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/set_memory.h>
  27 #include <linux/stringify.h>
  28 #include <linux/vmalloc.h>
  29 #include <asm/traps.h>
  30 #include <asm/ptrace.h>
  31 #include <asm/cacheflush.h>
  32 #include <asm/debug-monitors.h>
  33 #include <asm/system_misc.h>
  34 #include <asm/insn.h>
  35 #include <linux/uaccess.h>
  36 #include <asm/irq.h>
  37 #include <asm/sections.h>
  38
  39 #include "decode-insn.h"
  40
  41 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  42 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  43
  44 static void __kprobes
  45 post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
  46
  47 static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
  48 {
  49         void *addrs[1];
  50         u32 insns[1];
  51
  52         addrs[0] = addr;
  53         insns[0] = opcode;
  54
  55         return aarch64_insn_patch_text(addrs, insns, 1);
  56 }
  57
  58 static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
  59 {
  60         /* prepare insn slot */
  61         patch_text(p->ainsn.api.insn, p->opcode);
  62
  63         flush_icache_range((uintptr_t) (p->ainsn.api.insn),
  64                            (uintptr_t) (p->ainsn.api.insn) +
  65                            MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
  66
  67         /*
  68          * Needs restoring of return address after stepping xol.
  69          */
  70         p->ainsn.api.restore = (unsigned long) p->addr +
  71           sizeof(kprobe_opcode_t);
  72 }
  73
  74 static void __kprobes arch_prepare_simulate(struct kprobe *p)
  75 {
  76         /* This instructions is not executed xol. No need to adjust the PC */
  77         p->ainsn.api.restore = 0;
  78 }
  79
  80 static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
  81 {
  82         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  83
  84         if (p->ainsn.api.handler)
  85                 p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);
  86
  87         /* single step simulated, now go for post processing */
  88         post_kprobe_handler(kcb, regs);
  89 }
  90
  91 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  92 {
  93         unsigned long probe_addr = (unsigned long)p->addr;
  94         extern char __start_rodata[];
  95         extern char __end_rodata[];
  96
  97         if (probe_addr & 0x3)
  98                 return -EINVAL;
  99
 100         /* copy instruction */
 101         p->opcode = le32_to_cpu(*p->addr);
 102
 103         if (in_exception_text(probe_addr))
 104                 return -EINVAL;
 105         if (probe_addr >= (unsigned long) __start_rodata &&
 106             probe_addr <= (unsigned long) __end_rodata)
 107                 return -EINVAL;
 108
 109         /* decode instruction */
 110         switch (arm_kprobe_decode_insn(p->addr, &p->ainsn)) {
 111         case INSN_REJECTED:     /* insn not supported */
 112                 return -EINVAL;
 113
 114         case INSN_GOOD_NO_SLOT: /* insn need simulation */
 115                 p->ainsn.api.insn = NULL;
 116                 break;
 117
 118         case INSN_GOOD: /* instruction uses slot */
 119                 p->ainsn.api.insn = get_insn_slot();
 120                 if (!p->ainsn.api.insn)
 121                         return -ENOMEM;
 122                 break;
 123         };
 124
 125         /* prepare the instruction */
 126         if (p->ainsn.api.insn)
 127                 arch_prepare_ss_slot(p);
 128         else
 129                 arch_prepare_simulate(p);
 130
 131         return 0;
 132 }
 133
 134 void *alloc_insn_page(void)
 135 {
 136         void *page;
 137
 138         page = vmalloc_exec(PAGE_SIZE);
 139         if (page)
 140                 set_memory_ro((unsigned long)page, 1);
 141
 142         return page;
 143 }
 144
 145 /* arm kprobe: install breakpoint in text */
 146 void __kprobes arch_arm_kprobe(struct kprobe *p)
 147 {
 148         patch_text(p->addr, BRK64_OPCODE_KPROBES);
 149 }
 150
 151 /* disarm kprobe: remove breakpoint from text */
 152 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 153 {
 154         patch_text(p->addr, p->opcode);
 155 }
 156
 157 void __kprobes arch_remove_kprobe(struct kprobe *p)
 158 {
 159         if (p->ainsn.api.insn) {
 160                 free_insn_slot(p->ainsn.api.insn, 0);
 161                 p->ainsn.api.insn = NULL;
 162         }
 163 }
 164
 165 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 166 {
 167         kcb->prev_kprobe.kp = kprobe_running();
 168         kcb->prev_kprobe.status = kcb->kprobe_status;
 169 }
 170
 171 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 172 {
 173         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 174         kcb->kprobe_status = kcb->prev_kprobe.status;
 175 }
 176
 177 static void __kprobes set_current_kprobe(struct kprobe *p)
 178 {
 179         __this_cpu_write(current_kprobe, p);
 180 }
 181
 182 /*
 183  * When PSTATE.D is set (masked), then software step exceptions can not be
 184  * generated.
 185  * SPSR's D bit shows the value of PSTATE.D immediately before the
 186  * exception was taken. PSTATE.D is set while entering into any exception
 187  * mode, however software clears it for any normal (none-debug-exception)
 188  * mode in the exception entry. Therefore, when we are entering into kprobe
 189  * breakpoint handler from any normal mode then SPSR.D bit is already
 190  * cleared, however it is set when we are entering from any debug exception
 191  * mode.
 192  * Since we always need to generate single step exception after a kprobe
 193  * breakpoint exception therefore we need to clear it unconditionally, when
 194  * we become sure that the current breakpoint exception is for kprobe.
 195  */
 196 static void __kprobes
 197 spsr_set_debug_flag(struct pt_regs *regs, int mask)
 198 {
 199         unsigned long spsr = regs->pstate;
 200
 201         if (mask)
 202                 spsr |= PSR_D_BIT;
 203         else
 204                 spsr &= ~PSR_D_BIT;
 205
 206         regs->pstate = spsr;
 207 }
 208
 209 /*
 210  * Interrupts need to be disabled before single-step mode is set, and not
 211  * reenabled until after single-step mode ends.
 212  * Without disabling interrupt on local CPU, there is a chance of
 213  * interrupt occurrence in the period of exception return and  start of
 214  * out-of-line single-step, that result in wrongly single stepping
 215  * into the interrupt handler.
 216  */
 217 static void __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb,
 218                                                 struct pt_regs *regs)
 219 {
 220         kcb->saved_irqflag = regs->pstate;
 221         regs->pstate |= PSR_I_BIT;
 222 }
 223
 224 static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
 225                                                 struct pt_regs *regs)
 226 {
 227         if (kcb->saved_irqflag & PSR_I_BIT)
 228                 regs->pstate |= PSR_I_BIT;
 229         else
 230                 regs->pstate &= ~PSR_I_BIT;
 231 }
 232
 233 static void __kprobes
 234 set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr)
 235 {
 236         kcb->ss_ctx.ss_pending = true;
 237         kcb->ss_ctx.match_addr = addr + sizeof(kprobe_opcode_t);
 238 }
 239
 240 static void __kprobes clear_ss_context(struct kprobe_ctlblk *kcb)
 241 {
 242         kcb->ss_ctx.ss_pending = false;
 243         kcb->ss_ctx.match_addr = 0;
 244 }
 245
 246 static void __kprobes setup_singlestep(struct kprobe *p,
 247                                        struct pt_regs *regs,
 248                                        struct kprobe_ctlblk *kcb, int reenter)
 249 {
 250         unsigned long slot;
 251
 252         if (reenter) {
 253                 save_previous_kprobe(kcb);
 254                 set_current_kprobe(p);
 255                 kcb->kprobe_status = KPROBE_REENTER;
 256         } else {
 257                 kcb->kprobe_status = KPROBE_HIT_SS;
 258         }
 259
 260
 261         if (p->ainsn.api.insn) {
 262                 /* prepare for single stepping */
 263                 slot = (unsigned long)p->ainsn.api.insn;
 264
 265                 set_ss_context(kcb, slot);      /* mark pending ss */
 266
 267                 spsr_set_debug_flag(regs, 0);
 268
 269                 /* IRQs and single stepping do not mix well. */
 270                 kprobes_save_local_irqflag(kcb, regs);
 271                 kernel_enable_single_step(regs);
 272                 instruction_pointer_set(regs, slot);
 273         } else {
 274                 /* insn simulation */
 275                 arch_simulate_insn(p, regs);
 276         }
 277 }
 278
 279 static int __kprobes reenter_kprobe(struct kprobe *p,
 280                                     struct pt_regs *regs,
 281                                     struct kprobe_ctlblk *kcb)
 282 {
 283         switch (kcb->kprobe_status) {
 284         case KPROBE_HIT_SSDONE:
 285         case KPROBE_HIT_ACTIVE:
 286                 kprobes_inc_nmissed_count(p);
 287                 setup_singlestep(p, regs, kcb, 1);
 288                 break;
 289         case KPROBE_HIT_SS:
 290         case KPROBE_REENTER:
 291                 pr_warn("Unrecoverable kprobe detected.\n");
 292                 dump_kprobe(p);
 293                 BUG();
 294                 break;
 295         default:
 296                 WARN_ON(1);
 297                 return 0;
 298         }
 299
 300         return 1;
 301 }
 302
 303 static void __kprobes
 304 post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
 305 {
 306         struct kprobe *cur = kprobe_running();
 307
 308         if (!cur)
 309                 return;
 310
 311         /* return addr restore if non-branching insn */
 312         if (cur->ainsn.api.restore != 0)
 313                 instruction_pointer_set(regs, cur->ainsn.api.restore);
 314
 315         /* restore back original saved kprobe variables and continue */
 316         if (kcb->kprobe_status == KPROBE_REENTER) {
 317                 restore_previous_kprobe(kcb);
 318                 return;
 319         }
 320         /* call post handler */
 321         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 322         if (cur->post_handler)  {
 323                 /* post_handler can hit breakpoint and single step
 324                  * again, so we enable D-flag for recursive exception.
 325                  */
 326                 cur->post_handler(cur, regs, 0);
 327         }
 328
 329         reset_current_kprobe();
 330 }
 331
 332 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 333 {
 334         struct kprobe *cur = kprobe_running();
 335         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 336
 337         switch (kcb->kprobe_status) {
 338         case KPROBE_HIT_SS:
 339         case KPROBE_REENTER:
 340                 /*
 341                  * We are here because the instruction being single
 342                  * stepped caused a page fault. We reset the current
 343                  * kprobe and the ip points back to the probe address
 344                  * and allow the page fault handler to continue as a
 345                  * normal page fault.
 346                  */
 347                 instruction_pointer_set(regs, (unsigned long) cur->addr);
 348                 if (!instruction_pointer(regs))
 349                         BUG();
 350
 351                 kernel_disable_single_step();
 352
 353                 if (kcb->kprobe_status == KPROBE_REENTER)
 354                         restore_previous_kprobe(kcb);
 355                 else
 356                         reset_current_kprobe();
 357
 358                 break;
 359         case KPROBE_HIT_ACTIVE:
 360         case KPROBE_HIT_SSDONE:
 361                 /*
 362                  * We increment the nmissed count for accounting,
 363                  * we can also use npre/npostfault count for accounting
 364                  * these specific fault cases.
 365                  */
 366                 kprobes_inc_nmissed_count(cur);
 367
 368                 /*
 369                  * We come here because instructions in the pre/post
 370                  * handler caused the page_fault, this could happen
 371                  * if handler tries to access user space by
 372                  * copy_from_user(), get_user() etc. Let the
 373                  * user-specified handler try to fix it first.
 374                  */
 375                 if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
 376                         return 1;
 377
 378                 /*
 379                  * In case the user-specified fault handler returned
 380                  * zero, try to fix up.
 381                  */
 382                 if (fixup_exception(regs))
 383                         return 1;
 384         }
 385         return 0;
 386 }
 387
 388 static void __kprobes kprobe_handler(struct pt_regs *regs)
 389 {
 390         struct kprobe *p, *cur_kprobe;
 391         struct kprobe_ctlblk *kcb;
 392         unsigned long addr = instruction_pointer(regs);
 393
 394         kcb = get_kprobe_ctlblk();
 395         cur_kprobe = kprobe_running();
 396
 397         p = get_kprobe((kprobe_opcode_t *) addr);
 398
 399         if (p) {
 400                 if (cur_kprobe) {
 401                         if (reenter_kprobe(p, regs, kcb))
 402                                 return;
 403                 } else {
 404                         /* Probe hit */
 405                         set_current_kprobe(p);
 406                         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 407
 408                         /*
 409                          * If we have no pre-handler or it returned 0, we
 410                          * continue with normal processing.  If we have a
 411                          * pre-handler and it returned non-zero, it prepped
 412                          * for calling the break_handler below on re-entry,
 413                          * so get out doing nothing more here.
 414                          *
 415                          * pre_handler can hit a breakpoint and can step thru
 416                          * before return, keep PSTATE D-flag enabled until
 417                          * pre_handler return back.
 418                          */
 419                         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 420                                 setup_singlestep(p, regs, kcb, 0);
 421                                 return;
 422                         }
 423                 }
 424         } else if ((le32_to_cpu(*(kprobe_opcode_t *) addr) ==
 425             BRK64_OPCODE_KPROBES) && cur_kprobe) {
 426                 /* We probably hit a jprobe.  Call its break handler. */
 427                 if (cur_kprobe->break_handler  &&
 428                      cur_kprobe->break_handler(cur_kprobe, regs)) {
 429                         setup_singlestep(cur_kprobe, regs, kcb, 0);
 430                         return;
 431                 }
 432         }
 433         /*
 434          * The breakpoint instruction was removed right
 435          * after we hit it.  Another cpu has removed
 436          * either a probepoint or a debugger breakpoint
 437          * at this address.  In either case, no further
 438          * handling of this interrupt is appropriate.
 439          * Return back to original instruction, and continue.
 440          */
 441 }
 442
 443 static int __kprobes
 444 kprobe_ss_hit(struct kprobe_ctlblk *kcb, unsigned long addr)
 445 {
 446         if ((kcb->ss_ctx.ss_pending)
 447             && (kcb->ss_ctx.match_addr == addr)) {
 448                 clear_ss_context(kcb);  /* clear pending ss */
 449                 return DBG_HOOK_HANDLED;
 450         }
 451         /* not ours, kprobes should ignore it */
 452         return DBG_HOOK_ERROR;
 453 }
 454
 455 int __kprobes
 456 kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
 457 {
 458         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 459         int retval;
 460
 461         if (user_mode(regs))
 462                 return DBG_HOOK_ERROR;
 463
 464         /* return error if this is not our step */
 465         retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
 466
 467         if (retval == DBG_HOOK_HANDLED) {
 468                 kprobes_restore_local_irqflag(kcb, regs);
 469                 kernel_disable_single_step();
 470
 471                 post_kprobe_handler(kcb, regs);
 472         }
 473
 474         return retval;
 475 }
 476
 477 int __kprobes
 478 kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
 479 {
 480         if (user_mode(regs))
 481                 return DBG_HOOK_ERROR;
 482
 483         kprobe_handler(regs);
 484         return DBG_HOOK_HANDLED;
 485 }
 486
 487 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 488 {
 489         struct jprobe *jp = container_of(p, struct jprobe, kp);
 490         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 491
 492         kcb->jprobe_saved_regs = *regs;
 493         /*
 494          * Since we can't be sure where in the stack frame "stacked"
 495          * pass-by-value arguments are stored we just don't try to
 496          * duplicate any of the stack. Do not use jprobes on functions that
 497          * use more than 64 bytes (after padding each to an 8 byte boundary)
 498          * of arguments, or pass individual arguments larger than 16 bytes.
 499          */
 500
 501         instruction_pointer_set(regs, (unsigned long) jp->entry);
 502         preempt_disable();
 503         pause_graph_tracing();
 504         return 1;
 505 }
 506
 507 void __kprobes jprobe_return(void)
 508 {
 509         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 510
 511         /*
 512          * Jprobe handler return by entering break exception,
 513          * encoded same as kprobe, but with following conditions
 514          * -a special PC to identify it from the other kprobes.
 515          * -restore stack addr to original saved pt_regs
 516          */
 517         asm volatile("                          mov sp, %0      \n"
 518                      "jprobe_return_break:      brk %1          \n"
 519                      :
 520                      : "r" (kcb->jprobe_saved_regs.sp),
 521                        "I" (BRK64_ESR_KPROBES)
 522                      : "memory");
 523
 524         unreachable();
 525 }
 526
 527 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 528 {
 529         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 530         long stack_addr = kcb->jprobe_saved_regs.sp;
 531         long orig_sp = kernel_stack_pointer(regs);
 532         struct jprobe *jp = container_of(p, struct jprobe, kp);
 533         extern const char jprobe_return_break[];
 534
 535         if (instruction_pointer(regs) != (u64) jprobe_return_break)
 536                 return 0;
 537
 538         if (orig_sp != stack_addr) {
 539                 struct pt_regs *saved_regs =
 540                     (struct pt_regs *)kcb->jprobe_saved_regs.sp;
 541                 pr_err("current sp %lx does not match saved sp %lx\n",
 542                        orig_sp, stack_addr);
 543                 pr_err("Saved registers for jprobe %p\n", jp);
 544                 __show_regs(saved_regs);
 545                 pr_err("Current registers\n");
 546                 __show_regs(regs);
 547                 BUG();
 548         }
 549         unpause_graph_tracing();
 550         *regs = kcb->jprobe_saved_regs;
 551         preempt_enable_no_resched();
 552         return 1;
 553 }
 554
 555 bool arch_within_kprobe_blacklist(unsigned long addr)
 556 {
 557         if ((addr >= (unsigned long)__kprobes_text_start &&
 558             addr < (unsigned long)__kprobes_text_end) ||
 559             (addr >= (unsigned long)__entry_text_start &&
 560             addr < (unsigned long)__entry_text_end) ||
 561             (addr >= (unsigned long)__idmap_text_start &&
 562             addr < (unsigned long)__idmap_text_end) ||
 563             (addr >= (unsigned long)__hyp_text_start &&
 564             addr < (unsigned long)__hyp_text_end) ||
 565             !!search_exception_tables(addr))
 566                 return true;
 567
 568         if (!is_kernel_in_hyp_mode()) {
 569                 if ((addr >= (unsigned long)__hyp_idmap_text_start &&
 570                     addr < (unsigned long)__hyp_idmap_text_end))
 571                         return true;
 572         }
 573
 574         return false;
 575 }
 576
 577 void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
 578 {
 579         struct kretprobe_instance *ri = NULL;
 580         struct hlist_head *head, empty_rp;
 581         struct hlist_node *tmp;
 582         unsigned long flags, orig_ret_address = 0;
 583         unsigned long trampoline_address =
 584                 (unsigned long)&kretprobe_trampoline;
 585         kprobe_opcode_t *correct_ret_addr = NULL;
 586
 587         INIT_HLIST_HEAD(&empty_rp);
 588         kretprobe_hash_lock(current, &head, &flags);
 589
 590         /*
 591          * It is possible to have multiple instances associated with a given
 592          * task either because multiple functions in the call path have
 593          * return probes installed on them, and/or more than one
 594          * return probe was registered for a target function.
 595          *
 596          * We can handle this because:
 597          *     - instances are always pushed into the head of the list
 598          *     - when multiple return probes are registered for the same
 599          *       function, the (chronologically) first instance's ret_addr
 600          *       will be the real return address, and all the rest will
 601          *       point to kretprobe_trampoline.
 602          */
 603         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 604                 if (ri->task != current)
 605                         /* another task is sharing our hash bucket */
 606                         continue;
 607
 608                 orig_ret_address = (unsigned long)ri->ret_addr;
 609
 610                 if (orig_ret_address != trampoline_address)
 611                         /*
 612                          * This is the real return address. Any other
 613                          * instances associated with this task are for
 614                          * other calls deeper on the call stack
 615                          */
 616                         break;
 617         }
 618
 619         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 620
 621         correct_ret_addr = ri->ret_addr;
 622         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 623                 if (ri->task != current)
 624                         /* another task is sharing our hash bucket */
 625                         continue;
 626
 627                 orig_ret_address = (unsigned long)ri->ret_addr;
 628                 if (ri->rp && ri->rp->handler) {
 629                         __this_cpu_write(current_kprobe, &ri->rp->kp);
 630                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 631                         ri->ret_addr = correct_ret_addr;
 632                         ri->rp->handler(ri, regs);
 633                         __this_cpu_write(current_kprobe, NULL);
 634                 }
 635
 636                 recycle_rp_inst(ri, &empty_rp);
 637
 638                 if (orig_ret_address != trampoline_address)
 639                         /*
 640                          * This is the real return address. Any other
 641                          * instances associated with this task are for
 642                          * other calls deeper on the call stack
 643                          */
 644                         break;
 645         }
 646
 647         kretprobe_hash_unlock(current, &flags);
 648
 649         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
 650                 hlist_del(&ri->hlist);
 651                 kfree(ri);
 652         }
 653         return (void *)orig_ret_address;
 654 }
 655
 656 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 657                                       struct pt_regs *regs)
 658 {
 659         ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
 660
 661         /* replace return addr (x30) with trampoline */
 662         regs->regs[30] = (long)&kretprobe_trampoline;
 663 }
 664
 665 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 666 {
 667         return 0;
 668 }
 669
 670 int __init arch_init_kprobes(void)
 671 {
 672         return 0;
 673 }