libssp/ssp.c

   1 /* Stack protector support.
   2    Copyright (C) 2005-2017 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$"   */
  57 #if defined (_WIN32) && !defined (__CYGWIN__)
  58 #include <windows.h>
  59 #include <wincrypt.h>
  60 # define _PATH_TTY "CONOUT$"
  61 #else
  62 # define _PATH_TTY "/dev/tty"
  63 #endif
  64 #endif
  65 #ifdef HAVE_SYSLOG_H
  66 # include <syslog.h>
  67 #endif
  68
  69 void *__stack_chk_guard = 0;
  70
  71 static void __attribute__ ((constructor))
  72 __guard_setup (void)
  73 {
  74   unsigned char *p;
  75   int fd;
  76
  77   if (__stack_chk_guard != 0)
  78     return;
  79
  80 #if defined (_WIN32) && !defined (__CYGWIN__)
  81   HCRYPTPROV hprovider = 0;
  82   if (CryptAcquireContext(&hprovider, NULL, NULL, PROV_RSA_FULL,
  83                           CRYPT_VERIFYCONTEXT | CRYPT_SILENT))
  84     {
  85       if (CryptGenRandom(hprovider, sizeof (__stack_chk_guard),
  86           (BYTE *)&__stack_chk_guard) &&  __stack_chk_guard != 0)
  87         {
  88            CryptReleaseContext(hprovider, 0);
  89            return;
  90         }
  91       CryptReleaseContext(hprovider, 0);
  92     }
  93 #else
  94   fd = open ("/dev/urandom", O_RDONLY);
  95   if (fd != -1)
  96     {
  97       ssize_t size = read (fd, &__stack_chk_guard,
  98                            sizeof (__stack_chk_guard));
  99       close (fd);
 100       if (size == sizeof(__stack_chk_guard) && __stack_chk_guard != 0)
 101         return;
 102     }
 103
 104 #endif
 105   /* If a random generator can't be used, the protector switches the guard
 106      to the "terminator canary".  */
 107   p = (unsigned char *) &__stack_chk_guard;
 108   p[sizeof(__stack_chk_guard)-1] = 255;
 109   p[sizeof(__stack_chk_guard)-2] = '\n';
 110   p[0] = 0;
 111 }
 112
 113 static void
 114 fail (const char *msg1, size_t msg1len, const char *msg3)
 115 {
 116 #ifdef __GNU_LIBRARY__
 117   extern char * __progname;
 118 #else
 119   static const char __progname[] = "";
 120 #endif
 121   int fd;
 122
 123   /* Print error message directly to the tty.  This avoids Bad Things
 124      happening if stderr is redirected.  */
 125   fd = open (_PATH_TTY, O_WRONLY);
 126   if (fd != -1)
 127     {
 128       static const char msg2[] = " terminated\n";
 129       size_t progname_len, len;
 130       char *buf, *p;
 131
 132       progname_len = strlen (__progname);
 133       len = msg1len + progname_len + sizeof(msg2)-1 + 1;
 134       p = buf = alloca (len);
 135
 136       memcpy (p, msg1, msg1len);
 137       p += msg1len;
 138       memcpy (p, __progname, progname_len);
 139       p += progname_len;
 140       memcpy (p, msg2, sizeof(msg2));
 141
 142       while (len > 0)
 143         {
 144           ssize_t wrote = write (fd, buf, len);
 145           if (wrote < 0)
 146             break;
 147           buf += wrote;
 148           len -= wrote;
 149         }
 150       close (fd);
 151     }
 152
 153 #ifdef HAVE_SYSLOG_H
 154   /* Only send the error to syslog if there was no tty available.  */
 155   else
 156     syslog (LOG_CRIT, "%s", msg3);
 157 #endif /* HAVE_SYSLOG_H */
 158
 159   /* Try very hard to exit.  Note that signals may be blocked preventing
 160      the first two options from working.  The use of volatile is here to
 161      prevent optimizers from "knowing" that __builtin_trap is called first,
 162      and that it doesn't return, and so "obviously" the rest of the code
 163      is dead.  */
 164   {
 165     volatile int state;
 166     for (state = 0; ; state++)
 167       switch (state)
 168         {
 169         case 0:
 170           __builtin_trap ();
 171           break;
 172         case 1:
 173           *(volatile int *)-1L = 0;
 174           break;
 175         case 2:
 176           _exit (127);
 177           break;
 178         }
 179   }
 180 }
 181
 182 void
 183 __stack_chk_fail (void)
 184 {
 185   const char *msg = "*** stack smashing detected ***: ";
 186   fail (msg, strlen (msg), "stack smashing detected: terminated");
 187 }
 188
 189 void
 190 __chk_fail (void)
 191 {
 192   const char *msg = "*** buffer overflow detected ***: ";
 193   fail (msg, strlen (msg), "buffer overflow detected: terminated");
 194 }
 195
 196 #ifdef HAVE_HIDDEN_VISIBILITY
 197 void
 198 __attribute__((visibility ("hidden")))
 199 __stack_chk_fail_local (void)
 200 {
 201   __stack_chk_fail ();
 202 }
 203 #endif