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/kprobes.h>
  32 #include <linux/ptrace.h>
  33 #include <linux/preempt.h>
  34 #include <linux/kdebug.h>
  35 #include <asm/cacheflush.h>
  36 #include <asm/desc.h>
  37 #include <asm/uaccess.h>
  38 #include <asm/alternative.h>
  39
  40 void jprobe_return_end(void);
  41
  42 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  43 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  44
  45 /* insert a jmp code */
  46 static __always_inline void set_jmp_op(void *from, void *to)
  47 {
  48         struct __arch_jmp_op {
  49                 char op;
  50                 long raddr;
  51         } __attribute__((packed)) *jop;
  52         jop = (struct __arch_jmp_op *)from;
  53         jop->raddr = (long)(to) - ((long)(from) + 5);
  54         jop->op = RELATIVEJUMP_INSTRUCTION;
  55 }
  56
  57 /*
  58  * returns non-zero if opcodes can be boosted.
  59  */
  60 static __always_inline int can_boost(kprobe_opcode_t *opcodes)
  61 {
  62 #define W(row,b0,b1,b2,b3,b4,b5,b6,b7,b8,b9,ba,bb,bc,bd,be,bf)                \
  63         (((b0##UL << 0x0)|(b1##UL << 0x1)|(b2##UL << 0x2)|(b3##UL << 0x3) |   \
  64           (b4##UL << 0x4)|(b5##UL << 0x5)|(b6##UL << 0x6)|(b7##UL << 0x7) |   \
  65           (b8##UL << 0x8)|(b9##UL << 0x9)|(ba##UL << 0xa)|(bb##UL << 0xb) |   \
  66           (bc##UL << 0xc)|(bd##UL << 0xd)|(be##UL << 0xe)|(bf##UL << 0xf))    \
  67          << (row % 32))
  68         /*
  69          * Undefined/reserved opcodes, conditional jump, Opcode Extension
  70          * Groups, and some special opcodes can not be boost.
  71          */
  72         static const unsigned long twobyte_is_boostable[256 / 32] = {
  73                 /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
  74                 /*      -------------------------------         */
  75                 W(0x00, 0,0,1,1,0,0,1,0,1,1,0,0,0,0,0,0)| /* 00 */
  76                 W(0x10, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 10 */
  77                 W(0x20, 1,1,1,1,0,0,0,0,0,0,0,0,0,0,0,0)| /* 20 */
  78                 W(0x30, 0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 30 */
  79                 W(0x40, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 40 */
  80                 W(0x50, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 50 */
  81                 W(0x60, 1,1,1,1,1,1,1,1,1,1,1,1,0,0,1,1)| /* 60 */
  82                 W(0x70, 0,0,0,0,1,1,1,1,0,0,0,0,0,0,1,1), /* 70 */
  83                 W(0x80, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 80 */
  84                 W(0x90, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1), /* 90 */
  85                 W(0xa0, 1,1,0,1,1,1,0,0,1,1,0,1,1,1,0,1)| /* a0 */
  86                 W(0xb0, 1,1,1,1,1,1,1,1,0,0,0,1,1,1,1,1), /* b0 */
  87                 W(0xc0, 1,1,0,0,0,0,0,0,1,1,1,1,1,1,1,1)| /* c0 */
  88                 W(0xd0, 0,1,1,1,0,1,0,0,1,1,0,1,1,1,0,1), /* d0 */
  89                 W(0xe0, 0,1,1,0,0,1,0,0,1,1,0,1,1,1,0,1)| /* e0 */
  90                 W(0xf0, 0,1,1,1,0,1,0,0,1,1,1,0,1,1,1,0)  /* f0 */
  91                 /*      -------------------------------         */
  92                 /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
  93         };
  94 #undef W
  95         kprobe_opcode_t opcode;
  96         kprobe_opcode_t *orig_opcodes = opcodes;
  97 retry:
  98         if (opcodes - orig_opcodes > MAX_INSN_SIZE - 1)
  99                 return 0;
 100         opcode = *(opcodes++);
 101
 102         /* 2nd-byte opcode */
 103         if (opcode == 0x0f) {
 104                 if (opcodes - orig_opcodes > MAX_INSN_SIZE - 1)
 105                         return 0;
 106                 return test_bit(*opcodes, twobyte_is_boostable);
 107         }
 108
 109         switch (opcode & 0xf0) {
 110         case 0x60:
 111                 if (0x63 < opcode && opcode < 0x67)
 112                         goto retry; /* prefixes */
 113                 /* can't boost Address-size override and bound */
 114                 return (opcode != 0x62 && opcode != 0x67);
 115         case 0x70:
 116                 return 0; /* can't boost conditional jump */
 117         case 0xc0:
 118                 /* can't boost software-interruptions */
 119                 return (0xc1 < opcode && opcode < 0xcc) || opcode == 0xcf;
 120         case 0xd0:
 121                 /* can boost AA* and XLAT */
 122                 return (opcode == 0xd4 || opcode == 0xd5 || opcode == 0xd7);
 123         case 0xe0:
 124                 /* can boost in/out and absolute jmps */
 125                 return ((opcode & 0x04) || opcode == 0xea);
 126         case 0xf0:
 127                 if ((opcode & 0x0c) == 0 && opcode != 0xf1)
 128                         goto retry; /* lock/rep(ne) prefix */
 129                 /* clear and set flags can be boost */
 130                 return (opcode == 0xf5 || (0xf7 < opcode && opcode < 0xfe));
 131         default:
 132                 if (opcode == 0x26 || opcode == 0x36 || opcode == 0x3e)
 133                         goto retry; /* prefixes */
 134                 /* can't boost CS override and call */
 135                 return (opcode != 0x2e && opcode != 0x9a);
 136         }
 137 }
 138
 139 /*
 140  * returns non-zero if opcode modifies the interrupt flag.
 141  */
 142 static int __kprobes is_IF_modifier(kprobe_opcode_t opcode)
 143 {
 144         switch (opcode) {
 145         case 0xfa:              /* cli */
 146         case 0xfb:              /* sti */
 147         case 0xcf:              /* iret/iretd */
 148         case 0x9d:              /* popf/popfd */
 149                 return 1;
 150         }
 151         return 0;
 152 }
 153
 154 int __kprobes arch_prepare_kprobe(struct kprobe *p)
 155 {
 156         /* insn: must be on special executable page on i386. */
 157         p->ainsn.insn = get_insn_slot();
 158         if (!p->ainsn.insn)
 159                 return -ENOMEM;
 160
 161         memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
 162         p->opcode = *p->addr;
 163         if (can_boost(p->addr)) {
 164                 p->ainsn.boostable = 0;
 165         } else {
 166                 p->ainsn.boostable = -1;
 167         }
 168         return 0;
 169 }
 170
 171 void __kprobes arch_arm_kprobe(struct kprobe *p)
 172 {
 173         text_poke(p->addr, ((unsigned char []){BREAKPOINT_INSTRUCTION}), 1);
 174 }
 175
 176 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 177 {
 178         text_poke(p->addr, &p->opcode, 1);
 179 }
 180
 181 void __kprobes arch_remove_kprobe(struct kprobe *p)
 182 {
 183         mutex_lock(&kprobe_mutex);
 184         free_insn_slot(p->ainsn.insn, (p->ainsn.boostable == 1));
 185         mutex_unlock(&kprobe_mutex);
 186 }
 187
 188 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 189 {
 190         kcb->prev_kprobe.kp = kprobe_running();
 191         kcb->prev_kprobe.status = kcb->kprobe_status;
 192         kcb->prev_kprobe.old_eflags = kcb->kprobe_old_eflags;
 193         kcb->prev_kprobe.saved_eflags = kcb->kprobe_saved_eflags;
 194 }
 195
 196 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 197 {
 198         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
 199         kcb->kprobe_status = kcb->prev_kprobe.status;
 200         kcb->kprobe_old_eflags = kcb->prev_kprobe.old_eflags;
 201         kcb->kprobe_saved_eflags = kcb->prev_kprobe.saved_eflags;
 202 }
 203
 204 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
 205                                 struct kprobe_ctlblk *kcb)
 206 {
 207         __get_cpu_var(current_kprobe) = p;
 208         kcb->kprobe_saved_eflags = kcb->kprobe_old_eflags
 209                 = (regs->eflags & (TF_MASK | IF_MASK));
 210         if (is_IF_modifier(p->opcode))
 211                 kcb->kprobe_saved_eflags &= ~IF_MASK;
 212 }
 213
 214 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 215 {
 216         regs->eflags |= TF_MASK;
 217         regs->eflags &= ~IF_MASK;
 218         /*single step inline if the instruction is an int3*/
 219         if (p->opcode == BREAKPOINT_INSTRUCTION)
 220                 regs->eip = (unsigned long)p->addr;
 221         else
 222                 regs->eip = (unsigned long)p->ainsn.insn;
 223 }
 224
 225 /* Called with kretprobe_lock held */
 226 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 227                                       struct pt_regs *regs)
 228 {
 229         unsigned long *sara = (unsigned long *)&regs->esp;
 230
 231         ri->ret_addr = (kprobe_opcode_t *) *sara;
 232
 233         /* Replace the return addr with trampoline addr */
 234         *sara = (unsigned long) &kretprobe_trampoline;
 235 }
 236
 237 /*
 238  * Interrupts are disabled on entry as trap3 is an interrupt gate and they
 239  * remain disabled thorough out this function.
 240  */
 241 static int __kprobes kprobe_handler(struct pt_regs *regs)
 242 {
 243         struct kprobe *p;
 244         int ret = 0;
 245         kprobe_opcode_t *addr;
 246         struct kprobe_ctlblk *kcb;
 247
 248         addr = (kprobe_opcode_t *)(regs->eip - sizeof(kprobe_opcode_t));
 249
 250         /*
 251          * We don't want to be preempted for the entire
 252          * duration of kprobe processing
 253          */
 254         preempt_disable();
 255         kcb = get_kprobe_ctlblk();
 256
 257         /* Check we're not actually recursing */
 258         if (kprobe_running()) {
 259                 p = get_kprobe(addr);
 260                 if (p) {
 261                         if (kcb->kprobe_status == KPROBE_HIT_SS &&
 262                                 *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
 263                                 regs->eflags &= ~TF_MASK;
 264                                 regs->eflags |= kcb->kprobe_saved_eflags;
 265                                 goto no_kprobe;
 266                         }
 267                         /* We have reentered the kprobe_handler(), since
 268                          * another probe was hit while within the handler.
 269                          * We here save the original kprobes variables and
 270                          * just single step on the instruction of the new probe
 271                          * without calling any user handlers.
 272                          */
 273                         save_previous_kprobe(kcb);
 274                         set_current_kprobe(p, regs, kcb);
 275                         kprobes_inc_nmissed_count(p);
 276                         prepare_singlestep(p, regs);
 277                         kcb->kprobe_status = KPROBE_REENTER;
 278                         return 1;
 279                 } else {
 280                         if (*addr != BREAKPOINT_INSTRUCTION) {
 281                         /* The breakpoint instruction was removed by
 282                          * another cpu right after we hit, no further
 283                          * handling of this interrupt is appropriate
 284                          */
 285                                 regs->eip -= sizeof(kprobe_opcode_t);
 286                                 ret = 1;
 287                                 goto no_kprobe;
 288                         }
 289                         p = __get_cpu_var(current_kprobe);
 290                         if (p->break_handler && p->break_handler(p, regs)) {
 291                                 goto ss_probe;
 292                         }
 293                 }
 294                 goto no_kprobe;
 295         }
 296
 297         p = get_kprobe(addr);
 298         if (!p) {
 299                 if (*addr != BREAKPOINT_INSTRUCTION) {
 300                         /*
 301                          * The breakpoint instruction was removed right
 302                          * after we hit it.  Another cpu has removed
 303                          * either a probepoint or a debugger breakpoint
 304                          * at this address.  In either case, no further
 305                          * handling of this interrupt is appropriate.
 306                          * Back up over the (now missing) int3 and run
 307                          * the original instruction.
 308                          */
 309                         regs->eip -= sizeof(kprobe_opcode_t);
 310                         ret = 1;
 311                 }
 312                 /* Not one of ours: let kernel handle it */
 313                 goto no_kprobe;
 314         }
 315
 316         set_current_kprobe(p, regs, kcb);
 317         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 318
 319         if (p->pre_handler && p->pre_handler(p, regs))
 320                 /* handler has already set things up, so skip ss setup */
 321                 return 1;
 322
 323 ss_probe:
 324 #if !defined(CONFIG_PREEMPT) || defined(CONFIG_PM)
 325         if (p->ainsn.boostable == 1 && !p->post_handler){
 326                 /* Boost up -- we can execute copied instructions directly */
 327                 reset_current_kprobe();
 328                 regs->eip = (unsigned long)p->ainsn.insn;
 329                 preempt_enable_no_resched();
 330                 return 1;
 331         }
 332 #endif
 333         prepare_singlestep(p, regs);
 334         kcb->kprobe_status = KPROBE_HIT_SS;
 335         return 1;
 336
 337 no_kprobe:
 338         preempt_enable_no_resched();
 339         return ret;
 340 }
 341
 342 /*
 343  * For function-return probes, init_kprobes() establishes a probepoint
 344  * here. When a retprobed function returns, this probe is hit and
 345  * trampoline_probe_handler() runs, calling the kretprobe's handler.
 346  */
 347  void __kprobes kretprobe_trampoline_holder(void)
 348  {
 349         asm volatile ( ".global kretprobe_trampoline\n"
 350                         "kretprobe_trampoline: \n"
 351                         "       pushf\n"
 352                         /* skip cs, eip, orig_eax */
 353                         "       subl $12, %esp\n"
 354                         "       pushl %fs\n"
 355                         "       pushl %ds\n"
 356                         "       pushl %es\n"
 357                         "       pushl %eax\n"
 358                         "       pushl %ebp\n"
 359                         "       pushl %edi\n"
 360                         "       pushl %esi\n"
 361                         "       pushl %edx\n"
 362                         "       pushl %ecx\n"
 363                         "       pushl %ebx\n"
 364                         "       movl %esp, %eax\n"
 365                         "       call trampoline_handler\n"
 366                         /* move eflags to cs */
 367                         "       movl 52(%esp), %edx\n"
 368                         "       movl %edx, 48(%esp)\n"
 369                         /* save true return address on eflags */
 370                         "       movl %eax, 52(%esp)\n"
 371                         "       popl %ebx\n"
 372                         "       popl %ecx\n"
 373                         "       popl %edx\n"
 374                         "       popl %esi\n"
 375                         "       popl %edi\n"
 376                         "       popl %ebp\n"
 377                         "       popl %eax\n"
 378                         /* skip eip, orig_eax, es, ds, fs */
 379                         "       addl $20, %esp\n"
 380                         "       popf\n"
 381                         "       ret\n");
 382 }
 383
 384 /*
 385  * Called from kretprobe_trampoline
 386  */
 387 fastcall void *__kprobes trampoline_handler(struct pt_regs *regs)
 388 {
 389         struct kretprobe_instance *ri = NULL;
 390         struct hlist_head *head, empty_rp;
 391         struct hlist_node *node, *tmp;
 392         unsigned long flags, orig_ret_address = 0;
 393         unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
 394
 395         INIT_HLIST_HEAD(&empty_rp);
 396         spin_lock_irqsave(&kretprobe_lock, flags);
 397         head = kretprobe_inst_table_head(current);
 398         /* fixup registers */
 399         regs->xcs = __KERNEL_CS | get_kernel_rpl();
 400         regs->eip = trampoline_address;
 401         regs->orig_eax = 0xffffffff;
 402
 403         /*
 404          * It is possible to have multiple instances associated with a given
 405          * task either because an multiple functions in the call path
 406          * have a return probe installed on them, and/or more then one return
 407          * return probe was registered for a target function.
 408          *
 409          * We can handle this because:
 410          *     - instances are always inserted at the head of the list
 411          *     - when multiple return probes are registered for the same
 412          *       function, the first instance's ret_addr will point to the
 413          *       real return address, and all the rest will point to
 414          *       kretprobe_trampoline
 415          */
 416         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
 417                 if (ri->task != current)
 418                         /* another task is sharing our hash bucket */
 419                         continue;
 420
 421                 if (ri->rp && ri->rp->handler){
 422                         __get_cpu_var(current_kprobe) = &ri->rp->kp;
 423                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 424                         ri->rp->handler(ri, regs);
 425                         __get_cpu_var(current_kprobe) = NULL;
 426                 }
 427
 428                 orig_ret_address = (unsigned long)ri->ret_addr;
 429                 recycle_rp_inst(ri, &empty_rp);
 430
 431                 if (orig_ret_address != trampoline_address)
 432                         /*
 433                          * This is the real return address. Any other
 434                          * instances associated with this task are for
 435                          * other calls deeper on the call stack
 436                          */
 437                         break;
 438         }
 439
 440         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 441         spin_unlock_irqrestore(&kretprobe_lock, flags);
 442
 443         hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
 444                 hlist_del(&ri->hlist);
 445                 kfree(ri);
 446         }
 447         return (void*)orig_ret_address;
 448 }
 449
 450 /*
 451  * Called after single-stepping.  p->addr is the address of the
 452  * instruction whose first byte has been replaced by the "int 3"
 453  * instruction.  To avoid the SMP problems that can occur when we
 454  * temporarily put back the original opcode to single-step, we
 455  * single-stepped a copy of the instruction.  The address of this
 456  * copy is p->ainsn.insn.
 457  *
 458  * This function prepares to return from the post-single-step
 459  * interrupt.  We have to fix up the stack as follows:
 460  *
 461  * 0) Except in the case of absolute or indirect jump or call instructions,
 462  * the new eip is relative to the copied instruction.  We need to make
 463  * it relative to the original instruction.
 464  *
 465  * 1) If the single-stepped instruction was pushfl, then the TF and IF
 466  * flags are set in the just-pushed eflags, and may need to be cleared.
 467  *
 468  * 2) If the single-stepped instruction was a call, the return address
 469  * that is atop the stack is the address following the copied instruction.
 470  * We need to make it the address following the original instruction.
 471  *
 472  * This function also checks instruction size for preparing direct execution.
 473  */
 474 static void __kprobes resume_execution(struct kprobe *p,
 475                 struct pt_regs *regs, struct kprobe_ctlblk *kcb)
 476 {
 477         unsigned long *tos = (unsigned long *)&regs->esp;
 478         unsigned long copy_eip = (unsigned long)p->ainsn.insn;
 479         unsigned long orig_eip = (unsigned long)p->addr;
 480
 481         regs->eflags &= ~TF_MASK;
 482         switch (p->ainsn.insn[0]) {
 483         case 0x9c:              /* pushfl */
 484                 *tos &= ~(TF_MASK | IF_MASK);
 485                 *tos |= kcb->kprobe_old_eflags;
 486                 break;
 487         case 0xc2:              /* iret/ret/lret */
 488         case 0xc3:
 489         case 0xca:
 490         case 0xcb:
 491         case 0xcf:
 492         case 0xea:              /* jmp absolute -- eip is correct */
 493                 /* eip is already adjusted, no more changes required */
 494                 p->ainsn.boostable = 1;
 495                 goto no_change;
 496         case 0xe8:              /* call relative - Fix return addr */
 497                 *tos = orig_eip + (*tos - copy_eip);
 498                 break;
 499         case 0x9a:              /* call absolute -- same as call absolute, indirect */
 500                 *tos = orig_eip + (*tos - copy_eip);
 501                 goto no_change;
 502         case 0xff:
 503                 if ((p->ainsn.insn[1] & 0x30) == 0x10) {
 504                         /*
 505                          * call absolute, indirect
 506                          * Fix return addr; eip is correct.
 507                          * But this is not boostable
 508                          */
 509                         *tos = orig_eip + (*tos - copy_eip);
 510                         goto no_change;
 511                 } else if (((p->ainsn.insn[1] & 0x31) == 0x20) ||       /* jmp near, absolute indirect */
 512                            ((p->ainsn.insn[1] & 0x31) == 0x21)) {       /* jmp far, absolute indirect */
 513                         /* eip is correct. And this is boostable */
 514                         p->ainsn.boostable = 1;
 515                         goto no_change;
 516                 }
 517         default:
 518                 break;
 519         }
 520
 521         if (p->ainsn.boostable == 0) {
 522                 if ((regs->eip > copy_eip) &&
 523                     (regs->eip - copy_eip) + 5 < MAX_INSN_SIZE) {
 524                         /*
 525                          * These instructions can be executed directly if it
 526                          * jumps back to correct address.
 527                          */
 528                         set_jmp_op((void *)regs->eip,
 529                                    (void *)orig_eip + (regs->eip - copy_eip));
 530                         p->ainsn.boostable = 1;
 531                 } else {
 532                         p->ainsn.boostable = -1;
 533                 }
 534         }
 535
 536         regs->eip = orig_eip + (regs->eip - copy_eip);
 537
 538 no_change:
 539         return;
 540 }
 541
 542 /*
 543  * Interrupts are disabled on entry as trap1 is an interrupt gate and they
 544  * remain disabled thoroughout this function.
 545  */
 546 static int __kprobes post_kprobe_handler(struct pt_regs *regs)
 547 {
 548         struct kprobe *cur = kprobe_running();
 549         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 550
 551         if (!cur)
 552                 return 0;
 553
 554         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
 555                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
 556                 cur->post_handler(cur, regs, 0);
 557         }
 558
 559         resume_execution(cur, regs, kcb);
 560         regs->eflags |= kcb->kprobe_saved_eflags;
 561
 562         /*Restore back the original saved kprobes variables and continue. */
 563         if (kcb->kprobe_status == KPROBE_REENTER) {
 564                 restore_previous_kprobe(kcb);
 565                 goto out;
 566         }
 567         reset_current_kprobe();
 568 out:
 569         preempt_enable_no_resched();
 570
 571         /*
 572          * if somebody else is singlestepping across a probe point, eflags
 573          * will have TF set, in which case, continue the remaining processing
 574          * of do_debug, as if this is not a probe hit.
 575          */
 576         if (regs->eflags & TF_MASK)
 577                 return 0;
 578
 579         return 1;
 580 }
 581
 582 static int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 583 {
 584         struct kprobe *cur = kprobe_running();
 585         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 586
 587         switch(kcb->kprobe_status) {
 588         case KPROBE_HIT_SS:
 589         case KPROBE_REENTER:
 590                 /*
 591                  * We are here because the instruction being single
 592                  * stepped caused a page fault. We reset the current
 593                  * kprobe and the eip points back to the probe address
 594                  * and allow the page fault handler to continue as a
 595                  * normal page fault.
 596                  */
 597                 regs->eip = (unsigned long)cur->addr;
 598                 regs->eflags |= kcb->kprobe_old_eflags;
 599                 if (kcb->kprobe_status == KPROBE_REENTER)
 600                         restore_previous_kprobe(kcb);
 601                 else
 602                         reset_current_kprobe();
 603                 preempt_enable_no_resched();
 604                 break;
 605         case KPROBE_HIT_ACTIVE:
 606         case KPROBE_HIT_SSDONE:
 607                 /*
 608                  * We increment the nmissed count for accounting,
 609                  * we can also use npre/npostfault count for accouting
 610                  * these specific fault cases.
 611                  */
 612                 kprobes_inc_nmissed_count(cur);
 613
 614                 /*
 615                  * We come here because instructions in the pre/post
 616                  * handler caused the page_fault, this could happen
 617                  * if handler tries to access user space by
 618                  * copy_from_user(), get_user() etc. Let the
 619                  * user-specified handler try to fix it first.
 620                  */
 621                 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
 622                         return 1;
 623
 624                 /*
 625                  * In case the user-specified fault handler returned
 626                  * zero, try to fix up.
 627                  */
 628                 if (fixup_exception(regs))
 629                         return 1;
 630
 631                 /*
 632                  * fixup_exception() could not handle it,
 633                  * Let do_page_fault() fix it.
 634                  */
 635                 break;
 636         default:
 637                 break;
 638         }
 639         return 0;
 640 }
 641
 642 /*
 643  * Wrapper routine to for handling exceptions.
 644  */
 645 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 646                                        unsigned long val, void *data)
 647 {
 648         struct die_args *args = (struct die_args *)data;
 649         int ret = NOTIFY_DONE;
 650
 651         if (args->regs && user_mode_vm(args->regs))
 652                 return ret;
 653
 654         switch (val) {
 655         case DIE_INT3:
 656                 if (kprobe_handler(args->regs))
 657                         ret = NOTIFY_STOP;
 658                 break;
 659         case DIE_DEBUG:
 660                 if (post_kprobe_handler(args->regs))
 661                         ret = NOTIFY_STOP;
 662                 break;
 663         case DIE_GPF:
 664         case DIE_PAGE_FAULT:
 665                 /* kprobe_running() needs smp_processor_id() */
 666                 preempt_disable();
 667                 if (kprobe_running() &&
 668                     kprobe_fault_handler(args->regs, args->trapnr))
 669                         ret = NOTIFY_STOP;
 670                 preempt_enable();
 671                 break;
 672         default:
 673                 break;
 674         }
 675         return ret;
 676 }
 677
 678 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 679 {
 680         struct jprobe *jp = container_of(p, struct jprobe, kp);
 681         unsigned long addr;
 682         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 683
 684         kcb->jprobe_saved_regs = *regs;
 685         kcb->jprobe_saved_esp = &regs->esp;
 686         addr = (unsigned long)(kcb->jprobe_saved_esp);
 687
 688         /*
 689          * TBD: As Linus pointed out, gcc assumes that the callee
 690          * owns the argument space and could overwrite it, e.g.
 691          * tailcall optimization. So, to be absolutely safe
 692          * we also save and restore enough stack bytes to cover
 693          * the argument area.
 694          */
 695         memcpy(kcb->jprobes_stack, (kprobe_opcode_t *)addr,
 696                         MIN_STACK_SIZE(addr));
 697         regs->eflags &= ~IF_MASK;
 698         regs->eip = (unsigned long)(jp->entry);
 699         return 1;
 700 }
 701
 702 void __kprobes jprobe_return(void)
 703 {
 704         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 705
 706         asm volatile ("       xchgl   %%ebx,%%esp     \n"
 707                       "       int3                      \n"
 708                       "       .globl jprobe_return_end  \n"
 709                       "       jprobe_return_end:        \n"
 710                       "       nop                       \n"::"b"
 711                       (kcb->jprobe_saved_esp):"memory");
 712 }
 713
 714 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 715 {
 716         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 717         u8 *addr = (u8 *) (regs->eip - 1);
 718         unsigned long stack_addr = (unsigned long)(kcb->jprobe_saved_esp);
 719         struct jprobe *jp = container_of(p, struct jprobe, kp);
 720
 721         if ((addr > (u8 *) jprobe_return) && (addr < (u8 *) jprobe_return_end)) {
 722                 if (&regs->esp != kcb->jprobe_saved_esp) {
 723                         struct pt_regs *saved_regs =
 724                             container_of(kcb->jprobe_saved_esp,
 725                                             struct pt_regs, esp);
 726                         printk("current esp %p does not match saved esp %p\n",
 727                                &regs->esp, kcb->jprobe_saved_esp);
 728                         printk("Saved registers for jprobe %p\n", jp);
 729                         show_registers(saved_regs);
 730                         printk("Current registers\n");
 731                         show_registers(regs);
 732                         BUG();
 733                 }
 734                 *regs = kcb->jprobe_saved_regs;
 735                 memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
 736                        MIN_STACK_SIZE(stack_addr));
 737                 preempt_enable_no_resched();
 738                 return 1;
 739         }
 740         return 0;
 741 }
 742
 743 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 744 {
 745         return 0;
 746 }
 747
 748 int __init arch_init_kprobes(void)
 749 {
 750         return 0;
 751 }