src/probes/lttng-probe-user.c

   1 /* SPDX-License-Identifier: (GPL-2.0-only or LGPL-2.1-only)
   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 <lttng/probe-user.h>
  12
  13 #define LTTNG_MAX_USER_STRING_LEN 1048576 /* 1MB */
  14
  15 /*
  16  * Calculate string length. Include final null terminating character if there is
  17  * one, or ends at first fault. Disabling page faults ensures that we can safely
  18  * call this from pretty much any context, including those where the caller
  19  * holds mmap_sem, or any lock which nests in mmap_sem.
  20  */
  21 long lttng_strlen_user_inatomic(const char *addr)
  22 {
  23         long count = 0;
  24
  25         if (!addr)
  26                 return 0;
  27
  28         pagefault_disable();
  29         for (;;) {
  30                 char v;
  31                 unsigned long ret;
  32
  33                 if (unlikely(!lttng_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(count > LTTNG_MAX_USER_STRING_LEN))
  44                         break;
  45                 if (unlikely(!v))
  46                         break;
  47                 addr++;
  48         }
  49         pagefault_enable();
  50         return count;
  51 }
  52 EXPORT_SYMBOL_GPL(lttng_strlen_user_inatomic);