arch/arm/kernel/kprobes.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/stringify.h>
  28 #include <asm/traps.h>
  29 #include <asm/cacheflush.h>
  30
  31 #define MIN_STACK_SIZE(addr)                            \
  32         min((unsigned long)MAX_STACK_SIZE,              \
  33             (unsigned long)current_thread_info() + THREAD_START_SP - (addr))
  34
  35 #define flush_insns(addr, cnt)                          \
  36         flush_icache_range((unsigned long)(addr),       \
  37                            (unsigned long)(addr) +      \
  38                            sizeof(kprobe_opcode_t) * (cnt))
  39
  40 /* Used as a marker in ARM_pc to note when we're in a jprobe. */
  41 #define JPROBE_MAGIC_ADDR               0xffffffff
  42
  43 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  44 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  45
  46
  47 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  48 {
  49         kprobe_opcode_t insn;
  50         kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
  51         unsigned long addr = (unsigned long)p->addr;
  52         int is;
  53
  54         if (addr & 0x3 || in_exception_text(addr))
  55                 return -EINVAL;
  56
  57         insn = *p->addr;
  58         p->opcode = insn;
  59         p->ainsn.insn = tmp_insn;
  60
  61         switch (arm_kprobe_decode_insn(insn, &p->ainsn)) {
  62         case INSN_REJECTED:     /* not supported */
  63                 return -EINVAL;
  64
  65         case INSN_GOOD:         /* instruction uses slot */
  66                 p->ainsn.insn = get_insn_slot();
  67                 if (!p->ainsn.insn)
  68                         return -ENOMEM;
  69                 for (is = 0; is < MAX_INSN_SIZE; ++is)
  70                         p->ainsn.insn[is] = tmp_insn[is];
  71                 flush_insns(p->ainsn.insn, MAX_INSN_SIZE);
  72                 break;
  73
  74         case INSN_GOOD_NO_SLOT: /* instruction doesn't need insn slot */
  75                 p->ainsn.insn = NULL;
  76                 break;
  77         }
  78
  79         return 0;
  80 }
  81
  82 void __kprobes arch_arm_kprobe(struct kprobe *p)
  83 {
  84         *p->addr = KPROBE_BREAKPOINT_INSTRUCTION;
  85         flush_insns(p->addr, 1);
  86 }
  87
  88 /*
  89  * The actual disarming is done here on each CPU and synchronized using
  90  * stop_machine. This synchronization is necessary on SMP to avoid removing
  91  * a probe between the moment the 'Undefined Instruction' exception is raised
  92  * and the moment the exception handler reads the faulting instruction from
  93  * memory.
  94  */
  95 int __kprobes __arch_disarm_kprobe(void *p)
  96 {
  97         struct kprobe *kp = p;
  98         *kp->addr = kp->opcode;
  99         flush_insns(kp->addr, 1);
 100         return 0;
 101 }
 102
 103 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 104 {
 105         stop_machine(__arch_disarm_kprobe, p, &cpu_online_map);
 106 }
 107
 108 void __kprobes arch_remove_kprobe(struct kprobe *p)
 109 {
 110         if (p->ainsn.insn) {
 111                 free_insn_slot(p->ainsn.insn, 0);
 112                 p->ainsn.insn = NULL;
 113         }
 114 }
 115
 116 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 117 {
 118         kcb->prev_kprobe.kp = kprobe_running();
 119         kcb->prev_kprobe.status = kcb->kprobe_status;
 120 }
 121
 122 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 123 {
 124         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
 125         kcb->kprobe_status = kcb->prev_kprobe.status;
 126 }
 127
 128 static void __kprobes set_current_kprobe(struct kprobe *p)
 129 {
 130         __get_cpu_var(current_kprobe) = p;
 131 }
 132
 133 static void __kprobes singlestep(struct kprobe *p, struct pt_regs *regs,
 134                                  struct kprobe_ctlblk *kcb)
 135 {
 136         regs->ARM_pc += 4;
 137         p->ainsn.insn_handler(p, regs);
 138 }
 139
 140 /*
 141  * Called with IRQs disabled. IRQs must remain disabled from that point
 142  * all the way until processing this kprobe is complete.  The current
 143  * kprobes implementation cannot process more than one nested level of
 144  * kprobe, and that level is reserved for user kprobe handlers, so we can't
 145  * risk encountering a new kprobe in an interrupt handler.
 146  */
 147 void __kprobes kprobe_handler(struct pt_regs *regs)
 148 {
 149         struct kprobe *p, *cur;
 150         struct kprobe_ctlblk *kcb;
 151         kprobe_opcode_t *addr = (kprobe_opcode_t *)regs->ARM_pc;
 152
 153         kcb = get_kprobe_ctlblk();
 154         cur = kprobe_running();
 155         p = get_kprobe(addr);
 156
 157         if (p) {
 158                 if (cur) {
 159                         /* Kprobe is pending, so we're recursing. */
 160                         switch (kcb->kprobe_status) {
 161                         case KPROBE_HIT_ACTIVE:
 162                         case KPROBE_HIT_SSDONE:
 163                                 /* A pre- or post-handler probe got us here. */
 164                                 kprobes_inc_nmissed_count(p);
 165                                 save_previous_kprobe(kcb);
 166                                 set_current_kprobe(p);
 167                                 kcb->kprobe_status = KPROBE_REENTER;
 168                                 singlestep(p, regs, kcb);
 169                                 restore_previous_kprobe(kcb);
 170                                 break;
 171                         default:
 172                                 /* impossible cases */
 173                                 BUG();
 174                         }
 175                 } else {
 176                         set_current_kprobe(p);
 177                         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 178
 179                         /*
 180                          * If we have no pre-handler or it returned 0, we
 181                          * continue with normal processing.  If we have a
 182                          * pre-handler and it returned non-zero, it prepped
 183                          * for calling the break_handler below on re-entry,
 184                          * so get out doing nothing more here.
 185                          */
 186                         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 187                                 kcb->kprobe_status = KPROBE_HIT_SS;
 188                                 singlestep(p, regs, kcb);
 189                                 if (p->post_handler) {
 190                                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 191                                         p->post_handler(p, regs, 0);
 192                                 }
 193                                 reset_current_kprobe();
 194                         }
 195                 }
 196         } else if (cur) {
 197                 /* We probably hit a jprobe.  Call its break handler. */
 198                 if (cur->break_handler && cur->break_handler(cur, regs)) {
 199                         kcb->kprobe_status = KPROBE_HIT_SS;
 200                         singlestep(cur, regs, kcb);
 201                         if (cur->post_handler) {
 202                                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
 203                                 cur->post_handler(cur, regs, 0);
 204                         }
 205                 }
 206                 reset_current_kprobe();
 207         } else {
 208                 /*
 209                  * The probe was removed and a race is in progress.
 210                  * There is nothing we can do about it.  Let's restart
 211                  * the instruction.  By the time we can restart, the
 212                  * real instruction will be there.
 213                  */
 214         }
 215 }
 216
 217 static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
 218 {
 219         unsigned long flags;
 220         local_irq_save(flags);
 221         kprobe_handler(regs);
 222         local_irq_restore(flags);
 223         return 0;
 224 }
 225
 226 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 227 {
 228         struct kprobe *cur = kprobe_running();
 229         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 230
 231         switch (kcb->kprobe_status) {
 232         case KPROBE_HIT_SS:
 233         case KPROBE_REENTER:
 234                 /*
 235                  * We are here because the instruction being single
 236                  * stepped caused a page fault. We reset the current
 237                  * kprobe and the PC to point back to the probe address
 238                  * and allow the page fault handler to continue as a
 239                  * normal page fault.
 240                  */
 241                 regs->ARM_pc = (long)cur->addr;
 242                 if (kcb->kprobe_status == KPROBE_REENTER) {
 243                         restore_previous_kprobe(kcb);
 244                 } else {
 245                         reset_current_kprobe();
 246                 }
 247                 break;
 248
 249         case KPROBE_HIT_ACTIVE:
 250         case KPROBE_HIT_SSDONE:
 251                 /*
 252                  * We increment the nmissed count for accounting,
 253                  * we can also use npre/npostfault count for accounting
 254                  * these specific fault cases.
 255                  */
 256                 kprobes_inc_nmissed_count(cur);
 257
 258                 /*
 259                  * We come here because instructions in the pre/post
 260                  * handler caused the page_fault, this could happen
 261                  * if handler tries to access user space by
 262                  * copy_from_user(), get_user() etc. Let the
 263                  * user-specified handler try to fix it.
 264                  */
 265                 if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
 266                         return 1;
 267                 break;
 268
 269         default:
 270                 break;
 271         }
 272
 273         return 0;
 274 }
 275
 276 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 277                                        unsigned long val, void *data)
 278 {
 279         /*
 280          * notify_die() is currently never called on ARM,
 281          * so this callback is currently empty.
 282          */
 283         return NOTIFY_DONE;
 284 }
 285
 286 /*
 287  * When a retprobed function returns, trampoline_handler() is called,
 288  * calling the kretprobe's handler. We construct a struct pt_regs to
 289  * give a view of registers r0-r11 to the user return-handler.  This is
 290  * not a complete pt_regs structure, but that should be plenty sufficient
 291  * for kretprobe handlers which should normally be interested in r0 only
 292  * anyway.
 293  */
 294 void __naked __kprobes kretprobe_trampoline(void)
 295 {
 296         __asm__ __volatile__ (
 297                 "stmdb  sp!, {r0 - r11}         \n\t"
 298                 "mov    r0, sp                  \n\t"
 299                 "bl     trampoline_handler      \n\t"
 300                 "mov    lr, r0                  \n\t"
 301                 "ldmia  sp!, {r0 - r11}         \n\t"
 302                 "mov    pc, lr                  \n\t"
 303                 : : : "memory");
 304 }
 305
 306 /* Called from kretprobe_trampoline */
 307 static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
 308 {
 309         struct kretprobe_instance *ri = NULL;
 310         struct hlist_head *head, empty_rp;
 311         struct hlist_node *node, *tmp;
 312         unsigned long flags, orig_ret_address = 0;
 313         unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
 314
 315         INIT_HLIST_HEAD(&empty_rp);
 316         kretprobe_hash_lock(current, &head, &flags);
 317
 318         /*
 319          * It is possible to have multiple instances associated with a given
 320          * task either because multiple functions in the call path have
 321          * a return probe installed on them, and/or more than one return
 322          * probe was registered for a target function.
 323          *
 324          * We can handle this because:
 325          *     - instances are always inserted at the head of the list
 326          *     - when multiple return probes are registered for the same
 327          *       function, the first instance's ret_addr will point to the
 328          *       real return address, and all the rest will point to
 329          *       kretprobe_trampoline
 330          */
 331         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
 332                 if (ri->task != current)
 333                         /* another task is sharing our hash bucket */
 334                         continue;
 335
 336                 if (ri->rp && ri->rp->handler) {
 337                         __get_cpu_var(current_kprobe) = &ri->rp->kp;
 338                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 339                         ri->rp->handler(ri, regs);
 340                         __get_cpu_var(current_kprobe) = NULL;
 341                 }
 342
 343                 orig_ret_address = (unsigned long)ri->ret_addr;
 344                 recycle_rp_inst(ri, &empty_rp);
 345
 346                 if (orig_ret_address != trampoline_address)
 347                         /*
 348                          * This is the real return address. Any other
 349                          * instances associated with this task are for
 350                          * other calls deeper on the call stack
 351                          */
 352                         break;
 353         }
 354
 355         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 356         kretprobe_hash_unlock(current, &flags);
 357
 358         hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
 359                 hlist_del(&ri->hlist);
 360                 kfree(ri);
 361         }
 362
 363         return (void *)orig_ret_address;
 364 }
 365
 366 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 367                                       struct pt_regs *regs)
 368 {
 369         ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr;
 370
 371         /* Replace the return addr with trampoline addr. */
 372         regs->ARM_lr = (unsigned long)&kretprobe_trampoline;
 373 }
 374
 375 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 376 {
 377         struct jprobe *jp = container_of(p, struct jprobe, kp);
 378         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 379         long sp_addr = regs->ARM_sp;
 380
 381         kcb->jprobe_saved_regs = *regs;
 382         memcpy(kcb->jprobes_stack, (void *)sp_addr, MIN_STACK_SIZE(sp_addr));
 383         regs->ARM_pc = (long)jp->entry;
 384         regs->ARM_cpsr |= PSR_I_BIT;
 385         preempt_disable();
 386         return 1;
 387 }
 388
 389 void __kprobes jprobe_return(void)
 390 {
 391         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 392
 393         __asm__ __volatile__ (
 394                 /*
 395                  * Setup an empty pt_regs. Fill SP and PC fields as
 396                  * they're needed by longjmp_break_handler.
 397                  *
 398                  * We allocate some slack between the original SP and start of
 399                  * our fabricated regs. To be precise we want to have worst case
 400                  * covered which is STMFD with all 16 regs so we allocate 2 *
 401                  * sizeof(struct_pt_regs)).
 402                  *
 403                  * This is to prevent any simulated instruction from writing
 404                  * over the regs when they are accessing the stack.
 405                  */
 406                 "sub    sp, %0, %1              \n\t"
 407                 "ldr    r0, ="__stringify(JPROBE_MAGIC_ADDR)"\n\t"
 408                 "str    %0, [sp, %2]            \n\t"
 409                 "str    r0, [sp, %3]            \n\t"
 410                 "mov    r0, sp                  \n\t"
 411                 "bl     kprobe_handler          \n\t"
 412
 413                 /*
 414                  * Return to the context saved by setjmp_pre_handler
 415                  * and restored by longjmp_break_handler.
 416                  */
 417                 "ldr    r0, [sp, %4]            \n\t"
 418                 "msr    cpsr_cxsf, r0           \n\t"
 419                 "ldmia  sp, {r0 - pc}           \n\t"
 420                 :
 421                 : "r" (kcb->jprobe_saved_regs.ARM_sp),
 422                   "I" (sizeof(struct pt_regs) * 2),
 423                   "J" (offsetof(struct pt_regs, ARM_sp)),
 424                   "J" (offsetof(struct pt_regs, ARM_pc)),
 425                   "J" (offsetof(struct pt_regs, ARM_cpsr))
 426                 : "memory", "cc");
 427 }
 428
 429 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 430 {
 431         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 432         long stack_addr = kcb->jprobe_saved_regs.ARM_sp;
 433         long orig_sp = regs->ARM_sp;
 434         struct jprobe *jp = container_of(p, struct jprobe, kp);
 435
 436         if (regs->ARM_pc == JPROBE_MAGIC_ADDR) {
 437                 if (orig_sp != stack_addr) {
 438                         struct pt_regs *saved_regs =
 439                                 (struct pt_regs *)kcb->jprobe_saved_regs.ARM_sp;
 440                         printk("current sp %lx does not match saved sp %lx\n",
 441                                orig_sp, stack_addr);
 442                         printk("Saved registers for jprobe %p\n", jp);
 443                         show_regs(saved_regs);
 444                         printk("Current registers\n");
 445                         show_regs(regs);
 446                         BUG();
 447                 }
 448                 *regs = kcb->jprobe_saved_regs;
 449                 memcpy((void *)stack_addr, kcb->jprobes_stack,
 450                        MIN_STACK_SIZE(stack_addr));
 451                 preempt_enable_no_resched();
 452                 return 1;
 453         }
 454         return 0;
 455 }
 456
 457 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 458 {
 459         return 0;
 460 }
 461
 462 static struct undef_hook kprobes_break_hook = {
 463         .instr_mask     = 0xffffffff,
 464         .instr_val      = KPROBE_BREAKPOINT_INSTRUCTION,
 465         .cpsr_mask      = MODE_MASK,
 466         .cpsr_val       = SVC_MODE,
 467         .fn             = kprobe_trap_handler,
 468 };
 469
 470 int __init arch_init_kprobes()
 471 {
 472         arm_kprobe_decode_init();
 473         register_undef_hook(&kprobes_break_hook);
 474         return 0;
 475 }