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traps.c

/*
 *  linux/arch/arm/kernel/traps.c
 *
 *  Copyright (C) 1995-2002 Russell King
 *  Fragments that appear the same as linux/arch/i386/kernel/traps.c (C) Linus Torvalds
 *
 * 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.
 *
 *  'traps.c' handles hardware exceptions after we have saved some state in
 *  'linux/arch/arm/lib/traps.S'.  Mostly a debugging aid, but will probably
 *  kill the offending process.
 */
#include <linux/module.h>
#include <linux/signal.h>
#include <linux/spinlock.h>
#include <linux/personality.h>
#include <linux/kallsyms.h>
#include <linux/delay.h>
#include <linux/init.h>

#include <asm/atomic.h>
#include <asm/cacheflush.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include <asm/unistd.h>
#include <asm/traps.h>
#include <asm/io.h>

#include "ptrace.h"
#include "signal.h"

static const char *handler[]= { "prefetch abort", "data abort", "address exception", "interrupt" };

#ifdef CONFIG_DEBUG_USER
unsigned int user_debug;

static int __init user_debug_setup(char *str)
{
      get_option(&str, &user_debug);
      return 1;
}
__setup("user_debug=", user_debug_setup);
#endif

static void dump_mem(const char *str, unsigned long bottom, unsigned long top);

static inline int in_exception_text(unsigned long ptr)
{
      extern char __exception_text_start[];
      extern char __exception_text_end[];

      return ptr >= (unsigned long)&__exception_text_start &&
             ptr < (unsigned long)&__exception_text_end;
}

void dump_backtrace_entry(unsigned long where, unsigned long from, unsigned long frame)
{
#ifdef CONFIG_KALLSYMS
      printk("[<%08lx>] ", where);
      print_symbol("(%s) ", where);
      printk("from [<%08lx>] ", from);
      print_symbol("(%s)\n", from);
#else
      printk("Function entered at [<%08lx>] from [<%08lx>]\n", where, from);
#endif

      if (in_exception_text(where))
            dump_mem("Exception stack", frame + 4, frame + 4 + sizeof(struct pt_regs));
}

/*
 * Stack pointers should always be within the kernels view of
 * physical memory.  If it is not there, then we can't dump
 * out any information relating to the stack.
 */
static int verify_stack(unsigned long sp)
{
      if (sp < PAGE_OFFSET || (sp > (unsigned long)high_memory && high_memory != 0))
            return -EFAULT;

      return 0;
}

/*
 * Dump out the contents of some memory nicely...
 */
static void dump_mem(const char *str, unsigned long bottom, unsigned long top)
{
      unsigned long p = bottom & ~31;
      mm_segment_t fs;
      int i;

      /*
       * We need to switch to kernel mode so that we can use __get_user
       * to safely read from kernel space.  Note that we now dump the
       * code first, just in case the backtrace kills us.
       */
      fs = get_fs();
      set_fs(KERNEL_DS);

      printk("%s(0x%08lx to 0x%08lx)\n", str, bottom, top);

      for (p = bottom & ~31; p < top;) {
            printk("%04lx: ", p & 0xffff);

            for (i = 0; i < 8; i++, p += 4) {
                  unsigned int val;

                  if (p < bottom || p >= top)
                        printk("         ");
                  else {
                        __get_user(val, (unsigned long *)p);
                        printk("%08x ", val);
                  }
            }
            printk ("\n");
      }

      set_fs(fs);
}

static void dump_instr(struct pt_regs *regs)
{
      unsigned long addr = instruction_pointer(regs);
      const int thumb = thumb_mode(regs);
      const int width = thumb ? 4 : 8;
      mm_segment_t fs;
      int i;

      /*
       * We need to switch to kernel mode so that we can use __get_user
       * to safely read from kernel space.  Note that we now dump the
       * code first, just in case the backtrace kills us.
       */
      fs = get_fs();
      set_fs(KERNEL_DS);

      printk("Code: ");
      for (i = -4; i < 1; i++) {
            unsigned int val, bad;

            if (thumb)
                  bad = __get_user(val, &((u16 *)addr)[i]);
            else
                  bad = __get_user(val, &((u32 *)addr)[i]);

            if (!bad)
                  printk(i == 0 ? "(%0*x) " : "%0*x ", width, val);
            else {
                  printk("bad PC value.");
                  break;
            }
      }
      printk("\n");

      set_fs(fs);
}

static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
{
      unsigned int fp;
      int ok = 1;

      printk("Backtrace: ");
      fp = regs->ARM_fp;
      if (!fp) {
            printk("no frame pointer");
            ok = 0;
      } else if (verify_stack(fp)) {
            printk("invalid frame pointer 0x%08x", fp);
            ok = 0;
      } else if (fp < (unsigned long)end_of_stack(tsk))
            printk("frame pointer underflow");
      printk("\n");

      if (ok)
            c_backtrace(fp, processor_mode(regs));
}

void dump_stack(void)
{
      __backtrace();
}

EXPORT_SYMBOL(dump_stack);

void show_stack(struct task_struct *tsk, unsigned long *sp)
{
      unsigned long fp;

      if (!tsk)
            tsk = current;

      if (tsk != current)
            fp = thread_saved_fp(tsk);
      else
            asm("mov %0, fp" : "=r" (fp) : : "cc");

      c_backtrace(fp, 0x10);
      barrier();
}

#ifdef CONFIG_PREEMPT
#define S_PREEMPT " PREEMPT"
#else
#define S_PREEMPT ""
#endif
#ifdef CONFIG_SMP
#define S_SMP " SMP"
#else
#define S_SMP ""
#endif

static void __die(const char *str, int err, struct thread_info *thread, struct pt_regs *regs)
{
      struct task_struct *tsk = thread->task;
      static int die_counter;

      printk("Internal error: %s: %x [#%d]" S_PREEMPT S_SMP "\n",
             str, err, ++die_counter);
      print_modules();
      __show_regs(regs);
      printk("Process %s (pid: %d, stack limit = 0x%p)\n",
            tsk->comm, task_pid_nr(tsk), thread + 1);

      if (!user_mode(regs) || in_interrupt()) {
            dump_mem("Stack: ", regs->ARM_sp,
                   THREAD_SIZE + (unsigned long)task_stack_page(tsk));
            dump_backtrace(regs, tsk);
            dump_instr(regs);
      }
}

DEFINE_SPINLOCK(die_lock);

/*
 * This function is protected against re-entrancy.
 */
NORET_TYPE void die(const char *str, struct pt_regs *regs, int err)
{
      struct thread_info *thread = current_thread_info();

      oops_enter();

      console_verbose();
      spin_lock_irq(&die_lock);
      bust_spinlocks(1);
      __die(str, err, thread, regs);
      bust_spinlocks(0);
      add_taint(TAINT_DIE);
      spin_unlock_irq(&die_lock);

      if (in_interrupt())
            panic("Fatal exception in interrupt");

      if (panic_on_oops)
            panic("Fatal exception");

      oops_exit();
      do_exit(SIGSEGV);
}

void arm_notify_die(const char *str, struct pt_regs *regs,
            struct siginfo *info, unsigned long err, unsigned long trap)
{
      if (user_mode(regs)) {
            current->thread.error_code = err;
            current->thread.trap_no = trap;

            force_sig_info(info->si_signo, info, current);
      } else {
            die(str, regs, err);
      }
}

static LIST_HEAD(undef_hook);
static DEFINE_SPINLOCK(undef_lock);

void register_undef_hook(struct undef_hook *hook)
{
      unsigned long flags;

      spin_lock_irqsave(&undef_lock, flags);
      list_add(&hook->node, &undef_hook);
      spin_unlock_irqrestore(&undef_lock, flags);
}

void unregister_undef_hook(struct undef_hook *hook)
{
      unsigned long flags;

      spin_lock_irqsave(&undef_lock, flags);
      list_del(&hook->node);
      spin_unlock_irqrestore(&undef_lock, flags);
}

asmlinkage void __exception do_undefinstr(struct pt_regs *regs)
{
      unsigned int correction = thumb_mode(regs) ? 2 : 4;
      unsigned int instr;
      struct undef_hook *hook;
      siginfo_t info;
      void __user *pc;
      unsigned long flags;

      /*
       * According to the ARM ARM, PC is 2 or 4 bytes ahead,
       * depending whether we're in Thumb mode or not.
       * Correct this offset.
       */
      regs->ARM_pc -= correction;

      pc = (void __user *)instruction_pointer(regs);

      if (processor_mode(regs) == SVC_MODE) {
            instr = *(u32 *) pc;
      } else if (thumb_mode(regs)) {
            get_user(instr, (u16 __user *)pc);
      } else {
            get_user(instr, (u32 __user *)pc);
      }

      spin_lock_irqsave(&undef_lock, flags);
      list_for_each_entry(hook, &undef_hook, node) {
            if ((instr & hook->instr_mask) == hook->instr_val &&
                (regs->ARM_cpsr & hook->cpsr_mask) == hook->cpsr_val) {
                  if (hook->fn(regs, instr) == 0) {
                        spin_unlock_irqrestore(&undef_lock, flags);
                        return;
                  }
            }
      }
      spin_unlock_irqrestore(&undef_lock, flags);

#ifdef CONFIG_DEBUG_USER
      if (user_debug & UDBG_UNDEFINED) {
            printk(KERN_INFO "%s (%d): undefined instruction: pc=%p\n",
                  current->comm, task_pid_nr(current), pc);
            dump_instr(regs);
      }
#endif

      info.si_signo = SIGILL;
      info.si_errno = 0;
      info.si_code  = ILL_ILLOPC;
      info.si_addr  = pc;

      arm_notify_die("Oops - undefined instruction", regs, &info, 0, 6);
}

asmlinkage void do_unexp_fiq (struct pt_regs *regs)
{
      printk("Hmm.  Unexpected FIQ received, but trying to continue\n");
      printk("You may have a hardware problem...\n");
}

/*
 * bad_mode handles the impossible case in the vectors.  If you see one of
 * these, then it's extremely serious, and could mean you have buggy hardware.
 * It never returns, and never tries to sync.  We hope that we can at least
 * dump out some state information...
 */
asmlinkage void bad_mode(struct pt_regs *regs, int reason)
{
      console_verbose();

      printk(KERN_CRIT "Bad mode in %s handler detected\n", handler[reason]);

      die("Oops - bad mode", regs, 0);
      local_irq_disable();
      panic("bad mode");
}

static int bad_syscall(int n, struct pt_regs *regs)
{
      struct thread_info *thread = current_thread_info();
      siginfo_t info;

      if (current->personality != PER_LINUX &&
          current->personality != PER_LINUX_32BIT &&
          thread->exec_domain->handler) {
            thread->exec_domain->handler(n, regs);
            return regs->ARM_r0;
      }

#ifdef CONFIG_DEBUG_USER
      if (user_debug & UDBG_SYSCALL) {
            printk(KERN_ERR "[%d] %s: obsolete system call %08x.\n",
                  task_pid_nr(current), current->comm, n);
            dump_instr(regs);
      }
#endif

      info.si_signo = SIGILL;
      info.si_errno = 0;
      info.si_code  = ILL_ILLTRP;
      info.si_addr  = (void __user *)instruction_pointer(regs) -
                   (thumb_mode(regs) ? 2 : 4);

      arm_notify_die("Oops - bad syscall", regs, &info, n, 0);

      return regs->ARM_r0;
}

static inline void
do_cache_op(unsigned long start, unsigned long end, int flags)
{
      struct vm_area_struct *vma;

      if (end < start || flags)
            return;

      vma = find_vma(current->active_mm, start);
      if (vma && vma->vm_start < end) {
            if (start < vma->vm_start)
                  start = vma->vm_start;
            if (end > vma->vm_end)
                  end = vma->vm_end;

            flush_cache_user_range(vma, start, end);
      }
}

/*
 * Handle all unrecognised system calls.
 *  0x9f0000 - 0x9fffff are some more esoteric system calls
 */
#define NR(x) ((__ARM_NR_##x) - __ARM_NR_BASE)
asmlinkage int arm_syscall(int no, struct pt_regs *regs)
{
      struct thread_info *thread = current_thread_info();
      siginfo_t info;

      if ((no >> 16) != (__ARM_NR_BASE>> 16))
            return bad_syscall(no, regs);

      switch (no & 0xffff) {
      case 0: /* branch through 0 */
            info.si_signo = SIGSEGV;
            info.si_errno = 0;
            info.si_code  = SEGV_MAPERR;
            info.si_addr  = NULL;

            arm_notify_die("branch through zero", regs, &info, 0, 0);
            return 0;

      case NR(breakpoint): /* SWI BREAK_POINT */
            regs->ARM_pc -= thumb_mode(regs) ? 2 : 4;
            ptrace_break(current, regs);
            return regs->ARM_r0;

      /*
       * Flush a region from virtual address 'r0' to virtual address 'r1'
       * _exclusive_.  There is no alignment requirement on either address;
       * user space does not need to know the hardware cache layout.
       *
       * r2 contains flags.  It should ALWAYS be passed as ZERO until it
       * is defined to be something else.  For now we ignore it, but may
       * the fires of hell burn in your belly if you break this rule. ;)
       *
       * (at a later date, we may want to allow this call to not flush
       * various aspects of the cache.  Passing '0' will guarantee that
       * everything necessary gets flushed to maintain consistency in
       * the specified region).
       */
      case NR(cacheflush):
            do_cache_op(regs->ARM_r0, regs->ARM_r1, regs->ARM_r2);
            return 0;

      case NR(usr26):
            if (!(elf_hwcap & HWCAP_26BIT))
                  break;
            regs->ARM_cpsr &= ~MODE32_BIT;
            return regs->ARM_r0;

      case NR(usr32):
            if (!(elf_hwcap & HWCAP_26BIT))
                  break;
            regs->ARM_cpsr |= MODE32_BIT;
            return regs->ARM_r0;

      case NR(set_tls):
            thread->tp_value = regs->ARM_r0;
#if defined(CONFIG_HAS_TLS_REG)
            asm ("mcr p15, 0, %0, c13, c0, 3" : : "r" (regs->ARM_r0) );
#elif !defined(CONFIG_TLS_REG_EMUL)
            /*
             * User space must never try to access this directly.
             * Expect your app to break eventually if you do so.
             * The user helper at 0xffff0fe0 must be used instead.
             * (see entry-armv.S for details)
             */
            *((unsigned int *)0xffff0ff0) = regs->ARM_r0;
#endif
            return 0;

#ifdef CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG
      /*
       * Atomically store r1 in *r2 if *r2 is equal to r0 for user space.
       * Return zero in r0 if *MEM was changed or non-zero if no exchange
       * happened.  Also set the user C flag accordingly.
       * If access permissions have to be fixed up then non-zero is
       * returned and the operation has to be re-attempted.
       *
       * *NOTE*: This is a ghost syscall private to the kernel.  Only the
       * __kuser_cmpxchg code in entry-armv.S should be aware of its
       * existence.  Don't ever use this from user code.
       */
      case 0xfff0:
      for (;;) {
            extern void do_DataAbort(unsigned long addr, unsigned int fsr,
                               struct pt_regs *regs);
            unsigned long val;
            unsigned long addr = regs->ARM_r2;
            struct mm_struct *mm = current->mm;
            pgd_t *pgd; pmd_t *pmd; pte_t *pte;
            spinlock_t *ptl;

            regs->ARM_cpsr &= ~PSR_C_BIT;
            down_read(&mm->mmap_sem);
            pgd = pgd_offset(mm, addr);
            if (!pgd_present(*pgd))
                  goto bad_access;
            pmd = pmd_offset(pgd, addr);
            if (!pmd_present(*pmd))
                  goto bad_access;
            pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
            if (!pte_present(*pte) || !pte_dirty(*pte)) {
                  pte_unmap_unlock(pte, ptl);
                  goto bad_access;
            }
            val = *(unsigned long *)addr;
            val -= regs->ARM_r0;
            if (val == 0) {
                  *(unsigned long *)addr = regs->ARM_r1;
                  regs->ARM_cpsr |= PSR_C_BIT;
            }
            pte_unmap_unlock(pte, ptl);
            up_read(&mm->mmap_sem);
            return val;

            bad_access:
            up_read(&mm->mmap_sem);
            /* simulate a write access fault */
            do_DataAbort(addr, 15 + (1 << 11), regs);
      }
#endif

      default:
            /* Calls 9f00xx..9f07ff are defined to return -ENOSYS
               if not implemented, rather than raising SIGILL.  This
               way the calling program can gracefully determine whether
               a feature is supported.  */
            if (no <= 0x7ff)
                  return -ENOSYS;
            break;
      }
#ifdef CONFIG_DEBUG_USER
      /*
       * experience shows that these seem to indicate that
       * something catastrophic has happened
       */
      if (user_debug & UDBG_SYSCALL) {
            printk("[%d] %s: arm syscall %d\n",
                   task_pid_nr(current), current->comm, no);
            dump_instr(regs);
            if (user_mode(regs)) {
                  __show_regs(regs);
                  c_backtrace(regs->ARM_fp, processor_mode(regs));
            }
      }
#endif
      info.si_signo = SIGILL;
      info.si_errno = 0;
      info.si_code  = ILL_ILLTRP;
      info.si_addr  = (void __user *)instruction_pointer(regs) -
                   (thumb_mode(regs) ? 2 : 4);

      arm_notify_die("Oops - bad syscall(2)", regs, &info, no, 0);
      return 0;
}

#ifdef CONFIG_TLS_REG_EMUL

/*
 * We might be running on an ARMv6+ processor which should have the TLS
 * register but for some reason we can't use it, or maybe an SMP system
 * using a pre-ARMv6 processor (there are apparently a few prototypes like
 * that in existence) and therefore access to that register must be
 * emulated.
 */

static int get_tp_trap(struct pt_regs *regs, unsigned int instr)
{
      int reg = (instr >> 12) & 15;
      if (reg == 15)
            return 1;
      regs->uregs[reg] = current_thread_info()->tp_value;
      regs->ARM_pc += 4;
      return 0;
}

static struct undef_hook arm_mrc_hook = {
      .instr_mask = 0x0fff0fff,
      .instr_val  = 0x0e1d0f70,
      .cpsr_mask  = PSR_T_BIT,
      .cpsr_val   = 0,
      .fn         = get_tp_trap,
};

static int __init arm_mrc_hook_init(void)
{
      register_undef_hook(&arm_mrc_hook);
      return 0;
}

late_initcall(arm_mrc_hook_init);

#endif

void __bad_xchg(volatile void *ptr, int size)
{
      printk("xchg: bad data size: pc 0x%p, ptr 0x%p, size %d\n",
            __builtin_return_address(0), ptr, size);
      BUG();
}
EXPORT_SYMBOL(__bad_xchg);

/*
 * A data abort trap was taken, but we did not handle the instruction.
 * Try to abort the user program, or panic if it was the kernel.
 */
asmlinkage void
baddataabort(int code, unsigned long instr, struct pt_regs *regs)
{
      unsigned long addr = instruction_pointer(regs);
      siginfo_t info;

#ifdef CONFIG_DEBUG_USER
      if (user_debug & UDBG_BADABORT) {
            printk(KERN_ERR "[%d] %s: bad data abort: code %d instr 0x%08lx\n",
                  task_pid_nr(current), current->comm, code, instr);
            dump_instr(regs);
            show_pte(current->mm, addr);
      }
#endif

      info.si_signo = SIGILL;
      info.si_errno = 0;
      info.si_code  = ILL_ILLOPC;
      info.si_addr  = (void __user *)addr;

      arm_notify_die("unknown data abort code", regs, &info, instr, 0);
}

void __attribute__((noreturn)) __bug(const char *file, int line)
{
      printk(KERN_CRIT"kernel BUG at %s:%d!\n", file, line);
      *(int *)0 = 0;

      /* Avoid "noreturn function does return" */
      for (;;);
}
EXPORT_SYMBOL(__bug);

void __readwrite_bug(const char *fn)
{
      printk("%s called, but not implemented\n", fn);
      BUG();
}
EXPORT_SYMBOL(__readwrite_bug);

void __pte_error(const char *file, int line, unsigned long val)
{
      printk("%s:%d: bad pte %08lx.\n", file, line, val);
}

void __pmd_error(const char *file, int line, unsigned long val)
{
      printk("%s:%d: bad pmd %08lx.\n", file, line, val);
}

void __pgd_error(const char *file, int line, unsigned long val)
{
      printk("%s:%d: bad pgd %08lx.\n", file, line, val);
}

asmlinkage void __div0(void)
{
      printk("Division by zero in kernel.\n");
      dump_stack();
}
EXPORT_SYMBOL(__div0);

void abort(void)
{
      BUG();

      /* if that doesn't kill us, halt */
      panic("Oops failed to kill thread");
}
EXPORT_SYMBOL(abort);

void __init trap_init(void)
{
      unsigned long vectors = CONFIG_VECTORS_BASE;
      extern char __stubs_start[], __stubs_end[];
      extern char __vectors_start[], __vectors_end[];
      extern char __kuser_helper_start[], __kuser_helper_end[];
      int kuser_sz = __kuser_helper_end - __kuser_helper_start;

      /*
       * Copy the vectors, stubs and kuser helpers (in entry-armv.S)
       * into the vector page, mapped at 0xffff0000, and ensure these
       * are visible to the instruction stream.
       */
      memcpy((void *)vectors, __vectors_start, __vectors_end - __vectors_start);
      memcpy((void *)vectors + 0x200, __stubs_start, __stubs_end - __stubs_start);
      memcpy((void *)vectors + 0x1000 - kuser_sz, __kuser_helper_start, kuser_sz);

      /*
       * Copy signal return handlers into the vector page, and
       * set sigreturn to be a pointer to these.
       */
      memcpy((void *)KERN_SIGRETURN_CODE, sigreturn_codes,
             sizeof(sigreturn_codes));

      flush_icache_range(vectors, vectors + PAGE_SIZE);
      modify_domain(DOMAIN_USER, DOMAIN_CLIENT);
}

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