libssp/ssp.c

   1 /* Stack protector support.
   2    Copyright (C) 2005, 2009 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify it under
   7 the terms of the GNU General Public License as published by the Free
   8 Software Foundation; either version 3, or (at your option) any later
   9 version.
  10
  11 In addition to the permissions in the GNU General Public License, the
  12 Free Software Foundation gives you unlimited permission to link the
  13 compiled version of this file into combinations with other programs,
  14 and to distribute those combinations without any restriction coming
  15 from the use of this file.  (The General Public License restrictions
  16 do apply in other respects; for example, they cover modification of
  17 the file, and distribution when not linked into a combine
  18 executable.)
  19
  20 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  21 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  22 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  23 for more details.
  24
  25 Under Section 7 of GPL version 3, you are granted additional
  26 permissions described in the GCC Runtime Library Exception, version
  27 3.1, as published by the Free Software Foundation.
  28
  29 You should have received a copy of the GNU General Public License and
  30 a copy of the GCC Runtime Library Exception along with this program;
  31 see 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$"   */
  57 #if defined (_WIN32) && !defined (__CYGWIN__)
  58 # define _PATH_TTY "CONOUT$"
  59 #else
  60 # define _PATH_TTY "/dev/tty"
  61 #endif
  62 #endif
  63 #ifdef HAVE_SYSLOG_H
  64 # include <syslog.h>
  65 #endif
  66
  67 void *__stack_chk_guard = 0;
  68
  69 static void __attribute__ ((constructor))
  70 __guard_setup (void)
  71 {
  72   unsigned char *p;
  73   int fd;
  74
  75   if (__stack_chk_guard != 0)
  76     return;
  77
  78   fd = open ("/dev/urandom", O_RDONLY);
  79   if (fd != -1)
  80     {
  81       ssize_t size = read (fd, &__stack_chk_guard,
  82                            sizeof (__stack_chk_guard));
  83       close (fd);
  84       if (size == sizeof(__stack_chk_guard) && __stack_chk_guard != 0)
  85         return;
  86     }
  87
  88   /* If a random generator can't be used, the protector switches the guard
  89      to the "terminator canary".  */
  90   p = (unsigned char *) &__stack_chk_guard;
  91   p[sizeof(__stack_chk_guard)-1] = 255;
  92   p[sizeof(__stack_chk_guard)-2] = '\n';
  93   p[0] = 0;
  94 }
  95
  96 static void
  97 fail (const char *msg1, size_t msg1len, const char *msg3)
  98 {
  99 #ifdef __GNU_LIBRARY__
 100   extern char * __progname;
 101 #else
 102   static const char __progname[] = "";
 103 #endif
 104   int fd;
 105
 106   /* Print error message directly to the tty.  This avoids Bad Things
 107      happening if stderr is redirected.  */
 108   fd = open (_PATH_TTY, O_WRONLY);
 109   if (fd != -1)
 110     {
 111       static const char msg2[] = " terminated\n";
 112       size_t progname_len, len;
 113       char *buf, *p;
 114
 115       progname_len = strlen (__progname);
 116       len = msg1len + progname_len + sizeof(msg2)-1 + 1;
 117       p = buf = alloca (len);
 118
 119       memcpy (p, msg1, msg1len);
 120       p += msg1len;
 121       memcpy (p, __progname, progname_len);
 122       p += progname_len;
 123       memcpy (p, msg2, sizeof(msg2));
 124
 125       while (len > 0)
 126         {
 127           ssize_t wrote = write (fd, buf, len);
 128           if (wrote < 0)
 129             break;
 130           buf += wrote;
 131           len -= wrote;
 132         }
 133       close (fd);
 134     }
 135
 136 #ifdef HAVE_SYSLOG_H
 137   /* Only send the error to syslog if there was no tty available.  */
 138   else
 139     syslog (LOG_CRIT, msg3);
 140 #endif /* HAVE_SYSLOG_H */
 141
 142   /* Try very hard to exit.  Note that signals may be blocked preventing
 143      the first two options from working.  The use of volatile is here to
 144      prevent optimizers from "knowing" that __builtin_trap is called first,
 145      and that it doesn't return, and so "obviously" the rest of the code
 146      is dead.  */
 147   {
 148     volatile int state;
 149     for (state = 0; ; state++)
 150       switch (state)
 151         {
 152         case 0:
 153           __builtin_trap ();
 154           break;
 155         case 1:
 156           *(volatile int *)-1L = 0;
 157           break;
 158         case 2:
 159           _exit (127);
 160           break;
 161         }
 162   }
 163 }
 164
 165 void
 166 __stack_chk_fail (void)
 167 {
 168   const char *msg = "*** stack smashing detected ***: ";
 169   fail (msg, strlen (msg), "stack smashing detected: terminated");
 170 }
 171
 172 void
 173 __chk_fail (void)
 174 {
 175   const char *msg = "*** buffer overflow detected ***: ";
 176   fail (msg, strlen (msg), "buffer overflow detected: terminated");
 177 }
 178
 179 #ifdef HAVE_HIDDEN_VISIBILITY
 180 void
 181 __attribute__((visibility ("hidden")))
 182 __stack_chk_fail_local (void)
 183 {
 184   __stack_chk_fail ();
 185 }
 186 #endif