summaryrefslogtreecommitdiffstats
path: root/toolkit/crashreporter/google-breakpad/src/processor/exploitability_win.cc
blob: a1f8703a6ef0c14fd365e9f3e3b31eac1ba0f726 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
// Copyright (c) 2010 Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// exploitability_win.cc: Windows specific exploitability engine.
//
// Provides a guess at the exploitability of the crash for the Windows
// platform given a minidump and process_state.
//
// Author: Cris Neckar

#include <vector>

#include "processor/exploitability_win.h"

#include "common/scoped_ptr.h"
#include "google_breakpad/common/minidump_exception_win32.h"
#include "google_breakpad/processor/minidump.h"
#include "processor/disassembler_x86.h"
#include "processor/logging.h"

#include "third_party/libdisasm/libdis.h"

namespace google_breakpad {

// The cutoff that we use to judge if and address is likely an offset
// from various interesting addresses.
static const uint64_t kProbableNullOffset = 4096;
static const uint64_t kProbableStackOffset = 8192;

// The various cutoffs for the different ratings.
static const size_t kHighCutoff        = 100;
static const size_t kMediumCutoff      = 80;
static const size_t kLowCutoff         = 50;
static const size_t kInterestingCutoff = 25;

// Predefined incremental values for conditional weighting.
static const size_t kTinyBump          = 5;
static const size_t kSmallBump         = 20;
static const size_t kMediumBump        = 50;
static const size_t kLargeBump         = 70;
static const size_t kHugeBump          = 90;

// The maximum number of bytes to disassemble past the program counter.
static const size_t kDisassembleBytesBeyondPC = 2048;

ExploitabilityWin::ExploitabilityWin(Minidump *dump,
                                     ProcessState *process_state)
    : Exploitability(dump, process_state) { }

ExploitabilityRating ExploitabilityWin::CheckPlatformExploitability() {
  MinidumpException *exception = dump_->GetException();
  if (!exception) {
    BPLOG(INFO) << "Minidump does not have exception record.";
    return EXPLOITABILITY_ERR_PROCESSING;
  }

  const MDRawExceptionStream *raw_exception = exception->exception();
  if (!raw_exception) {
    BPLOG(INFO) << "Could not obtain raw exception info.";
    return EXPLOITABILITY_ERR_PROCESSING;
  }

  const MinidumpContext *context = exception->GetContext();
  if (!context) {
    BPLOG(INFO) << "Could not obtain exception context.";
    return EXPLOITABILITY_ERR_PROCESSING;
  }

  MinidumpMemoryList *memory_list = dump_->GetMemoryList();
  bool memory_available = true;
  if (!memory_list) {
    BPLOG(INFO) << "Minidump memory segments not available.";
    memory_available = false;
  }
  uint64_t address = process_state_->crash_address();
  uint32_t exception_code = raw_exception->exception_record.exception_code;

  uint32_t exploitability_weight = 0;

  uint64_t stack_ptr = 0;
  uint64_t instruction_ptr = 0;

  // Getting the instruction pointer.
  if (!context->GetInstructionPointer(&instruction_ptr)) {
    return EXPLOITABILITY_ERR_PROCESSING;
  }

  // Getting the stack pointer.
  if (!context->GetStackPointer(&stack_ptr)) {
    return EXPLOITABILITY_ERR_PROCESSING;
  }

  // Check if we are executing on the stack.
  if (instruction_ptr <= (stack_ptr + kProbableStackOffset) &&
      instruction_ptr >= (stack_ptr - kProbableStackOffset))
    exploitability_weight += kHugeBump;

  switch (exception_code) {
    // This is almost certainly recursion.
    case MD_EXCEPTION_CODE_WIN_STACK_OVERFLOW:
      exploitability_weight += kTinyBump;
      break;

    // These exceptions tend to be benign and we can generally ignore them.
    case MD_EXCEPTION_CODE_WIN_INTEGER_DIVIDE_BY_ZERO:
    case MD_EXCEPTION_CODE_WIN_INTEGER_OVERFLOW:
    case MD_EXCEPTION_CODE_WIN_FLOAT_DIVIDE_BY_ZERO:
    case MD_EXCEPTION_CODE_WIN_FLOAT_INEXACT_RESULT:
    case MD_EXCEPTION_CODE_WIN_FLOAT_OVERFLOW:
    case MD_EXCEPTION_CODE_WIN_FLOAT_UNDERFLOW:
    case MD_EXCEPTION_CODE_WIN_IN_PAGE_ERROR:
      exploitability_weight += kTinyBump;
      break;

    // These exceptions will typically mean that we have jumped where we
    // shouldn't.
    case MD_EXCEPTION_CODE_WIN_ILLEGAL_INSTRUCTION:
    case MD_EXCEPTION_CODE_WIN_FLOAT_INVALID_OPERATION:
    case MD_EXCEPTION_CODE_WIN_PRIVILEGED_INSTRUCTION:
      exploitability_weight += kLargeBump;
      break;

    // These represent bugs in exception handlers.
    case MD_EXCEPTION_CODE_WIN_INVALID_DISPOSITION:
    case MD_EXCEPTION_CODE_WIN_NONCONTINUABLE_EXCEPTION:
      exploitability_weight += kSmallBump;
      break;

    case MD_EXCEPTION_CODE_WIN_HEAP_CORRUPTION:
    case MD_EXCEPTION_CODE_WIN_STACK_BUFFER_OVERRUN:
      exploitability_weight += kHugeBump;
      break;

    case MD_EXCEPTION_CODE_WIN_GUARD_PAGE_VIOLATION:
      exploitability_weight += kLargeBump;
      break;

    case MD_EXCEPTION_CODE_WIN_ACCESS_VIOLATION:
      bool near_null = (address <= kProbableNullOffset);
      bool bad_read = false;
      bool bad_write = false;
      if (raw_exception->exception_record.number_parameters >= 1) {
        MDAccessViolationTypeWin av_type =
            static_cast<MDAccessViolationTypeWin>
            (raw_exception->exception_record.exception_information[0]);
        switch (av_type) {
          case MD_ACCESS_VIOLATION_WIN_READ:
            bad_read = true;
            if (near_null)
              exploitability_weight += kSmallBump;
            else
              exploitability_weight += kMediumBump;
            break;
          case MD_ACCESS_VIOLATION_WIN_WRITE:
            bad_write = true;
            if (near_null)
              exploitability_weight += kSmallBump;
            else
              exploitability_weight += kHugeBump;
            break;
          case MD_ACCESS_VIOLATION_WIN_EXEC:
            if (near_null)
              exploitability_weight += kSmallBump;
            else
              exploitability_weight += kHugeBump;
            break;
          default:
            BPLOG(INFO) << "Unrecognized access violation type.";
            return EXPLOITABILITY_ERR_PROCESSING;
            break;
        }
        MinidumpMemoryRegion *instruction_region = 0;
        if (memory_available) {
          instruction_region =
              memory_list->GetMemoryRegionForAddress(instruction_ptr);
        }
        if (!near_null && instruction_region &&
            context->GetContextCPU() == MD_CONTEXT_X86 &&
            (bad_read || bad_write)) {
          // Perform checks related to memory around instruction pointer.
          uint32_t memory_offset =
              instruction_ptr - instruction_region->GetBase();
          uint32_t available_memory =
              instruction_region->GetSize() - memory_offset;
          available_memory = available_memory > kDisassembleBytesBeyondPC ?
              kDisassembleBytesBeyondPC : available_memory;
          if (available_memory) {
            const uint8_t *raw_memory =
                instruction_region->GetMemory() + memory_offset;
            DisassemblerX86 disassembler(raw_memory,
                                         available_memory,
                                         instruction_ptr);
            disassembler.NextInstruction();
            if (bad_read)
              disassembler.setBadRead();
            else
              disassembler.setBadWrite();
            if (disassembler.currentInstructionValid()) {
              // Check if the faulting instruction falls into one of
              // several interesting groups.
              switch (disassembler.currentInstructionGroup()) {
                case libdis::insn_controlflow:
                  exploitability_weight += kLargeBump;
                  break;
                case libdis::insn_string:
                  exploitability_weight += kHugeBump;
                  break;
                default:
                  break;
              }
              // Loop the disassembler through the code and check if it
              // IDed any interesting conditions in the near future.
              // Multiple flags may be set so treat each equally.
              while (disassembler.NextInstruction() &&
                     disassembler.currentInstructionValid() &&
                     !disassembler.endOfBlock())
                continue;
              if (disassembler.flags() & DISX86_BAD_BRANCH_TARGET)
                exploitability_weight += kLargeBump;
              if (disassembler.flags() & DISX86_BAD_ARGUMENT_PASSED)
                exploitability_weight += kTinyBump;
              if (disassembler.flags() & DISX86_BAD_WRITE)
                exploitability_weight += kMediumBump;
              if (disassembler.flags() & DISX86_BAD_BLOCK_WRITE)
                exploitability_weight += kMediumBump;
              if (disassembler.flags() & DISX86_BAD_READ)
                exploitability_weight += kTinyBump;
              if (disassembler.flags() & DISX86_BAD_BLOCK_READ)
                exploitability_weight += kTinyBump;
              if (disassembler.flags() & DISX86_BAD_COMPARISON)
                exploitability_weight += kTinyBump;
            }
          }
        }
        if (!near_null && AddressIsAscii(address))
          exploitability_weight += kMediumBump;
      } else {
        BPLOG(INFO) << "Access violation type parameter missing.";
        return EXPLOITABILITY_ERR_PROCESSING;
      }
  }

  // Based on the calculated weight we return a simplified classification.
  BPLOG(INFO) << "Calculated exploitability weight: " << exploitability_weight;
  if (exploitability_weight >= kHighCutoff)
    return EXPLOITABILITY_HIGH;
  if (exploitability_weight >= kMediumCutoff)
    return EXPLOITABLITY_MEDIUM;
  if (exploitability_weight >= kLowCutoff)
    return EXPLOITABILITY_LOW;
  if (exploitability_weight >= kInterestingCutoff)
    return EXPLOITABILITY_INTERESTING;

  return EXPLOITABILITY_NONE;
}

}  // namespace google_breakpad