1 /* Stack overflow handling. 2 3 Copyright (C) 2002, 2004, 2006, 2008, 2009, 2010 Free Software Foundation, 4 Inc. 5 6 This program is free software: you can redistribute it and/or modify 7 it under the terms of the GNU General Public License as published by 8 the Free Software Foundation; either version 3 of the License, or 9 (at your option) any later version. 10 11 This program is distributed in the hope that it will be useful, 12 but WITHOUT ANY WARRANTY; without even the implied warranty of 13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14 GNU General Public License for more details. 15 16 You should have received a copy of the GNU General Public License 17 along with this program. If not, see <http://www.gnu.org/licenses/>. */ 18 19 /* Written by Paul Eggert. */ 20 21 /* NOTES: 22 23 A program that uses alloca, dynamic arrays, or large local 24 variables may extend the stack by more than a page at a time. If 25 so, when the stack overflows the operating system may not detect 26 the overflow until the program uses the array, and this module may 27 incorrectly report a program error instead of a stack overflow. 28 29 To avoid this problem, allocate only small objects on the stack; a 30 program should be OK if it limits single allocations to a page or 31 less. Allocate larger arrays in static storage, or on the heap 32 (e.g., with malloc). Yes, this is a pain, but we don't know of any 33 better solution that is portable. 34 35 No attempt has been made to deal with multithreaded applications. */ 36 37 #include <config.h> 38 39 #ifndef __attribute__ 40 # if __GNUC__ < 3 41 # define __attribute__(x) 42 # endif 43 #endif 44 45 #include "gettext.h" 46 #define _(msgid) gettext (msgid) 47 48 #include <errno.h> 49 50 #include <signal.h> 51 #if ! HAVE_STACK_T && ! defined stack_t 52 typedef struct sigaltstack stack_t; 53 #endif 54 #ifndef SIGSTKSZ 55 # define SIGSTKSZ 16384 56 #endif 57 58 #include <stdlib.h> 59 #include <string.h> 60 61 /* Posix 2001 declares ucontext_t in <ucontext.h>, Posix 200x in 62 <signal.h>. */ 63 #if HAVE_UCONTEXT_H 64 # include <ucontext.h> 65 #endif 66 67 #include <unistd.h> 68 69 #if HAVE_LIBSIGSEGV 70 # include <sigsegv.h> 71 #endif 72 73 #include "c-stack.h" 74 #include "exitfail.h" 75 #include "ignore-value.h" 76 77 #if defined SA_ONSTACK && defined SA_SIGINFO 78 # define SIGACTION_WORKS 1 79 #else 80 # define SIGACTION_WORKS 0 81 # ifndef SA_ONSTACK 82 # define SA_ONSTACK 0 83 # endif 84 #endif 85 86 extern char *program_name; 87 88 /* The user-specified action to take when a SEGV-related program error 89 or stack overflow occurs. */ 90 static void (* volatile segv_action) (int); 91 92 /* Translated messages for program errors and stack overflow. Do not 93 translate them in the signal handler, since gettext is not 94 async-signal-safe. */ 95 static char const * volatile program_error_message; 96 static char const * volatile stack_overflow_message; 97 98 /* Output an error message, then exit with status EXIT_FAILURE if it 99 appears to have been a stack overflow, or with a core dump 100 otherwise. This function is async-signal-safe. */ 101 102 static void die (int) __attribute__ ((noreturn)); 103 static void 104 die (int signo) 105 { 106 char const *message; 107 segv_action (signo); 108 message = signo ? program_error_message : stack_overflow_message; 109 ignore_value (write (STDERR_FILENO, program_name, strlen (program_name))); 110 ignore_value (write (STDERR_FILENO, ": ", 2)); 111 ignore_value (write (STDERR_FILENO, message, strlen (message))); 112 ignore_value (write (STDERR_FILENO, "\n", 1)); 113 if (! signo) 114 _exit (exit_failure); 115 raise (signo); 116 abort (); 117 } 118 119 #if (HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK \ 120 && HAVE_STACK_OVERFLOW_HANDLING) || HAVE_LIBSIGSEGV 121 122 /* Storage for the alternate signal stack. */ 123 static union 124 { 125 char buffer[SIGSTKSZ]; 126 127 /* These other members are for proper alignment. There's no 128 standard way to guarantee stack alignment, but this seems enough 129 in practice. */ 130 long double ld; 131 long l; 132 void *p; 133 } alternate_signal_stack; 134 135 static void 136 null_action (int signo __attribute__ ((unused))) 137 { 138 } 139 140 #endif /* SIGALTSTACK || LIBSIGSEGV */ 141 142 /* Only use libsigsegv if we need it; platforms like Solaris can 143 detect stack overflow without the overhead of an external 144 library. */ 145 #if HAVE_LIBSIGSEGV && ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC 146 147 /* Nonzero if general segv handler could not be installed. */ 148 static volatile int segv_handler_missing; 149 150 /* Handle a segmentation violation and exit if it cannot be stack 151 overflow. This function is async-signal-safe. */ 152 153 static int segv_handler (void *address __attribute__ ((unused)), 154 int serious) 155 { 156 # if DEBUG 157 { 158 char buf[1024]; 159 sprintf (buf, "segv_handler serious=%d\n", serious); 160 write (STDERR_FILENO, buf, strlen (buf)); 161 } 162 # endif 163 164 /* If this fault is not serious, return 0 to let the stack overflow 165 handler take a shot at it. */ 166 if (!serious) 167 return 0; 168 die (SIGSEGV); 169 } 170 171 /* Handle a segmentation violation that is likely to be a stack 172 overflow and exit. This function is async-signal-safe. */ 173 174 static void overflow_handler (int, stackoverflow_context_t) 175 __attribute__ ((noreturn)); 176 static void 177 overflow_handler (int emergency, 178 stackoverflow_context_t context __attribute__ ((unused))) 179 { 180 # if DEBUG 181 { 182 char buf[1024]; 183 sprintf (buf, "overflow_handler emergency=%d segv_handler_missing=%d\n", 184 emergency, segv_handler_missing); 185 write (STDERR_FILENO, buf, strlen (buf)); 186 } 187 # endif 188 189 die ((!emergency || segv_handler_missing) ? 0 : SIGSEGV); 190 } 191 192 int 193 c_stack_action (void (*action) (int)) 194 { 195 segv_action = action ? action : null_action; 196 program_error_message = _("program error"); 197 stack_overflow_message = _("stack overflow"); 198 199 /* Always install the overflow handler. */ 200 if (stackoverflow_install_handler (overflow_handler, 201 alternate_signal_stack.buffer, 202 sizeof alternate_signal_stack.buffer)) 203 { 204 errno = ENOTSUP; 205 return -1; 206 } 207 /* Try installing a general handler; if it fails, then treat all 208 segv as stack overflow. */ 209 segv_handler_missing = sigsegv_install_handler (segv_handler); 210 return 0; 211 } 212 213 #elif HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK && HAVE_STACK_OVERFLOW_HANDLING 214 215 /* Direction of the C runtime stack. This function is 216 async-signal-safe. */ 217 218 # if STACK_DIRECTION 219 # define find_stack_direction(ptr) STACK_DIRECTION 220 # else 221 # if ! SIGACTION_WORKS || HAVE_XSI_STACK_OVERFLOW_HEURISTIC 222 static int 223 find_stack_direction (char const *addr) 224 { 225 char dummy; 226 return ! addr ? find_stack_direction (&dummy) : addr < &dummy ? 1 : -1; 227 } 228 # endif 229 # endif 230 231 # if SIGACTION_WORKS 232 233 /* Handle a segmentation violation and exit. This function is 234 async-signal-safe. */ 235 236 static void segv_handler (int, siginfo_t *, void *) __attribute__((noreturn)); 237 static void 238 segv_handler (int signo, siginfo_t *info, 239 void *context __attribute__ ((unused))) 240 { 241 /* Clear SIGNO if it seems to have been a stack overflow. */ 242 # if ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC 243 /* We can't easily determine whether it is a stack overflow; so 244 assume that the rest of our program is perfect (!) and that 245 this segmentation violation is a stack overflow. 246 247 Note that although both Linux and Solaris provide 248 sigaltstack, SA_ONSTACK, and SA_SIGINFO, currently only 249 Solaris satisfies the XSI heueristic. This is because 250 Solaris populates uc_stack with the details of the 251 interrupted stack, while Linux populates it with the details 252 of the current stack. */ 253 signo = 0; 254 # else 255 if (0 < info->si_code) 256 { 257 /* If the faulting address is within the stack, or within one 258 page of the stack end, assume that it is a stack 259 overflow. */ 260 ucontext_t const *user_context = context; 261 char const *stack_base = user_context->uc_stack.ss_sp; 262 size_t stack_size = user_context->uc_stack.ss_size; 263 char const *faulting_address = info->si_addr; 264 size_t s = faulting_address - stack_base; 265 size_t page_size = sysconf (_SC_PAGESIZE); 266 if (find_stack_direction (NULL) < 0) 267 s += page_size; 268 if (s < stack_size + page_size) 269 signo = 0; 270 271 # if DEBUG 272 { 273 char buf[1024]; 274 sprintf (buf, 275 "segv_handler fault=%p base=%p size=%lx page=%lx signo=%d\n", 276 faulting_address, stack_base, (unsigned long) stack_size, 277 (unsigned long) page_size, signo); 278 write (STDERR_FILENO, buf, strlen (buf)); 279 } 280 # endif 281 } 282 # endif 283 284 die (signo); 285 } 286 # endif 287 288 int 289 c_stack_action (void (*action) (int)) 290 { 291 int r; 292 stack_t st; 293 struct sigaction act; 294 st.ss_flags = 0; 295 # if SIGALTSTACK_SS_REVERSED 296 /* Irix mistakenly treats ss_sp as the upper bound, rather than 297 lower bound, of the alternate stack. */ 298 st.ss_sp = alternate_signal_stack.buffer + SIGSTKSZ - sizeof (void *); 299 st.ss_size = sizeof alternate_signal_stack.buffer - sizeof (void *); 300 # else 301 st.ss_sp = alternate_signal_stack.buffer; 302 st.ss_size = sizeof alternate_signal_stack.buffer; 303 # endif 304 r = sigaltstack (&st, NULL); 305 if (r != 0) 306 return r; 307 308 segv_action = action ? action : null_action; 309 program_error_message = _("program error"); 310 stack_overflow_message = _("stack overflow"); 311 312 sigemptyset (&act.sa_mask); 313 314 # if SIGACTION_WORKS 315 /* POSIX 1003.1-2001 says SA_RESETHAND implies SA_NODEFER, but 316 this is not true on Solaris 8 at least. It doesn't hurt to use 317 SA_NODEFER here, so leave it in. */ 318 act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND | SA_SIGINFO; 319 act.sa_sigaction = segv_handler; 320 # else 321 act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND; 322 act.sa_handler = die; 323 # endif 324 325 # if FAULT_YIELDS_SIGBUS 326 if (sigaction (SIGBUS, &act, NULL) < 0) 327 return -1; 328 # endif 329 return sigaction (SIGSEGV, &act, NULL); 330 } 331 332 #else /* ! ((HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK 333 && HAVE_STACK_OVERFLOW_HANDLING) || HAVE_LIBSIGSEGV) */ 334 335 int 336 c_stack_action (void (*action) (int) __attribute__ ((unused))) 337 { 338 errno = ENOTSUP; 339 return -1; 340 } 341 342 #endif 343