libvtv/vtv_fail.cc

   1 /* Copyright (C) 2012-2013
   2  Free Software Foundation
   3
   4  This file is part of GCC.
   5
   6  GCC 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, or (at your option)
   9  any later version.
  10
  11  GCC 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  Under Section 7 of GPL version 3, you are granted additional
  17  permissions described in the GCC Runtime Library Exception, version
  18  3.1, as published by the Free Software Foundation.
  19
  20  You should have received a copy of the GNU General Public License and
  21  a copy of the GCC Runtime Library Exception along with this program;
  22  see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23  <http://www.gnu.org/licenses/>.  */
  24
  25 /* This file is part of the vtable security feature implementation.
  26    The vtable security feature is designed to detect when a virtual
  27    call is about to be made through an invalid vtable pointer
  28    (possibly due to data corruption or malicious attacks).
  29
  30    This file also contains the failure functions that get called when
  31    a vtable pointer is not found in the data set.  Two particularly
  32    important functions are __vtv_verify_fail and __vtv_really_fail.
  33    They are both externally visible.  __vtv_verify_fail is defined in
  34    such a way that it can be replaced by a programmer, if desired.  It
  35    is the function that __VLTVerifyVtablePointer calls if it can't
  36    find the pointer in the data set.  Allowing the programmer to
  37    overwrite this function means that he/she can do some alternate
  38    verification, including NOT failing in certain specific cases, if
  39    desired.  This may be the case if the programmer has to deal wtih
  40    unverified third party software, for example.  __vtv_really_fail is
  41    available for the programmer to call from his version of
  42    __vtv_verify_fail, if he decides the failure is real.
  43
  44 */
  45
  46 #include <stdlib.h>
  47 #include <stdio.h>
  48 #include <string.h>
  49 #include <execinfo.h>
  50 #include <unistd.h>
  51
  52 #include "vtv_utils.h"
  53 #include "vtv_fail.h"
  54
  55 /* This is used to disable aborts for debugging purposes.  */
  56 bool vtv_no_abort = false;
  57
  58
  59 extern "C" {
  60
  61   /* __fortify_fail is a function in glibc that calls __libc_message,
  62      causing it to print out a program termination error message
  63      (including the name of the binary being terminated), a stack
  64      trace where the error occurred, and a memory map dump.  Ideally
  65      we would have called __libc_message directly, but that function
  66      does not appear to be accessible to functions outside glibc,
  67      whereas __fortify_fail is.  We call __fortify_fail from
  68      __vtv_really_fail.  We looked at calling __libc_fatal, which is
  69      externally accessible, but it does not do the back trace and
  70      memory dump.  */
  71
  72   extern void __fortify_fail (const char *) __attribute__((noreturn));
  73
  74 } /* extern "C" */
  75
  76 const unsigned long SET_HANDLE_HANDLE_BIT = 0x2;
  77
  78 /* Instantiate the template classes (in vtv_set.h) for our particular
  79    hash table needs.  */
  80 typedef void * vtv_set_handle;
  81 typedef vtv_set_handle * vtv_set_handle_handle;
  82
  83 static int vtv_failures_log_fd = -1;
  84
  85 /* Open error logging file, if not already open, and write vtable
  86    verification failure messages (LOG_MSG) to the log file.  Also
  87    generate a backtrace in the log file, if GENERATE_BACKTRACE is
  88    set.  */
  89
  90 static void
  91 log_error_message (const char *log_msg, bool generate_backtrace)
  92 {
  93   if (vtv_failures_log_fd == -1)
  94     vtv_failures_log_fd = vtv_open_log ("vtable_verification_failures.log");
  95
  96   if (vtv_failures_log_fd == -1)
  97     return;
  98
  99   vtv_add_to_log (vtv_failures_log_fd, "%s", log_msg);
 100
 101   if (generate_backtrace)
 102     {
 103 #define STACK_DEPTH 20
 104       void *callers[STACK_DEPTH];
 105       int actual_depth = backtrace (callers, STACK_DEPTH);
 106       backtrace_symbols_fd (callers, actual_depth, vtv_failures_log_fd);
 107     }
 108 }
 109
 110 /* In the case where a vtable map variable is the only instance of the
 111    variable we have seen, it points directly to the set of valid
 112    vtable pointers.  All subsequent instances of the 'same' vtable map
 113    variable point to the first vtable map variable.  This function,
 114    given a vtable map variable PTR, checks a bit to see whether it's
 115    pointing directly to the data set or to the first vtable map
 116    variable.  */
 117
 118 static inline bool
 119 is_set_handle_handle (void * ptr)
 120 {
 121   return ((unsigned long) ptr & SET_HANDLE_HANDLE_BIT)
 122                                                       == SET_HANDLE_HANDLE_BIT;
 123 }
 124
 125 /* Returns the actual pointer value of a vtable map variable, PTR (see
 126    comments for is_set_handle_handle for more details).  */
 127
 128 static inline vtv_set_handle *
 129 ptr_from_set_handle_handle (void * ptr)
 130 {
 131   return (vtv_set_handle *) ((unsigned long) ptr & ~SET_HANDLE_HANDLE_BIT);
 132 }
 133
 134 /* Given a vtable map variable, PTR, this function sets the bit that
 135    says this is the second (or later) instance of a vtable map
 136    variable.  */
 137
 138 static inline vtv_set_handle_handle
 139 set_handle_handle (vtv_set_handle * ptr)
 140 {
 141   return (vtv_set_handle_handle) ((unsigned long) ptr | SET_HANDLE_HANDLE_BIT);
 142 }
 143
 144 /* This function is called from __VLTVerifyVtablePointerDebug; it
 145    sends as much debugging information as it can to the error log
 146    file, then calls __vtv_verify_fail.  SET_HANDLE_PTR is the pointer
 147    to the set of valid vtable pointers, VTBL_PTR is the pointer that
 148    was not found in the set, and DEBUG_MSG is the message to be
 149    written to the log file before failing. n */
 150
 151 void
 152 __vtv_verify_fail_debug (void **set_handle_ptr, const void *vtbl_ptr,
 153                          const char *debug_msg)
 154 {
 155   log_error_message (debug_msg, false);
 156
 157   /* Call the public interface in case it has been overwritten by
 158      user.  */
 159   __vtv_verify_fail (set_handle_ptr, vtbl_ptr);
 160
 161   log_error_message ("Returned from __vtv_verify_fail."
 162                      " Secondary verification succeeded.\n", false);
 163 }
 164
 165 /* This function calls __fortify_fail with a FAILURE_MSG and then
 166    calls abort.  */
 167
 168 void
 169 __vtv_really_fail (const char *failure_msg)
 170 {
 171   __fortify_fail (failure_msg);
 172
 173   /* We should never get this far; __fortify_fail calls __libc_message
 174      which prints out a back trace and a memory dump and then is
 175      supposed to call abort, but let's play it safe anyway and call abort
 176      ourselves.  */
 177   abort ();
 178 }
 179
 180 /* This function takes an error MSG, a vtable map variable
 181    (DATA_SET_PTR) and a vtable pointer (VTBL_PTR).  It is called when
 182    an attempt to verify VTBL_PTR with the set pointed to by
 183    DATA_SET_PTR failed.  It outputs a failure message with the
 184    addresses involved, and calls __vtv_really_fail.  */
 185
 186 static void
 187 vtv_fail (const char *msg, void **data_set_ptr, const void *vtbl_ptr)
 188 {
 189   char buffer[128];
 190   int buf_len;
 191   const char *format_str =
 192                  "*** Unable to verify vtable pointer (%p) in set (%p) *** \n";
 193
 194   snprintf (buffer, sizeof (buffer), format_str, vtbl_ptr,
 195             is_set_handle_handle(*data_set_ptr) ?
 196               ptr_from_set_handle_handle (*data_set_ptr) :
 197               *data_set_ptr);
 198   buf_len = strlen (buffer);
 199   /*  Send this to to stderr.  */
 200   write (2, buffer, buf_len);
 201
 202   if (!vtv_no_abort)
 203     __vtv_really_fail (msg);
 204 }
 205
 206 /* Send information about what we were trying to do when verification
 207    failed to the error log, then call vtv_fail.  This function can be
 208    overwritten/replaced by the user, to implement a secondary
 209    verification function instead.  DATA_SET_PTR is the vtable map
 210    variable used for the failed verification, and VTBL_PTR is the
 211    vtable pointer that was not found in the set.  */
 212
 213 void
 214 __vtv_verify_fail (void **data_set_ptr, const void *vtbl_ptr)
 215 {
 216   char log_msg[256];
 217   snprintf (log_msg, sizeof (log_msg), "Looking for vtable %p in set %p.\n",
 218             vtbl_ptr,
 219             is_set_handle_handle (*data_set_ptr) ?
 220               ptr_from_set_handle_handle (*data_set_ptr) :
 221               *data_set_ptr);
 222   log_error_message (log_msg, false);
 223
 224   const char *format_str =
 225             "*** Unable to verify vtable pointer (%p) in set (%p) *** \n";
 226   snprintf (log_msg, sizeof (log_msg), format_str, vtbl_ptr, *data_set_ptr);
 227   log_error_message (log_msg, false);
 228   log_error_message ("  Backtrace: \n", true);
 229
 230   const char *fail_msg = "Potential vtable pointer corruption detected!!\n";
 231   vtv_fail (fail_msg, data_set_ptr, vtbl_ptr);
 232 }
 233