unix/elfhack/elfxx.h

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include <stdexcept>
#include <list>
#include <vector>
#include <cstring>
#include <iostream>
#include <fstream>
#include <algorithm>
#include <elf.h>
#include <asm/byteorder.h>

// Technically, __*_to_cpu and __cpu_to* function are equivalent,
// so swap can use either of both.
#define def_swap(endian, type, bits)                    \
  static inline type##bits##_t swap(type##bits##_t i) { \
    return __##endian##bits##_to_cpu(i);                \
  }

class little_endian {
 public:
  def_swap(le, uint, 16);
  def_swap(le, uint, 32);
  def_swap(le, uint, 64);
  def_swap(le, int, 16);
  def_swap(le, int, 32);
  def_swap(le, int, 64);
};

class big_endian {
 public:
  def_swap(be, uint, 16);
  def_swap(be, uint, 32);
  def_swap(be, uint, 64);
  def_swap(be, int, 16);
  def_swap(be, int, 32);
  def_swap(be, int, 64);
};

// forward declaration
class ElfSection;
class ElfSegment;
// TODO: Rename Elf_* types
class Elf_Ehdr;
class Elf_Phdr;
class Elf;
class ElfDynamic_Section;
class ElfStrtab_Section;

template <typename X>
class FixedSizeData {
 public:
  struct Wrapper {
    X value;
  };
  typedef Wrapper Type32;
  typedef Wrapper Type64;

  template <class endian, typename R, typename T>
  static void swap(T& t, R& r) {
    r.value = endian::swap(t.value);
  }
};

class Elf_Ehdr_Traits {
 public:
  typedef Elf32_Ehdr Type32;
  typedef Elf64_Ehdr Type64;

  template <class endian, typename R, typename T>
  static void swap(T& t, R& r);
};

class Elf_Phdr_Traits {
 public:
  typedef Elf32_Phdr Type32;
  typedef Elf64_Phdr Type64;

  template <class endian, typename R, typename T>
  static void swap(T& t, R& r);
};

class Elf_Shdr_Traits {
 public:
  typedef Elf32_Shdr Type32;
  typedef Elf64_Shdr Type64;

  template <class endian, typename R, typename T>
  static void swap(T& t, R& r);
};

class Elf_Dyn_Traits {
 public:
  typedef Elf32_Dyn Type32;
  typedef Elf64_Dyn Type64;

  template <class endian, typename R, typename T>
  static void swap(T& t, R& r);
};

class Elf_Sym_Traits {
 public:
  typedef Elf32_Sym Type32;
  typedef Elf64_Sym Type64;

  template <class endian, typename R, typename T>
  static void swap(T& t, R& r);
};

class Elf_Rel_Traits {
 public:
  typedef Elf32_Rel Type32;
  typedef Elf64_Rel Type64;

  template <class endian, typename R, typename T>
  static void swap(T& t, R& r);
};

class Elf_Rela_Traits {
 public:
  typedef Elf32_Rela Type32;
  typedef Elf64_Rela Type64;

  template <class endian, typename R, typename T>
  static void swap(T& t, R& r);
};

class ElfValue {
 public:
  virtual unsigned int getValue() { return 0; }
  virtual ElfSection* getSection() { return nullptr; }
};

class ElfPlainValue : public ElfValue {
  unsigned int value;

 public:
  ElfPlainValue(unsigned int val) : value(val){};
  unsigned int getValue() { return value; }
};

class ElfLocation : public ElfValue {
  ElfSection* section;
  unsigned int offset;

 public:
  enum position { ABSOLUTE, RELATIVE };
  ElfLocation() : section(nullptr), offset(0){};
  ElfLocation(ElfSection* section, unsigned int off,
              enum position pos = RELATIVE);
  ElfLocation(unsigned int location, Elf* elf);
  unsigned int getValue();
  ElfSection* getSection() { return section; }
  const char* getBuffer();
};

class ElfSize : public ElfValue {
  ElfSection* section;

 public:
  ElfSize(ElfSection* s) : section(s){};
  unsigned int getValue();
  ElfSection* getSection() { return section; }
};

class ElfEntSize : public ElfValue {
  ElfSection* section;

 public:
  ElfEntSize(ElfSection* s) : section(s){};
  unsigned int getValue();
  ElfSection* getSection() { return section; }
};

template <typename T>
class serializable : public T::Type32 {
 public:
  serializable(){};
  serializable(const typename T::Type32& p) : T::Type32(p){};

 private:
  template <typename R>
  void init(const char* buf, size_t len, char ei_data) {
    R e;
    assert(len >= sizeof(e));
    memcpy(&e, buf, sizeof(e));
    if (ei_data == ELFDATA2LSB) {
      T::template swap<little_endian>(e, *this);
      return;
    } else if (ei_data == ELFDATA2MSB) {
      T::template swap<big_endian>(e, *this);
      return;
    }
    throw std::runtime_error("Unsupported ELF data encoding");
  }

  template <typename R>
  void serialize(const char* buf, size_t len, char ei_data) {
    assert(len >= sizeof(R));
    if (ei_data == ELFDATA2LSB) {
      T::template swap<little_endian>(*this, *(R*)buf);
      return;
    } else if (ei_data == ELFDATA2MSB) {
      T::template swap<big_endian>(*this, *(R*)buf);
      return;
    }
    throw std::runtime_error("Unsupported ELF data encoding");
  }

 public:
  serializable(const char* buf, size_t len, char ei_class, char ei_data) {
    if (ei_class == ELFCLASS32) {
      init<typename T::Type32>(buf, len, ei_data);
      return;
    } else if (ei_class == ELFCLASS64) {
      init<typename T::Type64>(buf, len, ei_data);
      return;
    }
    throw std::runtime_error("Unsupported ELF class");
  }

  serializable(std::ifstream& file, char ei_class, char ei_data) {
    if (ei_class == ELFCLASS32) {
      typename T::Type32 e;
      file.read((char*)&e, sizeof(e));
      init<typename T::Type32>((char*)&e, sizeof(e), ei_data);
      return;
    } else if (ei_class == ELFCLASS64) {
      typename T::Type64 e;
      file.read((char*)&e, sizeof(e));
      init<typename T::Type64>((char*)&e, sizeof(e), ei_data);
      return;
    }
    throw std::runtime_error("Unsupported ELF class or data encoding");
  }

  void serialize(std::ofstream& file, char ei_class, char ei_data) {
    if (ei_class == ELFCLASS32) {
      typename T::Type32 e;
      serialize<typename T::Type32>((char*)&e, sizeof(e), ei_data);
      file.write((char*)&e, sizeof(e));
      return;
    } else if (ei_class == ELFCLASS64) {
      typename T::Type64 e;
      serialize<typename T::Type64>((char*)&e, sizeof(e), ei_data);
      file.write((char*)&e, sizeof(e));
      return;
    }
    throw std::runtime_error("Unsupported ELF class or data encoding");
  }

  void serialize(char* buf, size_t len, char ei_class, char ei_data) {
    if (ei_class == ELFCLASS32) {
      serialize<typename T::Type32>(buf, len, ei_data);
      return;
    } else if (ei_class == ELFCLASS64) {
      serialize<typename T::Type64>(buf, len, ei_data);
      return;
    }
    throw std::runtime_error("Unsupported ELF class");
  }

  static inline unsigned int size(char ei_class) {
    if (ei_class == ELFCLASS32)
      return sizeof(typename T::Type32);
    else if (ei_class == ELFCLASS64)
      return sizeof(typename T::Type64);
    return 0;
  }
};

typedef serializable<Elf_Shdr_Traits> Elf_Shdr;

class Elf {
 public:
  Elf(std::ifstream& file);
  ~Elf();

  /* index == -1 is treated as index == ehdr.e_shstrndx */
  ElfSection* getSection(int index);

  ElfSection* getSectionAt(unsigned int offset);

  ElfSegment* getSegmentByType(unsigned int type, ElfSegment* last = nullptr);

  ElfDynamic_Section* getDynSection();

  void normalize();
  void write(std::ofstream& file);

  char getClass();
  char getData();
  char getType();
  char getMachine();
  unsigned int getSize();

  void insertSegmentAfter(ElfSegment* previous, ElfSegment* segment) {
    std::vector<ElfSegment*>::iterator prev =
        std::find(segments.begin(), segments.end(), previous);
    segments.insert(prev + 1, segment);
  }

  void removeSegment(ElfSegment* segment);

 private:
  Elf_Ehdr* ehdr;
  ElfLocation eh_entry;
  ElfStrtab_Section* eh_shstrndx;
  ElfSection** sections;
  std::vector<ElfSegment*> segments;
  ElfSection *shdr_section, *phdr_section;
  /* Values used only during initialization */
  Elf_Shdr** tmp_shdr;
  std::ifstream* tmp_file;
};

class ElfSection {
 public:
  typedef union {
    ElfSection* section;
    int index;
  } SectionInfo;

  ElfSection(Elf_Shdr& s, std::ifstream* file, Elf* parent);

  virtual ~ElfSection() { free(data); }

  const char* getName() { return name; }
  unsigned int getType() { return shdr.sh_type; }
  unsigned int getFlags() { return shdr.sh_flags; }
  unsigned int getAddr();
  unsigned int getSize() { return shdr.sh_size; }
  unsigned int getAddrAlign() { return shdr.sh_addralign; }
  unsigned int getEntSize() { return shdr.sh_entsize; }
  const char* getData() { return data; }
  ElfSection* getLink() { return link; }
  SectionInfo getInfo() { return info; }

  void shrink(unsigned int newsize) {
    if (newsize < shdr.sh_size) {
      shdr.sh_size = newsize;
      markDirty();
    }
  }

  void grow(unsigned int newsize) {
    if (newsize > shdr.sh_size) {
      data = static_cast<char*>(realloc(data, newsize));
      memset(data + shdr.sh_size, 0, newsize - shdr.sh_size);
      shdr.sh_size = newsize;
      markDirty();
    }
  }

  unsigned int getOffset();
  int getIndex();
  Elf_Shdr& getShdr();

  ElfSection* getNext() { return next; }
  ElfSection* getPrevious() { return previous; }

  virtual bool isRelocatable() {
    return ((getType() == SHT_SYMTAB) || (getType() == SHT_STRTAB) ||
            (getType() == SHT_RELA) || (getType() == SHT_HASH) ||
            (getType() == SHT_NOTE) || (getType() == SHT_REL) ||
            (getType() == SHT_DYNSYM) || (getType() == SHT_GNU_HASH) ||
            (getType() == SHT_GNU_verdef) || (getType() == SHT_GNU_verneed) ||
            (getType() == SHT_GNU_versym) || getSegmentByType(PT_INTERP)) &&
           (getFlags() & SHF_ALLOC);
  }

  void insertAfter(ElfSection* section, bool dirty = true) {
    if (previous != nullptr) previous->next = next;
    if (next != nullptr) next->previous = previous;
    previous = section;
    if (section != nullptr) {
      next = section->next;
      section->next = this;
    } else
      next = nullptr;
    if (next != nullptr) next->previous = this;
    if (dirty) markDirty();
    insertInSegments(section->segments);
  }

  virtual void insertBefore(ElfSection* section, bool dirty = true) {
    if (previous != nullptr) previous->next = next;
    if (next != nullptr) next->previous = previous;
    next = section;
    if (section != nullptr) {
      previous = section->previous;
      section->previous = this;
    } else
      previous = nullptr;
    if (previous != nullptr) previous->next = this;
    if (dirty) markDirty();
    insertInSegments(section->segments);
  }

  void markDirty() {
    if (link != nullptr) shdr.sh_link = -1;
    if (info.index) shdr.sh_info = -1;
    shdr.sh_offset = -1;
    if (isRelocatable()) shdr.sh_addr = -1;
    if (next) next->markDirty();
  }

  virtual void serialize(std::ofstream& file, char ei_class, char ei_data) {
    if (getType() == SHT_NOBITS) return;
    file.seekp(getOffset());
    file.write(data, getSize());
  }

  ElfSegment* getSegmentByType(unsigned int type);

 private:
  friend class ElfSegment;

  void addToSegment(ElfSegment* segment) { segments.push_back(segment); }

  void removeFromSegment(ElfSegment* segment) {
    std::vector<ElfSegment*>::iterator i =
        std::find(segments.begin(), segments.end(), segment);
    segments.erase(i, i + 1);
  }

  void insertInSegments(std::vector<ElfSegment*>& segs);

 protected:
  Elf_Shdr shdr;
  char* data;
  const char* name;

 private:
  ElfSection* link;
  SectionInfo info;
  ElfSection *next, *previous;
  int index;
  std::vector<ElfSegment*> segments;
};

class ElfSegment {
 public:
  ElfSegment(Elf_Phdr* phdr);

  unsigned int getType() { return type; }
  unsigned int getFlags() { return flags; }
  unsigned int getAlign() { return align; }

  ElfSection* getFirstSection() {
    return sections.empty() ? nullptr : sections.front();
  }
  int getVPDiff() { return v_p_diff; }
  unsigned int getFileSize();
  unsigned int getMemSize();
  unsigned int getOffset();
  unsigned int getAddr();

  void addSection(ElfSection* section);
  void removeSection(ElfSection* section);

  std::list<ElfSection*>::iterator begin() { return sections.begin(); }
  std::list<ElfSection*>::iterator end() { return sections.end(); }

  void clear();

 private:
  unsigned int type;
  int v_p_diff;  // Difference between physical and virtual address
  unsigned int flags;
  unsigned int align;
  std::list<ElfSection*> sections;
  // The following are only really used for PT_GNU_RELRO until something
  // better is found.
  unsigned int vaddr;
  unsigned int filesz, memsz;
};

class Elf_Ehdr : public serializable<Elf_Ehdr_Traits>, public ElfSection {
 public:
  Elf_Ehdr(std::ifstream& file, char ei_class, char ei_data);
  void serialize(std::ofstream& file, char ei_class, char ei_data) {
    serializable<Elf_Ehdr_Traits>::serialize(file, ei_class, ei_data);
  }
};

class Elf_Phdr : public serializable<Elf_Phdr_Traits> {
 public:
  Elf_Phdr(){};
  Elf_Phdr(std::ifstream& file, char ei_class, char ei_data)
      : serializable<Elf_Phdr_Traits>(file, ei_class, ei_data){};
  bool contains(ElfSection* section) {
    unsigned int size = section->getSize();
    unsigned int addr = section->getAddr();
    // This may be biased, but should work in most cases
    if ((section->getFlags() & SHF_ALLOC) == 0) return false;
    // Special case for PT_DYNAMIC. Eventually, this should
    // be better handled than special cases
    if ((p_type == PT_DYNAMIC) && (section->getType() != SHT_DYNAMIC))
      return false;
    // Special case for PT_TLS.
    if ((p_type == PT_TLS) && !(section->getFlags() & SHF_TLS)) return false;
    return (addr >= p_vaddr) && (addr + size <= p_vaddr + p_memsz);
  }
};

typedef serializable<Elf_Dyn_Traits> Elf_Dyn;

struct Elf_DynValue {
  unsigned int tag;
  ElfValue* value;
};

class ElfDynamic_Section : public ElfSection {
 public:
  ElfDynamic_Section(Elf_Shdr& s, std::ifstream* file, Elf* parent);
  ~ElfDynamic_Section();

  void serialize(std::ofstream& file, char ei_class, char ei_data);

  ElfValue* getValueForType(unsigned int tag);
  ElfSection* getSectionForType(unsigned int tag);
  bool setValueForType(unsigned int tag, ElfValue* val);

 private:
  std::vector<Elf_DynValue> dyns;
};

typedef serializable<Elf_Sym_Traits> Elf_Sym;

struct Elf_SymValue {
  const char* name;
  unsigned char info;
  unsigned char other;
  ElfLocation value;
  unsigned int size;
  bool defined;
};

#define STT(type) (1 << STT_##type)

class ElfSymtab_Section : public ElfSection {
 public:
  ElfSymtab_Section(Elf_Shdr& s, std::ifstream* file, Elf* parent);

  void serialize(std::ofstream& file, char ei_class, char ei_data);

  Elf_SymValue* lookup(const char* name,
                       unsigned int type_filter = STT(OBJECT) | STT(FUNC));

  // private: // Until we have a real API
  std::vector<Elf_SymValue> syms;
};

class Elf_Rel : public serializable<Elf_Rel_Traits> {
 public:
  Elf_Rel() : serializable<Elf_Rel_Traits>(){};

  Elf_Rel(std::ifstream& file, char ei_class, char ei_data)
      : serializable<Elf_Rel_Traits>(file, ei_class, ei_data){};

  static const unsigned int sh_type = SHT_REL;
  static const unsigned int d_tag = DT_REL;
  static const unsigned int d_tag_count = DT_RELCOUNT;
};

class Elf_Rela : public serializable<Elf_Rela_Traits> {
 public:
  Elf_Rela() : serializable<Elf_Rela_Traits>(){};

  Elf_Rela(std::ifstream& file, char ei_class, char ei_data)
      : serializable<Elf_Rela_Traits>(file, ei_class, ei_data){};

  static const unsigned int sh_type = SHT_RELA;
  static const unsigned int d_tag = DT_RELA;
  static const unsigned int d_tag_count = DT_RELACOUNT;
};

template <class Rel>
class ElfRel_Section : public ElfSection {
 public:
  ElfRel_Section(Elf_Shdr& s, std::ifstream* file, Elf* parent)
      : ElfSection(s, file, parent) {
    auto pos = file->tellg();
    file->seekg(shdr.sh_offset);
    for (unsigned int i = 0; i < s.sh_size / s.sh_entsize; i++) {
      Rel r(*file, parent->getClass(), parent->getData());
      rels.push_back(r);
    }
    file->seekg(pos);
  }

  void serialize(std::ofstream& file, char ei_class, char ei_data) {
    for (typename std::vector<Rel>::iterator i = rels.begin(); i != rels.end();
         ++i)
      (*i).serialize(file, ei_class, ei_data);
  }
  // private: // Until we have a real API
  std::vector<Rel> rels;
};

class ElfStrtab_Section : public ElfSection {
 public:
  ElfStrtab_Section(Elf_Shdr& s, std::ifstream* file, Elf* parent)
      : ElfSection(s, file, parent) {
    table.push_back(table_storage(data, shdr.sh_size));
  }

  ~ElfStrtab_Section() {
    for (std::vector<table_storage>::iterator t = table.begin() + 1;
         t != table.end(); ++t)
      delete[] t->buf;
  }

  const char* getStr(unsigned int index);

  const char* getStr(const char* string);

  unsigned int getStrIndex(const char* string);

  void serialize(std::ofstream& file, char ei_class, char ei_data);

 private:
  struct table_storage {
    unsigned int size, used;
    char* buf;

    table_storage() : size(4096), used(0), buf(new char[4096]) {}
    table_storage(const char* data, unsigned int sz)
        : size(sz), used(sz), buf(const_cast<char*>(data)) {}
  };
  std::vector<table_storage> table;
};

inline char Elf::getClass() { return ehdr->e_ident[EI_CLASS]; }

inline char Elf::getData() { return ehdr->e_ident[EI_DATA]; }

inline char Elf::getType() { return ehdr->e_type; }

inline char Elf::getMachine() { return ehdr->e_machine; }

inline unsigned int Elf::getSize() {
  ElfSection* section;
  for (section = shdr_section /* It's usually not far from the end */;
       section->getNext() != nullptr; section = section->getNext())
    ;
  return section->getOffset() + section->getSize();
}

inline ElfSegment* ElfSection::getSegmentByType(unsigned int type) {
  for (std::vector<ElfSegment*>::iterator seg = segments.begin();
       seg != segments.end(); ++seg)
    if ((*seg)->getType() == type) return *seg;
  return nullptr;
}

inline void ElfSection::insertInSegments(std::vector<ElfSegment*>& segs) {
  for (std::vector<ElfSegment*>::iterator it = segs.begin(); it != segs.end();
       ++it) {
    (*it)->addSection(this);
  }
}

inline ElfLocation::ElfLocation(ElfSection* section, unsigned int off,
                                enum position pos)
    : section(section) {
  if ((pos == ABSOLUTE) && section)
    offset = off - section->getAddr();
  else
    offset = off;
}

inline ElfLocation::ElfLocation(unsigned int location, Elf* elf) {
  section = elf->getSectionAt(location);
  offset = location - (section ? section->getAddr() : 0);
}

inline unsigned int ElfLocation::getValue() {
  return (section ? section->getAddr() : 0) + offset;
}

inline const char* ElfLocation::getBuffer() {
  return section ? section->getData() + offset : nullptr;
}

inline unsigned int ElfSize::getValue() { return section->getSize(); }

inline unsigned int ElfEntSize::getValue() { return section->getEntSize(); }