arch/arm/include/asm/uaccess.h

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /*
   3  *  arch/arm/include/asm/uaccess.h
   4  */
   5 #ifndef _ASMARM_UACCESS_H
   6 #define _ASMARM_UACCESS_H
   7
   8 /*
   9  * User space memory access functions
  10  */
  11 #include <linux/string.h>
  12 #include <asm/memory.h>
  13 #include <asm/domain.h>
  14 #include <asm/unified.h>
  15 #include <asm/compiler.h>
  16
  17 #include <asm/extable.h>
  18
  19 /*
  20  * These two functions allow hooking accesses to userspace to increase
  21  * system integrity by ensuring that the kernel can not inadvertantly
  22  * perform such accesses (eg, via list poison values) which could then
  23  * be exploited for priviledge escalation.
  24  */
  25 static __always_inline unsigned int uaccess_save_and_enable(void)
  26 {
  27 #ifdef CONFIG_CPU_SW_DOMAIN_PAN
  28         unsigned int old_domain = get_domain();
  29
  30         /* Set the current domain access to permit user accesses */
  31         set_domain((old_domain & ~domain_mask(DOMAIN_USER)) |
  32                    domain_val(DOMAIN_USER, DOMAIN_CLIENT));
  33
  34         return old_domain;
  35 #else
  36         return 0;
  37 #endif
  38 }
  39
  40 static __always_inline void uaccess_restore(unsigned int flags)
  41 {
  42 #ifdef CONFIG_CPU_SW_DOMAIN_PAN
  43         /* Restore the user access mask */
  44         set_domain(flags);
  45 #endif
  46 }
  47
  48 /*
  49  * These two are intentionally not defined anywhere - if the kernel
  50  * code generates any references to them, that's a bug.
  51  */
  52 extern int __get_user_bad(void);
  53 extern int __put_user_bad(void);
  54
  55 /*
  56  * Note that this is actually 0x1,0000,0000
  57  */
  58 #define KERNEL_DS       0x00000000
  59
  60 #ifdef CONFIG_MMU
  61
  62 #define USER_DS         TASK_SIZE
  63 #define get_fs()        (current_thread_info()->addr_limit)
  64
  65 static inline void set_fs(mm_segment_t fs)
  66 {
  67         current_thread_info()->addr_limit = fs;
  68
  69         /*
  70          * Prevent a mispredicted conditional call to set_fs from forwarding
  71          * the wrong address limit to access_ok under speculation.
  72          */
  73         dsb(nsh);
  74         isb();
  75
  76         modify_domain(DOMAIN_KERNEL, fs ? DOMAIN_CLIENT : DOMAIN_MANAGER);
  77 }
  78
  79 #define uaccess_kernel()        (get_fs() == KERNEL_DS)
  80
  81 /*
  82  * We use 33-bit arithmetic here.  Success returns zero, failure returns
  83  * addr_limit.  We take advantage that addr_limit will be zero for KERNEL_DS,
  84  * so this will always return success in that case.
  85  */
  86 #define __range_ok(addr, size) ({ \
  87         unsigned long flag, roksum; \
  88         __chk_user_ptr(addr);   \
  89         __asm__(".syntax unified\n" \
  90                 "adds %1, %2, %3; sbcscc %1, %1, %0; movcc %0, #0" \
  91                 : "=&r" (flag), "=&r" (roksum) \
  92                 : "r" (addr), "Ir" (size), "0" (current_thread_info()->addr_limit) \
  93                 : "cc"); \
  94         flag; })
  95
  96 /*
  97  * This is a type: either unsigned long, if the argument fits into
  98  * that type, or otherwise unsigned long long.
  99  */
 100 #define __inttype(x) \
 101         __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
 102
 103 /*
 104  * Sanitise a uaccess pointer such that it becomes NULL if addr+size
 105  * is above the current addr_limit.
 106  */
 107 #define uaccess_mask_range_ptr(ptr, size)                       \
 108         ((__typeof__(ptr))__uaccess_mask_range_ptr(ptr, size))
 109 static inline void __user *__uaccess_mask_range_ptr(const void __user *ptr,
 110                                                     size_t size)
 111 {
 112         void __user *safe_ptr = (void __user *)ptr;
 113         unsigned long tmp;
 114
 115         asm volatile(
 116         "       .syntax unified\n"
 117         "       sub     %1, %3, #1\n"
 118         "       subs    %1, %1, %0\n"
 119         "       addhs   %1, %1, #1\n"
 120         "       subshs  %1, %1, %2\n"
 121         "       movlo   %0, #0\n"
 122         : "+r" (safe_ptr), "=&r" (tmp)
 123         : "r" (size), "r" (current_thread_info()->addr_limit)
 124         : "cc");
 125
 126         csdb();
 127         return safe_ptr;
 128 }
 129
 130 /*
 131  * Single-value transfer routines.  They automatically use the right
 132  * size if we just have the right pointer type.  Note that the functions
 133  * which read from user space (*get_*) need to take care not to leak
 134  * kernel data even if the calling code is buggy and fails to check
 135  * the return value.  This means zeroing out the destination variable
 136  * or buffer on error.  Normally this is done out of line by the
 137  * fixup code, but there are a few places where it intrudes on the
 138  * main code path.  When we only write to user space, there is no
 139  * problem.
 140  */
 141 extern int __get_user_1(void *);
 142 extern int __get_user_2(void *);
 143 extern int __get_user_4(void *);
 144 extern int __get_user_32t_8(void *);
 145 extern int __get_user_8(void *);
 146 extern int __get_user_64t_1(void *);
 147 extern int __get_user_64t_2(void *);
 148 extern int __get_user_64t_4(void *);
 149
 150 #define __GUP_CLOBBER_1 "lr", "cc"
 151 #ifdef CONFIG_CPU_USE_DOMAINS
 152 #define __GUP_CLOBBER_2 "ip", "lr", "cc"
 153 #else
 154 #define __GUP_CLOBBER_2 "lr", "cc"
 155 #endif
 156 #define __GUP_CLOBBER_4 "lr", "cc"
 157 #define __GUP_CLOBBER_32t_8 "lr", "cc"
 158 #define __GUP_CLOBBER_8 "lr", "cc"
 159
 160 #define __get_user_x(__r2, __p, __e, __l, __s)                          \
 161            __asm__ __volatile__ (                                       \
 162                 __asmeq("%0", "r0") __asmeq("%1", "r2")                 \
 163                 __asmeq("%3", "r1")                                     \
 164                 "bl     __get_user_" #__s                               \
 165                 : "=&r" (__e), "=r" (__r2)                              \
 166                 : "0" (__p), "r" (__l)                                  \
 167                 : __GUP_CLOBBER_##__s)
 168
 169 /* narrowing a double-word get into a single 32bit word register: */
 170 #ifdef __ARMEB__
 171 #define __get_user_x_32t(__r2, __p, __e, __l, __s)                      \
 172         __get_user_x(__r2, __p, __e, __l, 32t_8)
 173 #else
 174 #define __get_user_x_32t __get_user_x
 175 #endif
 176
 177 /*
 178  * storing result into proper least significant word of 64bit target var,
 179  * different only for big endian case where 64 bit __r2 lsw is r3:
 180  */
 181 #ifdef __ARMEB__
 182 #define __get_user_x_64t(__r2, __p, __e, __l, __s)                      \
 183            __asm__ __volatile__ (                                       \
 184                 __asmeq("%0", "r0") __asmeq("%1", "r2")                 \
 185                 __asmeq("%3", "r1")                                     \
 186                 "bl     __get_user_64t_" #__s                           \
 187                 : "=&r" (__e), "=r" (__r2)                              \
 188                 : "0" (__p), "r" (__l)                                  \
 189                 : __GUP_CLOBBER_##__s)
 190 #else
 191 #define __get_user_x_64t __get_user_x
 192 #endif
 193
 194
 195 #define __get_user_check(x, p)                                          \
 196         ({                                                              \
 197                 unsigned long __limit = current_thread_info()->addr_limit - 1; \
 198                 register typeof(*(p)) __user *__p asm("r0") = (p);      \
 199                 register __inttype(x) __r2 asm("r2");                   \
 200                 register unsigned long __l asm("r1") = __limit;         \
 201                 register int __e asm("r0");                             \
 202                 unsigned int __ua_flags = uaccess_save_and_enable();    \
 203                 switch (sizeof(*(__p))) {                               \
 204                 case 1:                                                 \
 205                         if (sizeof((x)) >= 8)                           \
 206                                 __get_user_x_64t(__r2, __p, __e, __l, 1); \
 207                         else                                            \
 208                                 __get_user_x(__r2, __p, __e, __l, 1);   \
 209                         break;                                          \
 210                 case 2:                                                 \
 211                         if (sizeof((x)) >= 8)                           \
 212                                 __get_user_x_64t(__r2, __p, __e, __l, 2); \
 213                         else                                            \
 214                                 __get_user_x(__r2, __p, __e, __l, 2);   \
 215                         break;                                          \
 216                 case 4:                                                 \
 217                         if (sizeof((x)) >= 8)                           \
 218                                 __get_user_x_64t(__r2, __p, __e, __l, 4); \
 219                         else                                            \
 220                                 __get_user_x(__r2, __p, __e, __l, 4);   \
 221                         break;                                          \
 222                 case 8:                                                 \
 223                         if (sizeof((x)) < 8)                            \
 224                                 __get_user_x_32t(__r2, __p, __e, __l, 4); \
 225                         else                                            \
 226                                 __get_user_x(__r2, __p, __e, __l, 8);   \
 227                         break;                                          \
 228                 default: __e = __get_user_bad(); break;                 \
 229                 }                                                       \
 230                 uaccess_restore(__ua_flags);                            \
 231                 x = (typeof(*(p))) __r2;                                \
 232                 __e;                                                    \
 233         })
 234
 235 #define get_user(x, p)                                                  \
 236         ({                                                              \
 237                 might_fault();                                          \
 238                 __get_user_check(x, p);                                 \
 239          })
 240
 241 extern int __put_user_1(void *, unsigned int);
 242 extern int __put_user_2(void *, unsigned int);
 243 extern int __put_user_4(void *, unsigned int);
 244 extern int __put_user_8(void *, unsigned long long);
 245
 246 #define __put_user_check(__pu_val, __ptr, __err, __s)                   \
 247         ({                                                              \
 248                 unsigned long __limit = current_thread_info()->addr_limit - 1; \
 249                 register typeof(__pu_val) __r2 asm("r2") = __pu_val;    \
 250                 register const void __user *__p asm("r0") = __ptr;      \
 251                 register unsigned long __l asm("r1") = __limit;         \
 252                 register int __e asm("r0");                             \
 253                 __asm__ __volatile__ (                                  \
 254                         __asmeq("%0", "r0") __asmeq("%2", "r2")         \
 255                         __asmeq("%3", "r1")                             \
 256                         "bl     __put_user_" #__s                       \
 257                         : "=&r" (__e)                                   \
 258                         : "0" (__p), "r" (__r2), "r" (__l)              \
 259                         : "ip", "lr", "cc");                            \
 260                 __err = __e;                                            \
 261         })
 262
 263 #else /* CONFIG_MMU */
 264
 265 /*
 266  * uClinux has only one addr space, so has simplified address limits.
 267  */
 268 #define USER_DS                 KERNEL_DS
 269
 270 #define uaccess_kernel()        (true)
 271 #define __addr_ok(addr)         ((void)(addr), 1)
 272 #define __range_ok(addr, size)  ((void)(addr), 0)
 273 #define get_fs()                (KERNEL_DS)
 274
 275 static inline void set_fs(mm_segment_t fs)
 276 {
 277 }
 278
 279 #define get_user(x, p)  __get_user(x, p)
 280 #define __put_user_check __put_user_nocheck
 281
 282 #endif /* CONFIG_MMU */
 283
 284 #define access_ok(addr, size)   (__range_ok(addr, size) == 0)
 285
 286 #define user_addr_max() \
 287         (uaccess_kernel() ? ~0UL : get_fs())
 288
 289 #ifdef CONFIG_CPU_SPECTRE
 290 /*
 291  * When mitigating Spectre variant 1, it is not worth fixing the non-
 292  * verifying accessors, because we need to add verification of the
 293  * address space there.  Force these to use the standard get_user()
 294  * version instead.
 295  */
 296 #define __get_user(x, ptr) get_user(x, ptr)
 297 #else
 298
 299 /*
 300  * The "__xxx" versions of the user access functions do not verify the
 301  * address space - it must have been done previously with a separate
 302  * "access_ok()" call.
 303  *
 304  * The "xxx_error" versions set the third argument to EFAULT if an
 305  * error occurs, and leave it unchanged on success.  Note that these
 306  * versions are void (ie, don't return a value as such).
 307  */
 308 #define __get_user(x, ptr)                                              \
 309 ({                                                                      \
 310         long __gu_err = 0;                                              \
 311         __get_user_err((x), (ptr), __gu_err);                           \
 312         __gu_err;                                                       \
 313 })
 314
 315 #define __get_user_err(x, ptr, err)                                     \
 316 do {                                                                    \
 317         unsigned long __gu_addr = (unsigned long)(ptr);                 \
 318         unsigned long __gu_val;                                         \
 319         unsigned int __ua_flags;                                        \
 320         __chk_user_ptr(ptr);                                            \
 321         might_fault();                                                  \
 322         __ua_flags = uaccess_save_and_enable();                         \
 323         switch (sizeof(*(ptr))) {                                       \
 324         case 1: __get_user_asm_byte(__gu_val, __gu_addr, err);  break;  \
 325         case 2: __get_user_asm_half(__gu_val, __gu_addr, err);  break;  \
 326         case 4: __get_user_asm_word(__gu_val, __gu_addr, err);  break;  \
 327         default: (__gu_val) = __get_user_bad();                         \
 328         }                                                               \
 329         uaccess_restore(__ua_flags);                                    \
 330         (x) = (__typeof__(*(ptr)))__gu_val;                             \
 331 } while (0)
 332
 333 #define __get_user_asm(x, addr, err, instr)                     \
 334         __asm__ __volatile__(                                   \
 335         "1:     " TUSER(instr) " %1, [%2], #0\n"                \
 336         "2:\n"                                                  \
 337         "       .pushsection .text.fixup,\"ax\"\n"              \
 338         "       .align  2\n"                                    \
 339         "3:     mov     %0, %3\n"                               \
 340         "       mov     %1, #0\n"                               \
 341         "       b       2b\n"                                   \
 342         "       .popsection\n"                                  \
 343         "       .pushsection __ex_table,\"a\"\n"                \
 344         "       .align  3\n"                                    \
 345         "       .long   1b, 3b\n"                               \
 346         "       .popsection"                                    \
 347         : "+r" (err), "=&r" (x)                                 \
 348         : "r" (addr), "i" (-EFAULT)                             \
 349         : "cc")
 350
 351 #define __get_user_asm_byte(x, addr, err)                       \
 352         __get_user_asm(x, addr, err, ldrb)
 353
 354 #if __LINUX_ARM_ARCH__ >= 6
 355
 356 #define __get_user_asm_half(x, addr, err)                       \
 357         __get_user_asm(x, addr, err, ldrh)
 358
 359 #else
 360
 361 #ifndef __ARMEB__
 362 #define __get_user_asm_half(x, __gu_addr, err)                  \
 363 ({                                                              \
 364         unsigned long __b1, __b2;                               \
 365         __get_user_asm_byte(__b1, __gu_addr, err);              \
 366         __get_user_asm_byte(__b2, __gu_addr + 1, err);          \
 367         (x) = __b1 | (__b2 << 8);                               \
 368 })
 369 #else
 370 #define __get_user_asm_half(x, __gu_addr, err)                  \
 371 ({                                                              \
 372         unsigned long __b1, __b2;                               \
 373         __get_user_asm_byte(__b1, __gu_addr, err);              \
 374         __get_user_asm_byte(__b2, __gu_addr + 1, err);          \
 375         (x) = (__b1 << 8) | __b2;                               \
 376 })
 377 #endif
 378
 379 #endif /* __LINUX_ARM_ARCH__ >= 6 */
 380
 381 #define __get_user_asm_word(x, addr, err)                       \
 382         __get_user_asm(x, addr, err, ldr)
 383 #endif
 384
 385
 386 #define __put_user_switch(x, ptr, __err, __fn)                          \
 387         do {                                                            \
 388                 const __typeof__(*(ptr)) __user *__pu_ptr = (ptr);      \
 389                 __typeof__(*(ptr)) __pu_val = (x);                      \
 390                 unsigned int __ua_flags;                                \
 391                 might_fault();                                          \
 392                 __ua_flags = uaccess_save_and_enable();                 \
 393                 switch (sizeof(*(ptr))) {                               \
 394                 case 1: __fn(__pu_val, __pu_ptr, __err, 1); break;      \
 395                 case 2: __fn(__pu_val, __pu_ptr, __err, 2); break;      \
 396                 case 4: __fn(__pu_val, __pu_ptr, __err, 4); break;      \
 397                 case 8: __fn(__pu_val, __pu_ptr, __err, 8); break;      \
 398                 default: __err = __put_user_bad(); break;               \
 399                 }                                                       \
 400                 uaccess_restore(__ua_flags);                            \
 401         } while (0)
 402
 403 #define put_user(x, ptr)                                                \
 404 ({                                                                      \
 405         int __pu_err = 0;                                               \
 406         __put_user_switch((x), (ptr), __pu_err, __put_user_check);      \
 407         __pu_err;                                                       \
 408 })
 409
 410 #ifdef CONFIG_CPU_SPECTRE
 411 /*
 412  * When mitigating Spectre variant 1.1, all accessors need to include
 413  * verification of the address space.
 414  */
 415 #define __put_user(x, ptr) put_user(x, ptr)
 416
 417 #else
 418 #define __put_user(x, ptr)                                              \
 419 ({                                                                      \
 420         long __pu_err = 0;                                              \
 421         __put_user_switch((x), (ptr), __pu_err, __put_user_nocheck);    \
 422         __pu_err;                                                       \
 423 })
 424
 425 #define __put_user_nocheck(x, __pu_ptr, __err, __size)                  \
 426         do {                                                            \
 427                 unsigned long __pu_addr = (unsigned long)__pu_ptr;      \
 428                 __put_user_nocheck_##__size(x, __pu_addr, __err);       \
 429         } while (0)
 430
 431 #define __put_user_nocheck_1 __put_user_asm_byte
 432 #define __put_user_nocheck_2 __put_user_asm_half
 433 #define __put_user_nocheck_4 __put_user_asm_word
 434 #define __put_user_nocheck_8 __put_user_asm_dword
 435
 436 #define __put_user_asm(x, __pu_addr, err, instr)                \
 437         __asm__ __volatile__(                                   \
 438         "1:     " TUSER(instr) " %1, [%2], #0\n"                \
 439         "2:\n"                                                  \
 440         "       .pushsection .text.fixup,\"ax\"\n"              \
 441         "       .align  2\n"                                    \
 442         "3:     mov     %0, %3\n"                               \
 443         "       b       2b\n"                                   \
 444         "       .popsection\n"                                  \
 445         "       .pushsection __ex_table,\"a\"\n"                \
 446         "       .align  3\n"                                    \
 447         "       .long   1b, 3b\n"                               \
 448         "       .popsection"                                    \
 449         : "+r" (err)                                            \
 450         : "r" (x), "r" (__pu_addr), "i" (-EFAULT)               \
 451         : "cc")
 452
 453 #define __put_user_asm_byte(x, __pu_addr, err)                  \
 454         __put_user_asm(x, __pu_addr, err, strb)
 455
 456 #if __LINUX_ARM_ARCH__ >= 6
 457
 458 #define __put_user_asm_half(x, __pu_addr, err)                  \
 459         __put_user_asm(x, __pu_addr, err, strh)
 460
 461 #else
 462
 463 #ifndef __ARMEB__
 464 #define __put_user_asm_half(x, __pu_addr, err)                  \
 465 ({                                                              \
 466         unsigned long __temp = (__force unsigned long)(x);      \
 467         __put_user_asm_byte(__temp, __pu_addr, err);            \
 468         __put_user_asm_byte(__temp >> 8, __pu_addr + 1, err);   \
 469 })
 470 #else
 471 #define __put_user_asm_half(x, __pu_addr, err)                  \
 472 ({                                                              \
 473         unsigned long __temp = (__force unsigned long)(x);      \
 474         __put_user_asm_byte(__temp >> 8, __pu_addr, err);       \
 475         __put_user_asm_byte(__temp, __pu_addr + 1, err);        \
 476 })
 477 #endif
 478
 479 #endif /* __LINUX_ARM_ARCH__ >= 6 */
 480
 481 #define __put_user_asm_word(x, __pu_addr, err)                  \
 482         __put_user_asm(x, __pu_addr, err, str)
 483
 484 #ifndef __ARMEB__
 485 #define __reg_oper0     "%R2"
 486 #define __reg_oper1     "%Q2"
 487 #else
 488 #define __reg_oper0     "%Q2"
 489 #define __reg_oper1     "%R2"
 490 #endif
 491
 492 #define __put_user_asm_dword(x, __pu_addr, err)                 \
 493         __asm__ __volatile__(                                   \
 494  ARM(   "1:     " TUSER(str) "  " __reg_oper1 ", [%1], #4\n"    ) \
 495  ARM(   "2:     " TUSER(str) "  " __reg_oper0 ", [%1]\n"        ) \
 496  THUMB( "1:     " TUSER(str) "  " __reg_oper1 ", [%1]\n"        ) \
 497  THUMB( "2:     " TUSER(str) "  " __reg_oper0 ", [%1, #4]\n"    ) \
 498         "3:\n"                                                  \
 499         "       .pushsection .text.fixup,\"ax\"\n"              \
 500         "       .align  2\n"                                    \
 501         "4:     mov     %0, %3\n"                               \
 502         "       b       3b\n"                                   \
 503         "       .popsection\n"                                  \
 504         "       .pushsection __ex_table,\"a\"\n"                \
 505         "       .align  3\n"                                    \
 506         "       .long   1b, 4b\n"                               \
 507         "       .long   2b, 4b\n"                               \
 508         "       .popsection"                                    \
 509         : "+r" (err), "+r" (__pu_addr)                          \
 510         : "r" (x), "i" (-EFAULT)                                \
 511         : "cc")
 512
 513 #endif /* !CONFIG_CPU_SPECTRE */
 514
 515 #ifdef CONFIG_MMU
 516 extern unsigned long __must_check
 517 arm_copy_from_user(void *to, const void __user *from, unsigned long n);
 518
 519 static inline unsigned long __must_check
 520 raw_copy_from_user(void *to, const void __user *from, unsigned long n)
 521 {
 522         unsigned int __ua_flags;
 523
 524         __ua_flags = uaccess_save_and_enable();
 525         n = arm_copy_from_user(to, from, n);
 526         uaccess_restore(__ua_flags);
 527         return n;
 528 }
 529
 530 extern unsigned long __must_check
 531 arm_copy_to_user(void __user *to, const void *from, unsigned long n);
 532 extern unsigned long __must_check
 533 __copy_to_user_std(void __user *to, const void *from, unsigned long n);
 534
 535 static inline unsigned long __must_check
 536 raw_copy_to_user(void __user *to, const void *from, unsigned long n)
 537 {
 538 #ifndef CONFIG_UACCESS_WITH_MEMCPY
 539         unsigned int __ua_flags;
 540         __ua_flags = uaccess_save_and_enable();
 541         n = arm_copy_to_user(to, from, n);
 542         uaccess_restore(__ua_flags);
 543         return n;
 544 #else
 545         return arm_copy_to_user(to, from, n);
 546 #endif
 547 }
 548
 549 extern unsigned long __must_check
 550 arm_clear_user(void __user *addr, unsigned long n);
 551 extern unsigned long __must_check
 552 __clear_user_std(void __user *addr, unsigned long n);
 553
 554 static inline unsigned long __must_check
 555 __clear_user(void __user *addr, unsigned long n)
 556 {
 557         unsigned int __ua_flags = uaccess_save_and_enable();
 558         n = arm_clear_user(addr, n);
 559         uaccess_restore(__ua_flags);
 560         return n;
 561 }
 562
 563 #else
 564 static inline unsigned long
 565 raw_copy_from_user(void *to, const void __user *from, unsigned long n)
 566 {
 567         memcpy(to, (const void __force *)from, n);
 568         return 0;
 569 }
 570 static inline unsigned long
 571 raw_copy_to_user(void __user *to, const void *from, unsigned long n)
 572 {
 573         memcpy((void __force *)to, from, n);
 574         return 0;
 575 }
 576 #define __clear_user(addr, n)           (memset((void __force *)addr, 0, n), 0)
 577 #endif
 578 #define INLINE_COPY_TO_USER
 579 #define INLINE_COPY_FROM_USER
 580
 581 static inline unsigned long __must_check clear_user(void __user *to, unsigned long n)
 582 {
 583         if (access_ok(to, n))
 584                 n = __clear_user(to, n);
 585         return n;
 586 }
 587
 588 /* These are from lib/ code, and use __get_user() and friends */
 589 extern long strncpy_from_user(char *dest, const char __user *src, long count);
 590
 591 extern __must_check long strnlen_user(const char __user *str, long n);
 592
 593 #endif /* _ASMARM_UACCESS_H */