The Tor Browser: build/unix/elfhack/elfxx.h@ac0c01689b40 (annotated)

build/unix/elfhack/elfxx.h@ac0c01689b40 (annotated)

build/unix/elfhack/elfxx.h

Thu, 15 Jan 2015 15:59:08 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 15 Jan 2015 15:59:08 +0100
branch: TOR_BUG_9701
changeset 10: ac0c01689b40
permissions: -rw-r--r--

Implement a real Private Browsing Mode condition by changing the API/ABI;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 /* 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 "mozilla/NullPtr.h"
 #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;
 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() {
         delete[] 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;
     }
     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);
     }
     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());
     }
 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);
     }
     ElfSegment *getSegmentByType(unsigned int type);
     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();
     bool isElfHackFillerSegment() {
       return type == PT_LOAD && flags == 0;
     }
 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(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(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)
     {
         int 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();
 }

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build/unix/elfhack/elfxx.h@ac0c01689b40 (annotated)

build/unix/elfhack/elfxx.h