arch/i386/lib/usercopy.c

   1 /*
   2  * User address space access functions.
   3  * The non inlined parts of asm-i386/uaccess.h are here.
   4  *
   5  * Copyright 1997 Andi Kleen <ak@muc.de>
   6  * Copyright 1997 Linus Torvalds
   7  */
   8 #include <linux/config.h>
   9 #include <linux/mm.h>
  10 #include <linux/highmem.h>
  11 #include <linux/blkdev.h>
  12 #include <linux/module.h>
  13 #include <asm/uaccess.h>
  14 #include <asm/mmx.h>
  15
  16 static inline int __movsl_is_ok(unsigned long a1, unsigned long a2, unsigned long n)
  17 {
  18 #ifdef CONFIG_X86_INTEL_USERCOPY
  19         if (n >= 64 && ((a1 ^ a2) & movsl_mask.mask))
  20                 return 0;
  21 #endif
  22         return 1;
  23 }
  24 #define movsl_is_ok(a1,a2,n) \
  25         __movsl_is_ok((unsigned long)(a1),(unsigned long)(a2),(n))
  26
  27 /*
  28  * Copy a null terminated string from userspace.
  29  */
  30
  31 #define __do_strncpy_from_user(dst,src,count,res)                          \
  32 do {                                                                       \
  33         int __d0, __d1, __d2;                                              \
  34         __asm__ __volatile__(                                              \
  35                 "       testl %1,%1\n"                                     \
  36                 "       jz 2f\n"                                           \
  37                 "0:     lodsb\n"                                           \
  38                 "       stosb\n"                                           \
  39                 "       testb %%al,%%al\n"                                 \
  40                 "       jz 1f\n"                                           \
  41                 "       decl %1\n"                                         \
  42                 "       jnz 0b\n"                                          \
  43                 "1:     subl %1,%0\n"                                      \
  44                 "2:\n"                                                     \
  45                 ".section .fixup,\"ax\"\n"                                 \
  46                 "3:     movl %5,%0\n"                                      \
  47                 "       jmp 2b\n"                                          \
  48                 ".previous\n"                                              \
  49                 ".section __ex_table,\"a\"\n"                              \
  50                 "       .align 4\n"                                        \
  51                 "       .long 0b,3b\n"                                     \
  52                 ".previous"                                                \
  53                 : "=d"(res), "=c"(count), "=&a" (__d0), "=&S" (__d1),      \
  54                   "=&D" (__d2)                                             \
  55                 : "i"(-EFAULT), "0"(count), "1"(count), "3"(src), "4"(dst) \
  56                 : "memory");                                               \
  57 } while (0)
  58
  59 /**
  60  * __strncpy_from_user: - Copy a NUL terminated string from userspace, with less checking.
  61  * @dst:   Destination address, in kernel space.  This buffer must be at
  62  *         least @count bytes long.
  63  * @src:   Source address, in user space.
  64  * @count: Maximum number of bytes to copy, including the trailing NUL.
  65  *
  66  * Copies a NUL-terminated string from userspace to kernel space.
  67  * Caller must check the specified block with access_ok() before calling
  68  * this function.
  69  *
  70  * On success, returns the length of the string (not including the trailing
  71  * NUL).
  72  *
  73  * If access to userspace fails, returns -EFAULT (some data may have been
  74  * copied).
  75  *
  76  * If @count is smaller than the length of the string, copies @count bytes
  77  * and returns @count.
  78  */
  79 long
  80 __strncpy_from_user(char *dst, const char __user *src, long count)
  81 {
  82         long res;
  83         __do_strncpy_from_user(dst, src, count, res);
  84         return res;
  85 }
  86
  87 /**
  88  * strncpy_from_user: - Copy a NUL terminated string from userspace.
  89  * @dst:   Destination address, in kernel space.  This buffer must be at
  90  *         least @count bytes long.
  91  * @src:   Source address, in user space.
  92  * @count: Maximum number of bytes to copy, including the trailing NUL.
  93  *
  94  * Copies a NUL-terminated string from userspace to kernel space.
  95  *
  96  * On success, returns the length of the string (not including the trailing
  97  * NUL).
  98  *
  99  * If access to userspace fails, returns -EFAULT (some data may have been
 100  * copied).
 101  *
 102  * If @count is smaller than the length of the string, copies @count bytes
 103  * and returns @count.
 104  */
 105 long
 106 strncpy_from_user(char *dst, const char __user *src, long count)
 107 {
 108         long res = -EFAULT;
 109         if (access_ok(VERIFY_READ, src, 1))
 110                 __do_strncpy_from_user(dst, src, count, res);
 111         return res;
 112 }
 113
 114
 115 /*
 116  * Zero Userspace
 117  */
 118
 119 #define __do_clear_user(addr,size)                                      \
 120 do {                                                                    \
 121         int __d0;                                                       \
 122         __asm__ __volatile__(                                           \
 123                 "0:     rep; stosl\n"                                   \
 124                 "       movl %2,%0\n"                                   \
 125                 "1:     rep; stosb\n"                                   \
 126                 "2:\n"                                                  \
 127                 ".section .fixup,\"ax\"\n"                              \
 128                 "3:     lea 0(%2,%0,4),%0\n"                            \
 129                 "       jmp 2b\n"                                       \
 130                 ".previous\n"                                           \
 131                 ".section __ex_table,\"a\"\n"                           \
 132                 "       .align 4\n"                                     \
 133                 "       .long 0b,3b\n"                                  \
 134                 "       .long 1b,2b\n"                                  \
 135                 ".previous"                                             \
 136                 : "=&c"(size), "=&D" (__d0)                             \
 137                 : "r"(size & 3), "0"(size / 4), "1"(addr), "a"(0));     \
 138 } while (0)
 139
 140 /**
 141  * clear_user: - Zero a block of memory in user space.
 142  * @to:   Destination address, in user space.
 143  * @n:    Number of bytes to zero.
 144  *
 145  * Zero a block of memory in user space.
 146  *
 147  * Returns number of bytes that could not be cleared.
 148  * On success, this will be zero.
 149  */
 150 unsigned long
 151 clear_user(void __user *to, unsigned long n)
 152 {
 153         might_sleep();
 154         if (access_ok(VERIFY_WRITE, to, n))
 155                 __do_clear_user(to, n);
 156         return n;
 157 }
 158
 159 /**
 160  * __clear_user: - Zero a block of memory in user space, with less checking.
 161  * @to:   Destination address, in user space.
 162  * @n:    Number of bytes to zero.
 163  *
 164  * Zero a block of memory in user space.  Caller must check
 165  * the specified block with access_ok() before calling this function.
 166  *
 167  * Returns number of bytes that could not be cleared.
 168  * On success, this will be zero.
 169  */
 170 unsigned long
 171 __clear_user(void __user *to, unsigned long n)
 172 {
 173         __do_clear_user(to, n);
 174         return n;
 175 }
 176
 177 /**
 178  * strlen_user: - Get the size of a string in user space.
 179  * @s: The string to measure.
 180  * @n: The maximum valid length
 181  *
 182  * Get the size of a NUL-terminated string in user space.
 183  *
 184  * Returns the size of the string INCLUDING the terminating NUL.
 185  * On exception, returns 0.
 186  * If the string is too long, returns a value greater than @n.
 187  */
 188 long strnlen_user(const char __user *s, long n)
 189 {
 190         unsigned long mask = -__addr_ok(s);
 191         unsigned long res, tmp;
 192
 193         might_sleep();
 194
 195         __asm__ __volatile__(
 196                 "       testl %0, %0\n"
 197                 "       jz 3f\n"
 198                 "       andl %0,%%ecx\n"
 199                 "0:     repne; scasb\n"
 200                 "       setne %%al\n"
 201                 "       subl %%ecx,%0\n"
 202                 "       addl %0,%%eax\n"
 203                 "1:\n"
 204                 ".section .fixup,\"ax\"\n"
 205                 "2:     xorl %%eax,%%eax\n"
 206                 "       jmp 1b\n"
 207                 "3:     movb $1,%%al\n"
 208                 "       jmp 1b\n"
 209                 ".previous\n"
 210                 ".section __ex_table,\"a\"\n"
 211                 "       .align 4\n"
 212                 "       .long 0b,2b\n"
 213                 ".previous"
 214                 :"=r" (n), "=D" (s), "=a" (res), "=c" (tmp)
 215                 :"0" (n), "1" (s), "2" (0), "3" (mask)
 216                 :"cc");
 217         return res & mask;
 218 }
 219
 220 #ifdef CONFIG_X86_INTEL_USERCOPY
 221 static unsigned long
 222 __copy_user_intel(void *to, const void *from,unsigned long size)
 223 {
 224         int d0, d1;
 225         __asm__ __volatile__(
 226                        "       .align 2,0x90\n"
 227                        "1:     movl 32(%4), %%eax\n"
 228                        "       cmpl $67, %0\n"
 229                        "       jbe 3f\n"
 230                        "2:     movl 64(%4), %%eax\n"
 231                        "       .align 2,0x90\n"
 232                        "3:     movl 0(%4), %%eax\n"
 233                        "4:     movl 4(%4), %%edx\n"
 234                        "5:     movl %%eax, 0(%3)\n"
 235                        "6:     movl %%edx, 4(%3)\n"
 236                        "7:     movl 8(%4), %%eax\n"
 237                        "8:     movl 12(%4),%%edx\n"
 238                        "9:     movl %%eax, 8(%3)\n"
 239                        "10:    movl %%edx, 12(%3)\n"
 240                        "11:    movl 16(%4), %%eax\n"
 241                        "12:    movl 20(%4), %%edx\n"
 242                        "13:    movl %%eax, 16(%3)\n"
 243                        "14:    movl %%edx, 20(%3)\n"
 244                        "15:    movl 24(%4), %%eax\n"
 245                        "16:    movl 28(%4), %%edx\n"
 246                        "17:    movl %%eax, 24(%3)\n"
 247                        "18:    movl %%edx, 28(%3)\n"
 248                        "19:    movl 32(%4), %%eax\n"
 249                        "20:    movl 36(%4), %%edx\n"
 250                        "21:    movl %%eax, 32(%3)\n"
 251                        "22:    movl %%edx, 36(%3)\n"
 252                        "23:    movl 40(%4), %%eax\n"
 253                        "24:    movl 44(%4), %%edx\n"
 254                        "25:    movl %%eax, 40(%3)\n"
 255                        "26:    movl %%edx, 44(%3)\n"
 256                        "27:    movl 48(%4), %%eax\n"
 257                        "28:    movl 52(%4), %%edx\n"
 258                        "29:    movl %%eax, 48(%3)\n"
 259                        "30:    movl %%edx, 52(%3)\n"
 260                        "31:    movl 56(%4), %%eax\n"
 261                        "32:    movl 60(%4), %%edx\n"
 262                        "33:    movl %%eax, 56(%3)\n"
 263                        "34:    movl %%edx, 60(%3)\n"
 264                        "       addl $-64, %0\n"
 265                        "       addl $64, %4\n"
 266                        "       addl $64, %3\n"
 267                        "       cmpl $63, %0\n"
 268                        "       ja  1b\n"
 269                        "35:    movl  %0, %%eax\n"
 270                        "       shrl  $2, %0\n"
 271                        "       andl  $3, %%eax\n"
 272                        "       cld\n"
 273                        "99:    rep; movsl\n"
 274                        "36:    movl %%eax, %0\n"
 275                        "37:    rep; movsb\n"
 276                        "100:\n"
 277                        ".section .fixup,\"ax\"\n"
 278                        "101:   lea 0(%%eax,%0,4),%0\n"
 279                        "       jmp 100b\n"
 280                        ".previous\n"
 281                        ".section __ex_table,\"a\"\n"
 282                        "       .align 4\n"
 283                        "       .long 1b,100b\n"
 284                        "       .long 2b,100b\n"
 285                        "       .long 3b,100b\n"
 286                        "       .long 4b,100b\n"
 287                        "       .long 5b,100b\n"
 288                        "       .long 6b,100b\n"
 289                        "       .long 7b,100b\n"
 290                        "       .long 8b,100b\n"
 291                        "       .long 9b,100b\n"
 292                        "       .long 10b,100b\n"
 293                        "       .long 11b,100b\n"
 294                        "       .long 12b,100b\n"
 295                        "       .long 13b,100b\n"
 296                        "       .long 14b,100b\n"
 297                        "       .long 15b,100b\n"
 298                        "       .long 16b,100b\n"
 299                        "       .long 17b,100b\n"
 300                        "       .long 18b,100b\n"
 301                        "       .long 19b,100b\n"
 302                        "       .long 20b,100b\n"
 303                        "       .long 21b,100b\n"
 304                        "       .long 22b,100b\n"
 305                        "       .long 23b,100b\n"
 306                        "       .long 24b,100b\n"
 307                        "       .long 25b,100b\n"
 308                        "       .long 26b,100b\n"
 309                        "       .long 27b,100b\n"
 310                        "       .long 28b,100b\n"
 311                        "       .long 29b,100b\n"
 312                        "       .long 30b,100b\n"
 313                        "       .long 31b,100b\n"
 314                        "       .long 32b,100b\n"
 315                        "       .long 33b,100b\n"
 316                        "       .long 34b,100b\n"
 317                        "       .long 35b,100b\n"
 318                        "       .long 36b,100b\n"
 319                        "       .long 37b,100b\n"
 320                        "       .long 99b,101b\n"
 321                        ".previous"
 322                        : "=&c"(size), "=&D" (d0), "=&S" (d1)
 323                        :  "1"(to), "2"(from), "0"(size)
 324                        : "eax", "edx", "memory");
 325         return size;
 326 }
 327
 328 static unsigned long
 329 __copy_user_zeroing_intel(void *to, const void *from, unsigned long size)
 330 {
 331         int d0, d1;
 332         __asm__ __volatile__(
 333                        "        .align 2,0x90\n"
 334                        "0:      movl 32(%4), %%eax\n"
 335                        "        cmpl $67, %0\n"
 336                        "        jbe 2f\n"
 337                        "1:      movl 64(%4), %%eax\n"
 338                        "        .align 2,0x90\n"
 339                        "2:      movl 0(%4), %%eax\n"
 340                        "21:     movl 4(%4), %%edx\n"
 341                        "        movl %%eax, 0(%3)\n"
 342                        "        movl %%edx, 4(%3)\n"
 343                        "3:      movl 8(%4), %%eax\n"
 344                        "31:     movl 12(%4),%%edx\n"
 345                        "        movl %%eax, 8(%3)\n"
 346                        "        movl %%edx, 12(%3)\n"
 347                        "4:      movl 16(%4), %%eax\n"
 348                        "41:     movl 20(%4), %%edx\n"
 349                        "        movl %%eax, 16(%3)\n"
 350                        "        movl %%edx, 20(%3)\n"
 351                        "10:     movl 24(%4), %%eax\n"
 352                        "51:     movl 28(%4), %%edx\n"
 353                        "        movl %%eax, 24(%3)\n"
 354                        "        movl %%edx, 28(%3)\n"
 355                        "11:     movl 32(%4), %%eax\n"
 356                        "61:     movl 36(%4), %%edx\n"
 357                        "        movl %%eax, 32(%3)\n"
 358                        "        movl %%edx, 36(%3)\n"
 359                        "12:     movl 40(%4), %%eax\n"
 360                        "71:     movl 44(%4), %%edx\n"
 361                        "        movl %%eax, 40(%3)\n"
 362                        "        movl %%edx, 44(%3)\n"
 363                        "13:     movl 48(%4), %%eax\n"
 364                        "81:     movl 52(%4), %%edx\n"
 365                        "        movl %%eax, 48(%3)\n"
 366                        "        movl %%edx, 52(%3)\n"
 367                        "14:     movl 56(%4), %%eax\n"
 368                        "91:     movl 60(%4), %%edx\n"
 369                        "        movl %%eax, 56(%3)\n"
 370                        "        movl %%edx, 60(%3)\n"
 371                        "        addl $-64, %0\n"
 372                        "        addl $64, %4\n"
 373                        "        addl $64, %3\n"
 374                        "        cmpl $63, %0\n"
 375                        "        ja  0b\n"
 376                        "5:      movl  %0, %%eax\n"
 377                        "        shrl  $2, %0\n"
 378                        "        andl $3, %%eax\n"
 379                        "        cld\n"
 380                        "6:      rep; movsl\n"
 381                        "        movl %%eax,%0\n"
 382                        "7:      rep; movsb\n"
 383                        "8:\n"
 384                        ".section .fixup,\"ax\"\n"
 385                        "9:      lea 0(%%eax,%0,4),%0\n"
 386                        "16:     pushl %0\n"
 387                        "        pushl %%eax\n"
 388                        "        xorl %%eax,%%eax\n"
 389                        "        rep; stosb\n"
 390                        "        popl %%eax\n"
 391                        "        popl %0\n"
 392                        "        jmp 8b\n"
 393                        ".previous\n"
 394                        ".section __ex_table,\"a\"\n"
 395                        "        .align 4\n"
 396                        "        .long 0b,16b\n"
 397                        "        .long 1b,16b\n"
 398                        "        .long 2b,16b\n"
 399                        "        .long 21b,16b\n"
 400                        "        .long 3b,16b\n"
 401                        "        .long 31b,16b\n"
 402                        "        .long 4b,16b\n"
 403                        "        .long 41b,16b\n"
 404                        "        .long 10b,16b\n"
 405                        "        .long 51b,16b\n"
 406                        "        .long 11b,16b\n"
 407                        "        .long 61b,16b\n"
 408                        "        .long 12b,16b\n"
 409                        "        .long 71b,16b\n"
 410                        "        .long 13b,16b\n"
 411                        "        .long 81b,16b\n"
 412                        "        .long 14b,16b\n"
 413                        "        .long 91b,16b\n"
 414                        "        .long 6b,9b\n"
 415                        "        .long 7b,16b\n"
 416                        ".previous"
 417                        : "=&c"(size), "=&D" (d0), "=&S" (d1)
 418                        :  "1"(to), "2"(from), "0"(size)
 419                        : "eax", "edx", "memory");
 420         return size;
 421 }
 422 #else
 423 /*
 424  * Leave these declared but undefined.  They should not be any references to
 425  * them
 426  */
 427 unsigned long
 428 __copy_user_zeroing_intel(void *to, const void *from, unsigned long size);
 429 unsigned long
 430 __copy_user_intel(void *to, const void *from,unsigned long size);
 431 #endif /* CONFIG_X86_INTEL_USERCOPY */
 432
 433 /* Generic arbitrary sized copy.  */
 434 #define __copy_user(to,from,size)                                       \
 435 do {                                                                    \
 436         int __d0, __d1, __d2;                                           \
 437         __asm__ __volatile__(                                           \
 438                 "       cmp  $7,%0\n"                                   \
 439                 "       jbe  1f\n"                                      \
 440                 "       movl %1,%0\n"                                   \
 441                 "       negl %0\n"                                      \
 442                 "       andl $7,%0\n"                                   \
 443                 "       subl %0,%3\n"                                   \
 444                 "4:     rep; movsb\n"                                   \
 445                 "       movl %3,%0\n"                                   \
 446                 "       shrl $2,%0\n"                                   \
 447                 "       andl $3,%3\n"                                   \
 448                 "       .align 2,0x90\n"                                \
 449                 "0:     rep; movsl\n"                                   \
 450                 "       movl %3,%0\n"                                   \
 451                 "1:     rep; movsb\n"                                   \
 452                 "2:\n"                                                  \
 453                 ".section .fixup,\"ax\"\n"                              \
 454                 "5:     addl %3,%0\n"                                   \
 455                 "       jmp 2b\n"                                       \
 456                 "3:     lea 0(%3,%0,4),%0\n"                            \
 457                 "       jmp 2b\n"                                       \
 458                 ".previous\n"                                           \
 459                 ".section __ex_table,\"a\"\n"                           \
 460                 "       .align 4\n"                                     \
 461                 "       .long 4b,5b\n"                                  \
 462                 "       .long 0b,3b\n"                                  \
 463                 "       .long 1b,2b\n"                                  \
 464                 ".previous"                                             \
 465                 : "=&c"(size), "=&D" (__d0), "=&S" (__d1), "=r"(__d2)   \
 466                 : "3"(size), "0"(size), "1"(to), "2"(from)              \
 467                 : "memory");                                            \
 468 } while (0)
 469
 470 #define __copy_user_zeroing(to,from,size)                               \
 471 do {                                                                    \
 472         int __d0, __d1, __d2;                                           \
 473         __asm__ __volatile__(                                           \
 474                 "       cmp  $7,%0\n"                                   \
 475                 "       jbe  1f\n"                                      \
 476                 "       movl %1,%0\n"                                   \
 477                 "       negl %0\n"                                      \
 478                 "       andl $7,%0\n"                                   \
 479                 "       subl %0,%3\n"                                   \
 480                 "4:     rep; movsb\n"                                   \
 481                 "       movl %3,%0\n"                                   \
 482                 "       shrl $2,%0\n"                                   \
 483                 "       andl $3,%3\n"                                   \
 484                 "       .align 2,0x90\n"                                \
 485                 "0:     rep; movsl\n"                                   \
 486                 "       movl %3,%0\n"                                   \
 487                 "1:     rep; movsb\n"                                   \
 488                 "2:\n"                                                  \
 489                 ".section .fixup,\"ax\"\n"                              \
 490                 "5:     addl %3,%0\n"                                   \
 491                 "       jmp 6f\n"                                       \
 492                 "3:     lea 0(%3,%0,4),%0\n"                            \
 493                 "6:     pushl %0\n"                                     \
 494                 "       pushl %%eax\n"                                  \
 495                 "       xorl %%eax,%%eax\n"                             \
 496                 "       rep; stosb\n"                                   \
 497                 "       popl %%eax\n"                                   \
 498                 "       popl %0\n"                                      \
 499                 "       jmp 2b\n"                                       \
 500                 ".previous\n"                                           \
 501                 ".section __ex_table,\"a\"\n"                           \
 502                 "       .align 4\n"                                     \
 503                 "       .long 4b,5b\n"                                  \
 504                 "       .long 0b,3b\n"                                  \
 505                 "       .long 1b,6b\n"                                  \
 506                 ".previous"                                             \
 507                 : "=&c"(size), "=&D" (__d0), "=&S" (__d1), "=r"(__d2)   \
 508                 : "3"(size), "0"(size), "1"(to), "2"(from)              \
 509                 : "memory");                                            \
 510 } while (0)
 511
 512
 513 unsigned long __copy_to_user_ll(void __user *to, const void *from, unsigned long n)
 514 {
 515 #ifndef CONFIG_X86_WP_WORKS_OK
 516         if (unlikely(boot_cpu_data.wp_works_ok == 0) &&
 517                         ((unsigned long )to) < TASK_SIZE) {
 518                 /*
 519                  * CPU does not honor the WP bit when writing
 520                  * from supervisory mode, and due to preemption or SMP,
 521                  * the page tables can change at any time.
 522                  * Do it manually.      Manfred <manfred@colorfullife.com>
 523                  */
 524                 while (n) {
 525                         unsigned long offset = ((unsigned long)to)%PAGE_SIZE;
 526                         unsigned long len = PAGE_SIZE - offset;
 527                         int retval;
 528                         struct page *pg;
 529                         void *maddr;
 530
 531                         if (len > n)
 532                                 len = n;
 533
 534 survive:
 535                         down_read(&current->mm->mmap_sem);
 536                         retval = get_user_pages(current, current->mm,
 537                                         (unsigned long )to, 1, 1, 0, &pg, NULL);
 538
 539                         if (retval == -ENOMEM && current->pid == 1) {
 540                                 up_read(&current->mm->mmap_sem);
 541                                 blk_congestion_wait(WRITE, HZ/50);
 542                                 goto survive;
 543                         }
 544
 545                         if (retval != 1) {
 546                                 up_read(&current->mm->mmap_sem);
 547                                 break;
 548                         }
 549
 550                         maddr = kmap_atomic(pg, KM_USER0);
 551                         memcpy(maddr + offset, from, len);
 552                         kunmap_atomic(maddr, KM_USER0);
 553                         set_page_dirty_lock(pg);
 554                         put_page(pg);
 555                         up_read(&current->mm->mmap_sem);
 556
 557                         from += len;
 558                         to += len;
 559                         n -= len;
 560                 }
 561                 return n;
 562         }
 563 #endif
 564         if (movsl_is_ok(to, from, n))
 565                 __copy_user((void *)to, from, n);
 566         else
 567                 n = __copy_user_intel((void *)to, from, n);
 568         return n;
 569 }
 570
 571 unsigned long
 572 __copy_from_user_ll(void *to, const void __user *from, unsigned long n)
 573 {
 574         if (movsl_is_ok(to, from, n))
 575                 __copy_user_zeroing(to, (const void *) from, n);
 576         else
 577                 n = __copy_user_zeroing_intel(to, (const void *) from, n);
 578         return n;
 579 }
 580
 581 /**
 582  * copy_to_user: - Copy a block of data into user space.
 583  * @to:   Destination address, in user space.
 584  * @from: Source address, in kernel space.
 585  * @n:    Number of bytes to copy.
 586  *
 587  * Context: User context only.  This function may sleep.
 588  *
 589  * Copy data from kernel space to user space.
 590  *
 591  * Returns number of bytes that could not be copied.
 592  * On success, this will be zero.
 593  */
 594 unsigned long
 595 copy_to_user(void __user *to, const void *from, unsigned long n)
 596 {
 597         might_sleep();
 598         if (access_ok(VERIFY_WRITE, to, n))
 599                 n = __copy_to_user(to, from, n);
 600         return n;
 601 }
 602 EXPORT_SYMBOL(copy_to_user);
 603
 604 /**
 605  * copy_from_user: - Copy a block of data from user space.
 606  * @to:   Destination address, in kernel space.
 607  * @from: Source address, in user space.
 608  * @n:    Number of bytes to copy.
 609  *
 610  * Context: User context only.  This function may sleep.
 611  *
 612  * Copy data from user space to kernel space.
 613  *
 614  * Returns number of bytes that could not be copied.
 615  * On success, this will be zero.
 616  *
 617  * If some data could not be copied, this function will pad the copied
 618  * data to the requested size using zero bytes.
 619  */
 620 unsigned long
 621 copy_from_user(void *to, const void __user *from, unsigned long n)
 622 {
 623         might_sleep();
 624         if (access_ok(VERIFY_READ, from, n))
 625                 n = __copy_from_user(to, from, n);
 626         else
 627                 memset(to, 0, n);
 628         return n;
 629 }
 630 EXPORT_SYMBOL(copy_from_user);