/*
   * Access kernel memory without faulting.
   */
  #include <linux/export.h>
  #include <linux/mm.h>
  #include <linux/uaccess.h>
  
  /**
   * probe_kernel_read(): safely attempt to read from a location
   * @dst: pointer to the buffer that shall take the data
   * @src: address to read from
   * @size: size of the data chunk
   *
   * Safely read from address @src to the buffer at @dst.  If a kernel fault
   * happens, handle that and return -EFAULT.
   */
  
  long __weak probe_kernel_read(void *dst, const void *src, size_t size)
      __attribute__((alias("__probe_kernel_read")));
  
  long __probe_kernel_read(void *dst, const void *src, size_t size)
  {
  	long ret;
  	mm_segment_t old_fs = get_fs();
  
  	set_fs(KERNEL_DS);
  	pagefault_disable();
  	ret = __copy_from_user_inatomic(dst,
  			(__force const void __user *)src, size);
  	pagefault_enable();
  	set_fs(old_fs);
  
  	return ret ? -EFAULT : 0;
  }
  EXPORT_SYMBOL_GPL(probe_kernel_read);
  
  /**
   * probe_kernel_write(): safely attempt to write to a location
   * @dst: address to write to
   * @src: pointer to the data that shall be written
   * @size: size of the data chunk
   *
   * Safely write to address @dst from the buffer at @src.  If a kernel fault
   * happens, handle that and return -EFAULT.
   */
  long __weak probe_kernel_write(void *dst, const void *src, size_t size)
      __attribute__((alias("__probe_kernel_write")));
  
  long __probe_kernel_write(void *dst, const void *src, size_t size)
  {
  	long ret;
  	mm_segment_t old_fs = get_fs();
  
  	set_fs(KERNEL_DS);
  	pagefault_disable();
  	ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
  	pagefault_enable();
  	set_fs(old_fs);
  
  	return ret ? -EFAULT : 0;
  }
  EXPORT_SYMBOL_GPL(probe_kernel_write);