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kprobes.c

/* arch/sparc64/kernel/kprobes.c
 *
 * Copyright (C) 2004 David S. Miller <davem@davemloft.net>
 */

#include <linux/kernel.h>
#include <linux/kprobes.h>
#include <linux/module.h>
#include <linux/kdebug.h>
#include <asm/signal.h>
#include <asm/cacheflush.h>
#include <asm/uaccess.h>

/* We do not have hardware single-stepping on sparc64.
 * So we implement software single-stepping with breakpoint
 * traps.  The top-level scheme is similar to that used
 * in the x86 kprobes implementation.
 *
 * In the kprobe->ainsn.insn[] array we store the original
 * instruction at index zero and a break instruction at
 * index one.
 *
 * When we hit a kprobe we:
 * - Run the pre-handler
 * - Remember "regs->tnpc" and interrupt level stored in
 *   "regs->tstate" so we can restore them later
 * - Disable PIL interrupts
 * - Set regs->tpc to point to kprobe->ainsn.insn[0]
 * - Set regs->tnpc to point to kprobe->ainsn.insn[1]
 * - Mark that we are actively in a kprobe
 *
 * At this point we wait for the second breakpoint at
 * kprobe->ainsn.insn[1] to hit.  When it does we:
 * - Run the post-handler
 * - Set regs->tpc to "remembered" regs->tnpc stored above,
 *   restore the PIL interrupt level in "regs->tstate" as well
 * - Make any adjustments necessary to regs->tnpc in order
 *   to handle relative branches correctly.  See below.
 * - Mark that we are no longer actively in a kprobe.
 */

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)
{
      p->ainsn.insn[0] = *p->addr;
      flushi(&p->ainsn.insn[0]);

      p->ainsn.insn[1] = BREAKPOINT_INSTRUCTION_2;
      flushi(&p->ainsn.insn[1]);

      p->opcode = *p->addr;
      return 0;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
      *p->addr = BREAKPOINT_INSTRUCTION;
      flushi(p->addr);
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
      *p->addr = p->opcode;
      flushi(p->addr);
}

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.orig_tnpc = kcb->kprobe_orig_tnpc;
      kcb->prev_kprobe.orig_tstate_pil = kcb->kprobe_orig_tstate_pil;
}

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_orig_tnpc = kcb->prev_kprobe.orig_tnpc;
      kcb->kprobe_orig_tstate_pil = kcb->prev_kprobe.orig_tstate_pil;
}

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_orig_tnpc = regs->tnpc;
      kcb->kprobe_orig_tstate_pil = (regs->tstate & TSTATE_PIL);
}

static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs,
                  struct kprobe_ctlblk *kcb)
{
      regs->tstate |= TSTATE_PIL;

      /*single step inline, if it a breakpoint instruction*/
      if (p->opcode == BREAKPOINT_INSTRUCTION) {
            regs->tpc = (unsigned long) p->addr;
            regs->tnpc = kcb->kprobe_orig_tnpc;
      } else {
            regs->tpc = (unsigned long) &p->ainsn.insn[0];
            regs->tnpc = (unsigned long) &p->ainsn.insn[1];
      }
}

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

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

      if (kprobe_running()) {
            p = get_kprobe(addr);
            if (p) {
                  if (kcb->kprobe_status == KPROBE_HIT_SS) {
                        regs->tstate = ((regs->tstate & ~TSTATE_PIL) |
                              kcb->kprobe_orig_tstate_pil);
                        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);
                  kcb->kprobe_status = KPROBE_REENTER;
                  prepare_singlestep(p, regs, kcb);
                  return 1;
            } else {
                  if (*(u32 *)addr != BREAKPOINT_INSTRUCTION) {
                  /* 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 (*(u32 *)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.
                   */
                  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))
            return 1;

ss_probe:
      prepare_singlestep(p, regs, kcb);
      kcb->kprobe_status = KPROBE_HIT_SS;
      return 1;

no_kprobe:
      preempt_enable_no_resched();
      return ret;
}

/* If INSN is a relative control transfer instruction,
 * return the corrected branch destination value.
 *
 * regs->tpc and regs->tnpc still hold the values of the
 * program counters at the time of trap due to the execution
 * of the BREAKPOINT_INSTRUCTION_2 at p->ainsn.insn[1]
 * 
 */
static unsigned long __kprobes relbranch_fixup(u32 insn, struct kprobe *p,
                                     struct pt_regs *regs)
{
      unsigned long real_pc = (unsigned long) p->addr;

      /* Branch not taken, no mods necessary.  */
      if (regs->tnpc == regs->tpc + 0x4UL)
            return real_pc + 0x8UL;

      /* The three cases are call, branch w/prediction,
       * and traditional branch.
       */
      if ((insn & 0xc0000000) == 0x40000000 ||
          (insn & 0xc1c00000) == 0x00400000 ||
          (insn & 0xc1c00000) == 0x00800000) {
            unsigned long ainsn_addr;

            ainsn_addr = (unsigned long) &p->ainsn.insn[0];

            /* The instruction did all the work for us
             * already, just apply the offset to the correct
             * instruction location.
             */
            return (real_pc + (regs->tnpc - ainsn_addr));
      }

      /* It is jmpl or some other absolute PC modification instruction,
       * leave NPC as-is.
       */
      return regs->tnpc;
}

/* If INSN is an instruction which writes it's PC location
 * into a destination register, fix that up.
 */
static void __kprobes retpc_fixup(struct pt_regs *regs, u32 insn,
                          unsigned long real_pc)
{
      unsigned long *slot = NULL;

      /* Simplest case is 'call', which always uses %o7 */
      if ((insn & 0xc0000000) == 0x40000000) {
            slot = &regs->u_regs[UREG_I7];
      }

      /* 'jmpl' encodes the register inside of the opcode */
      if ((insn & 0xc1f80000) == 0x81c00000) {
            unsigned long rd = ((insn >> 25) & 0x1f);

            if (rd <= 15) {
                  slot = &regs->u_regs[rd];
            } else {
                  /* Hard case, it goes onto the stack. */
                  flushw_all();

                  rd -= 16;
                  slot = (unsigned long *)
                        (regs->u_regs[UREG_FP] + STACK_BIAS);
                  slot += rd;
            }
      }
      if (slot != NULL)
            *slot = real_pc;
}

/*
 * Called after single-stepping.  p->addr is the address of the
 * instruction which 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[0].
 *
 * This function prepares to return from the post-single-step
 * breakpoint trap.
 */
static void __kprobes resume_execution(struct kprobe *p,
            struct pt_regs *regs, struct kprobe_ctlblk *kcb)
{
      u32 insn = p->ainsn.insn[0];

      regs->tnpc = relbranch_fixup(insn, p, regs);

      /* This assignment must occur after relbranch_fixup() */
      regs->tpc = kcb->kprobe_orig_tnpc;

      retpc_fixup(regs, insn, (unsigned long) p->addr);

      regs->tstate = ((regs->tstate & ~TSTATE_PIL) |
                  kcb->kprobe_orig_tstate_pil);
}

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);

      /*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();

      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 tpc points back to the probe address
             * and allow the page fault handler to continue as a
             * normal page fault.
             */
            regs->tpc = (unsigned long)cur->addr;
            regs->tnpc = kcb->kprobe_orig_tnpc;
            regs->tstate = ((regs->tstate & ~TSTATE_PIL) |
                        kcb->kprobe_orig_tstate_pil);
            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.
             */

            entry = search_exception_tables(regs->tpc);
            if (entry) {
                  regs->tpc = entry->fixup;
                  regs->tnpc = regs->tpc + 4;
                  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_DEBUG:
            if (kprobe_handler(args->regs))
                  ret = NOTIFY_STOP;
            break;
      case DIE_DEBUG_2:
            if (post_kprobe_handler(args->regs))
                  ret = NOTIFY_STOP;
            break;
      default:
            break;
      }
      return ret;
}

asmlinkage void __kprobes kprobe_trap(unsigned long trap_level,
                              struct pt_regs *regs)
{
      BUG_ON(trap_level != 0x170 && trap_level != 0x171);

      if (user_mode(regs)) {
            local_irq_enable();
            bad_trap(regs, trap_level);
            return;
      }

      /* trap_level == 0x170 --> ta 0x70
       * trap_level == 0x171 --> ta 0x71
       */
      if (notify_die((trap_level == 0x170) ? DIE_DEBUG : DIE_DEBUG_2,
                   (trap_level == 0x170) ? "debug" : "debug_2",
                   regs, 0, trap_level, SIGTRAP) != NOTIFY_STOP)
            bad_trap(regs, trap_level);
}

/* Jprobes support.  */
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(*regs));

      regs->tpc  = (unsigned long) jp->entry;
      regs->tnpc = ((unsigned long) jp->entry) + 0x4UL;
      regs->tstate |= TSTATE_PIL;

      return 1;
}

void __kprobes jprobe_return(void)
{
      struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
      register unsigned long orig_fp asm("g1");

      orig_fp = kcb->jprobe_saved_regs.u_regs[UREG_FP];
      __asm__ __volatile__("\n"
"1:   cmp         %%sp, %0\n\t"
      "blu,a,pt   %%xcc, 1b\n\t"
      " restore\n\t"
      ".globl           jprobe_return_trap_instruction\n"
"jprobe_return_trap_instruction:\n\t"
      "ta         0x70"
      : /* no outputs */
      : "r" (orig_fp));
}

extern void jprobe_return_trap_instruction(void);

int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
      u32 *addr = (u32 *) regs->tpc;
      struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

      if (addr == (u32 *) jprobe_return_trap_instruction) {
            memcpy(regs, &(kcb->jprobe_saved_regs), sizeof(*regs));
            preempt_enable_no_resched();
            return 1;
      }
      return 0;
}

/* The value stored in the return address register is actually 2
 * instructions before where the callee will return to.
 * Sequences usually look something like this
 *
 *          call  some_function     <--- return register points here
 *           nop              <--- call delay slot
 *          whatever          <--- where callee returns to
 *
 * To keep trampoline_probe_handler logic simpler, we normalize the
 * value kept in ri->ret_addr so we don't need to keep adjusting it
 * back and forth.
 */
void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
                              struct pt_regs *regs)
{
      ri->ret_addr = (kprobe_opcode_t *)(regs->u_regs[UREG_RETPC] + 8);

      /* Replace the return addr with trampoline addr */
      regs->u_regs[UREG_RETPC] =
            ((unsigned long)kretprobe_trampoline) - 8;
}

/*
 * Called when the probe at kretprobe trampoline is hit
 */
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->tpc = orig_ret_address;
      regs->tnpc = orig_ret_address + 4;

      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;
}

void kretprobe_trampoline_holder(void)
{
      asm volatile(".global kretprobe_trampoline\n"
                 "kretprobe_trampoline:\n"
                 "\tnop\n"
                 "\tnop\n");
}
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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