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kprobes.c

/*
 *  Kernel Probes (KProbes)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * Copyright (C) IBM Corporation, 2002, 2004
 *
 * 2002-Oct Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
 *          Probes initial implementation ( includes contributions from
 *          Rusty Russell).
 * 2004-July      Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
 *          interface to access function arguments.
 * 2004-Nov Ananth N Mavinakayanahalli <ananth@in.ibm.com> kprobes port
 *          for PPC64
 */

#include <linux/kprobes.h>
#include <linux/ptrace.h>
#include <linux/preempt.h>
#include <linux/module.h>
#include <linux/kdebug.h>
#include <asm/cacheflush.h>
#include <asm/sstep.h>
#include <asm/uaccess.h>
#include <asm/system.h>

#ifdef CONFIG_BOOKE
#define MSR_SINGLESTEP  (MSR_DE)
#else
#define MSR_SINGLESTEP  (MSR_SE)
#endif

DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);

struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
      int ret = 0;
      kprobe_opcode_t insn = *p->addr;

      if ((unsigned long)p->addr & 0x03) {
            printk("Attempt to register kprobe at an unaligned address\n");
            ret = -EINVAL;
      } else if (IS_MTMSRD(insn) || IS_RFID(insn) || IS_RFI(insn)) {
            printk("Cannot register a kprobe on rfi/rfid or mtmsr[d]\n");
            ret = -EINVAL;
      }

      /* insn must be on a special executable page on ppc64.  This is
       * not explicitly required on ppc32 (right now), but it doesn't hurt */
      if (!ret) {
            p->ainsn.insn = get_insn_slot();
            if (!p->ainsn.insn)
                  ret = -ENOMEM;
      }

      if (!ret) {
            memcpy(p->ainsn.insn, p->addr,
                        MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
            p->opcode = *p->addr;
            flush_icache_range((unsigned long)p->ainsn.insn,
                  (unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
      }

      p->ainsn.boostable = 0;
      return ret;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
      *p->addr = BREAKPOINT_INSTRUCTION;
      flush_icache_range((unsigned long) p->addr,
                     (unsigned long) p->addr + sizeof(kprobe_opcode_t));
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
      *p->addr = p->opcode;
      flush_icache_range((unsigned long) p->addr,
                     (unsigned long) p->addr + sizeof(kprobe_opcode_t));
}

void __kprobes arch_remove_kprobe(struct kprobe *p)
{
      mutex_lock(&kprobe_mutex);
      free_insn_slot(p->ainsn.insn, 0);
      mutex_unlock(&kprobe_mutex);
}

static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
{
      /* We turn off async exceptions to ensure that the single step will
       * be for the instruction we have the kprobe on, if we dont its
       * possible we'd get the single step reported for an exception handler
       * like Decrementer or External Interrupt */
      regs->msr &= ~MSR_EE;
      regs->msr |= MSR_SINGLESTEP;
#ifdef CONFIG_BOOKE
      regs->msr &= ~MSR_CE;
      mtspr(SPRN_DBCR0, mfspr(SPRN_DBCR0) | DBCR0_IC | DBCR0_IDM);
#endif

      /*
       * On powerpc we should single step on the original
       * instruction even if the probed insn is a trap
       * variant as values in regs could play a part in
       * if the trap is taken or not
       */
      regs->nip = (unsigned long)p->ainsn.insn;
}

static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
{
      kcb->prev_kprobe.kp = kprobe_running();
      kcb->prev_kprobe.status = kcb->kprobe_status;
      kcb->prev_kprobe.saved_msr = kcb->kprobe_saved_msr;
}

static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
{
      __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
      kcb->kprobe_status = kcb->prev_kprobe.status;
      kcb->kprobe_saved_msr = kcb->prev_kprobe.saved_msr;
}

static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
                        struct kprobe_ctlblk *kcb)
{
      __get_cpu_var(current_kprobe) = p;
      kcb->kprobe_saved_msr = regs->msr;
}

void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
                              struct pt_regs *regs)
{
      ri->ret_addr = (kprobe_opcode_t *)regs->link;

      /* Replace the return addr with trampoline addr */
      regs->link = (unsigned long)kretprobe_trampoline;
}

static int __kprobes kprobe_handler(struct pt_regs *regs)
{
      struct kprobe *p;
      int ret = 0;
      unsigned int *addr = (unsigned int *)regs->nip;
      struct kprobe_ctlblk *kcb;

      /*
       * We don't want to be preempted for the entire
       * duration of kprobe processing
       */
      preempt_disable();
      kcb = get_kprobe_ctlblk();

      /* Check we're not actually recursing */
      if (kprobe_running()) {
            p = get_kprobe(addr);
            if (p) {
                  kprobe_opcode_t insn = *p->ainsn.insn;
                  if (kcb->kprobe_status == KPROBE_HIT_SS &&
                              is_trap(insn)) {
                        /* Turn off 'trace' bits */
                        regs->msr &= ~MSR_SINGLESTEP;
                        regs->msr |= kcb->kprobe_saved_msr;
                        goto no_kprobe;
                  }
                  /* We have reentered the kprobe_handler(), since
                   * another probe was hit while within the handler.
                   * We here save the original kprobes variables and
                   * just single step on the instruction of the new probe
                   * without calling any user handlers.
                   */
                  save_previous_kprobe(kcb);
                  set_current_kprobe(p, regs, kcb);
                  kcb->kprobe_saved_msr = regs->msr;
                  kprobes_inc_nmissed_count(p);
                  prepare_singlestep(p, regs);
                  kcb->kprobe_status = KPROBE_REENTER;
                  return 1;
            } else {
                  if (*addr != BREAKPOINT_INSTRUCTION) {
                        /* If trap variant, then it belongs not to us */
                        kprobe_opcode_t cur_insn = *addr;
                        if (is_trap(cur_insn))
                                    goto no_kprobe;
                        /* The breakpoint instruction was removed by
                         * another cpu right after we hit, no further
                         * handling of this interrupt is appropriate
                         */
                        ret = 1;
                        goto no_kprobe;
                  }
                  p = __get_cpu_var(current_kprobe);
                  if (p->break_handler && p->break_handler(p, regs)) {
                        goto ss_probe;
                  }
            }
            goto no_kprobe;
      }

      p = get_kprobe(addr);
      if (!p) {
            if (*addr != BREAKPOINT_INSTRUCTION) {
                  /*
                   * PowerPC has multiple variants of the "trap"
                   * instruction. If the current instruction is a
                   * trap variant, it could belong to someone else
                   */
                  kprobe_opcode_t cur_insn = *addr;
                  if (is_trap(cur_insn))
                              goto no_kprobe;
                  /*
                   * The breakpoint instruction was removed right
                   * after we hit it.  Another cpu has removed
                   * either a probepoint or a debugger breakpoint
                   * at this address.  In either case, no further
                   * handling of this interrupt is appropriate.
                   */
                  ret = 1;
            }
            /* Not one of ours: let kernel handle it */
            goto no_kprobe;
      }

      kcb->kprobe_status = KPROBE_HIT_ACTIVE;
      set_current_kprobe(p, regs, kcb);
      if (p->pre_handler && p->pre_handler(p, regs))
            /* handler has already set things up, so skip ss setup */
            return 1;

ss_probe:
      if (p->ainsn.boostable >= 0) {
            unsigned int insn = *p->ainsn.insn;

            /* regs->nip is also adjusted if emulate_step returns 1 */
            ret = emulate_step(regs, insn);
            if (ret > 0) {
                  /*
                   * Once this instruction has been boosted
                   * successfully, set the boostable flag
                   */
                  if (unlikely(p->ainsn.boostable == 0))
                        p->ainsn.boostable = 1;

                  if (p->post_handler)
                        p->post_handler(p, regs, 0);

                  kcb->kprobe_status = KPROBE_HIT_SSDONE;
                  reset_current_kprobe();
                  preempt_enable_no_resched();
                  return 1;
            } else if (ret < 0) {
                  /*
                   * We don't allow kprobes on mtmsr(d)/rfi(d), etc.
                   * So, we should never get here... but, its still
                   * good to catch them, just in case...
                   */
                  printk("Can't step on instruction %x\n", insn);
                  BUG();
            } else if (ret == 0)
                  /* This instruction can't be boosted */
                  p->ainsn.boostable = -1;
      }
      prepare_singlestep(p, regs);
      kcb->kprobe_status = KPROBE_HIT_SS;
      return 1;

no_kprobe:
      preempt_enable_no_resched();
      return ret;
}

/*
 * Function return probe trampoline:
 *    - init_kprobes() establishes a probepoint here
 *    - When the probed function returns, this probe
 *          causes the handlers to fire
 */
static void __used kretprobe_trampoline_holder(void)
{
      asm volatile(".global kretprobe_trampoline\n"
                  "kretprobe_trampoline:\n"
                  "nop\n");
}

/*
 * Called when the probe at kretprobe trampoline is hit
 */
static int __kprobes trampoline_probe_handler(struct kprobe *p,
                                    struct pt_regs *regs)
{
      struct kretprobe_instance *ri = NULL;
      struct hlist_head *head, empty_rp;
      struct hlist_node *node, *tmp;
      unsigned long flags, orig_ret_address = 0;
      unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;

      INIT_HLIST_HEAD(&empty_rp);
      kretprobe_hash_lock(current, &head, &flags);

      /*
       * It is possible to have multiple instances associated with a given
       * task either because an multiple functions in the call path
       * have a return probe installed on them, and/or more then one return
       * return probe was registered for a target function.
       *
       * We can handle this because:
       *     - instances are always inserted at the head of the list
       *     - when multiple return probes are registered for the same
       *       function, the first instance's ret_addr will point to the
       *       real return address, and all the rest will point to
       *       kretprobe_trampoline
       */
      hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
            if (ri->task != current)
                  /* another task is sharing our hash bucket */
                  continue;

            if (ri->rp && ri->rp->handler)
                  ri->rp->handler(ri, regs);

            orig_ret_address = (unsigned long)ri->ret_addr;
            recycle_rp_inst(ri, &empty_rp);

            if (orig_ret_address != trampoline_address)
                  /*
                   * This is the real return address. Any other
                   * instances associated with this task are for
                   * other calls deeper on the call stack
                   */
                  break;
      }

      kretprobe_assert(ri, orig_ret_address, trampoline_address);
      regs->nip = orig_ret_address;

      reset_current_kprobe();
      kretprobe_hash_unlock(current, &flags);
      preempt_enable_no_resched();

      hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
            hlist_del(&ri->hlist);
            kfree(ri);
      }
      /*
       * By returning a non-zero value, we are telling
       * kprobe_handler() that we don't want the post_handler
       * to run (and have re-enabled preemption)
       */
      return 1;
}

/*
 * Called after single-stepping.  p->addr is the address of the
 * instruction whose first byte has been replaced by the "breakpoint"
 * instruction.  To avoid the SMP problems that can occur when we
 * temporarily put back the original opcode to single-step, we
 * single-stepped a copy of the instruction.  The address of this
 * copy is p->ainsn.insn.
 */
static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
{
      int ret;
      unsigned int insn = *p->ainsn.insn;

      regs->nip = (unsigned long)p->addr;
      ret = emulate_step(regs, insn);
      if (ret == 0)
            regs->nip = (unsigned long)p->addr + 4;
}

static int __kprobes post_kprobe_handler(struct pt_regs *regs)
{
      struct kprobe *cur = kprobe_running();
      struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

      if (!cur)
            return 0;

      /* make sure we got here for instruction we have a kprobe on */
      if (((unsigned long)cur->ainsn.insn + 4) != regs->nip)
            return 0;

      if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
            kcb->kprobe_status = KPROBE_HIT_SSDONE;
            cur->post_handler(cur, regs, 0);
      }

      resume_execution(cur, regs);
      regs->msr |= kcb->kprobe_saved_msr;

      /*Restore back the original saved kprobes variables and continue. */
      if (kcb->kprobe_status == KPROBE_REENTER) {
            restore_previous_kprobe(kcb);
            goto out;
      }
      reset_current_kprobe();
out:
      preempt_enable_no_resched();

      /*
       * if somebody else is singlestepping across a probe point, msr
       * will have DE/SE set, in which case, continue the remaining processing
       * of do_debug, as if this is not a probe hit.
       */
      if (regs->msr & MSR_SINGLESTEP)
            return 0;

      return 1;
}

int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
{
      struct kprobe *cur = kprobe_running();
      struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
      const struct exception_table_entry *entry;

      switch(kcb->kprobe_status) {
      case KPROBE_HIT_SS:
      case KPROBE_REENTER:
            /*
             * We are here because the instruction being single
             * stepped caused a page fault. We reset the current
             * kprobe and the nip points back to the probe address
             * and allow the page fault handler to continue as a
             * normal page fault.
             */
            regs->nip = (unsigned long)cur->addr;
            regs->msr &= ~MSR_SINGLESTEP; /* Turn off 'trace' bits */
            regs->msr |= kcb->kprobe_saved_msr;
            if (kcb->kprobe_status == KPROBE_REENTER)
                  restore_previous_kprobe(kcb);
            else
                  reset_current_kprobe();
            preempt_enable_no_resched();
            break;
      case KPROBE_HIT_ACTIVE:
      case KPROBE_HIT_SSDONE:
            /*
             * We increment the nmissed count for accounting,
             * we can also use npre/npostfault count for accouting
             * these specific fault cases.
             */
            kprobes_inc_nmissed_count(cur);

            /*
             * We come here because instructions in the pre/post
             * handler caused the page_fault, this could happen
             * if handler tries to access user space by
             * copy_from_user(), get_user() etc. Let the
             * user-specified handler try to fix it first.
             */
            if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
                  return 1;

            /*
             * In case the user-specified fault handler returned
             * zero, try to fix up.
             */
            if ((entry = search_exception_tables(regs->nip)) != NULL) {
                  regs->nip = entry->fixup;
                  return 1;
            }

            /*
             * fixup_exception() could not handle it,
             * Let do_page_fault() fix it.
             */
            break;
      default:
            break;
      }
      return 0;
}

/*
 * Wrapper routine to for handling exceptions.
 */
int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
                               unsigned long val, void *data)
{
      struct die_args *args = (struct die_args *)data;
      int ret = NOTIFY_DONE;

      if (args->regs && user_mode(args->regs))
            return ret;

      switch (val) {
      case DIE_BPT:
            if (kprobe_handler(args->regs))
                  ret = NOTIFY_STOP;
            break;
      case DIE_SSTEP:
            if (post_kprobe_handler(args->regs))
                  ret = NOTIFY_STOP;
            break;
      default:
            break;
      }
      return ret;
}

#ifdef CONFIG_PPC64
unsigned long arch_deref_entry_point(void *entry)
{
      return ((func_descr_t *)entry)->entry;
}
#endif

int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
{
      struct jprobe *jp = container_of(p, struct jprobe, kp);
      struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

      memcpy(&kcb->jprobe_saved_regs, regs, sizeof(struct pt_regs));

      /* setup return addr to the jprobe handler routine */
      regs->nip = arch_deref_entry_point(jp->entry);
#ifdef CONFIG_PPC64
      regs->gpr[2] = (unsigned long)(((func_descr_t *)jp->entry)->toc);
#endif

      return 1;
}

void __used __kprobes jprobe_return(void)
{
      asm volatile("trap" ::: "memory");
}

static void __used __kprobes jprobe_return_end(void)
{
};

int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
      struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

      /*
       * FIXME - we should ideally be validating that we got here 'cos
       * of the "trap" in jprobe_return() above, before restoring the
       * saved regs...
       */
      memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
      preempt_enable_no_resched();
      return 1;
}

static struct kprobe trampoline_p = {
      .addr = (kprobe_opcode_t *) &kretprobe_trampoline,
      .pre_handler = trampoline_probe_handler
};

int __init arch_init_kprobes(void)
{
      return register_kprobe(&trampoline_p);
}

int __kprobes arch_trampoline_kprobe(struct kprobe *p)
{
      if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
            return 1;

      return 0;
}

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