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 <wrapper/uaccess.h>
  11 #include <probes/lttng-probe-user.h>
  12
  13 /*
  14  * Calculate string length. Include final null terminating character if there is
  15  * one, or ends at first fault. Disabling page faults ensures that we can safely
  16  * call this from pretty much any context, including those where the caller
  17  * holds mmap_sem, or any lock which nests in mmap_sem.
  18  */
  19 long lttng_strlen_user_inatomic(const char *addr)
  20 {
  21         long count = 0;
  22         mm_segment_t old_fs;
  23
  24         if (!addr)
  25                 return 0;
  26
  27         old_fs = get_fs();
  28         set_fs(KERNEL_DS);
  29         pagefault_disable();
  30         for (;;) {
  31                 char v;
  32                 unsigned long ret;
  33
  34                 if (unlikely(!lttng_access_ok(VERIFY_READ,
  35                                 (__force const char __user *) addr,
  36                                 sizeof(v))))
  37                         break;
  38                 ret = __copy_from_user_inatomic(&v,
  39                         (__force const char __user *)(addr),
  40                         sizeof(v));
  41                 if (unlikely(ret > 0))
  42                         break;
  43                 count++;
  44                 if (unlikely(!v))
  45                         break;
  46                 addr++;
  47         }
  48         pagefault_enable();
  49         set_fs(old_fs);
  50         return count;
  51 }
  52 EXPORT_SYMBOL_GPL(lttng_strlen_user_inatomic);