common/linux/file_id.cc

// Copyright (c) 2006, 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.
//
// file_id.cc: Return a unique identifier for a file
//
// See file_id.h for documentation
//

#include "common/linux/file_id.h"

#include <arpa/inet.h>
#include <assert.h>
#include <string.h>

#include <algorithm>
#include <string>

#include "common/linux/elf_gnu_compat.h"
#include "common/linux/elfutils.h"
#include "common/linux/linux_libc_support.h"
#include "common/linux/memory_mapped_file.h"
#include "common/using_std_string.h"
#include "third_party/lss/linux_syscall_support.h"

namespace google_breakpad {

// Used in a few places for backwards-compatibility.
const size_t kMDGUIDSize = sizeof(MDGUID);

FileID::FileID(const char* path) : path_(path) {}

// ELF note name and desc are 32-bits word padded.
#define NOTE_PADDING(a) ((a + 3) & ~3)

// These functions are also used inside the crashed process, so be safe
// and use the syscall/libc wrappers instead of direct syscalls or libc.

static bool ElfClassBuildIDNoteIdentifier(const void *section, size_t length,
                                          wasteful_vector<uint8_t>& identifier) {
  static_assert(sizeof(ElfClass32::Nhdr) == sizeof(ElfClass64::Nhdr),
                "Elf32_Nhdr and Elf64_Nhdr should be the same");
  typedef typename ElfClass32::Nhdr Nhdr;

  const void* section_end = reinterpret_cast<const char*>(section) + length;
  const Nhdr* note_header = reinterpret_cast<const Nhdr*>(section);
  while (reinterpret_cast<const void *>(note_header) < section_end) {
    if (note_header->n_type == NT_GNU_BUILD_ID)
      break;
    note_header = reinterpret_cast<const Nhdr*>(
                  reinterpret_cast<const char*>(note_header) + sizeof(Nhdr) +
                  NOTE_PADDING(note_header->n_namesz) +
                  NOTE_PADDING(note_header->n_descsz));
  }
  if (reinterpret_cast<const void *>(note_header) >= section_end ||
      note_header->n_descsz == 0) {
    return false;
  }

  const uint8_t* build_id = reinterpret_cast<const uint8_t*>(note_header) +
    sizeof(Nhdr) + NOTE_PADDING(note_header->n_namesz);
  identifier.insert(identifier.end(),
                    build_id,
                    build_id + note_header->n_descsz);

  return true;
}

// Attempt to locate a .note.gnu.build-id section in an ELF binary
// and copy it into |identifier|.
static bool FindElfBuildIDNote(const void* elf_mapped_base,
                               wasteful_vector<uint8_t>& identifier) {
  PageAllocator allocator;
  // lld normally creates 2 PT_NOTEs, gold normally creates 1.
  auto_wasteful_vector<ElfSegment, 2> segs(&allocator);
  if (FindElfSegments(elf_mapped_base, PT_NOTE, &segs)) {
    for (ElfSegment& seg : segs) {
      if (ElfClassBuildIDNoteIdentifier(seg.start, seg.size, identifier)) {
        return true;
      }
    }
  }

  void* note_section;
  size_t note_size;
  if (FindElfSection(elf_mapped_base, ".note.gnu.build-id", SHT_NOTE,
                     (const void**)&note_section, &note_size)) {
    return ElfClassBuildIDNoteIdentifier(note_section, note_size, identifier);
  }

  return false;
}

// Attempt to locate the .text section of an ELF binary and generate
// a simple hash by XORing the first page worth of bytes into |identifier|.
static bool HashElfTextSection(const void* elf_mapped_base,
                               wasteful_vector<uint8_t>& identifier) {
  identifier.resize(kMDGUIDSize);

  void* text_section;
  size_t text_size;
  if (!FindElfSection(elf_mapped_base, ".text", SHT_PROGBITS,
                      (const void**)&text_section, &text_size) ||
      text_size == 0) {
    return false;
  }

  // Only provide |kMDGUIDSize| bytes to keep identifiers produced by this
  // function backwards-compatible.
  my_memset(&identifier[0], 0, kMDGUIDSize);
  const uint8_t* ptr = reinterpret_cast<const uint8_t*>(text_section);
  const uint8_t* ptr_end = ptr + std::min(text_size, static_cast<size_t>(4096));
  while (ptr < ptr_end) {
    for (unsigned i = 0; i < kMDGUIDSize; i++)
      identifier[i] ^= ptr[i];
    ptr += kMDGUIDSize;
  }
  return true;
}

// static
bool FileID::ElfFileIdentifierFromMappedFile(const void* base,
                                             wasteful_vector<uint8_t>& identifier) {
  // Look for a build id note first.
  if (FindElfBuildIDNote(base, identifier))
    return true;

  // Fall back on hashing the first page of the text section.
  return HashElfTextSection(base, identifier);
}

bool FileID::ElfFileIdentifier(wasteful_vector<uint8_t>& identifier) {
  MemoryMappedFile mapped_file(path_.c_str(), 0);
  if (!mapped_file.data())  // Should probably check if size >= ElfW(Ehdr)?
    return false;

  return ElfFileIdentifierFromMappedFile(mapped_file.data(), identifier);
}

// These three functions are not ever called in an unsafe context, so it's OK
// to allocate memory and use libc.
static string bytes_to_hex_string(const uint8_t* bytes, size_t count) {
  string result;
  for (unsigned int idx = 0; idx < count; ++idx) {
    char buf[3];
    snprintf(buf, sizeof(buf), "%02X", bytes[idx]);
    result.append(buf);
  }
  return result;
}

// static
string FileID::ConvertIdentifierToUUIDString(
    const wasteful_vector<uint8_t>& identifier) {
  uint8_t identifier_swapped[kMDGUIDSize] = { 0 };

  // Endian-ness swap to match dump processor expectation.
  memcpy(identifier_swapped, &identifier[0],
         std::min(kMDGUIDSize, identifier.size()));
  uint32_t* data1 = reinterpret_cast<uint32_t*>(identifier_swapped);
  *data1 = htonl(*data1);
  uint16_t* data2 = reinterpret_cast<uint16_t*>(identifier_swapped + 4);
  *data2 = htons(*data2);
  uint16_t* data3 = reinterpret_cast<uint16_t*>(identifier_swapped + 6);
  *data3 = htons(*data3);

  return bytes_to_hex_string(identifier_swapped, kMDGUIDSize);
}

// static
string FileID::ConvertIdentifierToString(
    const wasteful_vector<uint8_t>& identifier) {
  return bytes_to_hex_string(&identifier[0], identifier.size());
}

}  // namespace google_breakpad