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 void __kprobes arch_prepare_ss_slot(struct kprobe *p)
  40 {
  41         kprobe_opcode_t *addr = p->ainsn.api.insn;
  42         void *addrs[] = {addr, addr + 1};
  43         u32 insns[] = {p->opcode, BRK64_OPCODE_KPROBES_SS};
  44
  45         /* prepare insn slot */
  46         aarch64_insn_patch_text(addrs, insns, 2);
  47
  48         flush_icache_range((uintptr_t)addr, (uintptr_t)(addr + MAX_INSN_SIZE));
  49
  50         /*
  51          * Needs restoring of return address after stepping xol.
  52          */
  53         p->ainsn.api.restore = (unsigned long) p->addr +
  54           sizeof(kprobe_opcode_t);
  55 }
  56
  57 static void __kprobes arch_prepare_simulate(struct kprobe *p)
  58 {
  59         /* This instructions is not executed xol. No need to adjust the PC */
  60         p->ainsn.api.restore = 0;
  61 }
  62
  63 static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
  64 {
  65         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  66
  67         if (p->ainsn.api.handler)
  68                 p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);
  69
  70         /* single step simulated, now go for post processing */
  71         post_kprobe_handler(kcb, regs);
  72 }
  73
  74 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  75 {
  76         unsigned long probe_addr = (unsigned long)p->addr;
  77
  78         if (probe_addr & 0x3)
  79                 return -EINVAL;
  80
  81         /* copy instruction */
  82         p->opcode = le32_to_cpu(*p->addr);
  83
  84         if (search_exception_tables(probe_addr))
  85                 return -EINVAL;
  86
  87         /* decode instruction */
  88         switch (arm_kprobe_decode_insn(p->addr, &p->ainsn)) {
  89         case INSN_REJECTED:     /* insn not supported */
  90                 return -EINVAL;
  91
  92         case INSN_GOOD_NO_SLOT: /* insn need simulation */
  93                 p->ainsn.api.insn = NULL;
  94                 break;
  95
  96         case INSN_GOOD: /* instruction uses slot */
  97                 p->ainsn.api.insn = get_insn_slot();
  98                 if (!p->ainsn.api.insn)
  99                         return -ENOMEM;
 100                 break;
 101         }
 102
 103         /* prepare the instruction */
 104         if (p->ainsn.api.insn)
 105                 arch_prepare_ss_slot(p);
 106         else
 107                 arch_prepare_simulate(p);
 108
 109         return 0;
 110 }
 111
 112 void *alloc_insn_page(void)
 113 {
 114         void *page;
 115
 116         page = vmalloc_exec(PAGE_SIZE);
 117         if (page) {
 118                 set_memory_ro((unsigned long)page, 1);
 119                 set_vm_flush_reset_perms(page);
 120         }
 121
 122         return page;
 123 }
 124
 125 /* arm kprobe: install breakpoint in text */
 126 void __kprobes arch_arm_kprobe(struct kprobe *p)
 127 {
 128         void *addr = p->addr;
 129         u32 insn = BRK64_OPCODE_KPROBES;
 130
 131         aarch64_insn_patch_text(&addr, &insn, 1);
 132 }
 133
 134 /* disarm kprobe: remove breakpoint from text */
 135 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 136 {
 137         void *addr = p->addr;
 138
 139         aarch64_insn_patch_text(&addr, &p->opcode, 1);
 140 }
 141
 142 void __kprobes arch_remove_kprobe(struct kprobe *p)
 143 {
 144         if (p->ainsn.api.insn) {
 145                 free_insn_slot(p->ainsn.api.insn, 0);
 146                 p->ainsn.api.insn = NULL;
 147         }
 148 }
 149
 150 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 151 {
 152         kcb->prev_kprobe.kp = kprobe_running();
 153         kcb->prev_kprobe.status = kcb->kprobe_status;
 154 }
 155
 156 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 157 {
 158         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 159         kcb->kprobe_status = kcb->prev_kprobe.status;
 160 }
 161
 162 static void __kprobes set_current_kprobe(struct kprobe *p)
 163 {
 164         __this_cpu_write(current_kprobe, p);
 165 }
 166
 167 /*
 168  * Mask all of DAIF while executing the instruction out-of-line, to keep things
 169  * simple and avoid nesting exceptions. Interrupts do have to be disabled since
 170  * the kprobe state is per-CPU and doesn't get migrated.
 171  */
 172 static void __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb,
 173                                                 struct pt_regs *regs)
 174 {
 175         kcb->saved_irqflag = regs->pstate & DAIF_MASK;
 176         regs->pstate |= DAIF_MASK;
 177 }
 178
 179 static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
 180                                                 struct pt_regs *regs)
 181 {
 182         regs->pstate &= ~DAIF_MASK;
 183         regs->pstate |= kcb->saved_irqflag;
 184 }
 185
 186 static void __kprobes
 187 set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr)
 188 {
 189         kcb->ss_ctx.ss_pending = true;
 190         kcb->ss_ctx.match_addr = addr + sizeof(kprobe_opcode_t);
 191 }
 192
 193 static void __kprobes clear_ss_context(struct kprobe_ctlblk *kcb)
 194 {
 195         kcb->ss_ctx.ss_pending = false;
 196         kcb->ss_ctx.match_addr = 0;
 197 }
 198
 199 static void __kprobes setup_singlestep(struct kprobe *p,
 200                                        struct pt_regs *regs,
 201                                        struct kprobe_ctlblk *kcb, int reenter)
 202 {
 203         unsigned long slot;
 204
 205         if (reenter) {
 206                 save_previous_kprobe(kcb);
 207                 set_current_kprobe(p);
 208                 kcb->kprobe_status = KPROBE_REENTER;
 209         } else {
 210                 kcb->kprobe_status = KPROBE_HIT_SS;
 211         }
 212
 213
 214         if (p->ainsn.api.insn) {
 215                 /* prepare for single stepping */
 216                 slot = (unsigned long)p->ainsn.api.insn;
 217
 218                 set_ss_context(kcb, slot);      /* mark pending ss */
 219                 kprobes_save_local_irqflag(kcb, regs);
 220                 instruction_pointer_set(regs, slot);
 221         } else {
 222                 /* insn simulation */
 223                 arch_simulate_insn(p, regs);
 224         }
 225 }
 226
 227 static int __kprobes reenter_kprobe(struct kprobe *p,
 228                                     struct pt_regs *regs,
 229                                     struct kprobe_ctlblk *kcb)
 230 {
 231         switch (kcb->kprobe_status) {
 232         case KPROBE_HIT_SSDONE:
 233         case KPROBE_HIT_ACTIVE:
 234                 kprobes_inc_nmissed_count(p);
 235                 setup_singlestep(p, regs, kcb, 1);
 236                 break;
 237         case KPROBE_HIT_SS:
 238         case KPROBE_REENTER:
 239                 pr_warn("Unrecoverable kprobe detected.\n");
 240                 dump_kprobe(p);
 241                 BUG();
 242                 break;
 243         default:
 244                 WARN_ON(1);
 245                 return 0;
 246         }
 247
 248         return 1;
 249 }
 250
 251 static void __kprobes
 252 post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
 253 {
 254         struct kprobe *cur = kprobe_running();
 255
 256         if (!cur)
 257                 return;
 258
 259         /* return addr restore if non-branching insn */
 260         if (cur->ainsn.api.restore != 0)
 261                 instruction_pointer_set(regs, cur->ainsn.api.restore);
 262
 263         /* restore back original saved kprobe variables and continue */
 264         if (kcb->kprobe_status == KPROBE_REENTER) {
 265                 restore_previous_kprobe(kcb);
 266                 return;
 267         }
 268         /* call post handler */
 269         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 270         if (cur->post_handler)
 271                 cur->post_handler(cur, regs, 0);
 272
 273         reset_current_kprobe();
 274 }
 275
 276 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 277 {
 278         struct kprobe *cur = kprobe_running();
 279         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 280
 281         switch (kcb->kprobe_status) {
 282         case KPROBE_HIT_SS:
 283         case KPROBE_REENTER:
 284                 /*
 285                  * We are here because the instruction being single
 286                  * stepped caused a page fault. We reset the current
 287                  * kprobe and the ip points back to the probe address
 288                  * and allow the page fault handler to continue as a
 289                  * normal page fault.
 290                  */
 291                 instruction_pointer_set(regs, (unsigned long) cur->addr);
 292                 if (!instruction_pointer(regs))
 293                         BUG();
 294
 295                 if (kcb->kprobe_status == KPROBE_REENTER)
 296                         restore_previous_kprobe(kcb);
 297                 else
 298                         reset_current_kprobe();
 299
 300                 break;
 301         case KPROBE_HIT_ACTIVE:
 302         case KPROBE_HIT_SSDONE:
 303                 /*
 304                  * We increment the nmissed count for accounting,
 305                  * we can also use npre/npostfault count for accounting
 306                  * these specific fault cases.
 307                  */
 308                 kprobes_inc_nmissed_count(cur);
 309
 310                 /*
 311                  * We come here because instructions in the pre/post
 312                  * handler caused the page_fault, this could happen
 313                  * if handler tries to access user space by
 314                  * copy_from_user(), get_user() etc. Let the
 315                  * user-specified handler try to fix it first.
 316                  */
 317                 if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
 318                         return 1;
 319
 320                 /*
 321                  * In case the user-specified fault handler returned
 322                  * zero, try to fix up.
 323                  */
 324                 if (fixup_exception(regs))
 325                         return 1;
 326         }
 327         return 0;
 328 }
 329
 330 static void __kprobes kprobe_handler(struct pt_regs *regs)
 331 {
 332         struct kprobe *p, *cur_kprobe;
 333         struct kprobe_ctlblk *kcb;
 334         unsigned long addr = instruction_pointer(regs);
 335
 336         kcb = get_kprobe_ctlblk();
 337         cur_kprobe = kprobe_running();
 338
 339         p = get_kprobe((kprobe_opcode_t *) addr);
 340
 341         if (p) {
 342                 if (cur_kprobe) {
 343                         if (reenter_kprobe(p, regs, kcb))
 344                                 return;
 345                 } else {
 346                         /* Probe hit */
 347                         set_current_kprobe(p);
 348                         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 349
 350                         /*
 351                          * If we have no pre-handler or it returned 0, we
 352                          * continue with normal processing.  If we have a
 353                          * pre-handler and it returned non-zero, it will
 354                          * modify the execution path and no need to single
 355                          * stepping. Let's just reset current kprobe and exit.
 356                          */
 357                         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 358                                 setup_singlestep(p, regs, kcb, 0);
 359                         } else
 360                                 reset_current_kprobe();
 361                 }
 362         }
 363         /*
 364          * The breakpoint instruction was removed right
 365          * after we hit it.  Another cpu has removed
 366          * either a probepoint or a debugger breakpoint
 367          * at this address.  In either case, no further
 368          * handling of this interrupt is appropriate.
 369          * Return back to original instruction, and continue.
 370          */
 371 }
 372
 373 static int __kprobes
 374 kprobe_ss_hit(struct kprobe_ctlblk *kcb, unsigned long addr)
 375 {
 376         if ((kcb->ss_ctx.ss_pending)
 377             && (kcb->ss_ctx.match_addr == addr)) {
 378                 clear_ss_context(kcb);  /* clear pending ss */
 379                 return DBG_HOOK_HANDLED;
 380         }
 381         /* not ours, kprobes should ignore it */
 382         return DBG_HOOK_ERROR;
 383 }
 384
 385 static int __kprobes
 386 kprobe_breakpoint_ss_handler(struct pt_regs *regs, unsigned int esr)
 387 {
 388         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 389         int retval;
 390
 391         /* return error if this is not our step */
 392         retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
 393
 394         if (retval == DBG_HOOK_HANDLED) {
 395                 kprobes_restore_local_irqflag(kcb, regs);
 396                 post_kprobe_handler(kcb, regs);
 397         }
 398
 399         return retval;
 400 }
 401
 402 static struct break_hook kprobes_break_ss_hook = {
 403         .imm = KPROBES_BRK_SS_IMM,
 404         .fn = kprobe_breakpoint_ss_handler,
 405 };
 406
 407 static int __kprobes
 408 kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr)
 409 {
 410         kprobe_handler(regs);
 411         return DBG_HOOK_HANDLED;
 412 }
 413
 414 static struct break_hook kprobes_break_hook = {
 415         .imm = KPROBES_BRK_IMM,
 416         .fn = kprobe_breakpoint_handler,
 417 };
 418
 419 /*
 420  * Provide a blacklist of symbols identifying ranges which cannot be kprobed.
 421  * This blacklist is exposed to userspace via debugfs (kprobes/blacklist).
 422  */
 423 int __init arch_populate_kprobe_blacklist(void)
 424 {
 425         int ret;
 426
 427         ret = kprobe_add_area_blacklist((unsigned long)__entry_text_start,
 428                                         (unsigned long)__entry_text_end);
 429         if (ret)
 430                 return ret;
 431         ret = kprobe_add_area_blacklist((unsigned long)__irqentry_text_start,
 432                                         (unsigned long)__irqentry_text_end);
 433         if (ret)
 434                 return ret;
 435         ret = kprobe_add_area_blacklist((unsigned long)__exception_text_start,
 436                                         (unsigned long)__exception_text_end);
 437         if (ret)
 438                 return ret;
 439         ret = kprobe_add_area_blacklist((unsigned long)__idmap_text_start,
 440                                         (unsigned long)__idmap_text_end);
 441         if (ret)
 442                 return ret;
 443         ret = kprobe_add_area_blacklist((unsigned long)__hyp_text_start,
 444                                         (unsigned long)__hyp_text_end);
 445         if (ret || is_kernel_in_hyp_mode())
 446                 return ret;
 447         ret = kprobe_add_area_blacklist((unsigned long)__hyp_idmap_text_start,
 448                                         (unsigned long)__hyp_idmap_text_end);
 449         return ret;
 450 }
 451
 452 void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
 453 {
 454         struct kretprobe_instance *ri = NULL;
 455         struct hlist_head *head, empty_rp;
 456         struct hlist_node *tmp;
 457         unsigned long flags, orig_ret_address = 0;
 458         unsigned long trampoline_address =
 459                 (unsigned long)&kretprobe_trampoline;
 460         kprobe_opcode_t *correct_ret_addr = NULL;
 461
 462         INIT_HLIST_HEAD(&empty_rp);
 463         kretprobe_hash_lock(current, &head, &flags);
 464
 465         /*
 466          * It is possible to have multiple instances associated with a given
 467          * task either because multiple functions in the call path have
 468          * return probes installed on them, and/or more than one
 469          * return probe was registered for a target function.
 470          *
 471          * We can handle this because:
 472          *     - instances are always pushed into the head of the list
 473          *     - when multiple return probes are registered for the same
 474          *       function, the (chronologically) first instance's ret_addr
 475          *       will be the real return address, and all the rest will
 476          *       point to kretprobe_trampoline.
 477          */
 478         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 479                 if (ri->task != current)
 480                         /* another task is sharing our hash bucket */
 481                         continue;
 482
 483                 orig_ret_address = (unsigned long)ri->ret_addr;
 484
 485                 if (orig_ret_address != trampoline_address)
 486                         /*
 487                          * This is the real return address. Any other
 488                          * instances associated with this task are for
 489                          * other calls deeper on the call stack
 490                          */
 491                         break;
 492         }
 493
 494         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 495
 496         correct_ret_addr = ri->ret_addr;
 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                 if (ri->rp && ri->rp->handler) {
 504                         __this_cpu_write(current_kprobe, &ri->rp->kp);
 505                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 506                         ri->ret_addr = correct_ret_addr;
 507                         ri->rp->handler(ri, regs);
 508                         __this_cpu_write(current_kprobe, NULL);
 509                 }
 510
 511                 recycle_rp_inst(ri, &empty_rp);
 512
 513                 if (orig_ret_address != trampoline_address)
 514                         /*
 515                          * This is the real return address. Any other
 516                          * instances associated with this task are for
 517                          * other calls deeper on the call stack
 518                          */
 519                         break;
 520         }
 521
 522         kretprobe_hash_unlock(current, &flags);
 523
 524         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
 525                 hlist_del(&ri->hlist);
 526                 kfree(ri);
 527         }
 528         return (void *)orig_ret_address;
 529 }
 530
 531 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 532                                       struct pt_regs *regs)
 533 {
 534         ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
 535
 536         /* replace return addr (x30) with trampoline */
 537         regs->regs[30] = (long)&kretprobe_trampoline;
 538 }
 539
 540 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 541 {
 542         return 0;
 543 }
 544
 545 int __init arch_init_kprobes(void)
 546 {
 547         register_kernel_break_hook(&kprobes_break_hook);
 548         register_kernel_break_hook(&kprobes_break_ss_hook);
 549
 550         return 0;
 551 }