arch/x86/lib/usercopy.c

   1 /*
   2  * User address space access functions.
   3  *
   4  *  For licencing details see kernel-base/COPYING
   5  */
   6
   7 #include <linux/highmem.h>
   8 #include <linux/module.h>
   9
  10 #include <asm/word-at-a-time.h>
  11
  12 /*
  13  * best effort, GUP based copy_from_user() that is NMI-safe
  14  */
  15 unsigned long
  16 copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
  17 {
  18         unsigned long offset, addr = (unsigned long)from;
  19         unsigned long size, len = 0;
  20         struct page *page;
  21         void *map;
  22         int ret;
  23
  24         do {
  25                 ret = __get_user_pages_fast(addr, 1, 0, &page);
  26                 if (!ret)
  27                         break;
  28
  29                 offset = addr & (PAGE_SIZE - 1);
  30                 size = min(PAGE_SIZE - offset, n - len);
  31
  32                 map = kmap_atomic(page);
  33                 memcpy(to, map+offset, size);
  34                 kunmap_atomic(map);
  35                 put_page(page);
  36
  37                 len  += size;
  38                 to   += size;
  39                 addr += size;
  40
  41         } while (len < n);
  42
  43         return len;
  44 }
  45 EXPORT_SYMBOL_GPL(copy_from_user_nmi);
  46
  47 static inline unsigned long count_bytes(unsigned long mask)
  48 {
  49         mask = (mask - 1) & ~mask;
  50         mask >>= 7;
  51         return count_masked_bytes(mask);
  52 }
  53
  54 /*
  55  * Do a strncpy, return length of string without final '\0'.
  56  * 'count' is the user-supplied count (return 'count' if we
  57  * hit it), 'max' is the address space maximum (and we return
  58  * -EFAULT if we hit it).
  59  */
  60 static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, long max)
  61 {
  62         long res = 0;
  63
  64         /*
  65          * Truncate 'max' to the user-specified limit, so that
  66          * we only have one limit we need to check in the loop
  67          */
  68         if (max > count)
  69                 max = count;
  70
  71         while (max >= sizeof(unsigned long)) {
  72                 unsigned long c;
  73
  74                 /* Fall back to byte-at-a-time if we get a page fault */
  75                 if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))
  76                         break;
  77                 /* This can write a few bytes past the NUL character, but that's ok */
  78                 *(unsigned long *)(dst+res) = c;
  79                 c = has_zero(c);
  80                 if (c)
  81                         return res + count_bytes(c);
  82                 res += sizeof(unsigned long);
  83                 max -= sizeof(unsigned long);
  84         }
  85
  86         while (max) {
  87                 char c;
  88
  89                 if (unlikely(__get_user(c,src+res)))
  90                         return -EFAULT;
  91                 dst[res] = c;
  92                 if (!c)
  93                         return res;
  94                 res++;
  95                 max--;
  96         }
  97
  98         /*
  99          * Uhhuh. We hit 'max'. But was that the user-specified maximum
 100          * too? If so, that's ok - we got as much as the user asked for.
 101          */
 102         if (res >= count)
 103                 return count;
 104
 105         /*
 106          * Nope: we hit the address space limit, and we still had more
 107          * characters the caller would have wanted. That's an EFAULT.
 108          */
 109         return -EFAULT;
 110 }
 111
 112 /**
 113  * strncpy_from_user: - Copy a NUL terminated string from userspace.
 114  * @dst:   Destination address, in kernel space.  This buffer must be at
 115  *         least @count bytes long.
 116  * @src:   Source address, in user space.
 117  * @count: Maximum number of bytes to copy, including the trailing NUL.
 118  *
 119  * Copies a NUL-terminated string from userspace to kernel space.
 120  *
 121  * On success, returns the length of the string (not including the trailing
 122  * NUL).
 123  *
 124  * If access to userspace fails, returns -EFAULT (some data may have been
 125  * copied).
 126  *
 127  * If @count is smaller than the length of the string, copies @count bytes
 128  * and returns @count.
 129  */
 130 long
 131 strncpy_from_user(char *dst, const char __user *src, long count)
 132 {
 133         unsigned long max_addr, src_addr;
 134
 135         if (unlikely(count <= 0))
 136                 return 0;
 137
 138         max_addr = current_thread_info()->addr_limit.seg;
 139         src_addr = (unsigned long)src;
 140         if (likely(src_addr < max_addr)) {
 141                 unsigned long max = max_addr - src_addr;
 142                 return do_strncpy_from_user(dst, src, count, max);
 143         }
 144         return -EFAULT;
 145 }
 146 EXPORT_SYMBOL(strncpy_from_user);