forked from mirrors/gecko-dev
52c87462c7
When .rel.plt and .relr.dyn are the same size, after the section header for .relr.dyn has been updated, it matches the condition for .rel.plt, and we ended up undoing the change. Differential Revision: https://phabricator.services.mozilla.com/D192981
567 lines
20 KiB
C++
567 lines
20 KiB
C++
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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// This program acts as a linker wrapper. Its executable name is meant
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// to be that of a linker, and it will find the next linker with the same
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// name in $PATH. However, if for some reason the next linker cannot be
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// found this way, the caller may pass its path via the --real-linker
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// option.
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//
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// More in-depth background on https://glandium.org/blog/?p=4297
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#include "relrhack.h"
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#include <algorithm>
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#include <cstring>
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#include <filesystem>
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#include <fstream>
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#include <iostream>
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#include <optional>
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#include <spawn.h>
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#include <sstream>
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#include <stdexcept>
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#include <sys/wait.h>
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#include <unistd.h>
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#include <unordered_map>
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#include <utility>
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#include <vector>
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namespace fs = std::filesystem;
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class CantSwapSections : public std::runtime_error {
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public:
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CantSwapSections(const char* what) : std::runtime_error(what) {}
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};
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template <int bits>
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struct Elf {};
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#define ELF(bits) \
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template <> \
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struct Elf<bits> { \
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using Ehdr = Elf##bits##_Ehdr; \
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using Phdr = Elf##bits##_Phdr; \
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using Shdr = Elf##bits##_Shdr; \
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using Dyn = Elf##bits##_Dyn; \
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using Addr = Elf##bits##_Addr; \
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using Word = Elf##bits##_Word; \
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using Off = Elf##bits##_Off; \
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using Verneed = Elf##bits##_Verneed; \
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using Vernaux = Elf##bits##_Vernaux; \
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}
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ELF(32);
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ELF(64);
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template <int bits>
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struct RelR : public Elf<bits> {
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using Elf_Ehdr = typename Elf<bits>::Ehdr;
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using Elf_Phdr = typename Elf<bits>::Phdr;
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using Elf_Shdr = typename Elf<bits>::Shdr;
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using Elf_Dyn = typename Elf<bits>::Dyn;
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using Elf_Addr = typename Elf<bits>::Addr;
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using Elf_Word = typename Elf<bits>::Word;
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using Elf_Off = typename Elf<bits>::Off;
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using Elf_Verneed = typename Elf<bits>::Verneed;
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using Elf_Vernaux = typename Elf<bits>::Vernaux;
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#define TAG_NAME(t) \
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{ t, #t }
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class DynInfo {
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public:
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using Tag = decltype(Elf_Dyn::d_tag);
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using Value = decltype(Elf_Dyn::d_un.d_val);
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bool is_wanted(Tag tag) const { return tag_names.count(tag); }
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void insert(off_t offset, Tag tag, Value val) {
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data[tag] = std::make_pair(offset, val);
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}
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off_t offset(Tag tag) const { return data.at(tag).first; }
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bool contains(Tag tag) const { return data.count(tag); }
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Value& operator[](Tag tag) {
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if (!is_wanted(tag)) {
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std::stringstream msg;
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msg << "Tag 0x" << std::hex << tag << " is not in DynInfo::tag_names";
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throw std::runtime_error(msg.str());
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}
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return data[tag].second;
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}
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const char* name(Tag tag) const { return tag_names.at(tag); }
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private:
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std::unordered_map<Tag, std::pair<off_t, Value>> data;
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const std::unordered_map<Tag, const char*> tag_names = {
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TAG_NAME(DT_JMPREL), TAG_NAME(DT_PLTRELSZ), TAG_NAME(DT_RELR),
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TAG_NAME(DT_RELRENT), TAG_NAME(DT_RELRSZ), TAG_NAME(DT_RELA),
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TAG_NAME(DT_RELASZ), TAG_NAME(DT_RELAENT), TAG_NAME(DT_REL),
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TAG_NAME(DT_RELSZ), TAG_NAME(DT_RELENT), TAG_NAME(DT_STRTAB),
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TAG_NAME(DT_STRSZ), TAG_NAME(DT_VERNEED), TAG_NAME(DT_VERNEEDNUM),
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};
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};
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// Translate a virtual address into an offset in the file based on the program
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// headers' PT_LOAD.
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static Elf_Addr get_offset(const std::vector<Elf_Phdr>& phdr, Elf_Addr addr) {
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for (const auto& p : phdr) {
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if (p.p_type == PT_LOAD && addr >= p.p_vaddr &&
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addr < p.p_vaddr + p.p_filesz) {
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return addr - (p.p_vaddr - p.p_paddr);
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}
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}
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return 0;
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}
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static bool hack(std::fstream& f);
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};
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template <typename T>
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T read_one_at(std::istream& in, off_t pos) {
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T result;
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in.seekg(pos, std::ios::beg);
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in.read(reinterpret_cast<char*>(&result), sizeof(T));
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return result;
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}
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template <typename T>
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std::vector<T> read_vector_at(std::istream& in, off_t pos, size_t num) {
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std::vector<T> result(num);
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in.seekg(pos, std::ios::beg);
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in.read(reinterpret_cast<char*>(result.data()), num * sizeof(T));
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return result;
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}
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void write_at(std::ostream& out, off_t pos, const char* buf, size_t len) {
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out.seekp(pos, std::ios::beg);
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out.write(buf, len);
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}
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template <typename T>
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void write_one_at(std::ostream& out, off_t pos, const T& data) {
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write_at(out, pos, reinterpret_cast<const char*>(&data), sizeof(T));
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}
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template <typename T>
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void write_vector_at(std::ostream& out, off_t pos, const std::vector<T>& vec) {
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write_at(out, pos, reinterpret_cast<const char*>(&vec.front()),
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vec.size() * sizeof(T));
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}
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template <int bits>
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bool RelR<bits>::hack(std::fstream& f) {
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auto ehdr = read_one_at<Elf_Ehdr>(f, 0);
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if (ehdr.e_phentsize != sizeof(Elf_Phdr)) {
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throw std::runtime_error("Invalid ELF?");
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}
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auto phdr = read_vector_at<Elf_Phdr>(f, ehdr.e_phoff, ehdr.e_phnum);
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const auto& dyn_phdr =
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std::find_if(phdr.begin(), phdr.end(),
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[](const auto& p) { return p.p_type == PT_DYNAMIC; });
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if (dyn_phdr == phdr.end()) {
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return false;
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}
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if (dyn_phdr->p_filesz % sizeof(Elf_Dyn)) {
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throw std::runtime_error("Invalid ELF?");
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}
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auto dyn = read_vector_at<Elf_Dyn>(f, dyn_phdr->p_offset,
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dyn_phdr->p_filesz / sizeof(Elf_Dyn));
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off_t dyn_offset = dyn_phdr->p_offset;
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DynInfo dyn_info;
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for (const auto& d : dyn) {
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if (d.d_tag == DT_NULL) {
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break;
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}
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if (dyn_info.is_wanted(d.d_tag)) {
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if (dyn_info.contains(d.d_tag)) {
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std::stringstream msg;
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msg << dyn_info.name(d.d_tag) << " appears twice?";
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throw std::runtime_error(msg.str());
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}
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dyn_info.insert(dyn_offset, d.d_tag, d.d_un.d_val);
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}
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dyn_offset += sizeof(Elf_Dyn);
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}
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// Find the location and size of the SHT_RELR section, which contains the
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// packed-relative-relocs.
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Elf_Addr relr_off =
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dyn_info.contains(DT_RELR) ? get_offset(phdr, dyn_info[DT_RELR]) : 0;
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Elf_Off relrsz = dyn_info[DT_RELRSZ];
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const decltype(Elf_Dyn::d_tag) rel_tags[3][2] = {
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{DT_REL, DT_RELA}, {DT_RELSZ, DT_RELASZ}, {DT_RELENT, DT_RELAENT}};
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for (const auto& [rel_tag, rela_tag] : rel_tags) {
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if (dyn_info.contains(rel_tag) && dyn_info.contains(rela_tag)) {
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std::stringstream msg;
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msg << "Both " << dyn_info.name(rel_tag) << " and "
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<< dyn_info.name(rela_tag) << " appear?";
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throw std::runtime_error(msg.str());
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}
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}
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Elf_Off relent =
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dyn_info.contains(DT_RELENT) ? dyn_info[DT_RELENT] : dyn_info[DT_RELAENT];
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// Estimate the size of the unpacked relative relocations corresponding
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// to the SHT_RELR section.
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auto relr = read_vector_at<Elf_Addr>(f, relr_off, relrsz / sizeof(Elf_Addr));
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size_t relocs = 0;
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for (const auto& entry : relr) {
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if ((entry & 1) == 0) {
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// LSB is 0, this is a pointer for a single relocation.
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relocs++;
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} else {
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// LSB is 1, remaining bits are a bitmap. Each bit represents a
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// relocation.
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relocs += __builtin_popcount(entry) - 1;
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}
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}
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// If the packed relocations + some overhead (we pick 4K arbitrarily, the
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// real size would require digging into the section sizes of the injected
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// .o file, which is not worth the error) is larger than the estimated
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// unpacked relocations, we'll just relink without packed relocations.
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if (relocs * relent < relrsz + 4096) {
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return false;
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}
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// Change DT_RELR* tags to add DT_RELRHACK_BIT.
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for (const auto tag : {DT_RELR, DT_RELRSZ, DT_RELRENT}) {
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write_one_at(f, dyn_info.offset(tag), tag | DT_RELRHACK_BIT);
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}
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bool is_glibc = false;
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if (dyn_info.contains(DT_VERNEEDNUM) && dyn_info.contains(DT_VERNEED) &&
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dyn_info.contains(DT_STRSZ) && dyn_info.contains(DT_STRTAB)) {
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// Scan SHT_VERNEED for the GLIBC_ABI_DT_RELR version on the libc
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// library.
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Elf_Addr verneed_off = get_offset(phdr, dyn_info[DT_VERNEED]);
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Elf_Off verneednum = dyn_info[DT_VERNEEDNUM];
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// SHT_STRTAB section, which contains the string table for, among other
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// things, the symbol versions in the SHT_VERNEED section.
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auto strtab = read_vector_at<char>(f, get_offset(phdr, dyn_info[DT_STRTAB]),
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dyn_info[DT_STRSZ]);
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// Guarantee a nul character at the end of the string table.
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strtab.push_back(0);
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while (verneednum--) {
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auto verneed = read_one_at<Elf_Verneed>(f, verneed_off);
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if (std::string_view{"libc.so.6"} == &strtab.at(verneed.vn_file)) {
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is_glibc = true;
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Elf_Addr vernaux_off = verneed_off + verneed.vn_aux;
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Elf_Addr relr = 0;
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Elf_Vernaux reuse;
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for (auto n = 0; n < verneed.vn_cnt; n++) {
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auto vernaux = read_one_at<Elf_Vernaux>(f, vernaux_off);
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if (std::string_view{"GLIBC_ABI_DT_RELR"} ==
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&strtab.at(vernaux.vna_name)) {
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relr = vernaux_off;
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} else {
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reuse = vernaux;
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}
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vernaux_off += vernaux.vna_next;
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}
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// In the case where we do have the GLIBC_ABI_DT_RELR version, we
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// need to edit the binary to make the following changes:
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// - Remove the GLIBC_ABI_DT_RELR version, we replace it with an
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// arbitrary other version entry, which is simpler than completely
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// removing it. We need to remove it because older versions of glibc
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// don't have the version (after all, that's why the symbol version
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// is there in the first place, to avoid running against older versions
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// of glibc that don't support packed relocations).
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// - Alter the DT_RELR* tags in the dynamic section, so that they
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// are not recognized by ld.so, because, while all versions of ld.so
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// ignore tags they don't know, glibc's ld.so versions that support
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// packed relocations don't want to load a binary that has DT_RELR*
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// tags but *not* a dependency on the GLIBC_ABI_DT_RELR version.
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if (relr) {
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// Don't overwrite vn_aux.
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write_at(f, relr, reinterpret_cast<char*>(&reuse),
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sizeof(reuse) - sizeof(Elf_Word));
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}
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}
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verneed_off += verneed.vn_next;
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}
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}
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// Location of the .rel.plt section.
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Elf_Addr jmprel = dyn_info.contains(DT_JMPREL) ? dyn_info[DT_JMPREL] : 0;
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if (is_glibc) {
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#ifndef MOZ_STDCXX_COMPAT
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try {
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#endif
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// ld.so in glibc 2.16 to 2.23 expects .rel.plt to strictly follow
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// .rel.dyn. (https://sourceware.org/bugzilla/show_bug.cgi?id=14341)
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// BFD ld places .relr.dyn after .rel.plt, so this works fine, but lld
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// places it between both sections, which doesn't work out for us. In that
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// case, we want to swap .relr.dyn and .rel.plt.
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Elf_Addr rel_end = dyn_info.contains(DT_REL)
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? (dyn_info[DT_REL] + dyn_info[DT_RELSZ])
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: (dyn_info[DT_RELA] + dyn_info[DT_RELASZ]);
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if (dyn_info.contains(DT_JMPREL) && dyn_info[DT_PLTRELSZ] &&
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dyn_info[DT_JMPREL] != rel_end) {
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if (dyn_info[DT_RELR] != rel_end) {
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throw CantSwapSections("RELR section doesn't follow REL/RELA?");
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}
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if (dyn_info[DT_JMPREL] != dyn_info[DT_RELR] + dyn_info[DT_RELRSZ]) {
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throw CantSwapSections("PLT REL/RELA doesn't follow RELR?");
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}
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auto plt_rel = read_vector_at<char>(
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f, get_offset(phdr, dyn_info[DT_JMPREL]), dyn_info[DT_PLTRELSZ]);
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// Write the content of both sections swapped, and adjust the
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// corresponding PT_DYNAMIC entries.
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write_vector_at(f, relr_off, plt_rel);
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write_vector_at(f, relr_off + plt_rel.size(), relr);
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dyn_info[DT_JMPREL] = rel_end;
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dyn_info[DT_RELR] = rel_end + plt_rel.size();
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for (const auto tag : {DT_JMPREL, DT_RELR}) {
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write_one_at(f, dyn_info.offset(tag) + sizeof(typename DynInfo::Tag),
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dyn_info[tag]);
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}
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}
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#ifndef MOZ_STDCXX_COMPAT
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} catch (const CantSwapSections& err) {
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// When binary compatibility with older libstdc++/glibc is not enabled, we
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// only emit a warning about why swapping the sections is not happening.
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std::cerr << "WARNING: " << err.what() << std::endl;
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}
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#endif
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}
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off_t shdr_offset = ehdr.e_shoff;
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auto shdr = read_vector_at<Elf_Shdr>(f, ehdr.e_shoff, ehdr.e_shnum);
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for (auto& s : shdr) {
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// Some tools don't like sections of types they don't know, so change
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// SHT_RELR, which might be unknown on older systems, to SHT_PROGBITS.
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if (s.sh_type == SHT_RELR) {
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s.sh_type = SHT_PROGBITS;
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// If DT_RELR has been adjusted to swap with DT_JMPREL, also adjust
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// the corresponding SHT_RELR section header.
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if (s.sh_addr != dyn_info[DT_RELR]) {
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s.sh_offset += dyn_info[DT_RELR] - s.sh_addr;
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s.sh_addr = dyn_info[DT_RELR];
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}
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write_one_at(f, shdr_offset, s);
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} else if (jmprel && (s.sh_addr == jmprel) &&
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(s.sh_addr != dyn_info[DT_JMPREL])) {
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// If DT_JMPREL has been adjusted to swap with DT_RELR, also adjust
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// the corresponding section header.
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s.sh_offset -= s.sh_addr - dyn_info[DT_JMPREL];
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s.sh_addr = dyn_info[DT_JMPREL];
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write_one_at(f, shdr_offset, s);
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}
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shdr_offset += sizeof(Elf_Shdr);
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}
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return true;
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}
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std::vector<std::string> get_path() {
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std::vector<std::string> result;
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std::stringstream stream{std::getenv("PATH")};
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std::string item;
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while (std::getline(stream, item, ':')) {
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result.push_back(std::move(item));
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}
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return result;
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}
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std::optional<fs::path> next_program(fs::path& this_program,
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std::optional<fs::path>& program) {
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auto program_name = program ? *program : this_program.filename();
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for (const auto& dir : get_path()) {
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auto path = fs::path(dir) / program_name;
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auto status = fs::status(path);
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if ((status.type() == fs::file_type::regular) &&
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((status.permissions() & fs::perms::owner_exec) ==
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fs::perms::owner_exec) &&
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!fs::equivalent(path, this_program))
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return path;
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}
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return std::nullopt;
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}
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unsigned char get_elf_class(unsigned char (&e_ident)[EI_NIDENT]) {
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if (std::string_view{reinterpret_cast<char*>(e_ident), SELFMAG} !=
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std::string_view{ELFMAG, SELFMAG}) {
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throw std::runtime_error("Not ELF?");
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}
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#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
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if (e_ident[EI_DATA] != ELFDATA2LSB) {
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throw std::runtime_error("Not Little Endian ELF?");
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}
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#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
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if (e_ident[EI_DATA] != ELFDATA2MSB) {
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throw std::runtime_error("Not Big Endian ELF?");
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}
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#else
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# error Unknown byte order.
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#endif
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if (e_ident[EI_VERSION] != 1) {
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throw std::runtime_error("Not ELF version 1?");
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}
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auto elf_class = e_ident[EI_CLASS];
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if (elf_class != ELFCLASS32 && elf_class != ELFCLASS64) {
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throw std::runtime_error("Not 32 or 64-bits ELF?");
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}
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return elf_class;
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}
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unsigned char get_elf_class(std::istream& in) {
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unsigned char e_ident[EI_NIDENT];
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in.read(reinterpret_cast<char*>(e_ident), sizeof(e_ident));
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return get_elf_class(e_ident);
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}
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uint16_t get_elf_machine(std::istream& in) {
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// As far as e_machine is concerned, both Elf32_Ehdr and Elf64_Ehdr are equal.
|
|
Elf32_Ehdr ehdr;
|
|
in.read(reinterpret_cast<char*>(&ehdr), sizeof(ehdr));
|
|
// get_elf_class will throw exceptions for the cases we don't handle.
|
|
get_elf_class(ehdr.e_ident);
|
|
return ehdr.e_machine;
|
|
}
|
|
|
|
int run_command(std::vector<const char*>& args) {
|
|
pid_t child_pid;
|
|
if (posix_spawn(&child_pid, args[0], nullptr, nullptr,
|
|
const_cast<char* const*>(args.data()), environ) != 0) {
|
|
throw std::runtime_error("posix_spawn failed");
|
|
}
|
|
|
|
int status;
|
|
waitpid(child_pid, &status, 0);
|
|
return WEXITSTATUS(status);
|
|
}
|
|
|
|
int main(int argc, char* argv[]) {
|
|
auto this_program = fs::absolute(argv[0]);
|
|
|
|
std::vector<const char*> args;
|
|
|
|
int i, crti = 0;
|
|
std::optional<fs::path> output = std::nullopt;
|
|
std::optional<fs::path> real_linker = std::nullopt;
|
|
bool shared = false;
|
|
bool is_android = false;
|
|
uint16_t elf_machine = EM_NONE;
|
|
// Scan argv in order to prepare the following:
|
|
// - get the output file. That's the file we may need to adjust.
|
|
// - get the --real-linker if one was passed.
|
|
// - detect whether we're linking a shared library or something else. As of
|
|
// now, only shared libraries are handled. Technically speaking, programs
|
|
// could be handled as well, but for the purpose of Firefox, that actually
|
|
// doesn't work because programs contain a memory allocator that ends up
|
|
// being called before the injected code has any chance to apply relocations,
|
|
// and the allocator itself needs the relocations to have been applied.
|
|
// - detect the position of crti.o so that we can inject our own object
|
|
// right after it, and also to detect the machine type to pick the right
|
|
// object to inject.
|
|
//
|
|
// At the same time, we also construct a new list of arguments, with
|
|
// --real-linker filtered out. We'll later inject arguments in that list.
|
|
for (i = 1, argv++; i < argc && *argv; argv++, i++) {
|
|
std::string_view arg{*argv};
|
|
if (arg == "-shared") {
|
|
shared = true;
|
|
} else if (arg == "-o") {
|
|
args.push_back(*(argv++));
|
|
++i;
|
|
output = *argv;
|
|
} else if (arg == "--real-linker") {
|
|
++i;
|
|
real_linker = *(++argv);
|
|
continue;
|
|
} else if (elf_machine == EM_NONE) {
|
|
auto filename = fs::path(arg).filename();
|
|
if (filename == "crti.o" || filename == "crtbegin_so.o") {
|
|
is_android = (filename == "crtbegin_so.o");
|
|
crti = i;
|
|
std::fstream f{std::string(arg), f.binary | f.in};
|
|
f.exceptions(f.failbit);
|
|
elf_machine = get_elf_machine(f);
|
|
}
|
|
}
|
|
args.push_back(*argv);
|
|
}
|
|
|
|
if (!output) {
|
|
std::cerr << "Could not determine output file." << std::endl;
|
|
return 1;
|
|
}
|
|
|
|
if (!crti) {
|
|
std::cerr << "Could not find CRT object on the command line." << std::endl;
|
|
return 1;
|
|
}
|
|
|
|
if (!real_linker || !real_linker->has_parent_path()) {
|
|
auto linker = next_program(this_program, real_linker);
|
|
if (!linker) {
|
|
std::cerr << "Could not find next "
|
|
<< (real_linker ? real_linker->filename()
|
|
: this_program.filename())
|
|
<< std::endl;
|
|
return 1;
|
|
}
|
|
real_linker = linker;
|
|
}
|
|
args.insert(args.begin(), real_linker->c_str());
|
|
args.push_back(nullptr);
|
|
|
|
std::string stem;
|
|
switch (elf_machine) {
|
|
case EM_NONE:
|
|
std::cerr << "Could not determine target machine type." << std::endl;
|
|
return 1;
|
|
case EM_386:
|
|
stem = "x86";
|
|
break;
|
|
case EM_X86_64:
|
|
stem = "x86_64";
|
|
break;
|
|
case EM_ARM:
|
|
stem = "arm";
|
|
break;
|
|
case EM_AARCH64:
|
|
stem = "aarch64";
|
|
break;
|
|
default:
|
|
std::cerr << "Unsupported target machine type." << std::endl;
|
|
return 1;
|
|
}
|
|
if (is_android) {
|
|
stem += "-android";
|
|
}
|
|
|
|
if (shared) {
|
|
std::vector<const char*> hacked_args(args);
|
|
auto inject = this_program.parent_path() / "inject" / (stem + ".o");
|
|
hacked_args.insert(hacked_args.begin() + crti + 1, inject.c_str());
|
|
hacked_args.insert(hacked_args.end() - 1, {"-z", "pack-relative-relocs",
|
|
"-init=_relrhack_wrap_init"});
|
|
int status = run_command(hacked_args);
|
|
if (status) {
|
|
return status;
|
|
}
|
|
bool hacked = false;
|
|
try {
|
|
std::fstream f{*output, f.binary | f.in | f.out};
|
|
f.exceptions(f.failbit);
|
|
auto elf_class = get_elf_class(f);
|
|
f.seekg(0, std::ios::beg);
|
|
if (elf_class == ELFCLASS32) {
|
|
hacked = RelR<32>::hack(f);
|
|
} else if (elf_class == ELFCLASS64) {
|
|
hacked = RelR<64>::hack(f);
|
|
}
|
|
} catch (const std::runtime_error& err) {
|
|
std::cerr << "Failed to hack " << output->string() << ": " << err.what()
|
|
<< std::endl;
|
|
return 1;
|
|
}
|
|
if (hacked) {
|
|
return 0;
|
|
}
|
|
}
|
|
|
|
return run_command(args);
|
|
}
|