#include "crc32.h" #include "GPT.h" #include <cassert> #include <cerrno> #include <cstring> #include <fcntl.h> #include <iostream> #include <sys/mman.h> #include <unistd.h> // FIXME: don't assume 512 byte sectors #define SECTOR_SIZE 512 GPTFile::GPTFile(std::string_view path) : m_path(path) { m_fd = open(m_path.c_str(), O_RDWR); if (m_fd == -1) { std::cerr << "Could not open '" << m_path << "': " << std::strerror(errno) << std::endl; return; } if (fstat(m_fd, &m_stat) == -1) { std::cerr << "Could not stat '" << m_path << "': " << std::strerror(errno) << std::endl; return; } void* mmap_addr = mmap(nullptr, m_stat.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, m_fd, 0); if (mmap_addr == MAP_FAILED) { std::cerr << "Could not mmap '" << m_path << "': " << std::strerror(errno) << std::endl; return; } m_mmap = reinterpret_cast<uint8_t*>(mmap_addr); if (!validate_gpt_header()) return; m_success = true; } GPTFile::~GPTFile() { if (m_mmap) munmap(m_mmap, m_stat.st_size); m_mmap = nullptr; if (m_fd != -1) close(m_fd); m_fd = -1; } MBR& GPTFile::mbr() { return *reinterpret_cast<MBR*>(m_mmap); } const GPTHeader& GPTFile::gpt_header() const { return *reinterpret_cast<GPTHeader*>(m_mmap + SECTOR_SIZE); } bool GPTFile::install_stage1(std::span<const uint8_t> stage1) { auto& mbr = this->mbr(); if (stage1.size() > sizeof(mbr.boot_code)) { std::cerr << m_path << ": can't fit " << stage1.size() << " bytes of boot code in mbr (max is " << sizeof(mbr.boot_code) << ")" << std::endl; return false; } // copy boot code memcpy(mbr.boot_code, stage1.data(), stage1.size()); // setup mbr mbr.unique_mbr_disk_signature = 0xdeadbeef; mbr.unknown = 0; mbr.signature = 0xAA55; // setup mbr partition records mbr.partition_records[0].boot_indicator = 0x00; mbr.partition_records[0].starting_chs[0] = 0x00; mbr.partition_records[0].starting_chs[1] = 0x02; mbr.partition_records[0].starting_chs[2] = 0x00; mbr.partition_records[0].os_type = 0xEE; mbr.partition_records[0].ending_chs[0] = 0xFF; mbr.partition_records[0].ending_chs[1] = 0xFF; mbr.partition_records[0].ending_chs[2] = 0xFF; mbr.partition_records[0].starting_lba = 1; mbr.partition_records[0].size_in_lba = 0xFFFFFFFF; memset(&mbr.partition_records[1], 0x00, sizeof(MBRPartitionRecord)); memset(&mbr.partition_records[2], 0x00, sizeof(MBRPartitionRecord)); memset(&mbr.partition_records[3], 0x00, sizeof(MBRPartitionRecord)); return true; } bool GPTFile::install_stage2(std::span<const uint8_t> stage2, std::span<const uint8_t> data, const GUID& root_partition_guid) { if (data.size() < 16) { std::cerr << m_path << ": contains invalid .data section, too small for patches" << std::endl; return false; } // find GUID patch offsets std::size_t disk_guid_offset(-1); std::size_t part_guid_offset(-1); for (std::size_t i = 0; i < data.size() - 16; i++) { if (memcmp(data.data() + i, "root disk guid ", 16) == 0) { if (disk_guid_offset != std::size_t(-1)) { std::cerr << m_path << ": contains invalid .data section, multiple patchable disk guids" << std::endl; return false; } disk_guid_offset = i; } if (memcmp(data.data() + i, "root part guid ", 16) == 0) { if (part_guid_offset != std::size_t(-1)) { std::cerr << m_path << ": contains invalid .data section, multiple patchable partition guids" << std::endl; return false; } part_guid_offset = i; } } if (disk_guid_offset == std::size_t(-1)) { std::cerr << m_path << ": contains invalid .data section, no patchable disk guid" << std::endl; return false; } if (part_guid_offset == std::size_t(-1)) { std::cerr << m_path << ": contains invalid .data section, no patchable partition guid" << std::endl; return false; } auto partition = find_partition_with_type(bios_boot_guid); if (!partition.has_value()) { std::cerr << m_path << ": could not find partition with type " << bios_boot_guid << std::endl; return false; } const std::size_t partition_size = (partition->ending_lba - partition->starting_lba + 1) * SECTOR_SIZE; std::size_t data_offset = stage2.size(); if (std::size_t rem = data_offset % 512) data_offset += 512 - rem; if (data_offset + data.size() > partition_size) { std::cerr << m_path << ": can't fit " << stage2.size() + data.size() << " bytes of data to partition of size " << partition_size << std::endl; return false; } uint8_t* partition_start = m_mmap + partition->starting_lba * SECTOR_SIZE; memcpy(partition_start, stage2.data(), stage2.size()); memcpy(partition_start + data_offset, data.data(), data.size()); // patch GUIDs *reinterpret_cast<GUID*>(partition_start + data_offset + disk_guid_offset) = gpt_header().disk_guid; *reinterpret_cast<GUID*>(partition_start + data_offset + part_guid_offset) = root_partition_guid; return true; } bool GPTFile::install_bootloader(std::span<const uint8_t> stage1, std::span<const uint8_t> stage2, std::span<const uint8_t> data, const GUID& root_partition_guid) { if (!find_partition_with_guid(root_partition_guid).has_value()) { std::cerr << m_path << ": no partition with GUID " << root_partition_guid << std::endl; return false; } if (!install_stage1(stage1)) return false; if (!install_stage2(stage2, data, root_partition_guid)) return false; return true; } std::optional<GPTPartitionEntry> GPTFile::find_partition_with_guid(const GUID& guid) const { const auto& gpt_header = this->gpt_header(); const uint8_t* partition_entry_array_start = m_mmap + gpt_header.partition_entry_lba * SECTOR_SIZE; for (std::size_t i = 0; i < gpt_header.number_of_partition_entries; i++) { const auto& partition_entry = *reinterpret_cast<const GPTPartitionEntry*>(partition_entry_array_start + i * gpt_header.size_of_partition_entry); if (partition_entry.partition_guid != guid) continue; return partition_entry; } return {}; } std::optional<GPTPartitionEntry> GPTFile::find_partition_with_type(const GUID& type_guid) const { const auto& gpt_header = this->gpt_header(); const uint8_t* partition_entry_array_start = m_mmap + gpt_header.partition_entry_lba * SECTOR_SIZE; for (std::size_t i = 0; i < gpt_header.number_of_partition_entries; i++) { const auto& partition_entry = *reinterpret_cast<const GPTPartitionEntry*>(partition_entry_array_start + i * gpt_header.size_of_partition_entry); if (partition_entry.type_guid != type_guid) continue; return partition_entry; } return {}; } bool GPTFile::validate_gpt_header() const { if (SECTOR_SIZE + m_stat.st_size < sizeof(GPTHeader)) { std::cerr << m_path << " is too small to have GPT header" << std::endl; return false; } auto gpt_header = this->gpt_header(); if (std::memcmp(gpt_header.signature, "EFI PART", 8) != 0) { std::cerr << m_path << " doesn't contain GPT partition header signature" << std::endl; return false; } const uint32_t header_crc32 = gpt_header.header_crc32; gpt_header.header_crc32 = 0; if (header_crc32 != crc32_checksum(reinterpret_cast<uint8_t*>(&gpt_header), gpt_header.header_size)) { std::cerr << m_path << " has non-matching header crc32" << std::endl; return false; } const std::size_t partition_array_size = gpt_header.number_of_partition_entries * gpt_header.size_of_partition_entry; if (gpt_header.partition_entry_array_crc32 != crc32_checksum(m_mmap + gpt_header.partition_entry_lba * SECTOR_SIZE, partition_array_size)) { std::cerr << m_path << " has non-matching partition entry crc32" << std::endl; return false; } return true; }