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kprobes_32.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.
 * 2005-May Hien Nguyen <hien@us.ibm.com>, Jim Keniston
 *          <jkenisto@us.ibm.com> and Prasanna S Panchamukhi
 *          <prasanna@in.ibm.com> added function-return probes.
 */

#include <linux/kprobes.h>
#include <linux/ptrace.h>
#include <linux/preempt.h>
#include <linux/kdebug.h>
#include <asm/cacheflush.h>
#include <asm/desc.h>
#include <asm/uaccess.h>
#include <asm/alternative.h>

void jprobe_return_end(void);

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

struct kretprobe_blackpoint kretprobe_blacklist[] = {
      {"__switch_to", }, /* This function switches only current task, but
                       doesn't switch kernel stack.*/
      {NULL, NULL}      /* Terminator */
};
const int kretprobe_blacklist_size = ARRAY_SIZE(kretprobe_blacklist);

/* insert a jmp code */
static __always_inline void set_jmp_op(void *from, void *to)
{
      struct __arch_jmp_op {
            char op;
            long raddr;
      } __attribute__((packed)) *jop;
      jop = (struct __arch_jmp_op *)from;
      jop->raddr = (long)(to) - ((long)(from) + 5);
      jop->op = RELATIVEJUMP_INSTRUCTION;
}

/*
 * returns non-zero if opcodes can be boosted.
 */
static __always_inline int can_boost(kprobe_opcode_t *opcodes)
{
#define W(row,b0,b1,b2,b3,b4,b5,b6,b7,b8,b9,ba,bb,bc,bd,be,bf)                \
      (((b0##UL << 0x0)|(b1##UL << 0x1)|(b2##UL << 0x2)|(b3##UL << 0x3) |   \
        (b4##UL << 0x4)|(b5##UL << 0x5)|(b6##UL << 0x6)|(b7##UL << 0x7) |   \
        (b8##UL << 0x8)|(b9##UL << 0x9)|(ba##UL << 0xa)|(bb##UL << 0xb) |   \
        (bc##UL << 0xc)|(bd##UL << 0xd)|(be##UL << 0xe)|(bf##UL << 0xf))    \
       << (row % 32))
      /*
       * Undefined/reserved opcodes, conditional jump, Opcode Extension
       * Groups, and some special opcodes can not be boost.
       */
      static const unsigned long twobyte_is_boostable[256 / 32] = {
            /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
            /*      -------------------------------         */
            W(0x00, 0,0,1,1,0,0,1,0,1,1,0,0,0,0,0,0)| /* 00 */
            W(0x10, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 10 */
            W(0x20, 1,1,1,1,0,0,0,0,0,0,0,0,0,0,0,0)| /* 20 */
            W(0x30, 0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 30 */
            W(0x40, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 40 */
            W(0x50, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 50 */
            W(0x60, 1,1,1,1,1,1,1,1,1,1,1,1,0,0,1,1)| /* 60 */
            W(0x70, 0,0,0,0,1,1,1,1,0,0,0,0,0,0,1,1), /* 70 */
            W(0x80, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 80 */
            W(0x90, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1), /* 90 */
            W(0xa0, 1,1,0,1,1,1,0,0,1,1,0,1,1,1,0,1)| /* a0 */
            W(0xb0, 1,1,1,1,1,1,1,1,0,0,0,1,1,1,1,1), /* b0 */
            W(0xc0, 1,1,0,0,0,0,0,0,1,1,1,1,1,1,1,1)| /* c0 */
            W(0xd0, 0,1,1,1,0,1,0,0,1,1,0,1,1,1,0,1), /* d0 */
            W(0xe0, 0,1,1,0,0,1,0,0,1,1,0,1,1,1,0,1)| /* e0 */
            W(0xf0, 0,1,1,1,0,1,0,0,1,1,1,0,1,1,1,0)  /* f0 */
            /*      -------------------------------         */
            /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
      };
#undef W
      kprobe_opcode_t opcode;
      kprobe_opcode_t *orig_opcodes = opcodes;
retry:
      if (opcodes - orig_opcodes > MAX_INSN_SIZE - 1)
            return 0;
      opcode = *(opcodes++);

      /* 2nd-byte opcode */
      if (opcode == 0x0f) {
            if (opcodes - orig_opcodes > MAX_INSN_SIZE - 1)
                  return 0;
            return test_bit(*opcodes, twobyte_is_boostable);
      }

      switch (opcode & 0xf0) {
      case 0x60:
            if (0x63 < opcode && opcode < 0x67)
                  goto retry; /* prefixes */
            /* can't boost Address-size override and bound */
            return (opcode != 0x62 && opcode != 0x67);
      case 0x70:
            return 0; /* can't boost conditional jump */
      case 0xc0:
            /* can't boost software-interruptions */
            return (0xc1 < opcode && opcode < 0xcc) || opcode == 0xcf;
      case 0xd0:
            /* can boost AA* and XLAT */
            return (opcode == 0xd4 || opcode == 0xd5 || opcode == 0xd7);
      case 0xe0:
            /* can boost in/out and absolute jmps */
            return ((opcode & 0x04) || opcode == 0xea);
      case 0xf0:
            if ((opcode & 0x0c) == 0 && opcode != 0xf1)
                  goto retry; /* lock/rep(ne) prefix */
            /* clear and set flags can be boost */
            return (opcode == 0xf5 || (0xf7 < opcode && opcode < 0xfe));
      default:
            if (opcode == 0x26 || opcode == 0x36 || opcode == 0x3e)
                  goto retry; /* prefixes */
            /* can't boost CS override and call */
            return (opcode != 0x2e && opcode != 0x9a);
      }
}

/*
 * returns non-zero if opcode modifies the interrupt flag.
 */
static int __kprobes is_IF_modifier(kprobe_opcode_t opcode)
{
      switch (opcode) {
      case 0xfa:        /* cli */
      case 0xfb:        /* sti */
      case 0xcf:        /* iret/iretd */
      case 0x9d:        /* popf/popfd */
            return 1;
      }
      return 0;
}

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
      /* insn: must be on special executable page on i386. */
      p->ainsn.insn = get_insn_slot();
      if (!p->ainsn.insn)
            return -ENOMEM;

      memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
      p->opcode = *p->addr;
      if (can_boost(p->addr)) {
            p->ainsn.boostable = 0;
      } else {
            p->ainsn.boostable = -1;
      }
      return 0;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
      text_poke(p->addr, ((unsigned char []){BREAKPOINT_INSTRUCTION}), 1);
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
      text_poke(p->addr, &p->opcode, 1);
}

void __kprobes arch_remove_kprobe(struct kprobe *p)
{
      mutex_lock(&kprobe_mutex);
      free_insn_slot(p->ainsn.insn, (p->ainsn.boostable == 1));
      mutex_unlock(&kprobe_mutex);
}

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.old_eflags = kcb->kprobe_old_eflags;
      kcb->prev_kprobe.saved_eflags = kcb->kprobe_saved_eflags;
}

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_old_eflags = kcb->prev_kprobe.old_eflags;
      kcb->kprobe_saved_eflags = kcb->prev_kprobe.saved_eflags;
}

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_eflags = kcb->kprobe_old_eflags
            = (regs->eflags & (TF_MASK | IF_MASK));
      if (is_IF_modifier(p->opcode))
            kcb->kprobe_saved_eflags &= ~IF_MASK;
}

static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
{
      regs->eflags |= TF_MASK;
      regs->eflags &= ~IF_MASK;
      /*single step inline if the instruction is an int3*/
      if (p->opcode == BREAKPOINT_INSTRUCTION)
            regs->eip = (unsigned long)p->addr;
      else
            regs->eip = (unsigned long)p->ainsn.insn;
}

/* Called with kretprobe_lock held */
void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
                              struct pt_regs *regs)
{
      unsigned long *sara = (unsigned long *)&regs->esp;

      ri->ret_addr = (kprobe_opcode_t *) *sara;

      /* Replace the return addr with trampoline addr */
      *sara = (unsigned long) &kretprobe_trampoline;
}

/*
 * Interrupts are disabled on entry as trap3 is an interrupt gate and they
 * remain disabled thorough out this function.
 */
static int __kprobes kprobe_handler(struct pt_regs *regs)
{
      struct kprobe *p;
      int ret = 0;
      kprobe_opcode_t *addr;
      struct kprobe_ctlblk *kcb;

      addr = (kprobe_opcode_t *)(regs->eip - sizeof(kprobe_opcode_t));

      /*
       * 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) {
                  if (kcb->kprobe_status == KPROBE_HIT_SS &&
                        *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
                        regs->eflags &= ~TF_MASK;
                        regs->eflags |= kcb->kprobe_saved_eflags;
                        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);
                  kprobes_inc_nmissed_count(p);
                  prepare_singlestep(p, regs);
                  kcb->kprobe_status = KPROBE_REENTER;
                  return 1;
            } else {
                  if (*addr != BREAKPOINT_INSTRUCTION) {
                  /* The breakpoint instruction was removed by
                   * another cpu right after we hit, no further
                   * handling of this interrupt is appropriate
                   */
                        regs->eip -= sizeof(kprobe_opcode_t);
                        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) {
                  /*
                   * 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.
                   * Back up over the (now missing) int3 and run
                   * the original instruction.
                   */
                  regs->eip -= sizeof(kprobe_opcode_t);
                  ret = 1;
            }
            /* Not one of ours: let kernel handle it */
            goto no_kprobe;
      }

      set_current_kprobe(p, regs, kcb);
      kcb->kprobe_status = KPROBE_HIT_ACTIVE;

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

ss_probe:
#if !defined(CONFIG_PREEMPT) || defined(CONFIG_PM)
      if (p->ainsn.boostable == 1 && !p->post_handler){
            /* Boost up -- we can execute copied instructions directly */
            reset_current_kprobe();
            regs->eip = (unsigned long)p->ainsn.insn;
            preempt_enable_no_resched();
            return 1;
      }
#endif
      prepare_singlestep(p, regs);
      kcb->kprobe_status = KPROBE_HIT_SS;
      return 1;

no_kprobe:
      preempt_enable_no_resched();
      return ret;
}

/*
 * For function-return probes, init_kprobes() establishes a probepoint
 * here. When a retprobed function returns, this probe is hit and
 * trampoline_probe_handler() runs, calling the kretprobe's handler.
 */
 void __kprobes kretprobe_trampoline_holder(void)
 {
      asm volatile ( ".global kretprobe_trampoline\n"
                  "kretprobe_trampoline: \n"
                  "     pushf\n"
                  /* skip cs, eip, orig_eax */
                  "     subl $12, %esp\n"
                  "     pushl %fs\n"
                  "     pushl %ds\n"
                  "     pushl %es\n"
                  "     pushl %eax\n"
                  "     pushl %ebp\n"
                  "     pushl %edi\n"
                  "     pushl %esi\n"
                  "     pushl %edx\n"
                  "     pushl %ecx\n"
                  "     pushl %ebx\n"
                  "     movl %esp, %eax\n"
                  "     call trampoline_handler\n"
                  /* move eflags to cs */
                  "     movl 52(%esp), %edx\n"
                  "     movl %edx, 48(%esp)\n"
                  /* save true return address on eflags */
                  "     movl %eax, 52(%esp)\n"
                  "     popl %ebx\n"
                  "     popl %ecx\n"
                  "     popl %edx\n"
                  "     popl %esi\n"
                  "     popl %edi\n"
                  "     popl %ebp\n"
                  "     popl %eax\n"
                  /* skip eip, orig_eax, es, ds, fs */
                  "     addl $20, %esp\n"
                  "     popf\n"
                  "     ret\n");
}

/*
 * Called from kretprobe_trampoline
 */
fastcall void *__kprobes trampoline_handler(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);
      spin_lock_irqsave(&kretprobe_lock, flags);
      head = kretprobe_inst_table_head(current);
      /* fixup registers */
      regs->xcs = __KERNEL_CS | get_kernel_rpl();
      regs->eip = trampoline_address;
      regs->orig_eax = 0xffffffff;

      /*
       * 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){
                  __get_cpu_var(current_kprobe) = &ri->rp->kp;
                  get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
                  ri->rp->handler(ri, regs);
                  __get_cpu_var(current_kprobe) = NULL;
            }

            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);
      spin_unlock_irqrestore(&kretprobe_lock, flags);

      hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
            hlist_del(&ri->hlist);
            kfree(ri);
      }
      return (void*)orig_ret_address;
}

/*
 * Called after single-stepping.  p->addr is the address of the
 * instruction whose first byte has been replaced by the "int 3"
 * 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.
 *
 * This function prepares to return from the post-single-step
 * interrupt.  We have to fix up the stack as follows:
 *
 * 0) Except in the case of absolute or indirect jump or call instructions,
 * the new eip is relative to the copied instruction.  We need to make
 * it relative to the original instruction.
 *
 * 1) If the single-stepped instruction was pushfl, then the TF and IF
 * flags are set in the just-pushed eflags, and may need to be cleared.
 *
 * 2) If the single-stepped instruction was a call, the return address
 * that is atop the stack is the address following the copied instruction.
 * We need to make it the address following the original instruction.
 *
 * This function also checks instruction size for preparing direct execution.
 */
static void __kprobes resume_execution(struct kprobe *p,
            struct pt_regs *regs, struct kprobe_ctlblk *kcb)
{
      unsigned long *tos = (unsigned long *)&regs->esp;
      unsigned long copy_eip = (unsigned long)p->ainsn.insn;
      unsigned long orig_eip = (unsigned long)p->addr;

      regs->eflags &= ~TF_MASK;
      switch (p->ainsn.insn[0]) {
      case 0x9c:        /* pushfl */
            *tos &= ~(TF_MASK | IF_MASK);
            *tos |= kcb->kprobe_old_eflags;
            break;
      case 0xc2:        /* iret/ret/lret */
      case 0xc3:
      case 0xca:
      case 0xcb:
      case 0xcf:
      case 0xea:        /* jmp absolute -- eip is correct */
            /* eip is already adjusted, no more changes required */
            p->ainsn.boostable = 1;
            goto no_change;
      case 0xe8:        /* call relative - Fix return addr */
            *tos = orig_eip + (*tos - copy_eip);
            break;
      case 0x9a:        /* call absolute -- same as call absolute, indirect */
            *tos = orig_eip + (*tos - copy_eip);
            goto no_change;
      case 0xff:
            if ((p->ainsn.insn[1] & 0x30) == 0x10) {
                  /*
                   * call absolute, indirect
                   * Fix return addr; eip is correct.
                   * But this is not boostable
                   */
                  *tos = orig_eip + (*tos - copy_eip);
                  goto no_change;
            } else if (((p->ainsn.insn[1] & 0x31) == 0x20) ||     /* jmp near, absolute indirect */
                     ((p->ainsn.insn[1] & 0x31) == 0x21)) { /* jmp far, absolute indirect */
                  /* eip is correct. And this is boostable */
                  p->ainsn.boostable = 1;
                  goto no_change;
            }
      default:
            break;
      }

      if (p->ainsn.boostable == 0) {
            if ((regs->eip > copy_eip) &&
                (regs->eip - copy_eip) + 5 < MAX_INSN_SIZE) {
                  /*
                   * These instructions can be executed directly if it
                   * jumps back to correct address.
                   */
                  set_jmp_op((void *)regs->eip,
                           (void *)orig_eip + (regs->eip - copy_eip));
                  p->ainsn.boostable = 1;
            } else {
                  p->ainsn.boostable = -1;
            }
      }

      regs->eip = orig_eip + (regs->eip - copy_eip);

no_change:
      return;
}

/*
 * Interrupts are disabled on entry as trap1 is an interrupt gate and they
 * remain disabled thoroughout this function.
 */
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;

      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, kcb);
      regs->eflags |= kcb->kprobe_saved_eflags;
      trace_hardirqs_fixup_flags(regs->eflags);

      /*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, eflags
       * will have TF set, in which case, continue the remaining processing
       * of do_debug, as if this is not a probe hit.
       */
      if (regs->eflags & TF_MASK)
            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();

      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 eip points back to the probe address
             * and allow the page fault handler to continue as a
             * normal page fault.
             */
            regs->eip = (unsigned long)cur->addr;
            regs->eflags |= kcb->kprobe_old_eflags;
            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 (fixup_exception(regs))
                  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_vm(args->regs))
            return ret;

      switch (val) {
      case DIE_INT3:
            if (kprobe_handler(args->regs))
                  ret = NOTIFY_STOP;
            break;
      case DIE_DEBUG:
            if (post_kprobe_handler(args->regs))
                  ret = NOTIFY_STOP;
            break;
      case DIE_GPF:
            /* kprobe_running() needs smp_processor_id() */
            preempt_disable();
            if (kprobe_running() &&
                kprobe_fault_handler(args->regs, args->trapnr))
                  ret = NOTIFY_STOP;
            preempt_enable();
            break;
      default:
            break;
      }
      return ret;
}

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

      kcb->jprobe_saved_regs = *regs;
      kcb->jprobe_saved_esp = &regs->esp;
      addr = (unsigned long)(kcb->jprobe_saved_esp);

      /*
       * TBD: As Linus pointed out, gcc assumes that the callee
       * owns the argument space and could overwrite it, e.g.
       * tailcall optimization. So, to be absolutely safe
       * we also save and restore enough stack bytes to cover
       * the argument area.
       */
      memcpy(kcb->jprobes_stack, (kprobe_opcode_t *)addr,
                  MIN_STACK_SIZE(addr));
      regs->eflags &= ~IF_MASK;
      trace_hardirqs_off();
      regs->eip = (unsigned long)(jp->entry);
      return 1;
}

void __kprobes jprobe_return(void)
{
      struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

      asm volatile ("       xchgl   %%ebx,%%esp     \n"
                  "       int3                  \n"
                  "       .globl jprobe_return_end    \n"
                  "       jprobe_return_end:    \n"
                  "       nop             \n"::"b"
                  (kcb->jprobe_saved_esp):"memory");
}

int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
      struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
      u8 *addr = (u8 *) (regs->eip - 1);
      unsigned long stack_addr = (unsigned long)(kcb->jprobe_saved_esp);
      struct jprobe *jp = container_of(p, struct jprobe, kp);

      if ((addr > (u8 *) jprobe_return) && (addr < (u8 *) jprobe_return_end)) {
            if (&regs->esp != kcb->jprobe_saved_esp) {
                  struct pt_regs *saved_regs = &kcb->jprobe_saved_regs;
                  printk("current esp %p does not match saved esp %p\n",
                         &regs->esp, kcb->jprobe_saved_esp);
                  printk("Saved registers for jprobe %p\n", jp);
                  show_registers(saved_regs);
                  printk("Current registers\n");
                  show_registers(regs);
                  BUG();
            }
            *regs = kcb->jprobe_saved_regs;
            memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
                   MIN_STACK_SIZE(stack_addr));
            preempt_enable_no_resched();
            return 1;
      }
      return 0;
}

int __kprobes arch_trampoline_kprobe(struct kprobe *p)
{
      return 0;
}

int __init arch_init_kprobes(void)
{
      return 0;
}

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