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-rw-r--r--build/unix/elfhack/elfhack.cpp1325
1 files changed, 1325 insertions, 0 deletions
diff --git a/build/unix/elfhack/elfhack.cpp b/build/unix/elfhack/elfhack.cpp
new file mode 100644
index 0000000000..ec01e54674
--- /dev/null
+++ b/build/unix/elfhack/elfhack.cpp
@@ -0,0 +1,1325 @@
+/* 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"
+#include "mozilla/CheckedInt.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,
+ 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;
+ 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) > 0xffffff, where 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) {
+ 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, char ei_class, 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[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 = relhack_section.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) {
+ 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[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(X86_64, PLT32):
+ 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;
+ 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 = (unsigned int)-1;
+ phdr.p_memsz = (unsigned int)-1;
+ 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 char DW_EH_PE_absptr = 0x00;
+static const char DW_EH_PE_omit = 0xff;
+
+// Data size
+static const char DW_EH_PE_LEB128 = 0x01;
+static const char DW_EH_PE_data2 = 0x02;
+static const char DW_EH_PE_data4 = 0x03;
+static const char DW_EH_PE_data8 = 0x04;
+
+// Data signedness
+static const char DW_EH_PE_signed = 0x08;
+
+// Modifiers
+static const char DW_EH_PE_pcrel = 0x10;
+
+// Return the data size part of the encoding value
+static char encoding_data_size(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, 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, 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();
+ char LSDAencoding = DW_EH_PE_omit;
+ char FDEencoding = DW_EH_PE_absptr;
+ bool hasZ = false;
+
+ // Decoding of eh_frame based on https://www.airs.com/blog/archives/460
+ 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': {
+ char encoding = *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);
+
+ 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;
+ 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 (!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 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) ||
+ (ELF32_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 {
+ // 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;
+ }
+ 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);
+
+ 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 (ELF32_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 (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;
+ }
+ }
+
+ 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 = ELF32_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 = ELF32_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());
+
+ ElfRelHackCode_Section* relhackcode =
+ new ElfRelHackCode_Section(relhackcode_section, *elf, *relhack,
+ original_init, mprotect_cb, sysconf_cb);
+ // 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;
+ }
+
+ relhack->insertBefore(section);
+ relhackcode->insertBefore(first_executable);
+
+ // 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.
+ unsigned int distance = second->getAddr() - first->getAddr();
+ unsigned int 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();
+ 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_insert];
+ rel->r_info = ELF32_R_INFO(0, rel_type); // Set as a relative relocation
+ set_relative_reloc(rel, 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) {
+ 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;
+ }
+ 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;
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-20 22:32:46 +0000