The Tor Browser: build/unix/elfhack/elfhack.cpp@129ffea94266 (annotated)

build/unix/elfhack/elfhack.cpp@129ffea94266 (annotated)

build/unix/elfhack/elfhack.cpp

Sat, 03 Jan 2015 20:18:00 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Sat, 03 Jan 2015 20:18:00 +0100
branch: TOR_BUG_3246
changeset 7: 129ffea94266
permissions: -rw-r--r--

Conditionally enable double key logic according to:
private browsing mode or privacy.thirdparty.isolate preference and
implement in GetCookieStringCommon and FindCookie where it counts...
With some reservations of how to convince FindCookie users to test
condition and pass a nullptr when disabling double key logic.

 /* 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/. */
 #undef NDEBUG
 #include <assert.h>
 #include <cstring>
 #include <cstdlib>
 #include <cstdio>
 #include "elfxx.h"
 #define ver "0"
 #define elfhack_data ".elfhack.data.v" ver
 #define elfhack_text ".elfhack.text.v" ver
 #ifndef R_ARM_V4BX
 #define R_ARM_V4BX 0x28
 #endif
 #ifndef R_ARM_CALL
 #define R_ARM_CALL 0x1c
 #endif
 #ifndef R_ARM_JUMP24
 #define R_ARM_JUMP24 0x1d
 #endif
 #ifndef R_ARM_THM_JUMP24
 #define R_ARM_THM_JUMP24 0x1e
 #endif
 char *rundir = nullptr;
 template <typename T>
 struct wrapped {
     T value;
 };
 class Elf_Addr_Traits {
 public:
     typedef wrapped<Elf32_Addr> Type32;
     typedef wrapped<Elf64_Addr> Type64;
     template <class endian, typename R, typename T>
     static inline void swap(T &t, R &r) {
         r.value = endian::swap(t.value);
     }
 };
 typedef serializable<Elf_Addr_Traits> Elf_Addr;
 class Elf_RelHack_Traits {
 public:
     typedef Elf32_Rel Type32;
     typedef Elf32_Rel Type64;
     template <class endian, typename R, typename T>
     static inline void swap(T &t, R &r) {
         r.r_offset = endian::swap(t.r_offset);
         r.r_info = endian::swap(t.r_info);
     }
 };
 typedef serializable<Elf_RelHack_Traits> Elf_RelHack;
 class ElfRelHack_Section: public ElfSection {
 public:
     ElfRelHack_Section(Elf_Shdr &s)
     : ElfSection(s, nullptr, nullptr)
     {
         name = elfhack_data;
     };
     void serialize(std::ofstream &file, char ei_class, char ei_data)
     {
         for (std::vector<Elf_RelHack>::iterator i = rels.begin();
              i != rels.end(); ++i)
             (*i).serialize(file, ei_class, ei_data);
     }
     bool isRelocatable() {
         return true;
     }
     void push_back(Elf_RelHack &r) {
         rels.push_back(r);
         shdr.sh_size = rels.size() * shdr.sh_entsize;
     }
 private:
     std::vector<Elf_RelHack> rels;
 };
 class ElfRelHackCode_Section: public ElfSection {
 public:
     ElfRelHackCode_Section(Elf_Shdr &s, Elf &e, unsigned int init)
     : ElfSection(s, nullptr, nullptr), parent(e), init(init) {
         std::string file(rundir);
         file += "/inject/";
         switch (parent.getMachine()) {
         case EM_386:
             file += "x86";
             break;
         case EM_X86_64:
             file += "x86_64";
             break;
         case EM_ARM:
             file += "arm";
             break;
         default:
             throw std::runtime_error("unsupported architecture");
         }
         file += ".o";
         std::ifstream inject(file.c_str(), std::ios::in|std::ios::binary);
         elf = new Elf(inject);
         if (elf->getType() != ET_REL)
             throw std::runtime_error("object for injected code is not ET_REL");
         if (elf->getMachine() != parent.getMachine())
             throw std::runtime_error("architecture of object for injected code doesn't match");
         ElfSymtab_Section *symtab = nullptr;
         // Find the symbol table.
         for (ElfSection *section = elf->getSection(1); section != nullptr;
              section = section->getNext()) {
             if (section->getType() == SHT_SYMTAB)
                 symtab = (ElfSymtab_Section *) section;
         }
         if (symtab == nullptr)
             throw std::runtime_error("Couldn't find a symbol table for the injected code");
         // Find the init symbol
         entry_point = -1;
         Elf_SymValue *sym = symtab->lookup(init ? "init" : "init_noinit");
         if (!sym)
             throw std::runtime_error("Couldn't find an 'init' symbol in the injected code");
         entry_point = sym->value.getValue();
         // Get all relevant sections from the injected code object.
         add_code_section(sym->value.getSection());
         // Adjust code sections offsets according to their size
         std::vector<ElfSection *>::iterator c = code.begin();
         (*c)->getShdr().sh_addr = 0;
         for(ElfSection *last = *(c++); c != code.end(); c++) {
             unsigned int addr = last->getShdr().sh_addr + last->getSize();
             if (addr & ((*c)->getAddrAlign() - 1))
                 addr = (addr | ((*c)->getAddrAlign() - 1)) + 1;
             (*c)->getShdr().sh_addr = addr;
             // We need to align this section depending on the greater
             // alignment required by code sections.
             if (shdr.sh_addralign < (*c)->getAddrAlign())
                 shdr.sh_addralign = (*c)->getAddrAlign();
         }
         shdr.sh_size = code.back()->getAddr() + code.back()->getSize();
         data = new char[shdr.sh_size];
         char *buf = data;
         for (c = code.begin(); c != code.end(); c++) {
             memcpy(buf, (*c)->getData(), (*c)->getSize());
             buf += (*c)->getSize();
         }
         name = elfhack_text;
     }
     ~ElfRelHackCode_Section() {
         delete elf;
     }
     void serialize(std::ofstream &file, char ei_class, char ei_data)
     {
         // Readjust code offsets
         for (std::vector<ElfSection *>::iterator c = code.begin(); c != code.end(); c++)
             (*c)->getShdr().sh_addr += getAddr();
         // Apply relocations
         for (std::vector<ElfSection *>::iterator c = code.begin(); c != code.end(); c++) {
             for (ElfSection *rel = elf->getSection(1); rel != nullptr; rel = rel->getNext())
                 if (((rel->getType() == SHT_REL) ||
                      (rel->getType() == SHT_RELA)) &&
                     (rel->getInfo().section == *c)) {
                     if (rel->getType() == SHT_REL)
                         apply_relocations((ElfRel_Section<Elf_Rel> *)rel, *c);
                     else
                         apply_relocations((ElfRel_Section<Elf_Rela> *)rel, *c);
                 }
             }
         ElfSection::serialize(file, ei_class, ei_data);
     }
     bool isRelocatable() {
         return true;
     }
     unsigned int getEntryPoint() {
         return entry_point;
     }
 private:
     void add_code_section(ElfSection *section)
     {
         if (section) {
             /* Don't add section if it's already been added in the past */
             for (auto s = code.begin(); s != code.end(); ++s) {
                 if (section == *s)
                     return;
             }
             code.push_back(section);
             find_code(section);
         }
     }
     /* Look at the relocations associated to the given section to find other
      * sections that it requires */
     void find_code(ElfSection *section)
     {
         for (ElfSection *s = elf->getSection(1); s != nullptr;
              s = s->getNext()) {
             if (((s->getType() == SHT_REL) ||
                  (s->getType() == SHT_RELA)) &&
                 (s->getInfo().section == section)) {
                 if (s->getType() == SHT_REL)
                     scan_relocs_for_code((ElfRel_Section<Elf_Rel> *)s);
                 else
                     scan_relocs_for_code((ElfRel_Section<Elf_Rela> *)s);
             }
         }
     }
     template <typename Rel_Type>
     void scan_relocs_for_code(ElfRel_Section<Rel_Type> *rel)
     {
         ElfSymtab_Section *symtab = (ElfSymtab_Section *)rel->getLink();
         for (auto r = rel->rels.begin(); r != rel->rels.end(); r++) {
             ElfSection *section = symtab->syms[ELF32_R_SYM(r->r_info)].value.getSection();
             add_code_section(section);
         }
     }
     class pc32_relocation {
     public:
         Elf32_Addr operator()(unsigned int base_addr, Elf32_Off offset,
                               Elf32_Word addend, unsigned int addr)
         {
             return addr + addend - offset - base_addr;
         }
     };
     class arm_plt32_relocation {
     public:
         Elf32_Addr operator()(unsigned int base_addr, Elf32_Off offset,
                               Elf32_Word addend, unsigned int addr)
         {
             // We don't care about sign_extend because the only case where this is
             // going to be used only jumps forward.
             Elf32_Addr tmp = (Elf32_Addr) (addr - offset - base_addr) >> 2;
             tmp = (addend + tmp) & 0x00ffffff;
             return (addend & 0xff000000) | tmp;
         }
     };
     class arm_thm_jump24_relocation {
     public:
         Elf32_Addr operator()(unsigned int base_addr, Elf32_Off offset,
                               Elf32_Word addend, unsigned int addr)
         {
             /* Follows description of b.w and bl instructions as per
                ARM Architecture Reference Manual ARM® v7-A and ARM® v7-R edition, A8.6.16
                We limit ourselves to Encoding T4 of b.w and Encoding T1 of bl.
                We don't care about sign_extend because the only case where this is
                going to be used only jumps forward. */
             Elf32_Addr tmp = (Elf32_Addr) (addr - offset - base_addr);
             unsigned int word0 = addend & 0xffff,
                          word1 = addend >> 16;
             /* Encoding T4 of B.W is 10x1 ; Encoding T1 of BL is 11x1. */
             unsigned int type = (word1 & 0xd000) >> 12;
             if (((word0 & 0xf800) != 0xf000) || ((type & 0x9) != 0x9))
                 throw std::runtime_error("R_ARM_THM_JUMP24/R_ARM_THM_CALL relocation only supported for B.W <label> and BL <label>");
             /* When the target address points to ARM code, switch a BL to a
              * BLX. This however can't be done with a B.W without adding a
              * trampoline, which is not supported as of now. */
             if ((addr & 0x1) == 0) {
                 if (type == 0x9)
                     throw std::runtime_error("R_ARM_THM_JUMP24/R_ARM_THM_CALL relocation only supported for BL <label> when label points to ARM code");
                 /* The address of the target is always relative to a 4-bytes
                  * aligned address, so if the address of the BL instruction is
                  * not 4-bytes aligned, adjust for it. */
                 if ((base_addr + offset) & 0x2)
                     tmp += 2;
                 /* Encoding T2 of BLX is 11x0. */
                 type = 0xc;
             }
             unsigned int s = (word0 & (1 << 10)) >> 10;
             unsigned int j1 = (word1 & (1 << 13)) >> 13;
             unsigned int j2 = (word1 & (1 << 11)) >> 11;
             unsigned int i1 = j1 ^ s ? 0 : 1;
             unsigned int i2 = j2 ^ s ? 0 : 1;
             tmp += ((s << 24) | (i1 << 23) | (i2 << 22) | ((word0 & 0x3ff) << 12) | ((word1 & 0x7ff) << 1));
             s = (tmp & (1 << 24)) >> 24;
             j1 = ((tmp & (1 << 23)) >> 23) ^ !s;
             j2 = ((tmp & (1 << 22)) >> 22) ^ !s;
             return 0xf000 | (s << 10) | ((tmp & (0x3ff << 12)) >> 12) |
                    (type << 28) | (j1 << 29) | (j2 << 27) | ((tmp & 0xffe) << 15);
         }
     };
     class gotoff_relocation {
     public:
         Elf32_Addr operator()(unsigned int base_addr, Elf32_Off offset,
                               Elf32_Word addend, unsigned int addr)
         {
             return addr + addend;
         }
     };
     template <class relocation_type>
     void apply_relocation(ElfSection *the_code, char *base, Elf_Rel *r, unsigned int addr)
     {
         relocation_type relocation;
         Elf32_Addr value;
         memcpy(&value, base + r->r_offset, 4);
         value = relocation(the_code->getAddr(), r->r_offset, value, addr);
         memcpy(base + r->r_offset, &value, 4);
     }
     template <class relocation_type>
     void apply_relocation(ElfSection *the_code, char *base, Elf_Rela *r, unsigned int addr)
     {
         relocation_type relocation;
         Elf32_Addr value = relocation(the_code->getAddr(), r->r_offset, r->r_addend, addr);
         memcpy(base + r->r_offset, &value, 4);
     }
     template <typename Rel_Type>
     void apply_relocations(ElfRel_Section<Rel_Type> *rel, ElfSection *the_code)
     {
         assert(rel->getType() == Rel_Type::sh_type);
         char *buf = data + (the_code->getAddr() - code.front()->getAddr());
         // TODO: various checks on the sections
         ElfSymtab_Section *symtab = (ElfSymtab_Section *)rel->getLink();
         for (typename std::vector<Rel_Type>::iterator r = rel->rels.begin(); r != rel->rels.end(); r++) {
             // TODO: various checks on the symbol
             const char *name = symtab->syms[ELF32_R_SYM(r->r_info)].name;
             unsigned int addr;
             if (symtab->syms[ELF32_R_SYM(r->r_info)].value.getSection() == nullptr) {
                 if (strcmp(name, "relhack") == 0) {
                     addr = getNext()->getAddr();
                 } else if (strcmp(name, "elf_header") == 0) {
                     // TODO: change this ungly hack to something better
                     ElfSection *ehdr = parent.getSection(1)->getPrevious()->getPrevious();
                     addr = ehdr->getAddr();
                 } else if (strcmp(name, "original_init") == 0) {
                     addr = init;
                 } else if (strcmp(name, "_GLOBAL_OFFSET_TABLE_") == 0) {
                     // We actually don't need a GOT, but need it as a reference for
                     // GOTOFF relocations. We'll just use the start of the ELF file
                     addr = 0;
                 } else if (strcmp(name, "") == 0) {
                     // This is for R_ARM_V4BX, until we find something better
                     addr = -1;
                 } else {
                     throw std::runtime_error("Unsupported symbol in relocation");
                 }
             } else {
                 ElfSection *section = symtab->syms[ELF32_R_SYM(r->r_info)].value.getSection();
                 assert((section->getType() == SHT_PROGBITS) && (section->getFlags() & SHF_EXECINSTR));
                 addr = symtab->syms[ELF32_R_SYM(r->r_info)].value.getValue();
             }
             // Do the relocation
 #define REL(machine, type) (EM_ ## machine | (R_ ## machine ## _ ## type << 8))
             switch (elf->getMachine() | (ELF32_R_TYPE(r->r_info) << 8)) {
             case REL(X86_64, PC32):
             case REL(386, PC32):
             case REL(386, GOTPC):
             case REL(ARM, GOTPC):
             case REL(ARM, REL32):
                 apply_relocation<pc32_relocation>(the_code, buf, &*r, addr);
                 break;
             case REL(ARM, CALL):
             case REL(ARM, JUMP24):
             case REL(ARM, PLT32):
                 apply_relocation<arm_plt32_relocation>(the_code, buf, &*r, addr);
                 break;
             case REL(ARM, THM_PC22 /* THM_CALL */):
             case REL(ARM, THM_JUMP24):
                 apply_relocation<arm_thm_jump24_relocation>(the_code, buf, &*r, addr);
                 break;
             case REL(386, GOTOFF):
             case REL(ARM, GOTOFF):
                 apply_relocation<gotoff_relocation>(the_code, buf, &*r, addr);
                 break;
             case REL(ARM, V4BX):
                 // Ignore R_ARM_V4BX relocations
                 break;
             default:
                 throw std::runtime_error("Unsupported relocation type");
             }
         }
     }
     Elf *elf, &parent;
     std::vector<ElfSection *> code;
     unsigned int init;
     int entry_point;
 };
 unsigned int get_addend(Elf_Rel *rel, Elf *elf) {
     ElfLocation loc(rel->r_offset, elf);
     Elf_Addr addr(loc.getBuffer(), Elf_Addr::size(elf->getClass()), elf->getClass(), elf->getData());
     return addr.value;
 }
 unsigned int get_addend(Elf_Rela *rel, Elf *elf) {
     return rel->r_addend;
 }
 void set_relative_reloc(Elf_Rel *rel, Elf *elf, unsigned int value) {
     ElfLocation loc(rel->r_offset, elf);
     Elf_Addr addr;
     addr.value = value;
     addr.serialize(const_cast<char *>(loc.getBuffer()), Elf_Addr::size(elf->getClass()), elf->getClass(), elf->getData());
 }
 void set_relative_reloc(Elf_Rela *rel, Elf *elf, unsigned int value) {
     // ld puts the value of relocated relocations both in the addend and
     // at r_offset. For consistency, keep it that way.
     set_relative_reloc((Elf_Rel *)rel, elf, value);
     rel->r_addend = value;
 }
 void maybe_split_segment(Elf *elf, ElfSegment *segment, bool fill)
 {
     std::list<ElfSection *>::iterator it = segment->begin();
     for (ElfSection *last = *(it++); it != segment->end(); last = *(it++)) {
         // When two consecutive non-SHT_NOBITS sections are apart by more
         // than the alignment of the section, the second can be moved closer
         // to the first, but this requires the segment to be split.
         if (((*it)->getType() != SHT_NOBITS) && (last->getType() != SHT_NOBITS) &&
             ((*it)->getOffset() - last->getOffset() - last->getSize() > segment->getAlign())) {
             // Probably very wrong.
             Elf_Phdr phdr;
             phdr.p_type = PT_LOAD;
             phdr.p_vaddr = 0;
             phdr.p_paddr = phdr.p_vaddr + segment->getVPDiff();
             phdr.p_flags = segment->getFlags();
             phdr.p_align = segment->getAlign();
             phdr.p_filesz = (unsigned int)-1;
             phdr.p_memsz = (unsigned int)-1;
             ElfSegment *newSegment = new ElfSegment(&phdr);
             elf->insertSegmentAfter(segment, newSegment);
             ElfSection *section = *it;
             for (; it != segment->end(); ++it) {
                 newSegment->addSection(*it);
             }
             for (it = newSegment->begin(); it != newSegment->end(); it++) {
                 segment->removeSection(*it);
             }
             // Fill the virtual address space gap left between the two PT_LOADs
             // with a new PT_LOAD with no permissions. This avoids the linker
             // (especially bionic's) filling the gap with anonymous memory,
             // which breakpad doesn't like.
             // /!\ running strip on a elfhacked binary will break this filler
             // PT_LOAD.
             if (!fill)
                 break;
             // Insert dummy segment to normalize the entire Elf with the header
             // sizes adjusted, before inserting a filler segment.
             {
               memset(&phdr, 0, sizeof(phdr));
               ElfSegment dummySegment(&phdr);
               elf->insertSegmentAfter(segment, &dummySegment);
               elf->normalize();
               elf->removeSegment(&dummySegment);
             }
             ElfSection *previous = section->getPrevious();
             phdr.p_type = PT_LOAD;
             phdr.p_vaddr = (previous->getAddr() + previous->getSize() + segment->getAlign() - 1) & ~(segment->getAlign() - 1);
             phdr.p_paddr = phdr.p_vaddr + segment->getVPDiff();
             phdr.p_flags = 0;
             phdr.p_align = 0;
             phdr.p_filesz = (section->getAddr() & ~(newSegment->getAlign() - 1)) - phdr.p_vaddr;
             phdr.p_memsz = phdr.p_filesz;
             if (phdr.p_filesz) {
                 newSegment = new ElfSegment(&phdr);
                 assert(newSegment->isElfHackFillerSegment());
                 elf->insertSegmentAfter(segment, newSegment);
             } else {
                 elf->normalize();
             }
             break;
         }
     }
 }
 template <typename Rel_Type>
 int do_relocation_section(Elf *elf, unsigned int rel_type, unsigned int rel_type2, bool force, bool fill)
 {
     ElfDynamic_Section *dyn = elf->getDynSection();
     if (dyn == nullptr) {
         fprintf(stderr, "Couldn't find SHT_DYNAMIC section\n");
         return -1;
     }
     ElfSegment *relro = elf->getSegmentByType(PT_GNU_RELRO);
     ElfRel_Section<Rel_Type> *section = (ElfRel_Section<Rel_Type> *)dyn->getSectionForType(Rel_Type::d_tag);
     assert(section->getType() == Rel_Type::sh_type);
     Elf32_Shdr relhack32_section =
         { 0, SHT_PROGBITS, SHF_ALLOC, 0, (Elf32_Off)-1, 0, SHN_UNDEF, 0,
           Elf_RelHack::size(elf->getClass()), Elf_RelHack::size(elf->getClass()) }; // TODO: sh_addralign should be an alignment, not size
     Elf32_Shdr relhackcode32_section =
         { 0, SHT_PROGBITS, SHF_ALLOC | SHF_EXECINSTR, 0, (Elf32_Off)-1, 0,
           SHN_UNDEF, 0, 1, 0 };
     unsigned int entry_sz = Elf_Addr::size(elf->getClass());
     // The injected code needs to be executed before any init code in the
     // binary. There are three possible cases:
     // - The binary has no init code at all. In this case, we will add a
     //   DT_INIT entry pointing to the injected code.
     // - The binary has a DT_INIT entry. In this case, we will interpose:
     //   we change DT_INIT to point to the injected code, and have the
     //   injected code call the original DT_INIT entry point.
     // - The binary has no DT_INIT entry, but has a DT_INIT_ARRAY. In this
     //   case, we interpose as well, by replacing the first entry in the
     //   array to point to the injected code, and have the injected code
     //   call the original first entry.
     // The binary may have .ctors instead of DT_INIT_ARRAY, for its init
     // functions, but this falls into the second case above, since .ctors
     // are actually run by DT_INIT code.
     ElfValue *value = dyn->getValueForType(DT_INIT);
     unsigned int original_init = value ? value->getValue() : 0;
     ElfSection *init_array = nullptr;
     if (!value || !value->getValue()) {
         value = dyn->getValueForType(DT_INIT_ARRAYSZ);
         if (value && value->getValue() >= entry_sz)
             init_array = dyn->getSectionForType(DT_INIT_ARRAY);
     }
     Elf_Shdr relhack_section(relhack32_section);
     Elf_Shdr relhackcode_section(relhackcode32_section);
     ElfRelHack_Section *relhack = new ElfRelHack_Section(relhack_section);
     ElfSymtab_Section *symtab = (ElfSymtab_Section *) section->getLink();
     Elf_SymValue *sym = symtab->lookup("__cxa_pure_virtual");
     std::vector<Rel_Type> new_rels;
     Elf_RelHack relhack_entry;
     relhack_entry.r_offset = relhack_entry.r_info = 0;
     size_t init_array_reloc = 0;
     for (typename std::vector<Rel_Type>::iterator i = section->rels.begin();
          i != section->rels.end(); i++) {
         // We don't need to keep R_*_NONE relocations
         if (!ELF32_R_TYPE(i->r_info))
             continue;
         ElfLocation loc(i->r_offset, elf);
         // __cxa_pure_virtual is a function used in vtables to point at pure
         // virtual methods. The __cxa_pure_virtual function usually abort()s.
         // These functions are however normally never called. In the case
         // where they would, jumping to the null address instead of calling
         // __cxa_pure_virtual is going to work just as well. So we can remove
         // relocations for the __cxa_pure_virtual symbol and null out the
         // content at the offset pointed by the relocation.
         if (sym) {
             if (sym->defined) {
                 // If we are statically linked to libstdc++, the
                 // __cxa_pure_virtual symbol is defined in our lib, and we
                 // have relative relocations (rel_type) for it.
                 if (ELF32_R_TYPE(i->r_info) == rel_type) {
                     Elf_Addr addr(loc.getBuffer(), entry_sz, elf->getClass(), elf->getData());
                     if (addr.value == sym->value.getValue()) {
                         memset((char *)loc.getBuffer(), 0, entry_sz);
                         continue;
                     }
                 }
             } else {
                 // If we are dynamically linked to libstdc++, the
                 // __cxa_pure_virtual symbol is undefined in our lib, and we
                 // have absolute relocations (rel_type2) for it.
                 if ((ELF32_R_TYPE(i->r_info) == rel_type2) &&
                     (sym == &symtab->syms[ELF32_R_SYM(i->r_info)])) {
                     memset((char *)loc.getBuffer(), 0, entry_sz);
                     continue;
                 }
             }
         }
         // Keep track of the relocation associated with the first init_array entry.
         if (init_array && i->r_offset == init_array->getAddr()) {
             if (init_array_reloc) {
                 fprintf(stderr, "Found multiple relocations for the first init_array entry. Skipping\n");
                 return -1;
             }
             new_rels.push_back(*i);
             init_array_reloc = new_rels.size();
         } else if (!(loc.getSection()->getFlags() & SHF_WRITE) || (ELF32_R_TYPE(i->r_info) != rel_type) ||
                    (relro && (i->r_offset >= relro->getAddr()) &&
                    (i->r_offset < relro->getAddr() + relro->getMemSize()))) {
             // Don't pack relocations happening in non writable sections.
             // Our injected code is likely not to be allowed to write there.
             new_rels.push_back(*i);
         } else {
             // TODO: check that i->r_addend == *i->r_offset
             if (i->r_offset == relhack_entry.r_offset + relhack_entry.r_info * entry_sz) {
                 relhack_entry.r_info++;
             } else {
                 if (relhack_entry.r_offset)
                     relhack->push_back(relhack_entry);
                 relhack_entry.r_offset = i->r_offset;
                 relhack_entry.r_info = 1;
             }
         }
     }
     if (relhack_entry.r_offset)
         relhack->push_back(relhack_entry);
     // Last entry must be nullptr
     relhack_entry.r_offset = relhack_entry.r_info = 0;
     relhack->push_back(relhack_entry);
     unsigned int old_end = section->getOffset() + section->getSize();
     if (init_array) {
         if (! init_array_reloc) {
             fprintf(stderr, "Didn't find relocation for DT_INIT_ARRAY's first entry. Skipping\n");
             return -1;
         }
         Rel_Type *rel = &new_rels[init_array_reloc - 1];
         unsigned int addend = get_addend(rel, elf);
         // Use relocated value of DT_INIT_ARRAY's first entry for the
         // function to be called by the injected code.
         if (ELF32_R_TYPE(rel->r_info) == rel_type) {
             original_init = addend;
         } else if (ELF32_R_TYPE(rel->r_info) == rel_type2) {
             ElfSymtab_Section *symtab = (ElfSymtab_Section *)section->getLink();
             original_init = symtab->syms[ELF32_R_SYM(rel->r_info)].value.getValue() + addend;
         } else {
             fprintf(stderr, "Unsupported relocation type for DT_INIT_ARRAY's first entry. Skipping\n");
             return -1;
         }
     }
     section->rels.assign(new_rels.begin(), new_rels.end());
     section->shrink(new_rels.size() * section->getEntSize());
     ElfRelHackCode_Section *relhackcode = new ElfRelHackCode_Section(relhackcode_section, *elf, original_init);
     relhackcode->insertBefore(section);
     relhack->insertAfter(relhackcode);
     if (section->getOffset() + section->getSize() >= old_end) {
         fprintf(stderr, "No gain. Skipping\n");
         return -1;
     }
     // Adjust PT_LOAD segments
     for (ElfSegment *segment = elf->getSegmentByType(PT_LOAD); segment;
          segment = elf->getSegmentByType(PT_LOAD, segment)) {
         maybe_split_segment(elf, segment, fill);
     }
     // Ensure Elf sections will be at their final location.
     elf->normalize();
     ElfLocation *init = new ElfLocation(relhackcode, relhackcode->getEntryPoint());
     if (init_array) {
         // Adjust the first DT_INIT_ARRAY entry to point at the injected code
         // by transforming its relocation into a relative one pointing to the
         // address of the injected code.
         Rel_Type *rel = &section->rels[init_array_reloc - 1];
         rel->r_info = ELF32_R_INFO(0, rel_type); // Set as a relative relocation
         set_relative_reloc(&section->rels[init_array_reloc - 1], elf, init->getValue());
     } else if (!dyn->setValueForType(DT_INIT, init)) {
         fprintf(stderr, "Can't grow .dynamic section to set DT_INIT. Skipping\n");
         return -1;
     }
     // TODO: adjust the value according to the remaining number of relative relocations
     if (dyn->getValueForType(Rel_Type::d_tag_count))
         dyn->setValueForType(Rel_Type::d_tag_count, new ElfPlainValue(0));
     return 0;
 }
 static inline int backup_file(const char *name)
 {
     std::string fname(name);
     fname += ".bak";
     return rename(name, fname.c_str());
 }
 void do_file(const char *name, bool backup = false, bool force = false, bool fill = false)
 {
     std::ifstream file(name, std::ios::in|std::ios::binary);
     Elf elf(file);
     unsigned int size = elf.getSize();
     fprintf(stderr, "%s: ", name);
     if (elf.getType() != ET_DYN) {
         fprintf(stderr, "Not a shared object. Skipping\n");
         return;
     }
     for (ElfSection *section = elf.getSection(1); section != nullptr;
          section = section->getNext()) {
         if (section->getName() &&
             (strncmp(section->getName(), ".elfhack.", 9) == 0)) {
             fprintf(stderr, "Already elfhacked. Skipping\n");
             return;
         }
     }
     int exit = -1;
     switch (elf.getMachine()) {
     case EM_386:
         exit = do_relocation_section<Elf_Rel>(&elf, R_386_RELATIVE, R_386_32, force, fill);
         break;
     case EM_X86_64:
         exit = do_relocation_section<Elf_Rela>(&elf, R_X86_64_RELATIVE, R_X86_64_64, force, fill);
         break;
     case EM_ARM:
         exit = do_relocation_section<Elf_Rel>(&elf, R_ARM_RELATIVE, R_ARM_ABS32, force, fill);
         break;
     }
     if (exit == 0) {
         if (!force && (elf.getSize() >= size)) {
             fprintf(stderr, "No gain. Skipping\n");
         } else if (backup && backup_file(name) != 0) {
             fprintf(stderr, "Couln't create backup file\n");
         } else {
             std::ofstream ofile(name, std::ios::out|std::ios::binary|std::ios::trunc);
             elf.write(ofile);
             fprintf(stderr, "Reduced by %d bytes\n", size - elf.getSize());
         }
     }
 }
 void undo_file(const char *name, bool backup = false)
 {
     std::ifstream file(name, std::ios::in|std::ios::binary);
     Elf elf(file);
     unsigned int size = elf.getSize();
     fprintf(stderr, "%s: ", name);
     if (elf.getType() != ET_DYN) {
         fprintf(stderr, "Not a shared object. Skipping\n");
         return;
     }
     ElfSection *data = nullptr, *text = nullptr;
     for (ElfSection *section = elf.getSection(1); section != nullptr;
          section = section->getNext()) {
         if (section->getName() &&
             (strcmp(section->getName(), elfhack_data) == 0))
             data = section;
         if (section->getName() &&
             (strcmp(section->getName(), elfhack_text) == 0))
             text = section;
     }
     if (!data || !text) {
         fprintf(stderr, "Not elfhacked. Skipping\n");
         return;
     }
     if (data != text->getNext()) {
         fprintf(stderr, elfhack_data " section not following " elfhack_text ". Skipping\n");
         return;
     }
     ElfSegment *first = elf.getSegmentByType(PT_LOAD);
     ElfSegment *second = elf.getSegmentByType(PT_LOAD, first);
     ElfSegment *filler = nullptr;
     // If the second PT_LOAD is a filler from elfhack --fill, check the third.
     if (second->isElfHackFillerSegment()) {
         filler = second;
         second = elf.getSegmentByType(PT_LOAD, filler);
     }
     if (second->getFlags() != first->getFlags()) {
         fprintf(stderr, "Couldn't identify elfhacked PT_LOAD segments. Skipping\n");
         return;
     }
     // Move sections from the second PT_LOAD to the first, and remove the
     // second PT_LOAD segment.
     for (std::list<ElfSection *>::iterator section = second->begin();
          section != second->end(); ++section)
         first->addSection(*section);
     elf.removeSegment(second);
     if (filler)
         elf.removeSegment(filler);
     if (backup && backup_file(name) != 0) {
         fprintf(stderr, "Couln't create backup file\n");
     } else {
         std::ofstream ofile(name, std::ios::out|std::ios::binary|std::ios::trunc);
         elf.write(ofile);
         fprintf(stderr, "Grown by %d bytes\n", elf.getSize() - size);
     }
 }
 int main(int argc, char *argv[])
 {
     int arg;
     bool backup = false;
     bool force = false;
     bool revert = false;
     bool fill = false;
     char *lastSlash = rindex(argv[0], '/');
     if (lastSlash != nullptr)
         rundir = strndup(argv[0], lastSlash - argv[0]);
     for (arg = 1; arg < argc; arg++) {
         if (strcmp(argv[arg], "-f") == 0)
             force = true;
         else if (strcmp(argv[arg], "-b") == 0)
             backup = true;
         else if (strcmp(argv[arg], "-r") == 0)
             revert = true;
         else if (strcmp(argv[arg], "--fill") == 0)
             fill = true;
         else if (revert) {
             undo_file(argv[arg], backup);
         } else
             do_file(argv[arg], backup, force, fill);
     }
     free(rundir);
     return 0;
 }

The Tor Browser / annotate

build/unix/elfhack/elfhack.cpp@129ffea94266 (annotated)

build/unix/elfhack/elfhack.cpp