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