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kprobes.c

/*
 * arch/arm/kernel/kprobes.c
 *
 * Kprobes on ARM
 *
 * Abhishek Sagar <sagar.abhishek@gmail.com>
 * Copyright (C) 2006, 2007 Motorola Inc.
 *
 * Nicolas Pitre <nico@marvell.com>
 * Copyright (C) 2007 Marvell Ltd.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * 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.
 */

#include <linux/kernel.h>
#include <linux/kprobes.h>
#include <linux/module.h>
#include <linux/stringify.h>
#include <asm/traps.h>
#include <asm/cacheflush.h>

#define MIN_STACK_SIZE(addr)                    \
      min((unsigned long)MAX_STACK_SIZE,        \
          (unsigned long)current_thread_info() + THREAD_START_SP - (addr))

#define flush_insns(addr, cnt)                        \
      flush_icache_range((unsigned long)(addr), \
                     (unsigned long)(addr) +    \
                     sizeof(kprobe_opcode_t) * (cnt))

/* Used as a marker in ARM_pc to note when we're in a jprobe. */
#define JPROBE_MAGIC_ADDR           0xffffffff

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


int __kprobes arch_prepare_kprobe(struct kprobe *p)
{
      kprobe_opcode_t insn;
      kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
      unsigned long addr = (unsigned long)p->addr;
      int is;

      if (addr & 0x3 || in_exception_text(addr))
            return -EINVAL;

      insn = *p->addr;
      p->opcode = insn;
      p->ainsn.insn = tmp_insn;

      switch (arm_kprobe_decode_insn(insn, &p->ainsn)) {
      case INSN_REJECTED:     /* not supported */
            return -EINVAL;

      case INSN_GOOD:         /* instruction uses slot */
            p->ainsn.insn = get_insn_slot();
            if (!p->ainsn.insn)
                  return -ENOMEM;
            for (is = 0; is < MAX_INSN_SIZE; ++is)
                  p->ainsn.insn[is] = tmp_insn[is];
            flush_insns(p->ainsn.insn, MAX_INSN_SIZE);
            break;

      case INSN_GOOD_NO_SLOT: /* instruction doesn't need insn slot */
            p->ainsn.insn = NULL;
            break;
      }

      return 0;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
      *p->addr = KPROBE_BREAKPOINT_INSTRUCTION;
      flush_insns(p->addr, 1);
}

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

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

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

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;
}

static void __kprobes set_current_kprobe(struct kprobe *p)
{
      __get_cpu_var(current_kprobe) = p;
}

static void __kprobes singlestep(struct kprobe *p, struct pt_regs *regs,
                         struct kprobe_ctlblk *kcb)
{
      regs->ARM_pc += 4;
      p->ainsn.insn_handler(p, regs);
}

/*
 * Called with IRQs disabled. IRQs must remain disabled from that point
 * all the way until processing this kprobe is complete.  The current
 * kprobes implementation cannot process more than one nested level of
 * kprobe, and that level is reserved for user kprobe handlers, so we can't
 * risk encountering a new kprobe in an interrupt handler.
 */
void __kprobes kprobe_handler(struct pt_regs *regs)
{
      struct kprobe *p, *cur;
      struct kprobe_ctlblk *kcb;
      kprobe_opcode_t   *addr = (kprobe_opcode_t *)regs->ARM_pc;

      kcb = get_kprobe_ctlblk();
      cur = kprobe_running();
      p = get_kprobe(addr);

      if (p) {
            if (cur) {
                  /* Kprobe is pending, so we're recursing. */
                  switch (kcb->kprobe_status) {
                  case KPROBE_HIT_ACTIVE:
                  case KPROBE_HIT_SSDONE:
                        /* A pre- or post-handler probe got us here. */
                        kprobes_inc_nmissed_count(p);
                        save_previous_kprobe(kcb);
                        set_current_kprobe(p);
                        kcb->kprobe_status = KPROBE_REENTER;
                        singlestep(p, regs, kcb);
                        restore_previous_kprobe(kcb);
                        break;
                  default:
                        /* impossible cases */
                        BUG();
                  }
            } else {
                  set_current_kprobe(p);
                  kcb->kprobe_status = KPROBE_HIT_ACTIVE;

                  /*
                   * If we have no pre-handler or it returned 0, we
                   * continue with normal processing.  If we have a
                   * pre-handler and it returned non-zero, it prepped
                   * for calling the break_handler below on re-entry,
                   * so get out doing nothing more here.
                   */
                  if (!p->pre_handler || !p->pre_handler(p, regs)) {
                        kcb->kprobe_status = KPROBE_HIT_SS;
                        singlestep(p, regs, kcb);
                        if (p->post_handler) {
                              kcb->kprobe_status = KPROBE_HIT_SSDONE;
                              p->post_handler(p, regs, 0);
                        }
                        reset_current_kprobe();
                  }
            }
      } else if (cur) {
            /* We probably hit a jprobe.  Call its break handler. */
            if (cur->break_handler && cur->break_handler(cur, regs)) {
                  kcb->kprobe_status = KPROBE_HIT_SS;
                  singlestep(cur, regs, kcb);
                  if (cur->post_handler) {
                        kcb->kprobe_status = KPROBE_HIT_SSDONE;
                        cur->post_handler(cur, regs, 0);
                  }
            }
            reset_current_kprobe();
      } else {
            /*
             * The probe was removed and a race is in progress.
             * There is nothing we can do about it.  Let's restart
             * the instruction.  By the time we can restart, the
             * real instruction will be there.
             */
      }
}

static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
{
      unsigned long flags;
      local_irq_save(flags);
      kprobe_handler(regs);
      local_irq_restore(flags);
      return 0;
}

int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
{
      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 PC to point back to the probe address
             * and allow the page fault handler to continue as a
             * normal page fault.
             */
            regs->ARM_pc = (long)cur->addr;
            if (kcb->kprobe_status == KPROBE_REENTER) {
                  restore_previous_kprobe(kcb);
            } else {
                  reset_current_kprobe();
            }
            break;

      case KPROBE_HIT_ACTIVE:
      case KPROBE_HIT_SSDONE:
            /*
             * We increment the nmissed count for accounting,
             * we can also use npre/npostfault count for accounting
             * 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.
             */
            if (cur->fault_handler && cur->fault_handler(cur, regs, fsr))
                  return 1;
            break;

      default:
            break;
      }

      return 0;
}

int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
                               unsigned long val, void *data)
{
      /*
       * notify_die() is currently never called on ARM,
       * so this callback is currently empty.
       */
      return NOTIFY_DONE;
}

/*
 * When a retprobed function returns, trampoline_handler() is called,
 * calling the kretprobe's handler. We construct a struct pt_regs to
 * give a view of registers r0-r11 to the user return-handler.  This is
 * not a complete pt_regs structure, but that should be plenty sufficient
 * for kretprobe handlers which should normally be interested in r0 only
 * anyway.
 */
void __naked __kprobes kretprobe_trampoline(void)
{
      __asm__ __volatile__ (
            "stmdb      sp!, {r0 - r11}         \n\t"
            "mov  r0, sp                  \n\t"
            "bl   trampoline_handler      \n\t"
            "mov  lr, r0                  \n\t"
            "ldmia      sp!, {r0 - r11}         \n\t"
            "mov  pc, lr                  \n\t"
            : : : "memory");
}

/* Called from kretprobe_trampoline */
static __used __kprobes void *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);
      kretprobe_hash_lock(current, &head, &flags);

      /*
       * It is possible to have multiple instances associated with a given
       * task either because multiple functions in the call path have
       * a return probe installed on them, and/or more than one 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);
      kretprobe_hash_unlock(current, &flags);

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

      return (void *)orig_ret_address;
}

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

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

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();
      long sp_addr = regs->ARM_sp;

      kcb->jprobe_saved_regs = *regs;
      memcpy(kcb->jprobes_stack, (void *)sp_addr, MIN_STACK_SIZE(sp_addr));
      regs->ARM_pc = (long)jp->entry;
      regs->ARM_cpsr |= PSR_I_BIT;
      preempt_disable();
      return 1;
}

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

      __asm__ __volatile__ (
            /*
             * Setup an empty pt_regs. Fill SP and PC fields as
             * they're needed by longjmp_break_handler.
             */
            "sub    sp, %0, %1            \n\t"
            "ldr    r0, ="__stringify(JPROBE_MAGIC_ADDR)"\n\t"
            "str    %0, [sp, %2]          \n\t"
            "str    r0, [sp, %3]          \n\t"
            "mov    r0, sp                \n\t"
            "bl     kprobe_handler        \n\t"

            /*
             * Return to the context saved by setjmp_pre_handler
             * and restored by longjmp_break_handler.
             */
            "ldr  r0, [sp, %4]            \n\t"
            "msr  cpsr_cxsf, r0           \n\t"
            "ldmia      sp, {r0 - pc}           \n\t"
            :
            : "r" (kcb->jprobe_saved_regs.ARM_sp),
              "I" (sizeof(struct pt_regs)),
              "J" (offsetof(struct pt_regs, ARM_sp)),
              "J" (offsetof(struct pt_regs, ARM_pc)),
              "J" (offsetof(struct pt_regs, ARM_cpsr))
            : "memory", "cc");
}

int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
      struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
      long stack_addr = kcb->jprobe_saved_regs.ARM_sp;
      long orig_sp = regs->ARM_sp;
      struct jprobe *jp = container_of(p, struct jprobe, kp);

      if (regs->ARM_pc == JPROBE_MAGIC_ADDR) {
            if (orig_sp != stack_addr) {
                  struct pt_regs *saved_regs =
                        (struct pt_regs *)kcb->jprobe_saved_regs.ARM_sp;
                  printk("current sp %lx does not match saved sp %lx\n",
                         orig_sp, stack_addr);
                  printk("Saved registers for jprobe %p\n", jp);
                  show_regs(saved_regs);
                  printk("Current registers\n");
                  show_regs(regs);
                  BUG();
            }
            *regs = kcb->jprobe_saved_regs;
            memcpy((void *)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;
}

static struct undef_hook kprobes_break_hook = {
      .instr_mask = 0xffffffff,
      .instr_val  = KPROBE_BREAKPOINT_INSTRUCTION,
      .cpsr_mask  = MODE_MASK,
      .cpsr_val   = SVC_MODE,
      .fn         = kprobe_trap_handler,
};

int __init arch_init_kprobes()
{
      arm_kprobe_decode_init();
      register_undef_hook(&kprobes_break_hook);
      return 0;
}

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