arch/arm64/kernel/probes/kprobes.c

   1 /*
   2  * arch/arm64/kernel/probes/kprobes.c
   3  *
   4  * Kprobes support for ARM64
   5  *
   6  * Copyright (C) 2013 Linaro Limited.
   7  * Author: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
   8  *
   9  * This program is free software; you can redistribute it and/or modify
  10  * it under the terms of the GNU General Public License version 2 as
  11  * published by the Free Software Foundation.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * General Public License for more details.
  17  *
  18  */
  19 #include <linux/kasan.h>
  20 #include <linux/kernel.h>
  21 #include <linux/kprobes.h>
  22 #include <linux/extable.h>
  23 #include <linux/slab.h>
  24 #include <linux/stop_machine.h>
  25 #include <linux/sched/debug.h>
  26 #include <linux/stringify.h>
  27 #include <asm/traps.h>
  28 #include <asm/ptrace.h>
  29 #include <asm/cacheflush.h>
  30 #include <asm/debug-monitors.h>
  31 #include <asm/system_misc.h>
  32 #include <asm/insn.h>
  33 #include <linux/uaccess.h>
  34 #include <asm/irq.h>
  35 #include <asm/sections.h>
  36
  37 #include "decode-insn.h"
  38
  39 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  40 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  41
  42 static void __kprobes
  43 post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
  44
  45 static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
  46 {
  47         /* prepare insn slot */
  48         p->ainsn.api.insn[0] = cpu_to_le32(p->opcode);
  49
  50         flush_icache_range((uintptr_t) (p->ainsn.api.insn),
  51                            (uintptr_t) (p->ainsn.api.insn) +
  52                            MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
  53
  54         /*
  55          * Needs restoring of return address after stepping xol.
  56          */
  57         p->ainsn.api.restore = (unsigned long) p->addr +
  58           sizeof(kprobe_opcode_t);
  59 }
  60
  61 static void __kprobes arch_prepare_simulate(struct kprobe *p)
  62 {
  63         /* This instructions is not executed xol. No need to adjust the PC */
  64         p->ainsn.api.restore = 0;
  65 }
  66
  67 static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
  68 {
  69         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  70
  71         if (p->ainsn.api.handler)
  72                 p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);
  73
  74         /* single step simulated, now go for post processing */
  75         post_kprobe_handler(kcb, regs);
  76 }
  77
  78 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  79 {
  80         unsigned long probe_addr = (unsigned long)p->addr;
  81         extern char __start_rodata[];
  82         extern char __end_rodata[];
  83
  84         if (probe_addr & 0x3)
  85                 return -EINVAL;
  86
  87         /* copy instruction */
  88         p->opcode = le32_to_cpu(*p->addr);
  89
  90         if (in_exception_text(probe_addr))
  91                 return -EINVAL;
  92         if (probe_addr >= (unsigned long) __start_rodata &&
  93             probe_addr <= (unsigned long) __end_rodata)
  94                 return -EINVAL;
  95
  96         /* decode instruction */
  97         switch (arm_kprobe_decode_insn(p->addr, &p->ainsn)) {
  98         case INSN_REJECTED:     /* insn not supported */
  99                 return -EINVAL;
 100
 101         case INSN_GOOD_NO_SLOT: /* insn need simulation */
 102                 p->ainsn.api.insn = NULL;
 103                 break;
 104
 105         case INSN_GOOD: /* instruction uses slot */
 106                 p->ainsn.api.insn = get_insn_slot();
 107                 if (!p->ainsn.api.insn)
 108                         return -ENOMEM;
 109                 break;
 110         };
 111
 112         /* prepare the instruction */
 113         if (p->ainsn.api.insn)
 114                 arch_prepare_ss_slot(p);
 115         else
 116                 arch_prepare_simulate(p);
 117
 118         return 0;
 119 }
 120
 121 static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
 122 {
 123         void *addrs[1];
 124         u32 insns[1];
 125
 126         addrs[0] = (void *)addr;
 127         insns[0] = (u32)opcode;
 128
 129         return aarch64_insn_patch_text(addrs, insns, 1);
 130 }
 131
 132 /* arm kprobe: install breakpoint in text */
 133 void __kprobes arch_arm_kprobe(struct kprobe *p)
 134 {
 135         patch_text(p->addr, BRK64_OPCODE_KPROBES);
 136 }
 137
 138 /* disarm kprobe: remove breakpoint from text */
 139 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 140 {
 141         patch_text(p->addr, p->opcode);
 142 }
 143
 144 void __kprobes arch_remove_kprobe(struct kprobe *p)
 145 {
 146         if (p->ainsn.api.insn) {
 147                 free_insn_slot(p->ainsn.api.insn, 0);
 148                 p->ainsn.api.insn = NULL;
 149         }
 150 }
 151
 152 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 153 {
 154         kcb->prev_kprobe.kp = kprobe_running();
 155         kcb->prev_kprobe.status = kcb->kprobe_status;
 156 }
 157
 158 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 159 {
 160         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 161         kcb->kprobe_status = kcb->prev_kprobe.status;
 162 }
 163
 164 static void __kprobes set_current_kprobe(struct kprobe *p)
 165 {
 166         __this_cpu_write(current_kprobe, p);
 167 }
 168
 169 /*
 170  * When PSTATE.D is set (masked), then software step exceptions can not be
 171  * generated.
 172  * SPSR's D bit shows the value of PSTATE.D immediately before the
 173  * exception was taken. PSTATE.D is set while entering into any exception
 174  * mode, however software clears it for any normal (none-debug-exception)
 175  * mode in the exception entry. Therefore, when we are entering into kprobe
 176  * breakpoint handler from any normal mode then SPSR.D bit is already
 177  * cleared, however it is set when we are entering from any debug exception
 178  * mode.
 179  * Since we always need to generate single step exception after a kprobe
 180  * breakpoint exception therefore we need to clear it unconditionally, when
 181  * we become sure that the current breakpoint exception is for kprobe.
 182  */
 183 static void __kprobes
 184 spsr_set_debug_flag(struct pt_regs *regs, int mask)
 185 {
 186         unsigned long spsr = regs->pstate;
 187
 188         if (mask)
 189                 spsr |= PSR_D_BIT;
 190         else
 191                 spsr &= ~PSR_D_BIT;
 192
 193         regs->pstate = spsr;
 194 }
 195
 196 /*
 197  * Interrupts need to be disabled before single-step mode is set, and not
 198  * reenabled until after single-step mode ends.
 199  * Without disabling interrupt on local CPU, there is a chance of
 200  * interrupt occurrence in the period of exception return and  start of
 201  * out-of-line single-step, that result in wrongly single stepping
 202  * into the interrupt handler.
 203  */
 204 static void __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb,
 205                                                 struct pt_regs *regs)
 206 {
 207         kcb->saved_irqflag = regs->pstate;
 208         regs->pstate |= PSR_I_BIT;
 209 }
 210
 211 static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
 212                                                 struct pt_regs *regs)
 213 {
 214         if (kcb->saved_irqflag & PSR_I_BIT)
 215                 regs->pstate |= PSR_I_BIT;
 216         else
 217                 regs->pstate &= ~PSR_I_BIT;
 218 }
 219
 220 static void __kprobes
 221 set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr)
 222 {
 223         kcb->ss_ctx.ss_pending = true;
 224         kcb->ss_ctx.match_addr = addr + sizeof(kprobe_opcode_t);
 225 }
 226
 227 static void __kprobes clear_ss_context(struct kprobe_ctlblk *kcb)
 228 {
 229         kcb->ss_ctx.ss_pending = false;
 230         kcb->ss_ctx.match_addr = 0;
 231 }
 232
 233 static void __kprobes setup_singlestep(struct kprobe *p,
 234                                        struct pt_regs *regs,
 235                                        struct kprobe_ctlblk *kcb, int reenter)
 236 {
 237         unsigned long slot;
 238
 239         if (reenter) {
 240                 save_previous_kprobe(kcb);
 241                 set_current_kprobe(p);
 242                 kcb->kprobe_status = KPROBE_REENTER;
 243         } else {
 244                 kcb->kprobe_status = KPROBE_HIT_SS;
 245         }
 246
 247
 248         if (p->ainsn.api.insn) {
 249                 /* prepare for single stepping */
 250                 slot = (unsigned long)p->ainsn.api.insn;
 251
 252                 set_ss_context(kcb, slot);      /* mark pending ss */
 253
 254                 spsr_set_debug_flag(regs, 0);
 255
 256                 /* IRQs and single stepping do not mix well. */
 257                 kprobes_save_local_irqflag(kcb, regs);
 258                 kernel_enable_single_step(regs);
 259                 instruction_pointer_set(regs, slot);
 260         } else {
 261                 /* insn simulation */
 262                 arch_simulate_insn(p, regs);
 263         }
 264 }
 265
 266 static int __kprobes reenter_kprobe(struct kprobe *p,
 267                                     struct pt_regs *regs,
 268                                     struct kprobe_ctlblk *kcb)
 269 {
 270         switch (kcb->kprobe_status) {
 271         case KPROBE_HIT_SSDONE:
 272         case KPROBE_HIT_ACTIVE:
 273                 kprobes_inc_nmissed_count(p);
 274                 setup_singlestep(p, regs, kcb, 1);
 275                 break;
 276         case KPROBE_HIT_SS:
 277         case KPROBE_REENTER:
 278                 pr_warn("Unrecoverable kprobe detected at %p.\n", p->addr);
 279                 dump_kprobe(p);
 280                 BUG();
 281                 break;
 282         default:
 283                 WARN_ON(1);
 284                 return 0;
 285         }
 286
 287         return 1;
 288 }
 289
 290 static void __kprobes
 291 post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
 292 {
 293         struct kprobe *cur = kprobe_running();
 294
 295         if (!cur)
 296                 return;
 297
 298         /* return addr restore if non-branching insn */
 299         if (cur->ainsn.api.restore != 0)
 300                 instruction_pointer_set(regs, cur->ainsn.api.restore);
 301
 302         /* restore back original saved kprobe variables and continue */
 303         if (kcb->kprobe_status == KPROBE_REENTER) {
 304                 restore_previous_kprobe(kcb);
 305                 return;
 306         }
 307         /* call post handler */
 308         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 309         if (cur->post_handler)  {
 310                 /* post_handler can hit breakpoint and single step
 311                  * again, so we enable D-flag for recursive exception.
 312                  */
 313                 cur->post_handler(cur, regs, 0);
 314         }
 315
 316         reset_current_kprobe();
 317 }
 318
 319 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 320 {
 321         struct kprobe *cur = kprobe_running();
 322         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 323
 324         switch (kcb->kprobe_status) {
 325         case KPROBE_HIT_SS:
 326         case KPROBE_REENTER:
 327                 /*
 328                  * We are here because the instruction being single
 329                  * stepped caused a page fault. We reset the current
 330                  * kprobe and the ip points back to the probe address
 331                  * and allow the page fault handler to continue as a
 332                  * normal page fault.
 333                  */
 334                 instruction_pointer_set(regs, (unsigned long) cur->addr);
 335                 if (!instruction_pointer(regs))
 336                         BUG();
 337
 338                 kernel_disable_single_step();
 339
 340                 if (kcb->kprobe_status == KPROBE_REENTER)
 341                         restore_previous_kprobe(kcb);
 342                 else
 343                         reset_current_kprobe();
 344
 345                 break;
 346         case KPROBE_HIT_ACTIVE:
 347         case KPROBE_HIT_SSDONE:
 348                 /*
 349                  * We increment the nmissed count for accounting,
 350                  * we can also use npre/npostfault count for accounting
 351                  * these specific fault cases.
 352                  */
 353                 kprobes_inc_nmissed_count(cur);
 354
 355                 /*
 356                  * We come here because instructions in the pre/post
 357                  * handler caused the page_fault, this could happen
 358                  * if handler tries to access user space by
 359                  * copy_from_user(), get_user() etc. Let the
 360                  * user-specified handler try to fix it first.
 361                  */
 362                 if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
 363                         return 1;
 364
 365                 /*
 366                  * In case the user-specified fault handler returned
 367                  * zero, try to fix up.
 368                  */
 369                 if (fixup_exception(regs))
 370                         return 1;
 371         }
 372         return 0;
 373 }
 374
 375 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 376                                        unsigned long val, void *data)
 377 {
 378         return NOTIFY_DONE;
 379 }
 380
 381 static void __kprobes kprobe_handler(struct pt_regs *regs)
 382 {
 383         struct kprobe *p, *cur_kprobe;
 384         struct kprobe_ctlblk *kcb;
 385         unsigned long addr = instruction_pointer(regs);
 386
 387         kcb = get_kprobe_ctlblk();
 388         cur_kprobe = kprobe_running();
 389
 390         p = get_kprobe((kprobe_opcode_t *) addr);
 391
 392         if (p) {
 393                 if (cur_kprobe) {
 394                         if (reenter_kprobe(p, regs, kcb))
 395                                 return;
 396                 } else {
 397                         /* Probe hit */
 398                         set_current_kprobe(p);
 399                         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 400
 401                         /*
 402                          * If we have no pre-handler or it returned 0, we
 403                          * continue with normal processing.  If we have a
 404                          * pre-handler and it returned non-zero, it prepped
 405                          * for calling the break_handler below on re-entry,
 406                          * so get out doing nothing more here.
 407                          *
 408                          * pre_handler can hit a breakpoint and can step thru
 409                          * before return, keep PSTATE D-flag enabled until
 410                          * pre_handler return back.
 411                          */
 412                         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 413                                 setup_singlestep(p, regs, kcb, 0);
 414                                 return;
 415                         }
 416                 }
 417         } else if ((le32_to_cpu(*(kprobe_opcode_t *) addr) ==
 418             BRK64_OPCODE_KPROBES) && cur_kprobe) {
 419                 /* We probably hit a jprobe.  Call its break handler. */
 420                 if (cur_kprobe->break_handler  &&
 421                      cur_kprobe->break_handler(cur_kprobe, regs)) {
 422                         setup_singlestep(cur_kprobe, regs, kcb, 0);
 423                         return;
 424                 }
 425         }
 426         /*
 427          * The breakpoint instruction was removed right
 428          * after we hit it.  Another cpu has removed
 429          * either a probepoint or a debugger breakpoint
 430          * at this address.  In either case, no further
 431          * handling of this interrupt is appropriate.
 432          * Return back to original instruction, and continue.
 433          */
 434 }
 435
 436 static int __kprobes
 437 kprobe_ss_hit(struct kprobe_ctlblk *kcb, unsigned long addr)
 438 {
 439         if ((kcb->ss_ctx.ss_pending)
 440             && (kcb->ss_ctx.match_addr == addr)) {
 441                 clear_ss_context(kcb);  /* clear pending ss */
 442                 return DBG_HOOK_HANDLED;
 443         }
 444         /* not ours, kprobes should ignore it */
 445         return DBG_HOOK_ERROR;
 446 }
 447
 448 int __kprobes
 449 kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
 450 {
 451         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 452         int retval;
 453
 454         /* return error if this is not our step */
 455         retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
 456
 457         if (retval == DBG_HOOK_HANDLED) {
 458                 kprobes_restore_local_irqflag(kcb, regs);
 459                 kernel_disable_single_step();
 460
 461                 post_kprobe_handler(kcb, regs);
 462         }
 463
 464         return retval;
 465 }
 466
 467 int __kprobes
 468 kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
 469 {
 470         kprobe_handler(regs);
 471         return DBG_HOOK_HANDLED;
 472 }
 473
 474 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 475 {
 476         struct jprobe *jp = container_of(p, struct jprobe, kp);
 477         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 478
 479         kcb->jprobe_saved_regs = *regs;
 480         /*
 481          * Since we can't be sure where in the stack frame "stacked"
 482          * pass-by-value arguments are stored we just don't try to
 483          * duplicate any of the stack. Do not use jprobes on functions that
 484          * use more than 64 bytes (after padding each to an 8 byte boundary)
 485          * of arguments, or pass individual arguments larger than 16 bytes.
 486          */
 487
 488         instruction_pointer_set(regs, (unsigned long) jp->entry);
 489         preempt_disable();
 490         pause_graph_tracing();
 491         return 1;
 492 }
 493
 494 void __kprobes jprobe_return(void)
 495 {
 496         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 497
 498         /*
 499          * Jprobe handler return by entering break exception,
 500          * encoded same as kprobe, but with following conditions
 501          * -a special PC to identify it from the other kprobes.
 502          * -restore stack addr to original saved pt_regs
 503          */
 504         asm volatile("                          mov sp, %0      \n"
 505                      "jprobe_return_break:      brk %1          \n"
 506                      :
 507                      : "r" (kcb->jprobe_saved_regs.sp),
 508                        "I" (BRK64_ESR_KPROBES)
 509                      : "memory");
 510
 511         unreachable();
 512 }
 513
 514 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 515 {
 516         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 517         long stack_addr = kcb->jprobe_saved_regs.sp;
 518         long orig_sp = kernel_stack_pointer(regs);
 519         struct jprobe *jp = container_of(p, struct jprobe, kp);
 520         extern const char jprobe_return_break[];
 521
 522         if (instruction_pointer(regs) != (u64) jprobe_return_break)
 523                 return 0;
 524
 525         if (orig_sp != stack_addr) {
 526                 struct pt_regs *saved_regs =
 527                     (struct pt_regs *)kcb->jprobe_saved_regs.sp;
 528                 pr_err("current sp %lx does not match saved sp %lx\n",
 529                        orig_sp, stack_addr);
 530                 pr_err("Saved registers for jprobe %p\n", jp);
 531                 show_regs(saved_regs);
 532                 pr_err("Current registers\n");
 533                 show_regs(regs);
 534                 BUG();
 535         }
 536         unpause_graph_tracing();
 537         *regs = kcb->jprobe_saved_regs;
 538         preempt_enable_no_resched();
 539         return 1;
 540 }
 541
 542 bool arch_within_kprobe_blacklist(unsigned long addr)
 543 {
 544         if ((addr >= (unsigned long)__kprobes_text_start &&
 545             addr < (unsigned long)__kprobes_text_end) ||
 546             (addr >= (unsigned long)__entry_text_start &&
 547             addr < (unsigned long)__entry_text_end) ||
 548             (addr >= (unsigned long)__idmap_text_start &&
 549             addr < (unsigned long)__idmap_text_end) ||
 550             !!search_exception_tables(addr))
 551                 return true;
 552
 553         if (!is_kernel_in_hyp_mode()) {
 554                 if ((addr >= (unsigned long)__hyp_text_start &&
 555                     addr < (unsigned long)__hyp_text_end) ||
 556                     (addr >= (unsigned long)__hyp_idmap_text_start &&
 557                     addr < (unsigned long)__hyp_idmap_text_end))
 558                         return true;
 559         }
 560
 561         return false;
 562 }
 563
 564 void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
 565 {
 566         struct kretprobe_instance *ri = NULL;
 567         struct hlist_head *head, empty_rp;
 568         struct hlist_node *tmp;
 569         unsigned long flags, orig_ret_address = 0;
 570         unsigned long trampoline_address =
 571                 (unsigned long)&kretprobe_trampoline;
 572         kprobe_opcode_t *correct_ret_addr = NULL;
 573
 574         INIT_HLIST_HEAD(&empty_rp);
 575         kretprobe_hash_lock(current, &head, &flags);
 576
 577         /*
 578          * It is possible to have multiple instances associated with a given
 579          * task either because multiple functions in the call path have
 580          * return probes installed on them, and/or more than one
 581          * return probe was registered for a target function.
 582          *
 583          * We can handle this because:
 584          *     - instances are always pushed into the head of the list
 585          *     - when multiple return probes are registered for the same
 586          *       function, the (chronologically) first instance's ret_addr
 587          *       will be the real return address, and all the rest will
 588          *       point to kretprobe_trampoline.
 589          */
 590         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 591                 if (ri->task != current)
 592                         /* another task is sharing our hash bucket */
 593                         continue;
 594
 595                 orig_ret_address = (unsigned long)ri->ret_addr;
 596
 597                 if (orig_ret_address != trampoline_address)
 598                         /*
 599                          * This is the real return address. Any other
 600                          * instances associated with this task are for
 601                          * other calls deeper on the call stack
 602                          */
 603                         break;
 604         }
 605
 606         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 607
 608         correct_ret_addr = ri->ret_addr;
 609         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 610                 if (ri->task != current)
 611                         /* another task is sharing our hash bucket */
 612                         continue;
 613
 614                 orig_ret_address = (unsigned long)ri->ret_addr;
 615                 if (ri->rp && ri->rp->handler) {
 616                         __this_cpu_write(current_kprobe, &ri->rp->kp);
 617                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 618                         ri->ret_addr = correct_ret_addr;
 619                         ri->rp->handler(ri, regs);
 620                         __this_cpu_write(current_kprobe, NULL);
 621                 }
 622
 623                 recycle_rp_inst(ri, &empty_rp);
 624
 625                 if (orig_ret_address != trampoline_address)
 626                         /*
 627                          * This is the real return address. Any other
 628                          * instances associated with this task are for
 629                          * other calls deeper on the call stack
 630                          */
 631                         break;
 632         }
 633
 634         kretprobe_hash_unlock(current, &flags);
 635
 636         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
 637                 hlist_del(&ri->hlist);
 638                 kfree(ri);
 639         }
 640         return (void *)orig_ret_address;
 641 }
 642
 643 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 644                                       struct pt_regs *regs)
 645 {
 646         ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
 647
 648         /* replace return addr (x30) with trampoline */
 649         regs->regs[30] = (long)&kretprobe_trampoline;
 650 }
 651
 652 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 653 {
 654         return 0;
 655 }
 656
 657 int __init arch_init_kprobes(void)
 658 {
 659         return 0;
 660 }