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 /*
  30  * This undefined instruction must be unique and
  31  * reserved solely for kprobes' use.
  32  */
  33 #define KPROBE_BREAKPOINT_INSTRUCTION   0xe7f001f8
  34
  35 #define MIN_STACK_SIZE(addr)                            \
  36         min((unsigned long)MAX_STACK_SIZE,              \
  37             (unsigned long)current_thread_info() + THREAD_START_SP - (addr))
  38
  39 #define flush_insns(addr, cnt)                          \
  40         flush_icache_range((unsigned long)(addr),       \
  41                            (unsigned long)(addr) +      \
  42                            sizeof(kprobe_opcode_t) * (cnt))
  43
  44 /* Used as a marker in ARM_pc to note when we're in a jprobe. */
  45 #define JPROBE_MAGIC_ADDR               0xffffffff
  46
  47 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  48 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  49
  50
  51 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  52 {
  53         kprobe_opcode_t insn;
  54         kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
  55         unsigned long addr = (unsigned long)p->addr;
  56         int is;
  57
  58         if (addr & 0x3 || in_exception_text(addr))
  59                 return -EINVAL;
  60
  61         insn = *p->addr;
  62         p->opcode = insn;
  63         p->ainsn.insn = tmp_insn;
  64
  65         switch (arm_kprobe_decode_insn(insn, &p->ainsn)) {
  66         case INSN_REJECTED:     /* not supported */
  67                 return -EINVAL;
  68
  69         case INSN_GOOD:         /* instruction uses slot */
  70                 p->ainsn.insn = get_insn_slot();
  71                 if (!p->ainsn.insn)
  72                         return -ENOMEM;
  73                 for (is = 0; is < MAX_INSN_SIZE; ++is)
  74                         p->ainsn.insn[is] = tmp_insn[is];
  75                 flush_insns(&p->ainsn.insn, MAX_INSN_SIZE);
  76                 break;
  77
  78         case INSN_GOOD_NO_SLOT: /* instruction doesn't need insn slot */
  79                 p->ainsn.insn = NULL;
  80                 break;
  81         }
  82
  83         return 0;
  84 }
  85
  86 void __kprobes arch_arm_kprobe(struct kprobe *p)
  87 {
  88         *p->addr = KPROBE_BREAKPOINT_INSTRUCTION;
  89         flush_insns(p->addr, 1);
  90 }
  91
  92 void __kprobes arch_disarm_kprobe(struct kprobe *p)
  93 {
  94         *p->addr = p->opcode;
  95         flush_insns(p->addr, 1);
  96 }
  97
  98 void __kprobes arch_remove_kprobe(struct kprobe *p)
  99 {
 100         if (p->ainsn.insn) {
 101                 mutex_lock(&kprobe_mutex);
 102                 free_insn_slot(p->ainsn.insn, 0);
 103                 mutex_unlock(&kprobe_mutex);
 104                 p->ainsn.insn = NULL;
 105         }
 106 }
 107
 108 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 109 {
 110         kcb->prev_kprobe.kp = kprobe_running();
 111         kcb->prev_kprobe.status = kcb->kprobe_status;
 112 }
 113
 114 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 115 {
 116         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
 117         kcb->kprobe_status = kcb->prev_kprobe.status;
 118 }
 119
 120 static void __kprobes set_current_kprobe(struct kprobe *p)
 121 {
 122         __get_cpu_var(current_kprobe) = p;
 123 }
 124
 125 static void __kprobes singlestep(struct kprobe *p, struct pt_regs *regs,
 126                                  struct kprobe_ctlblk *kcb)
 127 {
 128         regs->ARM_pc += 4;
 129         p->ainsn.insn_handler(p, regs);
 130 }
 131
 132 /*
 133  * Called with IRQs disabled. IRQs must remain disabled from that point
 134  * all the way until processing this kprobe is complete.  The current
 135  * kprobes implementation cannot process more than one nested level of
 136  * kprobe, and that level is reserved for user kprobe handlers, so we can't
 137  * risk encountering a new kprobe in an interrupt handler.
 138  */
 139 void __kprobes kprobe_handler(struct pt_regs *regs)
 140 {
 141         struct kprobe *p, *cur;
 142         struct kprobe_ctlblk *kcb;
 143         kprobe_opcode_t *addr = (kprobe_opcode_t *)regs->ARM_pc;
 144
 145         kcb = get_kprobe_ctlblk();
 146         cur = kprobe_running();
 147         p = get_kprobe(addr);
 148
 149         if (p) {
 150                 if (cur) {
 151                         /* Kprobe is pending, so we're recursing. */
 152                         switch (kcb->kprobe_status) {
 153                         case KPROBE_HIT_ACTIVE:
 154                         case KPROBE_HIT_SSDONE:
 155                                 /* A pre- or post-handler probe got us here. */
 156                                 kprobes_inc_nmissed_count(p);
 157                                 save_previous_kprobe(kcb);
 158                                 set_current_kprobe(p);
 159                                 kcb->kprobe_status = KPROBE_REENTER;
 160                                 singlestep(p, regs, kcb);
 161                                 restore_previous_kprobe(kcb);
 162                                 break;
 163                         default:
 164                                 /* impossible cases */
 165                                 BUG();
 166                         }
 167                 } else {
 168                         set_current_kprobe(p);
 169                         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 170
 171                         /*
 172                          * If we have no pre-handler or it returned 0, we
 173                          * continue with normal processing.  If we have a
 174                          * pre-handler and it returned non-zero, it prepped
 175                          * for calling the break_handler below on re-entry,
 176                          * so get out doing nothing more here.
 177                          */
 178                         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 179                                 kcb->kprobe_status = KPROBE_HIT_SS;
 180                                 singlestep(p, regs, kcb);
 181                                 if (p->post_handler) {
 182                                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 183                                         p->post_handler(p, regs, 0);
 184                                 }
 185                                 reset_current_kprobe();
 186                         }
 187                 }
 188         } else if (cur) {
 189                 /* We probably hit a jprobe.  Call its break handler. */
 190                 if (cur->break_handler && cur->break_handler(cur, regs)) {
 191                         kcb->kprobe_status = KPROBE_HIT_SS;
 192                         singlestep(cur, regs, kcb);
 193                         if (cur->post_handler) {
 194                                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
 195                                 cur->post_handler(cur, regs, 0);
 196                         }
 197                 }
 198                 reset_current_kprobe();
 199         } else {
 200                 /*
 201                  * The probe was removed and a race is in progress.
 202                  * There is nothing we can do about it.  Let's restart
 203                  * the instruction.  By the time we can restart, the
 204                  * real instruction will be there.
 205                  */
 206         }
 207 }
 208
 209 static int kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
 210 {
 211         kprobe_handler(regs);
 212         return 0;
 213 }
 214
 215 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 216 {
 217         struct kprobe *cur = kprobe_running();
 218         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 219
 220         switch (kcb->kprobe_status) {
 221         case KPROBE_HIT_SS:
 222         case KPROBE_REENTER:
 223                 /*
 224                  * We are here because the instruction being single
 225                  * stepped caused a page fault. We reset the current
 226                  * kprobe and the PC to point back to the probe address
 227                  * and allow the page fault handler to continue as a
 228                  * normal page fault.
 229                  */
 230                 regs->ARM_pc = (long)cur->addr;
 231                 if (kcb->kprobe_status == KPROBE_REENTER) {
 232                         restore_previous_kprobe(kcb);
 233                 } else {
 234                         reset_current_kprobe();
 235                 }
 236                 break;
 237
 238         case KPROBE_HIT_ACTIVE:
 239         case KPROBE_HIT_SSDONE:
 240                 /*
 241                  * We increment the nmissed count for accounting,
 242                  * we can also use npre/npostfault count for accounting
 243                  * these specific fault cases.
 244                  */
 245                 kprobes_inc_nmissed_count(cur);
 246
 247                 /*
 248                  * We come here because instructions in the pre/post
 249                  * handler caused the page_fault, this could happen
 250                  * if handler tries to access user space by
 251                  * copy_from_user(), get_user() etc. Let the
 252                  * user-specified handler try to fix it.
 253                  */
 254                 if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
 255                         return 1;
 256                 break;
 257
 258         default:
 259                 break;
 260         }
 261
 262         return 0;
 263 }
 264
 265 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 266                                        unsigned long val, void *data)
 267 {
 268         /*
 269          * notify_die() is currently never called on ARM,
 270          * so this callback is currently empty.
 271          */
 272         return NOTIFY_DONE;
 273 }
 274
 275 /*
 276  * When a retprobed function returns, trampoline_handler() is called,
 277  * calling the kretprobe's handler. We construct a struct pt_regs to
 278  * give a view of registers r0-r11 to the user return-handler.  This is
 279  * not a complete pt_regs structure, but that should be plenty sufficient
 280  * for kretprobe handlers which should normally be interested in r0 only
 281  * anyway.
 282  */
 283 static void __attribute__((naked)) __kprobes kretprobe_trampoline(void)
 284 {
 285         __asm__ __volatile__ (
 286                 "stmdb  sp!, {r0 - r11}         \n\t"
 287                 "mov    r0, sp                  \n\t"
 288                 "bl     trampoline_handler      \n\t"
 289                 "mov    lr, r0                  \n\t"
 290                 "ldmia  sp!, {r0 - r11}         \n\t"
 291                 "mov    pc, lr                  \n\t"
 292                 : : : "memory");
 293 }
 294
 295 /* Called from kretprobe_trampoline */
 296 static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
 297 {
 298         struct kretprobe_instance *ri = NULL;
 299         struct hlist_head *head, empty_rp;
 300         struct hlist_node *node, *tmp;
 301         unsigned long flags, orig_ret_address = 0;
 302         unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
 303
 304         INIT_HLIST_HEAD(&empty_rp);
 305         spin_lock_irqsave(&kretprobe_lock, flags);
 306         head = kretprobe_inst_table_head(current);
 307
 308         /*
 309          * It is possible to have multiple instances associated with a given
 310          * task either because multiple functions in the call path have
 311          * a return probe installed on them, and/or more than one return
 312          * probe was registered for a target function.
 313          *
 314          * We can handle this because:
 315          *     - instances are always inserted at the head of the list
 316          *     - when multiple return probes are registered for the same
 317          *       function, the first instance's ret_addr will point to the
 318          *       real return address, and all the rest will point to
 319          *       kretprobe_trampoline
 320          */
 321         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
 322                 if (ri->task != current)
 323                         /* another task is sharing our hash bucket */
 324                         continue;
 325
 326                 if (ri->rp && ri->rp->handler) {
 327                         __get_cpu_var(current_kprobe) = &ri->rp->kp;
 328                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 329                         ri->rp->handler(ri, regs);
 330                         __get_cpu_var(current_kprobe) = NULL;
 331                 }
 332
 333                 orig_ret_address = (unsigned long)ri->ret_addr;
 334                 recycle_rp_inst(ri, &empty_rp);
 335
 336                 if (orig_ret_address != trampoline_address)
 337                         /*
 338                          * This is the real return address. Any other
 339                          * instances associated with this task are for
 340                          * other calls deeper on the call stack
 341                          */
 342                         break;
 343         }
 344
 345         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 346         spin_unlock_irqrestore(&kretprobe_lock, flags);
 347
 348         hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
 349                 hlist_del(&ri->hlist);
 350                 kfree(ri);
 351         }
 352
 353         return (void *)orig_ret_address;
 354 }
 355
 356 /* Called with kretprobe_lock held. */
 357 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 358                                       struct pt_regs *regs)
 359 {
 360         ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr;
 361
 362         /* Replace the return addr with trampoline addr. */
 363         regs->ARM_lr = (unsigned long)&kretprobe_trampoline;
 364 }
 365
 366 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 367 {
 368         struct jprobe *jp = container_of(p, struct jprobe, kp);
 369         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 370         long sp_addr = regs->ARM_sp;
 371
 372         kcb->jprobe_saved_regs = *regs;
 373         memcpy(kcb->jprobes_stack, (void *)sp_addr, MIN_STACK_SIZE(sp_addr));
 374         regs->ARM_pc = (long)jp->entry;
 375         regs->ARM_cpsr |= PSR_I_BIT;
 376         preempt_disable();
 377         return 1;
 378 }
 379
 380 void __kprobes jprobe_return(void)
 381 {
 382         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 383
 384         __asm__ __volatile__ (
 385                 /*
 386                  * Setup an empty pt_regs. Fill SP and PC fields as
 387                  * they're needed by longjmp_break_handler.
 388                  */
 389                 "sub    sp, %0, %1              \n\t"
 390                 "ldr    r0, ="__stringify(JPROBE_MAGIC_ADDR)"\n\t"
 391                 "str    %0, [sp, %2]            \n\t"
 392                 "str    r0, [sp, %3]            \n\t"
 393                 "mov    r0, sp                  \n\t"
 394                 "bl     kprobe_handler          \n\t"
 395
 396                 /*
 397                  * Return to the context saved by setjmp_pre_handler
 398                  * and restored by longjmp_break_handler.
 399                  */
 400                 "ldr    r0, [sp, %4]            \n\t"
 401                 "msr    cpsr_cxsf, r0           \n\t"
 402                 "ldmia  sp, {r0 - pc}           \n\t"
 403                 :
 404                 : "r" (kcb->jprobe_saved_regs.ARM_sp),
 405                   "I" (sizeof(struct pt_regs)),
 406                   "J" (offsetof(struct pt_regs, ARM_sp)),
 407                   "J" (offsetof(struct pt_regs, ARM_pc)),
 408                   "J" (offsetof(struct pt_regs, ARM_cpsr))
 409                 : "memory", "cc");
 410 }
 411
 412 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 413 {
 414         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 415         long stack_addr = kcb->jprobe_saved_regs.ARM_sp;
 416         long orig_sp = regs->ARM_sp;
 417         struct jprobe *jp = container_of(p, struct jprobe, kp);
 418
 419         if (regs->ARM_pc == JPROBE_MAGIC_ADDR) {
 420                 if (orig_sp != stack_addr) {
 421                         struct pt_regs *saved_regs =
 422                                 (struct pt_regs *)kcb->jprobe_saved_regs.ARM_sp;
 423                         printk("current sp %lx does not match saved sp %lx\n",
 424                                orig_sp, stack_addr);
 425                         printk("Saved registers for jprobe %p\n", jp);
 426                         show_regs(saved_regs);
 427                         printk("Current registers\n");
 428                         show_regs(regs);
 429                         BUG();
 430                 }
 431                 *regs = kcb->jprobe_saved_regs;
 432                 memcpy((void *)stack_addr, kcb->jprobes_stack,
 433                        MIN_STACK_SIZE(stack_addr));
 434                 preempt_enable_no_resched();
 435                 return 1;
 436         }
 437         return 0;
 438 }
 439
 440 static struct undef_hook kprobes_break_hook = {
 441         .instr_mask     = 0xffffffff,
 442         .instr_val      = KPROBE_BREAKPOINT_INSTRUCTION,
 443         .cpsr_mask      = MODE_MASK,
 444         .cpsr_val       = SVC_MODE,
 445         .fn             = kprobe_trap_handler,
 446 };
 447
 448 int __init arch_init_kprobes()
 449 {
 450         arm_kprobe_decode_init();
 451         register_undef_hook(&kprobes_break_hook);
 452         return 0;
 453 }