lib/c-stack.c

   1 /* Stack overflow handling.
   2
   3    Copyright (C) 2002, 2004, 2006, 2008-2020 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* Written by Paul Eggert.  */
  19
  20 /* NOTES:
  21
  22    A program that uses alloca, dynamic arrays, or large local
  23    variables may extend the stack by more than a page at a time.  If
  24    so, when the stack overflows the operating system may not detect
  25    the overflow until the program uses the array, and this module may
  26    incorrectly report a program error instead of a stack overflow.
  27
  28    To avoid this problem, allocate only small objects on the stack; a
  29    program should be OK if it limits single allocations to a page or
  30    less.  Allocate larger arrays in static storage, or on the heap
  31    (e.g., with malloc).  Yes, this is a pain, but we don't know of any
  32    better solution that is portable.
  33
  34    No attempt has been made to deal with multithreaded applications.  */
  35
  36 #include <config.h>
  37
  38 #include "gettext.h"
  39 #define _(msgid) gettext (msgid)
  40
  41 #include <errno.h>
  42
  43 #include <signal.h>
  44 #if ! HAVE_STACK_T && ! defined stack_t
  45 typedef struct sigaltstack stack_t;
  46 #endif
  47 #ifndef SIGSTKSZ
  48 # define SIGSTKSZ 16384
  49 #elif HAVE_LIBSIGSEGV && SIGSTKSZ < 16384
  50 /* libsigsegv 2.6 through 2.8 have a bug where some architectures use
  51    more than the Linux default of an 8k alternate stack when deciding
  52    if a fault was caused by stack overflow.  */
  53 # undef SIGSTKSZ
  54 # define SIGSTKSZ 16384
  55 #endif
  56
  57 #include <stdlib.h>
  58 #include <string.h>
  59
  60 /* Posix 2001 declares ucontext_t in <ucontext.h>, Posix 200x in
  61    <signal.h>.  */
  62 #if HAVE_UCONTEXT_H
  63 # include <ucontext.h>
  64 #endif
  65
  66 #include <unistd.h>
  67
  68 #if DEBUG
  69 # include <stdio.h>
  70 #endif
  71
  72 #if HAVE_LIBSIGSEGV
  73 # include <sigsegv.h>
  74 #endif
  75
  76 #include "c-stack.h"
  77 #include "exitfail.h"
  78 #include "ignore-value.h"
  79 #include "getprogname.h"
  80
  81 #if defined SA_ONSTACK && defined SA_SIGINFO
  82 # define SIGINFO_WORKS 1
  83 #else
  84 # define SIGINFO_WORKS 0
  85 # ifndef SA_ONSTACK
  86 #  define SA_ONSTACK 0
  87 # endif
  88 #endif
  89
  90 /* The user-specified action to take when a SEGV-related program error
  91    or stack overflow occurs.  */
  92 static _GL_ASYNC_SAFE void (* volatile segv_action) (int);
  93
  94 /* Translated messages for program errors and stack overflow.  Do not
  95    translate them in the signal handler, since gettext is not
  96    async-signal-safe.  */
  97 static char const * volatile program_error_message;
  98 static char const * volatile stack_overflow_message;
  99
 100 #if ((HAVE_LIBSIGSEGV && ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC) \
 101      || (HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK            \
 102          && HAVE_STACK_OVERFLOW_HANDLING))
 103
 104 /* Output an error message, then exit with status EXIT_FAILURE if it
 105    appears to have been a stack overflow, or with a core dump
 106    otherwise.  This function is async-signal-safe.  */
 107
 108 static char const * volatile progname;
 109
 110 static _GL_ASYNC_SAFE _Noreturn void
 111 die (int signo)
 112 {
 113   char const *message;
 114 #if !SIGINFO_WORKS && !HAVE_LIBSIGSEGV
 115   /* We can't easily determine whether it is a stack overflow; so
 116      assume that the rest of our program is perfect (!) and that
 117      this segmentation violation is a stack overflow.  */
 118   signo = 0;
 119 #endif /* !SIGINFO_WORKS && !HAVE_LIBSIGSEGV */
 120   segv_action (signo);
 121   message = signo ? program_error_message : stack_overflow_message;
 122   ignore_value (write (STDERR_FILENO, progname, strlen (progname)));
 123   ignore_value (write (STDERR_FILENO, ": ", 2));
 124   ignore_value (write (STDERR_FILENO, message, strlen (message)));
 125   ignore_value (write (STDERR_FILENO, "\n", 1));
 126   if (! signo)
 127     _exit (exit_failure);
 128   raise (signo);
 129   abort ();
 130 }
 131 #endif
 132
 133 #if (HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK \
 134      && HAVE_STACK_OVERFLOW_HANDLING) || HAVE_LIBSIGSEGV
 135
 136 /* Storage for the alternate signal stack.  */
 137 static union
 138 {
 139   char buffer[SIGSTKSZ];
 140
 141   /* These other members are for proper alignment.  There's no
 142      standard way to guarantee stack alignment, but this seems enough
 143      in practice.  */
 144   long double ld;
 145   long l;
 146   void *p;
 147 } alternate_signal_stack;
 148
 149 static _GL_ASYNC_SAFE void
 150 null_action (int signo _GL_UNUSED)
 151 {
 152 }
 153
 154 #endif /* SIGALTSTACK || LIBSIGSEGV */
 155
 156 /* Only use libsigsegv if we need it; platforms like Solaris can
 157    detect stack overflow without the overhead of an external
 158    library.  */
 159 #if HAVE_LIBSIGSEGV && ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC
 160
 161 /* Nonzero if general segv handler could not be installed.  */
 162 static volatile int segv_handler_missing;
 163
 164 /* Handle a segmentation violation and exit if it cannot be stack
 165    overflow.  This function is async-signal-safe.  */
 166
 167 static _GL_ASYNC_SAFE int
 168 segv_handler (void *address _GL_UNUSED, int serious)
 169 {
 170 # if DEBUG
 171   {
 172     char buf[1024];
 173     int saved_errno = errno;
 174     sprintf (buf, "segv_handler serious=%d\n", serious);
 175     ignore_value (write (STDERR_FILENO, buf, strlen (buf)));
 176     errno = saved_errno;
 177   }
 178 # endif
 179
 180   /* If this fault is not serious, return 0 to let the stack overflow
 181      handler take a shot at it.  */
 182   if (!serious)
 183     return 0;
 184   die (SIGSEGV);
 185 }
 186
 187 /* Handle a segmentation violation that is likely to be a stack
 188    overflow and exit.  This function is async-signal-safe.  */
 189
 190 static _GL_ASYNC_SAFE _Noreturn void
 191 overflow_handler (int emergency, stackoverflow_context_t context _GL_UNUSED)
 192 {
 193 # if DEBUG
 194   {
 195     char buf[1024];
 196     sprintf (buf, "overflow_handler emergency=%d segv_handler_missing=%d\n",
 197              emergency, segv_handler_missing);
 198     ignore_value (write (STDERR_FILENO, buf, strlen (buf)));
 199   }
 200 # endif
 201
 202   die ((!emergency || segv_handler_missing) ? 0 : SIGSEGV);
 203 }
 204
 205 int
 206 c_stack_action (_GL_ASYNC_SAFE void (*action) (int))
 207 {
 208   segv_action = action ? action : null_action;
 209   program_error_message = _("program error");
 210   stack_overflow_message = _("stack overflow");
 211   progname = getprogname ();
 212
 213   /* Always install the overflow handler.  */
 214   if (stackoverflow_install_handler (overflow_handler,
 215                                      alternate_signal_stack.buffer,
 216                                      sizeof alternate_signal_stack.buffer))
 217     {
 218       errno = ENOTSUP;
 219       return -1;
 220     }
 221   /* Try installing a general handler; if it fails, then treat all
 222      segv as stack overflow.  */
 223   segv_handler_missing = sigsegv_install_handler (segv_handler);
 224   return 0;
 225 }
 226
 227 #elif HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK && HAVE_STACK_OVERFLOW_HANDLING
 228
 229 # if SIGINFO_WORKS
 230
 231 /* Handle a segmentation violation and exit.  This function is
 232    async-signal-safe.  */
 233
 234 static _GL_ASYNC_SAFE _Noreturn void
 235 segv_handler (int signo, siginfo_t *info, void *context _GL_UNUSED)
 236 {
 237   /* Clear SIGNO if it seems to have been a stack overflow.  */
 238 #  if ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC
 239   /* We can't easily determine whether it is a stack overflow; so
 240      assume that the rest of our program is perfect (!) and that
 241      this segmentation violation is a stack overflow.
 242
 243      Note that although both Linux and Solaris provide
 244      sigaltstack, SA_ONSTACK, and SA_SIGINFO, currently only
 245      Solaris satisfies the XSI heuristic.  This is because
 246      Solaris populates uc_stack with the details of the
 247      interrupted stack, while Linux populates it with the details
 248      of the current stack.  */
 249   signo = 0;
 250 #  else
 251   if (0 < info->si_code)
 252     {
 253       /* If the faulting address is within the stack, or within one
 254          page of the stack, assume that it is a stack overflow.  */
 255       ucontext_t const *user_context = context;
 256       char const *stack_base = user_context->uc_stack.ss_sp;
 257       size_t stack_size = user_context->uc_stack.ss_size;
 258       char const *faulting_address = info->si_addr;
 259       size_t page_size = sysconf (_SC_PAGESIZE);
 260       size_t s = faulting_address - stack_base + page_size;
 261       if (s < stack_size + 2 * page_size)
 262         signo = 0;
 263
 264 #   if DEBUG
 265       {
 266         char buf[1024];
 267         sprintf (buf,
 268                  "segv_handler fault=%p base=%p size=%lx page=%lx signo=%d\n",
 269                  faulting_address, stack_base, (unsigned long) stack_size,
 270                  (unsigned long) page_size, signo);
 271         ignore_value (write (STDERR_FILENO, buf, strlen (buf)));
 272       }
 273 #   endif
 274     }
 275 #  endif
 276
 277   die (signo);
 278 }
 279 # endif
 280
 281 int
 282 c_stack_action (_GL_ASYNC_SAFE void (*action) (int))
 283 {
 284   int r;
 285   stack_t st;
 286   struct sigaction act;
 287   st.ss_flags = 0;
 288 # if SIGALTSTACK_SS_REVERSED
 289   /* Irix mistakenly treats ss_sp as the upper bound, rather than
 290      lower bound, of the alternate stack.  */
 291   st.ss_sp = alternate_signal_stack.buffer + SIGSTKSZ - sizeof (void *);
 292   st.ss_size = sizeof alternate_signal_stack.buffer - sizeof (void *);
 293 # else
 294   st.ss_sp = alternate_signal_stack.buffer;
 295   st.ss_size = sizeof alternate_signal_stack.buffer;
 296 # endif
 297   r = sigaltstack (&st, NULL);
 298   if (r != 0)
 299     return r;
 300
 301   segv_action = action ? action : null_action;
 302   program_error_message = _("program error");
 303   stack_overflow_message = _("stack overflow");
 304   progname = getprogname ();
 305
 306   sigemptyset (&act.sa_mask);
 307
 308 # if SIGINFO_WORKS
 309   /* POSIX 1003.1-2001 says SA_RESETHAND implies SA_NODEFER, but
 310      this is not true on Solaris 8 at least.  It doesn't hurt to use
 311      SA_NODEFER here, so leave it in.  */
 312   act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND | SA_SIGINFO;
 313   act.sa_sigaction = segv_handler;
 314 # else
 315   act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND;
 316   act.sa_handler = die;
 317 # endif
 318
 319 # if FAULT_YIELDS_SIGBUS
 320   if (sigaction (SIGBUS, &act, NULL) < 0)
 321     return -1;
 322 # endif
 323   return sigaction (SIGSEGV, &act, NULL);
 324 }
 325
 326 #else /* ! ((HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK
 327              && HAVE_STACK_OVERFLOW_HANDLING) || HAVE_LIBSIGSEGV) */
 328
 329 int
 330 c_stack_action (_GL_ASYNC_SAFE void (*action) (int)  _GL_UNUSED)
 331 {
 332   errno = ENOTSUP;
 333   return -1;
 334 }
 335
 336 #endif