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kprobes_64.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-Oct Jim Keniston <kenistoj@us.ibm.com> and Prasanna S Panchamukhi
 *          <prasanna@in.ibm.com> adapted for x86_64
 * 2005-Mar Roland McGrath <roland@redhat.com>
 *          Fixed to handle %rip-relative addressing mode correctly.
 * 2005-May     Rusty Lynch <rusty.lynch@intel.com>
 *              Added function return probes functionality
 */

#include <linux/kprobes.h>
#include <linux/ptrace.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/preempt.h>
#include <linux/module.h>
#include <linux/kdebug.h>

#include <asm/pgtable.h>
#include <asm/uaccess.h>
#include <asm/alternative.h>

void jprobe_return_end(void);
static void __kprobes arch_copy_kprobe(struct kprobe *p);

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);

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

      if (*insn  >= 0x40 && *insn <= 0x4f && *++insn == 0xcf)
            return 1;
      return 0;
}

int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
      /* insn: must be on special executable page on x86_64. */
      p->ainsn.insn = get_insn_slot();
      if (!p->ainsn.insn) {
            return -ENOMEM;
      }
      arch_copy_kprobe(p);
      return 0;
}

/*
 * Determine if the instruction uses the %rip-relative addressing mode.
 * If it does, return the address of the 32-bit displacement word.
 * If not, return null.
 */
static s32 __kprobes *is_riprel(u8 *insn)
{
#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 % 64))
      static const u64 onebyte_has_modrm[256 / 64] = {
            /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
            /*      -------------------------------         */
            W(0x00, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0)| /* 00 */
            W(0x10, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0)| /* 10 */
            W(0x20, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0)| /* 20 */
            W(0x30, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0), /* 30 */
            W(0x40, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 40 */
            W(0x50, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 50 */
            W(0x60, 0,0,1,1,0,0,0,0,0,1,0,1,0,0,0,0)| /* 60 */
            W(0x70, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 70 */
            W(0x80, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 80 */
            W(0x90, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 90 */
            W(0xa0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* a0 */
            W(0xb0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* b0 */
            W(0xc0, 1,1,0,0,1,1,1,1,0,0,0,0,0,0,0,0)| /* c0 */
            W(0xd0, 1,1,1,1,0,0,0,0,1,1,1,1,1,1,1,1)| /* d0 */
            W(0xe0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* e0 */
            W(0xf0, 0,0,0,0,0,0,1,1,0,0,0,0,0,0,1,1)  /* f0 */
            /*      -------------------------------         */
            /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
      };
      static const u64 twobyte_has_modrm[256 / 64] = {
            /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
            /*      -------------------------------         */
            W(0x00, 1,1,1,1,0,0,0,0,0,0,0,0,0,1,0,1)| /* 0f */
            W(0x10, 1,1,1,1,1,1,1,1,1,0,0,0,0,0,0,0)| /* 1f */
            W(0x20, 1,1,1,1,1,0,1,0,1,1,1,1,1,1,1,1)| /* 2f */
            W(0x30, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 3f */
            W(0x40, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 4f */
            W(0x50, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 5f */
            W(0x60, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 6f */
            W(0x70, 1,1,1,1,1,1,1,0,0,0,0,0,1,1,1,1), /* 7f */
            W(0x80, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 8f */
            W(0x90, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 9f */
            W(0xa0, 0,0,0,1,1,1,1,1,0,0,0,1,1,1,1,1)| /* af */
            W(0xb0, 1,1,1,1,1,1,1,1,0,0,1,1,1,1,1,1), /* bf */
            W(0xc0, 1,1,1,1,1,1,1,1,0,0,0,0,0,0,0,0)| /* cf */
            W(0xd0, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* df */
            W(0xe0, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* ef */
            W(0xf0, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0)  /* ff */
            /*      -------------------------------         */
            /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
      };
#undef      W
      int need_modrm;

      /* Skip legacy instruction prefixes.  */
      while (1) {
            switch (*insn) {
            case 0x66:
            case 0x67:
            case 0x2e:
            case 0x3e:
            case 0x26:
            case 0x64:
            case 0x65:
            case 0x36:
            case 0xf0:
            case 0xf3:
            case 0xf2:
                  ++insn;
                  continue;
            }
            break;
      }

      /* Skip REX instruction prefix.  */
      if ((*insn & 0xf0) == 0x40)
            ++insn;

      if (*insn == 0x0f) {    /* Two-byte opcode.  */
            ++insn;
            need_modrm = test_bit(*insn, twobyte_has_modrm);
      } else {          /* One-byte opcode.  */
            need_modrm = test_bit(*insn, onebyte_has_modrm);
      }

      if (need_modrm) {
            u8 modrm = *++insn;
            if ((modrm & 0xc7) == 0x05) { /* %rip+disp32 addressing mode */
                  /* Displacement follows ModRM byte.  */
                  return (s32 *) ++insn;
            }
      }

      /* No %rip-relative addressing mode here.  */
      return NULL;
}

static void __kprobes arch_copy_kprobe(struct kprobe *p)
{
      s32 *ripdisp;
      memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE);
      ripdisp = is_riprel(p->ainsn.insn);
      if (ripdisp) {
            /*
             * The copied instruction uses the %rip-relative
             * addressing mode.  Adjust the displacement for the
             * difference between the original location of this
             * instruction and the location of the copy that will
             * actually be run.  The tricky bit here is making sure
             * that the sign extension happens correctly in this
             * calculation, since we need a signed 32-bit result to
             * be sign-extended to 64 bits when it's added to the
             * %rip value and yield the same 64-bit result that the
             * sign-extension of the original signed 32-bit
             * displacement would have given.
             */
            s64 disp = (u8 *) p->addr + *ripdisp - (u8 *) p->ainsn.insn;
            BUG_ON((s64) (s32) disp != disp); /* Sanity check.  */
            *ripdisp = disp;
      }
      p->opcode = *p->addr;
}

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, 0);
      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_rflags = kcb->kprobe_old_rflags;
      kcb->prev_kprobe.saved_rflags = kcb->kprobe_saved_rflags;
}

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_rflags = kcb->prev_kprobe.old_rflags;
      kcb->kprobe_saved_rflags = kcb->prev_kprobe.saved_rflags;
}

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_rflags = kcb->kprobe_old_rflags
            = (regs->eflags & (TF_MASK | IF_MASK));
      if (is_IF_modifier(p->ainsn.insn))
            kcb->kprobe_saved_rflags &= ~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->rip = (unsigned long)p->addr;
      else
            regs->rip = (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->rsp;

      ri->ret_addr = (kprobe_opcode_t *) *sara;
      /* Replace the return addr with trampoline addr */
      *sara = (unsigned long) &kretprobe_trampoline;
}

int __kprobes kprobe_handler(struct pt_regs *regs)
{
      struct kprobe *p;
      int ret = 0;
      kprobe_opcode_t *addr = (kprobe_opcode_t *)(regs->rip - sizeof(kprobe_opcode_t));
      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) {
                  if (kcb->kprobe_status == KPROBE_HIT_SS &&
                        *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
                        regs->eflags &= ~TF_MASK;
                        regs->eflags |= kcb->kprobe_saved_rflags;
                        goto no_kprobe;
                  } else if (kcb->kprobe_status == KPROBE_HIT_SSDONE) {
                        /* TODO: Provide re-entrancy from
                         * post_kprobes_handler() and avoid exception
                         * stack corruption while single-stepping on
                         * the instruction of the new probe.
                         */
                        arch_disarm_kprobe(p);
                        regs->rip = (unsigned long)p->addr;
                        reset_current_kprobe();
                        ret = 1;
                  } else {
                        /* We have reentered the kprobe_handler(), since
                         * another probe was hit while within the
                         * handler. We here save the original kprobe
                         * variables and just single step on 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->rip = (unsigned long)addr;
                        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->rip = (unsigned long)addr;
                  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:
      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 kretprobe_trampoline_holder(void)
 {
      asm volatile (  ".global kretprobe_trampoline\n"
                  "kretprobe_trampoline: \n"
                  "nop\n");
 }

/*
 * Called when we hit the probe point at kretprobe_trampoline
 */
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);
      spin_lock_irqsave(&kretprobe_lock, flags);
      head = kretprobe_inst_table_head(current);

      /*
       * 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->rip = orig_ret_address;

      reset_current_kprobe();
      spin_unlock_irqrestore(&kretprobe_lock, 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 "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 rip 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.
 */
static void __kprobes resume_execution(struct kprobe *p,
            struct pt_regs *regs, struct kprobe_ctlblk *kcb)
{
      unsigned long *tos = (unsigned long *)regs->rsp;
      unsigned long copy_rip = (unsigned long)p->ainsn.insn;
      unsigned long orig_rip = (unsigned long)p->addr;
      kprobe_opcode_t *insn = p->ainsn.insn;

      /*skip the REX prefix*/
      if (*insn >= 0x40 && *insn <= 0x4f)
            insn++;

      regs->eflags &= ~TF_MASK;
      switch (*insn) {
      case 0x9c:  /* pushfl */
            *tos &= ~(TF_MASK | IF_MASK);
            *tos |= kcb->kprobe_old_rflags;
            break;
      case 0xc2:  /* iret/ret/lret */
      case 0xc3:
      case 0xca:
      case 0xcb:
      case 0xcf:
      case 0xea:  /* jmp absolute -- ip is correct */
            /* ip is already adjusted, no more changes required */
            goto no_change;
      case 0xe8:  /* call relative - Fix return addr */
            *tos = orig_rip + (*tos - copy_rip);
            break;
      case 0xff:
            if ((insn[1] & 0x30) == 0x10) {
                  /* call absolute, indirect */
                  /* Fix return addr; ip is correct. */
                  *tos = orig_rip + (*tos - copy_rip);
                  goto no_change;
            } else if (((insn[1] & 0x31) == 0x20) ||  /* jmp near, absolute indirect */
                     ((insn[1] & 0x31) == 0x21)) {    /* jmp far, absolute indirect */
                  /* ip is correct. */
                  goto no_change;
            }
      default:
            break;
      }

      regs->rip = orig_rip + (regs->rip - copy_rip);
no_change:

      return;
}

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_rflags;
      trace_hardirqs_fixup_flags(regs->eflags);

      /* Restore 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();
      const struct exception_table_entry *fixup;

      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 rip points back to the probe address
             * and allow the page fault handler to continue as a
             * normal page fault.
             */
            regs->rip = (unsigned long)cur->addr;
            regs->eflags |= kcb->kprobe_old_rflags;
            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.
             */
            fixup = search_exception_tables(regs->rip);
            if (fixup) {
                  regs->rip = fixup->fixup;
                  return 1;
            }

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

/*
 * Wrapper routine 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_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_rsp = (long *) regs->rsp;
      addr = (unsigned long)(kcb->jprobe_saved_rsp);
      /*
       * 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->rip = (unsigned long)(jp->entry);
      return 1;
}

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

      asm volatile ("       xchg   %%rbx,%%rsp     \n"
                  "       int3                  \n"
                  "       .globl jprobe_return_end    \n"
                  "       jprobe_return_end:    \n"
                  "       nop             \n"::"b"
                  (kcb->jprobe_saved_rsp):"memory");
}

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

      if ((addr > (u8 *) jprobe_return) && (addr < (u8 *) jprobe_return_end)) {
            if ((unsigned long *)regs->rsp != kcb->jprobe_saved_rsp) {
                  struct pt_regs *saved_regs = &kcb->jprobe_saved_regs;
                  printk("current rsp %p does not match saved rsp %p\n",
                         (long *)regs->rsp, kcb->jprobe_saved_rsp);
                  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;
}

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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