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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 <[email protected]>
*
* 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 bool clobberOldSections = true;
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_ALPHA:
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));
auto 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 another PT_LOAD segment loading the data we've split above. */
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>::hasReplacedSection(const SectionName & sectionName) const
{
return replacedSections.count(sectionName);
}
template<ElfFileParams>
bool ElfFile<ElfFileParamNames>::canReplaceSection(const SectionName & sectionName) const
{
auto shdr = findSectionHeader(sectionName);
return sectionName == ".interp" || rdi(shdr.sh_type) != SHT_PROGBITS;
}
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)
{
if (clobberOldSections) {
/* Overwrite the old section contents with 'Z'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), 'Z', 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; });
/* Compute the total space needed for the replaced sections, pessimistically
assuming we're going to need one more to account for new PT_LOAD covering
relocated PHDR */
off_t phtSize = roundUp((phdrs.size() + num_notes + 1) * sizeof(Elf_Phdr) + sizeof(Elf_Ehdr), sectionAlignment);
off_t shtSize = roundUp(rdi(hdr()->e_shnum) * rdi(hdr()->e_shentsize), sectionAlignment);
/* Check if we can keep PHT at the beginning of the file.
We'd like to do that, because it preverves compatibility with older
kernels¹ - but if the PHT has grown too much, we have no other option but
to move it at the end of the file.
¹ older kernels had a bug that prevented them from loading ELFs with
PHDRs not located at the beginning of the file; it was fixed over
0da1d5002745cdc721bc018b582a8a9704d56c42 (2022-03-02) */
bool relocatePht = false;
unsigned int i = 1;
while (i < rdi(hdr()->e_shnum) && ((off_t) rdi(shdrs.at(i).sh_offset)) <= phtSize) {
const auto & sectionName = getSectionName(shdrs.at(i));
if (!hasReplacedSection(sectionName) && !canReplaceSection(sectionName)) {
relocatePht = true;
break;
}
i++;
}
if (!relocatePht) {
unsigned int i = 1;
while (i < rdi(hdr()->e_shnum) && ((off_t) rdi(shdrs.at(i).sh_offset)) <= phtSize) {
const auto & sectionName = getSectionName(shdrs.at(i));
const auto sectionSize = rdi(shdrs.at(i).sh_size);
if (!hasReplacedSection(sectionName)) {
replaceSection(sectionName, sectionSize);
}
i++;
}
}
/* Calculate how much space we'll need. */
off_t neededSpace = shtSize;
if (relocatePht) {
neededSpace += phtSize;
}
for (auto & s : replacedSections)
neededSpace += roundUp(s.second.size(), sectionAlignment);
debug("needed space is %d\n", neededSpace);
Elf_Off startOffset = roundUp(fileContents->size(), alignStartPage);
// 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);
auto& lastSeg = phdrs.back();
Elf_Addr lastSegAddr = 0;
/* As an optimization, instead of allocating a new PT_LOAD segment, try
expanding the last one */
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), alignStartPage);
if (segEnd == startOffset) {
auto newSz = startOffset + neededSpace - rdi(lastSeg.p_offset);
wri(lastSeg.p_filesz, wri(lastSeg.p_memsz, newSz));
lastSegAddr = rdi(lastSeg.p_vaddr) + newSz - neededSpace;
}
}
if (lastSegAddr == 0) {
debug("allocating new PT_LOAD segment\n");
/* 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);
assert(startPage % alignStartPage == startOffset % alignStartPage);
lastSegAddr = startPage;
}
normalizeNoteSegments();
/* Write out the replaced sections. */
Elf_Off curOff = startOffset;
if (relocatePht) {
debug("rewriting pht from offset 0x%x to offset 0x%x (size %d)\n",
rdi(hdr()->e_phoff), curOff, phtSize);
wri(hdr()->e_phoff, curOff);
curOff += phtSize;
}
// ---
debug("rewriting sht from offset 0x%x to offset 0x%x (size %d)\n",
rdi(hdr()->e_shoff), curOff, shtSize);
wri(hdr()->e_shoff, curOff);
curOff += shtSize;
// ---
/* Write out the replaced sections. */
writeReplacedSections(curOff, startPage, startOffset);
assert(curOff == startOffset + neededSpace);
/* Write out the updated program and section headers */
if (relocatePht) {
rewriteHeaders(lastSegAddr);
} else {
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. */