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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, 2006
 *
 * s390 port, used ppc64 as template. Mike Grundy <grundym@us.ibm.com>
 */

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

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)
{
      /* Make sure the probe isn't going on a difficult instruction */
      if (is_prohibited_opcode((kprobe_opcode_t *) p->addr))
            return -EINVAL;

      if ((unsigned long)p->addr & 0x01) {
            printk("Attempt to register kprobe at an unaligned address\n");
            return -EINVAL;
            }

      /* Use the get_insn_slot() facility for correctness */
      if (!(p->ainsn.insn = get_insn_slot()))
            return -ENOMEM;

      memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t));

      get_instruction_type(&p->ainsn);
      p->opcode = *p->addr;
      return 0;
}

int __kprobes is_prohibited_opcode(kprobe_opcode_t *instruction)
{
      switch (*(__u8 *) instruction) {
      case 0x0c:  /* bassm */
      case 0x0b:  /* bsm       */
      case 0x83:  /* diag  */
      case 0x44:  /* ex  */
            return -EINVAL;
      }
      switch (*(__u16 *) instruction) {
      case 0x0101:      /* pr  */
      case 0xb25a:      /* bsa       */
      case 0xb240:      /* bakr  */
      case 0xb258:      /* bsg       */
      case 0xb218:      /* pc  */
      case 0xb228:      /* pt  */
            return -EINVAL;
      }
      return 0;
}

void __kprobes get_instruction_type(struct arch_specific_insn *ainsn)
{
      /* default fixup method */
      ainsn->fixup = FIXUP_PSW_NORMAL;

      /* save r1 operand */
      ainsn->reg = (*ainsn->insn & 0xf0) >> 4;

      /* save the instruction length (pop 5-5) in bytes */
      switch (*(__u8 *) (ainsn->insn) >> 6) {
      case 0:
            ainsn->ilen = 2;
            break;
      case 1:
      case 2:
            ainsn->ilen = 4;
            break;
      case 3:
            ainsn->ilen = 6;
            break;
      }

      switch (*(__u8 *) ainsn->insn) {
      case 0x05:  /* balr     */
      case 0x0d:  /* basr */
            ainsn->fixup = FIXUP_RETURN_REGISTER;
            /* if r2 = 0, no branch will be taken */
            if ((*ainsn->insn & 0x0f) == 0)
                  ainsn->fixup |= FIXUP_BRANCH_NOT_TAKEN;
            break;
      case 0x06:  /* bctr     */
      case 0x07:  /* bcr      */
            ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
            break;
      case 0x45:  /* bal      */
      case 0x4d:  /* bas      */
            ainsn->fixup = FIXUP_RETURN_REGISTER;
            break;
      case 0x47:  /* bc */
      case 0x46:  /* bct      */
      case 0x86:  /* bxh      */
      case 0x87:  /* bxle     */
            ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
            break;
      case 0x82:  /* lpsw     */
            ainsn->fixup = FIXUP_NOT_REQUIRED;
            break;
      case 0xb2:  /* lpswe */
            if (*(((__u8 *) ainsn->insn) + 1) == 0xb2) {
                  ainsn->fixup = FIXUP_NOT_REQUIRED;
            }
            break;
      case 0xa7:  /* bras     */
            if ((*ainsn->insn & 0x0f) == 0x05) {
                  ainsn->fixup |= FIXUP_RETURN_REGISTER;
            }
            break;
      case 0xc0:
            if ((*ainsn->insn & 0x0f) == 0x00  /* larl  */
                  || (*ainsn->insn & 0x0f) == 0x05) /* brasl */
            ainsn->fixup |= FIXUP_RETURN_REGISTER;
            break;
      case 0xeb:
            if (*(((__u8 *) ainsn->insn) + 5 ) == 0x44 ||   /* bxhg  */
                  *(((__u8 *) ainsn->insn) + 5) == 0x45) {/* bxleg */
                  ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
            }
            break;
      case 0xe3:  /* bctg     */
            if (*(((__u8 *) ainsn->insn) + 5) == 0x46) {
                  ainsn->fixup = FIXUP_BRANCH_NOT_TAKEN;
            }
            break;
      }
}

static int __kprobes swap_instruction(void *aref)
{
      struct ins_replace_args *args = aref;
      u32 *addr;
      u32 instr;
      int err = -EFAULT;

      /*
       * Text segment is read-only, hence we use stura to bypass dynamic
       * address translation to exchange the instruction. Since stura
       * always operates on four bytes, but we only want to exchange two
       * bytes do some calculations to get things right. In addition we
       * shall not cross any page boundaries (vmalloc area!) when writing
       * the new instruction.
       */
      addr = (u32 *)((unsigned long)args->ptr & -4UL);
      if ((unsigned long)args->ptr & 2)
            instr = ((*addr) & 0xffff0000) | args->new;
      else
            instr = ((*addr) & 0x0000ffff) | args->new << 16;

      asm volatile(
            "     lra   %1,0(%1)\n"
            "0:   stura %2,%1\n"
            "1:   la    %0,0\n"
            "2:\n"
            EX_TABLE(0b,2b)
            : "+d" (err)
            : "a" (addr), "d" (instr)
            : "memory", "cc");

      return err;
}

void __kprobes arch_arm_kprobe(struct kprobe *p)
{
      struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
      unsigned long status = kcb->kprobe_status;
      struct ins_replace_args args;

      args.ptr = p->addr;
      args.old = p->opcode;
      args.new = BREAKPOINT_INSTRUCTION;

      kcb->kprobe_status = KPROBE_SWAP_INST;
      stop_machine_run(swap_instruction, &args, NR_CPUS);
      kcb->kprobe_status = status;
}

void __kprobes arch_disarm_kprobe(struct kprobe *p)
{
      struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
      unsigned long status = kcb->kprobe_status;
      struct ins_replace_args args;

      args.ptr = p->addr;
      args.old = BREAKPOINT_INSTRUCTION;
      args.new = p->opcode;

      kcb->kprobe_status = KPROBE_SWAP_INST;
      stop_machine_run(swap_instruction, &args, NR_CPUS);
      kcb->kprobe_status = status;
}

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)
{
      per_cr_bits kprobe_per_regs[1];

      memset(kprobe_per_regs, 0, sizeof(per_cr_bits));
      regs->psw.addr = (unsigned long)p->ainsn.insn | PSW_ADDR_AMODE;

      /* Set up the per control reg info, will pass to lctl */
      kprobe_per_regs[0].em_instruction_fetch = 1;
      kprobe_per_regs[0].starting_addr = (unsigned long)p->ainsn.insn;
      kprobe_per_regs[0].ending_addr = (unsigned long)p->ainsn.insn + 1;

      /* Set the PER control regs, turns on single step for this address */
      __ctl_load(kprobe_per_regs, 9, 11);
      regs->psw.mask |= PSW_MASK_PER;
      regs->psw.mask &= ~(PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
}

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.kprobe_saved_imask = kcb->kprobe_saved_imask;
      memcpy(kcb->prev_kprobe.kprobe_saved_ctl, kcb->kprobe_saved_ctl,
                              sizeof(kcb->kprobe_saved_ctl));
}

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_imask = kcb->prev_kprobe.kprobe_saved_imask;
      memcpy(kcb->kprobe_saved_ctl, kcb->prev_kprobe.kprobe_saved_ctl,
                              sizeof(kcb->kprobe_saved_ctl));
}

static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
                                    struct kprobe_ctlblk *kcb)
{
      __get_cpu_var(current_kprobe) = p;
      /* Save the interrupt and per flags */
      kcb->kprobe_saved_imask = regs->psw.mask &
          (PSW_MASK_PER | PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK);
      /* Save the control regs that govern PER */
      __ctl_store(kcb->kprobe_saved_ctl, 9, 11);
}

/* Called with kretprobe_lock held */
void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
                              struct pt_regs *regs)
{
      ri->ret_addr = (kprobe_opcode_t *) regs->gprs[14];

      /* Replace the return addr with trampoline addr */
      regs->gprs[14] = (unsigned long)&kretprobe_trampoline;
}

static int __kprobes kprobe_handler(struct pt_regs *regs)
{
      struct kprobe *p;
      int ret = 0;
      unsigned long *addr = (unsigned long *)
            ((regs->psw.addr & PSW_ADDR_INSN) - 2);
      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->psw.mask &= ~PSW_MASK_PER;
                        regs->psw.mask |= kcb->kprobe_saved_imask;
                        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 {
                  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)
            /*
             * No kprobe at this address. The fault has not been
             * caused by a kprobe breakpoint. The race of breakpoint
             * vs. kprobe remove does not exist because on s390 we
             * use stop_machine_run to arm/disarm the breakpoints.
             */
            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:
      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
 */
void kretprobe_trampoline_holder(void)
{
      asm volatile(".global kretprobe_trampoline\n"
                 "kretprobe_trampoline: bcr 0,0\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);
      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->psw.addr = orig_ret_address | PSW_ADDR_AMODE;

      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 "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)
{
      struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

      regs->psw.addr &= PSW_ADDR_INSN;

      if (p->ainsn.fixup & FIXUP_PSW_NORMAL)
            regs->psw.addr = (unsigned long)p->addr +
                        ((unsigned long)regs->psw.addr -
                         (unsigned long)p->ainsn.insn);

      if (p->ainsn.fixup & FIXUP_BRANCH_NOT_TAKEN)
            if ((unsigned long)regs->psw.addr -
                (unsigned long)p->ainsn.insn == p->ainsn.ilen)
                  regs->psw.addr = (unsigned long)p->addr + p->ainsn.ilen;

      if (p->ainsn.fixup & FIXUP_RETURN_REGISTER)
            regs->gprs[p->ainsn.reg] = ((unsigned long)p->addr +
                                    (regs->gprs[p->ainsn.reg] -
                                    (unsigned long)p->ainsn.insn))
                                    | PSW_ADDR_AMODE;

      regs->psw.addr |= PSW_ADDR_AMODE;
      /* turn off PER mode */
      regs->psw.mask &= ~PSW_MASK_PER;
      /* Restore the original per control regs */
      __ctl_load(kcb->kprobe_saved_ctl, 9, 11);
      regs->psw.mask |= kcb->kprobe_saved_imask;
}

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);

      /*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, psw mask
       * will have PER set, in which case, continue the remaining processing
       * of do_single_step, as if this is not a probe hit.
       */
      if (regs->psw.mask & PSW_MASK_PER) {
            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_SWAP_INST:
            /* We are here because the instruction replacement failed */
            return 0;
      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->psw.addr = (unsigned long)cur->addr | PSW_ADDR_AMODE;
            regs->psw.mask &= ~PSW_MASK_PER;
            regs->psw.mask |= kcb->kprobe_saved_imask;
            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->psw.addr & PSW_ADDR_INSN);
            if (entry) {
                  regs->psw.addr = entry->fixup | PSW_ADDR_AMODE;
                  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;

      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;
      case DIE_TRAP:
            /* 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();

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

      /* setup return addr to the jprobe handler routine */
      regs->psw.addr = (unsigned long)(jp->entry) | PSW_ADDR_AMODE;

      /* r14 is the function return address */
      kcb->jprobe_saved_r14 = (unsigned long)regs->gprs[14];
      /* r15 is the stack pointer */
      kcb->jprobe_saved_r15 = (unsigned long)regs->gprs[15];
      addr = (unsigned long)kcb->jprobe_saved_r15;

      memcpy(kcb->jprobes_stack, (kprobe_opcode_t *) addr,
             MIN_STACK_SIZE(addr));
      return 1;
}

void __kprobes jprobe_return(void)
{
      asm volatile(".word 0x0002");
}

void __kprobes jprobe_return_end(void)
{
      asm volatile("bcr 0,0");
}

int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
{
      struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
      unsigned long stack_addr = (unsigned long)(kcb->jprobe_saved_r15);

      /* Put the regs back */
      memcpy(regs, &kcb->jprobe_saved_regs, sizeof(struct pt_regs));
      /* put the stack back */
      memcpy((kprobe_opcode_t *) stack_addr, kcb->jprobes_stack,
             MIN_STACK_SIZE(stack_addr));
      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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