diff --git a/virtualizationservice/src/aidl.rs b/virtualizationservice/src/aidl.rs
index 6d3f737..0089bfc 100644
--- a/virtualizationservice/src/aidl.rs
+++ b/virtualizationservice/src/aidl.rs
@@ -227,16 +227,21 @@
             ));
         }
 
-        let composite_image_filename =
-            make_composite_image_filename(temporary_directory, next_temporary_image_id);
-        let (image, partition_files) =
-            make_composite_image(&disk.partitions, &composite_image_filename).map_err(|e| {
-                error!("Failed to make composite image with config {:?}: {}", disk, e);
-                new_binder_exception(
-                    ExceptionCode::SERVICE_SPECIFIC,
-                    format!("Failed to make composite image: {}", e),
-                )
-            })?;
+        let composite_image_filenames =
+            make_composite_image_filenames(temporary_directory, next_temporary_image_id);
+        let (image, partition_files) = make_composite_image(
+            &disk.partitions,
+            &composite_image_filenames.composite,
+            &composite_image_filenames.header,
+            &composite_image_filenames.footer,
+        )
+        .map_err(|e| {
+            error!("Failed to make composite image with config {:?}: {}", disk, e);
+            new_binder_exception(
+                ExceptionCode::SERVICE_SPECIFIC,
+                format!("Failed to make composite image: {}", e),
+            )
+        })?;
 
         // Pass the file descriptors for the various partition files to crosvm when it
         // is run.
@@ -257,13 +262,28 @@
 }
 
 /// Generates a unique filename to use for a composite disk image.
-fn make_composite_image_filename(
+fn make_composite_image_filenames(
     temporary_directory: &Path,
     next_temporary_image_id: &mut u64,
-) -> PathBuf {
+) -> CompositeImageFilenames {
     let id = *next_temporary_image_id;
     *next_temporary_image_id += 1;
-    temporary_directory.join(format!("composite-{}.img", id))
+    CompositeImageFilenames {
+        composite: temporary_directory.join(format!("composite-{}.img", id)),
+        header: temporary_directory.join(format!("composite-{}-header.img", id)),
+        footer: temporary_directory.join(format!("composite-{}-footer.img", id)),
+    }
+}
+
+/// Filenames for a composite disk image, including header and footer partitions.
+#[derive(Clone, Debug, Eq, PartialEq)]
+struct CompositeImageFilenames {
+    /// The composite disk image itself.
+    composite: PathBuf,
+    /// The header partition image.
+    header: PathBuf,
+    /// The footer partition image.
+    footer: PathBuf,
 }
 
 /// Gets the calling SID of the current Binder thread.
diff --git a/virtualizationservice/src/composite.rs b/virtualizationservice/src/composite.rs
index 37428eb..fb8e783 100644
--- a/virtualizationservice/src/composite.rs
+++ b/virtualizationservice/src/composite.rs
@@ -12,76 +12,319 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-//! Functions for running `mk_cdisk`.
+//! Functions for creating a composite disk image.
 
-use android_system_virtualizationservice::aidl::android::system::virtualizationservice::Partition::Partition as AidlPartition;
-use anyhow::{bail, Context, Error};
-use command_fds::{CommandFdExt, FdMapping};
-use compositediskconfig::{Config, Partition};
-use log::info;
-use std::fs::File;
+use crate::gpt::{
+    write_gpt_header, write_protective_mbr, GptPartitionEntry, GPT_BEGINNING_SIZE, GPT_END_SIZE,
+    GPT_HEADER_SIZE, GPT_NUM_PARTITIONS, GPT_PARTITION_ENTRY_SIZE, SECTOR_SIZE,
+};
+use android_system_virtualizationservice::aidl::android::system::virtualizationservice::Partition::Partition;
+use anyhow::{anyhow, bail, Context, Error};
+use crc32fast::Hasher;
+use disk::create_disk_file;
+use log::{trace, warn};
+use protobuf::Message;
+use protos::cdisk_spec::{ComponentDisk, CompositeDisk, ReadWriteCapability};
+use std::convert::TryInto;
+use std::fs::{File, OpenOptions};
+use std::io::Write;
 use std::os::unix::io::AsRawFd;
-use std::panic;
-use std::path::Path;
-use std::process::{Command, Stdio};
-use std::str;
-use std::thread;
+use std::path::{Path, PathBuf};
+use uuid::Uuid;
 
-const MK_CDISK_PATH: &str = "/apex/com.android.virt/bin/mk_cdisk";
+/// A magic string placed at the beginning of a composite disk file to identify it.
+const CDISK_MAGIC: &str = "composite_disk\x1d";
+/// The version of the composite disk format supported by this implementation.
+const COMPOSITE_DISK_VERSION: u64 = 1;
+/// The amount of padding needed between the last partition entry and the first partition, to align
+/// the partition appropriately. The two sectors are for the MBR and the GPT header.
+const PARTITION_ALIGNMENT_SIZE: usize = GPT_BEGINNING_SIZE as usize
+    - 2 * SECTOR_SIZE as usize
+    - GPT_NUM_PARTITIONS as usize * GPT_PARTITION_ENTRY_SIZE as usize;
+const HEADER_PADDING_LENGTH: usize = SECTOR_SIZE as usize - GPT_HEADER_SIZE as usize;
+// Keep all partitions 4k aligned for performance.
+const PARTITION_SIZE_SHIFT: u8 = 12;
+// Keep the disk size a multiple of 64k for crosvm's virtio_blk driver.
+const DISK_SIZE_SHIFT: u8 = 16;
 
-/// Calls `mk_cdisk` to construct a composite disk image for the given list of partitions, and opens
-/// it ready to use. Returns the composite disk image file, and a list of FD mappings which must be
-/// applied to any process which wants to use it. This is necessary because the composite image
-/// contains paths of the form `/proc/self/fd/N` for the partition images.
-pub fn make_composite_image(
-    partitions: &[AidlPartition],
-    output_filename: &Path,
-) -> Result<(File, Vec<File>), Error> {
-    let (config_json, files) = make_config_json(partitions)?;
-    let fd_mappings: Vec<_> = files
-        .iter()
-        .map(|file| FdMapping { parent_fd: file.as_raw_fd(), child_fd: file.as_raw_fd() })
-        .collect();
+const LINUX_FILESYSTEM_GUID: Uuid = Uuid::from_u128(0x0FC63DAF_8483_4772_8E79_3D69D8477DE4);
+const EFI_SYSTEM_PARTITION_GUID: Uuid = Uuid::from_u128(0xC12A7328_F81F_11D2_BA4B_00A0C93EC93B);
 
-    let mut command = Command::new(MK_CDISK_PATH);
-    command
-        .arg("-") // Read config JSON from stdin.
-        .arg(&output_filename)
-        .stdin(Stdio::piped())
-        .stdout(Stdio::piped())
-        .stderr(Stdio::piped());
-    command.fd_mappings(fd_mappings)?;
-    let mut child = command.spawn().context("Failed to spawn mk_cdisk")?;
-    let stdin = child.stdin.take().unwrap();
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct PartitionInfo {
+    label: String,
+    path: PathBuf,
+    partition_type: ImagePartitionType,
+    writable: bool,
+    size: u64,
+}
 
-    // Write config to stdin of mk_cdisk on a separate thread to avoid deadlock, as it may not read
-    // all of stdin before it blocks on writing to stdout.
-    let writer_thread = thread::spawn(move || {
-        config_json.write_json(&stdin).context("Failed to write config JSON for mk_cdisk")
+/// Round `val` up to the next multiple of 2**`align_log`.
+fn align_to_power_of_2(val: u64, align_log: u8) -> u64 {
+    let align = 1 << align_log;
+    ((val + (align - 1)) / align) * align
+}
+
+impl PartitionInfo {
+    fn aligned_size(&self) -> u64 {
+        align_to_power_of_2(self.size, PARTITION_SIZE_SHIFT)
+    }
+}
+
+/// The type of partition.
+#[allow(dead_code)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub enum ImagePartitionType {
+    LinuxFilesystem,
+    EfiSystemPartition,
+}
+
+impl ImagePartitionType {
+    fn guid(self) -> Uuid {
+        match self {
+            Self::LinuxFilesystem => LINUX_FILESYSTEM_GUID,
+            Self::EfiSystemPartition => EFI_SYSTEM_PARTITION_GUID,
+        }
+    }
+}
+
+/// Write protective MBR and primary GPT table.
+fn write_beginning(
+    file: &mut impl Write,
+    disk_guid: Uuid,
+    partitions: &[u8],
+    partition_entries_crc32: u32,
+    secondary_table_offset: u64,
+    disk_size: u64,
+) -> Result<(), Error> {
+    // Write the protective MBR to the first sector.
+    write_protective_mbr(file, disk_size)?;
+
+    // Write the GPT header, and pad out to the end of the sector.
+    write_gpt_header(file, disk_guid, partition_entries_crc32, secondary_table_offset, false)?;
+    file.write_all(&[0; HEADER_PADDING_LENGTH])?;
+
+    // Write partition entries, including unused ones.
+    file.write_all(partitions)?;
+
+    // Write zeroes to align the first partition appropriately.
+    file.write_all(&[0; PARTITION_ALIGNMENT_SIZE])?;
+
+    Ok(())
+}
+
+/// Write secondary GPT table.
+fn write_end(
+    file: &mut impl Write,
+    disk_guid: Uuid,
+    partitions: &[u8],
+    partition_entries_crc32: u32,
+    secondary_table_offset: u64,
+    disk_size: u64,
+) -> Result<(), Error> {
+    // Write partition entries, including unused ones.
+    file.write_all(partitions)?;
+
+    // Write the GPT header, and pad out to the end of the sector.
+    write_gpt_header(file, disk_guid, partition_entries_crc32, secondary_table_offset, true)?;
+    file.write_all(&[0; HEADER_PADDING_LENGTH])?;
+
+    // Pad out to the aligned disk size.
+    let used_disk_size = secondary_table_offset + GPT_END_SIZE;
+    let padding = disk_size - used_disk_size;
+    file.write_all(&vec![0; padding as usize])?;
+
+    Ok(())
+}
+
+/// Create the `GptPartitionEntry` for the given partition.
+fn create_gpt_entry(partition: &PartitionInfo, offset: u64) -> GptPartitionEntry {
+    let mut partition_name: Vec<u16> = partition.label.encode_utf16().collect();
+    partition_name.resize(36, 0);
+
+    GptPartitionEntry {
+        partition_type_guid: partition.partition_type.guid(),
+        unique_partition_guid: Uuid::new_v4(),
+        first_lba: offset / SECTOR_SIZE,
+        last_lba: (offset + partition.aligned_size()) / SECTOR_SIZE - 1,
+        attributes: 0,
+        partition_name: partition_name.try_into().unwrap(),
+    }
+}
+
+/// Create one or more `ComponentDisk` proto messages for the given partition.
+fn create_component_disks(
+    partition: &PartitionInfo,
+    offset: u64,
+    header_path: &str,
+) -> Result<Vec<ComponentDisk>, Error> {
+    let aligned_size = partition.aligned_size();
+
+    let mut component_disks = vec![ComponentDisk {
+        offset,
+        file_path: partition.path.to_str().context("Invalid partition path")?.to_string(),
+        read_write_capability: if partition.writable {
+            ReadWriteCapability::READ_WRITE
+        } else {
+            ReadWriteCapability::READ_ONLY
+        },
+        ..ComponentDisk::new()
+    }];
+
+    if partition.size != aligned_size {
+        if partition.writable {
+            bail!(
+                "Read-write partition {:?} size is not a multiple of {}.",
+                partition,
+                1 << PARTITION_SIZE_SHIFT
+            );
+        } else {
+            // Fill in the gap by reusing the header file, because we know it is always bigger
+            // than the alignment size (i.e. GPT_BEGINNING_SIZE > 1 << PARTITION_SIZE_SHIFT).
+            warn!(
+                "Read-only partition {:?} size is not a multiple of {}, filling gap.",
+                partition,
+                1 << PARTITION_SIZE_SHIFT
+            );
+            component_disks.push(ComponentDisk {
+                offset: offset + partition.size,
+                file_path: header_path.to_owned(),
+                read_write_capability: ReadWriteCapability::READ_ONLY,
+                ..ComponentDisk::new()
+            });
+        }
+    }
+
+    Ok(component_disks)
+}
+
+/// Create a new composite disk containing the given partitions, and write it out to the given
+/// files.
+pub fn create_composite_disk(
+    partitions: &[PartitionInfo],
+    header_path: &Path,
+    header_file: &mut File,
+    footer_path: &Path,
+    footer_file: &mut File,
+    output_composite: &mut File,
+) -> Result<(), Error> {
+    let header_path = header_path.to_str().context("Invalid header path")?.to_string();
+    let footer_path = footer_path.to_str().context("Invalid footer path")?.to_string();
+
+    let mut composite_proto = CompositeDisk::new();
+    composite_proto.version = COMPOSITE_DISK_VERSION;
+    composite_proto.component_disks.push(ComponentDisk {
+        file_path: header_path.clone(),
+        offset: 0,
+        read_write_capability: ReadWriteCapability::READ_ONLY,
+        ..ComponentDisk::new()
     });
-    info!("Running {:?}", command);
-    let output = child.wait_with_output()?;
-    match writer_thread.join() {
-        Ok(result) => result?,
-        Err(panic_payload) => panic::resume_unwind(panic_payload),
-    }
 
-    if !output.status.success() {
-        info!("mk_cdisk stdout: {}", str::from_utf8(&output.stdout)?);
-        info!("mk_cdisk stderr: {}", str::from_utf8(&output.stderr)?);
-        bail!("mk_cdisk exited with error {}", output.status);
-    }
+    // Write partitions to a temporary buffer so that we can calculate the CRC, and construct the
+    // ComponentDisk proto messages at the same time.
+    let mut partitions_buffer =
+        [0u8; GPT_NUM_PARTITIONS as usize * GPT_PARTITION_ENTRY_SIZE as usize];
+    let mut writer: &mut [u8] = &mut partitions_buffer;
+    let mut next_disk_offset = GPT_BEGINNING_SIZE;
+    for partition in partitions {
+        create_gpt_entry(partition, next_disk_offset).write_bytes(&mut writer)?;
 
-    let composite_image = File::open(&output_filename)
-        .with_context(|| format!("Failed to open composite image {:?}", output_filename))?;
+        for component_disk in create_component_disks(partition, next_disk_offset, &header_path)? {
+            composite_proto.component_disks.push(component_disk);
+        }
+
+        next_disk_offset += partition.aligned_size();
+    }
+    let secondary_table_offset = next_disk_offset;
+    let disk_size = align_to_power_of_2(secondary_table_offset + GPT_END_SIZE, DISK_SIZE_SHIFT);
+    trace!("Partitions: {:#?}", partitions);
+    trace!("Secondary table offset: {} disk size: {}", secondary_table_offset, disk_size);
+
+    composite_proto.component_disks.push(ComponentDisk {
+        file_path: footer_path,
+        offset: secondary_table_offset,
+        read_write_capability: ReadWriteCapability::READ_ONLY,
+        ..ComponentDisk::new()
+    });
+
+    // Calculate CRC32 of partition entries.
+    let mut hasher = Hasher::new();
+    hasher.update(&partitions_buffer);
+    let partition_entries_crc32 = hasher.finalize();
+
+    let disk_guid = Uuid::new_v4();
+    write_beginning(
+        header_file,
+        disk_guid,
+        &partitions_buffer,
+        partition_entries_crc32,
+        secondary_table_offset,
+        disk_size,
+    )?;
+    write_end(
+        footer_file,
+        disk_guid,
+        &partitions_buffer,
+        partition_entries_crc32,
+        secondary_table_offset,
+        disk_size,
+    )?;
+
+    composite_proto.length = disk_size;
+    output_composite.write_all(CDISK_MAGIC.as_bytes())?;
+    composite_proto.write_to_writer(output_composite)?;
+
+    Ok(())
+}
+
+/// Constructs a composite disk image for the given list of partitions, and opens it ready to use.
+///
+/// Returns the composite disk image file, and a list of FD mappings which must be applied to any
+/// process which wants to use it. This is necessary because the composite image contains paths of
+/// the form `/proc/self/fd/N` for the partition images.
+pub fn make_composite_image(
+    partitions: &[Partition],
+    output_path: &Path,
+    header_path: &Path,
+    footer_path: &Path,
+) -> Result<(File, Vec<File>), Error> {
+    let (partitions, files) = convert_partitions(partitions)?;
+
+    let mut composite_image = OpenOptions::new()
+        .create_new(true)
+        .read(true)
+        .write(true)
+        .open(output_path)
+        .with_context(|| format!("Failed to create composite image {:?}", output_path))?;
+    let mut header_file =
+        OpenOptions::new().create_new(true).read(true).write(true).open(header_path).with_context(
+            || format!("Failed to create composite image header {:?}", header_path),
+        )?;
+    let mut footer_file =
+        OpenOptions::new().create_new(true).read(true).write(true).open(footer_path).with_context(
+            || format!("Failed to create composite image header {:?}", footer_path),
+        )?;
+
+    create_composite_disk(
+        &partitions,
+        header_path,
+        &mut header_file,
+        footer_path,
+        &mut footer_file,
+        &mut composite_image,
+    )?;
+
+    // Re-open the composite image as read-only.
+    let composite_image = File::open(&output_path)
+        .with_context(|| format!("Failed to open composite image {:?}", output_path))?;
 
     Ok((composite_image, files))
 }
 
 /// Given the AIDL config containing a list of partitions, with a [`ParcelFileDescriptor`] for each
 /// partition, return the list of file descriptors which must be passed to the mk_cdisk child
-/// process and the JSON configuration for it.
-fn make_config_json(partitions: &[AidlPartition]) -> Result<(Config, Vec<File>), Error> {
+/// process and the composite disk image partition configuration for it.
+fn convert_partitions(partitions: &[Partition]) -> Result<(Vec<PartitionInfo>, Vec<File>), Error> {
     // File descriptors to pass to child process.
     let mut files = vec![];
 
@@ -96,17 +339,89 @@
                 .as_ref()
                 .try_clone()
                 .context("Failed to clone partition image file descriptor")?;
+            let size = get_partition_size(&file)?;
             let fd = file.as_raw_fd();
             files.push(file);
 
-            Ok(Partition {
-                writable: partition.writable,
+            Ok(PartitionInfo {
                 label: partition.label.to_owned(),
                 path: format!("/proc/self/fd/{}", fd).into(),
+                partition_type: ImagePartitionType::LinuxFilesystem,
+                writable: partition.writable,
+                size,
             })
         })
         .collect::<Result<_, Error>>()?;
-    let config_json = Config { partitions };
 
-    Ok((config_json, files))
+    Ok((partitions, files))
+}
+
+/// Find the size of the partition image in the given file by parsing the header.
+///
+/// This will work for raw, QCOW2, composite and Android sparse images.
+fn get_partition_size(partition: &File) -> Result<u64, Error> {
+    // TODO: Use `context` once disk::Error implements std::error::Error.
+    Ok(create_disk_file(partition.try_clone()?)
+        .map_err(|e| anyhow!("Failed to open partition image: {}", e))?
+        .get_len()?)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn beginning_size() {
+        let mut buffer = vec![];
+        let partitions = [0u8; GPT_NUM_PARTITIONS as usize * GPT_PARTITION_ENTRY_SIZE as usize];
+        let disk_size = 1000 * SECTOR_SIZE;
+        write_beginning(
+            &mut buffer,
+            Uuid::from_u128(0x12345678_1234_5678_abcd_12345678abcd),
+            &partitions,
+            42,
+            disk_size - GPT_END_SIZE,
+            disk_size,
+        )
+        .unwrap();
+
+        assert_eq!(buffer.len(), GPT_BEGINNING_SIZE as usize);
+    }
+
+    #[test]
+    fn end_size() {
+        let mut buffer = vec![];
+        let partitions = [0u8; GPT_NUM_PARTITIONS as usize * GPT_PARTITION_ENTRY_SIZE as usize];
+        let disk_size = 1000 * SECTOR_SIZE;
+        write_end(
+            &mut buffer,
+            Uuid::from_u128(0x12345678_1234_5678_abcd_12345678abcd),
+            &partitions,
+            42,
+            disk_size - GPT_END_SIZE,
+            disk_size,
+        )
+        .unwrap();
+
+        assert_eq!(buffer.len(), GPT_END_SIZE as usize);
+    }
+
+    #[test]
+    fn end_size_with_padding() {
+        let mut buffer = vec![];
+        let partitions = [0u8; GPT_NUM_PARTITIONS as usize * GPT_PARTITION_ENTRY_SIZE as usize];
+        let disk_size = 1000 * SECTOR_SIZE;
+        let padding = 3 * SECTOR_SIZE;
+        write_end(
+            &mut buffer,
+            Uuid::from_u128(0x12345678_1234_5678_abcd_12345678abcd),
+            &partitions,
+            42,
+            disk_size - GPT_END_SIZE - padding,
+            disk_size,
+        )
+        .unwrap();
+
+        assert_eq!(buffer.len(), GPT_END_SIZE as usize + padding as usize);
+    }
 }
diff --git a/virtualizationservice/src/gpt.rs b/virtualizationservice/src/gpt.rs
new file mode 100644
index 0000000..346a40a
--- /dev/null
+++ b/virtualizationservice/src/gpt.rs
@@ -0,0 +1,240 @@
+// Copyright 2021, The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Functions for writing GUID Partition Tables for use in a composite disk image.
+
+use anyhow::Error;
+use crc32fast::Hasher;
+use std::convert::TryInto;
+use std::io::Write;
+use uuid::Uuid;
+
+/// The size in bytes of a disk sector (also called a block).
+pub const SECTOR_SIZE: u64 = 1 << 9;
+/// The size in bytes on an MBR partition entry.
+const MBR_PARTITION_ENTRY_SIZE: usize = 16;
+/// The size in bytes of a GPT header.
+pub const GPT_HEADER_SIZE: u32 = 92;
+/// The number of partition entries in the GPT, which is the maximum number of partitions which are
+/// supported.
+pub const GPT_NUM_PARTITIONS: u32 = 128;
+/// The size in bytes of a single GPT partition entry.
+pub const GPT_PARTITION_ENTRY_SIZE: u32 = 128;
+/// The size in bytes of everything before the first partition: i.e. the MBR, GPT header and GPT
+/// partition entries.
+pub const GPT_BEGINNING_SIZE: u64 = SECTOR_SIZE * 40;
+/// The size in bytes of everything after the last partition: i.e. the GPT partition entries and GPT
+/// footer.
+pub const GPT_END_SIZE: u64 = SECTOR_SIZE * 33;
+
+/// Write a protective MBR for a disk of the given total size (in bytes).
+///
+/// This should be written at the start of the disk, before the GPT header. It
+/// is one `SECTOR_SIZE` long.
+pub fn write_protective_mbr(file: &mut impl Write, disk_size: u64) -> Result<(), Error> {
+    // Bootstrap code
+    file.write_all(&[0; 446])?;
+
+    // Partition status
+    file.write_all(&[0x00])?;
+    // Begin CHS
+    file.write_all(&[0; 3])?;
+    // Partition type
+    file.write_all(&[0xEE])?;
+    // End CHS
+    file.write_all(&[0; 3])?;
+    let first_lba: u32 = 1;
+    file.write_all(&first_lba.to_le_bytes())?;
+    let number_of_sectors: u32 = (disk_size / SECTOR_SIZE).try_into()?;
+    file.write_all(&number_of_sectors.to_le_bytes())?;
+
+    // Three more empty partitions
+    file.write_all(&[0; MBR_PARTITION_ENTRY_SIZE * 3])?;
+
+    // Boot signature
+    file.write_all(&[0x55, 0xAA])?;
+
+    Ok(())
+}
+
+#[derive(Clone, Debug, Default, Eq, PartialEq)]
+struct GptHeader {
+    signature: [u8; 8],
+    revision: [u8; 4],
+    header_size: u32,
+    header_crc32: u32,
+    current_lba: u64,
+    backup_lba: u64,
+    first_usable_lba: u64,
+    last_usable_lba: u64,
+    disk_guid: Uuid,
+    partition_entries_lba: u64,
+    num_partition_entries: u32,
+    partition_entry_size: u32,
+    partition_entries_crc32: u32,
+}
+
+impl GptHeader {
+    fn write_bytes(&self, out: &mut impl Write) -> Result<(), Error> {
+        out.write_all(&self.signature)?;
+        out.write_all(&self.revision)?;
+        out.write_all(&self.header_size.to_le_bytes())?;
+        out.write_all(&self.header_crc32.to_le_bytes())?;
+        // Reserved
+        out.write_all(&[0; 4])?;
+        out.write_all(&self.current_lba.to_le_bytes())?;
+        out.write_all(&self.backup_lba.to_le_bytes())?;
+        out.write_all(&self.first_usable_lba.to_le_bytes())?;
+        out.write_all(&self.last_usable_lba.to_le_bytes())?;
+
+        // GUID is mixed-endian for some reason, so we can't just use `Uuid::as_bytes()`.
+        write_guid(out, self.disk_guid)?;
+
+        out.write_all(&self.partition_entries_lba.to_le_bytes())?;
+        out.write_all(&self.num_partition_entries.to_le_bytes())?;
+        out.write_all(&self.partition_entry_size.to_le_bytes())?;
+        out.write_all(&self.partition_entries_crc32.to_le_bytes())?;
+        Ok(())
+    }
+}
+
+/// Write a GPT header for the disk.
+///
+/// It may either be a primary header (which should go at LBA 1) or a secondary header (which should
+/// go at the end of the disk).
+pub fn write_gpt_header(
+    out: &mut impl Write,
+    disk_guid: Uuid,
+    partition_entries_crc32: u32,
+    secondary_table_offset: u64,
+    secondary: bool,
+) -> Result<(), Error> {
+    let primary_header_lba = 1;
+    let secondary_header_lba = (secondary_table_offset + GPT_END_SIZE) / SECTOR_SIZE - 1;
+    let mut gpt_header = GptHeader {
+        signature: *b"EFI PART",
+        revision: [0, 0, 1, 0],
+        header_size: GPT_HEADER_SIZE,
+        current_lba: if secondary { secondary_header_lba } else { primary_header_lba },
+        backup_lba: if secondary { primary_header_lba } else { secondary_header_lba },
+        first_usable_lba: GPT_BEGINNING_SIZE / SECTOR_SIZE,
+        last_usable_lba: secondary_table_offset / SECTOR_SIZE - 1,
+        disk_guid,
+        partition_entries_lba: 2,
+        num_partition_entries: GPT_NUM_PARTITIONS,
+        partition_entry_size: GPT_PARTITION_ENTRY_SIZE,
+        partition_entries_crc32,
+        header_crc32: 0,
+    };
+
+    // Write once to a temporary buffer to calculate the CRC.
+    let mut header_without_crc = [0u8; GPT_HEADER_SIZE as usize];
+    gpt_header.write_bytes(&mut &mut header_without_crc[..])?;
+    let mut hasher = Hasher::new();
+    hasher.update(&header_without_crc);
+    gpt_header.header_crc32 = hasher.finalize();
+
+    gpt_header.write_bytes(out)?;
+
+    Ok(())
+}
+
+/// A GPT entry for a particular partition.
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct GptPartitionEntry {
+    pub partition_type_guid: Uuid,
+    pub unique_partition_guid: Uuid,
+    pub first_lba: u64,
+    pub last_lba: u64,
+    pub attributes: u64,
+    /// UTF-16LE
+    pub partition_name: [u16; 36],
+}
+
+// TODO: Derive this once arrays of more than 32 elements have default values.
+impl Default for GptPartitionEntry {
+    fn default() -> Self {
+        Self {
+            partition_type_guid: Default::default(),
+            unique_partition_guid: Default::default(),
+            first_lba: 0,
+            last_lba: 0,
+            attributes: 0,
+            partition_name: [0; 36],
+        }
+    }
+}
+
+impl GptPartitionEntry {
+    /// Write out the partition table entry. It will take
+    /// `GPT_PARTITION_ENTRY_SIZE` bytes.
+    pub fn write_bytes(&self, out: &mut impl Write) -> Result<(), Error> {
+        write_guid(out, self.partition_type_guid)?;
+        write_guid(out, self.unique_partition_guid)?;
+        out.write_all(&self.first_lba.to_le_bytes())?;
+        out.write_all(&self.last_lba.to_le_bytes())?;
+        out.write_all(&self.attributes.to_le_bytes())?;
+        for code_unit in &self.partition_name {
+            out.write_all(&code_unit.to_le_bytes())?;
+        }
+        Ok(())
+    }
+}
+
+/// Write a UUID in the mixed-endian format which GPT uses for GUIDs.
+fn write_guid(out: &mut impl Write, guid: Uuid) -> Result<(), Error> {
+    let guid_fields = guid.as_fields();
+    out.write_all(&guid_fields.0.to_le_bytes())?;
+    out.write_all(&guid_fields.1.to_le_bytes())?;
+    out.write_all(&guid_fields.2.to_le_bytes())?;
+    out.write_all(guid_fields.3)?;
+
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn protective_mbr_size() {
+        let mut buffer = vec![];
+        write_protective_mbr(&mut buffer, 1000 * SECTOR_SIZE).unwrap();
+
+        assert_eq!(buffer.len(), SECTOR_SIZE as usize);
+    }
+
+    #[test]
+    fn header_size() {
+        let mut buffer = vec![];
+        write_gpt_header(
+            &mut buffer,
+            Uuid::from_u128(0x12345678_1234_5678_abcd_12345678abcd),
+            42,
+            1000 * SECTOR_SIZE,
+            false,
+        )
+        .unwrap();
+
+        assert_eq!(buffer.len(), GPT_HEADER_SIZE as usize);
+    }
+
+    #[test]
+    fn partition_entry_size() {
+        let mut buffer = vec![];
+        GptPartitionEntry::default().write_bytes(&mut buffer).unwrap();
+
+        assert_eq!(buffer.len(), GPT_PARTITION_ENTRY_SIZE as usize);
+    }
+}
diff --git a/virtualizationservice/src/main.rs b/virtualizationservice/src/main.rs
index a68e5eb..43b5fe4 100644
--- a/virtualizationservice/src/main.rs
+++ b/virtualizationservice/src/main.rs
@@ -17,6 +17,7 @@
 mod aidl;
 mod composite;
 mod crosvm;
+mod gpt;
 
 use crate::aidl::{VirtualizationService, BINDER_SERVICE_IDENTIFIER};
 use android_system_virtualizationservice::aidl::android::system::virtualizationservice::IVirtualizationService::BnVirtualizationService;