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pjs/build/unix/elfhack/elfhack.cpp

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21 KiB
C++
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/* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is elfhack.
*
* The Initial Developer of the Original Code is
* Mozilla Foundation.
* Portions created by the Initial Developer are Copyright (C) 2010
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
* Mike Hommey <mh@glandium.org>
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of either the GPL or the LGPL, and not to allow others to
* use your version of this file under the terms of the MPL, indicate your
* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
#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_THM_JUMP24
#define R_ARM_THM_JUMP24 0x1e
#endif
char *rundir = NULL;
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);
}
};
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, NULL, NULL)
{
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)
: ElfSection(s, NULL, NULL), parent(e) {
std::string file(rundir);
init = parent.getDynSection()->getSectionForType(DT_INIT);
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");
}
if (init == NULL)
file += "-noinit";
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 = NULL;
// Get all executable sections from the injected code object.
// Most of the time, there will only be one for the init function,
// but on e.g. x86, there is a separate section for
// __i686.get_pc_thunk.$reg
// Find the symbol table at the same time.
for (ElfSection *section = elf->getSection(1); section != NULL;
section = section->getNext()) {
if ((section->getType() == SHT_PROGBITS) &&
(section->getFlags() & SHF_EXECINSTR)) {
code.push_back(section);
// We need to align this section depending on the greater
// alignment required by code sections.
if (shdr.sh_addralign < section->getAddrAlign())
shdr.sh_addralign = section->getAddrAlign();
} else if (section->getType() == SHT_SYMTAB) {
symtab = (ElfSymtab_Section *) section;
}
}
assert(code.size() != 0);
if (symtab == NULL)
throw std::runtime_error("Couldn't find a symbol table for the injected code");
// Find the init symbol
entry_point = -1;
int shndx = 0;
Elf_SymValue *sym = symtab->lookup("init");
if (sym) {
entry_point = sym->value.getValue();
shndx = sym->value.getSection()->getIndex();
} else
throw std::runtime_error("Couldn't find an 'init' symbol in the injected code");
// 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;
}
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();
if ((*c)->getIndex() < shndx)
entry_point += (*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 (ElfSection *rel = elf->getSection(1); rel != NULL; rel = rel->getNext())
if ((rel->getType() == SHT_REL) || (rel->getType() == SHT_RELA)) {
ElfSection *section = rel->getInfo().section;
if ((section->getType() == SHT_PROGBITS) && (section->getFlags() & SHF_EXECINSTR)) {
if (rel->getType() == SHT_REL)
apply_relocations((ElfRel_Section<Elf_Rel> *)rel, section);
else
apply_relocations((ElfRel_Section<Elf_Rela> *)rel, section);
}
}
ElfSection::serialize(file, ei_class, ei_data);
}
bool isRelocatable() {
return true;
}
unsigned int getEntryPoint() {
return entry_point;
}
private:
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 instructions as per
ARM Architecture Reference Manual ARM® v7-A and ARM® v7-R edition, A8.6.16
We limit ourselves to Encoding T3.
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;
if (((word0 & 0xf800) != 0xf000) || ((word1 & 0xd000) != 0x9000))
throw std::runtime_error("R_ARM_THM_JUMP24 relocation only supported for B.W <label>");
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) |
(0x9000 << 16) | (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() == NULL) {
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->getAddr();
} 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, PLT32):
apply_relocation<arm_plt32_relocation>(the_code, buf, &*r, addr);
break;
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;
ElfSection *init;
int entry_point;
};
template <typename Rel_Type>
int do_relocation_section(Elf *elf, unsigned int rel_type, unsigned int rel_type2)
{
ElfDynamic_Section *dyn = elf->getDynSection();
if (dyn ==NULL) {
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 };
Elf_Shdr relhack_section(relhack32_section);
Elf_Shdr relhackcode_section(relhackcode32_section);
ElfRelHack_Section *relhack = new ElfRelHack_Section(relhack_section);
ElfRelHackCode_Section *relhackcode = new ElfRelHackCode_Section(relhackcode_section, *elf);
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;
int entry_sz = (elf->getClass() == ELFCLASS32) ? 4 : 8;
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;
ElfSection *section = elf->getSectionAt(i->r_offset);
// __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) {
serializable<Elf_Addr_Traits> addr(&section->getData()[i->r_offset - section->getAddr()], entry_sz, elf->getClass(), elf->getData());
if (addr.value == sym->value.getValue()) {
memset((char *)&section->getData()[i->r_offset - section->getAddr()], 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 *)&section->getData()[i->r_offset - section->getAddr()], 0, entry_sz);
continue;
}
}
}
// Don't pack relocations happening in non writable sections.
// Our injected code is likely not to be allowed to write there.
if (!(section->getFlags() & SHF_WRITE) || (ELF32_R_TYPE(i->r_info) != rel_type) ||
(relro && (i->r_offset >= relro->getAddr()) &&
(i->r_offset < relro->getAddr() + relro->getMemSize())))
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 NULL
relhack_entry.r_offset = relhack_entry.r_info = 0;
relhack->push_back(relhack_entry);
relhackcode->insertAfter(section);
relhack->insertAfter(relhackcode);
unsigned int old_end = section->getOffset() + section->getSize();
section->rels.assign(new_rels.begin(), new_rels.end());
section->shrink(new_rels.size() * section->getEntSize());
ElfLocation *init = new ElfLocation(relhackcode, relhackcode->getEntryPoint());
dyn->setValueForType(DT_INIT, init);
// 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));
if (relhack->getOffset() + relhack->getSize() >= old_end) {
fprintf(stderr, "No gain. Skipping\n");
return -1;
}
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)
{
std::ifstream file(name, std::ios::in|std::ios::binary);
Elf *elf = new Elf(file);
unsigned int size = elf->getSize();
fprintf(stderr, "%s: ", name);
for (ElfSection *section = elf->getSection(1); section != NULL;
section = section->getNext()) {
if (section->getName() &&
(strncmp(section->getName(), ".elfhack.", 9) == 0)) {
fprintf(stderr, "Already elfhacked. Skipping\n");
delete elf;
return;
}
}
int exit = -1;
switch (elf->getMachine()) {
case EM_386:
exit = do_relocation_section<Elf_Rel>(elf, R_386_RELATIVE, R_386_32);
break;
case EM_X86_64:
exit = do_relocation_section<Elf_Rela>(elf, R_X86_64_RELATIVE, R_X86_64_64);
break;
case EM_ARM:
exit = do_relocation_section<Elf_Rel>(elf, R_ARM_RELATIVE, R_ARM_ABS32);
break;
}
if (exit == 0) {
if (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());
}
}
delete elf;
}
int main(int argc, char *argv[])
{
int arg;
bool backup = false;
char *lastSlash = rindex(argv[0], '/');
if (lastSlash != NULL)
rundir = strndup(argv[0], lastSlash - argv[0]);
for (arg = 1; arg < argc; arg++) {
if (strcmp(argv[arg], "-b") == 0)
backup = true;
else
do_file(argv[arg], backup);
}
free(rundir);
return 0;
}
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