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 #include "kprobes.h"
  32
  33 #define MIN_STACK_SIZE(addr)                            \
  34         min((unsigned long)MAX_STACK_SIZE,              \
  35             (unsigned long)current_thread_info() + THREAD_START_SP - (addr))
  36
  37 #define flush_insns(addr, cnt)                          \
  38         flush_icache_range((unsigned long)(addr),       \
  39                            (unsigned long)(addr) +      \
  40                            sizeof(kprobe_opcode_t) * (cnt))
  41
  42 /* Used as a marker in ARM_pc to note when we're in a jprobe. */
  43 #define JPROBE_MAGIC_ADDR               0xffffffff
  44
  45 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  46 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  47
  48
  49 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  50 {
  51         kprobe_opcode_t insn;
  52         kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
  53         unsigned long addr = (unsigned long)p->addr;
  54         kprobe_decode_insn_t *decode_insn;
  55         int is;
  56
  57         if (in_exception_text(addr))
  58                 return -EINVAL;
  59
  60 #ifdef CONFIG_THUMB2_KERNEL
  61         addr &= ~1; /* Bit 0 would normally be set to indicate Thumb code */
  62         insn = ((u16 *)addr)[0];
  63         if (is_wide_instruction(insn)) {
  64                 insn <<= 16;
  65                 insn |= ((u16 *)addr)[1];
  66                 decode_insn = thumb32_kprobe_decode_insn;
  67         } else
  68                 decode_insn = thumb16_kprobe_decode_insn;
  69 #else /* !CONFIG_THUMB2_KERNEL */
  70         if (addr & 0x3)
  71                 return -EINVAL;
  72         insn = *p->addr;
  73         decode_insn = arm_kprobe_decode_insn;
  74 #endif
  75
  76         p->opcode = insn;
  77         p->ainsn.insn = tmp_insn;
  78
  79         switch ((*decode_insn)(insn, &p->ainsn)) {
  80         case INSN_REJECTED:     /* not supported */
  81                 return -EINVAL;
  82
  83         case INSN_GOOD:         /* instruction uses slot */
  84                 p->ainsn.insn = get_insn_slot();
  85                 if (!p->ainsn.insn)
  86                         return -ENOMEM;
  87                 for (is = 0; is < MAX_INSN_SIZE; ++is)
  88                         p->ainsn.insn[is] = tmp_insn[is];
  89                 flush_insns(p->ainsn.insn, MAX_INSN_SIZE);
  90                 break;
  91
  92         case INSN_GOOD_NO_SLOT: /* instruction doesn't need insn slot */
  93                 p->ainsn.insn = NULL;
  94                 break;
  95         }
  96
  97         return 0;
  98 }
  99
 100 void __kprobes arch_arm_kprobe(struct kprobe *p)
 101 {
 102         *p->addr = KPROBE_BREAKPOINT_INSTRUCTION;
 103         flush_insns(p->addr, 1);
 104 }
 105
 106 /*
 107  * The actual disarming is done here on each CPU and synchronized using
 108  * stop_machine. This synchronization is necessary on SMP to avoid removing
 109  * a probe between the moment the 'Undefined Instruction' exception is raised
 110  * and the moment the exception handler reads the faulting instruction from
 111  * memory.
 112  */
 113 int __kprobes __arch_disarm_kprobe(void *p)
 114 {
 115         struct kprobe *kp = p;
 116         *kp->addr = kp->opcode;
 117         flush_insns(kp->addr, 1);
 118         return 0;
 119 }
 120
 121 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 122 {
 123         stop_machine(__arch_disarm_kprobe, p, &cpu_online_map);
 124 }
 125
 126 void __kprobes arch_remove_kprobe(struct kprobe *p)
 127 {
 128         if (p->ainsn.insn) {
 129                 free_insn_slot(p->ainsn.insn, 0);
 130                 p->ainsn.insn = NULL;
 131         }
 132 }
 133
 134 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 135 {
 136         kcb->prev_kprobe.kp = kprobe_running();
 137         kcb->prev_kprobe.status = kcb->kprobe_status;
 138 }
 139
 140 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 141 {
 142         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
 143         kcb->kprobe_status = kcb->prev_kprobe.status;
 144 }
 145
 146 static void __kprobes set_current_kprobe(struct kprobe *p)
 147 {
 148         __get_cpu_var(current_kprobe) = p;
 149 }
 150
 151 static void __kprobes singlestep(struct kprobe *p, struct pt_regs *regs,
 152                                  struct kprobe_ctlblk *kcb)
 153 {
 154         regs->ARM_pc += 4;
 155         if (p->ainsn.insn_check_cc(regs->ARM_cpsr))
 156                 p->ainsn.insn_handler(p, regs);
 157 }
 158
 159 /*
 160  * Called with IRQs disabled. IRQs must remain disabled from that point
 161  * all the way until processing this kprobe is complete.  The current
 162  * kprobes implementation cannot process more than one nested level of
 163  * kprobe, and that level is reserved for user kprobe handlers, so we can't
 164  * risk encountering a new kprobe in an interrupt handler.
 165  */
 166 void __kprobes kprobe_handler(struct pt_regs *regs)
 167 {
 168         struct kprobe *p, *cur;
 169         struct kprobe_ctlblk *kcb;
 170         kprobe_opcode_t *addr = (kprobe_opcode_t *)regs->ARM_pc;
 171
 172         kcb = get_kprobe_ctlblk();
 173         cur = kprobe_running();
 174         p = get_kprobe(addr);
 175
 176         if (p) {
 177                 if (cur) {
 178                         /* Kprobe is pending, so we're recursing. */
 179                         switch (kcb->kprobe_status) {
 180                         case KPROBE_HIT_ACTIVE:
 181                         case KPROBE_HIT_SSDONE:
 182                                 /* A pre- or post-handler probe got us here. */
 183                                 kprobes_inc_nmissed_count(p);
 184                                 save_previous_kprobe(kcb);
 185                                 set_current_kprobe(p);
 186                                 kcb->kprobe_status = KPROBE_REENTER;
 187                                 singlestep(p, regs, kcb);
 188                                 restore_previous_kprobe(kcb);
 189                                 break;
 190                         default:
 191                                 /* impossible cases */
 192                                 BUG();
 193                         }
 194                 } else {
 195                         set_current_kprobe(p);
 196                         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 197
 198                         /*
 199                          * If we have no pre-handler or it returned 0, we
 200                          * continue with normal processing.  If we have a
 201                          * pre-handler and it returned non-zero, it prepped
 202                          * for calling the break_handler below on re-entry,
 203                          * so get out doing nothing more here.
 204                          */
 205                         if (!p->pre_handler || !p->pre_handler(p, regs)) {
 206                                 kcb->kprobe_status = KPROBE_HIT_SS;
 207                                 singlestep(p, regs, kcb);
 208                                 if (p->post_handler) {
 209                                         kcb->kprobe_status = KPROBE_HIT_SSDONE;
 210                                         p->post_handler(p, regs, 0);
 211                                 }
 212                                 reset_current_kprobe();
 213                         }
 214                 }
 215         } else if (cur) {
 216                 /* We probably hit a jprobe.  Call its break handler. */
 217                 if (cur->break_handler && cur->break_handler(cur, regs)) {
 218                         kcb->kprobe_status = KPROBE_HIT_SS;
 219                         singlestep(cur, regs, kcb);
 220                         if (cur->post_handler) {
 221                                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
 222                                 cur->post_handler(cur, regs, 0);
 223                         }
 224                 }
 225                 reset_current_kprobe();
 226         } else {
 227                 /*
 228                  * The probe was removed and a race is in progress.
 229                  * There is nothing we can do about it.  Let's restart
 230                  * the instruction.  By the time we can restart, the
 231                  * real instruction will be there.
 232                  */
 233         }
 234 }
 235
 236 static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
 237 {
 238         unsigned long flags;
 239         local_irq_save(flags);
 240         kprobe_handler(regs);
 241         local_irq_restore(flags);
 242         return 0;
 243 }
 244
 245 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
 246 {
 247         struct kprobe *cur = kprobe_running();
 248         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 249
 250         switch (kcb->kprobe_status) {
 251         case KPROBE_HIT_SS:
 252         case KPROBE_REENTER:
 253                 /*
 254                  * We are here because the instruction being single
 255                  * stepped caused a page fault. We reset the current
 256                  * kprobe and the PC to point back to the probe address
 257                  * and allow the page fault handler to continue as a
 258                  * normal page fault.
 259                  */
 260                 regs->ARM_pc = (long)cur->addr;
 261                 if (kcb->kprobe_status == KPROBE_REENTER) {
 262                         restore_previous_kprobe(kcb);
 263                 } else {
 264                         reset_current_kprobe();
 265                 }
 266                 break;
 267
 268         case KPROBE_HIT_ACTIVE:
 269         case KPROBE_HIT_SSDONE:
 270                 /*
 271                  * We increment the nmissed count for accounting,
 272                  * we can also use npre/npostfault count for accounting
 273                  * these specific fault cases.
 274                  */
 275                 kprobes_inc_nmissed_count(cur);
 276
 277                 /*
 278                  * We come here because instructions in the pre/post
 279                  * handler caused the page_fault, this could happen
 280                  * if handler tries to access user space by
 281                  * copy_from_user(), get_user() etc. Let the
 282                  * user-specified handler try to fix it.
 283                  */
 284                 if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
 285                         return 1;
 286                 break;
 287
 288         default:
 289                 break;
 290         }
 291
 292         return 0;
 293 }
 294
 295 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 296                                        unsigned long val, void *data)
 297 {
 298         /*
 299          * notify_die() is currently never called on ARM,
 300          * so this callback is currently empty.
 301          */
 302         return NOTIFY_DONE;
 303 }
 304
 305 /*
 306  * When a retprobed function returns, trampoline_handler() is called,
 307  * calling the kretprobe's handler. We construct a struct pt_regs to
 308  * give a view of registers r0-r11 to the user return-handler.  This is
 309  * not a complete pt_regs structure, but that should be plenty sufficient
 310  * for kretprobe handlers which should normally be interested in r0 only
 311  * anyway.
 312  */
 313 void __naked __kprobes kretprobe_trampoline(void)
 314 {
 315         __asm__ __volatile__ (
 316                 "stmdb  sp!, {r0 - r11}         \n\t"
 317                 "mov    r0, sp                  \n\t"
 318                 "bl     trampoline_handler      \n\t"
 319                 "mov    lr, r0                  \n\t"
 320                 "ldmia  sp!, {r0 - r11}         \n\t"
 321 #ifdef CONFIG_THUMB2_KERNEL
 322                 "bx     lr                      \n\t"
 323 #else
 324                 "mov    pc, lr                  \n\t"
 325 #endif
 326                 : : : "memory");
 327 }
 328
 329 /* Called from kretprobe_trampoline */
 330 static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
 331 {
 332         struct kretprobe_instance *ri = NULL;
 333         struct hlist_head *head, empty_rp;
 334         struct hlist_node *node, *tmp;
 335         unsigned long flags, orig_ret_address = 0;
 336         unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
 337
 338         INIT_HLIST_HEAD(&empty_rp);
 339         kretprobe_hash_lock(current, &head, &flags);
 340
 341         /*
 342          * It is possible to have multiple instances associated with a given
 343          * task either because multiple functions in the call path have
 344          * a return probe installed on them, and/or more than one return
 345          * probe was registered for a target function.
 346          *
 347          * We can handle this because:
 348          *     - instances are always inserted at the head of the list
 349          *     - when multiple return probes are registered for the same
 350          *       function, the first instance's ret_addr will point to the
 351          *       real return address, and all the rest will point to
 352          *       kretprobe_trampoline
 353          */
 354         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
 355                 if (ri->task != current)
 356                         /* another task is sharing our hash bucket */
 357                         continue;
 358
 359                 if (ri->rp && ri->rp->handler) {
 360                         __get_cpu_var(current_kprobe) = &ri->rp->kp;
 361                         get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
 362                         ri->rp->handler(ri, regs);
 363                         __get_cpu_var(current_kprobe) = NULL;
 364                 }
 365
 366                 orig_ret_address = (unsigned long)ri->ret_addr;
 367                 recycle_rp_inst(ri, &empty_rp);
 368
 369                 if (orig_ret_address != trampoline_address)
 370                         /*
 371                          * This is the real return address. Any other
 372                          * instances associated with this task are for
 373                          * other calls deeper on the call stack
 374                          */
 375                         break;
 376         }
 377
 378         kretprobe_assert(ri, orig_ret_address, trampoline_address);
 379         kretprobe_hash_unlock(current, &flags);
 380
 381         hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
 382                 hlist_del(&ri->hlist);
 383                 kfree(ri);
 384         }
 385
 386         return (void *)orig_ret_address;
 387 }
 388
 389 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 390                                       struct pt_regs *regs)
 391 {
 392         ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr;
 393
 394         /* Replace the return addr with trampoline addr. */
 395         regs->ARM_lr = (unsigned long)&kretprobe_trampoline;
 396 }
 397
 398 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 399 {
 400         struct jprobe *jp = container_of(p, struct jprobe, kp);
 401         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 402         long sp_addr = regs->ARM_sp;
 403         long cpsr;
 404
 405         kcb->jprobe_saved_regs = *regs;
 406         memcpy(kcb->jprobes_stack, (void *)sp_addr, MIN_STACK_SIZE(sp_addr));
 407         regs->ARM_pc = (long)jp->entry;
 408
 409         cpsr = regs->ARM_cpsr | PSR_I_BIT;
 410 #ifdef CONFIG_THUMB2_KERNEL
 411         /* Set correct Thumb state in cpsr */
 412         if (regs->ARM_pc & 1)
 413                 cpsr |= PSR_T_BIT;
 414         else
 415                 cpsr &= ~PSR_T_BIT;
 416 #endif
 417         regs->ARM_cpsr = cpsr;
 418
 419         preempt_disable();
 420         return 1;
 421 }
 422
 423 void __kprobes jprobe_return(void)
 424 {
 425         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 426
 427         __asm__ __volatile__ (
 428                 /*
 429                  * Setup an empty pt_regs. Fill SP and PC fields as
 430                  * they're needed by longjmp_break_handler.
 431                  *
 432                  * We allocate some slack between the original SP and start of
 433                  * our fabricated regs. To be precise we want to have worst case
 434                  * covered which is STMFD with all 16 regs so we allocate 2 *
 435                  * sizeof(struct_pt_regs)).
 436                  *
 437                  * This is to prevent any simulated instruction from writing
 438                  * over the regs when they are accessing the stack.
 439                  */
 440 #ifdef CONFIG_THUMB2_KERNEL
 441                 "sub    r0, %0, %1              \n\t"
 442                 "mov    sp, r0                  \n\t"
 443 #else
 444                 "sub    sp, %0, %1              \n\t"
 445 #endif
 446                 "ldr    r0, ="__stringify(JPROBE_MAGIC_ADDR)"\n\t"
 447                 "str    %0, [sp, %2]            \n\t"
 448                 "str    r0, [sp, %3]            \n\t"
 449                 "mov    r0, sp                  \n\t"
 450                 "bl     kprobe_handler          \n\t"
 451
 452                 /*
 453                  * Return to the context saved by setjmp_pre_handler
 454                  * and restored by longjmp_break_handler.
 455                  */
 456 #ifdef CONFIG_THUMB2_KERNEL
 457                 "ldr    lr, [sp, %2]            \n\t" /* lr = saved sp */
 458                 "ldrd   r0, r1, [sp, %5]        \n\t" /* r0,r1 = saved lr,pc */
 459                 "ldr    r2, [sp, %4]            \n\t" /* r2 = saved psr */
 460                 "stmdb  lr!, {r0, r1, r2}       \n\t" /* push saved lr and */
 461                                                       /* rfe context */
 462                 "ldmia  sp, {r0 - r12}          \n\t"
 463                 "mov    sp, lr                  \n\t"
 464                 "ldr    lr, [sp], #4            \n\t"
 465                 "rfeia  sp!                     \n\t"
 466 #else
 467                 "ldr    r0, [sp, %4]            \n\t"
 468                 "msr    cpsr_cxsf, r0           \n\t"
 469                 "ldmia  sp, {r0 - pc}           \n\t"
 470 #endif
 471                 :
 472                 : "r" (kcb->jprobe_saved_regs.ARM_sp),
 473                   "I" (sizeof(struct pt_regs) * 2),
 474                   "J" (offsetof(struct pt_regs, ARM_sp)),
 475                   "J" (offsetof(struct pt_regs, ARM_pc)),
 476                   "J" (offsetof(struct pt_regs, ARM_cpsr)),
 477                   "J" (offsetof(struct pt_regs, ARM_lr))
 478                 : "memory", "cc");
 479 }
 480
 481 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 482 {
 483         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 484         long stack_addr = kcb->jprobe_saved_regs.ARM_sp;
 485         long orig_sp = regs->ARM_sp;
 486         struct jprobe *jp = container_of(p, struct jprobe, kp);
 487
 488         if (regs->ARM_pc == JPROBE_MAGIC_ADDR) {
 489                 if (orig_sp != stack_addr) {
 490                         struct pt_regs *saved_regs =
 491                                 (struct pt_regs *)kcb->jprobe_saved_regs.ARM_sp;
 492                         printk("current sp %lx does not match saved sp %lx\n",
 493                                orig_sp, stack_addr);
 494                         printk("Saved registers for jprobe %p\n", jp);
 495                         show_regs(saved_regs);
 496                         printk("Current registers\n");
 497                         show_regs(regs);
 498                         BUG();
 499                 }
 500                 *regs = kcb->jprobe_saved_regs;
 501                 memcpy((void *)stack_addr, kcb->jprobes_stack,
 502                        MIN_STACK_SIZE(stack_addr));
 503                 preempt_enable_no_resched();
 504                 return 1;
 505         }
 506         return 0;
 507 }
 508
 509 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 510 {
 511         return 0;
 512 }
 513
 514 static struct undef_hook kprobes_break_hook = {
 515         .instr_mask     = 0xffffffff,
 516         .instr_val      = KPROBE_BREAKPOINT_INSTRUCTION,
 517         .cpsr_mask      = MODE_MASK,
 518         .cpsr_val       = SVC_MODE,
 519         .fn             = kprobe_trap_handler,
 520 };
 521
 522 int __init arch_init_kprobes()
 523 {
 524         arm_kprobe_decode_init();
 525         register_undef_hook(&kprobes_break_hook);
 526         return 0;
 527 }