handler-outside.cc 7.63 KB
Newer Older
eholk's avatar
eholk committed
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
// Copyright 2017 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// PLEASE READ BEFORE CHANGING THIS FILE!
//
// This file implements the support code for the out of bounds signal handler.
// Nothing in here actually runs in the signal handler, but the code here
// manipulates data structures used by the signal handler so we still need to be
// careful. In order to minimize this risk, here are some rules to follow.
//
// 1. Avoid introducing new external dependencies. The files in src/trap-handler
//    should be as self-contained as possible to make it easy to audit the code.
//
// 2. Any changes must be reviewed by someone from the crash reporting
//    or security team. Se OWNERS for suggested reviewers.
//
// For more information, see https://goo.gl/yMeyUY.
//
// For the code that runs in the signal handler itself, see handler-inside.cc.

#include <signal.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <atomic>
#include <limits>

#include "src/trap-handler/trap-handler-internal.h"
#include "src/trap-handler/trap-handler.h"

namespace {
size_t gNextCodeObject = 0;
36

37 38
#ifdef DEBUG
constexpr bool kEnableDebug = true;
39
#else
40
constexpr bool kEnableDebug = false;
41
#endif
eholk's avatar
eholk committed
42 43 44 45 46 47
}

namespace v8 {
namespace internal {
namespace trap_handler {

48 49
constexpr size_t kInitialCodeObjectSize = 1024;
constexpr size_t kCodeObjectGrowthFactor = 2;
eholk's avatar
eholk committed
50 51 52 53 54 55

constexpr size_t HandlerDataSize(size_t num_protected_instructions) {
  return offsetof(CodeProtectionInfo, instructions) +
         num_protected_instructions * sizeof(ProtectedInstructionData);
}

56
namespace {
57
#ifdef DEBUG
58 59 60 61
bool IsDisjoint(const CodeProtectionInfo* a, const CodeProtectionInfo* b) {
  if (a == nullptr || b == nullptr) {
    return true;
  }
62
  return a->base >= b->base + b->size || b->base >= a->base + a->size;
63
}
64
#endif
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

// Verify that the code range does not overlap any that have already been
// registered.
void VerifyCodeRangeIsDisjoint(const CodeProtectionInfo* code_info) {
  for (size_t i = 0; i < gNumCodeObjects; ++i) {
    DCHECK(IsDisjoint(code_info, gCodeObjects[i].code_info));
  }
}

void ValidateCodeObjects() {
  // Sanity-check the code objects
  for (unsigned i = 0; i < gNumCodeObjects; ++i) {
    const auto* data = gCodeObjects[i].code_info;

    if (data == nullptr) continue;

    // Do some sanity checks on the protected instruction data
    for (unsigned i = 0; i < data->num_protected_instructions; ++i) {
      DCHECK_GE(data->instructions[i].instr_offset, 0);
      DCHECK_LT(data->instructions[i].instr_offset, data->size);
      DCHECK_GE(data->instructions[i].landing_offset, 0);
      DCHECK_LT(data->instructions[i].landing_offset, data->size);
      DCHECK_GT(data->instructions[i].landing_offset,
                data->instructions[i].instr_offset);
    }
  }

  // Check the validity of the free list.
  size_t free_count = 0;
  for (size_t i = gNextCodeObject; i != gNumCodeObjects;
       i = gCodeObjects[i].next_free) {
    DCHECK_LT(i, gNumCodeObjects);
    ++free_count;
    // This check will fail if we encounter a cycle.
    DCHECK_LE(free_count, gNumCodeObjects);
  }

  // Check that all free entries are reachable via the free list.
  size_t free_count2 = 0;
  for (size_t i = 0; i < gNumCodeObjects; ++i) {
    if (gCodeObjects[i].code_info == nullptr) {
      ++free_count2;
    }
  }
  DCHECK_EQ(free_count, free_count2);
}
}  // namespace

eholk's avatar
eholk committed
113
CodeProtectionInfo* CreateHandlerData(
114
    Address base, size_t size, size_t num_protected_instructions,
115
    const ProtectedInstructionData* protected_instructions) {
eholk's avatar
eholk committed
116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133
  const size_t alloc_size = HandlerDataSize(num_protected_instructions);
  CodeProtectionInfo* data =
      reinterpret_cast<CodeProtectionInfo*>(malloc(alloc_size));

  if (data == nullptr) {
    return nullptr;
  }

  data->base = base;
  data->size = size;
  data->num_protected_instructions = num_protected_instructions;

  memcpy(data->instructions, protected_instructions,
         num_protected_instructions * sizeof(ProtectedInstructionData));

  return data;
}

134
int RegisterHandlerData(
135
    Address base, size_t size, size_t num_protected_instructions,
136
    const ProtectedInstructionData* protected_instructions) {
eholk's avatar
eholk committed
137 138 139 140 141 142 143 144 145 146 147
  // TODO(eholk): in debug builds, make sure this data isn't already registered.

  CodeProtectionInfo* data = CreateHandlerData(
      base, size, num_protected_instructions, protected_instructions);

  if (data == nullptr) {
    abort();
  }

  MetadataLock lock;

148 149 150 151
  if (kEnableDebug) {
    VerifyCodeRangeIsDisjoint(data);
  }

eholk's avatar
eholk committed
152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171
  size_t i = gNextCodeObject;

  // Explicitly convert std::numeric_limits<int>::max() to unsigned to avoid
  // compiler warnings about signed/unsigned comparisons. We aren't worried
  // about sign extension because we know std::numeric_limits<int>::max() is
  // positive.
  const size_t int_max = std::numeric_limits<int>::max();

  // We didn't find an opening in the available space, so grow.
  if (i == gNumCodeObjects) {
    size_t new_size = gNumCodeObjects > 0
                          ? gNumCodeObjects * kCodeObjectGrowthFactor
                          : kInitialCodeObjectSize;

    // Because we must return an int, there is no point in allocating space for
    // more objects than can fit in an int.
    if (new_size > int_max) {
      new_size = int_max;
    }
    if (new_size == gNumCodeObjects) {
172
      free(data);
173
      return kInvalidIndex;
eholk's avatar
eholk committed
174 175 176 177 178 179 180 181 182 183 184 185 186
    }

    // Now that we know our new size is valid, we can go ahead and realloc the
    // array.
    gCodeObjects = static_cast<CodeProtectionInfoListEntry*>(
        realloc(gCodeObjects, sizeof(*gCodeObjects) * new_size));

    if (gCodeObjects == nullptr) {
      abort();
    }

    memset(gCodeObjects + gNumCodeObjects, 0,
           sizeof(*gCodeObjects) * (new_size - gNumCodeObjects));
187 188 189
    for (size_t j = gNumCodeObjects; j < new_size; ++j) {
      gCodeObjects[j].next_free = j + 1;
    }
eholk's avatar
eholk committed
190 191 192 193 194 195
    gNumCodeObjects = new_size;
  }

  DCHECK(gCodeObjects[i].code_info == nullptr);

  // Find out where the next entry should go.
196
  gNextCodeObject = gCodeObjects[i].next_free;
eholk's avatar
eholk committed
197 198 199

  if (i <= int_max) {
    gCodeObjects[i].code_info = data;
200 201 202 203 204

    if (kEnableDebug) {
      ValidateCodeObjects();
    }

eholk's avatar
eholk committed
205 206
    return static_cast<int>(i);
  } else {
207
    free(data);
208
    return kInvalidIndex;
eholk's avatar
eholk committed
209 210 211 212
  }
}

void ReleaseHandlerData(int index) {
213 214 215 216 217
  if (index == kInvalidIndex) {
    return;
  }
  DCHECK_GE(index, 0);

eholk's avatar
eholk committed
218 219 220 221 222 223 224 225
  // Remove the data from the global list if it's there.
  CodeProtectionInfo* data = nullptr;
  {
    MetadataLock lock;

    data = gCodeObjects[index].code_info;
    gCodeObjects[index].code_info = nullptr;

226
    gCodeObjects[index].next_free = gNextCodeObject;
eholk's avatar
eholk committed
227
    gNextCodeObject = index;
228 229 230 231

    if (kEnableDebug) {
      ValidateCodeObjects();
    }
eholk's avatar
eholk committed
232 233 234
  }
  // TODO(eholk): on debug builds, ensure there are no more copies in
  // the list.
235
  DCHECK_NOT_NULL(data);  // make sure we're releasing legitimate handler data.
eholk's avatar
eholk committed
236 237 238
  free(data);
}

239 240 241 242
size_t GetRecoveredTrapCount() {
  return gRecoveredTrapCount.load(std::memory_order_relaxed);
}

243 244 245 246 247 248 249
#if !V8_TRAP_HANDLER_SUPPORTED
// This version is provided for systems that do not support trap handlers.
// Otherwise, the correct one should be implemented in the appropriate
// platform-specific handler-outside.cc.
bool RegisterDefaultTrapHandler() { return false; }
#endif

250 251 252 253 254 255 256
bool g_is_trap_handler_enabled;

bool EnableTrapHandler(bool use_v8_signal_handler) {
  if (!V8_TRAP_HANDLER_SUPPORTED) {
    return false;
  }
  if (use_v8_signal_handler) {
257
    g_is_trap_handler_enabled = RegisterDefaultTrapHandler();
258 259 260 261 262 263
    return g_is_trap_handler_enabled;
  }
  g_is_trap_handler_enabled = true;
  return true;
}

eholk's avatar
eholk committed
264 265 266
}  // namespace trap_handler
}  // namespace internal
}  // namespace v8