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
  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   int 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
 112 static void
 113 fail (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
 181 void
 182 __stack_chk_fail (void)
 183 {
 184   const char *msg = "*** stack smashing detected ***: ";
 185   fail (msg, strlen (msg), "stack smashing detected: terminated");
 186 }
 187
 188 void
 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
 196 void
 197 __attribute__((visibility ("hidden")))
 198 __stack_chk_fail_local (void)
 199 {
 200   __stack_chk_fail ();
 201 }
 202 #endif