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fault_32.c

/*
 *  linux/arch/i386/mm/fault.c
 *
 *  Copyright (C) 1995  Linus Torvalds
 */

#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/tty.h>
#include <linux/vt_kern.h>          /* For unblank_screen() */
#include <linux/highmem.h>
#include <linux/bootmem.h>          /* for max_low_pfn */
#include <linux/vmalloc.h>
#include <linux/module.h>
#include <linux/kprobes.h>
#include <linux/uaccess.h>
#include <linux/kdebug.h>
#include <linux/kprobes.h>

#include <asm/system.h>
#include <asm/desc.h>
#include <asm/segment.h>

extern void die(const char *,struct pt_regs *,long);

#ifdef CONFIG_KPROBES
static inline int notify_page_fault(struct pt_regs *regs)
{
      int ret = 0;

      /* kprobe_running() needs smp_processor_id() */
      if (!user_mode_vm(regs)) {
            preempt_disable();
            if (kprobe_running() && kprobe_fault_handler(regs, 14))
                  ret = 1;
            preempt_enable();
      }

      return ret;
}
#else
static inline int notify_page_fault(struct pt_regs *regs)
{
      return 0;
}
#endif

/*
 * Return EIP plus the CS segment base.  The segment limit is also
 * adjusted, clamped to the kernel/user address space (whichever is
 * appropriate), and returned in *eip_limit.
 *
 * The segment is checked, because it might have been changed by another
 * task between the original faulting instruction and here.
 *
 * If CS is no longer a valid code segment, or if EIP is beyond the
 * limit, or if it is a kernel address when CS is not a kernel segment,
 * then the returned value will be greater than *eip_limit.
 * 
 * This is slow, but is very rarely executed.
 */
static inline unsigned long get_segment_eip(struct pt_regs *regs,
                                  unsigned long *eip_limit)
{
      unsigned long eip = regs->eip;
      unsigned seg = regs->xcs & 0xffff;
      u32 seg_ar, seg_limit, base, *desc;

      /* Unlikely, but must come before segment checks. */
      if (unlikely(regs->eflags & VM_MASK)) {
            base = seg << 4;
            *eip_limit = base + 0xffff;
            return base + (eip & 0xffff);
      }

      /* The standard kernel/user address space limit. */
      *eip_limit = user_mode(regs) ? USER_DS.seg : KERNEL_DS.seg;
      
      /* By far the most common cases. */
      if (likely(SEGMENT_IS_FLAT_CODE(seg)))
            return eip;

      /* Check the segment exists, is within the current LDT/GDT size,
         that kernel/user (ring 0..3) has the appropriate privilege,
         that it's a code segment, and get the limit. */
      __asm__ ("larl %3,%0; lsll %3,%1"
             : "=&r" (seg_ar), "=r" (seg_limit) : "0" (0), "rm" (seg));
      if ((~seg_ar & 0x9800) || eip > seg_limit) {
            *eip_limit = 0;
            return 1;    /* So that returned eip > *eip_limit. */
      }

      /* Get the GDT/LDT descriptor base. 
         When you look for races in this code remember that
         LDT and other horrors are only used in user space. */
      if (seg & (1<<2)) {
            /* Must lock the LDT while reading it. */
            mutex_lock(&current->mm->context.lock);
            desc = current->mm->context.ldt;
            desc = (void *)desc + (seg & ~7);
      } else {
            /* Must disable preemption while reading the GDT. */
            desc = (u32 *)get_cpu_gdt_table(get_cpu());
            desc = (void *)desc + (seg & ~7);
      }

      /* Decode the code segment base from the descriptor */
      base = get_desc_base((unsigned long *)desc);

      if (seg & (1<<2)) { 
            mutex_unlock(&current->mm->context.lock);
      } else
            put_cpu();

      /* Adjust EIP and segment limit, and clamp at the kernel limit.
         It's legitimate for segments to wrap at 0xffffffff. */
      seg_limit += base;
      if (seg_limit < *eip_limit && seg_limit >= base)
            *eip_limit = seg_limit;
      return eip + base;
}

/* 
 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
 * Check that here and ignore it.
 */
static int __is_prefetch(struct pt_regs *regs, unsigned long addr)
{ 
      unsigned long limit;
      unsigned char *instr = (unsigned char *)get_segment_eip (regs, &limit);
      int scan_more = 1;
      int prefetch = 0; 
      int i;

      for (i = 0; scan_more && i < 15; i++) { 
            unsigned char opcode;
            unsigned char instr_hi;
            unsigned char instr_lo;

            if (instr > (unsigned char *)limit)
                  break;
            if (probe_kernel_address(instr, opcode))
                  break; 

            instr_hi = opcode & 0xf0; 
            instr_lo = opcode & 0x0f; 
            instr++;

            switch (instr_hi) { 
            case 0x20:
            case 0x30:
                  /* Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes. */
                  scan_more = ((instr_lo & 7) == 0x6);
                  break;
                  
            case 0x60:
                  /* 0x64 thru 0x67 are valid prefixes in all modes. */
                  scan_more = (instr_lo & 0xC) == 0x4;
                  break;            
            case 0xF0:
                  /* 0xF0, 0xF2, and 0xF3 are valid prefixes */
                  scan_more = !instr_lo || (instr_lo>>1) == 1;
                  break;                  
            case 0x00:
                  /* Prefetch instruction is 0x0F0D or 0x0F18 */
                  scan_more = 0;
                  if (instr > (unsigned char *)limit)
                        break;
                  if (probe_kernel_address(instr, opcode))
                        break;
                  prefetch = (instr_lo == 0xF) &&
                        (opcode == 0x0D || opcode == 0x18);
                  break;                  
            default:
                  scan_more = 0;
                  break;
            } 
      }
      return prefetch;
}

static inline int is_prefetch(struct pt_regs *regs, unsigned long addr,
                        unsigned long error_code)
{
      if (unlikely(boot_cpu_data.x86_vendor == X86_VENDOR_AMD &&
                 boot_cpu_data.x86 >= 6)) {
            /* Catch an obscure case of prefetch inside an NX page. */
            if (nx_enabled && (error_code & 16))
                  return 0;
            return __is_prefetch(regs, addr);
      }
      return 0;
} 

static noinline void force_sig_info_fault(int si_signo, int si_code,
      unsigned long address, struct task_struct *tsk)
{
      siginfo_t info;

      info.si_signo = si_signo;
      info.si_errno = 0;
      info.si_code = si_code;
      info.si_addr = (void __user *)address;
      force_sig_info(si_signo, &info, tsk);
}

fastcall void do_invalid_op(struct pt_regs *, unsigned long);

static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
{
      unsigned index = pgd_index(address);
      pgd_t *pgd_k;
      pud_t *pud, *pud_k;
      pmd_t *pmd, *pmd_k;

      pgd += index;
      pgd_k = init_mm.pgd + index;

      if (!pgd_present(*pgd_k))
            return NULL;

      /*
       * set_pgd(pgd, *pgd_k); here would be useless on PAE
       * and redundant with the set_pmd() on non-PAE. As would
       * set_pud.
       */

      pud = pud_offset(pgd, address);
      pud_k = pud_offset(pgd_k, address);
      if (!pud_present(*pud_k))
            return NULL;

      pmd = pmd_offset(pud, address);
      pmd_k = pmd_offset(pud_k, address);
      if (!pmd_present(*pmd_k))
            return NULL;
      if (!pmd_present(*pmd)) {
            set_pmd(pmd, *pmd_k);
            arch_flush_lazy_mmu_mode();
      } else
            BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k));
      return pmd_k;
}

/*
 * Handle a fault on the vmalloc or module mapping area
 *
 * This assumes no large pages in there.
 */
static inline int vmalloc_fault(unsigned long address)
{
      unsigned long pgd_paddr;
      pmd_t *pmd_k;
      pte_t *pte_k;
      /*
       * Synchronize this task's top level page-table
       * with the 'reference' page table.
       *
       * Do _not_ use "current" here. We might be inside
       * an interrupt in the middle of a task switch..
       */
      pgd_paddr = read_cr3();
      pmd_k = vmalloc_sync_one(__va(pgd_paddr), address);
      if (!pmd_k)
            return -1;
      pte_k = pte_offset_kernel(pmd_k, address);
      if (!pte_present(*pte_k))
            return -1;
      return 0;
}

int show_unhandled_signals = 1;

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 *
 * error_code:
 *    bit 0 == 0 means no page found, 1 means protection fault
 *    bit 1 == 0 means read, 1 means write
 *    bit 2 == 0 means kernel, 1 means user-mode
 *    bit 3 == 1 means use of reserved bit detected
 *    bit 4 == 1 means fault was an instruction fetch
 */
fastcall void __kprobes do_page_fault(struct pt_regs *regs,
                              unsigned long error_code)
{
      struct task_struct *tsk;
      struct mm_struct *mm;
      struct vm_area_struct * vma;
      unsigned long address;
      int write, si_code;
      int fault;

      /*
       * We can fault from pretty much anywhere, with unknown IRQ state.
       */
      trace_hardirqs_fixup();

      /* get the address */
        address = read_cr2();

      tsk = current;

      si_code = SEGV_MAPERR;

      /*
       * We fault-in kernel-space virtual memory on-demand. The
       * 'reference' page table is init_mm.pgd.
       *
       * NOTE! We MUST NOT take any locks for this case. We may
       * be in an interrupt or a critical region, and should
       * only copy the information from the master page table,
       * nothing more.
       *
       * This verifies that the fault happens in kernel space
       * (error_code & 4) == 0, and that the fault was not a
       * protection error (error_code & 9) == 0.
       */
      if (unlikely(address >= TASK_SIZE)) {
            if (!(error_code & 0x0000000d) && vmalloc_fault(address) >= 0)
                  return;
            if (notify_page_fault(regs))
                  return;
            /*
             * Don't take the mm semaphore here. If we fixup a prefetch
             * fault we could otherwise deadlock.
             */
            goto bad_area_nosemaphore;
      }

      if (notify_page_fault(regs))
            return;

      /* It's safe to allow irq's after cr2 has been saved and the vmalloc
         fault has been handled. */
      if (regs->eflags & (X86_EFLAGS_IF|VM_MASK))
            local_irq_enable();

      mm = tsk->mm;

      /*
       * If we're in an interrupt, have no user context or are running in an
       * atomic region then we must not take the fault..
       */
      if (in_atomic() || !mm)
            goto bad_area_nosemaphore;

      /* When running in the kernel we expect faults to occur only to
       * addresses in user space.  All other faults represent errors in the
       * kernel and should generate an OOPS.  Unfortunately, in the case of an
       * erroneous fault occurring in a code path which already holds mmap_sem
       * we will deadlock attempting to validate the fault against the
       * address space.  Luckily the kernel only validly references user
       * space from well defined areas of code, which are listed in the
       * exceptions table.
       *
       * As the vast majority of faults will be valid we will only perform
       * the source reference check when there is a possibility of a deadlock.
       * Attempt to lock the address space, if we cannot we then validate the
       * source.  If this is invalid we can skip the address space check,
       * thus avoiding the deadlock.
       */
      if (!down_read_trylock(&mm->mmap_sem)) {
            if ((error_code & 4) == 0 &&
                !search_exception_tables(regs->eip))
                  goto bad_area_nosemaphore;
            down_read(&mm->mmap_sem);
      }

      vma = find_vma(mm, address);
      if (!vma)
            goto bad_area;
      if (vma->vm_start <= address)
            goto good_area;
      if (!(vma->vm_flags & VM_GROWSDOWN))
            goto bad_area;
      if (error_code & 4) {
            /*
             * Accessing the stack below %esp is always a bug.
             * The large cushion allows instructions like enter
             * and pusha to work.  ("enter $65535,$31" pushes
             * 32 pointers and then decrements %esp by 65535.)
             */
            if (address + 65536 + 32 * sizeof(unsigned long) < regs->esp)
                  goto bad_area;
      }
      if (expand_stack(vma, address))
            goto bad_area;
/*
 * Ok, we have a good vm_area for this memory access, so
 * we can handle it..
 */
good_area:
      si_code = SEGV_ACCERR;
      write = 0;
      switch (error_code & 3) {
            default:    /* 3: write, present */
                        /* fall through */
            case 2:           /* write, not present */
                  if (!(vma->vm_flags & VM_WRITE))
                        goto bad_area;
                  write++;
                  break;
            case 1:           /* read, present */
                  goto bad_area;
            case 0:           /* read, not present */
                  if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
                        goto bad_area;
      }

 survive:
      /*
       * If for any reason at all we couldn't handle the fault,
       * make sure we exit gracefully rather than endlessly redo
       * the fault.
       */
      fault = handle_mm_fault(mm, vma, address, write);
      if (unlikely(fault & VM_FAULT_ERROR)) {
            if (fault & VM_FAULT_OOM)
                  goto out_of_memory;
            else if (fault & VM_FAULT_SIGBUS)
                  goto do_sigbus;
            BUG();
      }
      if (fault & VM_FAULT_MAJOR)
            tsk->maj_flt++;
      else
            tsk->min_flt++;

      /*
       * Did it hit the DOS screen memory VA from vm86 mode?
       */
      if (regs->eflags & VM_MASK) {
            unsigned long bit = (address - 0xA0000) >> PAGE_SHIFT;
            if (bit < 32)
                  tsk->thread.screen_bitmap |= 1 << bit;
      }
      up_read(&mm->mmap_sem);
      return;

/*
 * Something tried to access memory that isn't in our memory map..
 * Fix it, but check if it's kernel or user first..
 */
bad_area:
      up_read(&mm->mmap_sem);

bad_area_nosemaphore:
      /* User mode accesses just cause a SIGSEGV */
      if (error_code & 4) {
            /*
             * It's possible to have interrupts off here.
             */
            local_irq_enable();

            /* 
             * Valid to do another page fault here because this one came 
             * from user space.
             */
            if (is_prefetch(regs, address, error_code))
                  return;

            if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
                printk_ratelimit()) {
                  printk("%s%s[%d]: segfault at %08lx eip %08lx "
                      "esp %08lx error %lx\n",
                      task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
                      tsk->comm, task_pid_nr(tsk), address, regs->eip,
                      regs->esp, error_code);
            }
            tsk->thread.cr2 = address;
            /* Kernel addresses are always protection faults */
            tsk->thread.error_code = error_code | (address >= TASK_SIZE);
            tsk->thread.trap_no = 14;
            force_sig_info_fault(SIGSEGV, si_code, address, tsk);
            return;
      }

#ifdef CONFIG_X86_F00F_BUG
      /*
       * Pentium F0 0F C7 C8 bug workaround.
       */
      if (boot_cpu_data.f00f_bug) {
            unsigned long nr;
            
            nr = (address - idt_descr.address) >> 3;

            if (nr == 6) {
                  do_invalid_op(regs, 0);
                  return;
            }
      }
#endif

no_context:
      /* Are we prepared to handle this kernel fault?  */
      if (fixup_exception(regs))
            return;

      /* 
       * Valid to do another page fault here, because if this fault
       * had been triggered by is_prefetch fixup_exception would have 
       * handled it.
       */
      if (is_prefetch(regs, address, error_code))
            return;

/*
 * Oops. The kernel tried to access some bad page. We'll have to
 * terminate things with extreme prejudice.
 */

      bust_spinlocks(1);

      if (oops_may_print()) {
            __typeof__(pte_val(__pte(0))) page;

#ifdef CONFIG_X86_PAE
            if (error_code & 16) {
                  pte_t *pte = lookup_address(address);

                  if (pte && pte_present(*pte) && !pte_exec_kernel(*pte))
                        printk(KERN_CRIT "kernel tried to execute "
                              "NX-protected page - exploit attempt? "
                              "(uid: %d)\n", current->uid);
            }
#endif
            if (address < PAGE_SIZE)
                  printk(KERN_ALERT "BUG: unable to handle kernel NULL "
                              "pointer dereference");
            else
                  printk(KERN_ALERT "BUG: unable to handle kernel paging"
                              " request");
            printk(" at virtual address %08lx\n",address);
            printk(KERN_ALERT "printing eip: %08lx ", regs->eip);

            page = read_cr3();
            page = ((__typeof__(page) *) __va(page))[address >> PGDIR_SHIFT];
#ifdef CONFIG_X86_PAE
            printk("*pdpt = %016Lx ", page);
            if ((page >> PAGE_SHIFT) < max_low_pfn
                && page & _PAGE_PRESENT) {
                  page &= PAGE_MASK;
                  page = ((__typeof__(page) *) __va(page))[(address >> PMD_SHIFT)
                                                           & (PTRS_PER_PMD - 1)];
                  printk(KERN_CONT "*pde = %016Lx ", page);
                  page &= ~_PAGE_NX;
            }
#else
            printk("*pde = %08lx ", page);
#endif

            /*
             * We must not directly access the pte in the highpte
             * case if the page table is located in highmem.
             * And let's rather not kmap-atomic the pte, just in case
             * it's allocated already.
             */
            if ((page >> PAGE_SHIFT) < max_low_pfn
                && (page & _PAGE_PRESENT)
                && !(page & _PAGE_PSE)) {
                  page &= PAGE_MASK;
                  page = ((__typeof__(page) *) __va(page))[(address >> PAGE_SHIFT)
                                                           & (PTRS_PER_PTE - 1)];
                  printk("*pte = %0*Lx ", sizeof(page)*2, (u64)page);
            }

            printk("\n");
      }

      tsk->thread.cr2 = address;
      tsk->thread.trap_no = 14;
      tsk->thread.error_code = error_code;
      die("Oops", regs, error_code);
      bust_spinlocks(0);
      do_exit(SIGKILL);

/*
 * We ran out of memory, or some other thing happened to us that made
 * us unable to handle the page fault gracefully.
 */
out_of_memory:
      up_read(&mm->mmap_sem);
      if (is_global_init(tsk)) {
            yield();
            down_read(&mm->mmap_sem);
            goto survive;
      }
      printk("VM: killing process %s\n", tsk->comm);
      if (error_code & 4)
            do_group_exit(SIGKILL);
      goto no_context;

do_sigbus:
      up_read(&mm->mmap_sem);

      /* Kernel mode? Handle exceptions or die */
      if (!(error_code & 4))
            goto no_context;

      /* User space => ok to do another page fault */
      if (is_prefetch(regs, address, error_code))
            return;

      tsk->thread.cr2 = address;
      tsk->thread.error_code = error_code;
      tsk->thread.trap_no = 14;
      force_sig_info_fault(SIGBUS, BUS_ADRERR, address, tsk);
}

void vmalloc_sync_all(void)
{
      /*
       * Note that races in the updates of insync and start aren't
       * problematic: insync can only get set bits added, and updates to
       * start are only improving performance (without affecting correctness
       * if undone).
       */
      static DECLARE_BITMAP(insync, PTRS_PER_PGD);
      static unsigned long start = TASK_SIZE;
      unsigned long address;

      if (SHARED_KERNEL_PMD)
            return;

      BUILD_BUG_ON(TASK_SIZE & ~PGDIR_MASK);
      for (address = start; address >= TASK_SIZE; address += PGDIR_SIZE) {
            if (!test_bit(pgd_index(address), insync)) {
                  unsigned long flags;
                  struct page *page;

                  spin_lock_irqsave(&pgd_lock, flags);
                  for (page = pgd_list; page; page =
                              (struct page *)page->index)
                        if (!vmalloc_sync_one(page_address(page),
                                                address)) {
                              BUG_ON(page != pgd_list);
                              break;
                        }
                  spin_unlock_irqrestore(&pgd_lock, flags);
                  if (!page)
                        set_bit(pgd_index(address), insync);
            }
            if (address == start && test_bit(pgd_index(address), insync))
                  start = address + PGDIR_SIZE;
      }
}

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