ssp.c revision 169695
1/* Stack protector support. 2 Copyright (C) 2005 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 2, 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 25You should have received a copy of the GNU General Public License 26along with GCC; see the file COPYING. If not, write to the Free 27Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 2802110-1301, 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 59void *__stack_chk_guard = 0; 60 61static 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 88static void 89fail (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 157void 158__stack_chk_fail (void) 159{ 160 const char *msg = "*** stack smashing detected ***: "; 161 fail (msg, strlen (msg), "stack smashing detected: terminated"); 162} 163 164void 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 172void 173__attribute__((visibility ("hidden"))) 174__stack_chk_fail_local (void) 175{ 176 __stack_chk_fail (); 177} 178#endif 179