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/module.h>
  23 #include <linux/slab.h>
  24 #include <linux/stop_machine.h>
  25 #include <linux/stringify.h>
  26 #include <asm/traps.h>
  27 #include <asm/ptrace.h>
  28 #include <asm/cacheflush.h>
  29 #include <asm/debug-monitors.h>
  30 #include <asm/system_misc.h>
  31 #include <asm/insn.h>
  32 #include <asm/uaccess.h>
  33 #include <asm/irq.h>
  34 #include <asm-generic/sections.h>
  35
  36 #include "decode-insn.h"
  37
  38 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  39 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  40
  41 static void __kprobes
  42 post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
  43
  44 static inline unsigned long min_stack_size(unsigned long addr)
  45 {
  46         unsigned long size;
  47
  48         size = (unsigned long)current_thread_info() + THREAD_START_SP - addr;
  49
  50         return min(size, FIELD_SIZEOF(struct kprobe_ctlblk, jprobes_stack));
  51 }
  52
  53 static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
  54 {
  55         /* prepare insn slot */
  56         p->ainsn.insn[0] = cpu_to_le32(p->opcode);
  57
  58         flush_icache_range((uintptr_t) (p->ainsn.insn),
  59                            (uintptr_t) (p->ainsn.insn) +
  60                            MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
  61
  62         /*
  63          * Needs restoring of return address after stepping xol.
  64          */
  65         p->ainsn.restore = (unsigned long) p->addr +
  66           sizeof(kprobe_opcode_t);
  67 }
  68
  69 static void __kprobes arch_prepare_simulate(struct kprobe *p)
  70 {
  71         /* This instructions is not executed xol. No need to adjust the PC */
  72         p->ainsn.restore = 0;
  73 }
  74
  75 static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
  76 {
  77         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  78
  79         if (p->ainsn.handler)
  80                 p->ainsn.handler((u32)p->opcode, (long)p->addr, regs);
  81
  82         /* single step simulated, now go for post processing */
  83         post_kprobe_handler(kcb, regs);
  84 }
  85
  86 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  87 {
  88         unsigned long probe_addr = (unsigned long)p->addr;
  89         extern char __start_rodata[];
  90         extern char __end_rodata[];
  91
  92         if (probe_addr & 0x3)
  93                 return -EINVAL;
  94
  95         /* copy instruction */
  96         p->opcode = le32_to_cpu(*p->addr);
  97
  98         if (in_exception_text(probe_addr))
  99                 return -EINVAL;
 100         if (probe_addr >= (unsigned long) __start_rodata &&
 101             probe_addr <= (unsigned long) __end_rodata)
 102                 return -EINVAL;
 103
 104         /* decode instruction */
 105         switch (arm_kprobe_decode_insn(p->addr, &p->ainsn)) {
 106         case INSN_REJECTED:     /* insn not supported */
 107                 return -EINVAL;
 108
 109         case INSN_GOOD_NO_SLOT: /* insn need simulation */
 110                 p->ainsn.insn = NULL;
 111                 break;
 112
 113         case INSN_GOOD: /* instruction uses slot */
 114                 p->ainsn.insn = get_insn_slot();
 115                 if (!p->ainsn.insn)
 116                         return -ENOMEM;
 117                 break;
 118         };
 119
 120         /* prepare the instruction */
 121         if (p->ainsn.insn)
 122                 arch_prepare_ss_slot(p);
 123         else
 124                 arch_prepare_simulate(p);
 125
 126         return 0;
 127 }
 128
 129 static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
 130 {
 131         void *addrs[1];
 132         u32 insns[1];
 133
 134         addrs[0] = (void *)addr;
 135         insns[0] = (u32)opcode;
 136
 137         return aarch64_insn_patch_text(addrs, insns, 1);
 138 }
 139
 140 /* arm kprobe: install breakpoint in text */
 141 void __kprobes arch_arm_kprobe(struct kprobe *p)
 142 {
 143         patch_text(p->addr, BRK64_OPCODE_KPROBES);
 144 }
 145
 146 /* disarm kprobe: remove breakpoint from text */
 147 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 148 {
 149         patch_text(p->addr, p->opcode);
 150 }
 151
 152 void __kprobes arch_remove_kprobe(struct kprobe *p)
 153 {
 154         if (p->ainsn.insn) {
 155                 free_insn_slot(p->ainsn.insn, 0);
 156                 p->ainsn.insn = NULL;
 157         }
 158 }
 159
 160 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 161 {
 162         kcb->prev_kprobe.kp = kprobe_running();
 163         kcb->prev_kprobe.status = kcb->kprobe_status;
 164 }
 165
 166 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 167 {
 168         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 169         kcb->kprobe_status = kcb->prev_kprobe.status;
 170 }
 171
 172 static void __kprobes set_current_kprobe(struct kprobe *p)
 173 {
 174         __this_cpu_write(current_kprobe, p);
 175 }
 176
 177 /*
 178  * The D-flag (Debug mask) is set (masked) upon debug exception entry.
 179  * Kprobes needs to clear (unmask) D-flag -ONLY- in case of recursive
 180  * probe i.e. when probe hit from kprobe handler context upon
 181  * executing the pre/post handlers. In this case we return with
 182  * D-flag clear so that single-stepping can be carried-out.
 183  *
 184  * Leave D-flag set in all other cases.
 185  */
 186 static void __kprobes
 187 spsr_set_debug_flag(struct pt_regs *regs, int mask)
 188 {
 189         unsigned long spsr = regs->pstate;
 190
 191         if (mask)
 192                 spsr |= PSR_D_BIT;
 193         else
 194                 spsr &= ~PSR_D_BIT;
 195
 196         regs->pstate = spsr;
 197 }
 198
 199 /*
 200  * Interrupts need to be disabled before single-step mode is set, and not
 201  * reenabled until after single-step mode ends.
 202  * Without disabling interrupt on local CPU, there is a chance of
 203  * interrupt occurrence in the period of exception return and  start of
 204  * out-of-line single-step, that result in wrongly single stepping
 205  * into the interrupt handler.
 206  */
 207 static void __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb,
 208                                                 struct pt_regs *regs)
 209 {
 210         kcb->saved_irqflag = regs->pstate;
 211         regs->pstate |= PSR_I_BIT;
 212 }
 213
 214 static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
 215                                                 struct pt_regs *regs)
 216 {
 217         if (kcb->saved_irqflag & PSR_I_BIT)
 218                 regs->pstate |= PSR_I_BIT;
 219         else
 220                 regs->pstate &= ~PSR_I_BIT;
 221 }
 222
 223 static void __kprobes
 224 set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr)
 225 {
 226         kcb->ss_ctx.ss_pending = true;
 227         kcb->ss_ctx.match_addr = addr + sizeof(kprobe_opcode_t);
 228 }
 229
 230 static void __kprobes clear_ss_context(struct kprobe_ctlblk *kcb)
 231 {
 232         kcb->ss_ctx.ss_pending = false;
 233         kcb->ss_ctx.match_addr = 0;
 234 }
 235
 236 static void __kprobes setup_singlestep(struct kprobe *p,
 237                                        struct pt_regs *regs,
 238                                        struct kprobe_ctlblk *kcb, int reenter)
 239 {
 240         unsigned long slot;
 241
 242         if (reenter) {
 243                 save_previous_kprobe(kcb);
 244                 set_current_kprobe(p);
 245                 kcb->kprobe_status = KPROBE_REENTER;
 246         } else {
 247                 kcb->kprobe_status = KPROBE_HIT_SS;
 248         }
 249
 250
 251         if (p->ainsn.insn) {
 252                 /* prepare for single stepping */
 253                 slot = (unsigned long)p->ainsn.insn;
 254
 255                 set_ss_context(kcb, slot);      /* mark pending ss */
 256
 257                 if (kcb->kprobe_status == KPROBE_REENTER)
 258                         spsr_set_debug_flag(regs, 0);
 259                 else
 260                         WARN_ON(regs->pstate & PSR_D_BIT);
 261
 262                 /* IRQs and single stepping do not mix well. */
 263                 kprobes_save_local_irqflag(kcb, regs);
 264                 kernel_enable_single_step(regs);
 265                 instruction_pointer_set(regs, slot);
 266         } else {
 267                 /* insn simulation */
 268                 arch_simulate_insn(p, regs);
 269         }
 270 }
 271
 272 static int __kprobes reenter_kprobe(struct kprobe *p,
 273                                     struct pt_regs *regs,
 274                                     struct kprobe_ctlblk *kcb)
 275 {
 276         switch (kcb->kprobe_status) {
 277         case KPROBE_HIT_SSDONE:
 278         case KPROBE_HIT_ACTIVE:
 279                 kprobes_inc_nmissed_count(p);
 280                 setup_singlestep(p, regs, kcb, 1);
 281                 break;
 282         case KPROBE_HIT_SS:
 283         case KPROBE_REENTER:
 284                 pr_warn("Unrecoverable kprobe detected at %p.\n", p->addr);
 285                 dump_kprobe(p);
 286                 BUG();
 287                 break;
 288         default:
 289                 WARN_ON(1);
 290                 return 0;
 291         }
 292
 293         return 1;
 294 }
 295
 296 static void __kprobes
 297 post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
 298 {
 299         struct kprobe *cur = kprobe_running();
 300
 301         if (!cur)
 302                 return;
 303
 304         /* return addr restore if non-branching insn */
 305         if (cur->ainsn.restore != 0)
 306                 instruction_pointer_set(regs, cur->ainsn.restore);
 307
 308         /* restore back original saved kprobe variables and continue */
 309         if (kcb->kprobe_status == KPROBE_REENTER) {
 310                 restore_previous_kprobe(kcb);
 311                 return;
 312         }
 313         /* call post handler */
 314         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 315         if (cur->post_handler)  {
 316                 /* post_handler can hit breakpoint and single step
 317                  * again, so we enable D-flag for recursive exception.
 318                  */
 319                 cur->post_handler(cur, regs, 0);
 320         }
 321
 322         reset_current_kprobe();
 323 }
 324
 325 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 326 {
 327         struct kprobe *cur = kprobe_running();
 328         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 329
 330         switch (kcb->kprobe_status) {
 331         case KPROBE_HIT_SS:
 332         case KPROBE_REENTER:
 333                 /*
 334                  * We are here because the instruction being single
 335                  * stepped caused a page fault. We reset the current
 336                  * kprobe and the ip points back to the probe address
 337                  * and allow the page fault handler to continue as a
 338                  * normal page fault.
 339                  */
 340                 instruction_pointer_set(regs, (unsigned long) cur->addr);
 341                 if (!instruction_pointer(regs))
 342                         BUG();
 343
 344                 kernel_disable_single_step();
 345                 if (kcb->kprobe_status == KPROBE_REENTER)
 346                         spsr_set_debug_flag(regs, 1);
 347
 348                 if (kcb->kprobe_status == KPROBE_REENTER)
 349                         restore_previous_kprobe(kcb);
 350                 else
 351                         reset_current_kprobe();
 352
 353                 break;
 354         case KPROBE_HIT_ACTIVE:
 355         case KPROBE_HIT_SSDONE:
 356                 /*
 357                  * We increment the nmissed count for accounting,
 358                  * we can also use npre/npostfault count for accounting
 359                  * these specific fault cases.
 360                  */
 361                 kprobes_inc_nmissed_count(cur);
 362
 363                 /*
 364                  * We come here because instructions in the pre/post
 365                  * handler caused the page_fault, this could happen
 366                  * if handler tries to access user space by
 367                  * copy_from_user(), get_user() etc. Let the
 368                  * user-specified handler try to fix it first.
 369                  */
 370                 if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
 371                         return 1;
 372
 373                 /*
 374                  * In case the user-specified fault handler returned
 375                  * zero, try to fix up.
 376                  */
 377                 if (fixup_exception(regs))
 378                         return 1;
 379         }
 380         return 0;
 381 }
 382
 383 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 384                                        unsigned long val, void *data)
 385 {
 386         return NOTIFY_DONE;
 387 }
 388
 389 static void __kprobes kprobe_handler(struct pt_regs *regs)
 390 {
 391         struct kprobe *p, *cur_kprobe;
 392         struct kprobe_ctlblk *kcb;
 393         unsigned long addr = instruction_pointer(regs);
 394
 395         kcb = get_kprobe_ctlblk();
 396         cur_kprobe = kprobe_running();
 397
 398         p = get_kprobe((kprobe_opcode_t *) addr);
 399
 400         if (p) {
 401                 if (cur_kprobe) {
 402                         if (reenter_kprobe(p, regs, kcb))
 403                                 return;
 404                 } else {
 405                         /* Probe hit */
 406                         set_current_kprobe(p);
 407                         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 408
 409                         /*
 410                          * If we have no pre-handler or it returned 0, we
 411                          * continue with normal processing.  If we have a
 412                          * pre-handler and it returned non-zero, it prepped
 413                          * for calling the break_handler below on re-entry,
 414                          * so get out doing nothing more here.
 415                          *
 416                          * pre_handler can hit a breakpoint and can step thru
 417                          * before return, keep PSTATE D-flag enabled until
 418                          * pre_handler return back.
 419                          */
 420                         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 421                                 setup_singlestep(p, regs, kcb, 0);
 422                                 return;
 423                         }
 424                 }
 425         } else if ((le32_to_cpu(*(kprobe_opcode_t *) addr) ==
 426             BRK64_OPCODE_KPROBES) && cur_kprobe) {
 427                 /* We probably hit a jprobe.  Call its break handler. */
 428                 if (cur_kprobe->break_handler  &&
 429                      cur_kprobe->break_handler(cur_kprobe, regs)) {
 430                         setup_singlestep(cur_kprobe, regs, kcb, 0);
 431                         return;
 432                 }
 433         }
 434         /*
 435          * The breakpoint instruction was removed right
 436          * after we hit it.  Another cpu has removed
 437          * either a probepoint or a debugger breakpoint
 438          * at this address.  In either case, no further
 439          * handling of this interrupt is appropriate.
 440          * Return back to original instruction, and continue.
 441          */
 442 }
 443
 444 static int __kprobes
 445 kprobe_ss_hit(struct kprobe_ctlblk *kcb, unsigned long addr)
 446 {
 447         if ((kcb->ss_ctx.ss_pending)
 448             && (kcb->ss_ctx.match_addr == addr)) {
 449                 clear_ss_context(kcb);  /* clear pending ss */
 450                 return DBG_HOOK_HANDLED;
 451         }
 452         /* not ours, kprobes should ignore it */
 453         return DBG_HOOK_ERROR;
 454 }
 455
 456 int __kprobes
 457 kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
 458 {
 459         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 460         int retval;
 461
 462         /* return error if this is not our step */
 463         retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
 464
 465         if (retval == DBG_HOOK_HANDLED) {
 466                 kprobes_restore_local_irqflag(kcb, regs);
 467                 kernel_disable_single_step();
 468
 469                 if (kcb->kprobe_status == KPROBE_REENTER)
 470                         spsr_set_debug_flag(regs, 1);
 471
 472                 post_kprobe_handler(kcb, regs);
 473         }
 474
 475         return retval;
 476 }
 477
 478 int __kprobes
 479 kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
 480 {
 481         kprobe_handler(regs);
 482         return DBG_HOOK_HANDLED;
 483 }
 484
 485 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 486 {
 487         struct jprobe *jp = container_of(p, struct jprobe, kp);
 488         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 489         long stack_ptr = kernel_stack_pointer(regs);
 490
 491         kcb->jprobe_saved_regs = *regs;
 492         /*
 493          * As Linus pointed out, gcc assumes that the callee
 494          * owns the argument space and could overwrite it, e.g.
 495          * tailcall optimization. So, to be absolutely safe
 496          * we also save and restore enough stack bytes to cover
 497          * the argument area.
 498          */
 499         kasan_disable_current();
 500         memcpy(kcb->jprobes_stack, (void *)stack_ptr,
 501                min_stack_size(stack_ptr));
 502         kasan_enable_current();
 503
 504         instruction_pointer_set(regs, (unsigned long) jp->entry);
 505         preempt_disable();
 506         pause_graph_tracing();
 507         return 1;
 508 }
 509
 510 void __kprobes jprobe_return(void)
 511 {
 512         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 513
 514         /*
 515          * Jprobe handler return by entering break exception,
 516          * encoded same as kprobe, but with following conditions
 517          * -a special PC to identify it from the other kprobes.
 518          * -restore stack addr to original saved pt_regs
 519          */
 520         asm volatile("                          mov sp, %0      \n"
 521                      "jprobe_return_break:      brk %1          \n"
 522                      :
 523                      : "r" (kcb->jprobe_saved_regs.sp),
 524                        "I" (BRK64_ESR_KPROBES)
 525                      : "memory");
 526
 527         unreachable();
 528 }
 529
 530 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 531 {
 532         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 533         long stack_addr = kcb->jprobe_saved_regs.sp;
 534         long orig_sp = kernel_stack_pointer(regs);
 535         struct jprobe *jp = container_of(p, struct jprobe, kp);
 536         extern const char jprobe_return_break[];
 537
 538         if (instruction_pointer(regs) != (u64) jprobe_return_break)
 539                 return 0;
 540
 541         if (orig_sp != stack_addr) {
 542                 struct pt_regs *saved_regs =
 543                     (struct pt_regs *)kcb->jprobe_saved_regs.sp;
 544                 pr_err("current sp %lx does not match saved sp %lx\n",
 545                        orig_sp, stack_addr);
 546                 pr_err("Saved registers for jprobe %p\n", jp);
 547                 show_regs(saved_regs);
 548                 pr_err("Current registers\n");
 549                 show_regs(regs);
 550                 BUG();
 551         }
 552         unpause_graph_tracing();
 553         *regs = kcb->jprobe_saved_regs;
 554         kasan_disable_current();
 555         memcpy((void *)stack_addr, kcb->jprobes_stack,
 556                min_stack_size(stack_addr));
 557         kasan_enable_current();
 558         preempt_enable_no_resched();
 559         return 1;
 560 }
 561
 562 bool arch_within_kprobe_blacklist(unsigned long addr)
 563 {
 564         extern char __idmap_text_start[], __idmap_text_end[];
 565
 566         if ((addr >= (unsigned long)__kprobes_text_start &&
 567             addr < (unsigned long)__kprobes_text_end) ||
 568             (addr >= (unsigned long)__entry_text_start &&
 569             addr < (unsigned long)__entry_text_end) ||
 570             (addr >= (unsigned long)__idmap_text_start &&
 571             addr < (unsigned long)__idmap_text_end) ||
 572             !!search_exception_tables(addr))
 573                 return true;
 574
 575
 576         return false;
 577 }
 578
 579 void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
 580 {
 581         struct kretprobe_instance *ri = NULL;
 582         struct hlist_head *head, empty_rp;
 583         struct hlist_node *tmp;
 584         unsigned long flags, orig_ret_address = 0;
 585         unsigned long trampoline_address =
 586                 (unsigned long)&kretprobe_trampoline;
 587         kprobe_opcode_t *correct_ret_addr = NULL;
 588
 589         INIT_HLIST_HEAD(&empty_rp);
 590         kretprobe_hash_lock(current, &head, &flags);
 591
 592         /*
 593          * It is possible to have multiple instances associated with a given
 594          * task either because multiple functions in the call path have
 595          * return probes installed on them, and/or more than one
 596          * return probe was registered for a target function.
 597          *
 598          * We can handle this because:
 599          *     - instances are always pushed into the head of the list
 600          *     - when multiple return probes are registered for the same
 601          *       function, the (chronologically) first instance's ret_addr
 602          *       will be the real return address, and all the rest will
 603          *       point to kretprobe_trampoline.
 604          */
 605         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 606                 if (ri->task != current)
 607                         /* another task is sharing our hash bucket */
 608                         continue;
 609
 610                 orig_ret_address = (unsigned long)ri->ret_addr;
 611
 612                 if (orig_ret_address != trampoline_address)
 613                         /*
 614                          * This is the real return address. Any other
 615                          * instances associated with this task are for
 616                          * other calls deeper on the call stack
 617                          */
 618                         break;
 619         }
 620
 621         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 622
 623         correct_ret_addr = ri->ret_addr;
 624         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 625                 if (ri->task != current)
 626                         /* another task is sharing our hash bucket */
 627                         continue;
 628
 629                 orig_ret_address = (unsigned long)ri->ret_addr;
 630                 if (ri->rp && ri->rp->handler) {
 631                         __this_cpu_write(current_kprobe, &ri->rp->kp);
 632                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 633                         ri->ret_addr = correct_ret_addr;
 634                         ri->rp->handler(ri, regs);
 635                         __this_cpu_write(current_kprobe, NULL);
 636                 }
 637
 638                 recycle_rp_inst(ri, &empty_rp);
 639
 640                 if (orig_ret_address != trampoline_address)
 641                         /*
 642                          * This is the real return address. Any other
 643                          * instances associated with this task are for
 644                          * other calls deeper on the call stack
 645                          */
 646                         break;
 647         }
 648
 649         kretprobe_hash_unlock(current, &flags);
 650
 651         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
 652                 hlist_del(&ri->hlist);
 653                 kfree(ri);
 654         }
 655         return (void *)orig_ret_address;
 656 }
 657
 658 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 659                                       struct pt_regs *regs)
 660 {
 661         ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
 662
 663         /* replace return addr (x30) with trampoline */
 664         regs->regs[30] = (long)&kretprobe_trampoline;
 665 }
 666
 667 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 668 {
 669         return 0;
 670 }
 671
 672 int __init arch_init_kprobes(void)
 673 {
 674         return 0;
 675 }