1/* Stack protector support.
2   Copyright (C) 2005-2013 Free Software Foundation, Inc.
3
4This file is part of GCC.
5
6GCC is free software; you can redistribute it and/or modify it under
7the terms of the GNU General Public License as published by the Free
8Software Foundation; either version 3, or (at your option) any later
9version.
10
11In addition to the permissions in the GNU General Public License, the
12Free Software Foundation gives you unlimited permission to link the
13compiled version of this file into combinations with other programs,
14and to distribute those combinations without any restriction coming
15from the use of this file.  (The General Public License restrictions
16do apply in other respects; for example, they cover modification of
17the file, and distribution when not linked into a combine
18executable.)
19
20GCC is distributed in the hope that it will be useful, but WITHOUT ANY
21WARRANTY; without even the implied warranty of MERCHANTABILITY or
22FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
23for more details.
24
25Under Section 7 of GPL version 3, you are granted additional
26permissions described in the GCC Runtime Library Exception, version
273.1, as published by the Free Software Foundation.
28
29You should have received a copy of the GNU General Public License and
30a copy of the GCC Runtime Library Exception along with this program;
31see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
32<http://www.gnu.org/licenses/>.  */
33
34
35#include "config.h"
36#ifdef HAVE_ALLOCA_H
37# include <alloca.h>
38#endif
39#ifdef HAVE_MALLOC_H
40# include <malloc.h>
41#endif
42#ifdef HAVE_STRING_H
43# include <string.h>
44#endif
45#ifdef HAVE_UNISTD_H
46# include <unistd.h>
47#endif
48#ifdef HAVE_FCNTL_H
49# include <fcntl.h>
50#endif
51#ifdef HAVE_PATHS_H
52# include <paths.h>
53#endif
54#ifndef _PATH_TTY
55/* Native win32 apps don't know about /dev/tty but can print directly
56   to the console using  "CONOUT$"   */
57#if defined (_WIN32) && !defined (__CYGWIN__)
58#include <windows.h>
59# define _PATH_TTY "CONOUT$"
60#else
61# define _PATH_TTY "/dev/tty"
62#endif
63#endif
64#ifdef HAVE_SYSLOG_H
65# include <syslog.h>
66#endif
67
68void *__stack_chk_guard = 0;
69
70static void __attribute__ ((constructor))
71__guard_setup (void)
72{
73  unsigned char *p;
74  int fd;
75
76  if (__stack_chk_guard != 0)
77    return;
78
79#if defined (_WIN32) && !defined (__CYGWIN__)
80  HCRYPTPROV hprovider = 0;
81  if (CryptAcquireContext(&hprovider, NULL, NULL, PROV_RSA_FULL,
82                          CRYPT_VERIFYCONTEXT | CRYPT_SILENT))
83    {
84      if (CryptGenRandom(hprovider, sizeof (__stack_chk_guard),
85          (BYTE *)&__stack_chk_guard) &&  __stack_chk_guard != 0)
86        {
87           CryptReleaseContext(hprovider, 0);
88           return;
89        }
90      CryptReleaseContext(hprovider, 0);
91    }
92#else
93  fd = open ("/dev/urandom", O_RDONLY);
94  if (fd != -1)
95    {
96      ssize_t size = read (fd, &__stack_chk_guard,
97                           sizeof (__stack_chk_guard));
98      close (fd);
99      if (size == sizeof(__stack_chk_guard) && __stack_chk_guard != 0)
100        return;
101    }
102
103#endif
104  /* If a random generator can't be used, the protector switches the guard
105     to the "terminator canary".  */
106  p = (unsigned char *) &__stack_chk_guard;
107  p[sizeof(__stack_chk_guard)-1] = 255;
108  p[sizeof(__stack_chk_guard)-2] = '\n';
109  p[0] = 0;
110}
111
112static void
113fail (const char *msg1, size_t msg1len, const char *msg3)
114{
115#ifdef __GNU_LIBRARY__
116  extern char * __progname;
117#else
118  static const char __progname[] = "";
119#endif
120  int fd;
121
122  /* Print error message directly to the tty.  This avoids Bad Things
123     happening if stderr is redirected.  */
124  fd = open (_PATH_TTY, O_WRONLY);
125  if (fd != -1)
126    {
127      static const char msg2[] = " terminated\n";
128      size_t progname_len, len;
129      char *buf, *p;
130
131      progname_len = strlen (__progname);
132      len = msg1len + progname_len + sizeof(msg2)-1 + 1;
133      p = buf = alloca (len);
134
135      memcpy (p, msg1, msg1len);
136      p += msg1len;
137      memcpy (p, __progname, progname_len);
138      p += progname_len;
139      memcpy (p, msg2, sizeof(msg2));
140
141      while (len > 0)
142        {
143          ssize_t wrote = write (fd, buf, len);
144          if (wrote < 0)
145            break;
146          buf += wrote;
147          len -= wrote;
148        }
149      close (fd);
150    }
151
152#ifdef HAVE_SYSLOG_H
153  /* Only send the error to syslog if there was no tty available.  */
154  else
155    syslog (LOG_CRIT, "%s", msg3);
156#endif /* HAVE_SYSLOG_H */
157
158  /* Try very hard to exit.  Note that signals may be blocked preventing
159     the first two options from working.  The use of volatile is here to
160     prevent optimizers from "knowing" that __builtin_trap is called first,
161     and that it doesn't return, and so "obviously" the rest of the code
162     is dead.  */
163  {
164    volatile int state;
165    for (state = 0; ; state++)
166      switch (state)
167        {
168        case 0:
169          __builtin_trap ();
170          break;
171        case 1:
172          *(volatile int *)-1L = 0;
173          break;
174        case 2:
175          _exit (127);
176          break;
177        }
178  }
179}
180
181void
182__stack_chk_fail (void)
183{
184  const char *msg = "*** stack smashing detected ***: ";
185  fail (msg, strlen (msg), "stack smashing detected: terminated");
186}
187
188void
189__chk_fail (void)
190{
191  const char *msg = "*** buffer overflow detected ***: ";
192  fail (msg, strlen (msg), "buffer overflow detected: terminated");
193}
194
195#ifdef HAVE_HIDDEN_VISIBILITY
196void
197__attribute__((visibility ("hidden")))
198__stack_chk_fail_local (void)
199{
200  __stack_chk_fail ();
201}
202#endif
203