lib/c-stack.c

   1 /* Stack overflow handling.
   2
   3    Copyright (C) 2002, 2004, 2006, 2008-2019 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 #ifndef __attribute__
  39 # if __GNUC__ < 3
  40 #  define __attribute__(x)
  41 # endif
  42 #endif
  43
  44 #include "gettext.h"
  45 #define _(msgid) gettext (msgid)
  46
  47 #include <errno.h>
  48
  49 #include <signal.h>
  50 #if ! HAVE_STACK_T && ! defined stack_t
  51 typedef struct sigaltstack stack_t;
  52 #endif
  53 #ifndef SIGSTKSZ
  54 # define SIGSTKSZ 16384
  55 #elif HAVE_LIBSIGSEGV && SIGSTKSZ < 16384
  56 /* libsigsegv 2.6 through 2.8 have a bug where some architectures use
  57    more than the Linux default of an 8k alternate stack when deciding
  58    if a fault was caused by stack overflow.  */
  59 # undef SIGSTKSZ
  60 # define SIGSTKSZ 16384
  61 #endif
  62
  63 #include <stdlib.h>
  64 #include <string.h>
  65
  66 /* Posix 2001 declares ucontext_t in <ucontext.h>, Posix 200x in
  67    <signal.h>.  */
  68 #if HAVE_UCONTEXT_H
  69 # include <ucontext.h>
  70 #endif
  71
  72 #include <unistd.h>
  73
  74 #if HAVE_LIBSIGSEGV
  75 # include <sigsegv.h>
  76 #endif
  77
  78 #include "c-stack.h"
  79 #include "exitfail.h"
  80 #include "ignore-value.h"
  81 #include "getprogname.h"
  82
  83 #if defined SA_ONSTACK && defined SA_SIGINFO
  84 # define SIGINFO_WORKS 1
  85 #else
  86 # define SIGINFO_WORKS 0
  87 # ifndef SA_ONSTACK
  88 #  define SA_ONSTACK 0
  89 # endif
  90 #endif
  91
  92 /* The user-specified action to take when a SEGV-related program error
  93    or stack overflow occurs.  */
  94 static _GL_ASYNC_SAFE void (* volatile segv_action) (int);
  95
  96 /* Translated messages for program errors and stack overflow.  Do not
  97    translate them in the signal handler, since gettext is not
  98    async-signal-safe.  */
  99 static char const * volatile program_error_message;
 100 static char const * volatile stack_overflow_message;
 101
 102 #if ((HAVE_LIBSIGSEGV && ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC) \
 103      || (HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK            \
 104          && HAVE_STACK_OVERFLOW_HANDLING))
 105
 106 /* Output an error message, then exit with status EXIT_FAILURE if it
 107    appears to have been a stack overflow, or with a core dump
 108    otherwise.  This function is async-signal-safe.  */
 109
 110 static char const * volatile progname;
 111
 112 static _GL_ASYNC_SAFE _Noreturn void
 113 die (int signo)
 114 {
 115   char const *message;
 116 #if !SIGINFO_WORKS && !HAVE_LIBSIGSEGV
 117   /* We can't easily determine whether it is a stack overflow; so
 118      assume that the rest of our program is perfect (!) and that
 119      this segmentation violation is a stack overflow.  */
 120   signo = 0;
 121 #endif /* !SIGINFO_WORKS && !HAVE_LIBSIGSEGV */
 122   segv_action (signo);
 123   message = signo ? program_error_message : stack_overflow_message;
 124   ignore_value (write (STDERR_FILENO, progname, strlen (progname)));
 125   ignore_value (write (STDERR_FILENO, ": ", 2));
 126   ignore_value (write (STDERR_FILENO, message, strlen (message)));
 127   ignore_value (write (STDERR_FILENO, "\n", 1));
 128   if (! signo)
 129     _exit (exit_failure);
 130   raise (signo);
 131   abort ();
 132 }
 133 #endif
 134
 135 #if (HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK \
 136      && HAVE_STACK_OVERFLOW_HANDLING) || HAVE_LIBSIGSEGV
 137
 138 /* Storage for the alternate signal stack.  */
 139 static union
 140 {
 141   char buffer[SIGSTKSZ];
 142
 143   /* These other members are for proper alignment.  There's no
 144      standard way to guarantee stack alignment, but this seems enough
 145      in practice.  */
 146   long double ld;
 147   long l;
 148   void *p;
 149 } alternate_signal_stack;
 150
 151 static _GL_ASYNC_SAFE void
 152 null_action (int signo _GL_UNUSED)
 153 {
 154 }
 155
 156 #endif /* SIGALTSTACK || LIBSIGSEGV */
 157
 158 /* Only use libsigsegv if we need it; platforms like Solaris can
 159    detect stack overflow without the overhead of an external
 160    library.  */
 161 #if HAVE_LIBSIGSEGV && ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC
 162
 163 /* Nonzero if general segv handler could not be installed.  */
 164 static volatile int segv_handler_missing;
 165
 166 /* Handle a segmentation violation and exit if it cannot be stack
 167    overflow.  This function is async-signal-safe.  */
 168
 169 static _GL_ASYNC_SAFE int
 170 segv_handler (void *address _GL_UNUSED, int serious)
 171 {
 172 # if DEBUG
 173   {
 174     char buf[1024];
 175     int saved_errno = errno;
 176     sprintf (buf, "segv_handler serious=%d\n", serious);
 177     write (STDERR_FILENO, buf, strlen (buf));
 178     errno = saved_errno;
 179   }
 180 # endif
 181
 182   /* If this fault is not serious, return 0 to let the stack overflow
 183      handler take a shot at it.  */
 184   if (!serious)
 185     return 0;
 186   die (SIGSEGV);
 187 }
 188
 189 /* Handle a segmentation violation that is likely to be a stack
 190    overflow and exit.  This function is async-signal-safe.  */
 191
 192 static _GL_ASYNC_SAFE _Noreturn void
 193 overflow_handler (int emergency, stackoverflow_context_t context _GL_UNUSED)
 194 {
 195 # if DEBUG
 196   {
 197     char buf[1024];
 198     sprintf (buf, "overflow_handler emergency=%d segv_handler_missing=%d\n",
 199              emergency, segv_handler_missing);
 200     write (STDERR_FILENO, buf, strlen (buf));
 201   }
 202 # endif
 203
 204   die ((!emergency || segv_handler_missing) ? 0 : SIGSEGV);
 205 }
 206
 207 int
 208 c_stack_action (_GL_ASYNC_SAFE void (*action) (int))
 209 {
 210   segv_action = action ? action : null_action;
 211   program_error_message = _("program error");
 212   stack_overflow_message = _("stack overflow");
 213   progname = getprogname ();
 214
 215   /* Always install the overflow handler.  */
 216   if (stackoverflow_install_handler (overflow_handler,
 217                                      alternate_signal_stack.buffer,
 218                                      sizeof alternate_signal_stack.buffer))
 219     {
 220       errno = ENOTSUP;
 221       return -1;
 222     }
 223   /* Try installing a general handler; if it fails, then treat all
 224      segv as stack overflow.  */
 225   segv_handler_missing = sigsegv_install_handler (segv_handler);
 226   return 0;
 227 }
 228
 229 #elif HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK && HAVE_STACK_OVERFLOW_HANDLING
 230
 231 # if SIGINFO_WORKS
 232
 233 /* Handle a segmentation violation and exit.  This function is
 234    async-signal-safe.  */
 235
 236 static _GL_ASYNC_SAFE _Noreturn void
 237 segv_handler (int signo, siginfo_t *info, void *context _GL_UNUSED)
 238 {
 239   /* Clear SIGNO if it seems to have been a stack overflow.  */
 240 #  if ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC
 241   /* We can't easily determine whether it is a stack overflow; so
 242      assume that the rest of our program is perfect (!) and that
 243      this segmentation violation is a stack overflow.
 244
 245      Note that although both Linux and Solaris provide
 246      sigaltstack, SA_ONSTACK, and SA_SIGINFO, currently only
 247      Solaris satisfies the XSI heuristic.  This is because
 248      Solaris populates uc_stack with the details of the
 249      interrupted stack, while Linux populates it with the details
 250      of the current stack.  */
 251   signo = 0;
 252 #  else
 253   if (0 < info->si_code)
 254     {
 255       /* If the faulting address is within the stack, or within one
 256          page of the stack, assume that it is a stack overflow.  */
 257       ucontext_t const *user_context = context;
 258       char const *stack_base = user_context->uc_stack.ss_sp;
 259       size_t stack_size = user_context->uc_stack.ss_size;
 260       char const *faulting_address = info->si_addr;
 261       size_t page_size = sysconf (_SC_PAGESIZE);
 262       size_t s = faulting_address - stack_base + page_size;
 263       if (s < stack_size + 2 * page_size)
 264         signo = 0;
 265
 266 #   if DEBUG
 267       {
 268         char buf[1024];
 269         sprintf (buf,
 270                  "segv_handler fault=%p base=%p size=%lx page=%lx signo=%d\n",
 271                  faulting_address, stack_base, (unsigned long) stack_size,
 272                  (unsigned long) page_size, signo);
 273         write (STDERR_FILENO, buf, strlen (buf));
 274       }
 275 #   endif
 276     }
 277 #  endif
 278
 279   die (signo);
 280 }
 281 # endif
 282
 283 int
 284 c_stack_action (_GL_ASYNC_SAFE void (*action) (int))
 285 {
 286   int r;
 287   stack_t st;
 288   struct sigaction act;
 289   st.ss_flags = 0;
 290 # if SIGALTSTACK_SS_REVERSED
 291   /* Irix mistakenly treats ss_sp as the upper bound, rather than
 292      lower bound, of the alternate stack.  */
 293   st.ss_sp = alternate_signal_stack.buffer + SIGSTKSZ - sizeof (void *);
 294   st.ss_size = sizeof alternate_signal_stack.buffer - sizeof (void *);
 295 # else
 296   st.ss_sp = alternate_signal_stack.buffer;
 297   st.ss_size = sizeof alternate_signal_stack.buffer;
 298 # endif
 299   r = sigaltstack (&st, NULL);
 300   if (r != 0)
 301     return r;
 302
 303   segv_action = action ? action : null_action;
 304   program_error_message = _("program error");
 305   stack_overflow_message = _("stack overflow");
 306   progname = getprogname ();
 307
 308   sigemptyset (&act.sa_mask);
 309
 310 # if SIGINFO_WORKS
 311   /* POSIX 1003.1-2001 says SA_RESETHAND implies SA_NODEFER, but
 312      this is not true on Solaris 8 at least.  It doesn't hurt to use
 313      SA_NODEFER here, so leave it in.  */
 314   act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND | SA_SIGINFO;
 315   act.sa_sigaction = segv_handler;
 316 # else
 317   act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND;
 318   act.sa_handler = die;
 319 # endif
 320
 321 # if FAULT_YIELDS_SIGBUS
 322   if (sigaction (SIGBUS, &act, NULL) < 0)
 323     return -1;
 324 # endif
 325   return sigaction (SIGSEGV, &act, NULL);
 326 }
 327
 328 #else /* ! ((HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK
 329              && HAVE_STACK_OVERFLOW_HANDLING) || HAVE_LIBSIGSEGV) */
 330
 331 int
 332 c_stack_action (_GL_ASYNC_SAFE void (*action) (int)  _GL_UNUSED)
 333 {
 334   errno = ENOTSUP;
 335   return -1;
 336 }
 337
 338 #endif