arch/arm/probes/kprobes/core.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * arch/arm/kernel/kprobes.c
   4  *
   5  * Kprobes on ARM
   6  *
   7  * Abhishek Sagar <sagar.abhishek@gmail.com>
   8  * Copyright (C) 2006, 2007 Motorola Inc.
   9  *
  10  * Nicolas Pitre <nico@marvell.com>
  11  * Copyright (C) 2007 Marvell Ltd.
  12  */
  13
  14 #include <linux/kernel.h>
  15 #include <linux/kprobes.h>
  16 #include <linux/module.h>
  17 #include <linux/slab.h>
  18 #include <linux/stop_machine.h>
  19 #include <linux/sched/debug.h>
  20 #include <linux/stringify.h>
  21 #include <asm/traps.h>
  22 #include <asm/opcodes.h>
  23 #include <asm/cacheflush.h>
  24 #include <linux/percpu.h>
  25 #include <linux/bug.h>
  26 #include <asm/patch.h>
  27 #include <asm/sections.h>
  28
  29 #include "../decode-arm.h"
  30 #include "../decode-thumb.h"
  31 #include "core.h"
  32
  33 #define MIN_STACK_SIZE(addr)                            \
  34         min((unsigned long)MAX_STACK_SIZE,              \
  35             (unsigned long)current_thread_info() + THREAD_START_SP - (addr))
  36
  37 #define flush_insns(addr, size)                         \
  38         flush_icache_range((unsigned long)(addr),       \
  39                            (unsigned long)(addr) +      \
  40                            (size))
  41
  42 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  43 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  44
  45
  46 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  47 {
  48         kprobe_opcode_t insn;
  49         kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
  50         unsigned long addr = (unsigned long)p->addr;
  51         bool thumb;
  52         kprobe_decode_insn_t *decode_insn;
  53         const union decode_action *actions;
  54         int is;
  55         const struct decode_checker **checkers;
  56
  57 #ifdef CONFIG_THUMB2_KERNEL
  58         thumb = true;
  59         addr &= ~1; /* Bit 0 would normally be set to indicate Thumb code */
  60         insn = __mem_to_opcode_thumb16(((u16 *)addr)[0]);
  61         if (is_wide_instruction(insn)) {
  62                 u16 inst2 = __mem_to_opcode_thumb16(((u16 *)addr)[1]);
  63                 insn = __opcode_thumb32_compose(insn, inst2);
  64                 decode_insn = thumb32_probes_decode_insn;
  65                 actions = kprobes_t32_actions;
  66                 checkers = kprobes_t32_checkers;
  67         } else {
  68                 decode_insn = thumb16_probes_decode_insn;
  69                 actions = kprobes_t16_actions;
  70                 checkers = kprobes_t16_checkers;
  71         }
  72 #else /* !CONFIG_THUMB2_KERNEL */
  73         thumb = false;
  74         if (addr & 0x3)
  75                 return -EINVAL;
  76         insn = __mem_to_opcode_arm(*p->addr);
  77         decode_insn = arm_probes_decode_insn;
  78         actions = kprobes_arm_actions;
  79         checkers = kprobes_arm_checkers;
  80 #endif
  81
  82         p->opcode = insn;
  83         p->ainsn.insn = tmp_insn;
  84
  85         switch ((*decode_insn)(insn, &p->ainsn, true, actions, checkers)) {
  86         case INSN_REJECTED:     /* not supported */
  87                 return -EINVAL;
  88
  89         case INSN_GOOD:         /* instruction uses slot */
  90                 p->ainsn.insn = get_insn_slot();
  91                 if (!p->ainsn.insn)
  92                         return -ENOMEM;
  93                 for (is = 0; is < MAX_INSN_SIZE; ++is)
  94                         p->ainsn.insn[is] = tmp_insn[is];
  95                 flush_insns(p->ainsn.insn,
  96                                 sizeof(p->ainsn.insn[0]) * MAX_INSN_SIZE);
  97                 p->ainsn.insn_fn = (probes_insn_fn_t *)
  98                                         ((uintptr_t)p->ainsn.insn | thumb);
  99                 break;
 100
 101         case INSN_GOOD_NO_SLOT: /* instruction doesn't need insn slot */
 102                 p->ainsn.insn = NULL;
 103                 break;
 104         }
 105
 106         /*
 107          * Never instrument insn like 'str r0, [sp, +/-r1]'. Also, insn likes
 108          * 'str r0, [sp, #-68]' should also be prohibited.
 109          * See __und_svc.
 110          */
 111         if ((p->ainsn.stack_space < 0) ||
 112                         (p->ainsn.stack_space > MAX_STACK_SIZE))
 113                 return -EINVAL;
 114
 115         return 0;
 116 }
 117
 118 void __kprobes arch_arm_kprobe(struct kprobe *p)
 119 {
 120         unsigned int brkp;
 121         void *addr;
 122
 123         if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
 124                 /* Remove any Thumb flag */
 125                 addr = (void *)((uintptr_t)p->addr & ~1);
 126
 127                 if (is_wide_instruction(p->opcode))
 128                         brkp = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION;
 129                 else
 130                         brkp = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION;
 131         } else {
 132                 kprobe_opcode_t insn = p->opcode;
 133
 134                 addr = p->addr;
 135                 brkp = KPROBE_ARM_BREAKPOINT_INSTRUCTION;
 136
 137                 if (insn >= 0xe0000000)
 138                         brkp |= 0xe0000000;  /* Unconditional instruction */
 139                 else
 140                         brkp |= insn & 0xf0000000;  /* Copy condition from insn */
 141         }
 142
 143         patch_text(addr, brkp);
 144 }
 145
 146 /*
 147  * The actual disarming is done here on each CPU and synchronized using
 148  * stop_machine. This synchronization is necessary on SMP to avoid removing
 149  * a probe between the moment the 'Undefined Instruction' exception is raised
 150  * and the moment the exception handler reads the faulting instruction from
 151  * memory. It is also needed to atomically set the two half-words of a 32-bit
 152  * Thumb breakpoint.
 153  */
 154 struct patch {
 155         void *addr;
 156         unsigned int insn;
 157 };
 158
 159 static int __kprobes_remove_breakpoint(void *data)
 160 {
 161         struct patch *p = data;
 162         __patch_text(p->addr, p->insn);
 163         return 0;
 164 }
 165
 166 void __kprobes kprobes_remove_breakpoint(void *addr, unsigned int insn)
 167 {
 168         struct patch p = {
 169                 .addr = addr,
 170                 .insn = insn,
 171         };
 172         stop_machine_cpuslocked(__kprobes_remove_breakpoint, &p,
 173                                 cpu_online_mask);
 174 }
 175
 176 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 177 {
 178         kprobes_remove_breakpoint((void *)((uintptr_t)p->addr & ~1),
 179                         p->opcode);
 180 }
 181
 182 void __kprobes arch_remove_kprobe(struct kprobe *p)
 183 {
 184         if (p->ainsn.insn) {
 185                 free_insn_slot(p->ainsn.insn, 0);
 186                 p->ainsn.insn = NULL;
 187         }
 188 }
 189
 190 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 191 {
 192         kcb->prev_kprobe.kp = kprobe_running();
 193         kcb->prev_kprobe.status = kcb->kprobe_status;
 194 }
 195
 196 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 197 {
 198         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 199         kcb->kprobe_status = kcb->prev_kprobe.status;
 200 }
 201
 202 static void __kprobes set_current_kprobe(struct kprobe *p)
 203 {
 204         __this_cpu_write(current_kprobe, p);
 205 }
 206
 207 static void __kprobes
 208 singlestep_skip(struct kprobe *p, struct pt_regs *regs)
 209 {
 210 #ifdef CONFIG_THUMB2_KERNEL
 211         regs->ARM_cpsr = it_advance(regs->ARM_cpsr);
 212         if (is_wide_instruction(p->opcode))
 213                 regs->ARM_pc += 4;
 214         else
 215                 regs->ARM_pc += 2;
 216 #else
 217         regs->ARM_pc += 4;
 218 #endif
 219 }
 220
 221 static inline void __kprobes
 222 singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb)
 223 {
 224         p->ainsn.insn_singlestep(p->opcode, &p->ainsn, regs);
 225 }
 226
 227 /*
 228  * Called with IRQs disabled. IRQs must remain disabled from that point
 229  * all the way until processing this kprobe is complete.  The current
 230  * kprobes implementation cannot process more than one nested level of
 231  * kprobe, and that level is reserved for user kprobe handlers, so we can't
 232  * risk encountering a new kprobe in an interrupt handler.
 233  */
 234 void __kprobes kprobe_handler(struct pt_regs *regs)
 235 {
 236         struct kprobe *p, *cur;
 237         struct kprobe_ctlblk *kcb;
 238
 239         kcb = get_kprobe_ctlblk();
 240         cur = kprobe_running();
 241
 242 #ifdef CONFIG_THUMB2_KERNEL
 243         /*
 244          * First look for a probe which was registered using an address with
 245          * bit 0 set, this is the usual situation for pointers to Thumb code.
 246          * If not found, fallback to looking for one with bit 0 clear.
 247          */
 248         p = get_kprobe((kprobe_opcode_t *)(regs->ARM_pc | 1));
 249         if (!p)
 250                 p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
 251
 252 #else /* ! CONFIG_THUMB2_KERNEL */
 253         p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
 254 #endif
 255
 256         if (p) {
 257                 if (!p->ainsn.insn_check_cc(regs->ARM_cpsr)) {
 258                         /*
 259                          * Probe hit but conditional execution check failed,
 260                          * so just skip the instruction and continue as if
 261                          * nothing had happened.
 262                          * In this case, we can skip recursing check too.
 263                          */
 264                         singlestep_skip(p, regs);
 265                 } else if (cur) {
 266                         /* Kprobe is pending, so we're recursing. */
 267                         switch (kcb->kprobe_status) {
 268                         case KPROBE_HIT_ACTIVE:
 269                         case KPROBE_HIT_SSDONE:
 270                         case KPROBE_HIT_SS:
 271                                 /* A pre- or post-handler probe got us here. */
 272                                 kprobes_inc_nmissed_count(p);
 273                                 save_previous_kprobe(kcb);
 274                                 set_current_kprobe(p);
 275                                 kcb->kprobe_status = KPROBE_REENTER;
 276                                 singlestep(p, regs, kcb);
 277                                 restore_previous_kprobe(kcb);
 278                                 break;
 279                         case KPROBE_REENTER:
 280                                 /* A nested probe was hit in FIQ, it is a BUG */
 281                                 pr_warn("Unrecoverable kprobe detected.\n");
 282                                 dump_kprobe(p);
 283                                 /* fall through */
 284                         default:
 285                                 /* impossible cases */
 286                                 BUG();
 287                         }
 288                 } else {
 289                         /* Probe hit and conditional execution check ok. */
 290                         set_current_kprobe(p);
 291                         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 292
 293                         /*
 294                          * If we have no pre-handler or it returned 0, we
 295                          * continue with normal processing. If we have a
 296                          * pre-handler and it returned non-zero, it will
 297                          * modify the execution path and no need to single
 298                          * stepping. Let's just reset current kprobe and exit.
 299                          */
 300                         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 301                                 kcb->kprobe_status = KPROBE_HIT_SS;
 302                                 singlestep(p, regs, kcb);
 303                                 if (p->post_handler) {
 304                                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 305                                         p->post_handler(p, regs, 0);
 306                                 }
 307                         }
 308                         reset_current_kprobe();
 309                 }
 310         } else {
 311                 /*
 312                  * The probe was removed and a race is in progress.
 313                  * There is nothing we can do about it.  Let's restart
 314                  * the instruction.  By the time we can restart, the
 315                  * real instruction will be there.
 316                  */
 317         }
 318 }
 319
 320 static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
 321 {
 322         unsigned long flags;
 323         local_irq_save(flags);
 324         kprobe_handler(regs);
 325         local_irq_restore(flags);
 326         return 0;
 327 }
 328
 329 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 330 {
 331         struct kprobe *cur = kprobe_running();
 332         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 333
 334         switch (kcb->kprobe_status) {
 335         case KPROBE_HIT_SS:
 336         case KPROBE_REENTER:
 337                 /*
 338                  * We are here because the instruction being single
 339                  * stepped caused a page fault. We reset the current
 340                  * kprobe and the PC to point back to the probe address
 341                  * and allow the page fault handler to continue as a
 342                  * normal page fault.
 343                  */
 344                 regs->ARM_pc = (long)cur->addr;
 345                 if (kcb->kprobe_status == KPROBE_REENTER) {
 346                         restore_previous_kprobe(kcb);
 347                 } else {
 348                         reset_current_kprobe();
 349                 }
 350                 break;
 351
 352         case KPROBE_HIT_ACTIVE:
 353         case KPROBE_HIT_SSDONE:
 354                 /*
 355                  * We increment the nmissed count for accounting,
 356                  * we can also use npre/npostfault count for accounting
 357                  * these specific fault cases.
 358                  */
 359                 kprobes_inc_nmissed_count(cur);
 360
 361                 /*
 362                  * We come here because instructions in the pre/post
 363                  * handler caused the page_fault, this could happen
 364                  * if handler tries to access user space by
 365                  * copy_from_user(), get_user() etc. Let the
 366                  * user-specified handler try to fix it.
 367                  */
 368                 if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
 369                         return 1;
 370                 break;
 371
 372         default:
 373                 break;
 374         }
 375
 376         return 0;
 377 }
 378
 379 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 380                                        unsigned long val, void *data)
 381 {
 382         /*
 383          * notify_die() is currently never called on ARM,
 384          * so this callback is currently empty.
 385          */
 386         return NOTIFY_DONE;
 387 }
 388
 389 /*
 390  * When a retprobed function returns, trampoline_handler() is called,
 391  * calling the kretprobe's handler. We construct a struct pt_regs to
 392  * give a view of registers r0-r11 to the user return-handler.  This is
 393  * not a complete pt_regs structure, but that should be plenty sufficient
 394  * for kretprobe handlers which should normally be interested in r0 only
 395  * anyway.
 396  */
 397 void __naked __kprobes kretprobe_trampoline(void)
 398 {
 399         __asm__ __volatile__ (
 400                 "stmdb  sp!, {r0 - r11}         \n\t"
 401                 "mov    r0, sp                  \n\t"
 402                 "bl     trampoline_handler      \n\t"
 403                 "mov    lr, r0                  \n\t"
 404                 "ldmia  sp!, {r0 - r11}         \n\t"
 405 #ifdef CONFIG_THUMB2_KERNEL
 406                 "bx     lr                      \n\t"
 407 #else
 408                 "mov    pc, lr                  \n\t"
 409 #endif
 410                 : : : "memory");
 411 }
 412
 413 /* Called from kretprobe_trampoline */
 414 static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
 415 {
 416         struct kretprobe_instance *ri = NULL;
 417         struct hlist_head *head, empty_rp;
 418         struct hlist_node *tmp;
 419         unsigned long flags, orig_ret_address = 0;
 420         unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
 421         kprobe_opcode_t *correct_ret_addr = NULL;
 422
 423         INIT_HLIST_HEAD(&empty_rp);
 424         kretprobe_hash_lock(current, &head, &flags);
 425
 426         /*
 427          * It is possible to have multiple instances associated with a given
 428          * task either because multiple functions in the call path have
 429          * a return probe installed on them, and/or more than one return
 430          * probe was registered for a target function.
 431          *
 432          * We can handle this because:
 433          *     - instances are always inserted at the head of the list
 434          *     - when multiple return probes are registered for the same
 435          *       function, the first instance's ret_addr will point to the
 436          *       real return address, and all the rest will point to
 437          *       kretprobe_trampoline
 438          */
 439         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 440                 if (ri->task != current)
 441                         /* another task is sharing our hash bucket */
 442                         continue;
 443
 444                 orig_ret_address = (unsigned long)ri->ret_addr;
 445
 446                 if (orig_ret_address != trampoline_address)
 447                         /*
 448                          * This is the real return address. Any other
 449                          * instances associated with this task are for
 450                          * other calls deeper on the call stack
 451                          */
 452                         break;
 453         }
 454
 455         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 456
 457         correct_ret_addr = ri->ret_addr;
 458         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 459                 if (ri->task != current)
 460                         /* another task is sharing our hash bucket */
 461                         continue;
 462
 463                 orig_ret_address = (unsigned long)ri->ret_addr;
 464                 if (ri->rp && ri->rp->handler) {
 465                         __this_cpu_write(current_kprobe, &ri->rp->kp);
 466                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 467                         ri->ret_addr = correct_ret_addr;
 468                         ri->rp->handler(ri, regs);
 469                         __this_cpu_write(current_kprobe, NULL);
 470                 }
 471
 472                 recycle_rp_inst(ri, &empty_rp);
 473
 474                 if (orig_ret_address != trampoline_address)
 475                         /*
 476                          * This is the real return address. Any other
 477                          * instances associated with this task are for
 478                          * other calls deeper on the call stack
 479                          */
 480                         break;
 481         }
 482
 483         kretprobe_hash_unlock(current, &flags);
 484
 485         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
 486                 hlist_del(&ri->hlist);
 487                 kfree(ri);
 488         }
 489
 490         return (void *)orig_ret_address;
 491 }
 492
 493 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 494                                       struct pt_regs *regs)
 495 {
 496         ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr;
 497
 498         /* Replace the return addr with trampoline addr. */
 499         regs->ARM_lr = (unsigned long)&kretprobe_trampoline;
 500 }
 501
 502 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 503 {
 504         return 0;
 505 }
 506
 507 #ifdef CONFIG_THUMB2_KERNEL
 508
 509 static struct undef_hook kprobes_thumb16_break_hook = {
 510         .instr_mask     = 0xffff,
 511         .instr_val      = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION,
 512         .cpsr_mask      = MODE_MASK,
 513         .cpsr_val       = SVC_MODE,
 514         .fn             = kprobe_trap_handler,
 515 };
 516
 517 static struct undef_hook kprobes_thumb32_break_hook = {
 518         .instr_mask     = 0xffffffff,
 519         .instr_val      = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION,
 520         .cpsr_mask      = MODE_MASK,
 521         .cpsr_val       = SVC_MODE,
 522         .fn             = kprobe_trap_handler,
 523 };
 524
 525 #else  /* !CONFIG_THUMB2_KERNEL */
 526
 527 static struct undef_hook kprobes_arm_break_hook = {
 528         .instr_mask     = 0x0fffffff,
 529         .instr_val      = KPROBE_ARM_BREAKPOINT_INSTRUCTION,
 530         .cpsr_mask      = MODE_MASK,
 531         .cpsr_val       = SVC_MODE,
 532         .fn             = kprobe_trap_handler,
 533 };
 534
 535 #endif /* !CONFIG_THUMB2_KERNEL */
 536
 537 int __init arch_init_kprobes()
 538 {
 539         arm_probes_decode_init();
 540 #ifdef CONFIG_THUMB2_KERNEL
 541         register_undef_hook(&kprobes_thumb16_break_hook);
 542         register_undef_hook(&kprobes_thumb32_break_hook);
 543 #else
 544         register_undef_hook(&kprobes_arm_break_hook);
 545 #endif
 546         return 0;
 547 }
 548
 549 bool arch_within_kprobe_blacklist(unsigned long addr)
 550 {
 551         void *a = (void *)addr;
 552
 553         return __in_irqentry_text(addr) ||
 554                in_entry_text(addr) ||
 555                in_idmap_text(addr) ||
 556                memory_contains(__kprobes_text_start, __kprobes_text_end, a, 1);
 557 }