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         if (on_irq_stack(addr, raw_smp_processor_id()))
  49                 size = IRQ_STACK_PTR(raw_smp_processor_id()) - addr;
  50         else
  51                 size = (unsigned long)current_thread_info() + THREAD_START_SP - addr;
  52
  53         return min(size, FIELD_SIZEOF(struct kprobe_ctlblk, jprobes_stack));
  54 }
  55
  56 static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
  57 {
  58         /* prepare insn slot */
  59         p->ainsn.insn[0] = cpu_to_le32(p->opcode);
  60
  61         flush_icache_range((uintptr_t) (p->ainsn.insn),
  62                            (uintptr_t) (p->ainsn.insn) +
  63                            MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
  64
  65         /*
  66          * Needs restoring of return address after stepping xol.
  67          */
  68         p->ainsn.restore = (unsigned long) p->addr +
  69           sizeof(kprobe_opcode_t);
  70 }
  71
  72 static void __kprobes arch_prepare_simulate(struct kprobe *p)
  73 {
  74         /* This instructions is not executed xol. No need to adjust the PC */
  75         p->ainsn.restore = 0;
  76 }
  77
  78 static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
  79 {
  80         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  81
  82         if (p->ainsn.handler)
  83                 p->ainsn.handler((u32)p->opcode, (long)p->addr, regs);
  84
  85         /* single step simulated, now go for post processing */
  86         post_kprobe_handler(kcb, regs);
  87 }
  88
  89 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  90 {
  91         unsigned long probe_addr = (unsigned long)p->addr;
  92         extern char __start_rodata[];
  93         extern char __end_rodata[];
  94
  95         if (probe_addr & 0x3)
  96                 return -EINVAL;
  97
  98         /* copy instruction */
  99         p->opcode = le32_to_cpu(*p->addr);
 100
 101         if (in_exception_text(probe_addr))
 102                 return -EINVAL;
 103         if (probe_addr >= (unsigned long) __start_rodata &&
 104             probe_addr <= (unsigned long) __end_rodata)
 105                 return -EINVAL;
 106
 107         /* decode instruction */
 108         switch (arm_kprobe_decode_insn(p->addr, &p->ainsn)) {
 109         case INSN_REJECTED:     /* insn not supported */
 110                 return -EINVAL;
 111
 112         case INSN_GOOD_NO_SLOT: /* insn need simulation */
 113                 p->ainsn.insn = NULL;
 114                 break;
 115
 116         case INSN_GOOD: /* instruction uses slot */
 117                 p->ainsn.insn = get_insn_slot();
 118                 if (!p->ainsn.insn)
 119                         return -ENOMEM;
 120                 break;
 121         };
 122
 123         /* prepare the instruction */
 124         if (p->ainsn.insn)
 125                 arch_prepare_ss_slot(p);
 126         else
 127                 arch_prepare_simulate(p);
 128
 129         return 0;
 130 }
 131
 132 static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
 133 {
 134         void *addrs[1];
 135         u32 insns[1];
 136
 137         addrs[0] = (void *)addr;
 138         insns[0] = (u32)opcode;
 139
 140         return aarch64_insn_patch_text(addrs, insns, 1);
 141 }
 142
 143 /* arm kprobe: install breakpoint in text */
 144 void __kprobes arch_arm_kprobe(struct kprobe *p)
 145 {
 146         patch_text(p->addr, BRK64_OPCODE_KPROBES);
 147 }
 148
 149 /* disarm kprobe: remove breakpoint from text */
 150 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 151 {
 152         patch_text(p->addr, p->opcode);
 153 }
 154
 155 void __kprobes arch_remove_kprobe(struct kprobe *p)
 156 {
 157         if (p->ainsn.insn) {
 158                 free_insn_slot(p->ainsn.insn, 0);
 159                 p->ainsn.insn = NULL;
 160         }
 161 }
 162
 163 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 164 {
 165         kcb->prev_kprobe.kp = kprobe_running();
 166         kcb->prev_kprobe.status = kcb->kprobe_status;
 167 }
 168
 169 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 170 {
 171         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 172         kcb->kprobe_status = kcb->prev_kprobe.status;
 173 }
 174
 175 static void __kprobes set_current_kprobe(struct kprobe *p)
 176 {
 177         __this_cpu_write(current_kprobe, p);
 178 }
 179
 180 /*
 181  * The D-flag (Debug mask) is set (masked) upon debug exception entry.
 182  * Kprobes needs to clear (unmask) D-flag -ONLY- in case of recursive
 183  * probe i.e. when probe hit from kprobe handler context upon
 184  * executing the pre/post handlers. In this case we return with
 185  * D-flag clear so that single-stepping can be carried-out.
 186  *
 187  * Leave D-flag set in all other cases.
 188  */
 189 static void __kprobes
 190 spsr_set_debug_flag(struct pt_regs *regs, int mask)
 191 {
 192         unsigned long spsr = regs->pstate;
 193
 194         if (mask)
 195                 spsr |= PSR_D_BIT;
 196         else
 197                 spsr &= ~PSR_D_BIT;
 198
 199         regs->pstate = spsr;
 200 }
 201
 202 /*
 203  * Interrupts need to be disabled before single-step mode is set, and not
 204  * reenabled until after single-step mode ends.
 205  * Without disabling interrupt on local CPU, there is a chance of
 206  * interrupt occurrence in the period of exception return and  start of
 207  * out-of-line single-step, that result in wrongly single stepping
 208  * into the interrupt handler.
 209  */
 210 static void __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb,
 211                                                 struct pt_regs *regs)
 212 {
 213         kcb->saved_irqflag = regs->pstate;
 214         regs->pstate |= PSR_I_BIT;
 215 }
 216
 217 static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
 218                                                 struct pt_regs *regs)
 219 {
 220         if (kcb->saved_irqflag & PSR_I_BIT)
 221                 regs->pstate |= PSR_I_BIT;
 222         else
 223                 regs->pstate &= ~PSR_I_BIT;
 224 }
 225
 226 static void __kprobes
 227 set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr)
 228 {
 229         kcb->ss_ctx.ss_pending = true;
 230         kcb->ss_ctx.match_addr = addr + sizeof(kprobe_opcode_t);
 231 }
 232
 233 static void __kprobes clear_ss_context(struct kprobe_ctlblk *kcb)
 234 {
 235         kcb->ss_ctx.ss_pending = false;
 236         kcb->ss_ctx.match_addr = 0;
 237 }
 238
 239 static void __kprobes setup_singlestep(struct kprobe *p,
 240                                        struct pt_regs *regs,
 241                                        struct kprobe_ctlblk *kcb, int reenter)
 242 {
 243         unsigned long slot;
 244
 245         if (reenter) {
 246                 save_previous_kprobe(kcb);
 247                 set_current_kprobe(p);
 248                 kcb->kprobe_status = KPROBE_REENTER;
 249         } else {
 250                 kcb->kprobe_status = KPROBE_HIT_SS;
 251         }
 252
 253
 254         if (p->ainsn.insn) {
 255                 /* prepare for single stepping */
 256                 slot = (unsigned long)p->ainsn.insn;
 257
 258                 set_ss_context(kcb, slot);      /* mark pending ss */
 259
 260                 if (kcb->kprobe_status == KPROBE_REENTER)
 261                         spsr_set_debug_flag(regs, 0);
 262                 else
 263                         WARN_ON(regs->pstate & PSR_D_BIT);
 264
 265                 /* IRQs and single stepping do not mix well. */
 266                 kprobes_save_local_irqflag(kcb, regs);
 267                 kernel_enable_single_step(regs);
 268                 instruction_pointer_set(regs, slot);
 269         } else {
 270                 /* insn simulation */
 271                 arch_simulate_insn(p, regs);
 272         }
 273 }
 274
 275 static int __kprobes reenter_kprobe(struct kprobe *p,
 276                                     struct pt_regs *regs,
 277                                     struct kprobe_ctlblk *kcb)
 278 {
 279         switch (kcb->kprobe_status) {
 280         case KPROBE_HIT_SSDONE:
 281         case KPROBE_HIT_ACTIVE:
 282                 kprobes_inc_nmissed_count(p);
 283                 setup_singlestep(p, regs, kcb, 1);
 284                 break;
 285         case KPROBE_HIT_SS:
 286         case KPROBE_REENTER:
 287                 pr_warn("Unrecoverable kprobe detected at %p.\n", p->addr);
 288                 dump_kprobe(p);
 289                 BUG();
 290                 break;
 291         default:
 292                 WARN_ON(1);
 293                 return 0;
 294         }
 295
 296         return 1;
 297 }
 298
 299 static void __kprobes
 300 post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
 301 {
 302         struct kprobe *cur = kprobe_running();
 303
 304         if (!cur)
 305                 return;
 306
 307         /* return addr restore if non-branching insn */
 308         if (cur->ainsn.restore != 0)
 309                 instruction_pointer_set(regs, cur->ainsn.restore);
 310
 311         /* restore back original saved kprobe variables and continue */
 312         if (kcb->kprobe_status == KPROBE_REENTER) {
 313                 restore_previous_kprobe(kcb);
 314                 return;
 315         }
 316         /* call post handler */
 317         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 318         if (cur->post_handler)  {
 319                 /* post_handler can hit breakpoint and single step
 320                  * again, so we enable D-flag for recursive exception.
 321                  */
 322                 cur->post_handler(cur, regs, 0);
 323         }
 324
 325         reset_current_kprobe();
 326 }
 327
 328 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 329 {
 330         struct kprobe *cur = kprobe_running();
 331         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 332
 333         switch (kcb->kprobe_status) {
 334         case KPROBE_HIT_SS:
 335         case KPROBE_REENTER:
 336                 /*
 337                  * We are here because the instruction being single
 338                  * stepped caused a page fault. We reset the current
 339                  * kprobe and the ip points back to the probe address
 340                  * and allow the page fault handler to continue as a
 341                  * normal page fault.
 342                  */
 343                 instruction_pointer_set(regs, (unsigned long) cur->addr);
 344                 if (!instruction_pointer(regs))
 345                         BUG();
 346
 347                 kernel_disable_single_step();
 348                 if (kcb->kprobe_status == KPROBE_REENTER)
 349                         spsr_set_debug_flag(regs, 1);
 350
 351                 if (kcb->kprobe_status == KPROBE_REENTER)
 352                         restore_previous_kprobe(kcb);
 353                 else
 354                         reset_current_kprobe();
 355
 356                 break;
 357         case KPROBE_HIT_ACTIVE:
 358         case KPROBE_HIT_SSDONE:
 359                 /*
 360                  * We increment the nmissed count for accounting,
 361                  * we can also use npre/npostfault count for accounting
 362                  * these specific fault cases.
 363                  */
 364                 kprobes_inc_nmissed_count(cur);
 365
 366                 /*
 367                  * We come here because instructions in the pre/post
 368                  * handler caused the page_fault, this could happen
 369                  * if handler tries to access user space by
 370                  * copy_from_user(), get_user() etc. Let the
 371                  * user-specified handler try to fix it first.
 372                  */
 373                 if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
 374                         return 1;
 375
 376                 /*
 377                  * In case the user-specified fault handler returned
 378                  * zero, try to fix up.
 379                  */
 380                 if (fixup_exception(regs))
 381                         return 1;
 382         }
 383         return 0;
 384 }
 385
 386 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 387                                        unsigned long val, void *data)
 388 {
 389         return NOTIFY_DONE;
 390 }
 391
 392 static void __kprobes kprobe_handler(struct pt_regs *regs)
 393 {
 394         struct kprobe *p, *cur_kprobe;
 395         struct kprobe_ctlblk *kcb;
 396         unsigned long addr = instruction_pointer(regs);
 397
 398         kcb = get_kprobe_ctlblk();
 399         cur_kprobe = kprobe_running();
 400
 401         p = get_kprobe((kprobe_opcode_t *) addr);
 402
 403         if (p) {
 404                 if (cur_kprobe) {
 405                         if (reenter_kprobe(p, regs, kcb))
 406                                 return;
 407                 } else {
 408                         /* Probe hit */
 409                         set_current_kprobe(p);
 410                         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 411
 412                         /*
 413                          * If we have no pre-handler or it returned 0, we
 414                          * continue with normal processing.  If we have a
 415                          * pre-handler and it returned non-zero, it prepped
 416                          * for calling the break_handler below on re-entry,
 417                          * so get out doing nothing more here.
 418                          *
 419                          * pre_handler can hit a breakpoint and can step thru
 420                          * before return, keep PSTATE D-flag enabled until
 421                          * pre_handler return back.
 422                          */
 423                         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 424                                 setup_singlestep(p, regs, kcb, 0);
 425                                 return;
 426                         }
 427                 }
 428         } else if ((le32_to_cpu(*(kprobe_opcode_t *) addr) ==
 429             BRK64_OPCODE_KPROBES) && cur_kprobe) {
 430                 /* We probably hit a jprobe.  Call its break handler. */
 431                 if (cur_kprobe->break_handler  &&
 432                      cur_kprobe->break_handler(cur_kprobe, regs)) {
 433                         setup_singlestep(cur_kprobe, regs, kcb, 0);
 434                         return;
 435                 }
 436         }
 437         /*
 438          * The breakpoint instruction was removed right
 439          * after we hit it.  Another cpu has removed
 440          * either a probepoint or a debugger breakpoint
 441          * at this address.  In either case, no further
 442          * handling of this interrupt is appropriate.
 443          * Return back to original instruction, and continue.
 444          */
 445 }
 446
 447 static int __kprobes
 448 kprobe_ss_hit(struct kprobe_ctlblk *kcb, unsigned long addr)
 449 {
 450         if ((kcb->ss_ctx.ss_pending)
 451             && (kcb->ss_ctx.match_addr == addr)) {
 452                 clear_ss_context(kcb);  /* clear pending ss */
 453                 return DBG_HOOK_HANDLED;
 454         }
 455         /* not ours, kprobes should ignore it */
 456         return DBG_HOOK_ERROR;
 457 }
 458
 459 int __kprobes
 460 kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
 461 {
 462         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 463         int retval;
 464
 465         /* return error if this is not our step */
 466         retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
 467
 468         if (retval == DBG_HOOK_HANDLED) {
 469                 kprobes_restore_local_irqflag(kcb, regs);
 470                 kernel_disable_single_step();
 471
 472                 if (kcb->kprobe_status == KPROBE_REENTER)
 473                         spsr_set_debug_flag(regs, 1);
 474
 475                 post_kprobe_handler(kcb, regs);
 476         }
 477
 478         return retval;
 479 }
 480
 481 int __kprobes
 482 kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
 483 {
 484         kprobe_handler(regs);
 485         return DBG_HOOK_HANDLED;
 486 }
 487
 488 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 489 {
 490         struct jprobe *jp = container_of(p, struct jprobe, kp);
 491         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 492         long stack_ptr = kernel_stack_pointer(regs);
 493
 494         kcb->jprobe_saved_regs = *regs;
 495         /*
 496          * As Linus pointed out, gcc assumes that the callee
 497          * owns the argument space and could overwrite it, e.g.
 498          * tailcall optimization. So, to be absolutely safe
 499          * we also save and restore enough stack bytes to cover
 500          * the argument area.
 501          */
 502         kasan_disable_current();
 503         memcpy(kcb->jprobes_stack, (void *)stack_ptr,
 504                min_stack_size(stack_ptr));
 505         kasan_enable_current();
 506
 507         instruction_pointer_set(regs, (unsigned long) jp->entry);
 508         preempt_disable();
 509         pause_graph_tracing();
 510         return 1;
 511 }
 512
 513 void __kprobes jprobe_return(void)
 514 {
 515         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 516
 517         /*
 518          * Jprobe handler return by entering break exception,
 519          * encoded same as kprobe, but with following conditions
 520          * -a special PC to identify it from the other kprobes.
 521          * -restore stack addr to original saved pt_regs
 522          */
 523         asm volatile("                          mov sp, %0      \n"
 524                      "jprobe_return_break:      brk %1          \n"
 525                      :
 526                      : "r" (kcb->jprobe_saved_regs.sp),
 527                        "I" (BRK64_ESR_KPROBES)
 528                      : "memory");
 529
 530         unreachable();
 531 }
 532
 533 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 534 {
 535         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 536         long stack_addr = kcb->jprobe_saved_regs.sp;
 537         long orig_sp = kernel_stack_pointer(regs);
 538         struct jprobe *jp = container_of(p, struct jprobe, kp);
 539         extern const char jprobe_return_break[];
 540
 541         if (instruction_pointer(regs) != (u64) jprobe_return_break)
 542                 return 0;
 543
 544         if (orig_sp != stack_addr) {
 545                 struct pt_regs *saved_regs =
 546                     (struct pt_regs *)kcb->jprobe_saved_regs.sp;
 547                 pr_err("current sp %lx does not match saved sp %lx\n",
 548                        orig_sp, stack_addr);
 549                 pr_err("Saved registers for jprobe %p\n", jp);
 550                 show_regs(saved_regs);
 551                 pr_err("Current registers\n");
 552                 show_regs(regs);
 553                 BUG();
 554         }
 555         unpause_graph_tracing();
 556         *regs = kcb->jprobe_saved_regs;
 557         kasan_disable_current();
 558         memcpy((void *)stack_addr, kcb->jprobes_stack,
 559                min_stack_size(stack_addr));
 560         kasan_enable_current();
 561         preempt_enable_no_resched();
 562         return 1;
 563 }
 564
 565 bool arch_within_kprobe_blacklist(unsigned long addr)
 566 {
 567         extern char __idmap_text_start[], __idmap_text_end[];
 568         extern char __hyp_idmap_text_start[], __hyp_idmap_text_end[];
 569
 570         if ((addr >= (unsigned long)__kprobes_text_start &&
 571             addr < (unsigned long)__kprobes_text_end) ||
 572             (addr >= (unsigned long)__entry_text_start &&
 573             addr < (unsigned long)__entry_text_end) ||
 574             (addr >= (unsigned long)__idmap_text_start &&
 575             addr < (unsigned long)__idmap_text_end) ||
 576             !!search_exception_tables(addr))
 577                 return true;
 578
 579         if (!is_kernel_in_hyp_mode()) {
 580                 if ((addr >= (unsigned long)__hyp_text_start &&
 581                     addr < (unsigned long)__hyp_text_end) ||
 582                     (addr >= (unsigned long)__hyp_idmap_text_start &&
 583                     addr < (unsigned long)__hyp_idmap_text_end))
 584                         return true;
 585         }
 586
 587         return false;
 588 }
 589
 590 void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
 591 {
 592         struct kretprobe_instance *ri = NULL;
 593         struct hlist_head *head, empty_rp;
 594         struct hlist_node *tmp;
 595         unsigned long flags, orig_ret_address = 0;
 596         unsigned long trampoline_address =
 597                 (unsigned long)&kretprobe_trampoline;
 598         kprobe_opcode_t *correct_ret_addr = NULL;
 599
 600         INIT_HLIST_HEAD(&empty_rp);
 601         kretprobe_hash_lock(current, &head, &flags);
 602
 603         /*
 604          * It is possible to have multiple instances associated with a given
 605          * task either because multiple functions in the call path have
 606          * return probes installed on them, and/or more than one
 607          * return probe was registered for a target function.
 608          *
 609          * We can handle this because:
 610          *     - instances are always pushed into the head of the list
 611          *     - when multiple return probes are registered for the same
 612          *       function, the (chronologically) first instance's ret_addr
 613          *       will be the real return address, and all the rest will
 614          *       point to kretprobe_trampoline.
 615          */
 616         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 617                 if (ri->task != current)
 618                         /* another task is sharing our hash bucket */
 619                         continue;
 620
 621                 orig_ret_address = (unsigned long)ri->ret_addr;
 622
 623                 if (orig_ret_address != trampoline_address)
 624                         /*
 625                          * This is the real return address. Any other
 626                          * instances associated with this task are for
 627                          * other calls deeper on the call stack
 628                          */
 629                         break;
 630         }
 631
 632         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 633
 634         correct_ret_addr = ri->ret_addr;
 635         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 636                 if (ri->task != current)
 637                         /* another task is sharing our hash bucket */
 638                         continue;
 639
 640                 orig_ret_address = (unsigned long)ri->ret_addr;
 641                 if (ri->rp && ri->rp->handler) {
 642                         __this_cpu_write(current_kprobe, &ri->rp->kp);
 643                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 644                         ri->ret_addr = correct_ret_addr;
 645                         ri->rp->handler(ri, regs);
 646                         __this_cpu_write(current_kprobe, NULL);
 647                 }
 648
 649                 recycle_rp_inst(ri, &empty_rp);
 650
 651                 if (orig_ret_address != trampoline_address)
 652                         /*
 653                          * This is the real return address. Any other
 654                          * instances associated with this task are for
 655                          * other calls deeper on the call stack
 656                          */
 657                         break;
 658         }
 659
 660         kretprobe_hash_unlock(current, &flags);
 661
 662         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
 663                 hlist_del(&ri->hlist);
 664                 kfree(ri);
 665         }
 666         return (void *)orig_ret_address;
 667 }
 668
 669 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 670                                       struct pt_regs *regs)
 671 {
 672         ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
 673
 674         /* replace return addr (x30) with trampoline */
 675         regs->regs[30] = (long)&kretprobe_trampoline;
 676 }
 677
 678 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 679 {
 680         return 0;
 681 }
 682
 683 int __init arch_init_kprobes(void)
 684 {
 685         return 0;
 686 }