mm/maccess.c

   1 /*
   2  * Access kernel memory without faulting.
   3  */
   4 #include <linux/module.h>
   5 #include <linux/mm.h>
   6 #include <linux/uaccess.h>
   7
   8 /**
   9  * probe_kernel_read(): safely attempt to read from a location
  10  * @dst: pointer to the buffer that shall take the data
  11  * @src: address to read from
  12  * @size: size of the data chunk
  13  *
  14  * Safely read from address @src to the buffer at @dst.  If a kernel fault
  15  * happens, handle that and return -EFAULT.
  16  */
  17
  18 long __weak probe_kernel_read(void *dst, void *src, size_t size)
  19     __attribute__((alias("__probe_kernel_read")));
  20
  21 long __probe_kernel_read(void *dst, void *src, size_t size)
  22 {
  23         long ret;
  24         mm_segment_t old_fs = get_fs();
  25
  26         set_fs(KERNEL_DS);
  27         pagefault_disable();
  28         ret = __copy_from_user_inatomic(dst,
  29                         (__force const void __user *)src, size);
  30         pagefault_enable();
  31         set_fs(old_fs);
  32
  33         return ret ? -EFAULT : 0;
  34 }
  35 EXPORT_SYMBOL_GPL(probe_kernel_read);
  36
  37 /**
  38  * probe_kernel_write(): safely attempt to write to a location
  39  * @dst: address to write to
  40  * @src: pointer to the data that shall be written
  41  * @size: size of the data chunk
  42  *
  43  * Safely write to address @dst from the buffer at @src.  If a kernel fault
  44  * happens, handle that and return -EFAULT.
  45  */
  46 long __weak probe_kernel_write(void *dst, void *src, size_t size)
  47     __attribute__((alias("__probe_kernel_write")));
  48
  49 long __probe_kernel_write(void *dst, void *src, size_t size)
  50 {
  51         long ret;
  52         mm_segment_t old_fs = get_fs();
  53
  54         set_fs(KERNEL_DS);
  55         pagefault_disable();
  56         ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
  57         pagefault_enable();
  58         set_fs(old_fs);
  59
  60         return ret ? -EFAULT : 0;
  61 }
  62 EXPORT_SYMBOL_GPL(probe_kernel_write);