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patchelf.cc
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patchelf.cc
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/*
* PatchELF is a utility to modify properties of ELF executables and libraries
* Copyright (C) 2004-2016 Eelco Dolstra <edolstra@gmail.com>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or (at
* your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <algorithm>
#include <fstream>
#include <limits>
#include <map>
#include <memory>
#include <optional>
#include <set>
#include <sstream>
#include <stdexcept>
#include <string>
#include <string_view>
#include <unordered_map>
#include <unordered_set>
#include <vector>
#include <cassert>
#include <cerrno>
#include <cstdarg>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include "elf.h"
#include "patchelf.h"
#ifndef PACKAGE_STRING
#define PACKAGE_STRING "patchelf"
#endif
// This is needed for Windows/mingw
#ifndef O_BINARY
#define O_BINARY 0
#endif
static bool debugMode = false;
static bool forceRPath = false;
static std::vector<std::string> fileNames;
static std::string outputFileName;
static bool alwaysWrite = false;
#ifdef DEFAULT_PAGESIZE
static int forcedPageSize = DEFAULT_PAGESIZE;
#else
static int forcedPageSize = -1;
#endif
#ifndef EM_LOONGARCH
#define EM_LOONGARCH 258
#endif
[[nodiscard]] static std::vector<std::string> splitColonDelimitedString(std::string_view s)
{
std::vector<std::string> parts;
size_t pos;
while ((pos = s.find(':')) != std::string_view::npos) {
parts.emplace_back(s.substr(0, pos));
s = s.substr(pos + 1);
}
if (!s.empty())
parts.emplace_back(s);
return parts;
}
static bool hasAllowedPrefix(const std::string & s, const std::vector<std::string> & allowedPrefixes)
{
return std::any_of(allowedPrefixes.begin(), allowedPrefixes.end(), [&](const std::string & i) { return !s.compare(0, i.size(), i); });
}
static std::string trim(std::string s)
{
s.erase(s.begin(), std::find_if(s.begin(), s.end(), [](unsigned char ch) { return !std::isspace(ch); }));
s.erase(std::find_if(s.rbegin(), s.rend(), [](unsigned char ch) { return !std::isspace(ch); }).base(), s.end());
return s;
}
static std::string downcase(std::string s)
{
std::transform(s.begin(), s.end(), s.begin(), [](unsigned char c){ return std::tolower(c); });
return s;
}
/* !!! G++ creates broken code if this function is inlined, don't know
why... */
template<ElfFileParams>
template<class I>
constexpr I ElfFile<ElfFileParamNames>::rdi(I i) const noexcept
{
I r = 0;
if (littleEndian) {
for (unsigned int n = 0; n < sizeof(I); ++n) {
r |= ((I) *(((unsigned char *) &i) + n)) << (n * 8);
}
} else {
for (unsigned int n = 0; n < sizeof(I); ++n) {
r |= ((I) *(((unsigned char *) &i) + n)) << ((sizeof(I) - n - 1) * 8);
}
}
return r;
}
static void debug(const char * format, ...)
{
if (debugMode) {
va_list ap;
va_start(ap, format);
vfprintf(stderr, format, ap);
va_end(ap);
}
}
static void fmt2([[maybe_unused]] std::ostringstream & out)
{
}
template<typename T, typename... Args>
void fmt2(std::ostringstream & out, T x, Args... args)
{
out << x;
fmt2(out, args...);
}
template<typename... Args>
std::string fmt(Args... args)
{
std::ostringstream out;
fmt2(out, args...);
return out.str();
}
struct SysError : std::runtime_error
{
int errNo;
explicit SysError(const std::string & msg)
: std::runtime_error(fmt(msg + ": " + strerror(errno)))
, errNo(errno)
{ }
};
[[noreturn]] static void error(const std::string & msg)
{
if (errno)
throw SysError(msg);
throw std::runtime_error(msg);
}
static FileContents readFile(const std::string & fileName,
size_t cutOff = std::numeric_limits<size_t>::max())
{
struct stat st;
if (stat(fileName.c_str(), &st) != 0)
throw SysError(fmt("getting info about '", fileName, "'"));
if (static_cast<uint64_t>(st.st_size) > static_cast<uint64_t>(std::numeric_limits<size_t>::max()))
throw SysError(fmt("cannot read file of size ", st.st_size, " into memory"));
size_t size = std::min(cutOff, static_cast<size_t>(st.st_size));
FileContents contents = std::make_shared<std::vector<unsigned char>>(size);
int fd = open(fileName.c_str(), O_RDONLY | O_BINARY);
if (fd == -1) throw SysError(fmt("opening '", fileName, "'"));
size_t bytesRead = 0;
ssize_t portion;
while ((portion = read(fd, contents->data() + bytesRead, size - bytesRead)) > 0)
bytesRead += portion;
close(fd);
if (bytesRead != size)
throw SysError(fmt("reading '", fileName, "'"));
return contents;
}
struct ElfType
{
bool is32Bit;
int machine; // one of EM_*
};
[[nodiscard]] static ElfType getElfType(const FileContents & fileContents)
{
/* Check the ELF header for basic validity. */
if (fileContents->size() < sizeof(Elf32_Ehdr))
error("missing ELF header");
auto contents = fileContents->data();
if (memcmp(contents, ELFMAG, SELFMAG) != 0)
error("not an ELF executable");
if (contents[EI_VERSION] != EV_CURRENT)
error("unsupported ELF version");
if (contents[EI_CLASS] != ELFCLASS32 && contents[EI_CLASS] != ELFCLASS64)
error("ELF executable is not 32 or 64 bit");
bool is32Bit = contents[EI_CLASS] == ELFCLASS32;
// FIXME: endianness
return ElfType { is32Bit, is32Bit ? (reinterpret_cast<Elf32_Ehdr *>(contents))->e_machine : (reinterpret_cast<Elf64_Ehdr *>(contents))->e_machine };
}
static void checkPointer(const FileContents & contents, const void * p, size_t size)
{
if (p < contents->data() || size > contents->size() || p > contents->data() + contents->size() - size)
error("data region extends past file end");
}
static void checkOffset(const FileContents & contents, size_t offset, size_t size)
{
size_t end;
if (offset > contents->size()
|| size > contents->size()
|| __builtin_add_overflow(offset, size, &end)
|| end > contents->size())
error("data offset extends past file end");
}
static std::string extractString(const FileContents & contents, size_t offset, size_t size)
{
checkOffset(contents, offset, size);
return { reinterpret_cast<const char *>(contents->data()) + offset, size };
}
template<ElfFileParams>
ElfFile<ElfFileParamNames>::ElfFile(FileContents fContents)
: fileContents(fContents)
{
/* Check the ELF header for basic validity. */
if (fileContents->size() < (off_t) sizeof(Elf_Ehdr)) error("missing ELF header");
if (memcmp(hdr()->e_ident, ELFMAG, SELFMAG) != 0)
error("not an ELF executable");
littleEndian = hdr()->e_ident[EI_DATA] == ELFDATA2LSB;
if (rdi(hdr()->e_type) != ET_EXEC && rdi(hdr()->e_type) != ET_DYN)
error("wrong ELF type");
{
auto ph_offset = rdi(hdr()->e_phoff);
auto ph_num = rdi(hdr()->e_phnum);
auto ph_entsize = rdi(hdr()->e_phentsize);
size_t ph_size, ph_end;
if (__builtin_mul_overflow(ph_num, ph_entsize, &ph_size)
|| __builtin_add_overflow(ph_offset, ph_size, &ph_end)
|| ph_end > fileContents->size()) {
error("program header table out of bounds");
}
}
if (rdi(hdr()->e_shnum) == 0)
error("no section headers. The input file is probably a statically linked, self-decompressing binary");
{
auto sh_offset = rdi(hdr()->e_shoff);
auto sh_num = rdi(hdr()->e_shnum);
auto sh_entsize = rdi(hdr()->e_shentsize);
size_t sh_size, sh_end;
if (__builtin_mul_overflow(sh_num, sh_entsize, &sh_size)
|| __builtin_add_overflow(sh_offset, sh_size, &sh_end)
|| sh_end > fileContents->size()) {
error("section header table out of bounds");
}
}
if (rdi(hdr()->e_phentsize) != sizeof(Elf_Phdr))
error("program headers have wrong size");
/* Copy the program and section headers. */
for (int i = 0; i < rdi(hdr()->e_phnum); ++i) {
Elf_Phdr *phdr = (Elf_Phdr *) (fileContents->data() + rdi(hdr()->e_phoff)) + i;
checkPointer(fileContents, phdr, sizeof(*phdr));
phdrs.push_back(*phdr);
if (rdi(phdrs[i].p_type) == PT_INTERP) isExecutable = true;
}
for (int i = 0; i < rdi(hdr()->e_shnum); ++i) {
Elf_Shdr *shdr = (Elf_Shdr *) (fileContents->data() + rdi(hdr()->e_shoff)) + i;
checkPointer(fileContents, shdr, sizeof(*shdr));
shdrs.push_back(*shdr);
}
/* Get the section header string table section (".shstrtab"). Its
index in the section header table is given by e_shstrndx field
of the ELF header. */
auto shstrtabIndex = rdi(hdr()->e_shstrndx);
if (shstrtabIndex >= shdrs.size())
error("string table index out of bounds");
auto shstrtabSize = rdi(shdrs[shstrtabIndex].sh_size);
size_t shstrtabptr;
if (__builtin_add_overflow(reinterpret_cast<size_t>(fileContents->data()), rdi(shdrs[shstrtabIndex].sh_offset), &shstrtabptr))
error("string table overflow");
const char *shstrtab = reinterpret_cast<const char *>(shstrtabptr);
checkPointer(fileContents, shstrtab, shstrtabSize);
if (shstrtabSize == 0)
error("string table size is zero");
if (shstrtab[shstrtabSize - 1] != 0)
error("string table is not zero terminated");
sectionNames = std::string(shstrtab, shstrtabSize);
sectionsByOldIndex.resize(shdrs.size());
for (size_t i = 1; i < shdrs.size(); ++i)
sectionsByOldIndex.at(i) = getSectionName(shdrs.at(i));
}
template<ElfFileParams>
unsigned int ElfFile<ElfFileParamNames>::getPageSize() const noexcept
{
if (forcedPageSize > 0)
return forcedPageSize;
// Architectures (and ABIs) can have different minimum section alignment
// requirements. There is no authoritative list of these values. The
// current list is extracted from GNU gold's source code (abi_pagesize).
switch (rdi(hdr()->e_machine)) {
case EM_IA_64:
case EM_MIPS:
case EM_PPC:
case EM_PPC64:
case EM_AARCH64:
case EM_TILEGX:
case EM_LOONGARCH:
return 0x10000;
case EM_SPARC: // This should be sparc 32-bit. According to the linux
// kernel 4KB should be also fine, but it seems that solaris is doing 8KB
case EM_SPARCV9: /* SPARC64 support */
return 0x2000;
default:
return 0x1000;
}
}
template<ElfFileParams>
void ElfFile<ElfFileParamNames>::sortPhdrs()
{
/* Sort the segments by offset. */
CompPhdr comp;
comp.elfFile = this;
stable_sort(phdrs.begin(), phdrs.end(), comp);
}
template<ElfFileParams>
void ElfFile<ElfFileParamNames>::sortShdrs()
{
/* Translate sh_link mappings to section names, since sorting the
sections will invalidate the sh_link fields. */
std::map<SectionName, SectionName> linkage;
for (unsigned int i = 1; i < rdi(hdr()->e_shnum); ++i)
if (rdi(shdrs.at(i).sh_link) != 0)
linkage[getSectionName(shdrs.at(i))] = getSectionName(shdrs.at(rdi(shdrs.at(i).sh_link)));
/* Idem for sh_info on certain sections. */
std::map<SectionName, SectionName> info;
for (unsigned int i = 1; i < rdi(hdr()->e_shnum); ++i)
if (rdi(shdrs.at(i).sh_info) != 0 &&
(rdi(shdrs.at(i).sh_type) == SHT_REL || rdi(shdrs.at(i).sh_type) == SHT_RELA))
info[getSectionName(shdrs.at(i))] = getSectionName(shdrs.at(rdi(shdrs.at(i).sh_info)));
/* Idem for the index of the .shstrtab section in the ELF header. */
Elf_Shdr shstrtab = shdrs.at(rdi(hdr()->e_shstrndx));
/* Sort the sections by offset. */
CompShdr comp;
comp.elfFile = this;
stable_sort(shdrs.begin() + 1, shdrs.end(), comp);
/* Restore the sh_link mappings. */
for (unsigned int i = 1; i < rdi(hdr()->e_shnum); ++i)
if (rdi(shdrs[i].sh_link) != 0)
wri(shdrs[i].sh_link,
getSectionIndex(linkage[getSectionName(shdrs[i])]));
/* And the st_info mappings. */
for (unsigned int i = 1; i < rdi(hdr()->e_shnum); ++i)
if (rdi(shdrs.at(i).sh_info) != 0 &&
(rdi(shdrs.at(i).sh_type) == SHT_REL || rdi(shdrs.at(i).sh_type) == SHT_RELA))
wri(shdrs.at(i).sh_info,
getSectionIndex(info.at(getSectionName(shdrs.at(i)))));
/* And the .shstrtab index. Note: the match here is done by checking the offset as searching
* by name can yield incorrect results in case there are multiple sections with the same
* name as the one initially pointed by hdr()->e_shstrndx */
for (unsigned int i = 1; i < rdi(hdr()->e_shnum); ++i) {
if (shdrs.at(i).sh_offset == shstrtab.sh_offset) {
wri(hdr()->e_shstrndx, i);
}
}
}
static void writeFile(const std::string & fileName, const FileContents & contents)
{
debug("writing %s\n", fileName.c_str());
int fd = open(fileName.c_str(), O_CREAT | O_TRUNC | O_WRONLY | O_BINARY, 0777);
if (fd == -1)
error("open");
size_t bytesWritten = 0;
ssize_t portion;
while (bytesWritten < contents->size()) {
if ((portion = write(fd, contents->data() + bytesWritten, contents->size() - bytesWritten)) < 0) {
if (errno == EINTR)
continue;
error("write");
}
bytesWritten += portion;
}
if (close(fd) >= 0)
return;
/*
* Just ignore EINTR; a retry loop is the wrong thing to do.
*
* http://lkml.indiana.edu/hypermail/linux/kernel/0509.1/0877.html
* https://bugzilla.gnome.org/show_bug.cgi?id=682819
* http://utcc.utoronto.ca/~cks/space/blog/unix/CloseEINTR
* https://sites.google.com/site/michaelsafyan/software-engineering/checkforeintrwheninvokingclosethinkagain
*/
if (errno == EINTR)
return;
error("close");
}
static uint64_t roundUp(uint64_t n, uint64_t m)
{
if (n == 0)
return m;
return ((n - 1) / m + 1) * m;
}
template<ElfFileParams>
void ElfFile<ElfFileParamNames>::shiftFile(unsigned int extraPages, size_t startOffset, size_t extraBytes)
{
assert(startOffset >= sizeof(Elf_Ehdr));
unsigned int oldSize = fileContents->size();
assert(oldSize > startOffset);
/* Move the entire contents of the file after 'startOffset' by 'extraPages' pages further. */
unsigned int shift = extraPages * getPageSize();
fileContents->resize(oldSize + shift, 0);
memmove(fileContents->data() + startOffset + shift, fileContents->data() + startOffset, oldSize - startOffset);
memset(fileContents->data() + startOffset, 0, shift);
/* Adjust the ELF header. */
wri(hdr()->e_phoff, sizeof(Elf_Ehdr));
if (rdi(hdr()->e_shoff) >= startOffset)
wri(hdr()->e_shoff, rdi(hdr()->e_shoff) + shift);
/* Update the offsets in the section headers. */
for (int i = 1; i < rdi(hdr()->e_shnum); ++i) {
size_t sh_offset = rdi(shdrs.at(i).sh_offset);
if (sh_offset >= startOffset)
wri(shdrs.at(i).sh_offset, sh_offset + shift);
}
int splitIndex = -1;
size_t splitShift = 0;
/* Update the offsets in the program headers. */
for (int i = 0; i < rdi(hdr()->e_phnum); ++i) {
Elf_Off p_start = rdi(phdrs.at(i).p_offset);
if (p_start <= startOffset && p_start + rdi(phdrs.at(i).p_filesz) > startOffset && rdi(phdrs.at(i).p_type) == PT_LOAD) {
assert(splitIndex == -1);
splitIndex = i;
splitShift = startOffset - p_start;
/* This is the load segment we're currently extending within, so we split it. */
wri(phdrs.at(i).p_offset, startOffset);
wri(phdrs.at(i).p_memsz, rdi(phdrs.at(i).p_memsz) - splitShift);
wri(phdrs.at(i).p_filesz, rdi(phdrs.at(i).p_filesz) - splitShift);
wri(phdrs.at(i).p_paddr, rdi(phdrs.at(i).p_paddr) + splitShift);
wri(phdrs.at(i).p_vaddr, rdi(phdrs.at(i).p_vaddr) + splitShift);
p_start = startOffset;
}
if (p_start >= startOffset) {
wri(phdrs.at(i).p_offset, p_start + shift);
if (rdi(phdrs.at(i).p_align) != 0 &&
(rdi(phdrs.at(i).p_vaddr) - rdi(phdrs.at(i).p_offset)) % rdi(phdrs.at(i).p_align) != 0) {
debug("changing alignment of program header %d from %d to %d\n", i,
rdi(phdrs.at(i).p_align), getPageSize());
wri(phdrs.at(i).p_align, getPageSize());
}
} else {
/* If we're not physically shifting, shift back virtual memory. */
if (rdi(phdrs.at(i).p_paddr) >= shift)
wri(phdrs.at(i).p_paddr, rdi(phdrs.at(i).p_paddr) - shift);
if (rdi(phdrs.at(i).p_vaddr) >= shift)
wri(phdrs.at(i).p_vaddr, rdi(phdrs.at(i).p_vaddr) - shift);
}
}
assert(splitIndex != -1);
/* Add a segment that maps the new program/section headers and
PT_INTERP segment into memory. Otherwise glibc will choke. */
phdrs.resize(rdi(hdr()->e_phnum) + 1);
wri(hdr()->e_phnum, rdi(hdr()->e_phnum) + 1);
Elf_Phdr & phdr = phdrs.at(rdi(hdr()->e_phnum) - 1);
wri(phdr.p_type, PT_LOAD);
wri(phdr.p_offset, phdrs.at(splitIndex).p_offset - splitShift - shift);
wri(phdr.p_paddr, phdrs.at(splitIndex).p_paddr - splitShift - shift);
wri(phdr.p_vaddr, phdrs.at(splitIndex).p_vaddr - splitShift - shift);
wri(phdr.p_filesz, wri(phdr.p_memsz, splitShift + extraBytes));
wri(phdr.p_flags, PF_R | PF_W);
wri(phdr.p_align, getPageSize());
}
template<ElfFileParams>
std::string ElfFile<ElfFileParamNames>::getSectionName(const Elf_Shdr & shdr) const
{
const size_t name_off = rdi(shdr.sh_name);
if (name_off >= sectionNames.size())
error("section name offset out of bounds");
return std::string(sectionNames.c_str() + name_off);
}
template<ElfFileParams>
const Elf_Shdr & ElfFile<ElfFileParamNames>::findSectionHeader(const SectionName & sectionName) const
{
auto shdr = tryFindSectionHeader(sectionName);
if (!shdr) {
std::string extraMsg;
if (sectionName == ".interp" || sectionName == ".dynamic" || sectionName == ".dynstr")
extraMsg = ". The input file is most likely statically linked";
error("cannot find section '" + sectionName + "'" + extraMsg);
}
return *shdr;
}
template<ElfFileParams>
std::optional<std::reference_wrapper<const Elf_Shdr>> ElfFile<ElfFileParamNames>::tryFindSectionHeader(const SectionName & sectionName) const
{
auto i = getSectionIndex(sectionName);
if (i)
return shdrs.at(i);
return {};
}
template<ElfFileParams>
template<class T>
span<T> ElfFile<ElfFileParamNames>::getSectionSpan(const Elf_Shdr & shdr) const
{
return span((T*)(fileContents->data() + rdi(shdr.sh_offset)), rdi(shdr.sh_size)/sizeof(T));
}
template<ElfFileParams>
template<class T>
span<T> ElfFile<ElfFileParamNames>::getSectionSpan(const SectionName & sectionName)
{
return getSectionSpan<T>(findSectionHeader(sectionName));
}
template<ElfFileParams>
template<class T>
span<T> ElfFile<ElfFileParamNames>::tryGetSectionSpan(const SectionName & sectionName)
{
auto shdrOpt = tryFindSectionHeader(sectionName);
return shdrOpt ? getSectionSpan<T>(*shdrOpt) : span<T>();
}
template<ElfFileParams>
unsigned int ElfFile<ElfFileParamNames>::getSectionIndex(const SectionName & sectionName) const
{
for (unsigned int i = 1; i < rdi(hdr()->e_shnum); ++i)
if (getSectionName(shdrs.at(i)) == sectionName) return i;
return 0;
}
template<ElfFileParams>
bool ElfFile<ElfFileParamNames>::haveReplacedSection(const SectionName & sectionName) const
{
return replacedSections.count(sectionName);
}
template<ElfFileParams>
std::string & ElfFile<ElfFileParamNames>::replaceSection(const SectionName & sectionName,
unsigned int size)
{
auto i = replacedSections.find(sectionName);
std::string s;
if (i != replacedSections.end()) {
s = std::string(i->second);
} else {
auto shdr = findSectionHeader(sectionName);
s = extractString(fileContents, rdi(shdr.sh_offset), rdi(shdr.sh_size));
}
s.resize(size);
replacedSections[sectionName] = s;
return replacedSections[sectionName];
}
template<ElfFileParams>
void ElfFile<ElfFileParamNames>::writeReplacedSections(Elf_Off & curOff,
Elf_Addr startAddr, Elf_Off startOffset)
{
/* Overwrite the old section contents with 'X's. Do this
*before* writing the new section contents (below) to prevent
clobbering previously written new section contents. */
for (auto & i : replacedSections) {
const std::string & sectionName = i.first;
const Elf_Shdr & shdr = findSectionHeader(sectionName);
if (rdi(shdr.sh_type) != SHT_NOBITS)
memset(fileContents->data() + rdi(shdr.sh_offset), 'X', rdi(shdr.sh_size));
}
std::set<unsigned int> noted_phdrs = {};
/* We iterate over the sorted section headers here, so that the relative
position between replaced sections stays the same. */
for (auto & shdr : shdrs) {
std::string sectionName = getSectionName(shdr);
auto i = replacedSections.find(sectionName);
if (i == replacedSections.end())
continue;
Elf_Shdr orig_shdr = shdr;
debug("rewriting section '%s' from offset 0x%x (size %d) to offset 0x%x (size %d)\n",
sectionName.c_str(), rdi(shdr.sh_offset), rdi(shdr.sh_size), curOff, i->second.size());
memcpy(fileContents->data() + curOff, i->second.c_str(),
i->second.size());
/* Update the section header for this section. */
wri(shdr.sh_offset, curOff);
wri(shdr.sh_addr, startAddr + (curOff - startOffset));
wri(shdr.sh_size, i->second.size());
wri(shdr.sh_addralign, sectionAlignment);
/* If this is the .interp section, then the PT_INTERP segment
must be sync'ed with it. */
if (sectionName == ".interp") {
for (auto & phdr : phdrs) {
if (rdi(phdr.p_type) == PT_INTERP) {
phdr.p_offset = shdr.sh_offset;
phdr.p_vaddr = phdr.p_paddr = shdr.sh_addr;
phdr.p_filesz = phdr.p_memsz = shdr.sh_size;
}
}
}
/* If this is the .dynamic section, then the PT_DYNAMIC segment
must be sync'ed with it. */
else if (sectionName == ".dynamic") {
for (auto & phdr : phdrs) {
if (rdi(phdr.p_type) == PT_DYNAMIC) {
phdr.p_offset = shdr.sh_offset;
phdr.p_vaddr = phdr.p_paddr = shdr.sh_addr;
phdr.p_filesz = phdr.p_memsz = shdr.sh_size;
}
}
}
/* If this is a note section, there might be a PT_NOTE segment that
must be sync'ed with it. Note that normalizeNoteSegments() will have
already taken care of PT_NOTE segments containing multiple note
sections. At this point, we can assume that the segment will map to
exactly one section.
Note sections also have particular alignment constraints: the
data inside the section is formatted differently depending on the
section alignment. Keep the original alignment if possible. */
if (rdi(shdr.sh_type) == SHT_NOTE) {
if (orig_shdr.sh_addralign < sectionAlignment)
shdr.sh_addralign = orig_shdr.sh_addralign;
for (unsigned int j = 0; j < phdrs.size(); ++j) {
auto &phdr = phdrs.at(j);
if (rdi(phdr.p_type) == PT_NOTE && !noted_phdrs.count(j)) {
Elf_Off p_start = rdi(phdr.p_offset);
Elf_Off p_end = p_start + rdi(phdr.p_filesz);
Elf_Off s_start = rdi(orig_shdr.sh_offset);
Elf_Off s_end = s_start + rdi(orig_shdr.sh_size);
/* Skip if no overlap. */
if (!(s_start >= p_start && s_start < p_end) &&
!(s_end > p_start && s_end <= p_end))
continue;
/* We only support exact matches. */
if (p_start != s_start || p_end != s_end)
error("unsupported overlap of SHT_NOTE and PT_NOTE");
phdr.p_offset = shdr.sh_offset;
phdr.p_vaddr = phdr.p_paddr = shdr.sh_addr;
phdr.p_filesz = phdr.p_memsz = shdr.sh_size;
noted_phdrs.insert(j);
}
}
}
/* If there is .MIPS.abiflags section, then the PT_MIPS_ABIFLAGS
segment must be sync'ed with it. */
if (sectionName == ".MIPS.abiflags") {
for (auto & phdr : phdrs) {
if (rdi(phdr.p_type) == PT_MIPS_ABIFLAGS) {
phdr.p_offset = shdr.sh_offset;
phdr.p_vaddr = phdr.p_paddr = shdr.sh_addr;
phdr.p_filesz = phdr.p_memsz = shdr.sh_size;
}
}
}
/* If there is .note.gnu.property section, then the PT_GNU_PROPERTY
segment must be sync'ed with it. */
if (sectionName == ".note.gnu.property") {
for (auto & phdr : phdrs) {
if (rdi(phdr.p_type) == PT_GNU_PROPERTY) {
phdr.p_offset = shdr.sh_offset;
phdr.p_vaddr = phdr.p_paddr = shdr.sh_addr;
phdr.p_filesz = phdr.p_memsz = shdr.sh_size;
}
}
}
curOff += roundUp(i->second.size(), sectionAlignment);
}
replacedSections.clear();
}
template<ElfFileParams>
void ElfFile<ElfFileParamNames>::rewriteSectionsLibrary()
{
/* For dynamic libraries, we just place the replacement sections
at the end of the file. They're mapped into memory by a
PT_LOAD segment located directly after the last virtual address
page of other segments. */
Elf_Addr startPage = 0;
Elf_Addr firstPage = 0;
unsigned alignStartPage = getPageSize();
for (auto & phdr : phdrs) {
Elf_Addr thisPage = rdi(phdr.p_vaddr) + rdi(phdr.p_memsz);
if (thisPage > startPage) startPage = thisPage;
if (rdi(phdr.p_type) == PT_PHDR) firstPage = rdi(phdr.p_vaddr) - rdi(phdr.p_offset);
unsigned thisAlign = rdi(phdr.p_align);
alignStartPage = std::max(alignStartPage, thisAlign);
}
startPage = roundUp(startPage, alignStartPage);
debug("last page is 0x%llx\n", (unsigned long long) startPage);
debug("first page is 0x%llx\n", (unsigned long long) firstPage);
/* When normalizing note segments we will in the worst case be adding
1 program header for each SHT_NOTE section. */
unsigned int num_notes = std::count_if(shdrs.begin(), shdrs.end(),
[this](Elf_Shdr shdr) { return rdi(shdr.sh_type) == SHT_NOTE; });
/* Because we're adding a new section header, we're necessarily increasing
the size of the program header table. This can cause the first section
to overlap the program header table in memory; we need to shift the first
few segments to someplace else. */
/* Some sections may already be replaced so account for that */
unsigned int i = 1;
Elf_Addr pht_size = sizeof(Elf_Ehdr) + (phdrs.size() + num_notes + 1)*sizeof(Elf_Phdr);
while( i < rdi(hdr()->e_shnum) && rdi(shdrs.at(i).sh_offset) <= pht_size ) {
if (not haveReplacedSection(getSectionName(shdrs.at(i))))
replaceSection(getSectionName(shdrs.at(i)), rdi(shdrs.at(i).sh_size));
i++;
}
bool moveHeaderTableToTheEnd = rdi(hdr()->e_shoff) < pht_size;
/* Compute the total space needed for the replaced sections */
off_t neededSpace = 0;
for (auto & s : replacedSections)
neededSpace += roundUp(s.second.size(), sectionAlignment);
off_t headerTableSpace = roundUp(rdi(hdr()->e_shnum) * rdi(hdr()->e_shentsize), sectionAlignment);
if (moveHeaderTableToTheEnd)
neededSpace += headerTableSpace;
debug("needed space is %d\n", neededSpace);
Elf_Off startOffset = roundUp(fileContents->size(), getPageSize());
// In older version of binutils (2.30), readelf would check if the dynamic
// section segment is strictly smaller than the file (and not same size).
// By making it one byte larger, we don't break readelf.
off_t binutilsQuirkPadding = 1;
fileContents->resize(startOffset + neededSpace + binutilsQuirkPadding, 0);
/* Even though this file is of type ET_DYN, it could actually be
an executable. For instance, Gold produces executables marked
ET_DYN as does LD when linking with pie. If we move PT_PHDR, it
has to stay in the first PT_LOAD segment or any subsequent ones
if they're continuous in memory due to linux kernel constraints
(see BUGS). Since the end of the file would be after bss, we can't
move PHDR there, we therefore choose to leave PT_PHDR where it is but
move enough following sections such that we can add the extra PT_LOAD
section to it. This PT_LOAD segment ensures the sections at the end of
the file are mapped into memory for ld.so to process.
We can't use the approach in rewriteSectionsExecutable()
since DYN executables tend to start at virtual address 0, so
rewriteSectionsExecutable() won't work because it doesn't have
any virtual address space to grow downwards into. */
if (isExecutable && startOffset > startPage) {
debug("shifting new PT_LOAD segment by %d bytes to work around a Linux kernel bug\n", startOffset - startPage);
startPage = startOffset;
}
wri(hdr()->e_phoff, sizeof(Elf_Ehdr));
bool needNewSegment = true;
auto& lastSeg = phdrs.back();
/* Try to extend the last segment to include replaced sections */
if (!phdrs.empty() &&
rdi(lastSeg.p_type) == PT_LOAD &&
rdi(lastSeg.p_flags) == (PF_R | PF_W) &&
rdi(lastSeg.p_align) == alignStartPage) {
auto segEnd = roundUp(rdi(lastSeg.p_offset) + rdi(lastSeg.p_memsz), getPageSize());
if (segEnd == startOffset) {
auto newSz = startOffset + neededSpace - rdi(lastSeg.p_offset);
wri(lastSeg.p_filesz, wri(lastSeg.p_memsz, newSz));
needNewSegment = false;
}
}
if (needNewSegment) {
/* Add a segment that maps the replaced sections into memory. */
phdrs.resize(rdi(hdr()->e_phnum) + 1);
wri(hdr()->e_phnum, rdi(hdr()->e_phnum) + 1);
Elf_Phdr & phdr = phdrs.at(rdi(hdr()->e_phnum) - 1);
wri(phdr.p_type, PT_LOAD);
wri(phdr.p_offset, startOffset);
wri(phdr.p_vaddr, wri(phdr.p_paddr, startPage));
wri(phdr.p_filesz, wri(phdr.p_memsz, neededSpace));
wri(phdr.p_flags, PF_R | PF_W);
wri(phdr.p_align, alignStartPage);
}
normalizeNoteSegments();
/* Write out the replaced sections. */
Elf_Off curOff = startOffset;
if (moveHeaderTableToTheEnd) {
debug("Moving the shtable to offset %d\n", curOff);
wri(hdr()->e_shoff, curOff);
curOff += headerTableSpace;
}
writeReplacedSections(curOff, startPage, startOffset);
assert(curOff == startOffset + neededSpace);
/* Write out the updated program and section headers */
rewriteHeaders(firstPage + rdi(hdr()->e_phoff));
}
static bool noSort = false;
template<ElfFileParams>
void ElfFile<ElfFileParamNames>::rewriteSectionsExecutable()
{
if (!noSort) {
/* Sort the sections by offset, otherwise we won't correctly find
all the sections before the last replaced section. */
sortShdrs();
}
/* What is the index of the last replaced section? */
unsigned int lastReplaced = 0;
for (unsigned int i = 1; i < rdi(hdr()->e_shnum); ++i) {
std::string sectionName = getSectionName(shdrs.at(i));
if (replacedSections.count(sectionName)) {
debug("using replaced section '%s'\n", sectionName.c_str());
lastReplaced = i;
}
}
assert(lastReplaced != 0);
debug("last replaced is %d\n", lastReplaced);
/* Try to replace all sections before that, as far as possible.
Stop when we reach an irreplacable section (such as one of type
SHT_PROGBITS). These cannot be moved in virtual address space
since that would invalidate absolute references to them. */
assert(lastReplaced + 1 < shdrs.size()); /* !!! I'm lazy. */
size_t startOffset = rdi(shdrs.at(lastReplaced + 1).sh_offset);
Elf_Addr startAddr = rdi(shdrs.at(lastReplaced + 1).sh_addr);
std::string prevSection;
for (unsigned int i = 1; i <= lastReplaced; ++i) {
Elf_Shdr & shdr(shdrs.at(i));
std::string sectionName = getSectionName(shdr);
debug("looking at section '%s'\n", sectionName.c_str());
/* !!! Why do we stop after a .dynstr section? I can't
remember! */
if ((rdi(shdr.sh_type) == SHT_PROGBITS && sectionName != ".interp")
|| prevSection == ".dynstr")
{
startOffset = rdi(shdr.sh_offset);
startAddr = rdi(shdr.sh_addr);
lastReplaced = i - 1;
break;
}
if (!replacedSections.count(sectionName)) {
debug("replacing section '%s' which is in the way\n", sectionName.c_str());
replaceSection(sectionName, rdi(shdr.sh_size));
}
prevSection = std::move(sectionName);
}
debug("first reserved offset/addr is 0x%x/0x%llx\n",
startOffset, (unsigned long long) startAddr);
assert(startAddr % getPageSize() == startOffset % getPageSize());
Elf_Addr firstPage = startAddr - startOffset;
debug("first page is 0x%llx\n", (unsigned long long) firstPage);
if (rdi(hdr()->e_shoff) < startOffset) {
/* The section headers occur too early in the file and would be
overwritten by the replaced sections. Move them to the end of the file
before proceeding. */
off_t shoffNew = fileContents->size();
off_t shSize = rdi(hdr()->e_shoff) + rdi(hdr()->e_shnum) * rdi(hdr()->e_shentsize);
fileContents->resize(fileContents->size() + shSize, 0);
wri(hdr()->e_shoff, shoffNew);
/* Rewrite the section header table. For neatness, keep the
sections sorted. */
assert(rdi(hdr()->e_shnum) == shdrs.size());
sortShdrs();
for (unsigned int i = 1; i < rdi(hdr()->e_shnum); ++i)
* ((Elf_Shdr *) (fileContents->data() + rdi(hdr()->e_shoff)) + i) = shdrs.at(i);
}