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