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 <asm/cacheflush.h>
  35 #include <asm/kdebug.h>
  36 #include <asm/desc.h>
  37 #include <asm/uaccess.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 __always_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 __always_inline int can_boost(kprobe_opcode_t *opcodes)
  60 {
  61 #define W(row,b0,b1,b2,b3,b4,b5,b6,b7,b8,b9,ba,bb,bc,bd,be,bf)                \
  62         (((b0##UL << 0x0)|(b1##UL << 0x1)|(b2##UL << 0x2)|(b3##UL << 0x3) |   \
  63           (b4##UL << 0x4)|(b5##UL << 0x5)|(b6##UL << 0x6)|(b7##UL << 0x7) |   \
  64           (b8##UL << 0x8)|(b9##UL << 0x9)|(ba##UL << 0xa)|(bb##UL << 0xb) |   \
  65           (bc##UL << 0xc)|(bd##UL << 0xd)|(be##UL << 0xe)|(bf##UL << 0xf))    \
  66          << (row % 32))
  67         /*
  68          * Undefined/reserved opcodes, conditional jump, Opcode Extension
  69          * Groups, and some special opcodes can not be boost.
  70          */
  71         static const unsigned long twobyte_is_boostable[256 / 32] = {
  72                 /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
  73                 /*      -------------------------------         */
  74                 W(0x00, 0,0,1,1,0,0,1,0,1,1,0,0,0,0,0,0)| /* 00 */
  75                 W(0x10, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 10 */
  76                 W(0x20, 1,1,1,1,0,0,0,0,0,0,0,0,0,0,0,0)| /* 20 */
  77                 W(0x30, 0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 30 */
  78                 W(0x40, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 40 */
  79                 W(0x50, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 50 */
  80                 W(0x60, 1,1,1,1,1,1,1,1,1,1,1,1,0,0,1,1)| /* 60 */
  81                 W(0x70, 0,0,0,0,1,1,1,1,0,0,0,0,0,0,1,1), /* 70 */
  82                 W(0x80, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 80 */
  83                 W(0x90, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1), /* 90 */
  84                 W(0xa0, 1,1,0,1,1,1,0,0,1,1,0,1,1,1,0,1)| /* a0 */
  85                 W(0xb0, 1,1,1,1,1,1,1,1,0,0,0,1,1,1,1,1), /* b0 */
  86                 W(0xc0, 1,1,0,0,0,0,0,0,1,1,1,1,1,1,1,1)| /* c0 */
  87                 W(0xd0, 0,1,1,1,0,1,0,0,1,1,0,1,1,1,0,1), /* d0 */
  88                 W(0xe0, 0,1,1,0,0,1,0,0,1,1,0,1,1,1,0,1)| /* e0 */
  89                 W(0xf0, 0,1,1,1,0,1,0,0,1,1,1,0,1,1,1,0)  /* f0 */
  90                 /*      -------------------------------         */
  91                 /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
  92         };
  93 #undef W
  94         kprobe_opcode_t opcode;
  95         kprobe_opcode_t *orig_opcodes = opcodes;
  96 retry:
  97         if (opcodes - orig_opcodes > MAX_INSN_SIZE - 1)
  98                 return 0;
  99         opcode = *(opcodes++);
 100
 101         /* 2nd-byte opcode */
 102         if (opcode == 0x0f) {
 103                 if (opcodes - orig_opcodes > MAX_INSN_SIZE - 1)
 104                         return 0;
 105                 return test_bit(*opcodes, twobyte_is_boostable);
 106         }
 107
 108         switch (opcode & 0xf0) {
 109         case 0x60:
 110                 if (0x63 < opcode && opcode < 0x67)
 111                         goto retry; /* prefixes */
 112                 /* can't boost Address-size override and bound */
 113                 return (opcode != 0x62 && opcode != 0x67);
 114         case 0x70:
 115                 return 0; /* can't boost conditional jump */
 116         case 0xc0:
 117                 /* can't boost software-interruptions */
 118                 return (0xc1 < opcode && opcode < 0xcc) || opcode == 0xcf;
 119         case 0xd0:
 120                 /* can boost AA* and XLAT */
 121                 return (opcode == 0xd4 || opcode == 0xd5 || opcode == 0xd7);
 122         case 0xe0:
 123                 /* can boost in/out and absolute jmps */
 124                 return ((opcode & 0x04) || opcode == 0xea);
 125         case 0xf0:
 126                 if ((opcode & 0x0c) == 0 && opcode != 0xf1)
 127                         goto retry; /* lock/rep(ne) prefix */
 128                 /* clear and set flags can be boost */
 129                 return (opcode == 0xf5 || (0xf7 < opcode && opcode < 0xfe));
 130         default:
 131                 if (opcode == 0x26 || opcode == 0x36 || opcode == 0x3e)
 132                         goto retry; /* prefixes */
 133                 /* can't boost CS override and call */
 134                 return (opcode != 0x2e && opcode != 0x9a);
 135         }
 136 }
 137
 138 /*
 139  * returns non-zero if opcode modifies the interrupt flag.
 140  */
 141 static int __kprobes is_IF_modifier(kprobe_opcode_t opcode)
 142 {
 143         switch (opcode) {
 144         case 0xfa:              /* cli */
 145         case 0xfb:              /* sti */
 146         case 0xcf:              /* iret/iretd */
 147         case 0x9d:              /* popf/popfd */
 148                 return 1;
 149         }
 150         return 0;
 151 }
 152
 153 int __kprobes arch_prepare_kprobe(struct kprobe *p)
 154 {
 155         /* insn: must be on special executable page on i386. */
 156         p->ainsn.insn = get_insn_slot();
 157         if (!p->ainsn.insn)
 158                 return -ENOMEM;
 159
 160         memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
 161         p->opcode = *p->addr;
 162         if (can_boost(p->addr)) {
 163                 p->ainsn.boostable = 0;
 164         } else {
 165                 p->ainsn.boostable = -1;
 166         }
 167         return 0;
 168 }
 169
 170 void __kprobes arch_arm_kprobe(struct kprobe *p)
 171 {
 172         *p->addr = BREAKPOINT_INSTRUCTION;
 173         flush_icache_range((unsigned long) p->addr,
 174                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
 175 }
 176
 177 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 178 {
 179         *p->addr = p->opcode;
 180         flush_icache_range((unsigned long) p->addr,
 181                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
 182 }
 183
 184 void __kprobes arch_remove_kprobe(struct kprobe *p)
 185 {
 186         mutex_lock(&kprobe_mutex);
 187         free_insn_slot(p->ainsn.insn);
 188         mutex_unlock(&kprobe_mutex);
 189 }
 190
 191 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 192 {
 193         kcb->prev_kprobe.kp = kprobe_running();
 194         kcb->prev_kprobe.status = kcb->kprobe_status;
 195         kcb->prev_kprobe.old_eflags = kcb->kprobe_old_eflags;
 196         kcb->prev_kprobe.saved_eflags = kcb->kprobe_saved_eflags;
 197 }
 198
 199 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 200 {
 201         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
 202         kcb->kprobe_status = kcb->prev_kprobe.status;
 203         kcb->kprobe_old_eflags = kcb->prev_kprobe.old_eflags;
 204         kcb->kprobe_saved_eflags = kcb->prev_kprobe.saved_eflags;
 205 }
 206
 207 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
 208                                 struct kprobe_ctlblk *kcb)
 209 {
 210         __get_cpu_var(current_kprobe) = p;
 211         kcb->kprobe_saved_eflags = kcb->kprobe_old_eflags
 212                 = (regs->eflags & (TF_MASK | IF_MASK));
 213         if (is_IF_modifier(p->opcode))
 214                 kcb->kprobe_saved_eflags &= ~IF_MASK;
 215 }
 216
 217 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 218 {
 219         regs->eflags |= TF_MASK;
 220         regs->eflags &= ~IF_MASK;
 221         /*single step inline if the instruction is an int3*/
 222         if (p->opcode == BREAKPOINT_INSTRUCTION)
 223                 regs->eip = (unsigned long)p->addr;
 224         else
 225                 regs->eip = (unsigned long)p->ainsn.insn;
 226 }
 227
 228 /* Called with kretprobe_lock held */
 229 void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
 230                                       struct pt_regs *regs)
 231 {
 232         unsigned long *sara = (unsigned long *)&regs->esp;
 233
 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                 add_rp_inst(ri);
 244         } else {
 245                 rp->nmissed++;
 246         }
 247 }
 248
 249 /*
 250  * Interrupts are disabled on entry as trap3 is an interrupt gate and they
 251  * remain disabled thorough out this function.
 252  */
 253 static int __kprobes kprobe_handler(struct pt_regs *regs)
 254 {
 255         struct kprobe *p;
 256         int ret = 0;
 257         kprobe_opcode_t *addr;
 258         struct kprobe_ctlblk *kcb;
 259
 260         addr = (kprobe_opcode_t *)(regs->eip - sizeof(kprobe_opcode_t));
 261
 262         /*
 263          * We don't want to be preempted for the entire
 264          * duration of kprobe processing
 265          */
 266         preempt_disable();
 267         kcb = get_kprobe_ctlblk();
 268
 269         /* Check we're not actually recursing */
 270         if (kprobe_running()) {
 271                 p = get_kprobe(addr);
 272                 if (p) {
 273                         if (kcb->kprobe_status == KPROBE_HIT_SS &&
 274                                 *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
 275                                 regs->eflags &= ~TF_MASK;
 276                                 regs->eflags |= kcb->kprobe_saved_eflags;
 277                                 goto no_kprobe;
 278                         }
 279                         /* We have reentered the kprobe_handler(), since
 280                          * another probe was hit while within the handler.
 281                          * We here save the original kprobes variables and
 282                          * just single step on the instruction of the new probe
 283                          * without calling any user handlers.
 284                          */
 285                         save_previous_kprobe(kcb);
 286                         set_current_kprobe(p, regs, kcb);
 287                         kprobes_inc_nmissed_count(p);
 288                         prepare_singlestep(p, regs);
 289                         kcb->kprobe_status = KPROBE_REENTER;
 290                         return 1;
 291                 } else {
 292                         if (*addr != BREAKPOINT_INSTRUCTION) {
 293                         /* The breakpoint instruction was removed by
 294                          * another cpu right after we hit, no further
 295                          * handling of this interrupt is appropriate
 296                          */
 297                                 regs->eip -= sizeof(kprobe_opcode_t);
 298                                 ret = 1;
 299                                 goto no_kprobe;
 300                         }
 301                         p = __get_cpu_var(current_kprobe);
 302                         if (p->break_handler && p->break_handler(p, regs)) {
 303                                 goto ss_probe;
 304                         }
 305                 }
 306                 goto no_kprobe;
 307         }
 308
 309         p = get_kprobe(addr);
 310         if (!p) {
 311                 if (*addr != BREAKPOINT_INSTRUCTION) {
 312                         /*
 313                          * The breakpoint instruction was removed right
 314                          * after we hit it.  Another cpu has removed
 315                          * either a probepoint or a debugger breakpoint
 316                          * at this address.  In either case, no further
 317                          * handling of this interrupt is appropriate.
 318                          * Back up over the (now missing) int3 and run
 319                          * the original instruction.
 320                          */
 321                         regs->eip -= sizeof(kprobe_opcode_t);
 322                         ret = 1;
 323                 }
 324                 /* Not one of ours: let kernel handle it */
 325                 goto no_kprobe;
 326         }
 327
 328         set_current_kprobe(p, regs, kcb);
 329         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 330
 331         if (p->pre_handler && p->pre_handler(p, regs))
 332                 /* handler has already set things up, so skip ss setup */
 333                 return 1;
 334
 335 ss_probe:
 336 #ifndef CONFIG_PREEMPT
 337         if (p->ainsn.boostable == 1 && !p->post_handler){
 338                 /* Boost up -- we can execute copied instructions directly */
 339                 reset_current_kprobe();
 340                 regs->eip = (unsigned long)p->ainsn.insn;
 341                 preempt_enable_no_resched();
 342                 return 1;
 343         }
 344 #endif
 345         prepare_singlestep(p, regs);
 346         kcb->kprobe_status = KPROBE_HIT_SS;
 347         return 1;
 348
 349 no_kprobe:
 350         preempt_enable_no_resched();
 351         return ret;
 352 }
 353
 354 /*
 355  * For function-return probes, init_kprobes() establishes a probepoint
 356  * here. When a retprobed function returns, this probe is hit and
 357  * trampoline_probe_handler() runs, calling the kretprobe's handler.
 358  */
 359  void __kprobes kretprobe_trampoline_holder(void)
 360  {
 361         asm volatile ( ".global kretprobe_trampoline\n"
 362                         "kretprobe_trampoline: \n"
 363                         "       pushf\n"
 364                         /* skip cs, eip, orig_eax */
 365                         "       subl $12, %esp\n"
 366                         "       pushl %gs\n"
 367                         "       pushl %ds\n"
 368                         "       pushl %es\n"
 369                         "       pushl %eax\n"
 370                         "       pushl %ebp\n"
 371                         "       pushl %edi\n"
 372                         "       pushl %esi\n"
 373                         "       pushl %edx\n"
 374                         "       pushl %ecx\n"
 375                         "       pushl %ebx\n"
 376                         "       movl %esp, %eax\n"
 377                         "       call trampoline_handler\n"
 378                         /* move eflags to cs */
 379                         "       movl 52(%esp), %edx\n"
 380                         "       movl %edx, 48(%esp)\n"
 381                         /* save true return address on eflags */
 382                         "       movl %eax, 52(%esp)\n"
 383                         "       popl %ebx\n"
 384                         "       popl %ecx\n"
 385                         "       popl %edx\n"
 386                         "       popl %esi\n"
 387                         "       popl %edi\n"
 388                         "       popl %ebp\n"
 389                         "       popl %eax\n"
 390                         /* skip eip, orig_eax, es, ds, gs */
 391                         "       addl $20, %esp\n"
 392                         "       popf\n"
 393                         "       ret\n");
 394 }
 395
 396 /*
 397  * Called from kretprobe_trampoline
 398  */
 399 fastcall void *__kprobes trampoline_handler(struct pt_regs *regs)
 400 {
 401         struct kretprobe_instance *ri = NULL;
 402         struct hlist_head *head, empty_rp;
 403         struct hlist_node *node, *tmp;
 404         unsigned long flags, orig_ret_address = 0;
 405         unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
 406
 407         INIT_HLIST_HEAD(&empty_rp);
 408         spin_lock_irqsave(&kretprobe_lock, flags);
 409         head = kretprobe_inst_table_head(current);
 410         /* fixup registers */
 411         regs->xcs = __KERNEL_CS;
 412         regs->eip = trampoline_address;
 413         regs->orig_eax = 0xffffffff;
 414
 415         /*
 416          * It is possible to have multiple instances associated with a given
 417          * task either because an multiple functions in the call path
 418          * have a return probe installed on them, and/or more then one return
 419          * return probe was registered for a target function.
 420          *
 421          * We can handle this because:
 422          *     - instances are always inserted at the head of the list
 423          *     - when multiple return probes are registered for the same
 424          *       function, the first instance's ret_addr will point to the
 425          *       real return address, and all the rest will point to
 426          *       kretprobe_trampoline
 427          */
 428         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
 429                 if (ri->task != current)
 430                         /* another task is sharing our hash bucket */
 431                         continue;
 432
 433                 if (ri->rp && ri->rp->handler){
 434                         __get_cpu_var(current_kprobe) = &ri->rp->kp;
 435                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 436                         ri->rp->handler(ri, regs);
 437                         __get_cpu_var(current_kprobe) = NULL;
 438                 }
 439
 440                 orig_ret_address = (unsigned long)ri->ret_addr;
 441                 recycle_rp_inst(ri, &empty_rp);
 442
 443                 if (orig_ret_address != trampoline_address)
 444                         /*
 445                          * This is the real return address. Any other
 446                          * instances associated with this task are for
 447                          * other calls deeper on the call stack
 448                          */
 449                         break;
 450         }
 451
 452         BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
 453
 454         spin_unlock_irqrestore(&kretprobe_lock, flags);
 455
 456         hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
 457                 hlist_del(&ri->hlist);
 458                 kfree(ri);
 459         }
 460         return (void*)orig_ret_address;
 461 }
 462
 463 /*
 464  * Called after single-stepping.  p->addr is the address of the
 465  * instruction whose first byte has been replaced by the "int 3"
 466  * instruction.  To avoid the SMP problems that can occur when we
 467  * temporarily put back the original opcode to single-step, we
 468  * single-stepped a copy of the instruction.  The address of this
 469  * copy is p->ainsn.insn.
 470  *
 471  * This function prepares to return from the post-single-step
 472  * interrupt.  We have to fix up the stack as follows:
 473  *
 474  * 0) Except in the case of absolute or indirect jump or call instructions,
 475  * the new eip is relative to the copied instruction.  We need to make
 476  * it relative to the original instruction.
 477  *
 478  * 1) If the single-stepped instruction was pushfl, then the TF and IF
 479  * flags are set in the just-pushed eflags, and may need to be cleared.
 480  *
 481  * 2) If the single-stepped instruction was a call, the return address
 482  * that is atop the stack is the address following the copied instruction.
 483  * We need to make it the address following the original instruction.
 484  *
 485  * This function also checks instruction size for preparing direct execution.
 486  */
 487 static void __kprobes resume_execution(struct kprobe *p,
 488                 struct pt_regs *regs, struct kprobe_ctlblk *kcb)
 489 {
 490         unsigned long *tos = (unsigned long *)&regs->esp;
 491         unsigned long copy_eip = (unsigned long)p->ainsn.insn;
 492         unsigned long orig_eip = (unsigned long)p->addr;
 493
 494         regs->eflags &= ~TF_MASK;
 495         switch (p->ainsn.insn[0]) {
 496         case 0x9c:              /* pushfl */
 497                 *tos &= ~(TF_MASK | IF_MASK);
 498                 *tos |= kcb->kprobe_old_eflags;
 499                 break;
 500         case 0xc2:              /* iret/ret/lret */
 501         case 0xc3:
 502         case 0xca:
 503         case 0xcb:
 504         case 0xcf:
 505         case 0xea:              /* jmp absolute -- eip is correct */
 506                 /* eip is already adjusted, no more changes required */
 507                 p->ainsn.boostable = 1;
 508                 goto no_change;
 509         case 0xe8:              /* call relative - Fix return addr */
 510                 *tos = orig_eip + (*tos - copy_eip);
 511                 break;
 512         case 0x9a:              /* call absolute -- same as call absolute, indirect */
 513                 *tos = orig_eip + (*tos - copy_eip);
 514                 goto no_change;
 515         case 0xff:
 516                 if ((p->ainsn.insn[1] & 0x30) == 0x10) {
 517                         /*
 518                          * call absolute, indirect
 519                          * Fix return addr; eip is correct.
 520                          * But this is not boostable
 521                          */
 522                         *tos = orig_eip + (*tos - copy_eip);
 523                         goto no_change;
 524                 } else if (((p->ainsn.insn[1] & 0x31) == 0x20) ||       /* jmp near, absolute indirect */
 525                            ((p->ainsn.insn[1] & 0x31) == 0x21)) {       /* jmp far, absolute indirect */
 526                         /* eip is correct. And this is boostable */
 527                         p->ainsn.boostable = 1;
 528                         goto no_change;
 529                 }
 530         default:
 531                 break;
 532         }
 533
 534         if (p->ainsn.boostable == 0) {
 535                 if ((regs->eip > copy_eip) &&
 536                     (regs->eip - copy_eip) + 5 < MAX_INSN_SIZE) {
 537                         /*
 538                          * These instructions can be executed directly if it
 539                          * jumps back to correct address.
 540                          */
 541                         set_jmp_op((void *)regs->eip,
 542                                    (void *)orig_eip + (regs->eip - copy_eip));
 543                         p->ainsn.boostable = 1;
 544                 } else {
 545                         p->ainsn.boostable = -1;
 546                 }
 547         }
 548
 549         regs->eip = orig_eip + (regs->eip - copy_eip);
 550
 551 no_change:
 552         return;
 553 }
 554
 555 /*
 556  * Interrupts are disabled on entry as trap1 is an interrupt gate and they
 557  * remain disabled thoroughout this function.
 558  */
 559 static int __kprobes post_kprobe_handler(struct pt_regs *regs)
 560 {
 561         struct kprobe *cur = kprobe_running();
 562         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 563
 564         if (!cur)
 565                 return 0;
 566
 567         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
 568                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
 569                 cur->post_handler(cur, regs, 0);
 570         }
 571
 572         resume_execution(cur, regs, kcb);
 573         regs->eflags |= kcb->kprobe_saved_eflags;
 574
 575         /*Restore back the original saved kprobes variables and continue. */
 576         if (kcb->kprobe_status == KPROBE_REENTER) {
 577                 restore_previous_kprobe(kcb);
 578                 goto out;
 579         }
 580         reset_current_kprobe();
 581 out:
 582         preempt_enable_no_resched();
 583
 584         /*
 585          * if somebody else is singlestepping across a probe point, eflags
 586          * will have TF set, in which case, continue the remaining processing
 587          * of do_debug, as if this is not a probe hit.
 588          */
 589         if (regs->eflags & TF_MASK)
 590                 return 0;
 591
 592         return 1;
 593 }
 594
 595 static int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 596 {
 597         struct kprobe *cur = kprobe_running();
 598         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 599
 600         switch(kcb->kprobe_status) {
 601         case KPROBE_HIT_SS:
 602         case KPROBE_REENTER:
 603                 /*
 604                  * We are here because the instruction being single
 605                  * stepped caused a page fault. We reset the current
 606                  * kprobe and the eip points back to the probe address
 607                  * and allow the page fault handler to continue as a
 608                  * normal page fault.
 609                  */
 610                 regs->eip = (unsigned long)cur->addr;
 611                 regs->eflags |= kcb->kprobe_old_eflags;
 612                 if (kcb->kprobe_status == KPROBE_REENTER)
 613                         restore_previous_kprobe(kcb);
 614                 else
 615                         reset_current_kprobe();
 616                 preempt_enable_no_resched();
 617                 break;
 618         case KPROBE_HIT_ACTIVE:
 619         case KPROBE_HIT_SSDONE:
 620                 /*
 621                  * We increment the nmissed count for accounting,
 622                  * we can also use npre/npostfault count for accouting
 623                  * these specific fault cases.
 624                  */
 625                 kprobes_inc_nmissed_count(cur);
 626
 627                 /*
 628                  * We come here because instructions in the pre/post
 629                  * handler caused the page_fault, this could happen
 630                  * if handler tries to access user space by
 631                  * copy_from_user(), get_user() etc. Let the
 632                  * user-specified handler try to fix it first.
 633                  */
 634                 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
 635                         return 1;
 636
 637                 /*
 638                  * In case the user-specified fault handler returned
 639                  * zero, try to fix up.
 640                  */
 641                 if (fixup_exception(regs))
 642                         return 1;
 643
 644                 /*
 645                  * fixup_exception() could not handle it,
 646                  * Let do_page_fault() fix it.
 647                  */
 648                 break;
 649         default:
 650                 break;
 651         }
 652         return 0;
 653 }
 654
 655 /*
 656  * Wrapper routine to for handling exceptions.
 657  */
 658 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 659                                        unsigned long val, void *data)
 660 {
 661         struct die_args *args = (struct die_args *)data;
 662         int ret = NOTIFY_DONE;
 663
 664         if (args->regs && user_mode_vm(args->regs))
 665                 return ret;
 666
 667         switch (val) {
 668         case DIE_INT3:
 669                 if (kprobe_handler(args->regs))
 670                         ret = NOTIFY_STOP;
 671                 break;
 672         case DIE_DEBUG:
 673                 if (post_kprobe_handler(args->regs))
 674                         ret = NOTIFY_STOP;
 675                 break;
 676         case DIE_GPF:
 677         case DIE_PAGE_FAULT:
 678                 /* kprobe_running() needs smp_processor_id() */
 679                 preempt_disable();
 680                 if (kprobe_running() &&
 681                     kprobe_fault_handler(args->regs, args->trapnr))
 682                         ret = NOTIFY_STOP;
 683                 preempt_enable();
 684                 break;
 685         default:
 686                 break;
 687         }
 688         return ret;
 689 }
 690
 691 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 692 {
 693         struct jprobe *jp = container_of(p, struct jprobe, kp);
 694         unsigned long addr;
 695         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 696
 697         kcb->jprobe_saved_regs = *regs;
 698         kcb->jprobe_saved_esp = &regs->esp;
 699         addr = (unsigned long)(kcb->jprobe_saved_esp);
 700
 701         /*
 702          * TBD: As Linus pointed out, gcc assumes that the callee
 703          * owns the argument space and could overwrite it, e.g.
 704          * tailcall optimization. So, to be absolutely safe
 705          * we also save and restore enough stack bytes to cover
 706          * the argument area.
 707          */
 708         memcpy(kcb->jprobes_stack, (kprobe_opcode_t *)addr,
 709                         MIN_STACK_SIZE(addr));
 710         regs->eflags &= ~IF_MASK;
 711         regs->eip = (unsigned long)(jp->entry);
 712         return 1;
 713 }
 714
 715 void __kprobes jprobe_return(void)
 716 {
 717         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 718
 719         asm volatile ("       xchgl   %%ebx,%%esp     \n"
 720                       "       int3                      \n"
 721                       "       .globl jprobe_return_end  \n"
 722                       "       jprobe_return_end:        \n"
 723                       "       nop                       \n"::"b"
 724                       (kcb->jprobe_saved_esp):"memory");
 725 }
 726
 727 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 728 {
 729         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 730         u8 *addr = (u8 *) (regs->eip - 1);
 731         unsigned long stack_addr = (unsigned long)(kcb->jprobe_saved_esp);
 732         struct jprobe *jp = container_of(p, struct jprobe, kp);
 733
 734         if ((addr > (u8 *) jprobe_return) && (addr < (u8 *) jprobe_return_end)) {
 735                 if (&regs->esp != kcb->jprobe_saved_esp) {
 736                         struct pt_regs *saved_regs =
 737                             container_of(kcb->jprobe_saved_esp,
 738                                             struct pt_regs, esp);
 739                         printk("current esp %p does not match saved esp %p\n",
 740                                &regs->esp, kcb->jprobe_saved_esp);
 741                         printk("Saved registers for jprobe %p\n", jp);
 742                         show_registers(saved_regs);
 743                         printk("Current registers\n");
 744                         show_registers(regs);
 745                         BUG();
 746                 }
 747                 *regs = kcb->jprobe_saved_regs;
 748                 memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
 749                        MIN_STACK_SIZE(stack_addr));
 750                 preempt_enable_no_resched();
 751                 return 1;
 752         }
 753         return 0;
 754 }
 755
 756 int __init arch_init_kprobes(void)
 757 {
 758         return 0;
 759 }