probes/lttng-probe-user.c

   1 /* SPDX-License-Identifier: (GPL-2.0 or LGPL-2.1)
   2  *
   3  * lttng-probe-user.c
   4  *
   5  * Copyright (C) 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   6  */
   7
   8 #include <linux/uaccess.h>
   9 #include <linux/module.h>
  10 #include <probes/lttng-probe-user.h>
  11
  12 /*
  13  * Calculate string length. Include final null terminating character if there is
  14  * one, or ends at first fault. Disabling page faults ensures that we can safely
  15  * call this from pretty much any context, including those where the caller
  16  * holds mmap_sem, or any lock which nests in mmap_sem.
  17  */
  18 long lttng_strlen_user_inatomic(const char *addr)
  19 {
  20         long count = 0;
  21         mm_segment_t old_fs;
  22
  23         if (!addr)
  24                 return 0;
  25
  26         old_fs = get_fs();
  27         set_fs(KERNEL_DS);
  28         pagefault_disable();
  29         for (;;) {
  30                 char v;
  31                 unsigned long ret;
  32
  33                 if (unlikely(!access_ok(VERIFY_READ,
  34                                 (__force const char __user *) addr,
  35                                 sizeof(v))))
  36                         break;
  37                 ret = __copy_from_user_inatomic(&v,
  38                         (__force const char __user *)(addr),
  39                         sizeof(v));
  40                 if (unlikely(ret > 0))
  41                         break;
  42                 count++;
  43                 if (unlikely(!v))
  44                         break;
  45                 addr++;
  46         }
  47         pagefault_enable();
  48         set_fs(old_fs);
  49         return count;
  50 }
  51 EXPORT_SYMBOL_GPL(lttng_strlen_user_inatomic);