diff --git a/src/patchelf.cc b/src/patchelf.cc index ca247c12..5dd320da 100644 --- a/src/patchelf.cc +++ b/src/patchelf.cc @@ -826,11 +826,16 @@ void ElfFile::rewriteSectionsLibrary() 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()); @@ -860,24 +865,48 @@ void ElfFile::rewriteSectionsLibrary() startPage = startOffset; } - /* Add a segment that maps the replaced sections into memory. */ wri(hdr()->e_phoff, sizeof(Elf_Ehdr)); - 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, getPageSize()); + 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) == getPageSize()) { + 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, getPageSize()); + } 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); diff --git a/tests/Makefile.am b/tests/Makefile.am index 4a08c145..55a8f756 100644 --- a/tests/Makefile.am +++ b/tests/Makefile.am @@ -43,6 +43,7 @@ src_TESTS = \ replace-needed.sh \ replace-add-needed.sh \ add-debug-tag.sh \ + repeated-updates.sh \ empty-note.sh \ print-execstack.sh \ modify-execstack.sh \ diff --git a/tests/repeated-updates.sh b/tests/repeated-updates.sh new file mode 100755 index 00000000..669b11d5 --- /dev/null +++ b/tests/repeated-updates.sh @@ -0,0 +1,39 @@ +#! /bin/sh -e + +SCRATCH=scratch/$(basename "$0" .sh) +PATCHELF=$(readlink -f "../src/patchelf") + +rm -rf "${SCRATCH}" +mkdir -p "${SCRATCH}" + +cp simple "${SCRATCH}/" +cp libfoo.so "${SCRATCH}/" +cp libbar.so "${SCRATCH}/" + +cd "${SCRATCH}" + +${PATCHELF} --add-needed ./libbar.so simple + +############################################################################### +# Test that repeatedly modifying a string inside a shared library does not +# corrupt it due to the addition of multiple PT_LOAD entries +############################################################################### +load_segments_before=$(readelf -W -l libbar.so | grep -c LOAD) + +for _ in $(seq 1 100) +do + ${PATCHELF} --set-soname ./libbar.so libbar.so + ${PATCHELF} --set-soname libbar.so libbar.so + ./simple || exit 1 +done + +load_segments_after=$(readelf -W -l libbar.so | grep -c LOAD) + +############################################################################### +# To be even more strict, check that we don't add too many extra LOAD entries +############################################################################### +echo "Segments before: ${load_segments_before} and after: ${load_segments_after}" +if [ "${load_segments_after}" -gt $((load_segments_before + 2)) ] +then + exit 1 +fi