libssp/ssp.c

   1 /* Stack protector support.
   2    Copyright (C) 2005 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 2, 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 You should have received a copy of the GNU General Public License
  26 along with GCC; see the file COPYING.  If not, write to the Free
  27 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
  28 02110-1301, USA.  */
  29
  30 /* As a special exception, if you link this library with files compiled with
  31    GCC to produce an executable, this does not cause the resulting executable
  32    to be covered by the GNU General Public License. This exception does not
  33    however invalidate any other reasons why the executable file might be
  34    covered by the GNU General Public License.  */
  35
  36 #include "config.h"
  37 #ifdef HAVE_ALLOCA_H
  38 # include <alloca.h>
  39 #endif
  40 #ifdef HAVE_STRING_H
  41 # include <string.h>
  42 #endif
  43 #ifdef HAVE_UNISTD_H
  44 # include <unistd.h>
  45 #endif
  46 #ifdef HAVE_FCNTL_H
  47 # include <fcntl.h>
  48 #endif
  49 #ifdef HAVE_PATHS_H
  50 # include <paths.h>
  51 #endif
  52 #ifndef _PATH_TTY
  53 # define _PATH_TTY "/dev/tty"
  54 #endif
  55 #ifdef HAVE_SYSLOG_H
  56 # include <syslog.h>
  57 #endif
  58
  59 void *__stack_chk_guard = 0;
  60
  61 static void __attribute__ ((constructor))
  62 __guard_setup (void)
  63 {
  64   unsigned char *p;
  65   int fd;
  66
  67   if (__stack_chk_guard != 0)
  68     return;
  69
  70   fd = open ("/dev/urandom", O_RDONLY);
  71   if (fd != -1)
  72     {
  73       ssize_t size = read (fd, &__stack_chk_guard,
  74                            sizeof (__stack_chk_guard));
  75       close (fd);
  76       if (size == sizeof(__stack_chk_guard) && __stack_chk_guard != 0)
  77         return;
  78     }
  79
  80   /* If a random generator can't be used, the protector switches the guard
  81      to the "terminator canary".  */
  82   p = (unsigned char *) &__stack_chk_guard;
  83   p[sizeof(__stack_chk_guard)-1] = 255;
  84   p[sizeof(__stack_chk_guard)-2] = '\n';
  85   p[0] = 0;
  86 }
  87
  88 static void
  89 fail (const char *msg1, size_t msg1len, const char *msg3)
  90 {
  91 #ifdef __GNU_LIBRARY__
  92   extern char * __progname;
  93 #else
  94   static const char __progname[] = "";
  95 #endif
  96   int fd;
  97
  98   /* Print error message directly to the tty.  This avoids Bad Things
  99      happening if stderr is redirected.  */
 100   fd = open (_PATH_TTY, O_WRONLY);
 101   if (fd != -1)
 102     {
 103       static const char msg2[] = " terminated\n";
 104       size_t progname_len, len;
 105       char *buf, *p;
 106
 107       progname_len = strlen (__progname);
 108       len = msg1len + progname_len + sizeof(msg2)-1 + 1;
 109       p = buf = alloca (len);
 110
 111       memcpy (p, msg1, msg1len);
 112       p += msg1len;
 113       memcpy (p, __progname, progname_len);
 114       p += progname_len;
 115       memcpy (p, msg2, sizeof(msg2));
 116
 117       while (len > 0)
 118         {
 119           ssize_t wrote = write (fd, buf, len);
 120           if (wrote < 0)
 121             break;
 122           buf += wrote;
 123           len -= wrote;
 124         }
 125       close (fd);
 126     }
 127
 128 #ifdef HAVE_SYSLOG_H
 129   /* Only send the error to syslog if there was no tty available.  */
 130   else
 131     syslog (LOG_CRIT, msg3);
 132 #endif /* HAVE_SYSLOG_H */
 133
 134   /* Try very hard to exit.  Note that signals may be blocked preventing
 135      the first two options from working.  The use of volatile is here to
 136      prevent optimizers from "knowing" that __builtin_trap is called first,
 137      and that it doesn't return, and so "obviously" the rest of the code
 138      is dead.  */
 139   {
 140     volatile int state;
 141     for (state = 0; ; state++)
 142       switch (state)
 143         {
 144         case 0:
 145           __builtin_trap ();
 146           break;
 147         case 1:
 148           *(volatile int *)-1L = 0;
 149           break;
 150         case 2:
 151           _exit (127);
 152           break;
 153         }
 154   }
 155 }
 156
 157 void
 158 __stack_chk_fail (void)
 159 {
 160   const char *msg = "*** stack smashing detected ***: ";
 161   fail (msg, strlen (msg), "stack smashing detected: terminated");
 162 }
 163
 164 void
 165 __chk_fail (void)
 166 {
 167   const char *msg = "*** buffer overflow detected ***: ";
 168   fail (msg, strlen (msg), "buffer overflow detected: terminated");
 169 }
 170
 171 #ifdef HAVE_HIDDEN_VISIBILITY
 172 void
 173 __attribute__((visibility ("hidden")))
 174 __stack_chk_fail_local (void)
 175 {
 176   __stack_chk_fail ();
 177 }
 178 #endif