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uaccess_pt.c

/*
 *  arch/s390/lib/uaccess_pt.c
 *
 *  User access functions based on page table walks for enhanced
 *  system layout without hardware support.
 *
 *    Copyright IBM Corp. 2006
 *    Author(s): Gerald Schaefer (gerald.schaefer@de.ibm.com)
 */

#include <linux/errno.h>
#include <linux/hardirq.h>
#include <linux/mm.h>
#include <asm/uaccess.h>
#include <asm/futex.h>
#include "uaccess.h"

static inline pte_t *follow_table(struct mm_struct *mm, unsigned long addr)
{
      pgd_t *pgd;
      pud_t *pud;
      pmd_t *pmd;

      pgd = pgd_offset(mm, addr);
      if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
            return NULL;

      pud = pud_offset(pgd, addr);
      if (pud_none(*pud) || unlikely(pud_bad(*pud)))
            return NULL;

      pmd = pmd_offset(pud, addr);
      if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
            return NULL;

      return pte_offset_map(pmd, addr);
}

static int __handle_fault(struct mm_struct *mm, unsigned long address,
                    int write_access)
{
      struct vm_area_struct *vma;
      int ret = -EFAULT;
      int fault;

      if (in_atomic())
            return ret;
      down_read(&mm->mmap_sem);
      vma = find_vma(mm, address);
      if (unlikely(!vma))
            goto out;
      if (unlikely(vma->vm_start > address)) {
            if (!(vma->vm_flags & VM_GROWSDOWN))
                  goto out;
            if (expand_stack(vma, address))
                  goto out;
      }

      if (!write_access) {
            /* page not present, check vm flags */
            if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
                  goto out;
      } else {
            if (!(vma->vm_flags & VM_WRITE))
                  goto out;
      }

survive:
      fault = handle_mm_fault(mm, vma, address, write_access);
      if (unlikely(fault & VM_FAULT_ERROR)) {
            if (fault & VM_FAULT_OOM)
                  goto out_of_memory;
            else if (fault & VM_FAULT_SIGBUS)
                  goto out_sigbus;
            BUG();
      }
      if (fault & VM_FAULT_MAJOR)
            current->maj_flt++;
      else
            current->min_flt++;
      ret = 0;
out:
      up_read(&mm->mmap_sem);
      return ret;

out_of_memory:
      up_read(&mm->mmap_sem);
      if (is_global_init(current)) {
            yield();
            down_read(&mm->mmap_sem);
            goto survive;
      }
      printk("VM: killing process %s\n", current->comm);
      return ret;

out_sigbus:
      up_read(&mm->mmap_sem);
      current->thread.prot_addr = address;
      current->thread.trap_no = 0x11;
      force_sig(SIGBUS, current);
      return ret;
}

static size_t __user_copy_pt(unsigned long uaddr, void *kptr,
                       size_t n, int write_user)
{
      struct mm_struct *mm = current->mm;
      unsigned long offset, pfn, done, size;
      pte_t *pte;
      void *from, *to;

      done = 0;
retry:
      spin_lock(&mm->page_table_lock);
      do {
            pte = follow_table(mm, uaddr);
            if (!pte || !pte_present(*pte) ||
                (write_user && !pte_write(*pte)))
                  goto fault;

            pfn = pte_pfn(*pte);
            if (!pfn_valid(pfn))
                  goto out;

            offset = uaddr & (PAGE_SIZE - 1);
            size = min(n - done, PAGE_SIZE - offset);
            if (write_user) {
                  to = (void *)((pfn << PAGE_SHIFT) + offset);
                  from = kptr + done;
            } else {
                  from = (void *)((pfn << PAGE_SHIFT) + offset);
                  to = kptr + done;
            }
            memcpy(to, from, size);
            done += size;
            uaddr += size;
      } while (done < n);
out:
      spin_unlock(&mm->page_table_lock);
      return n - done;
fault:
      spin_unlock(&mm->page_table_lock);
      if (__handle_fault(mm, uaddr, write_user))
            return n - done;
      goto retry;
}

/*
 * Do DAT for user address by page table walk, return kernel address.
 * This function needs to be called with current->mm->page_table_lock held.
 */
static unsigned long __dat_user_addr(unsigned long uaddr)
{
      struct mm_struct *mm = current->mm;
      unsigned long pfn, ret;
      pte_t *pte;
      int rc;

      ret = 0;
retry:
      pte = follow_table(mm, uaddr);
      if (!pte || !pte_present(*pte))
            goto fault;

      pfn = pte_pfn(*pte);
      if (!pfn_valid(pfn))
            goto out;

      ret = (pfn << PAGE_SHIFT) + (uaddr & (PAGE_SIZE - 1));
out:
      return ret;
fault:
      spin_unlock(&mm->page_table_lock);
      rc = __handle_fault(mm, uaddr, 0);
      spin_lock(&mm->page_table_lock);
      if (rc)
            goto out;
      goto retry;
}

size_t copy_from_user_pt(size_t n, const void __user *from, void *to)
{
      size_t rc;

      if (segment_eq(get_fs(), KERNEL_DS)) {
            memcpy(to, (void __kernel __force *) from, n);
            return 0;
      }
      rc = __user_copy_pt((unsigned long) from, to, n, 0);
      if (unlikely(rc))
            memset(to + n - rc, 0, rc);
      return rc;
}

size_t copy_to_user_pt(size_t n, void __user *to, const void *from)
{
      if (segment_eq(get_fs(), KERNEL_DS)) {
            memcpy((void __kernel __force *) to, from, n);
            return 0;
      }
      return __user_copy_pt((unsigned long) to, (void *) from, n, 1);
}

static size_t clear_user_pt(size_t n, void __user *to)
{
      long done, size, ret;

      if (segment_eq(get_fs(), KERNEL_DS)) {
            memset((void __kernel __force *) to, 0, n);
            return 0;
      }
      done = 0;
      do {
            if (n - done > PAGE_SIZE)
                  size = PAGE_SIZE;
            else
                  size = n - done;
            ret = __user_copy_pt((unsigned long) to + done,
                              &empty_zero_page, size, 1);
            done += size;
            if (ret)
                  return ret + n - done;
      } while (done < n);
      return 0;
}

static size_t strnlen_user_pt(size_t count, const char __user *src)
{
      char *addr;
      unsigned long uaddr = (unsigned long) src;
      struct mm_struct *mm = current->mm;
      unsigned long offset, pfn, done, len;
      pte_t *pte;
      size_t len_str;

      if (segment_eq(get_fs(), KERNEL_DS))
            return strnlen((const char __kernel __force *) src, count) + 1;
      done = 0;
retry:
      spin_lock(&mm->page_table_lock);
      do {
            pte = follow_table(mm, uaddr);
            if (!pte || !pte_present(*pte))
                  goto fault;

            pfn = pte_pfn(*pte);
            if (!pfn_valid(pfn)) {
                  done = -1;
                  goto out;
            }

            offset = uaddr & (PAGE_SIZE-1);
            addr = (char *)(pfn << PAGE_SHIFT) + offset;
            len = min(count - done, PAGE_SIZE - offset);
            len_str = strnlen(addr, len);
            done += len_str;
            uaddr += len_str;
      } while ((len_str == len) && (done < count));
out:
      spin_unlock(&mm->page_table_lock);
      return done + 1;
fault:
      spin_unlock(&mm->page_table_lock);
      if (__handle_fault(mm, uaddr, 0)) {
            return 0;
      }
      goto retry;
}

static size_t strncpy_from_user_pt(size_t count, const char __user *src,
                           char *dst)
{
      size_t n = strnlen_user_pt(count, src);

      if (!n)
            return -EFAULT;
      if (n > count)
            n = count;
      if (segment_eq(get_fs(), KERNEL_DS)) {
            memcpy(dst, (const char __kernel __force *) src, n);
            if (dst[n-1] == '\0')
                  return n-1;
            else
                  return n;
      }
      if (__user_copy_pt((unsigned long) src, dst, n, 0))
            return -EFAULT;
      if (dst[n-1] == '\0')
            return n-1;
      else
            return n;
}

static size_t copy_in_user_pt(size_t n, void __user *to,
                        const void __user *from)
{
      struct mm_struct *mm = current->mm;
      unsigned long offset_from, offset_to, offset_max, pfn_from, pfn_to,
                  uaddr, done, size;
      unsigned long uaddr_from = (unsigned long) from;
      unsigned long uaddr_to = (unsigned long) to;
      pte_t *pte_from, *pte_to;
      int write_user;

      done = 0;
retry:
      spin_lock(&mm->page_table_lock);
      do {
            pte_from = follow_table(mm, uaddr_from);
            if (!pte_from || !pte_present(*pte_from)) {
                  uaddr = uaddr_from;
                  write_user = 0;
                  goto fault;
            }

            pte_to = follow_table(mm, uaddr_to);
            if (!pte_to || !pte_present(*pte_to) || !pte_write(*pte_to)) {
                  uaddr = uaddr_to;
                  write_user = 1;
                  goto fault;
            }

            pfn_from = pte_pfn(*pte_from);
            if (!pfn_valid(pfn_from))
                  goto out;
            pfn_to = pte_pfn(*pte_to);
            if (!pfn_valid(pfn_to))
                  goto out;

            offset_from = uaddr_from & (PAGE_SIZE-1);
            offset_to = uaddr_from & (PAGE_SIZE-1);
            offset_max = max(offset_from, offset_to);
            size = min(n - done, PAGE_SIZE - offset_max);

            memcpy((void *)(pfn_to << PAGE_SHIFT) + offset_to,
                   (void *)(pfn_from << PAGE_SHIFT) + offset_from, size);
            done += size;
            uaddr_from += size;
            uaddr_to += size;
      } while (done < n);
out:
      spin_unlock(&mm->page_table_lock);
      return n - done;
fault:
      spin_unlock(&mm->page_table_lock);
      if (__handle_fault(mm, uaddr, write_user))
            return n - done;
      goto retry;
}

#define __futex_atomic_op(insn, ret, oldval, newval, uaddr, oparg)      \
      asm volatile("0: l   %1,0(%6)\n"                      \
                 "1: " insn                                 \
                 "2: cs  %1,%2,0(%6)\n"                     \
                 "3: jl  1b\n"                              \
                 "   lhi %0,0\n"                            \
                 "4:\n"                               \
                 EX_TABLE(0b,4b) EX_TABLE(2b,4b) EX_TABLE(3b,4b)  \
                 : "=d" (ret), "=&d" (oldval), "=&d" (newval),    \
                   "=m" (*uaddr)                            \
                 : "0" (-EFAULT), "d" (oparg), "a" (uaddr),       \
                   "m" (*uaddr) : "cc" );

int futex_atomic_op_pt(int op, int __user *uaddr, int oparg, int *old)
{
      int oldval = 0, newval, ret;

      spin_lock(&current->mm->page_table_lock);
      uaddr = (int __user *) __dat_user_addr((unsigned long) uaddr);
      if (!uaddr) {
            spin_unlock(&current->mm->page_table_lock);
            return -EFAULT;
      }
      get_page(virt_to_page(uaddr));
      spin_unlock(&current->mm->page_table_lock);
      switch (op) {
      case FUTEX_OP_SET:
            __futex_atomic_op("lr %2,%5\n",
                          ret, oldval, newval, uaddr, oparg);
            break;
      case FUTEX_OP_ADD:
            __futex_atomic_op("lr %2,%1\nar %2,%5\n",
                          ret, oldval, newval, uaddr, oparg);
            break;
      case FUTEX_OP_OR:
            __futex_atomic_op("lr %2,%1\nor %2,%5\n",
                          ret, oldval, newval, uaddr, oparg);
            break;
      case FUTEX_OP_ANDN:
            __futex_atomic_op("lr %2,%1\nnr %2,%5\n",
                          ret, oldval, newval, uaddr, oparg);
            break;
      case FUTEX_OP_XOR:
            __futex_atomic_op("lr %2,%1\nxr %2,%5\n",
                          ret, oldval, newval, uaddr, oparg);
            break;
      default:
            ret = -ENOSYS;
      }
      put_page(virt_to_page(uaddr));
      *old = oldval;
      return ret;
}

int futex_atomic_cmpxchg_pt(int __user *uaddr, int oldval, int newval)
{
      int ret;

      spin_lock(&current->mm->page_table_lock);
      uaddr = (int __user *) __dat_user_addr((unsigned long) uaddr);
      if (!uaddr) {
            spin_unlock(&current->mm->page_table_lock);
            return -EFAULT;
      }
      get_page(virt_to_page(uaddr));
      spin_unlock(&current->mm->page_table_lock);
      asm volatile("   cs   %1,%4,0(%5)\n"
                 "0: lr   %0,%1\n"
                 "1:\n"
                 EX_TABLE(0b,1b)
                 : "=d" (ret), "+d" (oldval), "=m" (*uaddr)
                 : "0" (-EFAULT), "d" (newval), "a" (uaddr), "m" (*uaddr)
                 : "cc", "memory" );
      put_page(virt_to_page(uaddr));
      return ret;
}

struct uaccess_ops uaccess_pt = {
      .copy_from_user         = copy_from_user_pt,
      .copy_from_user_small   = copy_from_user_pt,
      .copy_to_user           = copy_to_user_pt,
      .copy_to_user_small     = copy_to_user_pt,
      .copy_in_user           = copy_in_user_pt,
      .clear_user       = clear_user_pt,
      .strnlen_user           = strnlen_user_pt,
      .strncpy_from_user      = strncpy_from_user_pt,
      .futex_atomic_op  = futex_atomic_op_pt,
      .futex_atomic_cmpxchg   = futex_atomic_cmpxchg_pt,
};

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