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Diffstat (limited to 'build/unix/elfhack/elfhack.cpp')
| -rw-r--r-- | build/unix/elfhack/elfhack.cpp | 1450 |
1 files changed, 1450 insertions, 0 deletions
diff --git a/build/unix/elfhack/elfhack.cpp b/build/unix/elfhack/elfhack.cpp new file mode 100644 index 0000000000..0a056eef19 --- /dev/null +++ b/build/unix/elfhack/elfhack.cpp @@ -0,0 +1,1450 @@ +/* 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 <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) { + 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 + // https://groups.google.com/g/generic-abi/c/bX460iggiKg/m/Jnz1lgLJAgAJ + // 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() * 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) > 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, 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, "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[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): + 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; + + // 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': { + 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); + } + } + // Last entry must be a nullptr + relhack->push_back(0); + + 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; +} |