[0]) {
 460         case 0x9c:              /* pushfl */
 461                 *tos &= ~(TF_MASK | IF_MASK);
 462                 *tos |= kcb->kprobe_old_eflags;
 463                 break;
 464         case 0xc3:              /* ret/lret */
 465         case 0xcb:
 466         case 0xc2:
 467         case 0xca:
 468         case 0xea:              /* jmp absolute -- eip is correct */
 469                 /* eip is already adjusted, no more changes required */
 470                 p->ainsn.boostable = 1;
 471                 goto no_change;
 472         case 0xe8:              /* call relative - Fix return addr */
 473                 *tos = orig_eip + (*tos - copy_eip);
 474                 break;
 475         case 0xff:
 476                 if ((p->ainsn.insn[1] & 0x30) == 0x10) {
 477                         /* call absolute, indirect */
 478                         /*
 479                          * Fix return addr; eip is correct.
 480                          * But this is not boostable
 481                          */
 482                         *tos = orig_eip + (*tos - copy_eip);
 483                         goto no_change;
 484                 } else if (((p->ainsn.insn[1] & 0x31) == 0x20) ||       /* jmp near, absolute indirect */
 485                            ((p->ainsn.insn[1] & 0x31) == 0x21)) {       /* jmp far, absolute indirect */
 486                         /* eip is correct. And this is boostable */
 487                         p->ainsn.boostable = 1;
 488                         goto no_change;
 489                 }
 490         default:
 491                 break;
 492         }
 493
 494         if (p->ainsn.boostable == 0) {
 495                 if ((regs->eip > copy_eip) &&
 496                     (regs->eip - copy_eip) + 5 < MAX_INSN_SIZE) {
 497                         /*
 498                          * These instructions can be executed directly if it
 499                          * jumps back to correct address.
 500                          */
 501                         set_jmp_op((void *)regs->eip,
 502                                    (void *)orig_eip + (regs->eip - copy_eip));
 503                         p->ainsn.boostable = 1;
 504                 } else {
 505                         p->ainsn.boostable = -1;
 506                 }
 507         }
 508
 509         regs->eip = orig_eip + (regs->eip - copy_eip);
 510
 511 no_change:
 512         return;
 513 }
 514
 515 /*
 516  * Interrupts are disabled on entry as trap1 is an interrupt gate and they
 517  * remain disabled thoroughout this function.
 518  */
 519 static inline int post_kprobe_handler(struct pt_regs *regs)
 520 {
 521         struct kprobe *cur = kprobe_running();
 522         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 523
 524         if (!cur)
 525                 return 0;
 526
 527         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
 528                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
 529                 cur->post_handler(cur, regs, 0);
 530         }
 531
 532         resume_execution(cur, regs, kcb);
 533         regs->eflags |= kcb->kprobe_saved_eflags;
 534
 535         /*Restore back the original saved kprobes variables and continue. */
 536         if (kcb->kprobe_status == KPROBE_REENTER) {
 537                 restore_previous_kprobe(kcb);
 538                 goto out;
 539         }
 540         reset_current_kprobe();
 541 out:
 542         preempt_enable_no_resched();
 543
 544         /*
 545          * if somebody else is singlestepping across a probe point, eflags
 546          * will have TF set, in which case, continue the remaining processing
 547          * of do_debug, as if this is not a probe hit.
 548          */
 549         if (regs->eflags & TF_MASK)
 550                 return 0;
 551
 552         return 1;
 553 }
 554
 555 static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 556 {
 557         struct kprobe *cur = kprobe_running();
 558         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 559
 560         if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
 561                 return 1;
 562
 563         if (kcb->kprobe_status & KPROBE_HIT_SS) {
 564                 resume_execution(cur, regs, kcb);
 565                 regs->eflags |= kcb->kprobe_old_eflags;
 566
 567                 reset_current_kprobe();
 568                 preempt_enable_no_resched();
 569         }
 570         return 0;
 571 }
 572
 573 /*
 574  * Wrapper routine to for handling exceptions.
 575  */
 576 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 577                                        unsigned long val, void *data)
 578 {
 579         struct die_args *args = (struct die_args *)data;
 580         int ret = NOTIFY_DONE;
 581
 582         switch (val) {
 583         case DIE_INT3:
 584                 if (kprobe_handler(args->regs))
 585                         ret = NOTIFY_STOP;
 586                 break;
 587         case DIE_DEBUG:
 588                 if (post_kprobe_handler(args->regs))
 589                         ret = NOTIFY_STOP;
 590                 break;
 591         case DIE_GPF:
 592         case DIE_PAGE_FAULT:
 593                 /* kprobe_running() needs smp_processor_id() */
 594                 preempt_disable();
 595                 if (kprobe_running() &&
 596                     kprobe_fault_handler(args->regs, args->trapnr))
 597                         ret = NOTIFY_STOP;
 598                 preempt_enable();
 599                 break;
 600         default:
 601                 break;
 602         }
 603         return ret;
 604 }
 605
 606 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 607 {
 608         struct jprobe *jp = container_of(p, struct jprobe, kp);
 609         unsigned long addr;
 610         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 611
 612         kcb->jprobe_saved_regs = *regs;
 613         kcb->jprobe_saved_esp = &regs->esp;
 614         addr = (unsigned long)(kcb->jprobe_saved_esp);
 615
 616         /*
 617          * TBD: As Linus pointed out, gcc assumes that the callee
 618          * owns the argument space and could overwrite it, e.g.
 619          * tailcall optimization. So, to be absolutely safe
 620          * we also save and restore enough stack bytes to cover
 621          * the argument area.
 622          */
 623         memcpy(kcb->jprobes_stack, (kprobe_opcode_t *)addr,
 624                         MIN_STACK_SIZE(addr));
 625         regs->eflags &= ~IF_MASK;
 626         regs->eip = (unsigned long)(jp->entry);
 627         return 1;
 628 }
 629
 630 void __kprobes jprobe_return(void)
 631 {
 632         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 633
 634         asm volatile ("       xchgl   %%ebx,%%esp     \n"
 635                       "       int3                      \n"
 636                       "       .globl jprobe_return_end  \n"
 637                       "       jprobe_return_end:        \n"
 638                       "       nop                       \n"::"b"
 639                       (kcb->jprobe_saved_esp):"memory");
 640 }
 641
 642 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 643 {
 644         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 645         u8 *addr = (u8 *) (regs->eip - 1);
 646         unsigned long stack_addr = (unsigned long)(kcb->jprobe_saved_esp);
 647         struct jprobe *jp = container_of(p, struct jprobe, kp);
 648
 649         if ((addr > (u8 *) jprobe_return) && (addr < (u8 *) jprobe_return_end)) {
 650                 if (&regs->esp != kcb->jprobe_saved_esp) {
 651                         struct pt_regs *saved_regs =
 652                             container_of(kcb->jprobe_saved_esp,
 653                                             struct pt_regs, esp);
 654                         printk("current esp %p does not match saved esp %p\n",
 655                                &regs->esp, kcb->jprobe_saved_esp);
 656                         printk("Saved registers for jprobe %p\n", jp);
 657                         show_registers(saved_regs);
 658                         printk("Current registers\n");
 659                         show_registers(regs);
 660                         BUG();
 661                 }
 662                 *regs = kcb->jprobe_saved_regs;
 663                 memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
 664                        MIN_STACK_SIZE(stack_addr));
 665                 preempt_enable_no_resched();
 666                 return 1;
 667         }
 668         return 0;
 669 }
 670
 671 int __init arch_init_kprobes(void)
 672 {
 673         return 0;
 674 }