linux/arch/powerpc/kernel/kprobes.c
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   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/kprobes.h>
  30#include <linux/ptrace.h>
  31#include <linux/preempt.h>
  32#include <linux/module.h>
  33#include <linux/kdebug.h>
  34#include <linux/slab.h>
  35#include <asm/cacheflush.h>
  36#include <asm/sstep.h>
  37#include <asm/uaccess.h>
  38
  39#ifdef CONFIG_PPC_ADV_DEBUG_REGS
  40#define MSR_SINGLESTEP  (MSR_DE)
  41#else
  42#define MSR_SINGLESTEP  (MSR_SE)
  43#endif
  44
  45DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  46DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  47
  48struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
  49
  50int __kprobes arch_prepare_kprobe(struct kprobe *p)
  51{
  52        int ret = 0;
  53        kprobe_opcode_t insn = *p->addr;
  54
  55        if ((unsigned long)p->addr & 0x03) {
  56                printk("Attempt to register kprobe at an unaligned address\n");
  57                ret = -EINVAL;
  58        } else if (IS_MTMSRD(insn) || IS_RFID(insn) || IS_RFI(insn)) {
  59                printk("Cannot register a kprobe on rfi/rfid or mtmsr[d]\n");
  60                ret = -EINVAL;
  61        }
  62
  63        /* insn must be on a special executable page on ppc64.  This is
  64         * not explicitly required on ppc32 (right now), but it doesn't hurt */
  65        if (!ret) {
  66                p->ainsn.insn = get_insn_slot();
  67                if (!p->ainsn.insn)
  68                        ret = -ENOMEM;
  69        }
  70
  71        if (!ret) {
  72                memcpy(p->ainsn.insn, p->addr,
  73                                MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
  74                p->opcode = *p->addr;
  75                flush_icache_range((unsigned long)p->ainsn.insn,
  76                        (unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
  77        }
  78
  79        p->ainsn.boostable = 0;
  80        return ret;
  81}
  82
  83void __kprobes arch_arm_kprobe(struct kprobe *p)
  84{
  85        *p->addr = BREAKPOINT_INSTRUCTION;
  86        flush_icache_range((unsigned long) p->addr,
  87                           (unsigned long) p->addr + sizeof(kprobe_opcode_t));
  88}
  89
  90void __kprobes arch_disarm_kprobe(struct kprobe *p)
  91{
  92        *p->addr = p->opcode;
  93        flush_icache_range((unsigned long) p->addr,
  94                           (unsigned long) p->addr + sizeof(kprobe_opcode_t));
  95}
  96
  97void __kprobes arch_remove_kprobe(struct kprobe *p)
  98{
  99        if (p->ainsn.insn) {
 100                free_insn_slot(p->ainsn.insn, 0);
 101                p->ainsn.insn = NULL;
 102        }
 103}
 104
 105static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
 106{
 107        /* We turn off async exceptions to ensure that the single step will
 108         * be for the instruction we have the kprobe on, if we dont its
 109         * possible we'd get the single step reported for an exception handler
 110         * like Decrementer or External Interrupt */
 111        regs->msr &= ~MSR_EE;
 112        regs->msr |= MSR_SINGLESTEP;
 113#ifdef CONFIG_PPC_ADV_DEBUG_REGS
 114        regs->msr &= ~MSR_CE;
 115        mtspr(SPRN_DBCR0, mfspr(SPRN_DBCR0) | DBCR0_IC | DBCR0_IDM);
 116#ifdef CONFIG_PPC_47x
 117        isync();
 118#endif
 119#endif
 120
 121        /*
 122         * On powerpc we should single step on the original
 123         * instruction even if the probed insn is a trap
 124         * variant as values in regs could play a part in
 125         * if the trap is taken or not
 126         */
 127        regs->nip = (unsigned long)p->ainsn.insn;
 128}
 129
 130static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 131{
 132        kcb->prev_kprobe.kp = kprobe_running();
 133        kcb->prev_kprobe.status = kcb->kprobe_status;
 134        kcb->prev_kprobe.saved_msr = kcb->kprobe_saved_msr;
 135}
 136
 137static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 138{
 139        __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
 140        kcb->kprobe_status = kcb->prev_kprobe.status;
 141        kcb->kprobe_saved_msr = kcb->prev_kprobe.saved_msr;
 142}
 143
 144static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
 145                                struct kprobe_ctlblk *kcb)
 146{
 147        __get_cpu_var(current_kprobe) = p;
 148        kcb->kprobe_saved_msr = regs->msr;
 149}
 150
 151void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 152                                      struct pt_regs *regs)
 153{
 154        ri->ret_addr = (kprobe_opcode_t *)regs->link;
 155
 156        /* Replace the return addr with trampoline addr */
 157        regs->link = (unsigned long)kretprobe_trampoline;
 158}
 159
 160static int __kprobes kprobe_handler(struct pt_regs *regs)
 161{
 162        struct kprobe *p;
 163        int ret = 0;
 164        unsigned int *addr = (unsigned int *)regs->nip;
 165        struct kprobe_ctlblk *kcb;
 166
 167        /*
 168         * We don't want to be preempted for the entire
 169         * duration of kprobe processing
 170         */
 171        preempt_disable();
 172        kcb = get_kprobe_ctlblk();
 173
 174        /* Check we're not actually recursing */
 175        if (kprobe_running()) {
 176                p = get_kprobe(addr);
 177                if (p) {
 178                        kprobe_opcode_t insn = *p->ainsn.insn;
 179                        if (kcb->kprobe_status == KPROBE_HIT_SS &&
 180                                        is_trap(insn)) {
 181                                /* Turn off 'trace' bits */
 182                                regs->msr &= ~MSR_SINGLESTEP;
 183                                regs->msr |= kcb->kprobe_saved_msr;
 184                                goto no_kprobe;
 185                        }
 186                        /* We have reentered the kprobe_handler(), since
 187                         * another probe was hit while within the handler.
 188                         * We here save the original kprobes variables and
 189                         * just single step on the instruction of the new probe
 190                         * without calling any user handlers.
 191                         */
 192                        save_previous_kprobe(kcb);
 193                        set_current_kprobe(p, regs, kcb);
 194                        kcb->kprobe_saved_msr = regs->msr;
 195                        kprobes_inc_nmissed_count(p);
 196                        prepare_singlestep(p, regs);
 197                        kcb->kprobe_status = KPROBE_REENTER;
 198                        return 1;
 199                } else {
 200                        if (*addr != BREAKPOINT_INSTRUCTION) {
 201                                /* If trap variant, then it belongs not to us */
 202                                kprobe_opcode_t cur_insn = *addr;
 203                                if (is_trap(cur_insn))
 204                                        goto no_kprobe;
 205                                /* The breakpoint instruction was removed by
 206                                 * another cpu right after we hit, no further
 207                                 * handling of this interrupt is appropriate
 208                                 */
 209                                ret = 1;
 210                                goto no_kprobe;
 211                        }
 212                        p = __get_cpu_var(current_kprobe);
 213                        if (p->break_handler && p->break_handler(p, regs)) {
 214                                goto ss_probe;
 215                        }
 216                }
 217                goto no_kprobe;
 218        }
 219
 220        p = get_kprobe(addr);
 221        if (!p) {
 222                if (*addr != BREAKPOINT_INSTRUCTION) {
 223                        /*
 224                         * PowerPC has multiple variants of the "trap"
 225                         * instruction. If the current instruction is a
 226                         * trap variant, it could belong to someone else
 227                         */
 228                        kprobe_opcode_t cur_insn = *addr;
 229                        if (is_trap(cur_insn))
 230                                goto no_kprobe;
 231                        /*
 232                         * The breakpoint instruction was removed right
 233                         * after we hit it.  Another cpu has removed
 234                         * either a probepoint or a debugger breakpoint
 235                         * at this address.  In either case, no further
 236                         * handling of this interrupt is appropriate.
 237                         */
 238                        ret = 1;
 239                }
 240                /* Not one of ours: let kernel handle it */
 241                goto no_kprobe;
 242        }
 243
 244        kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 245        set_current_kprobe(p, regs, kcb);
 246        if (p->pre_handler && p->pre_handler(p, regs))
 247                /* handler has already set things up, so skip ss setup */
 248                return 1;
 249
 250ss_probe:
 251        if (p->ainsn.boostable >= 0) {
 252                unsigned int insn = *p->ainsn.insn;
 253
 254                /* regs->nip is also adjusted if emulate_step returns 1 */
 255                ret = emulate_step(regs, insn);
 256                if (ret > 0) {
 257                        /*
 258                         * Once this instruction has been boosted
 259                         * successfully, set the boostable flag
 260                         */
 261                        if (unlikely(p->ainsn.boostable == 0))
 262                                p->ainsn.boostable = 1;
 263
 264                        if (p->post_handler)
 265                                p->post_handler(p, regs, 0);
 266
 267                        kcb->kprobe_status = KPROBE_HIT_SSDONE;
 268                        reset_current_kprobe();
 269                        preempt_enable_no_resched();
 270                        return 1;
 271                } else if (ret < 0) {
 272                        /*
 273                         * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
 274                         * So, we should never get here... but, its still
 275                         * good to catch them, just in case...
 276                         */
 277                        printk("Can't step on instruction %x\n", insn);
 278                        BUG();
 279                } else if (ret == 0)
 280                        /* This instruction can't be boosted */
 281                        p->ainsn.boostable = -1;
 282        }
 283        prepare_singlestep(p, regs);
 284        kcb->kprobe_status = KPROBE_HIT_SS;
 285        return 1;
 286
 287no_kprobe:
 288        preempt_enable_no_resched();
 289        return ret;
 290}
 291
 292/*
 293 * Function return probe trampoline:
 294 *      - init_kprobes() establishes a probepoint here
 295 *      - When the probed function returns, this probe
 296 *              causes the handlers to fire
 297 */
 298static void __used kretprobe_trampoline_holder(void)
 299{
 300        asm volatile(".global kretprobe_trampoline\n"
 301                        "kretprobe_trampoline:\n"
 302                        "nop\n");
 303}
 304
 305/*
 306 * Called when the probe at kretprobe trampoline is hit
 307 */
 308static int __kprobes trampoline_probe_handler(struct kprobe *p,
 309                                                struct pt_regs *regs)
 310{
 311        struct kretprobe_instance *ri = NULL;
 312        struct hlist_head *head, empty_rp;
 313        struct hlist_node *node, *tmp;
 314        unsigned long flags, orig_ret_address = 0;
 315        unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;
 316
 317        INIT_HLIST_HEAD(&empty_rp);
 318        kretprobe_hash_lock(current, &head, &flags);
 319
 320        /*
 321         * It is possible to have multiple instances associated with a given
 322         * task either because an multiple functions in the call path
 323         * have a return probe installed on them, and/or more than one return
 324         * return probe was registered for a target function.
 325         *
 326         * We can handle this because:
 327         *     - instances are always inserted at the head of the list
 328         *     - when multiple return probes are registered for the same
 329         *       function, the first instance's ret_addr will point to the
 330         *       real return address, and all the rest will point to
 331         *       kretprobe_trampoline
 332         */
 333        hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
 334                if (ri->task != current)
 335                        /* another task is sharing our hash bucket */
 336                        continue;
 337
 338                if (ri->rp && ri->rp->handler)
 339                        ri->rp->handler(ri, regs);
 340
 341                orig_ret_address = (unsigned long)ri->ret_addr;
 342                recycle_rp_inst(ri, &empty_rp);
 343
 344                if (orig_ret_address != trampoline_address)
 345                        /*
 346                         * This is the real return address. Any other
 347                         * instances associated with this task are for
 348                         * other calls deeper on the call stack
 349                         */
 350                        break;
 351        }
 352
 353        kretprobe_assert(ri, orig_ret_address, trampoline_address);
 354        regs->nip = orig_ret_address;
 355
 356        reset_current_kprobe();
 357        kretprobe_hash_unlock(current, &flags);
 358        preempt_enable_no_resched();
 359
 360        hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
 361                hlist_del(&ri->hlist);
 362                kfree(ri);
 363        }
 364        /*
 365         * By returning a non-zero value, we are telling
 366         * kprobe_handler() that we don't want the post_handler
 367         * to run (and have re-enabled preemption)
 368         */
 369        return 1;
 370}
 371
 372/*
 373 * Called after single-stepping.  p->addr is the address of the
 374 * instruction whose first byte has been replaced by the "breakpoint"
 375 * instruction.  To avoid the SMP problems that can occur when we
 376 * temporarily put back the original opcode to single-step, we
 377 * single-stepped a copy of the instruction.  The address of this
 378 * copy is p->ainsn.insn.
 379 */
 380static int __kprobes post_kprobe_handler(struct pt_regs *regs)
 381{
 382        struct kprobe *cur = kprobe_running();
 383        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 384
 385        if (!cur)
 386                return 0;
 387
 388        /* make sure we got here for instruction we have a kprobe on */
 389        if (((unsigned long)cur->ainsn.insn + 4) != regs->nip)
 390                return 0;
 391
 392        if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
 393                kcb->kprobe_status = KPROBE_HIT_SSDONE;
 394                cur->post_handler(cur, regs, 0);
 395        }
 396
 397        /* Adjust nip to after the single-stepped instruction */
 398        regs->nip = (unsigned long)cur->addr + 4;
 399        regs->msr |= kcb->kprobe_saved_msr;
 400
 401        /*Restore back the original saved kprobes variables and continue. */
 402        if (kcb->kprobe_status == KPROBE_REENTER) {
 403                restore_previous_kprobe(kcb);
 404                goto out;
 405        }
 406        reset_current_kprobe();
 407out:
 408        preempt_enable_no_resched();
 409
 410        /*
 411         * if somebody else is singlestepping across a probe point, msr
 412         * will have DE/SE set, in which case, continue the remaining processing
 413         * of do_debug, as if this is not a probe hit.
 414         */
 415        if (regs->msr & MSR_SINGLESTEP)
 416                return 0;
 417
 418        return 1;
 419}
 420
 421int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 422{
 423        struct kprobe *cur = kprobe_running();
 424        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 425        const struct exception_table_entry *entry;
 426
 427        switch(kcb->kprobe_status) {
 428        case KPROBE_HIT_SS:
 429        case KPROBE_REENTER:
 430                /*
 431                 * We are here because the instruction being single
 432                 * stepped caused a page fault. We reset the current
 433                 * kprobe and the nip points back to the probe address
 434                 * and allow the page fault handler to continue as a
 435                 * normal page fault.
 436                 */
 437                regs->nip = (unsigned long)cur->addr;
 438                regs->msr &= ~MSR_SINGLESTEP; /* Turn off 'trace' bits */
 439                regs->msr |= kcb->kprobe_saved_msr;
 440                if (kcb->kprobe_status == KPROBE_REENTER)
 441                        restore_previous_kprobe(kcb);
 442                else
 443                        reset_current_kprobe();
 444                preempt_enable_no_resched();
 445                break;
 446        case KPROBE_HIT_ACTIVE:
 447        case KPROBE_HIT_SSDONE:
 448                /*
 449                 * We increment the nmissed count for accounting,
 450                 * we can also use npre/npostfault count for accouting
 451                 * these specific fault cases.
 452                 */
 453                kprobes_inc_nmissed_count(cur);
 454
 455                /*
 456                 * We come here because instructions in the pre/post
 457                 * handler caused the page_fault, this could happen
 458                 * if handler tries to access user space by
 459                 * copy_from_user(), get_user() etc. Let the
 460                 * user-specified handler try to fix it first.
 461                 */
 462                if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
 463                        return 1;
 464
 465                /*
 466                 * In case the user-specified fault handler returned
 467                 * zero, try to fix up.
 468                 */
 469                if ((entry = search_exception_tables(regs->nip)) != NULL) {
 470                        regs->nip = entry->fixup;
 471                        return 1;
 472                }
 473
 474                /*
 475                 * fixup_exception() could not handle it,
 476                 * Let do_page_fault() fix it.
 477                 */
 478                break;
 479        default:
 480                break;
 481        }
 482        return 0;
 483}
 484
 485/*
 486 * Wrapper routine to for handling exceptions.
 487 */
 488int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
 489                                       unsigned long val, void *data)
 490{
 491        struct die_args *args = (struct die_args *)data;
 492        int ret = NOTIFY_DONE;
 493
 494        if (args->regs && user_mode(args->regs))
 495                return ret;
 496
 497        switch (val) {
 498        case DIE_BPT:
 499                if (kprobe_handler(args->regs))
 500                        ret = NOTIFY_STOP;
 501                break;
 502        case DIE_SSTEP:
 503                if (post_kprobe_handler(args->regs))
 504                        ret = NOTIFY_STOP;
 505                break;
 506        default:
 507                break;
 508        }
 509        return ret;
 510}
 511
 512#ifdef CONFIG_PPC64
 513unsigned long arch_deref_entry_point(void *entry)
 514{
 515        return ((func_descr_t *)entry)->entry;
 516}
 517#endif
 518
 519int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
 520{
 521        struct jprobe *jp = container_of(p, struct jprobe, kp);
 522        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 523
 524        memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));
 525
 526        /* setup return addr to the jprobe handler routine */
 527        regs->nip = arch_deref_entry_point(jp->entry);
 528#ifdef CONFIG_PPC64
 529        regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
 530#endif
 531
 532        return 1;
 533}
 534
 535void __used __kprobes jprobe_return(void)
 536{
 537        asm volatile("trap" ::: "memory");
 538}
 539
 540static void __used __kprobes jprobe_return_end(void)
 541{
 542};
 543
 544int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
 545{
 546        struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 547
 548        /*
 549         * FIXME - we should ideally be validating that we got here 'cos
 550         * of the "trap" in jprobe_return() above, before restoring the
 551         * saved regs...
 552         */
 553        memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
 554        preempt_enable_no_resched();
 555        return 1;
 556}
 557
 558static struct kprobe trampoline_p = {
 559        .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
 560        .pre_handler = trampoline_probe_handler
 561};
 562
 563int __init arch_init_kprobes(void)
 564{
 565        return register_kprobe(&trampoline_p);
 566}
 567
 568int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 569{
 570        if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
 571                return 1;
 572
 573        return 0;
 574}
 575