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1 /* Mudflap: narrow-pointer bounds-checking by tree rewriting.
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2 Copyright (C) 2002, 2003, 2009 Free Software Foundation, Inc.
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3 Contributed by Frank Ch. Eigler <fche@redhat.com>
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4 and Graydon Hoare <graydon@redhat.com>
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5
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6 This file is part of GCC.
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7
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8 GCC is free software; you can redistribute it and/or modify it under
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9 the terms of the GNU General Public License as published by the Free
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10 Software Foundation; either version 3, or (at your option) any later
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11 version.
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12
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13 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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14 WARRANTY; without even the implied warranty of MERCHANTABILITY or
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15 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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16 for more details.
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17
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18 Under Section 7 of GPL version 3, you are granted additional
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19 permissions described in the GCC Runtime Library Exception, version
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20 3.1, as published by the Free Software Foundation.
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21
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22 You should have received a copy of the GNU General Public License and
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23 a copy of the GCC Runtime Library Exception along with this program;
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24 see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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25 <http://www.gnu.org/licenses/>. */
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26
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27 #include "config.h"
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28
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29 #include <stdio.h>
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30
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31 #include "mf-runtime.h"
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32 #include "mf-impl.h"
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33
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34 #ifdef _MUDFLAP
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35 #error "Do not compile this file with -fmudflap!"
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36 #endif
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37
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38
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39 extern char _end[];
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40 extern char ENTRY_POINT[];
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41
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42
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43 /* Run some quick validation of the given region.
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44 Return -1 / 0 / 1 if the access known-invalid, possibly-valid, or known-valid.
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45 */
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46 int
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47 __mf_heuristic_check (uintptr_t ptr, uintptr_t ptr_high)
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48 {
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49 VERBOSE_TRACE ("mf: heuristic check\n");
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50
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51 /* XXX: Disable the stack bounding check for libmudflapth. We do
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52 actually have enough information to track stack bounds (see
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53 __mf_pthread_info in mf-hooks.c), so with a bit of future work,
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54 this heuristic can be turned on. */
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55 #ifndef LIBMUDFLAPTH
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56
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57 /* The first heuristic is to check stack bounds. This is a
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58 transient condition and quick to check. */
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59 if (__mf_opts.heur_stack_bound)
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60 {
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61 uintptr_t stack_top_guess = (uintptr_t)__builtin_frame_address(0);
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62 #if defined(__i386__) && defined (__linux__)
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63 uintptr_t stack_segment_base = 0xC0000000; /* XXX: Bad assumption. */
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64 #else
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65 /* Cause tests to fail. */
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66 uintptr_t stack_segment_base = 0;
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67 #endif
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68
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69 VERBOSE_TRACE ("mf: stack estimated as %p-%p\n",
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70 (void *) stack_top_guess, (void *) stack_segment_base);
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71
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72 if (ptr_high <= stack_segment_base &&
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73 ptr >= stack_top_guess &&
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74 ptr_high >= ptr)
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75 {
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76 return 1;
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77 }
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78 }
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79 #endif
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80
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81
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82 /* The second heuristic is to scan the range of memory regions
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83 listed in /proc/self/maps, a special file provided by the Linux
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84 kernel. Its results may be cached, and in fact, a GUESS object
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85 may as well be recorded for interesting matching sections. */
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86 if (__mf_opts.heur_proc_map)
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87 {
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88 /* Keep a record of seen records from /proc/self/map. */
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89 enum { max_entries = 500 };
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90 struct proc_self_map_entry
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91 {
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92 uintptr_t low;
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93 uintptr_t high;
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94 };
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95 static struct proc_self_map_entry entry [max_entries];
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96 static unsigned entry_used [max_entries];
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97
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98 /* Look for a known proc_self_map entry that may cover this
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99 region. If one exists, then this heuristic has already run,
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100 and should not be run again. The check should be allowed to
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101 fail. */
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102 unsigned i;
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103 unsigned deja_vu = 0;
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104 for (i=0; i<max_entries; i++)
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105 {
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106 if (entry_used[i] &&
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107 (entry[i].low <= ptr) &&
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108 (entry[i].high >= ptr_high))
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109 deja_vu = 1;
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110 }
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111
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112 if (! deja_vu)
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113 {
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114 /* Time to run the heuristic. Rescan /proc/self/maps; update the
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115 entry[] array; XXX: remove expired entries, add new ones.
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116 XXX: Consider entries that have grown (e.g., stack). */
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117 char buf[512];
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118 char flags[4];
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119 void *low, *high;
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120 FILE *fp;
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121
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122 fp = fopen ("/proc/self/maps", "r");
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123 if (fp)
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124 {
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125 while (fgets (buf, sizeof(buf), fp))
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126 {
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127 if (sscanf (buf, "%p-%p %4c", &low, &high, flags) == 3)
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128 {
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129 if ((uintptr_t) low <= ptr &&
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130 (uintptr_t) high >= ptr_high)
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131 {
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132 for (i=0; i<max_entries; i++)
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133 {
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134 if (! entry_used[i])
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135 {
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136 entry[i].low = (uintptr_t) low;
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137 entry[i].high = (uintptr_t) high;
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138 entry_used[i] = 1;
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139 break;
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140 }
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141 }
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142
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143 VERBOSE_TRACE ("mf: registering region #%d "
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144 "%p-%p given %s",
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145 i, (void *) low, (void *) high, buf);
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146
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147 __mfu_register ((void *) low, (size_t) (high-low),
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148 __MF_TYPE_GUESS,
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149 "/proc/self/maps segment");
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150
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151 return 0; /* undecided (tending to cachable) */
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152 }
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153 }
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154 }
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155 fclose (fp);
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156 }
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157 }
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158 }
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159
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160
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161 /* The third heuristic is to approve all accesses between _start (or its
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162 equivalent for the given target) and _end, which should include all
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163 text and initialized data. */
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164 if (__mf_opts.heur_start_end)
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165 if (ptr >= (uintptr_t) & ENTRY_POINT && ptr_high <= (uintptr_t) & _end)
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166 return 1; /* uncacheable */
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167
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168 return 0; /* unknown */
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169 }
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