arch/powerpc/kernel/kprobes.c

   1 /*
   2  *  Kernel Probes (KProbes)
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  17  *
  18  * Copyright (C) IBM Corporation, 2002, 2004
  19  *
  20  * 2002-Oct     Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
  21  *              Probes initial implementation ( includes contributions from
  22  *              Rusty Russell).
  23  * 2004-July    Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
  24  *              interface to access function arguments.
  25  * 2004-Nov     Ananth N Mavinakayanahalli <ananth@in.ibm.com> kprobes port
  26  *              for PPC64
  27  */
  28
  29 #include <linux/config.h>
  30 #include <linux/kprobes.h>
  31 #include <linux/ptrace.h>
  32 #include <linux/preempt.h>
  33 #include <linux/module.h>
  34 #include <asm/cacheflush.h>
  35 #include <asm/kdebug.h>
  36 #include <asm/sstep.h>
  37 #include <asm/uaccess.h>
  38
  39 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  40 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  41
  42 int __kprobes arch_prepare_kprobe(struct kprobe *p)
  43 {
  44         int ret = 0;
  45         kprobe_opcode_t insn = *p->addr;
  46
  47         if ((unsigned long)p->addr & 0x03) {
  48                 printk("Attempt to register kprobe at an unaligned address\n");
  49                 ret = -EINVAL;
  50         } else if (IS_MTMSRD(insn) || IS_RFID(insn)) {
  51                 printk("Cannot register a kprobe on rfid or mtmsrd\n");
  52                 ret = -EINVAL;
  53         }
  54
  55         /* insn must be on a special executable page on ppc64 */
  56         if (!ret) {
  57                 p->ainsn.insn = get_insn_slot();
  58                 if (!p->ainsn.insn)
  59                         ret = -ENOMEM;
  60         }
  61
  62         if (!ret) {
  63                 memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
  64                 p->opcode = *p->addr;
  65         }
  66
  67         return ret;
  68 }
  69
  70 void __kprobes arch_arm_kprobe(struct kprobe *p)
  71 {
  72         *p->addr = BREAKPOINT_INSTRUCTION;
  73         flush_icache_range((unsigned long) p->addr,
  74                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
  75 }
  76
  77 void __kprobes arch_disarm_kprobe(struct kprobe *p)
  78 {
  79         *p->addr = p->opcode;
  80         flush_icache_range((unsigned long) p->addr,
  81                            (unsigned long) p->addr + sizeof(kprobe_opcode_t));
  82 }
  83
  84 void __kprobes arch_remove_kprobe(struct kprobe *p)
  85 {
  86         mutex_lock(&kprobe_mutex);
  87         free_insn_slot(p->ainsn.insn);
  88         mutex_unlock(&kprobe_mutex);
  89 }
  90
  91 static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
  92 {
  93         kprobe_opcode_t insn = *p->ainsn.insn;
  94
  95         regs->msr |= MSR_SE;
  96
  97         /* single step inline if it is a trap variant */
  98         if (is_trap(insn))
  99                 regs->nip = (unsigned long)p->addr;
 100         else
 101                 regs->nip = (unsigned long)p->ainsn.insn;
 102 }
 103
 104 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 105 {
 106         kcb->prev_kprobe.kp = kprobe_running();
 107         kcb->prev_kprobe.status = kcb->kprobe_status;
 108         kcb->prev_kprobe.saved_msr = kcb->kprobe_saved_msr;
 109 }
 110
 111 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 112 {
 113         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
 114         kcb->kprobe_status = kcb->prev_kprobe.status;
 115         kcb->kprobe_saved_msr = kcb->prev_kprobe.saved_msr;
 116 }
 117
 118 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
 119                                 struct kprobe_ctlblk *kcb)
 120 {
 121         __get_cpu_var(current_kprobe) = p;
 122         kcb->kprobe_saved_msr = regs->msr;
 123 }
 124
 125 /* Called with kretprobe_lock held */
 126 void __kprobes arch_prepare_kretprobe(struct kretprobe *rp,
 127                                       struct pt_regs *regs)
 128 {
 129         struct kretprobe_instance *ri;
 130
 131         if ((ri = get_free_rp_inst(rp)) != NULL) {
 132                 ri->rp = rp;
 133                 ri->task = current;
 134                 ri->ret_addr = (kprobe_opcode_t *)regs->link;
 135
 136                 /* Replace the return addr with trampoline addr */
 137                 regs->link = (unsigned long)kretprobe_trampoline;
 138                 add_rp_inst(ri);
 139         } else {
 140                 rp->nmissed++;
 141         }
 142 }
 143
 144 static int __kprobes kprobe_handler(struct pt_regs *regs)
 145 {
 146         struct kprobe *p;
 147         int ret = 0;
 148         unsigned int *addr = (unsigned int *)regs->nip;
 149         struct kprobe_ctlblk *kcb;
 150
 151         /*
 152          * We don't want to be preempted for the entire
 153          * duration of kprobe processing
 154          */
 155         preempt_disable();
 156         kcb = get_kprobe_ctlblk();
 157
 158         /* Check we're not actually recursing */
 159         if (kprobe_running()) {
 160                 p = get_kprobe(addr);
 161                 if (p) {
 162                         kprobe_opcode_t insn = *p->ainsn.insn;
 163                         if (kcb->kprobe_status == KPROBE_HIT_SS &&
 164                                         is_trap(insn)) {
 165                                 regs->msr &= ~MSR_SE;
 166                                 regs->msr |= kcb->kprobe_saved_msr;
 167                                 goto no_kprobe;
 168                         }
 169                         /* We have reentered the kprobe_handler(), since
 170                          * another probe was hit while within the handler.
 171                          * We here save the original kprobes variables and
 172                          * just single step on the instruction of the new probe
 173                          * without calling any user handlers.
 174                          */
 175                         save_previous_kprobe(kcb);
 176                         set_current_kprobe(p, regs, kcb);
 177                         kcb->kprobe_saved_msr = regs->msr;
 178                         kprobes_inc_nmissed_count(p);
 179                         prepare_singlestep(p, regs);
 180                         kcb->kprobe_status = KPROBE_REENTER;
 181                         return 1;
 182                 } else {
 183                         if (*addr != BREAKPOINT_INSTRUCTION) {
 184                                 /* If trap variant, then it belongs not to us */
 185                                 kprobe_opcode_t cur_insn = *addr;
 186                                 if (is_trap(cur_insn))
 187                                         goto no_kprobe;
 188                                 /* The breakpoint instruction was removed by
 189                                  * another cpu right after we hit, no further
 190                                  * handling of this interrupt is appropriate
 191                                  */
 192                                 ret = 1;
 193                                 goto no_kprobe;
 194                         }
 195                         p = __get_cpu_var(current_kprobe);
 196                         if (p->break_handler && p->break_handler(p, regs)) {
 197                                 goto ss_probe;
 198                         }
 199                 }
 200                 goto no_kprobe;
 201         }
 202
 203         p = get_kprobe(addr);
 204         if (!p) {
 205                 if (*addr != BREAKPOINT_INSTRUCTION) {
 206                         /*
 207                          * PowerPC has multiple variants of the "trap"
 208                          * instruction. If the current instruction is a
 209                          * trap variant, it could belong to someone else
 210                          */
 211                         kprobe_opcode_t cur_insn = *addr;
 212                         if (is_trap(cur_insn))
 213                                 goto no_kprobe;
 214                         /*
 215                          * The breakpoint instruction was removed right
 216                          * after we hit it.  Another cpu has removed
 217                          * either a probepoint or a debugger breakpoint
 218                          * at this address.  In either case, no further
 219                          * handling of this interrupt is appropriate.
 220                          */
 221                         ret = 1;
 222                 }
 223                 /* Not one of ours: let kernel handle it */
 224                 goto no_kprobe;
 225         }
 226
 227         kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 228         set_current_kprobe(p, regs, kcb);
 229         if (p->pre_handler && p->pre_handler(p, regs))
 230                 /* handler has already set things up, so skip ss setup */
 231                 return 1;
 232
 233 ss_probe:
 234         prepare_singlestep(p, regs);
 235         kcb->kprobe_status = KPROBE_HIT_SS;
 236         return 1;
 237
 238 no_kprobe:
 239         preempt_enable_no_resched();
 240         return ret;
 241 }
 242
 243 /*
 244  * Function return probe trampoline:
 245  *      - init_kprobes() establishes a probepoint here
 246  *      - When the probed function returns, this probe
 247  *              causes the handlers to fire
 248  */
 249 void kretprobe_trampoline_holder(void)
 250 {
 251         asm volatile(".global kretprobe_trampoline\n"
 252                         "kretprobe_trampoline:\n"
 253                         "nop\n");
 254 }
 255
 256 /*
 257  * Called when the probe at kretprobe trampoline is hit
 258  */
 259 int __kprobes trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
 260 {
 261         struct kretprobe_instance *ri = NULL;
 262         struct hlist_head *head;
 263         struct hlist_node *node, *tmp;
 264         unsigned long flags, orig_ret_address = 0;
 265         unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
 266
 267         spin_lock_irqsave(&kretprobe_lock, flags);
 268         head = kretprobe_inst_table_head(current);
 269
 270         /*
 271          * It is possible to have multiple instances associated with a given
 272          * task either because an multiple functions in the call path
 273          * have a return probe installed on them, and/or more then one return
 274          * return probe was registered for a target function.
 275          *
 276          * We can handle this because:
 277          *     - instances are always inserted at the head of the list
 278          *     - when multiple return probes are registered for the same
 279          *       function, the first instance's ret_addr will point to the
 280          *       real return address, and all the rest will point to
 281          *       kretprobe_trampoline
 282          */
 283         hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
 284                 if (ri->task != current)
 285                         /* another task is sharing our hash bucket */
 286                         continue;
 287
 288                 if (ri->rp && ri->rp->handler)
 289                         ri->rp->handler(ri, regs);
 290
 291                 orig_ret_address = (unsigned long)ri->ret_addr;
 292                 recycle_rp_inst(ri);
 293
 294                 if (orig_ret_address != trampoline_address)
 295                         /*
 296                          * This is the real return address. Any other
 297                          * instances associated with this task are for
 298                          * other calls deeper on the call stack
 299                          */
 300                         break;
 301         }
 302
 303         BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
 304         regs->nip = orig_ret_address;
 305
 306         reset_current_kprobe();
 307         spin_unlock_irqrestore(&kretprobe_lock, flags);
 308         preempt_enable_no_resched();
 309
 310         /*
 311          * By returning a non-zero value, we are telling
 312          * kprobe_handler() that we don't want the post_handler
 313          * to run (and have re-enabled preemption)
 314          */
 315         return 1;
 316 }
 317
 318 /*
 319  * Called after single-stepping.  p->addr is the address of the
 320  * instruction whose first byte has been replaced by the "breakpoint"
 321  * instruction.  To avoid the SMP problems that can occur when we
 322  * temporarily put back the original opcode to single-step, we
 323  * single-stepped a copy of the instruction.  The address of this
 324  * copy is p->ainsn.insn.
 325  */
 326 static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
 327 {
 328         int ret;
 329         unsigned int insn = *p->ainsn.insn;
 330
 331         regs->nip = (unsigned long)p->addr;
 332         ret = emulate_step(regs, insn);
 333         if (ret == 0)
 334                 regs->nip = (unsigned long)p->addr + 4;
 335 }
 336
 337 static int __kprobes post_kprobe_handler(struct pt_regs *regs)
 338 {
 339         struct kprobe *cur = kprobe_running();
 340         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 341
 342         if (!cur)
 343                 return 0;
 344
 345         if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
 346                 kcb->kprobe_status = KPROBE_HIT_SSDONE;
 347                 cur->post_handler(cur, regs, 0);
 348         }
 349
 350         resume_execution(cur, regs);
 351         regs->msr |= kcb->kprobe_saved_msr;
 352
 353         /*Restore back the original saved kprobes variables and continue. */
 354         if (kcb->kprobe_status == KPROBE_REENTER) {
 355                 restore_previous_kprobe(kcb);
 356                 goto out;
 357         }
 358         reset_current_kprobe();
 359 out:
 360         preempt_enable_no_resched();
 361
 362         /*
 363          * if somebody else is singlestepping across a probe point, msr
 364          * will have SE set, in which case, continue the remaining processing
 365          * of do_debug, as if this is not a probe hit.
 366          */
 367         if (regs->msr & MSR_SE)
 368                 return 0;
 369
 370         return 1;
 371 }
 372
 373 static int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 374 {
 375         struct kprobe *cur = kprobe_running();
 376         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 377         const struct exception_table_entry *entry;
 378
 379         switch(kcb->kprobe_status) {
 380         case KPROBE_HIT_SS:
 381         case KPROBE_REENTER:
 382                 /*
 383                  * We are here because the instruction being single
 384                  * stepped caused a page fault. We reset the current
 385                  * kprobe and the nip points back to the probe address
 386                  * and allow the page fault handler to continue as a
 387                  * normal page fault.
 388                  */
 389                 regs->nip = (unsigned long)cur->addr;
 390                 regs->msr &= ~MSR_SE;
 391                 regs->msr |= kcb->kprobe_saved_msr;
 392                 if (kcb->kprobe_status == KPROBE_REENTER)
 393                         restore_previous_kprobe(kcb);
 394                 else
 395                         reset_current_kprobe();
 396                 preempt_enable_no_resched();
 397                 break;
 398         case KPROBE_HIT_ACTIVE:
 399         case KPROBE_HIT_SSDONE:
 400                 /*
 401                  * We increment the nmissed count for accounting,
 402                  * we can also use npre/npostfault count for accouting
 403                  * these specific fault cases.
 404                  */
 405                 kprobes_inc_nmissed_count(cur);
 406
 407                 /*
 408                  * We come here because instructions in the pre/post
 409                  * handler caused the page_fault, this could happen
 410                  * if handler tries to access user space by
 411                  * copy_from_user(), get_user() etc. Let the
 412                  * user-specified handler try to fix it first.
 413                  */
 414                 if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
 415                         return 1;
 416
 417                 /*
 418                  * In case the user-specified fault handler returned
 419                  * zero, try to fix up.
 420                  */
 421                 if ((entry = search_exception_tables(regs->nip)) != NULL) {
 422                         regs->nip = entry->fixup;
 423                         return 1;
 424                 }
 425
 426                 /*
 427                  * fixup_exception() could not handle it,
 428                  * Let do_page_fault() fix it.
 429                  */
 430                 break;
 431         default:
 432                 break;
 433         }
 434         return 0;
 435 }
 436
 437 /*
 438  * Wrapper routine to for handling exceptions.
 439  */
 440 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 441                                        unsigned long val, void *data)
 442 {
 443         struct die_args *args = (struct die_args *)data;
 444         int ret = NOTIFY_DONE;
 445
 446         if (args->regs && user_mode(args->regs))
 447                 return ret;
 448
 449         switch (val) {
 450         case DIE_BPT:
 451                 if (kprobe_handler(args->regs))
 452                         ret = NOTIFY_STOP;
 453                 break;
 454         case DIE_SSTEP:
 455                 if (post_kprobe_handler(args->regs))
 456                         ret = NOTIFY_STOP;
 457                 break;
 458         case DIE_PAGE_FAULT:
 459                 /* kprobe_running() needs smp_processor_id() */
 460                 preempt_disable();
 461                 if (kprobe_running() &&
 462                     kprobe_fault_handler(args->regs, args->trapnr))
 463                         ret = NOTIFY_STOP;
 464                 preempt_enable();
 465                 break;
 466         default:
 467                 break;
 468         }
 469         return ret;
 470 }
 471
 472 int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 473 {
 474         struct jprobe *jp = container_of(p, struct jprobe, kp);
 475         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 476
 477         memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));
 478
 479         /* setup return addr to the jprobe handler routine */
 480         regs->nip = (unsigned long)(((func_descr_t *)jp->entry)->entry);
 481         regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
 482
 483         return 1;
 484 }
 485
 486 void __kprobes jprobe_return(void)
 487 {
 488         asm volatile("trap" ::: "memory");
 489 }
 490
 491 void __kprobes jprobe_return_end(void)
 492 {
 493 };
 494
 495 int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 496 {
 497         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 498
 499         /*
 500          * FIXME - we should ideally be validating that we got here 'cos
 501          * of the "trap" in jprobe_return() above, before restoring the
 502          * saved regs...
 503          */
 504         memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
 505         preempt_enable_no_resched();
 506         return 1;
 507 }
 508
 509 static struct kprobe trampoline_p = {
 510         .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
 511         .pre_handler = trampoline_probe_handler
 512 };
 513
 514 int __init arch_init_kprobes(void)
 515 {
 516         return register_kprobe(&trampoline_p);
 517 }