gecko/build/unix/elfhack/elfhack.cpp

824 lines
32 KiB
C++

/* 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;
}