limine/limine-install.c

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stddef.h>
#include <string.h>
#include <inttypes.h>

struct gpt_table_header {
    // the head
    char     signature[8];
    uint32_t revision;
    uint32_t header_size;
    uint32_t crc32;
    uint32_t _reserved0;

    // the partitioning info
    uint64_t my_lba;
    uint64_t alternate_lba;
    uint64_t first_usable_lba;
    uint64_t last_usable_lba;

    // the guid
    uint64_t disk_guid[2];

    // entries related
    uint64_t partition_entry_lba;
    uint32_t number_of_partition_entries;
    uint32_t size_of_partition_entry;
    uint32_t partition_entry_array_crc32;
} __attribute__((packed));

struct gpt_entry {
    uint64_t partition_type_guid[2];

    uint64_t unique_partition_guid[2];

    uint64_t starting_lba;
    uint64_t ending_lba;

    uint64_t attributes;

    uint16_t partition_name[36];
} __attribute__((packed));

// This table from https://web.mit.edu/freebsd/head/sys/libkern/crc32.c
const uint32_t crc32_table[] = {
	0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f,
	0xe963a535, 0x9e6495a3,	0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
	0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2,
	0xf3b97148, 0x84be41de,	0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
	0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec,	0x14015c4f, 0x63066cd9,
	0xfa0f3d63, 0x8d080df5,	0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
	0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,	0x35b5a8fa, 0x42b2986c,
	0xdbbbc9d6, 0xacbcf940,	0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
	0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423,
	0xcfba9599, 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
	0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d,	0x76dc4190, 0x01db7106,
	0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
	0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d,
	0x91646c97, 0xe6635c01, 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
	0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
	0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
	0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7,
	0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
	0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa,
	0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
	0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81,
	0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
	0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683, 0xe3630b12, 0x94643b84,
	0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
	0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
	0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
	0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8, 0xa1d1937e,
	0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
	0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55,
	0x316e8eef, 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
	0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28,
	0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
	0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f,
	0x72076785, 0x05005713, 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
	0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
	0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
	0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69,
	0x616bffd3, 0x166ccf45, 0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
	0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc,
	0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
	0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693,
	0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
	0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
};

static uint32_t crc32(void *_stream, size_t len) {
    uint8_t *stream = _stream;
    uint32_t ret = 0xffffffff;

    for (size_t i = 0; i < len; i++) {
        ret = (ret >> 8) ^ crc32_table[(ret ^ stream[i]) & 0xff];
    }

    ret ^= 0xffffffff;
    return ret;
}

int main(int argc, char *argv[]) {
    int      ok = 1;
    FILE    *bootloader_file = NULL, *device = NULL;
    uint8_t *bootloader_img = NULL;
    uint8_t  orig_mbr[70], timestamp[6];

    if (argc < 3) {
        printf("Usage: %s <bootloader image> <device> [GPT partition index]\n", argv[0]);
        return 1;
    }

    bootloader_file = fopen(argv[1], "rb");
    if (bootloader_file == NULL) {
        perror("Error: ");
        return 1;
    }

    fseek(bootloader_file, 0, SEEK_END);
    size_t bootloader_file_size = ftell(bootloader_file);

    bootloader_img = malloc(bootloader_file_size);
    if (bootloader_img == NULL) {
        perror("Error: ");
        goto cleanup;
    }

    // Load in bootloader image
    fseek(bootloader_file, 0, SEEK_SET);
    fread(bootloader_img, 1, bootloader_file_size, bootloader_file);

    device = fopen(argv[2], "r+b");
    if (device == NULL) {
        perror("Error: ");
        goto cleanup;
    }

    // Probe for GPT and logical block size
    int gpt = 0;
    struct gpt_table_header gpt_header;
    uint64_t lb_guesses[] = { 512, 4096 };
    uint64_t lb_size;
    for (size_t i = 0; i < sizeof(lb_guesses) / sizeof(uint64_t); i++) {
        fseek(device, lb_guesses[i], SEEK_SET);
        fread(&gpt_header, sizeof(struct gpt_table_header), 1, device);
        if (!strncmp(gpt_header.signature, "EFI PART", 8)) {
            gpt = 1;
            lb_size = lb_guesses[i];
            fprintf(stderr, "Installing to GPT. Logical block size of %" PRIu64 " bytes.\n",
                    lb_guesses[i]);
            break;
        }
    }

    struct gpt_table_header secondary_gpt_header;
    if (gpt) {
        fprintf(stderr, "Secondary header at LBA 0x%" PRIx64 ".\n",
                gpt_header.alternate_lba);
        fseek(device, lb_size * gpt_header.alternate_lba, SEEK_SET);
        fread(&secondary_gpt_header, sizeof(struct gpt_table_header), 1, device);
        if (!strncmp(secondary_gpt_header.signature, "EFI PART", 8)) {
            fprintf(stderr, "Secondary header valid.\n");
        } else {
            fprintf(stderr, "Secondary header not valid, aborting.\n");
            goto cleanup;
        }
    }

    size_t   stage2_size   = bootloader_file_size - 512;
    uint16_t stage2_size_a = stage2_size / 2 + stage2_size % 2;
    uint16_t stage2_size_b = stage2_size / 2;

    // Default split of stage2 for MBR (consecutive in post MBR gap)
    uint64_t stage2_loc_a = 512;
    uint64_t stage2_loc_b = stage2_loc_a + stage2_size_a;
    if (stage2_loc_b & (512 - 1))
        stage2_loc_b = (stage2_loc_b + 512) & ~(512 - 1);

    if (gpt) {
        if (argc > 3) {
            uint32_t partition_num;
            sscanf(argv[3], "%" SCNu32, &partition_num);
            partition_num--;
            if (partition_num > gpt_header.number_of_partition_entries) {
                fprintf(stderr, "error: Partition number is too large.\n");
                goto cleanup;
            }

            struct gpt_entry gpt_entry;
            fseek(device, (gpt_header.partition_entry_lba * lb_size)
                  + (partition_num * sizeof(struct gpt_entry)), SEEK_SET);
            fread(&gpt_entry, sizeof(struct gpt_entry), 1, device);

            if (gpt_entry.unique_partition_guid[0] == 0 &&
              gpt_entry.unique_partition_guid[1] == 0) {
                fprintf(stderr, "error: No such partition.\n");
                goto cleanup;
            }

            fprintf(stderr, "GPT partition specified. Installing there instead of embedding.\n");

            stage2_loc_a = gpt_entry.starting_lba * lb_size;
            stage2_loc_b = stage2_loc_a + stage2_size_a;
            if (stage2_loc_b & (lb_size - 1))
                stage2_loc_b = (stage2_loc_b + lb_size) & ~(lb_size - 1);
        } else {
            fprintf(stderr, "GPT partition NOT specified. Attempting GPT embedding.\n");

            ssize_t max_partition_entry_used = -1;
            for (ssize_t i = 0; i < gpt_header.number_of_partition_entries; i++) {
                struct gpt_entry gpt_entry;
                fseek(device, (gpt_header.partition_entry_lba * lb_size)
                      + (i * sizeof(struct gpt_entry)), SEEK_SET);
                fread(&gpt_entry, sizeof(struct gpt_entry), 1, device);

                if (gpt_entry.unique_partition_guid[0] != 0 ||
                  gpt_entry.unique_partition_guid[1] != 0) {
                    if (i > max_partition_entry_used)
                        max_partition_entry_used = i;
                }
            }

            stage2_loc_a  = (gpt_header.partition_entry_lba + 32) * lb_size;
            stage2_loc_a -= stage2_size_a;
            stage2_loc_a &= ~(lb_size - 1);
            stage2_loc_b  = (secondary_gpt_header.partition_entry_lba + 32) * lb_size;
            stage2_loc_b -= stage2_size_b;
            stage2_loc_b &= ~(lb_size - 1);

            size_t partition_entries_per_lb =
                lb_size / gpt_header.size_of_partition_entry;
            size_t new_partition_array_lba_size =
                stage2_loc_a / lb_size - gpt_header.partition_entry_lba;
            size_t new_partition_entry_count =
                new_partition_array_lba_size * partition_entries_per_lb;

            if ((ssize_t)new_partition_array_lba_size <= max_partition_entry_used) {
                fprintf(stderr, "error: Cannot embed because there are too many used partition entries.\n");
                goto cleanup;
            }

            uint8_t *partition_array =
                malloc(new_partition_entry_count * gpt_header.size_of_partition_entry);
            if (partition_array == NULL) {
                perror("Error: ");
                goto cleanup;
            }

            fseek(device, gpt_header.partition_entry_lba * lb_size, SEEK_SET);
            fread(partition_array,
                  new_partition_entry_count * gpt_header.size_of_partition_entry,
                  1, device);

            uint32_t crc32_partition_array =
                crc32(partition_array,
                      new_partition_entry_count * gpt_header.size_of_partition_entry);

            free(partition_array);

            gpt_header.partition_entry_array_crc32 = crc32_partition_array;
            gpt_header.number_of_partition_entries = new_partition_entry_count;
            gpt_header.crc32 = 0;
            gpt_header.crc32 = crc32(&gpt_header, sizeof(struct gpt_table_header));
            fseek(device, lb_size, SEEK_SET);
            fwrite(&gpt_header, sizeof(struct gpt_table_header), 1, device);

            secondary_gpt_header.partition_entry_array_crc32 = crc32_partition_array;
            secondary_gpt_header.number_of_partition_entries =
                new_partition_entry_count;
            secondary_gpt_header.crc32 = 0;
            secondary_gpt_header.crc32 =
                crc32(&secondary_gpt_header, sizeof(struct gpt_table_header));
            fseek(device, lb_size * gpt_header.alternate_lba, SEEK_SET);
            fwrite(&secondary_gpt_header, sizeof(struct gpt_table_header), 1, device);
        }
    } else {
        fprintf(stderr, "Installing to MBR.\n");
    }

    fprintf(stderr, "Stage 2 to be located at 0x%" PRIx64 " and 0x%" PRIx64 ".\n",
            stage2_loc_a, stage2_loc_b);

    // Save original timestamp
    fseek(device, 218, SEEK_SET);
    fread(timestamp, 1, 6, device);

    // Save the original partition table of the device
    fseek(device, 440, SEEK_SET);
    fread(orig_mbr, 1, 70, device);

    // Write the bootsector from the bootloader to the device
    fseek(device, 0, SEEK_SET);
    fwrite(&bootloader_img[0], 1, 512, device);

    // Write the rest of stage 2 to the device
    fseek(device, stage2_loc_a, SEEK_SET);
    fwrite(&bootloader_img[512], 1, stage2_size_a, device);
    fseek(device, stage2_loc_b, SEEK_SET);
    fwrite(&bootloader_img[512 + stage2_size_a], 1, stage2_size_b, device);

    // Hardcode in the bootsector the location of stage 2 halves
    fseek(device, 0x1a4, SEEK_SET);
    fwrite(&stage2_size_a, 1, sizeof(uint16_t), device);
    fwrite(&stage2_size_b, 1, sizeof(uint16_t), device);
    fwrite(&stage2_loc_a, 1, sizeof(uint64_t), device);
    fwrite(&stage2_loc_b, 1, sizeof(uint64_t), device);

    // Write back timestamp
    fseek(device, 218, SEEK_SET);
    fwrite(timestamp, 1, 6, device);

    // Write back the saved partition table to the device
    fseek(device, 440, SEEK_SET);
    fwrite(orig_mbr, 1, 70, device);

    ok = 0;

cleanup:
    if (device)
        fclose(device);
    if (bootloader_file)
        fclose(bootloader_file);
    if (bootloader_img)
        free(bootloader_img);

    return ok;
}