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