arch/arm/probes/kprobes/core.c

   1 /*
   2  * arch/arm/kernel/kprobes.c
   3  *
   4  * Kprobes on ARM
   5  *
   6  * Abhishek Sagar <sagar.abhishek@gmail.com>
   7  * Copyright (C) 2006, 2007 Motorola Inc.
   8  *
   9  * Nicolas Pitre <nico@marvell.com>
  10  * Copyright (C) 2007 Marvell Ltd.
  11  *
  12  * This program is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU General Public License version 2 as
  14  * published by the Free Software Foundation.
  15  *
  16  * This program is distributed in the hope that it will be useful,
  17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  19  * General Public License for more details.
  20  */
  21
  22 #include <linux/kernel.h>
  23 #include <linux/kprobes.h>
  24 #include <linux/module.h>
  25 #include <linux/slab.h>
  26 #include <linux/stop_machine.h>
  27 #include <linux/sched/debug.h>
  28 #include <linux/stringify.h>
  29 #include <asm/traps.h>
  30 #include <asm/opcodes.h>
  31 #include <asm/cacheflush.h>
  32 #include <linux/percpu.h>
  33 #include <linux/bug.h>
  34 #include <asm/patch.h>
  35 #include <asm/sections.h>
  36
  37 #include "../decode-arm.h"
  38 #include "../decode-thumb.h"
  39 #include "core.h"
  40
  41 #define MIN_STACK_SIZE(addr)                            \
  42         min((unsigned long)MAX_STACK_SIZE,              \
  43             (unsigned long)current_thread_info() + THREAD_START_SP - (addr))
  44
  45 #define flush_insns(addr, size)                         \
  46         flush_icache_range((unsigned long)(addr),       \
  47                            (unsigned long)(addr) +      \
  48                            (size))
  49
  50 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  51 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  52
  53
  54 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  55 {
  56         kprobe_opcode_t insn;
  57         kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
  58         unsigned long addr = (unsigned long)p->addr;
  59         bool thumb;
  60         kprobe_decode_insn_t *decode_insn;
  61         const union decode_action *actions;
  62         int is;
  63         const struct decode_checker **checkers;
  64
  65 #ifdef CONFIG_THUMB2_KERNEL
  66         thumb = true;
  67         addr &= ~1; /* Bit 0 would normally be set to indicate Thumb code */
  68         insn = __mem_to_opcode_thumb16(((u16 *)addr)[0]);
  69         if (is_wide_instruction(insn)) {
  70                 u16 inst2 = __mem_to_opcode_thumb16(((u16 *)addr)[1]);
  71                 insn = __opcode_thumb32_compose(insn, inst2);
  72                 decode_insn = thumb32_probes_decode_insn;
  73                 actions = kprobes_t32_actions;
  74                 checkers = kprobes_t32_checkers;
  75         } else {
  76                 decode_insn = thumb16_probes_decode_insn;
  77                 actions = kprobes_t16_actions;
  78                 checkers = kprobes_t16_checkers;
  79         }
  80 #else /* !CONFIG_THUMB2_KERNEL */
  81         thumb = false;
  82         if (addr & 0x3)
  83                 return -EINVAL;
  84         insn = __mem_to_opcode_arm(*p->addr);
  85         decode_insn = arm_probes_decode_insn;
  86         actions = kprobes_arm_actions;
  87         checkers = kprobes_arm_checkers;
  88 #endif
  89
  90         p->opcode = insn;
  91         p->ainsn.insn = tmp_insn;
  92
  93         switch ((*decode_insn)(insn, &p->ainsn, true, actions, checkers)) {
  94         case INSN_REJECTED:     /* not supported */
  95                 return -EINVAL;
  96
  97         case INSN_GOOD:         /* instruction uses slot */
  98                 p->ainsn.insn = get_insn_slot();
  99                 if (!p->ainsn.insn)
 100                         return -ENOMEM;
 101                 for (is = 0; is < MAX_INSN_SIZE; ++is)
 102                         p->ainsn.insn[is] = tmp_insn[is];
 103                 flush_insns(p->ainsn.insn,
 104                                 sizeof(p->ainsn.insn[0]) * MAX_INSN_SIZE);
 105                 p->ainsn.insn_fn = (probes_insn_fn_t *)
 106                                         ((uintptr_t)p->ainsn.insn | thumb);
 107                 break;
 108
 109         case INSN_GOOD_NO_SLOT: /* instruction doesn't need insn slot */
 110                 p->ainsn.insn = NULL;
 111                 break;
 112         }
 113
 114         /*
 115          * Never instrument insn like 'str r0, [sp, +/-r1]'. Also, insn likes
 116          * 'str r0, [sp, #-68]' should also be prohibited.
 117          * See __und_svc.
 118          */
 119         if ((p->ainsn.stack_space < 0) ||
 120                         (p->ainsn.stack_space > MAX_STACK_SIZE))
 121                 return -EINVAL;
 122
 123         return 0;
 124 }
 125
 126 void __kprobes arch_arm_kprobe(struct kprobe *p)
 127 {
 128         unsigned int brkp;
 129         void *addr;
 130
 131         if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
 132                 /* Remove any Thumb flag */
 133                 addr = (void *)((uintptr_t)p->addr & ~1);
 134
 135                 if (is_wide_instruction(p->opcode))
 136                         brkp = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION;
 137                 else
 138                         brkp = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION;
 139         } else {
 140                 kprobe_opcode_t insn = p->opcode;
 141
 142                 addr = p->addr;
 143                 brkp = KPROBE_ARM_BREAKPOINT_INSTRUCTION;
 144
 145                 if (insn >= 0xe0000000)
 146                         brkp |= 0xe0000000;  /* Unconditional instruction */
 147                 else
 148                         brkp |= insn & 0xf0000000;  /* Copy condition from insn */
 149         }
 150
 151         patch_text(addr, brkp);
 152 }
 153
 154 /*
 155  * The actual disarming is done here on each CPU and synchronized using
 156  * stop_machine. This synchronization is necessary on SMP to avoid removing
 157  * a probe between the moment the 'Undefined Instruction' exception is raised
 158  * and the moment the exception handler reads the faulting instruction from
 159  * memory. It is also needed to atomically set the two half-words of a 32-bit
 160  * Thumb breakpoint.
 161  */
 162 struct patch {
 163         void *addr;
 164         unsigned int insn;
 165 };
 166
 167 static int __kprobes_remove_breakpoint(void *data)
 168 {
 169         struct patch *p = data;
 170         __patch_text(p->addr, p->insn);
 171         return 0;
 172 }
 173
 174 void __kprobes kprobes_remove_breakpoint(void *addr, unsigned int insn)
 175 {
 176         struct patch p = {
 177                 .addr = addr,
 178                 .insn = insn,
 179         };
 180         stop_machine_cpuslocked(__kprobes_remove_breakpoint, &p,
 181                                 cpu_online_mask);
 182 }
 183
 184 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 185 {
 186         kprobes_remove_breakpoint((void *)((uintptr_t)p->addr & ~1),
 187                         p->opcode);
 188 }
 189
 190 void __kprobes arch_remove_kprobe(struct kprobe *p)
 191 {
 192         if (p->ainsn.insn) {
 193                 free_insn_slot(p->ainsn.insn, 0);
 194                 p->ainsn.insn = NULL;
 195         }
 196 }
 197
 198 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 199 {
 200         kcb->prev_kprobe.kp = kprobe_running();
 201         kcb->prev_kprobe.status = kcb->kprobe_status;
 202 }
 203
 204 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 205 {
 206         __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 207         kcb->kprobe_status = kcb->prev_kprobe.status;
 208 }
 209
 210 static void __kprobes set_current_kprobe(struct kprobe *p)
 211 {
 212         __this_cpu_write(current_kprobe, p);
 213 }
 214
 215 static void __kprobes
 216 singlestep_skip(struct kprobe *p, struct pt_regs *regs)
 217 {
 218 #ifdef CONFIG_THUMB2_KERNEL
 219         regs->ARM_cpsr = it_advance(regs->ARM_cpsr);
 220         if (is_wide_instruction(p->opcode))
 221                 regs->ARM_pc += 4;
 222         else
 223                 regs->ARM_pc += 2;
 224 #else
 225         regs->ARM_pc += 4;
 226 #endif
 227 }
 228
 229 static inline void __kprobes
 230 singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb)
 231 {
 232         p->ainsn.insn_singlestep(p->opcode, &p->ainsn, regs);
 233 }
 234
 235 /*
 236  * Called with IRQs disabled. IRQs must remain disabled from that point
 237  * all the way until processing this kprobe is complete.  The current
 238  * kprobes implementation cannot process more than one nested level of
 239  * kprobe, and that level is reserved for user kprobe handlers, so we can't
 240  * risk encountering a new kprobe in an interrupt handler.
 241  */
 242 void __kprobes kprobe_handler(struct pt_regs *regs)
 243 {
 244         struct kprobe *p, *cur;
 245         struct kprobe_ctlblk *kcb;
 246
 247         kcb = get_kprobe_ctlblk();
 248         cur = kprobe_running();
 249
 250 #ifdef CONFIG_THUMB2_KERNEL
 251         /*
 252          * First look for a probe which was registered using an address with
 253          * bit 0 set, this is the usual situation for pointers to Thumb code.
 254          * If not found, fallback to looking for one with bit 0 clear.
 255          */
 256         p = get_kprobe((kprobe_opcode_t *)(regs->ARM_pc | 1));
 257         if (!p)
 258                 p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
 259
 260 #else /* ! CONFIG_THUMB2_KERNEL */
 261         p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
 262 #endif
 263
 264         if (p) {
 265                 if (!p->ainsn.insn_check_cc(regs->ARM_cpsr)) {
 266                         /*
 267                          * Probe hit but conditional execution check failed,
 268                          * so just skip the instruction and continue as if
 269                          * nothing had happened.
 270                          * In this case, we can skip recursing check too.
 271                          */
 272                         singlestep_skip(p, regs);
 273                 } else if (cur) {
 274                         /* Kprobe is pending, so we're recursing. */
 275                         switch (kcb->kprobe_status) {
 276                         case KPROBE_HIT_ACTIVE:
 277                         case KPROBE_HIT_SSDONE:
 278                         case KPROBE_HIT_SS:
 279                                 /* A pre- or post-handler probe got us here. */
 280                                 kprobes_inc_nmissed_count(p);
 281                                 save_previous_kprobe(kcb);
 282                                 set_current_kprobe(p);
 283                                 kcb->kprobe_status = KPROBE_REENTER;
 284                                 singlestep(p, regs, kcb);
 285                                 restore_previous_kprobe(kcb);
 286                                 break;
 287                         case KPROBE_REENTER:
 288                                 /* A nested probe was hit in FIQ, it is a BUG */
 289                                 pr_warn("Unrecoverable kprobe detected.\n");
 290                                 dump_kprobe(p);
 291                                 /* fall through */
 292                         default:
 293                                 /* impossible cases */
 294                                 BUG();
 295                         }
 296                 } else {
 297                         /* Probe hit and conditional execution check ok. */
 298                         set_current_kprobe(p);
 299                         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 300
 301                         /*
 302                          * If we have no pre-handler or it returned 0, we
 303                          * continue with normal processing. If we have a
 304                          * pre-handler and it returned non-zero, it will
 305                          * modify the execution path and no need to single
 306                          * stepping. Let's just reset current kprobe and exit.
 307                          */
 308                         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 309                                 kcb->kprobe_status = KPROBE_HIT_SS;
 310                                 singlestep(p, regs, kcb);
 311                                 if (p->post_handler) {
 312                                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 313                                         p->post_handler(p, regs, 0);
 314                                 }
 315                         }
 316                         reset_current_kprobe();
 317                 }
 318         } else {
 319                 /*
 320                  * The probe was removed and a race is in progress.
 321                  * There is nothing we can do about it.  Let's restart
 322                  * the instruction.  By the time we can restart, the
 323                  * real instruction will be there.
 324                  */
 325         }
 326 }
 327
 328 static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
 329 {
 330         unsigned long flags;
 331         local_irq_save(flags);
 332         kprobe_handler(regs);
 333         local_irq_restore(flags);
 334         return 0;
 335 }
 336
 337 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 338 {
 339         struct kprobe *cur = kprobe_running();
 340         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 341
 342         switch (kcb->kprobe_status) {
 343         case KPROBE_HIT_SS:
 344         case KPROBE_REENTER:
 345                 /*
 346                  * We are here because the instruction being single
 347                  * stepped caused a page fault. We reset the current
 348                  * kprobe and the PC to point back to the probe address
 349                  * and allow the page fault handler to continue as a
 350                  * normal page fault.
 351                  */
 352                 regs->ARM_pc = (long)cur->addr;
 353                 if (kcb->kprobe_status == KPROBE_REENTER) {
 354                         restore_previous_kprobe(kcb);
 355                 } else {
 356                         reset_current_kprobe();
 357                 }
 358                 break;
 359
 360         case KPROBE_HIT_ACTIVE:
 361         case KPROBE_HIT_SSDONE:
 362                 /*
 363                  * We increment the nmissed count for accounting,
 364                  * we can also use npre/npostfault count for accounting
 365                  * these specific fault cases.
 366                  */
 367                 kprobes_inc_nmissed_count(cur);
 368
 369                 /*
 370                  * We come here because instructions in the pre/post
 371                  * handler caused the page_fault, this could happen
 372                  * if handler tries to access user space by
 373                  * copy_from_user(), get_user() etc. Let the
 374                  * user-specified handler try to fix it.
 375                  */
 376                 if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
 377                         return 1;
 378                 break;
 379
 380         default:
 381                 break;
 382         }
 383
 384         return 0;
 385 }
 386
 387 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 388                                        unsigned long val, void *data)
 389 {
 390         /*
 391          * notify_die() is currently never called on ARM,
 392          * so this callback is currently empty.
 393          */
 394         return NOTIFY_DONE;
 395 }
 396
 397 /*
 398  * When a retprobed function returns, trampoline_handler() is called,
 399  * calling the kretprobe's handler. We construct a struct pt_regs to
 400  * give a view of registers r0-r11 to the user return-handler.  This is
 401  * not a complete pt_regs structure, but that should be plenty sufficient
 402  * for kretprobe handlers which should normally be interested in r0 only
 403  * anyway.
 404  */
 405 void __naked __kprobes kretprobe_trampoline(void)
 406 {
 407         __asm__ __volatile__ (
 408                 "stmdb  sp!, {r0 - r11}         \n\t"
 409                 "mov    r0, sp                  \n\t"
 410                 "bl     trampoline_handler      \n\t"
 411                 "mov    lr, r0                  \n\t"
 412                 "ldmia  sp!, {r0 - r11}         \n\t"
 413 #ifdef CONFIG_THUMB2_KERNEL
 414                 "bx     lr                      \n\t"
 415 #else
 416                 "mov    pc, lr                  \n\t"
 417 #endif
 418                 : : : "memory");
 419 }
 420
 421 /* Called from kretprobe_trampoline */
 422 static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
 423 {
 424         struct kretprobe_instance *ri = NULL;
 425         struct hlist_head *head, empty_rp;
 426         struct hlist_node *tmp;
 427         unsigned long flags, orig_ret_address = 0;
 428         unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
 429         kprobe_opcode_t *correct_ret_addr = NULL;
 430
 431         INIT_HLIST_HEAD(&empty_rp);
 432         kretprobe_hash_lock(current, &head, &flags);
 433
 434         /*
 435          * It is possible to have multiple instances associated with a given
 436          * task either because multiple functions in the call path have
 437          * a return probe installed on them, and/or more than one return
 438          * probe was registered for a target function.
 439          *
 440          * We can handle this because:
 441          *     - instances are always inserted at the head of the list
 442          *     - when multiple return probes are registered for the same
 443          *       function, the first instance's ret_addr will point to the
 444          *       real return address, and all the rest will point to
 445          *       kretprobe_trampoline
 446          */
 447         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 448                 if (ri->task != current)
 449                         /* another task is sharing our hash bucket */
 450                         continue;
 451
 452                 orig_ret_address = (unsigned long)ri->ret_addr;
 453
 454                 if (orig_ret_address != trampoline_address)
 455                         /*
 456                          * This is the real return address. Any other
 457                          * instances associated with this task are for
 458                          * other calls deeper on the call stack
 459                          */
 460                         break;
 461         }
 462
 463         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 464
 465         correct_ret_addr = ri->ret_addr;
 466         hlist_for_each_entry_safe(ri, tmp, head, hlist) {
 467                 if (ri->task != current)
 468                         /* another task is sharing our hash bucket */
 469                         continue;
 470
 471                 orig_ret_address = (unsigned long)ri->ret_addr;
 472                 if (ri->rp && ri->rp->handler) {
 473                         __this_cpu_write(current_kprobe, &ri->rp->kp);
 474                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 475                         ri->ret_addr = correct_ret_addr;
 476                         ri->rp->handler(ri, regs);
 477                         __this_cpu_write(current_kprobe, NULL);
 478                 }
 479
 480                 recycle_rp_inst(ri, &empty_rp);
 481
 482                 if (orig_ret_address != trampoline_address)
 483                         /*
 484                          * This is the real return address. Any other
 485                          * instances associated with this task are for
 486                          * other calls deeper on the call stack
 487                          */
 488                         break;
 489         }
 490
 491         kretprobe_hash_unlock(current, &flags);
 492
 493         hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
 494                 hlist_del(&ri->hlist);
 495                 kfree(ri);
 496         }
 497
 498         return (void *)orig_ret_address;
 499 }
 500
 501 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 502                                       struct pt_regs *regs)
 503 {
 504         ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr;
 505
 506         /* Replace the return addr with trampoline addr. */
 507         regs->ARM_lr = (unsigned long)&kretprobe_trampoline;
 508 }
 509
 510 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 511 {
 512         return 0;
 513 }
 514
 515 #ifdef CONFIG_THUMB2_KERNEL
 516
 517 static struct undef_hook kprobes_thumb16_break_hook = {
 518         .instr_mask     = 0xffff,
 519         .instr_val      = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION,
 520         .cpsr_mask      = MODE_MASK,
 521         .cpsr_val       = SVC_MODE,
 522         .fn             = kprobe_trap_handler,
 523 };
 524
 525 static struct undef_hook kprobes_thumb32_break_hook = {
 526         .instr_mask     = 0xffffffff,
 527         .instr_val      = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION,
 528         .cpsr_mask      = MODE_MASK,
 529         .cpsr_val       = SVC_MODE,
 530         .fn             = kprobe_trap_handler,
 531 };
 532
 533 #else  /* !CONFIG_THUMB2_KERNEL */
 534
 535 static struct undef_hook kprobes_arm_break_hook = {
 536         .instr_mask     = 0x0fffffff,
 537         .instr_val      = KPROBE_ARM_BREAKPOINT_INSTRUCTION,
 538         .cpsr_mask      = MODE_MASK,
 539         .cpsr_val       = SVC_MODE,
 540         .fn             = kprobe_trap_handler,
 541 };
 542
 543 #endif /* !CONFIG_THUMB2_KERNEL */
 544
 545 int __init arch_init_kprobes()
 546 {
 547         arm_probes_decode_init();
 548 #ifdef CONFIG_THUMB2_KERNEL
 549         register_undef_hook(&kprobes_thumb16_break_hook);
 550         register_undef_hook(&kprobes_thumb32_break_hook);
 551 #else
 552         register_undef_hook(&kprobes_arm_break_hook);
 553 #endif
 554         return 0;
 555 }
 556
 557 bool arch_within_kprobe_blacklist(unsigned long addr)
 558 {
 559         void *a = (void *)addr;
 560
 561         return __in_irqentry_text(addr) ||
 562                in_entry_text(addr) ||
 563                in_idmap_text(addr) ||
 564                memory_contains(__kprobes_text_start, __kprobes_text_end, a, 1);
 565 }