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 #include <asm/uaccess.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         *p->addr = BREAKPOINT_INSTRUCTION;
 174         flush_icache_range((unsigned long) p->addr,
 175                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
 176 }
 177
 178 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 179 {
 180         *p->addr = p->opcode;
 181         flush_icache_range((unsigned long) p->addr,
 182                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
 183 }
 184
 185 void __kprobes arch_remove_kprobe(struct kprobe *p)
 186 {
 187         mutex_lock(&kprobe_mutex);
 188         free_insn_slot(p->ainsn.insn);
 189         mutex_unlock(&kprobe_mutex);
 190 }
 191
 192 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 193 {
 194         kcb->prev_kprobe.kp = kprobe_running();
 195         kcb->prev_kprobe.status = kcb->kprobe_status;
 196         kcb->prev_kprobe.old_eflags = kcb->kprobe_old_eflags;
 197         kcb->prev_kprobe.saved_eflags = kcb->kprobe_saved_eflags;
 198 }
 199
 200 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 201 {
 202         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
 203         kcb->kprobe_status = kcb->prev_kprobe.status;
 204         kcb->kprobe_old_eflags = kcb->prev_kprobe.old_eflags;
 205         kcb->kprobe_saved_eflags = kcb->prev_kprobe.saved_eflags;
 206 }
 207
 208 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
 209                                 struct kprobe_ctlblk *kcb)
 210 {
 211         __get_cpu_var(current_kprobe) = p;
 212         kcb->kprobe_saved_eflags = kcb->kprobe_old_eflags
 213                 = (regs->eflags & (TF_MASK | IF_MASK));
 214         if (is_IF_modifier(p->opcode))
 215                 kcb->kprobe_saved_eflags &= ~IF_MASK;
 216 }
 217
 218 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 219 {
 220         regs->eflags |= TF_MASK;
 221         regs->eflags &= ~IF_MASK;
 222         /*single step inline if the instruction is an int3*/
 223         if (p->opcode == BREAKPOINT_INSTRUCTION)
 224                 regs->eip = (unsigned long)p->addr;
 225         else
 226                 regs->eip = (unsigned long)p->ainsn.insn;
 227 }
 228
 229 /* Called with kretprobe_lock held */
 230 void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
 231                                       struct pt_regs *regs)
 232 {
 233         unsigned long *sara = (unsigned long *)&regs->esp;
 234         struct kretprobe_instance *ri;
 235
 236         if ((ri = get_free_rp_inst(rp)) != NULL) {
 237                 ri->rp = rp;
 238                 ri->task = current;
 239                 ri->ret_addr = (kprobe_opcode_t *) *sara;
 240
 241                 /* Replace the return addr with trampoline addr */
 242                 *sara = (unsigned long) &kretprobe_trampoline;
 243
 244                 add_rp_inst(ri);
 245         } else {
 246                 rp->nmissed++;
 247         }
 248 }
 249
 250 /*
 251  * Interrupts are disabled on entry as trap3 is an interrupt gate and they
 252  * remain disabled thorough out this function.
 253  */
 254 static int __kprobes kprobe_handler(struct pt_regs *regs)
 255 {
 256         struct kprobe *p;
 257         int ret = 0;
 258         kprobe_opcode_t *addr;
 259         struct kprobe_ctlblk *kcb;
 260 #ifdef CONFIG_PREEMPT
 261         unsigned pre_preempt_count = preempt_count();
 262 #endif /* CONFIG_PREEMPT */
 263
 264         addr = (kprobe_opcode_t *)(regs->eip - sizeof(kprobe_opcode_t));
 265
 266         /*
 267          * We don't want to be preempted for the entire
 268          * duration of kprobe processing
 269          */
 270         preempt_disable();
 271         kcb = get_kprobe_ctlblk();
 272
 273         /* Check we're not actually recursing */
 274         if (kprobe_running()) {
 275                 p = get_kprobe(addr);
 276                 if (p) {
 277                         if (kcb->kprobe_status == KPROBE_HIT_SS &&
 278                                 *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
 279                                 regs->eflags &= ~TF_MASK;
 280                                 regs->eflags |= kcb->kprobe_saved_eflags;
 281                                 goto no_kprobe;
 282                         }
 283                         /* We have reentered the kprobe_handler(), since
 284                          * another probe was hit while within the handler.
 285                          * We here save the original kprobes variables and
 286                          * just single step on the instruction of the new probe
 287                          * without calling any user handlers.
 288                          */
 289                         save_previous_kprobe(kcb);
 290                         set_current_kprobe(p, regs, kcb);
 291                         kprobes_inc_nmissed_count(p);
 292                         prepare_singlestep(p, regs);
 293                         kcb->kprobe_status = KPROBE_REENTER;
 294                         return 1;
 295                 } else {
 296                         if (*addr != BREAKPOINT_INSTRUCTION) {
 297                         /* The breakpoint instruction was removed by
 298                          * another cpu right after we hit, no further
 299                          * handling of this interrupt is appropriate
 300                          */
 301                                 regs->eip -= sizeof(kprobe_opcode_t);
 302                                 ret = 1;
 303                                 goto no_kprobe;
 304                         }
 305                         p = __get_cpu_var(current_kprobe);
 306                         if (p->break_handler && p->break_handler(p, regs)) {
 307                                 goto ss_probe;
 308                         }
 309                 }
 310                 goto no_kprobe;
 311         }
 312
 313         p = get_kprobe(addr);
 314         if (!p) {
 315                 if (*addr != BREAKPOINT_INSTRUCTION) {
 316                         /*
 317                          * The breakpoint instruction was removed right
 318                          * after we hit it.  Another cpu has removed
 319                          * either a probepoint or a debugger breakpoint
 320                          * at this address.  In either case, no further
 321                          * handling of this interrupt is appropriate.
 322                          * Back up over the (now missing) int3 and run
 323                          * the original instruction.
 324                          */
 325                         regs->eip -= sizeof(kprobe_opcode_t);
 326                         ret = 1;
 327                 }
 328                 /* Not one of ours: let kernel handle it */
 329                 goto no_kprobe;
 330         }
 331
 332         set_current_kprobe(p, regs, kcb);
 333         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 334
 335         if (p->pre_handler && p->pre_handler(p, regs))
 336                 /* handler has already set things up, so skip ss setup */
 337                 return 1;
 338
 339         if (p->ainsn.boostable == 1 &&
 340 #ifdef CONFIG_PREEMPT
 341             !(pre_preempt_count) && /*
 342                                        * This enables booster when the direct
 343                                        * execution path aren't preempted.
 344                                        */
 345 #endif /* CONFIG_PREEMPT */
 346             !p->post_handler && !p->break_handler ) {
 347                 /* Boost up -- we can execute copied instructions directly */
 348                 reset_current_kprobe();
 349                 regs->eip = (unsigned long)p->ainsn.insn;
 350                 preempt_enable_no_resched();
 351                 return 1;
 352         }
 353
 354 ss_probe:
 355         prepare_singlestep(p, regs);
 356         kcb->kprobe_status = KPROBE_HIT_SS;
 357         return 1;
 358
 359 no_kprobe:
 360         preempt_enable_no_resched();
 361         return ret;
 362 }
 363
 364 /*
 365  * For function-return probes, init_kprobes() establishes a probepoint
 366  * here. When a retprobed function returns, this probe is hit and
 367  * trampoline_probe_handler() runs, calling the kretprobe's handler.
 368  */
 369  void __kprobes kretprobe_trampoline_holder(void)
 370  {
 371         asm volatile ( ".global kretprobe_trampoline\n"
 372                         "kretprobe_trampoline: \n"
 373                         "       pushf\n"
 374                         /* skip cs, eip, orig_eax, es, ds */
 375                         "       subl $20, %esp\n"
 376                         "       pushl %eax\n"
 377                         "       pushl %ebp\n"
 378                         "       pushl %edi\n"
 379                         "       pushl %esi\n"
 380                         "       pushl %edx\n"
 381                         "       pushl %ecx\n"
 382                         "       pushl %ebx\n"
 383                         "       movl %esp, %eax\n"
 384                         "       call trampoline_handler\n"
 385                         /* move eflags to cs */
 386                         "       movl 48(%esp), %edx\n"
 387                         "       movl %edx, 44(%esp)\n"
 388                         /* save true return address on eflags */
 389                         "       movl %eax, 48(%esp)\n"
 390                         "       popl %ebx\n"
 391                         "       popl %ecx\n"
 392                         "       popl %edx\n"
 393                         "       popl %esi\n"
 394                         "       popl %edi\n"
 395                         "       popl %ebp\n"
 396                         "       popl %eax\n"
 397                         /* skip eip, orig_eax, es, ds */
 398                         "       addl $16, %esp\n"
 399                         "       popf\n"
 400                         "       ret\n");
 401 }
 402
 403 /*
 404  * Called from kretprobe_trampoline
 405  */
 406 fastcall void *__kprobes trampoline_handler(struct pt_regs *regs)
 407 {
 408         struct kretprobe_instance *ri = NULL;
 409         struct hlist_head *head;
 410         struct hlist_node *node, *tmp;
 411         unsigned long flags, orig_ret_address = 0;
 412         unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
 413
 414         spin_lock_irqsave(&kretprobe_lock, flags);
 415         head = kretprobe_inst_table_head(current);
 416
 417         /*
 418          * It is possible to have multiple instances associated with a given
 419          * task either because an multiple functions in the call path
 420          * have a return probe installed on them, and/or more then one return
 421          * return probe was registered for a target function.
 422          *
 423          * We can handle this because:
 424          *     - instances are always inserted at the head of the list
 425          *     - when multiple return probes are registered for the same
 426          *       function, the first instance's ret_addr will point to the
 427          *       real return address, and all the rest will point to
 428          *       kretprobe_trampoline
 429          */
 430         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
 431                 if (ri->task != current)
 432                         /* another task is sharing our hash bucket */
 433                         continue;
 434
 435                 if (ri->rp && ri->rp->handler){
 436                         __get_cpu_var(current_kprobe) = &ri->rp->kp;
 437                         ri->rp->handler(ri, regs);
 438                         __get_cpu_var(current_kprobe) = NULL;
 439                 }
 440
 441                 orig_ret_address = (unsigned long)ri->ret_addr;
 442                 recycle_rp_inst(ri);
 443
 444                 if (orig_ret_address != trampoline_address)
 445                         /*
 446                          * This is the real return address. Any other
 447                          * instances associated with this task are for
 448                          * other calls deeper on the call stack
 449                          */
 450                         break;
 451         }
 452
 453         BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
 454
 455         spin_unlock_irqrestore(&kretprobe_lock, flags);
 456
 457         return (void*)orig_ret_address;
 458 }
 459
 460 /*
 461  * Called after single-stepping.  p->addr is the address of the
 462  * instruction whose first byte has been replaced by the "int 3"
 463  * instruction.  To avoid the SMP problems that can occur when we
 464  * temporarily put back the original opcode to single-step, we
 465  * single-stepped a copy of the instruction.  The address of this
 466  * copy is p->ainsn.insn.
 467  *
 468  * This function prepares to return from the post-single-step
 469  * interrupt.  We have to fix up the stack as follows:
 470  *
 471  * 0) Except in the case of absolute or indirect jump or call instructions,
 472  * the new eip is relative to the copied instruction.  We need to make
 473  * it relative to the original instruction.
 474  *
 475  * 1) If the single-stepped instruction was pushfl, then the TF and IF
 476  * flags are set in the just-pushed eflags, and may need to be cleared.
 477  *
 478  * 2) If the single-stepped instruction was a call, the return address
 479  * that is atop the stack is the address following the copied instruction.
 480  * We need to make it the address following the original instruction.
 481  *
 482  * This function also checks instruction size for preparing direct execution.
 483  */
 484 static void __kprobes resume_execution(struct kprobe *p,
 485                 struct pt_regs *regs, struct kprobe_ctlblk *kcb)
 486 {
 487         unsigned long *tos = (unsigned long *)&regs->esp;
 488         unsigned long copy_eip = (unsigned long)p->ainsn.insn;
 489         unsigned long orig_eip = (unsigned long)p->addr;
 490
 491         regs->eflags &= ~TF_MASK;
 492         switch (p->ainsn.insn[0]) {
 493         case 0x9c:              /* pushfl */
 494                 *tos &= ~(TF_MASK | IF_MASK);
 495                 *tos |= kcb->kprobe_old_eflags;
 496                 break;
 497         case 0xc2:              /* iret/ret/lret */
 498         case 0xc3:
 499         case 0xca:
 500         case 0xcb:
 501         case 0xcf:
 502         case 0xea:              /* jmp absolute -- eip is correct */
 503                 /* eip is already adjusted, no more changes required */
 504                 p->ainsn.boostable = 1;
 505                 goto no_change;
 506         case 0xe8:              /* call relative - Fix return addr */
 507                 *tos = orig_eip + (*tos - copy_eip);
 508                 break;
 509         case 0x9a:              /* call absolute -- same as call absolute, indirect */
 510                 *tos = orig_eip + (*tos - copy_eip);
 511                 goto no_change;
 512         case 0xff:
 513                 if ((p->ainsn.insn[1] & 0x30) == 0x10) {
 514                         /*
 515                          * call absolute, indirect
 516                          * Fix return addr; eip is correct.
 517                          * But this is not boostable
 518                          */
 519                         *tos = orig_eip + (*tos - copy_eip);
 520                         goto no_change;
 521                 } else if (((p->ainsn.insn[1] & 0x31) == 0x20) ||       /* jmp near, absolute indirect */
 522                            ((p->ainsn.insn[1] & 0x31) == 0x21)) {       /* jmp far, absolute indirect */
 523                         /* eip is correct. And this is boostable */
 524                         p->ainsn.boostable = 1;
 525                         goto no_change;
 526                 }
 527         default:
 528                 break;
 529         }
 530
 531         if (p->ainsn.boostable == 0) {
 532                 if ((regs->eip > copy_eip) &&
 533                     (regs->eip - copy_eip) + 5 < MAX_INSN_SIZE) {
 534                         /*
 535                          * These instructions can be executed directly if it
 536                          * jumps back to correct address.
 537                          */
 538                         set_jmp_op((void *)regs->eip,
 539                                    (void *)orig_eip + (regs->eip - copy_eip));
 540                         p->ainsn.boostable = 1;
 541                 } else {
 542                         p->ainsn.boostable = -1;
 543                 }
 544         }
 545
 546         regs->eip = orig_eip + (regs->eip - copy_eip);
 547
 548 no_change:
 549         return;
 550 }
 551
 552 /*
 553  * Interrupts are disabled on entry as trap1 is an interrupt gate and they
 554  * remain disabled thoroughout this function.
 555  */
 556 static int __kprobes post_kprobe_handler(struct pt_regs *regs)
 557 {
 558         struct kprobe *cur = kprobe_running();
 559         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 560
 561         if (!cur)
 562                 return 0;
 563
 564         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
 565                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
 566                 cur->post_handler(cur, regs, 0);
 567         }
 568
 569         resume_execution(cur, regs, kcb);
 570         regs->eflags |= kcb->kprobe_saved_eflags;
 571
 572         /*Restore back the original saved kprobes variables and continue. */
 573         if (kcb->kprobe_status == KPROBE_REENTER) {
 574                 restore_previous_kprobe(kcb);
 575                 goto out;
 576         }
 577         reset_current_kprobe();
 578 out:
 579         preempt_enable_no_resched();
 580
 581         /*
 582          * if somebody else is singlestepping across a probe point, eflags
 583          * will have TF set, in which case, continue the remaining processing
 584          * of do_debug, as if this is not a probe hit.
 585          */
 586         if (regs->eflags & TF_MASK)
 587                 return 0;
 588
 589         return 1;
 590 }
 591
 592 static int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 593 {
 594         struct kprobe *cur = kprobe_running();
 595         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 596
 597         switch(kcb->kprobe_status) {
 598         case KPROBE_HIT_SS:
 599         case KPROBE_REENTER:
 600                 /*
 601                  * We are here because the instruction being single
 602                  * stepped caused a page fault. We reset the current
 603                  * kprobe and the eip points back to the probe address
 604                  * and allow the page fault handler to continue as a
 605                  * normal page fault.
 606                  */
 607                 regs->eip = (unsigned long)cur->addr;
 608                 regs->eflags |= kcb->kprobe_old_eflags;
 609                 if (kcb->kprobe_status == KPROBE_REENTER)
 610                         restore_previous_kprobe(kcb);
 611                 else
 612                         reset_current_kprobe();
 613                 preempt_enable_no_resched();
 614                 break;
 615         case KPROBE_HIT_ACTIVE:
 616         case KPROBE_HIT_SSDONE:
 617                 /*
 618                  * We increment the nmissed count for accounting,
 619                  * we can also use npre/npostfault count for accouting
 620                  * these specific fault cases.
 621                  */
 622                 kprobes_inc_nmissed_count(cur);
 623
 624                 /*
 625                  * We come here because instructions in the pre/post
 626                  * handler caused the page_fault, this could happen
 627                  * if handler tries to access user space by
 628                  * copy_from_user(), get_user() etc. Let the
 629                  * user-specified handler try to fix it first.
 630                  */
 631                 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
 632                         return 1;
 633
 634                 /*
 635                  * In case the user-specified fault handler returned
 636                  * zero, try to fix up.
 637                  */
 638                 if (fixup_exception(regs))
 639                         return 1;
 640
 641                 /*
 642                  * fixup_exception() could not handle it,
 643                  * Let do_page_fault() fix it.
 644                  */
 645                 break;
 646         default:
 647                 break;
 648         }
 649         return 0;
 650 }
 651
 652 /*
 653  * Wrapper routine to for handling exceptions.
 654  */
 655 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 656                                        unsigned long val, void *data)
 657 {
 658         struct die_args *args = (struct die_args *)data;
 659         int ret = NOTIFY_DONE;
 660
 661         if (args->regs && user_mode_vm(args->regs))
 662                 return ret;
 663
 664         switch (val) {
 665         case DIE_INT3:
 666                 if (kprobe_handler(args->regs))
 667                         ret = NOTIFY_STOP;
 668                 break;
 669         case DIE_DEBUG:
 670                 if (post_kprobe_handler(args->regs))
 671                         ret = NOTIFY_STOP;
 672                 break;
 673         case DIE_GPF:
 674         case DIE_PAGE_FAULT:
 675                 /* kprobe_running() needs smp_processor_id() */
 676                 preempt_disable();
 677                 if (kprobe_running() &&
 678                     kprobe_fault_handler(args->regs, args->trapnr))
 679                         ret = NOTIFY_STOP;
 680                 preempt_enable();
 681                 break;
 682         default:
 683                 break;
 684         }
 685         return ret;
 686 }
 687
 688 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 689 {
 690         struct jprobe *jp = container_of(p, struct jprobe, kp);
 691         unsigned long addr;
 692         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 693
 694         kcb->jprobe_saved_regs = *regs;
 695         kcb->jprobe_saved_esp = &regs->esp;
 696         addr = (unsigned long)(kcb->jprobe_saved_esp);
 697
 698         /*
 699          * TBD: As Linus pointed out, gcc assumes that the callee
 700          * owns the argument space and could overwrite it, e.g.
 701          * tailcall optimization. So, to be absolutely safe
 702          * we also save and restore enough stack bytes to cover
 703          * the argument area.
 704          */
 705         memcpy(kcb->jprobes_stack, (kprobe_opcode_t *)addr,
 706                         MIN_STACK_SIZE(addr));
 707         regs->eflags &= ~IF_MASK;
 708         regs->eip = (unsigned long)(jp->entry);
 709         return 1;
 710 }
 711
 712 void __kprobes jprobe_return(void)
 713 {
 714         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 715
 716         asm volatile ("       xchgl   %%ebx,%%esp     \n"
 717                       "       int3                      \n"
 718                       "       .globl jprobe_return_end  \n"
 719                       "       jprobe_return_end:        \n"
 720                       "       nop                       \n"::"b"
 721                       (kcb->jprobe_saved_esp):"memory");
 722 }
 723
 724 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 725 {
 726         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 727         u8 *addr = (u8 *) (regs->eip - 1);
 728         unsigned long stack_addr = (unsigned long)(kcb->jprobe_saved_esp);
 729         struct jprobe *jp = container_of(p, struct jprobe, kp);
 730
 731         if ((addr > (u8 *) jprobe_return) && (addr < (u8 *) jprobe_return_end)) {
 732                 if (&regs->esp != kcb->jprobe_saved_esp) {
 733                         struct pt_regs *saved_regs =
 734                             container_of(kcb->jprobe_saved_esp,
 735                                             struct pt_regs, esp);
 736                         printk("current esp %p does not match saved esp %p\n",
 737                                &regs->esp, kcb->jprobe_saved_esp);
 738                         printk("Saved registers for jprobe %p\n", jp);
 739                         show_registers(saved_regs);
 740                         printk("Current registers\n");
 741                         show_registers(regs);
 742                         BUG();
 743                 }
 744                 *regs = kcb->jprobe_saved_regs;
 745                 memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
 746                        MIN_STACK_SIZE(stack_addr));
 747                 preempt_enable_no_resched();
 748                 return 1;
 749         }
 750         return 0;
 751 }
 752
 753 int __init arch_init_kprobes(void)
 754 {
 755         return 0;
 756 }