arch/arm64/kernel/probes/kprobes.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * arch/arm64/kernel/probes/kprobes.c
   4  *
   5  * Kprobes support for ARM64
   6  *
   7  * Copyright (C) 2013 Linaro Limited.
   8  * Author: Sandeepa Prabhu <sandeepa.prabhu@linaro.org>
   9  */
  10 #include <linux/kasan.h>
  11 #include <linux/kernel.h>
  12 #include <linux/kprobes.h>
  13 #include <linux/extable.h>
  14 #include <linux/slab.h>
  15 #include <linux/stop_machine.h>
  16 #include <linux/sched/debug.h>
  17 #include <linux/set_memory.h>
  18 #include <linux/stringify.h>
  19 #include <linux/vmalloc.h>
  20 #include <asm/traps.h>
  21 #include <asm/ptrace.h>
  22 #include <asm/cacheflush.h>
  23 #include <asm/debug-monitors.h>
  24 #include <asm/daifflags.h>
  25 #include <asm/system_misc.h>
  26 #include <asm/insn.h>
  27 #include <linux/uaccess.h>
  28 #include <asm/irq.h>
  29 #include <asm/sections.h>
  30
  31 #include "decode-insn.h"
  32
  33 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  34 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  35
  36 static void __kprobes
  37 post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
  38
  39 static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
  40 {
  41         void *addrs[1];
  42         u32 insns[1];
  43
  44         addrs[0] = addr;
  45         insns[0] = opcode;
  46
  47         return aarch64_insn_patch_text(addrs, insns, 1);
  48 }
  49
  50 static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
  51 {
  52         /* prepare insn slot */
  53         patch_text(p->ainsn.api.insn, p->opcode);
  54
  55         flush_icache_range((uintptr_t) (p->ainsn.api.insn),
  56                            (uintptr_t) (p->ainsn.api.insn) +
  57                            MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
  58
  59         /*
  60          * Needs restoring of return address after stepping xol.
  61          */
  62         p->ainsn.api.restore = (unsigned long) p->addr +
  63           sizeof(kprobe_opcode_t);
  64 }
  65
  66 static void __kprobes arch_prepare_simulate(struct kprobe *p)
  67 {
  68         /* This instructions is not executed xol. No need to adjust the PC */
  69         p->ainsn.api.restore = 0;
  70 }
  71
  72 static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
  73 {
  74         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  75
  76         if (p->ainsn.api.handler)
  77                 p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);
  78
  79         /* single step simulated, now go for post processing */
  80         post_kprobe_handler(kcb, regs);
  81 }
  82
  83 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  84 {
  85         unsigned long probe_addr = (unsigned long)p->addr;
  86
  87         if (probe_addr & 0x3)
  88                 return -EINVAL;
  89
  90         /* copy instruction */
  91         p->opcode = le32_to_cpu(*p->addr);
  92
  93         if (search_exception_tables(probe_addr))
  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 void *alloc_insn_page(void)
 122 {
 123         void *page;
 124
 125         page = vmalloc_exec(PAGE_SIZE);
 126         if (page) {
 127                 set_memory_ro((unsigned long)page, 1);
 128                 set_vm_flush_reset_perms(page);
 129         }
 130
 131         return page;
 132 }
 133
 134 /* arm kprobe: install breakpoint in text */
 135 void __kprobes arch_arm_kprobe(struct kprobe *p)
 136 {
 137         patch_text(p->addr, BRK64_OPCODE_KPROBES);
 138 }
 139
 140 /* disarm kprobe: remove breakpoint from text */
 141 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 142 {
 143         patch_text(p->addr, p->opcode);
 144 }
 145
 146 void __kprobes arch_remove_kprobe(struct kprobe *p)
 147 {
 148         if (p->ainsn.api.insn) {
 149                 free_insn_slot(p->ainsn.api.insn, 0);
 150                 p->ainsn.api.insn = NULL;
 151         }
 152 }
 153
 154 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 155 {
 156         kcb->prev_kprobe.kp = kprobe_running();
 157         kcb->prev_kprobe.status = kcb->kprobe_status;
 158 }
 159
 160 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 161 {
 162         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 163         kcb->kprobe_status = kcb->prev_kprobe.status;
 164 }
 165
 166 static void __kprobes set_current_kprobe(struct kprobe *p)
 167 {
 168         __this_cpu_write(current_kprobe, p);
 169 }
 170
 171 /*
 172  * Interrupts need to be disabled before single-step mode is set, and not
 173  * reenabled until after single-step mode ends.
 174  * Without disabling interrupt on local CPU, there is a chance of
 175  * interrupt occurrence in the period of exception return and  start of
 176  * out-of-line single-step, that result in wrongly single stepping
 177  * into the interrupt handler.
 178  */
 179 static void __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb,
 180                                                 struct pt_regs *regs)
 181 {
 182         kcb->saved_irqflag = regs->pstate & DAIF_MASK;
 183         regs->pstate |= PSR_I_BIT;
 184         /* Unmask PSTATE.D for enabling software step exceptions. */
 185         regs->pstate &= ~PSR_D_BIT;
 186 }
 187
 188 static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
 189                                                 struct pt_regs *regs)
 190 {
 191         regs->pstate &= ~DAIF_MASK;
 192         regs->pstate |= kcb->saved_irqflag;
 193 }
 194
 195 static void __kprobes
 196 set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr)
 197 {
 198         kcb->ss_ctx.ss_pending = true;
 199         kcb->ss_ctx.match_addr = addr + sizeof(kprobe_opcode_t);
 200 }
 201
 202 static void __kprobes clear_ss_context(struct kprobe_ctlblk *kcb)
 203 {
 204         kcb->ss_ctx.ss_pending = false;
 205         kcb->ss_ctx.match_addr = 0;
 206 }
 207
 208 static void __kprobes setup_singlestep(struct kprobe *p,
 209                                        struct pt_regs *regs,
 210                                        struct kprobe_ctlblk *kcb, int reenter)
 211 {
 212         unsigned long slot;
 213
 214         if (reenter) {
 215                 save_previous_kprobe(kcb);
 216                 set_current_kprobe(p);
 217                 kcb->kprobe_status = KPROBE_REENTER;
 218         } else {
 219                 kcb->kprobe_status = KPROBE_HIT_SS;
 220         }
 221
 222
 223         if (p->ainsn.api.insn) {
 224                 /* prepare for single stepping */
 225                 slot = (unsigned long)p->ainsn.api.insn;
 226
 227                 set_ss_context(kcb, slot);      /* mark pending ss */
 228
 229                 /* IRQs and single stepping do not mix well. */
 230                 kprobes_save_local_irqflag(kcb, regs);
 231                 kernel_enable_single_step(regs);
 232                 instruction_pointer_set(regs, slot);
 233         } else {
 234                 /* insn simulation */
 235                 arch_simulate_insn(p, regs);
 236         }
 237 }
 238
 239 static int __kprobes reenter_kprobe(struct kprobe *p,
 240                                     struct pt_regs *regs,
 241                                     struct kprobe_ctlblk *kcb)
 242 {
 243         switch (kcb->kprobe_status) {
 244         case KPROBE_HIT_SSDONE:
 245         case KPROBE_HIT_ACTIVE:
 246                 kprobes_inc_nmissed_count(p);
 247                 setup_singlestep(p, regs, kcb, 1);
 248                 break;
 249         case KPROBE_HIT_SS:
 250         case KPROBE_REENTER:
 251                 pr_warn("Unrecoverable kprobe detected.\n");
 252                 dump_kprobe(p);
 253                 BUG();
 254                 break;
 255         default:
 256                 WARN_ON(1);
 257                 return 0;
 258         }
 259
 260         return 1;
 261 }
 262
 263 static void __kprobes
 264 post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
 265 {
 266         struct kprobe *cur = kprobe_running();
 267
 268         if (!cur)
 269                 return;
 270
 271         /* return addr restore if non-branching insn */
 272         if (cur->ainsn.api.restore != 0)
 273                 instruction_pointer_set(regs, cur->ainsn.api.restore);
 274
 275         /* restore back original saved kprobe variables and continue */
 276         if (kcb->kprobe_status == KPROBE_REENTER) {
 277                 restore_previous_kprobe(kcb);
 278                 return;
 279         }
 280         /* call post handler */
 281         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 282         if (cur->post_handler)  {
 283                 /* post_handler can hit breakpoint and single step
 284                  * again, so we enable D-flag for recursive exception.
 285                  */
 286                 cur->post_handler(cur, regs, 0);
 287         }
 288
 289         reset_current_kprobe();
 290 }
 291
 292 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 293 {
 294         struct kprobe *cur = kprobe_running();
 295         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 296
 297         switch (kcb->kprobe_status) {
 298         case KPROBE_HIT_SS:
 299         case KPROBE_REENTER:
 300                 /*
 301                  * We are here because the instruction being single
 302                  * stepped caused a page fault. We reset the current
 303                  * kprobe and the ip points back to the probe address
 304                  * and allow the page fault handler to continue as a
 305                  * normal page fault.
 306                  */
 307                 instruction_pointer_set(regs, (unsigned long) cur->addr);
 308                 if (!instruction_pointer(regs))
 309                         BUG();
 310
 311                 kernel_disable_single_step();
 312
 313                 if (kcb->kprobe_status == KPROBE_REENTER)
 314                         restore_previous_kprobe(kcb);
 315                 else
 316                         reset_current_kprobe();
 317
 318                 break;
 319         case KPROBE_HIT_ACTIVE:
 320         case KPROBE_HIT_SSDONE:
 321                 /*
 322                  * We increment the nmissed count for accounting,
 323                  * we can also use npre/npostfault count for accounting
 324                  * these specific fault cases.
 325                  */
 326                 kprobes_inc_nmissed_count(cur);
 327
 328                 /*
 329                  * We come here because instructions in the pre/post
 330                  * handler caused the page_fault, this could happen
 331                  * if handler tries to access user space by
 332                  * copy_from_user(), get_user() etc. Let the
 333                  * user-specified handler try to fix it first.
 334                  */
 335                 if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
 336                         return 1;
 337
 338                 /*
 339                  * In case the user-specified fault handler returned
 340                  * zero, try to fix up.
 341                  */
 342                 if (fixup_exception(regs))
 343                         return 1;
 344         }
 345         return 0;
 346 }
 347
 348 static void __kprobes kprobe_handler(struct pt_regs *regs)
 349 {
 350         struct kprobe *p, *cur_kprobe;
 351         struct kprobe_ctlblk *kcb;
 352         unsigned long addr = instruction_pointer(regs);
 353
 354         kcb = get_kprobe_ctlblk();
 355         cur_kprobe = kprobe_running();
 356
 357         p = get_kprobe((kprobe_opcode_t *) addr);
 358
 359         if (p) {
 360                 if (cur_kprobe) {
 361                         if (reenter_kprobe(p, regs, kcb))
 362                                 return;
 363                 } else {
 364                         /* Probe hit */
 365                         set_current_kprobe(p);
 366                         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 367
 368                         /*
 369                          * If we have no pre-handler or it returned 0, we
 370                          * continue with normal processing.  If we have a
 371                          * pre-handler and it returned non-zero, it will
 372                          * modify the execution path and no need to single
 373                          * stepping. Let's just reset current kprobe and exit.
 374                          *
 375                          * pre_handler can hit a breakpoint and can step thru
 376                          * before return, keep PSTATE D-flag enabled until
 377                          * pre_handler return back.
 378                          */
 379                         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 380                                 setup_singlestep(p, regs, kcb, 0);
 381                         } else
 382                                 reset_current_kprobe();
 383                 }
 384         }
 385         /*
 386          * The breakpoint instruction was removed right
 387          * after we hit it.  Another cpu has removed
 388          * either a probepoint or a debugger breakpoint
 389          * at this address.  In either case, no further
 390          * handling of this interrupt is appropriate.
 391          * Return back to original instruction, and continue.
 392          */
 393 }
 394
 395 static int __kprobes
 396 kprobe_ss_hit(struct kprobe_ctlblk *kcb, unsigned long addr)
 397 {
 398         if ((kcb->ss_ctx.ss_pending)
 399             && (kcb->ss_ctx.match_addr == addr)) {
 400                 clear_ss_context(kcb);  /* clear pending ss */
 401                 return DBG_HOOK_HANDLED;
 402         }
 403         /* not ours, kprobes should ignore it */
 404         return DBG_HOOK_ERROR;
 405 }
 406
 407 static int __kprobes
 408 kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr)
 409 {
 410         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 411         int retval;
 412
 413         /* return error if this is not our step */
 414         retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
 415
 416         if (retval == DBG_HOOK_HANDLED) {
 417                 kprobes_restore_local_irqflag(kcb, regs);
 418                 kernel_disable_single_step();
 419
 420                 post_kprobe_handler(kcb, regs);
 421         }
 422
 423         return retval;
 424 }
 425
 426 static struct step_hook kprobes_step_hook = {
 427         .fn = kprobe_single_step_handler,
 428 };
 429
 430 static int __kprobes
 431 kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
 432 {
 433         kprobe_handler(regs);
 434         return DBG_HOOK_HANDLED;
 435 }
 436
 437 static struct break_hook kprobes_break_hook = {
 438         .imm = KPROBES_BRK_IMM,
 439         .fn = kprobe_breakpoint_handler,
 440 };
 441
 442 /*
 443  * Provide a blacklist of symbols identifying ranges which cannot be kprobed.
 444  * This blacklist is exposed to userspace via debugfs (kprobes/blacklist).
 445  */
 446 int __init arch_populate_kprobe_blacklist(void)
 447 {
 448         int ret;
 449
 450         ret = kprobe_add_area_blacklist((unsigned long)__entry_text_start,
 451                                         (unsigned long)__entry_text_end);
 452         if (ret)
 453                 return ret;
 454         ret = kprobe_add_area_blacklist((unsigned long)__irqentry_text_start,
 455                                         (unsigned long)__irqentry_text_end);
 456         if (ret)
 457                 return ret;
 458         ret = kprobe_add_area_blacklist((unsigned long)__idmap_text_start,
 459                                         (unsigned long)__idmap_text_end);
 460         if (ret)
 461                 return ret;
 462         ret = kprobe_add_area_blacklist((unsigned long)__hyp_text_start,
 463                                         (unsigned long)__hyp_text_end);
 464         if (ret || is_kernel_in_hyp_mode())
 465                 return ret;
 466         ret = kprobe_add_area_blacklist((unsigned long)__hyp_idmap_text_start,
 467                                         (unsigned long)__hyp_idmap_text_end);
 468         return ret;
 469 }
 470
 471 void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
 472 {
 473         struct kretprobe_instance *ri = NULL;
 474         struct hlist_head *head, empty_rp;
 475         struct hlist_node *tmp;
 476         unsigned long flags, orig_ret_address = 0;
 477         unsigned long trampoline_address =
 478                 (unsigned long)&kretprobe_trampoline;
 479         kprobe_opcode_t *correct_ret_addr = NULL;
 480
 481         INIT_HLIST_HEAD(&empty_rp);
 482         kretprobe_hash_lock(current, &head, &flags);
 483
 484         /*
 485          * It is possible to have multiple instances associated with a given
 486          * task either because multiple functions in the call path have
 487          * return probes installed on them, and/or more than one
 488          * return probe was registered for a target function.
 489          *
 490          * We can handle this because:
 491          *     - instances are always pushed into the head of the list
 492          *     - when multiple return probes are registered for the same
 493          *       function, the (chronologically) first instance's ret_addr
 494          *       will be the real return address, and all the rest will
 495          *       point to kretprobe_trampoline.
 496          */
 497         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 498                 if (ri->task != current)
 499                         /* another task is sharing our hash bucket */
 500                         continue;
 501
 502                 orig_ret_address = (unsigned long)ri->ret_addr;
 503
 504                 if (orig_ret_address != trampoline_address)
 505                         /*
 506                          * This is the real return address. Any other
 507                          * instances associated with this task are for
 508                          * other calls deeper on the call stack
 509                          */
 510                         break;
 511         }
 512
 513         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 514
 515         correct_ret_addr = ri->ret_addr;
 516         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 517                 if (ri->task != current)
 518                         /* another task is sharing our hash bucket */
 519                         continue;
 520
 521                 orig_ret_address = (unsigned long)ri->ret_addr;
 522                 if (ri->rp && ri->rp->handler) {
 523                         __this_cpu_write(current_kprobe, &ri->rp->kp);
 524                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 525                         ri->ret_addr = correct_ret_addr;
 526                         ri->rp->handler(ri, regs);
 527                         __this_cpu_write(current_kprobe, NULL);
 528                 }
 529
 530                 recycle_rp_inst(ri, &empty_rp);
 531
 532                 if (orig_ret_address != trampoline_address)
 533                         /*
 534                          * This is the real return address. Any other
 535                          * instances associated with this task are for
 536                          * other calls deeper on the call stack
 537                          */
 538                         break;
 539         }
 540
 541         kretprobe_hash_unlock(current, &flags);
 542
 543         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
 544                 hlist_del(&ri->hlist);
 545                 kfree(ri);
 546         }
 547         return (void *)orig_ret_address;
 548 }
 549
 550 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 551                                       struct pt_regs *regs)
 552 {
 553         ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
 554
 555         /* replace return addr (x30) with trampoline */
 556         regs->regs[30] = (long)&kretprobe_trampoline;
 557 }
 558
 559 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 560 {
 561         return 0;
 562 }
 563
 564 int __init arch_init_kprobes(void)
 565 {
 566         register_kernel_break_hook(&kprobes_break_hook);
 567         register_kernel_step_hook(&kprobes_step_hook);
 568
 569         return 0;
 570 }