include/linux/uaccess.h

   1 #ifndef __LINUX_UACCESS_H__
   2 #define __LINUX_UACCESS_H__
   3
   4 #include <linux/preempt.h>
   5 #include <asm/uaccess.h>
   6
   7 /*
   8  * These routines enable/disable the pagefault handler in that
   9  * it will not take any locks and go straight to the fixup table.
  10  *
  11  * They have great resemblance to the preempt_disable/enable calls
  12  * and in fact they are identical; this is because currently there is
  13  * no other way to make the pagefault handlers do this. So we do
  14  * disable preemption but we don't necessarily care about that.
  15  */
  16 static inline void pagefault_disable(void)
  17 {
  18         inc_preempt_count();
  19         /*
  20          * make sure to have issued the store before a pagefault
  21          * can hit.
  22          */
  23         barrier();
  24 }
  25
  26 static inline void pagefault_enable(void)
  27 {
  28         /*
  29          * make sure to issue those last loads/stores before enabling
  30          * the pagefault handler again.
  31          */
  32         barrier();
  33         dec_preempt_count();
  34         /*
  35          * make sure we do..
  36          */
  37         barrier();
  38         preempt_check_resched();
  39 }
  40
  41 #ifndef ARCH_HAS_NOCACHE_UACCESS
  42
  43 static inline unsigned long __copy_from_user_inatomic_nocache(void *to,
  44                                 const void __user *from, unsigned long n)
  45 {
  46         return __copy_from_user_inatomic(to, from, n);
  47 }
  48
  49 static inline unsigned long __copy_from_user_nocache(void *to,
  50                                 const void __user *from, unsigned long n)
  51 {
  52         return __copy_from_user(to, from, n);
  53 }
  54
  55 #endif          /* ARCH_HAS_NOCACHE_UACCESS */
  56
  57 /**
  58  * probe_kernel_address(): safely attempt to read from a location
  59  * @addr: address to read from - its type is type typeof(retval)*
  60  * @retval: read into this variable
  61  *
  62  * Safely read from address @addr into variable @revtal.  If a kernel fault
  63  * happens, handle that and return -EFAULT.
  64  * We ensure that the __get_user() is executed in atomic context so that
  65  * do_page_fault() doesn't attempt to take mmap_sem.  This makes
  66  * probe_kernel_address() suitable for use within regions where the caller
  67  * already holds mmap_sem, or other locks which nest inside mmap_sem.
  68  * This must be a macro because __get_user() needs to know the types of the
  69  * args.
  70  *
  71  * We don't include enough header files to be able to do the set_fs().  We
  72  * require that the probe_kernel_address() caller will do that.
  73  */
  74 #define probe_kernel_address(addr, retval)              \
  75         ({                                              \
  76                 long ret;                               \
  77                 mm_segment_t old_fs = get_fs();         \
  78                                                         \
  79                 set_fs(KERNEL_DS);                      \
  80                 pagefault_disable();                    \
  81                 ret = __get_user(retval, (__force typeof(retval) __user *)(addr));              \
  82                 pagefault_enable();                     \
  83                 set_fs(old_fs);                         \
  84                 ret;                                    \
  85         })
  86
  87 #endif          /* __LINUX_UACCESS_H__ */