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fault_64.c

/*
 *  linux/arch/x86-64/mm/fault.c
 *
 *  Copyright (C) 1995  Linus Torvalds
 *  Copyright (C) 2001,2002 Andi Kleen, SuSE Labs.
 */

#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/compiler.h>
#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/pgalloc.h>
#include <asm/smp.h>
#include <asm/tlbflush.h>
#include <asm/proto.h>
#include <asm-generic/sections.h>

/* Page fault error code bits */
#define PF_PROT   (1<<0)            /* or no page found */
#define PF_WRITE  (1<<1)
#define PF_USER   (1<<2)
#define PF_RSVD   (1<<3)
#define PF_INSTR  (1<<4)

#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(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

/* Sometimes the CPU reports invalid exceptions on prefetch.
   Check that here and ignore.
   Opcode checker based on code by Richard Brunner */
static noinline int is_prefetch(struct pt_regs *regs, unsigned long addr,
                        unsigned long error_code)
{ 
      unsigned char *instr;
      int scan_more = 1;
      int prefetch = 0; 
      unsigned char *max_instr;

      /* If it was a exec fault ignore */
      if (error_code & PF_INSTR)
            return 0;
      
      instr = (unsigned char __user *)convert_rip_to_linear(current, regs);
      max_instr = instr + 15;

      if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE)
            return 0;

      while (scan_more && instr < max_instr) { 
            unsigned char opcode;
            unsigned char instr_hi;
            unsigned char instr_lo;

            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.  In long mode, the CPU will signal
                     invalid opcode if some of these prefixes are
                     present so we will never get here anyway */
                  scan_more = ((instr_lo & 7) == 0x6);
                  break;
                  
            case 0x40:
                  /* In AMD64 long mode, 0x40 to 0x4F are valid REX prefixes
                     Need to figure out under what instruction mode the
                     instruction was issued ... */
                  /* Could check the LDT for lm, but for now it's good
                     enough to assume that long mode only uses well known
                     segments or kernel. */
                  scan_more = (!user_mode(regs)) || (regs->cs == __USER_CS);
                  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 in all modes. */
                  scan_more = !instr_lo || (instr_lo>>1) == 1;
                  break;                  
            case 0x00:
                  /* Prefetch instruction is 0x0F0D or 0x0F18 */
                  scan_more = 0;
                  if (probe_kernel_address(instr, opcode))
                        break;
                  prefetch = (instr_lo == 0xF) &&
                        (opcode == 0x0D || opcode == 0x18);
                  break;                  
            default:
                  scan_more = 0;
                  break;
            } 
      }
      return prefetch;
}

static int bad_address(void *p) 
{ 
      unsigned long dummy;
      return probe_kernel_address((unsigned long *)p, dummy);
} 

void dump_pagetable(unsigned long address)
{
      pgd_t *pgd;
      pud_t *pud;
      pmd_t *pmd;
      pte_t *pte;

      pgd = (pgd_t *)read_cr3();

      pgd = __va((unsigned long)pgd & PHYSICAL_PAGE_MASK); 
      pgd += pgd_index(address);
      if (bad_address(pgd)) goto bad;
      printk("PGD %lx ", pgd_val(*pgd));
      if (!pgd_present(*pgd)) goto ret; 

      pud = pud_offset(pgd, address);
      if (bad_address(pud)) goto bad;
      printk("PUD %lx ", pud_val(*pud));
      if (!pud_present(*pud)) goto ret;

      pmd = pmd_offset(pud, address);
      if (bad_address(pmd)) goto bad;
      printk("PMD %lx ", pmd_val(*pmd));
      if (!pmd_present(*pmd) || pmd_large(*pmd)) goto ret;

      pte = pte_offset_kernel(pmd, address);
      if (bad_address(pte)) goto bad;
      printk("PTE %lx", pte_val(*pte)); 
ret:
      printk("\n");
      return;
bad:
      printk("BAD\n");
}

static const char errata93_warning[] = 
KERN_ERR "******* Your BIOS seems to not contain a fix for K8 errata #93\n"
KERN_ERR "******* Working around it, but it may cause SEGVs or burn power.\n"
KERN_ERR "******* Please consider a BIOS update.\n"
KERN_ERR "******* Disabling USB legacy in the BIOS may also help.\n";

/* Workaround for K8 erratum #93 & buggy BIOS.
   BIOS SMM functions are required to use a specific workaround
   to avoid corruption of the 64bit RIP register on C stepping K8. 
   A lot of BIOS that didn't get tested properly miss this. 
   The OS sees this as a page fault with the upper 32bits of RIP cleared.
   Try to work around it here.
   Note we only handle faults in kernel here. */

static int is_errata93(struct pt_regs *regs, unsigned long address) 
{
      static int warned;
      if (address != regs->rip)
            return 0;
      if ((address >> 32) != 0) 
            return 0;
      address |= 0xffffffffUL << 32;
      if ((address >= (u64)_stext && address <= (u64)_etext) || 
          (address >= MODULES_VADDR && address <= MODULES_END)) { 
            if (!warned) {
                  printk(errata93_warning);           
                  warned = 1;
            }
            regs->rip = address;
            return 1;
      }
      return 0;
} 

static noinline void pgtable_bad(unsigned long address, struct pt_regs *regs,
                         unsigned long error_code)
{
      unsigned long flags = oops_begin();
      struct task_struct *tsk;

      printk(KERN_ALERT "%s: Corrupted page table at address %lx\n",
             current->comm, address);
      dump_pagetable(address);
      tsk = current;
      tsk->thread.cr2 = address;
      tsk->thread.trap_no = 14;
      tsk->thread.error_code = error_code;
      __die("Bad pagetable", regs, error_code);
      oops_end(flags);
      do_exit(SIGKILL);
}

/*
 * Handle a fault on the vmalloc area
 *
 * This assumes no large pages in there.
 */
static int vmalloc_fault(unsigned long address)
{
      pgd_t *pgd, *pgd_ref;
      pud_t *pud, *pud_ref;
      pmd_t *pmd, *pmd_ref;
      pte_t *pte, *pte_ref;

      /* Copy kernel mappings over when needed. This can also
         happen within a race in page table update. In the later
         case just flush. */

      pgd = pgd_offset(current->mm ?: &init_mm, address);
      pgd_ref = pgd_offset_k(address);
      if (pgd_none(*pgd_ref))
            return -1;
      if (pgd_none(*pgd))
            set_pgd(pgd, *pgd_ref);
      else
            BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref));

      /* Below here mismatches are bugs because these lower tables
         are shared */

      pud = pud_offset(pgd, address);
      pud_ref = pud_offset(pgd_ref, address);
      if (pud_none(*pud_ref))
            return -1;
      if (pud_none(*pud) || pud_page_vaddr(*pud) != pud_page_vaddr(*pud_ref))
            BUG();
      pmd = pmd_offset(pud, address);
      pmd_ref = pmd_offset(pud_ref, address);
      if (pmd_none(*pmd_ref))
            return -1;
      if (pmd_none(*pmd) || pmd_page(*pmd) != pmd_page(*pmd_ref))
            BUG();
      pte_ref = pte_offset_kernel(pmd_ref, address);
      if (!pte_present(*pte_ref))
            return -1;
      pte = pte_offset_kernel(pmd, address);
      /* Don't use pte_page here, because the mappings can point
         outside mem_map, and the NUMA hash lookup cannot handle
         that. */
      if (!pte_present(*pte) || pte_pfn(*pte) != pte_pfn(*pte_ref))
            BUG();
      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.
 */
asmlinkage 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;
      const struct exception_table_entry *fixup;
      int write, fault;
      unsigned long flags;
      siginfo_t info;

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

      tsk = current;
      mm = tsk->mm;
      prefetchw(&mm->mmap_sem);

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

      info.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_SIZE64)) {
            /*
             * Don't check for the module range here: its PML4
             * is always initialized because it's shared with the main
             * kernel text. Only vmalloc may need PML4 syncups.
             */
            if (!(error_code & (PF_RSVD|PF_USER|PF_PROT)) &&
                  ((address >= VMALLOC_START && address < VMALLOC_END))) {
                  if (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;

      if (likely(regs->eflags & X86_EFLAGS_IF))
            local_irq_enable();

      if (unlikely(error_code & PF_RSVD))
            pgtable_bad(address, regs, error_code);

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

      /*
       * User-mode registers count as a user access even for any
       * potential system fault or CPU buglet.
       */
      if (user_mode_vm(regs))
            error_code |= PF_USER;

 again:
      /* 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 & PF_USER) == 0 &&
                !search_exception_tables(regs->rip))
                  goto bad_area_nosemaphore;
            down_read(&mm->mmap_sem);
      }

      vma = find_vma(mm, address);
      if (!vma)
            goto bad_area;
      if (likely(vma->vm_start <= address))
            goto good_area;
      if (!(vma->vm_flags & VM_GROWSDOWN))
            goto bad_area;
      if (error_code & 4) {
            /* Allow userspace just enough access below the stack pointer
             * to let the 'enter' instruction work.
             */
            if (address + 65536 + 32 * sizeof(unsigned long) < regs->rsp)
                  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:
      info.si_code = SEGV_ACCERR;
      write = 0;
      switch (error_code & (PF_PROT|PF_WRITE)) {
            default:    /* 3: write, present */
                  /* fall through */
            case PF_WRITE:          /* write, not present */
                  if (!(vma->vm_flags & VM_WRITE))
                        goto bad_area;
                  write++;
                  break;
            case PF_PROT:           /* read, present */
                  goto bad_area;
            case 0:                 /* read, not present */
                  if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
                        goto bad_area;
      }

      /*
       * 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++;
      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 & PF_USER) {

            /*
             * It's possible to have interrupts off here.
             */
            local_irq_enable();

            if (is_prefetch(regs, address, error_code))
                  return;

            /* Work around K8 erratum #100 K8 in compat mode
               occasionally jumps to illegal addresses >4GB.  We
               catch this here in the page fault handler because
               these addresses are not reachable. Just detect this
               case and return.  Any code segment in LDT is
               compatibility mode. */
            if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) &&
                (address >> 32))
                  return;

            if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
                printk_ratelimit()) {
                  printk(
                   "%s%s[%d]: segfault at %lx rip %lx rsp %lx error %lx\n",
                              tsk->pid > 1 ? KERN_INFO : KERN_EMERG,
                              tsk->comm, tsk->pid, address, regs->rip,
                              regs->rsp, 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;
            info.si_signo = SIGSEGV;
            info.si_errno = 0;
            /* info.si_code has been set above */
            info.si_addr = (void __user *)address;
            force_sig_info(SIGSEGV, &info, tsk);
            return;
      }

no_context:
      
      /* Are we prepared to handle this kernel fault?  */
      fixup = search_exception_tables(regs->rip);
      if (fixup) {
            regs->rip = fixup->fixup;
            return;
      }

      /* 
       * Hall of shame of CPU/BIOS bugs.
       */

      if (is_prefetch(regs, address, error_code))
            return;

      if (is_errata93(regs, address))
            return; 

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

      flags = oops_begin();

      if (address < PAGE_SIZE)
            printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference");
      else
            printk(KERN_ALERT "Unable to handle kernel paging request");
      printk(" at %016lx RIP: \n" KERN_ALERT,address);
      printk_address(regs->rip);
      dump_pagetable(address);
      tsk->thread.cr2 = address;
      tsk->thread.trap_no = 14;
      tsk->thread.error_code = error_code;
      __die("Oops", regs, error_code);
      /* Executive summary in case the body of the oops scrolled away */
      printk(KERN_EMERG "CR2: %016lx\n", address);
      oops_end(flags);
      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(current)) {
            yield();
            goto again;
      }
      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 & PF_USER))
            goto no_context;

      tsk->thread.cr2 = address;
      tsk->thread.error_code = error_code;
      tsk->thread.trap_no = 14;
      info.si_signo = SIGBUS;
      info.si_errno = 0;
      info.si_code = BUS_ADRERR;
      info.si_addr = (void __user *)address;
      force_sig_info(SIGBUS, &info, tsk);
      return;
}

DEFINE_SPINLOCK(pgd_lock);
LIST_HEAD(pgd_list);

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 = VMALLOC_START & PGDIR_MASK;
      unsigned long address;

      for (address = start; address <= VMALLOC_END; address += PGDIR_SIZE) {
            if (!test_bit(pgd_index(address), insync)) {
                  const pgd_t *pgd_ref = pgd_offset_k(address);
                  struct page *page;

                  if (pgd_none(*pgd_ref))
                        continue;
                  spin_lock(&pgd_lock);
                  list_for_each_entry(page, &pgd_list, lru) {
                        pgd_t *pgd;
                        pgd = (pgd_t *)page_address(page) + pgd_index(address);
                        if (pgd_none(*pgd))
                              set_pgd(pgd, *pgd_ref);
                        else
                              BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref));
                  }
                  spin_unlock(&pgd_lock);
                  set_bit(pgd_index(address), insync);
            }
            if (address == start)
                  start = address + PGDIR_SIZE;
      }
      /* Check that there is no need to do the same for the modules area. */
      BUILD_BUG_ON(!(MODULES_VADDR > __START_KERNEL));
      BUILD_BUG_ON(!(((MODULES_END - 1) & PGDIR_MASK) == 
                        (__START_KERNEL & PGDIR_MASK)));
}

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