Linux-2.6.12-rc2
[linux-2.6.git] / 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         might_sleep();                                                     \
35         __asm__ __volatile__(                                              \
36                 "       testl %1,%1\n"                                     \
37                 "       jz 2f\n"                                           \
38                 "0:     lodsb\n"                                           \
39                 "       stosb\n"                                           \
40                 "       testb %%al,%%al\n"                                 \
41                 "       jz 1f\n"                                           \
42                 "       decl %1\n"                                         \
43                 "       jnz 0b\n"                                          \
44                 "1:     subl %1,%0\n"                                      \
45                 "2:\n"                                                     \
46                 ".section .fixup,\"ax\"\n"                                 \
47                 "3:     movl %5,%0\n"                                      \
48                 "       jmp 2b\n"                                          \
49                 ".previous\n"                                              \
50                 ".section __ex_table,\"a\"\n"                              \
51                 "       .align 4\n"                                        \
52                 "       .long 0b,3b\n"                                     \
53                 ".previous"                                                \
54                 : "=d"(res), "=c"(count), "=&a" (__d0), "=&S" (__d1),      \
55                   "=&D" (__d2)                                             \
56                 : "i"(-EFAULT), "0"(count), "1"(count), "3"(src), "4"(dst) \
57                 : "memory");                                               \
58 } while (0)
59
60 /**
61  * __strncpy_from_user: - Copy a NUL terminated string from userspace, with less checking.
62  * @dst:   Destination address, in kernel space.  This buffer must be at
63  *         least @count bytes long.
64  * @src:   Source address, in user space.
65  * @count: Maximum number of bytes to copy, including the trailing NUL.
66  * 
67  * Copies a NUL-terminated string from userspace to kernel space.
68  * Caller must check the specified block with access_ok() before calling
69  * this function.
70  *
71  * On success, returns the length of the string (not including the trailing
72  * NUL).
73  *
74  * If access to userspace fails, returns -EFAULT (some data may have been
75  * copied).
76  *
77  * If @count is smaller than the length of the string, copies @count bytes
78  * and returns @count.
79  */
80 long
81 __strncpy_from_user(char *dst, const char __user *src, long count)
82 {
83         long res;
84         __do_strncpy_from_user(dst, src, count, res);
85         return res;
86 }
87
88 /**
89  * strncpy_from_user: - Copy a NUL terminated string from userspace.
90  * @dst:   Destination address, in kernel space.  This buffer must be at
91  *         least @count bytes long.
92  * @src:   Source address, in user space.
93  * @count: Maximum number of bytes to copy, including the trailing NUL.
94  * 
95  * Copies a NUL-terminated string from userspace to kernel space.
96  *
97  * On success, returns the length of the string (not including the trailing
98  * NUL).
99  *
100  * If access to userspace fails, returns -EFAULT (some data may have been
101  * copied).
102  *
103  * If @count is smaller than the length of the string, copies @count bytes
104  * and returns @count.
105  */
106 long
107 strncpy_from_user(char *dst, const char __user *src, long count)
108 {
109         long res = -EFAULT;
110         if (access_ok(VERIFY_READ, src, 1))
111                 __do_strncpy_from_user(dst, src, count, res);
112         return res;
113 }
114
115
116 /*
117  * Zero Userspace
118  */
119
120 #define __do_clear_user(addr,size)                                      \
121 do {                                                                    \
122         int __d0;                                                       \
123         might_sleep();                                                  \
124         __asm__ __volatile__(                                           \
125                 "0:     rep; stosl\n"                                   \
126                 "       movl %2,%0\n"                                   \
127                 "1:     rep; stosb\n"                                   \
128                 "2:\n"                                                  \
129                 ".section .fixup,\"ax\"\n"                              \
130                 "3:     lea 0(%2,%0,4),%0\n"                            \
131                 "       jmp 2b\n"                                       \
132                 ".previous\n"                                           \
133                 ".section __ex_table,\"a\"\n"                           \
134                 "       .align 4\n"                                     \
135                 "       .long 0b,3b\n"                                  \
136                 "       .long 1b,2b\n"                                  \
137                 ".previous"                                             \
138                 : "=&c"(size), "=&D" (__d0)                             \
139                 : "r"(size & 3), "0"(size / 4), "1"(addr), "a"(0));     \
140 } while (0)
141
142 /**
143  * clear_user: - Zero a block of memory in user space.
144  * @to:   Destination address, in user space.
145  * @n:    Number of bytes to zero.
146  *
147  * Zero a block of memory in user space.
148  *
149  * Returns number of bytes that could not be cleared.
150  * On success, this will be zero.
151  */
152 unsigned long
153 clear_user(void __user *to, unsigned long n)
154 {
155         might_sleep();
156         if (access_ok(VERIFY_WRITE, to, n))
157                 __do_clear_user(to, n);
158         return n;
159 }
160
161 /**
162  * __clear_user: - Zero a block of memory in user space, with less checking.
163  * @to:   Destination address, in user space.
164  * @n:    Number of bytes to zero.
165  *
166  * Zero a block of memory in user space.  Caller must check
167  * the specified block with access_ok() before calling this function.
168  *
169  * Returns number of bytes that could not be cleared.
170  * On success, this will be zero.
171  */
172 unsigned long
173 __clear_user(void __user *to, unsigned long n)
174 {
175         __do_clear_user(to, n);
176         return n;
177 }
178
179 /**
180  * strlen_user: - Get the size of a string in user space.
181  * @s: The string to measure.
182  * @n: The maximum valid length
183  *
184  * Get the size of a NUL-terminated string in user space.
185  *
186  * Returns the size of the string INCLUDING the terminating NUL.
187  * On exception, returns 0.
188  * If the string is too long, returns a value greater than @n.
189  */
190 long strnlen_user(const char __user *s, long n)
191 {
192         unsigned long mask = -__addr_ok(s);
193         unsigned long res, tmp;
194
195         might_sleep();
196
197         __asm__ __volatile__(
198                 "       testl %0, %0\n"
199                 "       jz 3f\n"
200                 "       andl %0,%%ecx\n"
201                 "0:     repne; scasb\n"
202                 "       setne %%al\n"
203                 "       subl %%ecx,%0\n"
204                 "       addl %0,%%eax\n"
205                 "1:\n"
206                 ".section .fixup,\"ax\"\n"
207                 "2:     xorl %%eax,%%eax\n"
208                 "       jmp 1b\n"
209                 "3:     movb $1,%%al\n"
210                 "       jmp 1b\n"
211                 ".previous\n"
212                 ".section __ex_table,\"a\"\n"
213                 "       .align 4\n"
214                 "       .long 0b,2b\n"
215                 ".previous"
216                 :"=r" (n), "=D" (s), "=a" (res), "=c" (tmp)
217                 :"0" (n), "1" (s), "2" (0), "3" (mask)
218                 :"cc");
219         return res & mask;
220 }
221
222 #ifdef CONFIG_X86_INTEL_USERCOPY
223 static unsigned long
224 __copy_user_intel(void __user *to, const void *from, unsigned long size)
225 {
226         int d0, d1;
227         __asm__ __volatile__(
228                        "       .align 2,0x90\n"
229                        "1:     movl 32(%4), %%eax\n"
230                        "       cmpl $67, %0\n"
231                        "       jbe 3f\n"
232                        "2:     movl 64(%4), %%eax\n"
233                        "       .align 2,0x90\n"
234                        "3:     movl 0(%4), %%eax\n"
235                        "4:     movl 4(%4), %%edx\n"
236                        "5:     movl %%eax, 0(%3)\n"
237                        "6:     movl %%edx, 4(%3)\n"
238                        "7:     movl 8(%4), %%eax\n"
239                        "8:     movl 12(%4),%%edx\n"
240                        "9:     movl %%eax, 8(%3)\n"
241                        "10:    movl %%edx, 12(%3)\n"
242                        "11:    movl 16(%4), %%eax\n"
243                        "12:    movl 20(%4), %%edx\n"
244                        "13:    movl %%eax, 16(%3)\n"
245                        "14:    movl %%edx, 20(%3)\n"
246                        "15:    movl 24(%4), %%eax\n"
247                        "16:    movl 28(%4), %%edx\n"
248                        "17:    movl %%eax, 24(%3)\n"
249                        "18:    movl %%edx, 28(%3)\n"
250                        "19:    movl 32(%4), %%eax\n"
251                        "20:    movl 36(%4), %%edx\n"
252                        "21:    movl %%eax, 32(%3)\n"
253                        "22:    movl %%edx, 36(%3)\n"
254                        "23:    movl 40(%4), %%eax\n"
255                        "24:    movl 44(%4), %%edx\n"
256                        "25:    movl %%eax, 40(%3)\n"
257                        "26:    movl %%edx, 44(%3)\n"
258                        "27:    movl 48(%4), %%eax\n"
259                        "28:    movl 52(%4), %%edx\n"
260                        "29:    movl %%eax, 48(%3)\n"
261                        "30:    movl %%edx, 52(%3)\n"
262                        "31:    movl 56(%4), %%eax\n"
263                        "32:    movl 60(%4), %%edx\n"
264                        "33:    movl %%eax, 56(%3)\n"
265                        "34:    movl %%edx, 60(%3)\n"
266                        "       addl $-64, %0\n"
267                        "       addl $64, %4\n"
268                        "       addl $64, %3\n"
269                        "       cmpl $63, %0\n"
270                        "       ja  1b\n"
271                        "35:    movl  %0, %%eax\n"
272                        "       shrl  $2, %0\n"
273                        "       andl  $3, %%eax\n"
274                        "       cld\n"
275                        "99:    rep; movsl\n"
276                        "36:    movl %%eax, %0\n"
277                        "37:    rep; movsb\n"
278                        "100:\n"
279                        ".section .fixup,\"ax\"\n"
280                        "101:   lea 0(%%eax,%0,4),%0\n"
281                        "       jmp 100b\n"
282                        ".previous\n"
283                        ".section __ex_table,\"a\"\n"
284                        "       .align 4\n"
285                        "       .long 1b,100b\n"
286                        "       .long 2b,100b\n"
287                        "       .long 3b,100b\n"
288                        "       .long 4b,100b\n"
289                        "       .long 5b,100b\n"
290                        "       .long 6b,100b\n"
291                        "       .long 7b,100b\n"
292                        "       .long 8b,100b\n"
293                        "       .long 9b,100b\n"
294                        "       .long 10b,100b\n"
295                        "       .long 11b,100b\n"
296                        "       .long 12b,100b\n"
297                        "       .long 13b,100b\n"
298                        "       .long 14b,100b\n"
299                        "       .long 15b,100b\n"
300                        "       .long 16b,100b\n"
301                        "       .long 17b,100b\n"
302                        "       .long 18b,100b\n"
303                        "       .long 19b,100b\n"
304                        "       .long 20b,100b\n"
305                        "       .long 21b,100b\n"
306                        "       .long 22b,100b\n"
307                        "       .long 23b,100b\n"
308                        "       .long 24b,100b\n"
309                        "       .long 25b,100b\n"
310                        "       .long 26b,100b\n"
311                        "       .long 27b,100b\n"
312                        "       .long 28b,100b\n"
313                        "       .long 29b,100b\n"
314                        "       .long 30b,100b\n"
315                        "       .long 31b,100b\n"
316                        "       .long 32b,100b\n"
317                        "       .long 33b,100b\n"
318                        "       .long 34b,100b\n"
319                        "       .long 35b,100b\n"
320                        "       .long 36b,100b\n"
321                        "       .long 37b,100b\n"
322                        "       .long 99b,101b\n"
323                        ".previous"
324                        : "=&c"(size), "=&D" (d0), "=&S" (d1)
325                        :  "1"(to), "2"(from), "0"(size)
326                        : "eax", "edx", "memory");
327         return size;
328 }
329
330 static unsigned long
331 __copy_user_zeroing_intel(void *to, const void __user *from, unsigned long size)
332 {
333         int d0, d1;
334         __asm__ __volatile__(
335                        "        .align 2,0x90\n"
336                        "0:      movl 32(%4), %%eax\n"
337                        "        cmpl $67, %0\n"      
338                        "        jbe 2f\n"            
339                        "1:      movl 64(%4), %%eax\n"
340                        "        .align 2,0x90\n"     
341                        "2:      movl 0(%4), %%eax\n" 
342                        "21:     movl 4(%4), %%edx\n" 
343                        "        movl %%eax, 0(%3)\n" 
344                        "        movl %%edx, 4(%3)\n" 
345                        "3:      movl 8(%4), %%eax\n" 
346                        "31:     movl 12(%4),%%edx\n" 
347                        "        movl %%eax, 8(%3)\n" 
348                        "        movl %%edx, 12(%3)\n"
349                        "4:      movl 16(%4), %%eax\n"
350                        "41:     movl 20(%4), %%edx\n"
351                        "        movl %%eax, 16(%3)\n"
352                        "        movl %%edx, 20(%3)\n"
353                        "10:     movl 24(%4), %%eax\n"
354                        "51:     movl 28(%4), %%edx\n"
355                        "        movl %%eax, 24(%3)\n"
356                        "        movl %%edx, 28(%3)\n"
357                        "11:     movl 32(%4), %%eax\n"
358                        "61:     movl 36(%4), %%edx\n"
359                        "        movl %%eax, 32(%3)\n"
360                        "        movl %%edx, 36(%3)\n"
361                        "12:     movl 40(%4), %%eax\n"
362                        "71:     movl 44(%4), %%edx\n"
363                        "        movl %%eax, 40(%3)\n"
364                        "        movl %%edx, 44(%3)\n"
365                        "13:     movl 48(%4), %%eax\n"
366                        "81:     movl 52(%4), %%edx\n"
367                        "        movl %%eax, 48(%3)\n"
368                        "        movl %%edx, 52(%3)\n"
369                        "14:     movl 56(%4), %%eax\n"
370                        "91:     movl 60(%4), %%edx\n"
371                        "        movl %%eax, 56(%3)\n"
372                        "        movl %%edx, 60(%3)\n"
373                        "        addl $-64, %0\n"     
374                        "        addl $64, %4\n"      
375                        "        addl $64, %3\n"      
376                        "        cmpl $63, %0\n"      
377                        "        ja  0b\n"            
378                        "5:      movl  %0, %%eax\n"   
379                        "        shrl  $2, %0\n"      
380                        "        andl $3, %%eax\n"    
381                        "        cld\n"               
382                        "6:      rep; movsl\n"   
383                        "        movl %%eax,%0\n"
384                        "7:      rep; movsb\n"   
385                        "8:\n"                   
386                        ".section .fixup,\"ax\"\n"
387                        "9:      lea 0(%%eax,%0,4),%0\n" 
388                        "16:     pushl %0\n"     
389                        "        pushl %%eax\n"  
390                        "        xorl %%eax,%%eax\n"
391                        "        rep; stosb\n"   
392                        "        popl %%eax\n"   
393                        "        popl %0\n"      
394                        "        jmp 8b\n"       
395                        ".previous\n"            
396                        ".section __ex_table,\"a\"\n"
397                        "        .align 4\n"        
398                        "        .long 0b,16b\n"  
399                        "        .long 1b,16b\n"
400                        "        .long 2b,16b\n"
401                        "        .long 21b,16b\n"
402                        "        .long 3b,16b\n" 
403                        "        .long 31b,16b\n"
404                        "        .long 4b,16b\n" 
405                        "        .long 41b,16b\n"
406                        "        .long 10b,16b\n"
407                        "        .long 51b,16b\n"
408                        "        .long 11b,16b\n"
409                        "        .long 61b,16b\n"
410                        "        .long 12b,16b\n"
411                        "        .long 71b,16b\n"
412                        "        .long 13b,16b\n"
413                        "        .long 81b,16b\n"
414                        "        .long 14b,16b\n"
415                        "        .long 91b,16b\n"
416                        "        .long 6b,9b\n"  
417                        "        .long 7b,16b\n" 
418                        ".previous"              
419                        : "=&c"(size), "=&D" (d0), "=&S" (d1)
420                        :  "1"(to), "2"(from), "0"(size)
421                        : "eax", "edx", "memory");
422         return size;
423 }
424 #else
425 /*
426  * Leave these declared but undefined.  They should not be any references to
427  * them
428  */
429 unsigned long
430 __copy_user_zeroing_intel(void *to, const void __user *from, unsigned long size);
431 unsigned long
432 __copy_user_intel(void __user *to, const void *from, unsigned long size);
433 #endif /* CONFIG_X86_INTEL_USERCOPY */
434
435 /* Generic arbitrary sized copy.  */
436 #define __copy_user(to,from,size)                                       \
437 do {                                                                    \
438         int __d0, __d1, __d2;                                           \
439         __asm__ __volatile__(                                           \
440                 "       cmp  $7,%0\n"                                   \
441                 "       jbe  1f\n"                                      \
442                 "       movl %1,%0\n"                                   \
443                 "       negl %0\n"                                      \
444                 "       andl $7,%0\n"                                   \
445                 "       subl %0,%3\n"                                   \
446                 "4:     rep; movsb\n"                                   \
447                 "       movl %3,%0\n"                                   \
448                 "       shrl $2,%0\n"                                   \
449                 "       andl $3,%3\n"                                   \
450                 "       .align 2,0x90\n"                                \
451                 "0:     rep; movsl\n"                                   \
452                 "       movl %3,%0\n"                                   \
453                 "1:     rep; movsb\n"                                   \
454                 "2:\n"                                                  \
455                 ".section .fixup,\"ax\"\n"                              \
456                 "5:     addl %3,%0\n"                                   \
457                 "       jmp 2b\n"                                       \
458                 "3:     lea 0(%3,%0,4),%0\n"                            \
459                 "       jmp 2b\n"                                       \
460                 ".previous\n"                                           \
461                 ".section __ex_table,\"a\"\n"                           \
462                 "       .align 4\n"                                     \
463                 "       .long 4b,5b\n"                                  \
464                 "       .long 0b,3b\n"                                  \
465                 "       .long 1b,2b\n"                                  \
466                 ".previous"                                             \
467                 : "=&c"(size), "=&D" (__d0), "=&S" (__d1), "=r"(__d2)   \
468                 : "3"(size), "0"(size), "1"(to), "2"(from)              \
469                 : "memory");                                            \
470 } while (0)
471
472 #define __copy_user_zeroing(to,from,size)                               \
473 do {                                                                    \
474         int __d0, __d1, __d2;                                           \
475         __asm__ __volatile__(                                           \
476                 "       cmp  $7,%0\n"                                   \
477                 "       jbe  1f\n"                                      \
478                 "       movl %1,%0\n"                                   \
479                 "       negl %0\n"                                      \
480                 "       andl $7,%0\n"                                   \
481                 "       subl %0,%3\n"                                   \
482                 "4:     rep; movsb\n"                                   \
483                 "       movl %3,%0\n"                                   \
484                 "       shrl $2,%0\n"                                   \
485                 "       andl $3,%3\n"                                   \
486                 "       .align 2,0x90\n"                                \
487                 "0:     rep; movsl\n"                                   \
488                 "       movl %3,%0\n"                                   \
489                 "1:     rep; movsb\n"                                   \
490                 "2:\n"                                                  \
491                 ".section .fixup,\"ax\"\n"                              \
492                 "5:     addl %3,%0\n"                                   \
493                 "       jmp 6f\n"                                       \
494                 "3:     lea 0(%3,%0,4),%0\n"                            \
495                 "6:     pushl %0\n"                                     \
496                 "       pushl %%eax\n"                                  \
497                 "       xorl %%eax,%%eax\n"                             \
498                 "       rep; stosb\n"                                   \
499                 "       popl %%eax\n"                                   \
500                 "       popl %0\n"                                      \
501                 "       jmp 2b\n"                                       \
502                 ".previous\n"                                           \
503                 ".section __ex_table,\"a\"\n"                           \
504                 "       .align 4\n"                                     \
505                 "       .long 4b,5b\n"                                  \
506                 "       .long 0b,3b\n"                                  \
507                 "       .long 1b,6b\n"                                  \
508                 ".previous"                                             \
509                 : "=&c"(size), "=&D" (__d0), "=&S" (__d1), "=r"(__d2)   \
510                 : "3"(size), "0"(size), "1"(to), "2"(from)              \
511                 : "memory");                                            \
512 } while (0)
513
514
515 unsigned long __copy_to_user_ll(void __user *to, const void *from, unsigned long n)
516 {
517         BUG_ON((long) n < 0);
518 #ifndef CONFIG_X86_WP_WORKS_OK
519         if (unlikely(boot_cpu_data.wp_works_ok == 0) &&
520                         ((unsigned long )to) < TASK_SIZE) {
521                 /* 
522                  * CPU does not honor the WP bit when writing
523                  * from supervisory mode, and due to preemption or SMP,
524                  * the page tables can change at any time.
525                  * Do it manually.      Manfred <manfred@colorfullife.com>
526                  */
527                 while (n) {
528                         unsigned long offset = ((unsigned long)to)%PAGE_SIZE;
529                         unsigned long len = PAGE_SIZE - offset;
530                         int retval;
531                         struct page *pg;
532                         void *maddr;
533                         
534                         if (len > n)
535                                 len = n;
536
537 survive:
538                         down_read(&current->mm->mmap_sem);
539                         retval = get_user_pages(current, current->mm,
540                                         (unsigned long )to, 1, 1, 0, &pg, NULL);
541
542                         if (retval == -ENOMEM && current->pid == 1) {
543                                 up_read(&current->mm->mmap_sem);
544                                 blk_congestion_wait(WRITE, HZ/50);
545                                 goto survive;
546                         }
547
548                         if (retval != 1) {
549                                 up_read(&current->mm->mmap_sem);
550                                 break;
551                         }
552
553                         maddr = kmap_atomic(pg, KM_USER0);
554                         memcpy(maddr + offset, from, len);
555                         kunmap_atomic(maddr, KM_USER0);
556                         set_page_dirty_lock(pg);
557                         put_page(pg);
558                         up_read(&current->mm->mmap_sem);
559
560                         from += len;
561                         to += len;
562                         n -= len;
563                 }
564                 return n;
565         }
566 #endif
567         if (movsl_is_ok(to, from, n))
568                 __copy_user(to, from, n);
569         else
570                 n = __copy_user_intel(to, from, n);
571         return n;
572 }
573
574 unsigned long
575 __copy_from_user_ll(void *to, const void __user *from, unsigned long n)
576 {
577         BUG_ON((long)n < 0);
578         if (movsl_is_ok(to, from, n))
579                 __copy_user_zeroing(to, from, n);
580         else
581                 n = __copy_user_zeroing_intel(to, from, n);
582         return n;
583 }
584
585 /**
586  * copy_to_user: - Copy a block of data into user space.
587  * @to:   Destination address, in user space.
588  * @from: Source address, in kernel space.
589  * @n:    Number of bytes to copy.
590  *
591  * Context: User context only.  This function may sleep.
592  *
593  * Copy data from kernel space to user space.
594  *
595  * Returns number of bytes that could not be copied.
596  * On success, this will be zero.
597  */
598 unsigned long
599 copy_to_user(void __user *to, const void *from, unsigned long n)
600 {
601         might_sleep();
602         BUG_ON((long) n < 0);
603         if (access_ok(VERIFY_WRITE, to, n))
604                 n = __copy_to_user(to, from, n);
605         return n;
606 }
607 EXPORT_SYMBOL(copy_to_user);
608
609 /**
610  * copy_from_user: - Copy a block of data from user space.
611  * @to:   Destination address, in kernel space.
612  * @from: Source address, in user space.
613  * @n:    Number of bytes to copy.
614  *
615  * Context: User context only.  This function may sleep.
616  *
617  * Copy data from user space to kernel space.
618  *
619  * Returns number of bytes that could not be copied.
620  * On success, this will be zero.
621  *
622  * If some data could not be copied, this function will pad the copied
623  * data to the requested size using zero bytes.
624  */
625 unsigned long
626 copy_from_user(void *to, const void __user *from, unsigned long n)
627 {
628         might_sleep();
629         BUG_ON((long) n < 0);
630         if (access_ok(VERIFY_READ, from, n))
631                 n = __copy_from_user(to, from, n);
632         else
633                 memset(to, 0, n);
634         return n;
635 }
636 EXPORT_SYMBOL(copy_from_user);