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/* 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
#undef NDEBUG
#include <assert.h>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <memory>
#include "elfxx.h"
#include "mozilla/CheckedInt.h"
#define ver "1"
#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 ElfRelHack_Section : public ElfSection {
public:
ElfRelHack_Section(Elf_Shdr& s)
: ElfSection(s, nullptr, nullptr),
block_size((8 * s.sh_entsize - 1) * s.sh_entsize) {
name = elfhack_data;
};
void serialize(std::ofstream& file, unsigned char ei_class,
unsigned char ei_data) {
if (bitmap) {
relr.push_back((bitmap << 1) | 1);
}
for (std::vector<Elf64_Addr>::iterator i = relr.begin(); i != relr.end();
++i) {
Elf_Addr out;
out.value = *i;
out.serialize(file, ei_class, ei_data);
}
}
bool isRelocatable() { return true; }
void push_back(Elf64_Addr offset) {
// The format used for the packed relocations is SHT_RELR, described in
// The gist of it is that an address is recorded, and the following words,
// if their LSB is 1, represent a bitmap of word-size-spaced relocations
// at the addresses that follow. There can be multiple such bitmaps, such
// that very long streaks of (possibly spaced) relocations can be recorded
// in a very compact way.
for (;;) {
// [block_start; block_start + block_size] represents the range of offsets
// the current bitmap can record. If the offset doesn't fall in that
// range, or if doesn't align properly to be recorded, we record the
// bitmap, and slide the block corresponding to a new bitmap. If the
// offset doesn't fall in the range for the new bitmap, or if there wasn't
// an active bitmap in the first place, we record the offset and start a
// new bitmap for the block that follows it.
if (!block_start || offset < block_start ||
offset >= block_start + block_size ||
(offset - block_start) % shdr.sh_entsize) {
if (bitmap) {
relr.push_back((bitmap << 1) | 1);
block_start += block_size;
bitmap = 0;
continue;
}
relr.push_back(offset);
block_start = offset + shdr.sh_entsize;
break;
}
bitmap |= 1ULL << ((offset - block_start) / shdr.sh_entsize);
break;
}
shdr.sh_size = (relr.size() + (bitmap ? 1 : 0)) * shdr.sh_entsize;
}
private:
std::vector<Elf64_Addr> relr;
size_t block_size;
Elf64_Addr block_start = 0;
Elf64_Addr bitmap = 0;
};
class ElfRelHackCode_Section : public ElfSection {
public:
ElfRelHackCode_Section(Elf_Shdr& s, Elf& e,
ElfRelHack_Section& relhack_section, unsigned int init,
unsigned int mprotect_cb, unsigned int sysconf_cb)
: ElfSection(s, nullptr, nullptr),
parent(e),
relhack_section(relhack_section),
init(init),
init_trampoline(nullptr),
mprotect_cb(mprotect_cb),
sysconf_cb(sysconf_cb) {
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;
case EM_AARCH64:
file += "aarch64";
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");
relro = parent.getSegmentByType(PT_GNU_RELRO);
// Find the init symbol
entry_point = -1;
std::string symbol = "init";
if (!init) symbol += "_noinit";
if (relro) symbol += "_relro";
Elf_SymValue* sym = symtab->lookup(symbol.c_str());
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());
// If the original init function is located too far away, we're going to
// need to use a trampoline. See comment in inject.c.
// Theoretically, we should check for (init - instr) > boundary, where
// boundary is the platform-dependent limit, and instr is the virtual
// address of the instruction that calls the original init, but we don't
// have it at this point, so punt to just init.
if ((init > 0xffffff && parent.getMachine() == EM_ARM) ||
(init > 0x07ffffff && parent.getMachine() == EM_AARCH64)) {
Elf_SymValue* trampoline = symtab->lookup("init_trampoline");
if (!trampoline) {
throw std::runtime_error(
"Couldn't find an 'init_trampoline' symbol in the injected code");
}
init_trampoline = trampoline->value.getSection();
add_code_section(init_trampoline);
}
// 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();
last = *c;
}
shdr.sh_size = code.back()->getAddr() + code.back()->getSize();
data = static_cast<char*>(malloc(shdr.sh_size));
if (!data) {
throw std::runtime_error("Could not malloc ElfSection data");
}
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, unsigned char ei_class,
unsigned char ei_data) override {
// 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() override { return false; }
unsigned int getEntryPoint() { return entry_point; }
void insertBefore(ElfSection* section, bool dirty = true) override {
// Adjust the address so that this section is adjacent to the one it's
// being inserted before. This avoids creating holes which subsequently
// might lead the PHDR-adjusting code to create unnecessary additional
// PT_LOADs.
shdr.sh_addr =
(section->getAddr() - shdr.sh_size) & ~(shdr.sh_addralign - 1);
ElfSection::insertBefore(section, dirty);
}
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[ELF64_R_SYM(r->r_info)].value.getSection();
add_code_section(section);
}
}
// TODO: sort out which non-aarch64 relocation types should be using
// `value` (even though in practice it's either 0 or the same as addend)
class pc32_relocation {
public:
Elf32_Addr operator()(unsigned int base_addr, Elf64_Off offset,
Elf64_Sxword addend, unsigned int addr,
Elf64_Word value) {
return addr + addend - offset - base_addr;
}
};
class arm_plt32_relocation {
public:
Elf32_Addr operator()(unsigned int base_addr, Elf64_Off offset,
Elf64_Sxword addend, unsigned int addr,
Elf64_Word value) {
// 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, Elf64_Off offset,
Elf64_Sxword addend, unsigned int addr,
Elf64_Word value) {
/* 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, Elf64_Off offset,
Elf64_Sxword addend, unsigned int addr,
Elf64_Word value) {
return addr + addend;
}
};
template <int start, int end>
class abs_lo12_nc_relocation {
public:
Elf32_Addr operator()(unsigned int base_addr, Elf64_Off offset,
Elf64_Sxword addend, unsigned int addr,
Elf64_Word value) {
// Fill the bits [end:start] of the immediate value in an ADD, LDR or STR
// instruction, at bits [21:10].
// per ARM® Architecture Reference Manual ARMv8, for ARMv8-A architecture
// profile C5.6.4, C5.6.83 or C5.6.178 and ELF for the ARM® 64-bit
// Architecture (AArch64) 4.6.6, Table 4-9.
Elf64_Word mask = (1 << (end + 1)) - 1;
return value | (((((addr + addend) & mask) >> start) & 0xfff) << 10);
}
};
class adr_prel_pg_hi21_relocation {
public:
Elf32_Addr operator()(unsigned int base_addr, Elf64_Off offset,
Elf64_Sxword addend, unsigned int addr,
Elf64_Word value) {
// Fill the bits [32:12] of the immediate value in a ADRP instruction,
// at bits [23:5]+[30:29].
// per ARM® Architecture Reference Manual ARMv8, for ARMv8-A architecture
// profile C5.6.10 and ELF for the ARM® 64-bit Architecture
// (AArch64) 4.6.6, Table 4-9.
Elf64_Word imm = ((addr + addend) >> 12) - ((base_addr + offset) >> 12);
Elf64_Word immLo = (imm & 0x3) << 29;
Elf64_Word immHi = (imm & 0x1ffffc) << 3;
return value & 0x9f00001f | immLo | immHi;
}
};
class call26_relocation {
public:
Elf32_Addr operator()(unsigned int base_addr, Elf64_Off offset,
Elf64_Sxword addend, unsigned int addr,
Elf64_Word value) {
// Fill the bits [27:2] of the immediate value in a BL instruction,
// at bits [25:0].
// per ARM® Architecture Reference Manual ARMv8, for ARMv8-A architecture
// profile C5.6.26 and ELF for the ARM® 64-bit Architecture
// (AArch64) 4.6.6, Table 4-10.
return value | (((addr + addend - offset - base_addr) & 0x0ffffffc) >> 2);
}
};
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, value);
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;
Elf64_Word value;
memcpy(&value, base + r->r_offset, 4);
Elf32_Addr new_value =
relocation(the_code->getAddr(), r->r_offset, r->r_addend, addr, value);
memcpy(base + r->r_offset, &new_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[ELF64_R_SYM(r->r_info)].name;
unsigned int addr;
if (symtab->syms[ELF64_R_SYM(r->r_info)].value.getSection() == nullptr) {
if (strcmp(name, "relhack") == 0) {
addr = relhack_section.getAddr();
} else if (strcmp(name, "relhack_end") == 0) {
addr = relhack_section.getAddr() + relhack_section.getSize();
} else if (strcmp(name, "__ehdr_start") == 0) {
// TODO: change this ugly hack to something better
ElfSection* ehdr = parent.getSection(1)->getPrevious()->getPrevious();
addr = ehdr->getAddr();
} else if (strcmp(name, "original_init") == 0) {
if (init_trampoline) {
addr = init_trampoline->getAddr();
} else {
addr = init;
}
} else if (strcmp(name, "real_original_init") == 0) {
addr = init;
} else if (relro && strcmp(name, "mprotect_cb") == 0) {
addr = mprotect_cb;
} else if (relro && strcmp(name, "sysconf_cb") == 0) {
addr = sysconf_cb;
} else if (relro && strcmp(name, "relro_start") == 0) {
addr = relro->getAddr();
} else if (relro && strcmp(name, "relro_end") == 0) {
addr = (relro->getAddr() + relro->getMemSize());
} 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[ELF64_R_SYM(r->r_info)].value.getSection();
assert((section->getType() == SHT_PROGBITS) &&
(section->getFlags() & SHF_EXECINSTR));
addr = symtab->syms[ELF64_R_SYM(r->r_info)].value.getValue();
}
// Do the relocation
#define REL(machine, type) (EM_##machine | (R_##machine##_##type << 8))
switch (elf->getMachine() | (ELF64_R_TYPE(r->r_info) << 8)) {
case REL(X86_64, PC32):
case REL(X86_64, PLT32):
case REL(386, PC32):
case REL(386, GOTPC):
case REL(ARM, GOTPC):
case REL(ARM, REL32):
case REL(AARCH64, PREL32):
case REL(AARCH64,
PREL64): // In theory PREL64 should have its own relocation
// function, but in practice it doesn't matter.
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(AARCH64, ADD_ABS_LO12_NC):
apply_relocation<abs_lo12_nc_relocation<0, 11>>(the_code, buf, &*r,
addr);
break;
case REL(AARCH64, ADR_PREL_PG_HI21):
apply_relocation<adr_prel_pg_hi21_relocation>(the_code, buf, &*r,
addr);
break;
case REL(AARCH64, LDST32_ABS_LO12_NC):
apply_relocation<abs_lo12_nc_relocation<2, 11>>(the_code, buf, &*r,
addr);
break;
case REL(AARCH64, LDST64_ABS_LO12_NC):
apply_relocation<abs_lo12_nc_relocation<3, 11>>(the_code, buf, &*r,
addr);
break;
case REL(AARCH64, CALL26):
apply_relocation<call26_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;
ElfRelHack_Section& relhack_section;
std::vector<ElfSection*> code;
unsigned int init;
ElfSection* init_trampoline;
unsigned int mprotect_cb;
unsigned int sysconf_cb;
int entry_point;
ElfSegment* relro;
};
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) {
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 = (Elf64_Xword)-1LL;
phdr.p_memsz = (Elf64_Xword)-1LL;
ElfSegment* newSegment = new ElfSegment(&phdr);
elf->insertSegmentAfter(segment, newSegment);
for (; it != segment->end(); ++it) {
newSegment->addSection(*it);
}
for (it = newSegment->begin(); it != newSegment->end(); ++it) {
segment->removeSection(*it);
}
break;
}
}
}
// EH_FRAME constants
static const unsigned char DW_EH_PE_absptr = 0x00;
static const unsigned char DW_EH_PE_omit = 0xff;
// Data size
static const unsigned char DW_EH_PE_LEB128 = 0x01;
static const unsigned char DW_EH_PE_data2 = 0x02;
static const unsigned char DW_EH_PE_data4 = 0x03;
static const unsigned char DW_EH_PE_data8 = 0x04;
// Data signedness
static const unsigned char DW_EH_PE_signed = 0x08;
// Modifiers
static const unsigned char DW_EH_PE_pcrel = 0x10;
// Return the data size part of the encoding value
static unsigned char encoding_data_size(unsigned char encoding) {
return encoding & 0x07;
}
// Advance `step` bytes in the buffer at `data` with size `size`, returning
// the advanced buffer pointer and remaining size.
// Returns true if step <= size.
static bool advance_buffer(char** data, size_t* size, size_t step) {
if (step > *size) return false;
*data += step;
*size -= step;
return true;
}
// Advance in the given buffer, skipping the full length of the variable-length
// encoded LEB128 type in CIE/FDE data.
static bool skip_LEB128(char** data, size_t* size) {
if (!*size) return false;
while (*size && (*(*data)++ & (char)0x80)) {
(*size)--;
}
return true;
}
// Advance in the given buffer, skipping the full length of a pointer encoded
// with the given encoding.
static bool skip_eh_frame_pointer(char** data, size_t* size,
unsigned char encoding) {
switch (encoding_data_size(encoding)) {
case DW_EH_PE_data2:
return advance_buffer(data, size, 2);
case DW_EH_PE_data4:
return advance_buffer(data, size, 4);
case DW_EH_PE_data8:
return advance_buffer(data, size, 8);
case DW_EH_PE_LEB128:
return skip_LEB128(data, size);
}
throw std::runtime_error("unreachable");
}
// Specialized implementations for adjust_eh_frame_pointer().
template <typename T>
static bool adjust_eh_frame_sized_pointer(char** data, size_t* size,
ElfSection* eh_frame,
unsigned int origAddr, Elf* elf) {
if (*size < sizeof(T)) return false;
serializable<FixedSizeData<T>> pointer(*data, *size, elf->getClass(),
elf->getData());
mozilla::CheckedInt<T> value = pointer.value;
if (origAddr < eh_frame->getAddr()) {
unsigned int diff = eh_frame->getAddr() - origAddr;
value -= diff;
} else {
unsigned int diff = origAddr - eh_frame->getAddr();
value += diff;
}
if (!value.isValid())
throw std::runtime_error("Overflow while adjusting eh_frame");
pointer.value = value.value();
pointer.serialize(*data, *size, elf->getClass(), elf->getData());
return advance_buffer(data, size, sizeof(T));
}
// In the given eh_frame section, adjust the pointer with the given encoding,
// pointed to by the given buffer (`data`, `size`), considering the eh_frame
// section was originally at `origAddr`. Also advances in the buffer.
static bool adjust_eh_frame_pointer(char** data, size_t* size,
unsigned char encoding,
ElfSection* eh_frame, unsigned int origAddr,
Elf* elf) {
if ((encoding & 0x70) != DW_EH_PE_pcrel)
return skip_eh_frame_pointer(data, size, encoding);
if (encoding & DW_EH_PE_signed) {
switch (encoding_data_size(encoding)) {
case DW_EH_PE_data2:
return adjust_eh_frame_sized_pointer<int16_t>(data, size, eh_frame,
origAddr, elf);
case DW_EH_PE_data4:
return adjust_eh_frame_sized_pointer<int32_t>(data, size, eh_frame,
origAddr, elf);
case DW_EH_PE_data8:
return adjust_eh_frame_sized_pointer<int64_t>(data, size, eh_frame,
origAddr, elf);
}
} else {
switch (encoding_data_size(encoding)) {
case DW_EH_PE_data2:
return adjust_eh_frame_sized_pointer<uint16_t>(data, size, eh_frame,
origAddr, elf);
case DW_EH_PE_data4:
return adjust_eh_frame_sized_pointer<uint32_t>(data, size, eh_frame,
origAddr, elf);
case DW_EH_PE_data8:
return adjust_eh_frame_sized_pointer<uint64_t>(data, size, eh_frame,
origAddr, elf);
}
}
throw std::runtime_error("Unsupported eh_frame pointer encoding");
}
// The eh_frame section may contain "PC"-relative pointers. If we move the
// section, those need to be adjusted. Other type of pointers are relative to
// sections we don't touch.
static void adjust_eh_frame(ElfSection* eh_frame, unsigned int origAddr,
Elf* elf) {
if (eh_frame->getAddr() == origAddr) // nothing to do;
return;
char* data = const_cast<char*>(eh_frame->getData());
size_t size = eh_frame->getSize();
unsigned char LSDAencoding = DW_EH_PE_omit;
unsigned char FDEencoding = DW_EH_PE_absptr;
bool hasZ = false;
while (size) {
if (size < sizeof(uint32_t)) goto malformed;
serializable<FixedSizeData<uint32_t>> entryLength(
data, size, elf->getClass(), elf->getData());
if (!advance_buffer(&data, &size, sizeof(uint32_t))) goto malformed;
char* cursor = data;
size_t length = entryLength.value;
if (length == 0) {
continue;
}
if (size < sizeof(uint32_t)) goto malformed;
serializable<FixedSizeData<uint32_t>> id(data, size, elf->getClass(),
elf->getData());
if (!advance_buffer(&cursor, &length, sizeof(uint32_t))) goto malformed;
if (id.value == 0) {
// This is a Common Information Entry
if (length < 2) goto malformed;
// Reset LSDA and FDE encodings, and hasZ for subsequent FDEs.
LSDAencoding = DW_EH_PE_omit;
FDEencoding = DW_EH_PE_absptr;
hasZ = false;
// CIE version. Should only be 1 or 3.
char version = *cursor++;
length--;
if (version != 1 && version != 3) {
throw std::runtime_error("Unsupported eh_frame version");
}
// NUL terminated string.
const char* augmentationString = cursor;
size_t l = strnlen(augmentationString, length - 1);
if (l == length - 1) goto malformed;
if (!advance_buffer(&cursor, &length, l + 1)) goto malformed;
// Skip code alignment factor (LEB128)
if (!skip_LEB128(&cursor, &length)) goto malformed;
// Skip data alignment factor (LEB128)
if (!skip_LEB128(&cursor, &length)) goto malformed;
// Skip return address register (single byte in CIE version 1, LEB128
// in CIE version 3)
if (version == 1) {
if (!advance_buffer(&cursor, &length, 1)) goto malformed;
} else {
if (!skip_LEB128(&cursor, &length)) goto malformed;
}
// Past this, it's data driven by the contents of the augmentation string.
for (size_t i = 0; i < l; i++) {
if (!length) goto malformed;
switch (augmentationString[i]) {
case 'z':
if (!skip_LEB128(&cursor, &length)) goto malformed;
hasZ = true;
break;
case 'L':
LSDAencoding = *cursor++;
length--;
break;
case 'R':
FDEencoding = *cursor++;
length--;
break;
case 'P': {
unsigned char encoding = (unsigned char)*cursor++;
length--;
if (!adjust_eh_frame_pointer(&cursor, &length, encoding, eh_frame,
origAddr, elf))
goto malformed;
} break;
default:
goto malformed;
}
}
} else {
// This is a Frame Description Entry
// Starting address
if (!adjust_eh_frame_pointer(&cursor, &length, FDEencoding, eh_frame,
origAddr, elf))
goto malformed;
if (LSDAencoding != DW_EH_PE_omit) {
// Skip number of bytes, same size as the starting address.
if (!skip_eh_frame_pointer(&cursor, &length, FDEencoding))
goto malformed;
if (hasZ) {
if (!skip_LEB128(&cursor, &length)) goto malformed;
}
// pointer to the LSDA.
if (!adjust_eh_frame_pointer(&cursor, &length, LSDAencoding, eh_frame,
origAddr, elf))
goto malformed;
}
}
data += entryLength.value;
size -= entryLength.value;
}
return;
malformed:
throw std::runtime_error("malformed .eh_frame");
}
template <typename Rel_Type>
int do_relocation_section(Elf* elf, unsigned int rel_type,
unsigned int rel_type2, bool force) {
ElfDynamic_Section* dyn = elf->getDynSection();
if (dyn == nullptr) {
fprintf(stderr, "Couldn't find SHT_DYNAMIC section\n");
return -1;
}
ElfRel_Section<Rel_Type>* section =
(ElfRel_Section<Rel_Type>*)dyn->getSectionForType(Rel_Type::d_tag);
if (section == nullptr) {
fprintf(stderr, "No relocations\n");
return -1;
}
assert(section->getType() == Rel_Type::sh_type);
Elf64_Shdr relhack64_section = {0,
SHT_PROGBITS,
SHF_ALLOC,
0,
(Elf64_Off)-1LL,
0,
SHN_UNDEF,
0,
Elf_Addr::size(elf->getClass()),
Elf_Addr::size(elf->getClass())};
Elf64_Shdr relhackcode64_section = {0,
SHT_PROGBITS,
SHF_ALLOC | SHF_EXECINSTR,
0,
(Elf64_Off)-1LL,
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(relhack64_section);
Elf_Shdr relhackcode_section(relhackcode64_section);
auto relhack_ptr = std::make_unique<ElfRelHack_Section>(relhack_section);
auto relhack = relhack_ptr.get();
ElfSymtab_Section* symtab = (ElfSymtab_Section*)section->getLink();
Elf_SymValue* sym = symtab->lookup("__cxa_pure_virtual");
std::vector<Rel_Type> new_rels;
std::vector<Rel_Type> init_array_relocs;
size_t init_array_insert = 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 (!ELF64_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 (ELF64_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 ((ELF64_R_TYPE(i->r_info) == rel_type2) &&
(sym == &symtab->syms[ELF64_R_SYM(i->r_info)])) {
memset((char*)loc.getBuffer(), 0, entry_sz);
continue;
}
}
}
// Keep track of the relocations associated with the init_array section.
if (init_array && i->r_offset >= init_array->getAddr() &&
i->r_offset < init_array->getAddr() + init_array->getSize()) {
init_array_relocs.push_back(*i);
init_array_insert = new_rels.size();
} else if (!(loc.getSection()->getFlags() & SHF_WRITE) ||
(ELF64_R_TYPE(i->r_info) != rel_type)) {
// 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 if (i->r_offset & 1) {
// RELR packing doesn't support relocations at an odd address, but
// there shouldn't be any.
new_rels.push_back(*i);
} else {
// With Elf_Rel, the value pointed by the relocation offset is the addend.
// With Elf_Rela, the addend is in the relocation entry, but the elfhacked
// relocation info doesn't contain it. Elfhack relies on the value pointed
// by the relocation offset to also contain the addend. Which is true with
// BFD ld and gold, but not lld, which leaves that nulled out. So if that
// value is nulled out, we update it to the addend.
Elf_Addr addr(loc.getBuffer(), entry_sz, elf->getClass(), elf->getData());
unsigned int addend = get_addend(&*i, elf);
if (addr.value == 0) {
addr.value = addend;
addr.serialize(const_cast<char*>(loc.getBuffer()), entry_sz,
elf->getClass(), elf->getData());
} else if (addr.value != addend) {
fprintf(stderr,
"Relocation addend inconsistent with content. Skipping\n");
return -1;
}
relhack->push_back(i->r_offset);
}
}
if (init_array) {
// Some linkers create a DT_INIT_ARRAY section that, for all purposes,
// is empty: it only contains 0x0 or 0xffffffff pointers with no
// relocations. In some other cases, there can be null pointers with no
// relocations in the middle of the section. Example: crtend_so.o in the
// Android NDK contains a sized .init_array with a null pointer and no
// relocation, which ends up in all Android libraries, and in some cases it
// ends up in the middle of the final .init_array section. If we have such a
// reusable slot at the beginning of .init_array, we just use it. It we have
// one in the middle of .init_array, we slide its content to move the "hole"
// at the beginning and use it there (we need our injected code to run
// before any other). Otherwise, replace the first entry and keep the
// original pointer.
std::sort(init_array_relocs.begin(), init_array_relocs.end(),
[](Rel_Type& a, Rel_Type& b) { return a.r_offset < b.r_offset; });
size_t expected = init_array->getAddr();
const size_t zero = 0;
const size_t all = SIZE_MAX;
const char* data = init_array->getData();
size_t length = Elf_Addr::size(elf->getClass());
size_t off = 0;
for (; off < init_array_relocs.size(); off++) {
auto& r = init_array_relocs[off];
if (r.r_offset >= expected + length &&
(memcmp(data + off * length, &zero, length) == 0 ||
memcmp(data + off * length, &all, length) == 0)) {
// We found a hole, move the preceding entries.
while (off) {
auto& p = init_array_relocs[--off];
if (ELF64_R_TYPE(p.r_info) == rel_type) {
unsigned int addend = get_addend(&p, elf);
p.r_offset += length;
set_relative_reloc(&p, elf, addend);
} else {
fprintf(stderr,
"Unsupported relocation type in DT_INIT_ARRAY. Skipping\n");
return -1;
}
}
break;
}
expected = r.r_offset + length;
}
if (off == 0) {
// We either found a hole above, and can now use the first entry,
// or the init_array section is effectively empty (see further above)
// and we also can use the first entry.
// Either way, code further below will take care of actually setting
// the right r_info and r_added for the relocation.
Rel_Type rel;
rel.r_offset = init_array->getAddr();
init_array_relocs.insert(init_array_relocs.begin(), rel);
} else {
// Use relocated value of DT_INIT_ARRAY's first entry for the
// function to be called by the injected code.
auto& rel = init_array_relocs[0];
unsigned int addend = get_addend(&rel, elf);
if (ELF64_R_TYPE(rel.r_info) == rel_type) {
original_init = addend;
} else if (ELF64_R_TYPE(rel.r_info) == rel_type2) {
ElfSymtab_Section* symtab = (ElfSymtab_Section*)section->getLink();
original_init =
symtab->syms[ELF64_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;
}
}
new_rels.insert(std::next(new_rels.begin(), init_array_insert),
init_array_relocs.begin(), init_array_relocs.end());
}
unsigned int mprotect_cb = 0;
unsigned int sysconf_cb = 0;
// If there is a relro segment, our injected code will run after the linker
// sets the corresponding pages read-only. We need to make our code change
// that to read-write before applying relocations, which means it needs to
// call mprotect. To do that, we need to find a reference to the mprotect
// symbol. In case the library already has one, we use that, but otherwise, we
// add the symbol. Then the injected code needs to be able to call the
// corresponding function, which means it needs access to a pointer to it. We
// get such a pointer by making the linker apply a relocation for the symbol
// at an address our code can read. The problem here is that there is not much
// relocated space where we can put such a pointer, so we abuse the bss
// section temporarily (it will be restored to a null value before any code
// can actually use it)
if (elf->getSegmentByType(PT_GNU_RELRO)) {
ElfSection* gnu_versym = dyn->getSectionForType(DT_VERSYM);
auto lookup = [&symtab, &gnu_versym](const char* symbol) {
Elf_SymValue* sym_value = symtab->lookup(symbol, STT(FUNC));
if (!sym_value) {
symtab->syms.emplace_back();
sym_value = &symtab->syms.back();
symtab->grow(symtab->syms.size() * symtab->getEntSize());
sym_value->name =
((ElfStrtab_Section*)symtab->getLink())->getStr(symbol);
sym_value->info = ELF64_ST_INFO(STB_GLOBAL, STT_FUNC);
sym_value->other = STV_DEFAULT;
new (&sym_value->value) ElfLocation(nullptr, 0, ElfLocation::ABSOLUTE);
sym_value->size = 0;
sym_value->defined = false;
// The DT_VERSYM data (in the .gnu.version section) has the same number
// of entries as the symbols table. Since we added one entry there, we
// need to add one entry here. Zeroes in the extra data means no version
// for that symbol, which is the simplest thing to do.
if (gnu_versym) {
gnu_versym->grow(gnu_versym->getSize() + gnu_versym->getEntSize());
}
}
return sym_value;
};
Elf_SymValue* mprotect = lookup("mprotect");
Elf_SymValue* sysconf = lookup("sysconf");
// Add relocations for the mprotect and sysconf symbols.
auto add_relocation_to = [&new_rels, &symtab, rel_type2](
Elf_SymValue* symbol, unsigned int location) {
new_rels.emplace_back();
Rel_Type& rel = new_rels.back();
memset(&rel, 0, sizeof(rel));
rel.r_info = ELF64_R_INFO(
std::distance(symtab->syms.begin(),
std::vector<Elf_SymValue>::iterator(symbol)),
rel_type2);
rel.r_offset = location;
return location;
};
// Find the beginning of the bss section, and use an aligned location in
// there for the relocation.
for (ElfSection* s = elf->getSection(1); s != nullptr; s = s->getNext()) {
if (s->getType() != SHT_NOBITS ||
(s->getFlags() & (SHF_TLS | SHF_WRITE)) != SHF_WRITE) {
continue;
}
size_t ptr_size = Elf_Addr::size(elf->getClass());
size_t usable_start = (s->getAddr() + ptr_size - 1) & ~(ptr_size - 1);
size_t usable_end = (s->getAddr() + s->getSize()) & ~(ptr_size - 1);
if (usable_end - usable_start >= 2 * ptr_size) {
mprotect_cb = add_relocation_to(mprotect, usable_start);
sysconf_cb = add_relocation_to(sysconf, usable_start + ptr_size);
break;
}
}
if (mprotect_cb == 0 || sysconf_cb == 0) {
fprintf(stderr, "Couldn't find .bss. Skipping\n");
return -1;
}
}
size_t old_size = section->getSize();
section->rels.assign(new_rels.begin(), new_rels.end());
section->shrink(new_rels.size() * section->getEntSize());
auto relhackcode_ptr = std::make_unique<ElfRelHackCode_Section>(
relhackcode_section, *elf, *relhack, original_init, mprotect_cb,
sysconf_cb);
auto relhackcode = relhackcode_ptr.get();
// Find the first executable section, and insert the relhack code before
// that. The relhack data is inserted between .rel.dyn and .rel.plt.
ElfSection* first_executable = nullptr;
for (ElfSection* s = elf->getSection(1); s != nullptr; s = s->getNext()) {
if (s->getFlags() & SHF_EXECINSTR) {
first_executable = s;
break;
}
}
if (!first_executable) {
fprintf(stderr, "Couldn't find executable section. Skipping\n");
return -1;
}
// Once the pointers for relhack, relhackcode, and init are inserted,
// their ownership is transferred to the Elf object, which will free
// them when itself is freed. Hence the .release() calls here (and
// the init.release() call later on). Please note that the raw
// pointers will continue to be used after .release(), which is why
// we are caching them (since .release() will end up setting the
// smart pointer's internal raw pointer to nullptr).
relhack->insertBefore(section);
relhack_ptr.release();
relhackcode->insertBefore(first_executable);
relhackcode_ptr.release();
// Don't try further if we can't gain from the relocation section size change.
// We account for the fact we're going to split the PT_LOAD before the
// injected code section, so the overhead of the page alignment for section
// needs to be accounted for.
size_t align = first_executable->getSegmentByType(PT_LOAD)->getAlign();
size_t new_size = relhack->getSize() + section->getSize() +
relhackcode->getSize() +
(relhackcode->getAddr() & (align - 1));
if (!force && (new_size >= old_size || old_size - new_size < align)) {
fprintf(stderr, "No gain. Skipping\n");
return -1;
}
// .eh_frame/.eh_frame_hdr may be between the relocation sections and the
// executable sections. When that happens, we may end up creating a separate
// PT_LOAD for just both of them because they are not considered relocatable.
// But they are, in fact, kind of relocatable, albeit with some manual work.
// Which we'll do here.
ElfSegment* eh_frame_segment = elf->getSegmentByType(PT_GNU_EH_FRAME);
ElfSection* eh_frame_hdr =
eh_frame_segment ? eh_frame_segment->getFirstSection() : nullptr;
// The .eh_frame section usually follows the eh_frame_hdr section.
ElfSection* eh_frame = eh_frame_hdr ? eh_frame_hdr->getNext() : nullptr;
ElfSection* first = eh_frame_hdr;
ElfSection* second = eh_frame;
if (eh_frame && strcmp(eh_frame->getName(), ".eh_frame")) {
// But sometimes it appears *before* the eh_frame_hdr section.
eh_frame = eh_frame_hdr->getPrevious();
first = eh_frame;
second = eh_frame_hdr;
}
if (eh_frame_hdr && (!eh_frame || strcmp(eh_frame->getName(), ".eh_frame"))) {
throw std::runtime_error(
"Expected to find an .eh_frame section adjacent to .eh_frame_hdr");
}
if (eh_frame && first->getAddr() > relhack->getAddr() &&
second->getAddr() < first_executable->getAddr()) {
// The distance between both sections needs to be preserved because
// eh_frame_hdr contains relative offsets to eh_frame. Well, they could be
// relocated too, but it's not worth the effort for the few number of bytes
// this would save.
Elf64_Off distance = second->getAddr() - first->getAddr();
Elf64_Addr origAddr = eh_frame->getAddr();
ElfSection* previous = first->getPrevious();
first->getShdr().sh_addr = (previous->getAddr() + previous->getSize() +
first->getAddrAlign() - 1) &
~(first->getAddrAlign() - 1);
second->getShdr().sh_addr =
(first->getAddr() + std::min(first->getSize(), distance) +
second->getAddrAlign() - 1) &
~(second->getAddrAlign() - 1);
// Re-adjust to keep the original distance.
// If the first section has a smaller alignment requirement than the second,
// the second will be farther away, so we need to adjust the first.
// If the second section has a smaller alignment requirement than the first,
// it will already be at the right distance.
first->getShdr().sh_addr = second->getAddr() - distance;
assert(distance == second->getAddr() - first->getAddr());
first->markDirty();
adjust_eh_frame(eh_frame, origAddr, elf);
}
// Adjust PT_LOAD segments
for (ElfSegment* segment = elf->getSegmentByType(PT_LOAD); segment;
segment = elf->getSegmentByType(PT_LOAD, segment)) {
maybe_split_segment(elf, segment);
}
// Ensure Elf sections will be at their final location.
elf->normalize();
auto init =
std::make_unique<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 = §ion->rels[init_array_insert];
rel->r_info = ELF64_R_INFO(0, rel_type); // Set as a relative relocation
set_relative_reloc(rel, elf, init->getValue());
} else {
if (dyn->setValueForType(DT_INIT, init.get())) {
init.release();
} else {
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) {
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);
break;
case EM_X86_64:
exit = do_relocation_section<Elf_Rela>(&elf, R_X86_64_RELATIVE,
R_X86_64_64, force);
break;
case EM_ARM:
exit = do_relocation_section<Elf_Rel>(&elf, R_ARM_RELATIVE, R_ARM_ABS32,
force);
break;
case EM_AARCH64:
exit = do_relocation_section<Elf_Rela>(&elf, R_AARCH64_RELATIVE,
R_AARCH64_ABS64, force);
break;
default:
throw std::runtime_error("unsupported architecture");
}
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;
}
// When both elfhack sections are in the same segment, try to merge
// the segment that contains them both and the following segment.
// When the elfhack sections are in separate segments, try to merge
// those segments.
ElfSegment* first = data->getSegmentByType(PT_LOAD);
ElfSegment* second = text->getSegmentByType(PT_LOAD);
if (first == second) {
second = elf.getSegmentByType(PT_LOAD, first);
}
// Only merge the segments when their flags match.
if (second->getFlags() != first->getFlags()) {
fprintf(stderr, "Couldn't merge 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);
elf.normalize();
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;
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 (revert) {
undo_file(argv[arg], backup);
} else
do_file(argv[arg], backup, force);
}
free(rundir);
return 0;
}