added support for separate debug file and cleaned up iteration syntax
This commit is contained in:
Robin Nicholson
parent
b5be3bb5b0
commit
4f160a698c
253
ELFInfo.cpp
253
ELFInfo.cpp
@ -4,14 +4,16 @@
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#include <elf.h>
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#include <unistd.h>
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#include <string.h>
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#include <dirent.h>
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#include "elfspy/Report.h"
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#include "elfspy/Fail.h"
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#include "elfspy/MFile.h"
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#include "elfspy/SectionHeader.h"
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#ifdef __x86_64__
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using Elf_Phdr = Elf64_Phdr;
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using Elf_Ehdr = Elf64_Ehdr;
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using Elf_Shdr = Elf64_Shdr;
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using Elf_Rel = Elf64_Rel;
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using Elf_Rela = Elf64_Rela;
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using Elf_Sym = Elf64_Sym;
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@ -22,7 +24,6 @@ using Elf_Sym = Elf64_Sym;
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#else
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using Elf_Phdr = Elf32_Phdr;
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using Elf_Ehdr = Elf32_Ehdr;
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using Elf_Shdr = Elf32_Shdr;
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using Elf_Rel = Elf32_Rel;
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using Elf_Rela = Elf32_Rela;
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using Elf_Sym = Elf32_Sym;
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@ -34,7 +35,6 @@ using Elf_Sym = Elf32_Sym;
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namespace
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{
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long page_size = sysconf(_SC_PAGESIZE);
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union Address
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{
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@ -57,57 +57,118 @@ inline void Address::round_up()
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value_ *= page_size;
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}
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// see if a library has a corresponding debug file where the symbols are kept
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std::string get_debug_file_name(const char* file_name)
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{
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const char* slash = nullptr;
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for (const char* seek = file_name; *seek; ++seek) {
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if (*seek == '/') slash = seek;
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}
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if (!slash) return { };
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std::string name;
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name = "/usr/lib/debug";
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name.append(file_name, slash - file_name);
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DIR* dir = opendir(name.c_str());
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if (!dir) return { };
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const char* period = nullptr;
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for (const char* seek = slash; *seek; ++seek) {
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if (*seek == '.') {
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period = seek;
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break;
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}
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}
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if (!period) return { };
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const char* base_name = slash + 1;
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size_t name_root_len = period - base_name;
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struct dirent* entry;
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while ((entry = readdir(dir))) {
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if (strncmp(entry->d_name, base_name, name_root_len) == 0) {
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const char* after_root = entry->d_name + name_root_len;
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// files in debug dir seem to be named libxxx-major.minor.so
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if (*after_root == '-' || *after_root == '.') {
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closedir(dir);
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name += '/';
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name += entry->d_name;
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return name;
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}
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}
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}
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closedir(dir);
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return { };
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}
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} // namespace
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namespace spy
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{
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ELFInfo::ELFInfo(unsigned char* data, const char* name)
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ELFInfo::ELFInfo(const char* name)
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{
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data_ = data;
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name_ = name;
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files_.emplace_back(std::make_unique<MFile>(name));
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std::string debug_file_name = get_debug_file_name(name);
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if (!debug_file_name.empty()) {
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files_.emplace_back(std::make_unique<MFile>(debug_file_name.c_str()));
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}
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if (!is_elf()) {
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Fail() << "Not ELF data - no ELF header found in " << name;
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}
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}
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ELFInfo::~ELFInfo()
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{
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}
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ELFObject ELFInfo::prepare_object(unsigned char* base) const
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{
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ELFObject object;
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object.name_ = name_;
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object.base_ = base;
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object.size_ = files_[0]->size();
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unprotect(base);
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return object;
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}
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bool ELFInfo::is_elf() const
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{
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auto elf = reinterpret_cast<Elf_Ehdr*>(data_);
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auto elf = reinterpret_cast<const Elf_Ehdr*>(files_[0]->address());
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return elf->e_ident[EI_MAG0] == ELFMAG0
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&& elf->e_ident[EI_MAG1] == ELFMAG1
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&& elf->e_ident[EI_MAG2] == ELFMAG2
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&& elf->e_ident[EI_MAG3] == ELFMAG3;
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}
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void* ELFInfo::find_section(const char* name)
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SectionHeader ELFInfo::find_header(const char* name) const
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{
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auto elf = reinterpret_cast<Elf_Ehdr*>(data_);
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auto header = data_ + elf->e_shoff;
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auto section_names =
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reinterpret_cast<Elf_Shdr*>(header + elf->e_shstrndx * elf->e_shentsize);
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auto names = reinterpret_cast<char*>(elf) + section_names->sh_offset;
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// .shstrtab is the "section header" string table, it is indexed in elf header
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for (size_t n = 0; n != elf->e_shnum; ++n, header += elf->e_shentsize) {
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auto section = reinterpret_cast<Elf_Shdr*>(header);
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if (strcmp(names + section->sh_name, name) == 0) {
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return section;
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for (auto& file : files_) {
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auto elf = reinterpret_cast<const Elf_Ehdr*>(file->address());
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auto header = file->address() + elf->e_shoff;
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auto section_names =
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reinterpret_cast<const Elf_Shdr*>(header + elf->e_shstrndx * elf->e_shentsize);
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auto names = reinterpret_cast<const char*>(elf) + section_names->sh_offset;
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// .shstrtab is the "section header" string table
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// it is indexed in elf header
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for (size_t n = 0; n != elf->e_shnum; ++n, header += elf->e_shentsize) {
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auto section = reinterpret_cast<const Elf_Shdr*>(header);
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if (strcmp(names + section->sh_name, name) == 0) {
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return { file->address(), section };
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}
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}
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}
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if (strncmp(name_, "/lib", 4) != 0 && strncmp(name_, "/usr", 4) != 0) {
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Report() << "no " << name << " section found in " << name_;
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}
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return nullptr;
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return { };
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}
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void ELFInfo::unprotect(unsigned char* base, const char* name)
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void ELFInfo::unprotect(unsigned char* base, const char* name) const
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{
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auto section = reinterpret_cast<Elf_Shdr*>(find_section(name));
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SectionHeader section = find_header(name);
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if (section) {
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Address begin;
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Address end;
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begin.pointer_ = base + section->sh_addr;
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end.pointer_ = begin.pointer_ + section->sh_size;
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begin.pointer_ = base + section.header_->sh_addr;
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end.pointer_ = begin.pointer_ + section.header_->sh_size;
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begin.round_down();
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end.round_up();
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size_t size = end.value_ - begin.value_;
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@ -118,38 +179,34 @@ void ELFInfo::unprotect(unsigned char* base, const char* name)
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}
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}
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void ELFInfo::unprotect(unsigned char* base)
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void ELFInfo::unprotect(unsigned char* base) const
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{
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// by default this memory is read only - ELFspy needs to change it
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unprotect(base, ".got");
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unprotect(base, ".got.plt");
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}
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ELFInfo::Symbol ELFInfo::get_symbol_rela(size_t value)
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const char* ELFInfo::find_name(size_t name_offset) const
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{
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SectionHeader str_tab = find_header(".dynstr");
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if (!str_tab) {
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return nullptr;
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}
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return reinterpret_cast<const char*>(str_tab.begin()) + name_offset;
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}
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ELFInfo::Symbol ELFInfo::get_symbol_rela(size_t value) const
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{
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Symbol result;
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auto str_tab = reinterpret_cast<Elf_Shdr*>(find_section(".dynstr"));
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if (!str_tab) {
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return result;
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}
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auto strings = reinterpret_cast<const char*>(data_ + str_tab->sh_offset);
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// find dynamic symbol table
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auto symbol_table = reinterpret_cast<Elf_Shdr*>(find_section(".dynsym"));
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if (!symbol_table) {
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return result;
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}
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// find symbol by value in dynamic symbol table
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size_t index = 0;
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auto symbols = data_ + symbol_table->sh_offset;
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auto end = symbols + symbol_table->sh_size;
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for ( ; symbols < end; symbols += symbol_table->sh_entsize) {
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auto symbol = reinterpret_cast<Elf_Sym*>(symbols);
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if (ELF_STTYPE(symbol->st_info) == STT_FUNC && symbol->st_value == value) {
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for (auto& symbol : find_header(".dynsym").as_section<Elf_Sym>()) {
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if (ELF_STTYPE(symbol.st_info) == STT_FUNC && symbol.st_value == value) {
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// the symbol is defined in this file as 0 is undefined.
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// an STT_GNU_IFUNC will not match here as the function value will be the
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// the resulting function of the resolver function and therefore at a
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// different address
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result.name_ = strings + symbol->st_name;
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result.name_ = find_name(symbol.st_name);
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break;
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}
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++index;
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@ -157,24 +214,16 @@ ELFInfo::Symbol ELFInfo::get_symbol_rela(size_t value)
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if (!result.name_) {
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return result; // not found
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}
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auto rela_plt = reinterpret_cast<Elf_Shdr*>(find_section(".rela.plt"));
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if (!rela_plt) {
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return result;
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}
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size_t rela_plt_entries = rela_plt->sh_size / rela_plt->sh_entsize;
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unsigned char* rela = data_ + rela_plt->sh_offset;
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// attempt to find symbol in .rela.plt
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for (size_t n = 0; n != rela_plt_entries; ++n) {
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auto reloc = reinterpret_cast<Elf_Rela*>(rela);
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if (ELF_R_TYPE(reloc->r_info) == R_X86_64_JUMP_SLOT) {
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// attempt to find symbol in .rela.plt using index from symbol table
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for (auto& reloc : find_header(".rela.plt").as_section<Elf_Rela>()) {
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if (ELF_R_TYPE(reloc.r_info) == R_X86_64_JUMP_SLOT) {
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// find symbol by index
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size_t symbol_index = ELF_R_SYM(reloc->r_info);
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size_t symbol_index = ELF_R_SYM(reloc.r_info);
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if (symbol_index == index) {
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result.rela_offset_ = reloc->r_offset;
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result.rela_offset_ = reloc.r_offset;
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break;
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}
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}
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rela += rela_plt->sh_entsize;
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}
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// a symbol will only be present in .rela.plt iff it was used in the ELF
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// object - otherwise only .dynsym and .symtab will contain it
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@ -185,84 +234,44 @@ ELFInfo::Symbol ELFInfo::get_symbol_rela(size_t value)
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// look for STT_IFUNC symbols by finding the function address in the relocated
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// .rela.plt entries. STT_IFUNC are rare, but time(time_t*) is one of them
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ELFInfo::Symbol ELFInfo::get_indirect_symbol_rela(unsigned char* base,
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ELFInfo::Symbol ELFInfo::get_indirect_symbol_rela(const unsigned char* base,
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void* function)
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{
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Symbol result;
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auto str_tab = reinterpret_cast<Elf_Shdr*>(find_section(".dynstr"));
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if (!str_tab) {
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return result;
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}
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auto strings = reinterpret_cast<const char*>(data_ + str_tab->sh_offset);
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// find dynamic symbol table
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auto symbol_table = reinterpret_cast<Elf_Shdr*>(find_section(".dynsym"));
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if (!symbol_table) {
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return result;
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}
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auto symbols = data_ + symbol_table->sh_offset;
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// find function in relocated GOT
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auto rela_plt = reinterpret_cast<Elf_Shdr*>(find_section(".rela.plt"));
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if (!rela_plt) {
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return result;
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}
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size_t rela_plt_entries = rela_plt->sh_size / rela_plt->sh_entsize;
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unsigned char* rela = data_ + rela_plt->sh_offset;
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for (size_t n = 0; n != rela_plt_entries; ++n) {
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auto reloc = reinterpret_cast<Elf_Rela*>(rela);
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if (ELF_R_TYPE(reloc->r_info) == R_X86_64_IRELATIVE
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&& *reinterpret_cast<void**>(base + reloc->r_offset) == function) {
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result.rela_offset_ = reloc->r_offset;
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for (auto& reloc : find_header(".rela.plt").as_section<Elf_Rela>()) {
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if (ELF_R_TYPE(reloc.r_info) == R_X86_64_IRELATIVE &&
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*reinterpret_cast<void* const*>(base + reloc.r_offset) == function) {
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result.rela_offset_ = reloc.r_offset;
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// find symbol by r_addend in dynamic symbol table
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auto end = symbols + symbol_table->sh_size;
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for ( ; symbols < end; symbols += symbol_table->sh_entsize) {
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auto symbol = reinterpret_cast<Elf_Sym*>(symbols);
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if (ELF_STTYPE(symbol->st_info) == STT_GNU_IFUNC
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&& symbol->st_value == reloc->r_addend) {
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result.name_ = strings + symbol->st_name;
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for (auto& symbol : find_header(".dynsym").as_section<Elf_Sym>()) {
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if (ELF_STTYPE(symbol.st_info) == STT_GNU_IFUNC
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&& symbol.st_value == reloc.r_addend) {
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result.name_ = find_name(symbol.st_name);
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break;
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}
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}
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break;
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}
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rela += rela_plt->sh_entsize;
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}
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return result; // whether found or not
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}
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size_t ELFInfo::get_symbol_rela_dyn(const char* name)
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{
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auto str_tab = reinterpret_cast<Elf_Shdr*>(find_section(".dynstr"));
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if (!str_tab) {
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return 0;
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}
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auto strings = reinterpret_cast<const char*>(data_ + str_tab->sh_offset);
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// find symbol table
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auto symbol_table = reinterpret_cast<Elf_Shdr*>(find_section(".dynsym"));
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if (symbol_table == nullptr) {
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return 0;
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}
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auto symbols = data_ + symbol_table->sh_offset;
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size_t symbol_entries = symbol_table->sh_size / symbol_table->sh_entsize;
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auto symbol_table = find_header(".dynsym").as_section<Elf_Sym>();
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// find symbol in .rela.dyn
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for (const char* section : { ".rela.dyn", ".rela.plt" }) {
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auto rela_dyn = reinterpret_cast<Elf_Shdr*>(find_section(section));
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if (!rela_dyn) {
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return 0;
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}
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size_t rela_entries = rela_dyn->sh_size / rela_dyn->sh_entsize;
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unsigned char* rela = data_ + rela_dyn->sh_offset;
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for (size_t n = 0; n != rela_entries; ++n) {
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auto reloc = reinterpret_cast<Elf_Rel*>(rela);
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size_t symbol_index = ELF_R_SYM(reloc->r_info);
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if (symbol_index < symbol_entries) {
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symbol_index *= symbol_table->sh_entsize;
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auto symbol = reinterpret_cast<Elf_Sym*>(symbols + symbol_index);
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const char* symbol_name = strings + symbol->st_name;
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if (strcmp(name, symbol_name) == 0) {
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return reloc->r_offset;
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for (auto& reloc : find_header(section).as_section<Elf_Rel>()) {
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size_t symbol_index = ELF_R_SYM(reloc.r_info);
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if (symbol_index < symbol_table.entries()) {
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auto& symbol = symbol_table[symbol_index];
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const char* symbol_name = find_name(symbol.st_name);
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if (symbol_name && strcmp(name, symbol_name) == 0) {
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return reloc.r_offset;
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}
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}
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rela += rela_dyn->sh_entsize;
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}
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}
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return 0;
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@ -274,34 +283,24 @@ ELFInfo::get_vtables(unsigned char* base)
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if (!is_elf()) {
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return { };
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}
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auto elf = reinterpret_cast<Elf_Ehdr*>(data_);
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auto header = data_ + elf->e_shoff;
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// get string table by finding the right strtab section
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// .dynstr is for DYNSYM section (it has a non-zero address)
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// .shstrtab is the "section header" string table, it is indexed in elf header
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// .strtab is for SYMTAB, which is what we want here
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auto str_tab = reinterpret_cast<Elf_Shdr*>(find_section(".strtab"));
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SectionHeader str_tab = find_header(".strtab");
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if (!str_tab) {
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return { };
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}
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auto strings = reinterpret_cast<const char*>(data_ + str_tab->sh_offset);
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// find symbol table
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auto symbol_table = reinterpret_cast<Elf_Shdr*>(find_section(".symtab"));
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if (symbol_table == nullptr) {
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return { };
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}
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auto strings = reinterpret_cast<const char*>(str_tab.begin());
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std::unordered_map<std::string, unsigned char*> vtables;
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// look for virtual tables
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auto symbols = data_ + symbol_table->sh_offset;
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auto end = symbols + symbol_table->sh_size;
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for ( ; symbols < end; symbols += symbol_table->sh_entsize) {
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auto symbol = reinterpret_cast<Elf_Sym*>(symbols);
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// look for virtual tables in symbol table
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for (auto& symbol : find_header(".symtab").as_section<Elf_Sym>()) {
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// check if is defined (value != 0)
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if (symbol->st_value && ELF_STTYPE(symbol->st_info) == STT_OBJECT) {
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if (symbol.st_value && ELF_STTYPE(symbol.st_info) == STT_OBJECT) {
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// check if it is a virtual table (starts with "_ZTV")
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auto name = strings + symbol->st_name;
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auto name = strings + symbol.st_name;
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if (strncmp(name, "_ZTV", 4) == 0) {
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vtables[name + 4] = base + symbol->st_value;
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vtables[name + 4] = base + symbol.st_value;
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}
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}
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}
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27
ELFInfo.h
27
ELFInfo.h
@ -1,12 +1,18 @@
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#ifndef ELFSPY_ELFINFO_H
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#define ELFSPY_ELFINFO_H
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|
||||
#include <memory>
|
||||
#include <vector>
|
||||
#include <string>
|
||||
#include <unordered_map>
|
||||
|
||||
#include "elfspy/ELFObject.h"
|
||||
|
||||
namespace spy
|
||||
{
|
||||
class MFile;
|
||||
class ELFObject;
|
||||
class SectionHeader;
|
||||
|
||||
/**
|
||||
* @namespace spy
|
||||
@ -14,14 +20,15 @@ namespace spy
|
||||
* can read data in ELF format and extract information from it
|
||||
*/
|
||||
|
||||
class ELFInfo : public ELFObject
|
||||
class ELFInfo
|
||||
{
|
||||
public:
|
||||
/**
|
||||
* @param data ELF data
|
||||
* @param name name of ELF data for diagnostics
|
||||
*/
|
||||
ELFInfo(unsigned char* data, const char* name);
|
||||
ELFInfo(const char* name);
|
||||
~ELFInfo();
|
||||
|
||||
/// @return true if data is in ELF format
|
||||
bool is_elf() const;
|
||||
@ -35,14 +42,14 @@ public:
|
||||
* @param value symbol offset value expected to be in symtab
|
||||
* @return name and offset (empty if not defined in file)
|
||||
*/
|
||||
Symbol get_symbol_rela(size_t value);
|
||||
Symbol get_symbol_rela(size_t value) const;
|
||||
/**
|
||||
* find symbol and offset name in .rela.plt if symbol is defined as STT_IFUNC
|
||||
* @param base base address of ELF object in memory
|
||||
* @param function function pointer
|
||||
* @return name and offset (0 if not defined in file)
|
||||
*/
|
||||
Symbol get_indirect_symbol_rela(unsigned char* base, void* function);
|
||||
Symbol get_indirect_symbol_rela(const unsigned char* base, void* function);
|
||||
/**
|
||||
* find symbol offset in .rela.dyn if symbol is found as undefined in file
|
||||
* @param name symbol name
|
||||
@ -53,7 +60,7 @@ public:
|
||||
* remove write protection from the areas in memory that need to change
|
||||
* @param base base address in memory
|
||||
*/
|
||||
void unprotect(unsigned char* base);
|
||||
void unprotect(unsigned char* base) const;
|
||||
/**
|
||||
* find vtable adresses from symbol table
|
||||
* @param base - offset to return addresses relative to
|
||||
@ -62,10 +69,14 @@ public:
|
||||
std::unordered_map<std::string, unsigned char*>
|
||||
get_vtables(unsigned char* base = nullptr);
|
||||
|
||||
ELFObject prepare_object(unsigned char* base) const;
|
||||
|
||||
private:
|
||||
unsigned char* data_;
|
||||
void* find_section(const char* name);
|
||||
void unprotect(unsigned char* base, const char* name);
|
||||
const char* name_;
|
||||
std::vector<std::unique_ptr<MFile>> files_;
|
||||
SectionHeader find_header(const char* name) const;
|
||||
const char* find_name(size_t name_offset) const;
|
||||
void unprotect(unsigned char* base, const char* name) const;
|
||||
};
|
||||
|
||||
} // namespace spy
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user