Adding the VerifyModule function (and helpers) to safe browsing.

chrome/browser/safe_browsing/module_integrity_verifier_win.cc

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/safe_browsing/module_integrity_verifier_win.h"
+
+#include "base/containers/hash_tables.h"
+#include "base/files/file_path.h"
+#include "base/files/memory_mapped_file.h"
+#include "base/metrics/histogram.h"
+#include "base/scoped_native_library.h"
+#include "base/win/pe_image.h"
+
+namespace safe_browsing {
+
+struct ModuleVerificationState {
+  explicit ModuleVerificationState(HMODULE hModule);
+  ~ModuleVerificationState();
+
+  base::win::PEImageAsData disk_peimage;
+
+  // The module's preferred base address minus the base address it actually
+  // loaded at.
+  intptr_t image_base_delta;
+
+  // The location of the disk_peimage module's code section minus that of the
+  // mem_peimage module's code section.
+  intptr_t code_section_delta;
+
+  // The bytes corrected by relocs.
+  base::hash_set<uintptr_t> reloc_addr;
+
+  // Set true if the relocation table contains a reloc of type that we don't
+  // currently handle.
+  bool unknown_reloc_type;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ModuleVerificationState);
+};
+
+ModuleVerificationState::ModuleVerificationState(HMODULE hModule)
+    : disk_peimage(hModule),
+      image_base_delta(0),
+      code_section_delta(0),
+      reloc_addr(),
+      unknown_reloc_type(false) {
+}
+
+ModuleVerificationState::~ModuleVerificationState() {
+}
+
+namespace {
+
+struct Export {
+  Export(void* addr, const std::string& name);
+  ~Export();
+
+  bool operator<(const Export& other) const;
+
+  void* addr;
+  std::string name;
+};
+
+Export::Export(void* addr, const std::string& name) : addr(addr), name(name) {
+}
+
+Export::~Export() {
+}
+
+bool Export::operator<(const Export& other) const {
+  return addr < other.addr;
+}
+
+bool ByteAccountedForByReloc(uint8_t* byte_addr,
+                             ModuleVerificationState* state) {
+  return ((state->reloc_addr.count(reinterpret_cast<uintptr_t>(byte_addr))) >
+          0);
+}
+
+// Checks each byte in the module's code section again the corresponding byte on
+// disk.  The list |exports| must be sorted.  Returns a list of

[grt (UTC plus 2), 2014/08/06 15:07:08]

similarly, "the list |exports|" could be simply "|exports| must be sorted" since
it isn't a list.

[grt (UTC plus 2), 2014/08/06 15:07:08]

comment nitpick: consider something like "Adds the names of functions exported
by name to |modified_exports|." since it isn't a list and it isn't returned from
the function.

[grt (UTC plus 2), 2014/08/06 15:07:08]

"...on disk, returning the number of bytes differing between the two."

[krstnmnlsn, 2014/08/06 18:19:07]

Triple Done

+// the functions who may have been modified.
+int ExamineBytesDiffInMemory(uint8_t* disk_code_start,
+                             uint8_t* mem_code_start,
+                             uint32_t code_size,
+                             const std::vector<Export>& exports,
+                             ModuleVerificationState* state,

[grt (UTC plus 2), 2014/08/06 15:07:08]

const ModuleVerificationState& state here and in ByteAccountedForByReloc.

[krstnmnlsn, 2014/08/06 18:19:07]

Done.

+                             std::set<std::string>* modified_exports) {
+  int bytes_different = 0;
+  std::vector<Export>::const_iterator export_it = exports.begin();
+
+  for (uint8_t* end = mem_code_start + code_size; mem_code_start != end;
+       ++mem_code_start) {
+    if ((*disk_code_start++ != *mem_code_start) &&
+        !ByteAccountedForByReloc(mem_code_start, state)) {
+      // We get the largest export address still smaller than |addr|.  It is
+      // possible that |addr| belongs to some nonexported function located
+      // between this export and the following one.
+      Export addr(reinterpret_cast<void*>(mem_code_start), std::string());
+      std::vector<Export>::const_iterator modified_export_it =
+          std::upper_bound(export_it, exports.end(), addr);
+
+      if (modified_export_it != exports.begin())
+        modified_exports->insert((modified_export_it - 1)->name);
+      ++bytes_different;
+
+      // No later byte can belong to an earlier export.
+      export_it = modified_export_it;
+    }
+  }
+  return bytes_different;
+}
+
+// Adds to |state->reloc_addr| the bytes of the pointer at |address| that are
+// corrected by adding |image_base_delta|.
+void AddBytesCorrectedByReloc(uintptr_t address,
+                              ModuleVerificationState* state) {
+#if __BYTE_ORDER == __LITTLE_ENDIAN

[grt (UTC plus 2), 2014/08/06 15:07:08]

awesome. i think it's better to use the chromium macro for this, though:
#include "base/build_config.h"

#if defined(ARCH_CPU_LITTLE_ENDIAN)
...
#else
...
#endif

[krstnmnlsn, 2014/08/06 18:19:07]

Done.

+#  define OFFSET(i) i
+#elif __BYTE_ORDER == __BIG_ENDIAN
+#  define OFFSET(i) (sizeof(uintptr_t) - i)
+#endif
+
+  uintptr_t orig_mem_value = *reinterpret_cast<uintptr_t*>(address);
+  uintptr_t fixed_mem_value = orig_mem_value + state->image_base_delta;
+  uintptr_t disk_value =
+      *reinterpret_cast<uintptr_t*>(address + state->code_section_delta);
+
+  uintptr_t diff_before = orig_mem_value ^ disk_value;
+  uintptr_t shared_after = ~(fixed_mem_value ^ disk_value);
+  int i = 0;
+  for (uintptr_t fixed = diff_before & shared_after; fixed; fixed >>= 8, ++i) {
+    if (fixed & 0xFF)
+      state->reloc_addr.insert(address + OFFSET(i));
+  }
+#undef OFFSET
+}
+
+bool AddrIsInCodeSection(void* address,
+                         uint8_t* code_addr,
+                         uint32_t code_size) {
+  return (code_addr <= address && address < code_addr + code_size);
+}
+
+bool EnumRelocsCallback(const base::win::PEImage& mem_peimage,
+                        WORD type,
+                        void* address,
+                        void* cookie) {
+  ModuleVerificationState* state =
+      reinterpret_cast<ModuleVerificationState*>(cookie);
+
+  uint8_t* mem_code_addr = NULL;
+  uint8_t* disk_code_addr = NULL;
+  uint32_t code_size = 0;
+  if (!GetCodeAddrsAndSize(mem_peimage,
+                           state->disk_peimage,
+                           &mem_code_addr,
+                           &disk_code_addr,
+                           &code_size))
+    return false;
+
+  // If not in the code section return true to continue to the next reloc.
+  if (!AddrIsInCodeSection(address, mem_code_addr, code_size))
+    return true;
+
+  UMA_HISTOGRAM_ENUMERATION(
+      "SafeBrowsing.ModuleBaseRelocation", type, IMAGE_REL_BASED_DIR64 + 1);
+
+  switch (type) {
+    case IMAGE_REL_BASED_HIGHLOW: {
+      AddBytesCorrectedByReloc(reinterpret_cast<uintptr_t>(address), state);
+      break;
+    }
+    case IMAGE_REL_BASED_ABSOLUTE:
+      // Absolute type relocations are a noop, sometimes used to pad a section
+      // of relocations.
+      break;
+    default: {
+      // TODO(krstnmnlsn): Find a reliable description of the behaviour of the
+      // remaining types of relocation and handle them.
+      state->unknown_reloc_type = true;
+      break;
+    }
+  }
+  return true;
+}
+
+bool EnumExportsCallback(const base::win::PEImage& mem_peimage,
+                         DWORD ordinal,
+                         DWORD hint,
+                         LPCSTR name,
+                         PVOID function_addr,
+                         LPCSTR forward,
+                         PVOID cookie) {
+  std::vector<Export>* exports = reinterpret_cast<std::vector<Export>*>(cookie);
+  if (name)
+    exports->push_back(Export(function_addr, std::string(name)));
+  return true;
+}
+
+}  // namespace
+
+bool GetCodeAddrsAndSize(const base::win::PEImage& mem_peimage,
+                         const base::win::PEImageAsData& disk_peimage,
+                         uint8_t** mem_code_addr,
+                         uint8_t** disk_code_addr,
+                         uint32_t* code_size) {
+  DWORD base_of_code = mem_peimage.GetNTHeaders()->OptionalHeader.BaseOfCode;
+
+  // Get the address and size of the code section in the loaded module image.
+  PIMAGE_SECTION_HEADER mem_code_header =
+      mem_peimage.GetImageSectionFromAddr(mem_peimage.RVAToAddr(base_of_code));
+  if (mem_code_header == NULL)
+    return false;
+  *mem_code_addr = reinterpret_cast<uint8_t*>(
+      mem_peimage.RVAToAddr(mem_code_header->VirtualAddress));
+  // If the section is padded with zeros when mapped then |VirtualSize| can be
+  // larger.  Alternatively, |SizeOfRawData| can be rounded up to align
+  // according to OptionalHeader.FileAlignment.
+  *code_size = std::min(mem_code_header->Misc.VirtualSize,
+                        mem_code_header->SizeOfRawData);
+
+  // Get the address of the code section in the module mapped as data from disk.
+  DWORD disk_code_offset = 0;
+  if (!mem_peimage.ImageAddrToOnDiskOffset(
+          reinterpret_cast<void*>(*mem_code_addr), &disk_code_offset))
+    return false;
+  *disk_code_addr =
+      reinterpret_cast<uint8_t*>(disk_peimage.module()) + disk_code_offset;
+  return true;
+}
+
+ModuleState VerifyModule(const wchar_t* module_name,
+                         std::set<std::string>* modified_exports) {
+  // Get module handle, load a copy from disk as data and create PEImages.
+  HMODULE module_handle = NULL;
+  if (!GetModuleHandleEx(0, module_name, &module_handle))
+    return MODULE_STATE_UNKNOWN;
+  base::ScopedNativeLibrary native_library(module_handle);
+
+  WCHAR module_path[MAX_PATH] = {};
+  DWORD length =
+      GetModuleFileName(module_handle, module_path, arraysize(module_path));
+  if (!length || length == arraysize(module_path))
+    return MODULE_STATE_UNKNOWN;
+
+  base::MemoryMappedFile mapped_module;
+  if (!mapped_module.Initialize(base::FilePath(module_path)))
+    return MODULE_STATE_UNKNOWN;
+  ModuleVerificationState state(
+      reinterpret_cast<HMODULE>(const_cast<uint8*>(mapped_module.data())));
+
+  base::win::PEImage mem_peimage(module_handle);
+  if (!mem_peimage.VerifyMagic() || !state.disk_peimage.VerifyMagic())
+    return MODULE_STATE_UNKNOWN;
+
+  // Get the list of exports.
+  std::vector<Export> exports;
+  mem_peimage.EnumExports(EnumExportsCallback, &exports);
+  std::sort(exports.begin(), exports.end());
+
+  // Get the addresses of the code sections then calculate |code_section_delta|
+  // and |image_base_delta|.
+  uint8_t* mem_code_addr = NULL;
+  uint8_t* disk_code_addr = NULL;
+  uint32_t code_size = 0;
+  if (!GetCodeAddrsAndSize(mem_peimage,
+                           state.disk_peimage,
+                           &mem_code_addr,
+                           &disk_code_addr,
+                           &code_size))
+    return MODULE_STATE_UNKNOWN;
+
+  state.code_section_delta = disk_code_addr - mem_code_addr;
+
+  uint8_t* preferred_image_base = reinterpret_cast<uint8_t*>(
+      state.disk_peimage.GetNTHeaders()->OptionalHeader.ImageBase);
+  state.image_base_delta =
+      preferred_image_base - reinterpret_cast<uint8_t*>(mem_peimage.module());
+
+  // Get the relocations.
+  mem_peimage.EnumRelocs(EnumRelocsCallback, &state);
+  if (state.unknown_reloc_type)
+    return MODULE_STATE_UNKNOWN;
+
+  // Count the modified bytes (after accounting for relocs) and get the set of
+  // modified functions.
+  int num_bytes_different = ExamineBytesDiffInMemory(disk_code_addr,
+                                                     mem_code_addr,
+                                                     code_size,
+                                                     exports,
+                                                     &state,
+                                                     modified_exports);
+
+  return num_bytes_different ? MODULE_STATE_MODIFIED : MODULE_STATE_UNMODIFIED;
+}
+
+}  // namespace safe_browsing