Implement verity header and extension generation (3051d782) · Commits · e / os / android_frameworks_base

core/java/android/util/apk/ApkVerityBuilder.java

+157 −32

Original line number	Diff line number	Diff line
		@@ -68,31 +68,78 @@ abstract class ApkVerityBuilder {
		static ApkVerityResult generateApkVerity(RandomAccessFile apk,
		SignatureInfo signatureInfo, ByteBufferFactory bufferFactory)
		throws IOException, SecurityException, NoSuchAlgorithmException, DigestException {
		assertSigningBlockAlignedAndHasFullPages(signatureInfo);

		long signingBlockSize =
		signatureInfo.centralDirOffset - signatureInfo.apkSigningBlockOffset;
		long dataSize = apk.length() - signingBlockSize - ZIP_EOCD_CENTRAL_DIR_OFFSET_FIELD_SIZE;
		int[] levelOffset = calculateVerityLevelOffset(dataSize);

		ByteBuffer output = bufferFactory.create(
		CHUNK_SIZE_BYTES + // fsverity header + extensions + padding
		levelOffset[levelOffset.length - 1] + // Merkle tree size
		FSVERITY_HEADER_SIZE_BYTES); // second fsverity header (verbatim copy)
		levelOffset[levelOffset.length - 1]); // Merkle tree size
		output.order(ByteOrder.LITTLE_ENDIAN);

		// Start generating the tree from the block boundary as the kernel will expect.
		ByteBuffer treeOutput = slice(output, CHUNK_SIZE_BYTES,
		output.limit() - FSVERITY_HEADER_SIZE_BYTES);
		byte[] rootHash = generateApkVerityTree(apk, signatureInfo, DEFAULT_SALT, levelOffset,
		treeOutput);
		ByteBuffer header = slice(output, 0, FSVERITY_HEADER_SIZE_BYTES);
		ByteBuffer extensions = slice(output, FSVERITY_HEADER_SIZE_BYTES, CHUNK_SIZE_BYTES);
		ByteBuffer tree = slice(output, CHUNK_SIZE_BYTES, output.limit());
		byte[] apkDigestBytes = new byte[DIGEST_SIZE_BYTES];
		ByteBuffer apkDigest = ByteBuffer.wrap(apkDigestBytes);
		apkDigest.order(ByteOrder.LITTLE_ENDIAN);

		ByteBuffer integrityHeader = generateFsverityHeader(apk.length(), DEFAULT_SALT);
		output.put(integrityHeader);
		output.put(generateFsverityExtensions());
		calculateFsveritySignatureInternal(apk, signatureInfo, tree, apkDigest, header, extensions);

		integrityHeader.rewind();
		output.put(integrityHeader);
		output.rewind();
		return new ApkVerityResult(output, rootHash);
		return new ApkVerityResult(output, apkDigestBytes);
		}

		/**
		* Calculates the fsverity root hash for integrity measurement. This needs to be consistent to
		* what kernel returns.
		*/
		static byte[] generateFsverityRootHash(RandomAccessFile apk, ByteBuffer apkDigest,
		SignatureInfo signatureInfo)
		throws NoSuchAlgorithmException, DigestException, IOException {
		ByteBuffer verityBlock = ByteBuffer.allocate(CHUNK_SIZE_BYTES)
		.order(ByteOrder.LITTLE_ENDIAN);
		ByteBuffer header = slice(verityBlock, 0, FSVERITY_HEADER_SIZE_BYTES);
		ByteBuffer extensions = slice(verityBlock, FSVERITY_HEADER_SIZE_BYTES, CHUNK_SIZE_BYTES);

		calculateFsveritySignatureInternal(apk, signatureInfo, null, null, header, extensions);

		MessageDigest md = MessageDigest.getInstance(JCA_DIGEST_ALGORITHM);
		md.update(DEFAULT_SALT);
		md.update(verityBlock);
		md.update(apkDigest);
		return md.digest();
		}

		private static void calculateFsveritySignatureInternal(
		RandomAccessFile apk, SignatureInfo signatureInfo, ByteBuffer treeOutput,
		ByteBuffer rootHashOutput, ByteBuffer headerOutput, ByteBuffer extensionsOutput)
		throws IOException, NoSuchAlgorithmException, DigestException {
		assertSigningBlockAlignedAndHasFullPages(signatureInfo);

		long signingBlockSize =
		signatureInfo.centralDirOffset - signatureInfo.apkSigningBlockOffset;
		long dataSize = apk.length() - signingBlockSize - ZIP_EOCD_CENTRAL_DIR_OFFSET_FIELD_SIZE;
		int[] levelOffset = calculateVerityLevelOffset(dataSize);

		if (treeOutput != null) {
		byte[] apkRootHash = generateApkVerityTree(apk, signatureInfo, DEFAULT_SALT,
		levelOffset, treeOutput);
		if (rootHashOutput != null) {
		rootHashOutput.put(apkRootHash);
		}
		}

		if (headerOutput != null) {
		generateFsverityHeader(headerOutput, apk.length(), levelOffset.length - 1,
		DEFAULT_SALT);
		}

		if (extensionsOutput != null) {
		generateFsverityExtensions(extensionsOutput, signatureInfo.apkSigningBlockOffset,
		signingBlockSize, signatureInfo.eocdOffset);
		}
		}

		/**
		@@ -211,7 +258,7 @@ abstract class ApkVerityBuilder {
		eocdCdOffsetFieldPosition - signatureInfo.centralDirOffset),
		MMAP_REGION_SIZE_BYTES);

		// 3. Fill up the rest of buffer with 0s.
		// 3. Consume offset of Signing Block as an alternative EoCD.
		ByteBuffer alternativeCentralDirOffset = ByteBuffer.allocate(
		ZIP_EOCD_CENTRAL_DIR_OFFSET_FIELD_SIZE).order(ByteOrder.LITTLE_ENDIAN);
		alternativeCentralDirOffset.putInt(Math.toIntExact(signatureInfo.apkSigningBlockOffset));
		@@ -259,36 +306,109 @@ abstract class ApkVerityBuilder {
		return rootHash;
		}

		private static ByteBuffer generateFsverityHeader(long fileSize, byte[] salt) {
		private static ByteBuffer generateFsverityHeader(ByteBuffer buffer, long fileSize, int depth,
		byte[] salt) {
		if (salt.length != 8) {
		throw new IllegalArgumentException("salt is not 8 bytes long");
		}

		ByteBuffer buffer = ByteBuffer.allocate(FSVERITY_HEADER_SIZE_BYTES);
		buffer.order(ByteOrder.LITTLE_ENDIAN);

		// TODO(b/30972906): insert a reference when there is a public one.
		// TODO(b/30972906): update the reference when there is a better one in public.
		buffer.put("TrueBrew".getBytes()); // magic

		buffer.put((byte) 1); // major version
		buffer.put((byte) 0); // minor version
		buffer.put((byte) 12); // log2(block-size) == log2(4096)
		buffer.put((byte) 7); // log2(leaves-per-node) == log2(block-size / digest-size)
		// == log2(4096 / 32)
		buffer.putShort((short) 1); // meta algorithm, 1: SHA-256 FIXME finalize constant
		buffer.putShort((short) 1); // data algorithm, 1: SHA-256 FIXME finalize constant
		buffer.putInt(0x1); // flags, 0x1: has extension, FIXME also hide it
		buffer.put((byte) 12); // log2(block-size): log2(4096)
		buffer.put((byte) 7); // log2(leaves-per-node): log2(4096 / 32)

		buffer.putShort((short) 1); // meta algorithm, SHA256_MODE == 1
		buffer.putShort((short) 1); // data algorithm, SHA256_MODE == 1

		buffer.putInt(0x1); // flags, 0x1: has extension
		buffer.putInt(0); // reserved
		buffer.putLong(fileSize); // original i_size
		buffer.put(salt); // salt (8 bytes)

		// TODO(b/30972906): Add extension.
		buffer.putLong(fileSize); // original file size

		buffer.put((byte) 0); // auth block offset, disabled here
		buffer.put(salt); // salt (8 bytes)
		// skip(buffer, 22); // reserved

		buffer.rewind();
		return buffer;
		}

		private static ByteBuffer generateFsverityExtensions() {
		return ByteBuffer.allocate(64); // TODO(b/30972906): implement this.
		private static ByteBuffer generateFsverityExtensions(ByteBuffer buffer, long signingBlockOffset,
		long signingBlockSize, long eocdOffset) {
		// Snapshot of the FSVerity structs (subject to change once upstreamed).
		//
		// struct fsverity_header_extension {
		// u8 extension_count;
		// u8 reserved[7];
		// };
		//
		// struct fsverity_extension {
		// __le16 length;
		// u8 type;
		// u8 reserved[5];
		// };
		//
		// struct fsverity_extension_elide {
		// __le64 offset;
		// __le64 length;
		// }
		//
		// struct fsverity_extension_patch {
		// __le64 offset;
		// u8 length;
		// u8 reserved[7];
		// u8 databytes[];
		// };

		// struct fsverity_header_extension
		buffer.put((byte) 2); // extension count
		skip(buffer, 3); // reserved

		final int kSizeOfFsverityExtensionHeader = 8;

		{
		// struct fsverity_extension #1
		final int kSizeOfFsverityElidedExtension = 16;

		buffer.putShort((short) // total size of extension, padded to 64-bit alignment
		(kSizeOfFsverityExtensionHeader + kSizeOfFsverityElidedExtension));
		buffer.put((byte) 0); // ID of elide extension
		skip(buffer, 5); // reserved

		// struct fsverity_extension_elide
		buffer.putLong(signingBlockOffset);
		buffer.putLong(signingBlockSize);
		}

		{
		// struct fsverity_extension #2
		final int kSizeOfFsverityPatchExtension =
		8 + // offset size
		1 + // size of length from offset (up to 255)
		7 + // reserved
		ZIP_EOCD_CENTRAL_DIR_OFFSET_FIELD_SIZE;
		final int kPadding = (int) divideRoundup(kSizeOfFsverityPatchExtension % 8, 8);

		buffer.putShort((short) // total size of extension, padded to 64-bit alignment
		(kSizeOfFsverityExtensionHeader + kSizeOfFsverityPatchExtension + kPadding));
		buffer.put((byte) 1); // ID of patch extension
		skip(buffer, 5); // reserved

		// struct fsverity_extension_patch
		buffer.putLong(eocdOffset); // offset
		buffer.put((byte) ZIP_EOCD_CENTRAL_DIR_OFFSET_FIELD_SIZE); // length
		skip(buffer, 7); // reserved
		buffer.putInt(Math.toIntExact(signingBlockOffset)); // databytes

		// There are extra kPadding bytes of 0s here, included in the total size field of the
		// extension header. The output ByteBuffer is assumed to be initialized to 0.
		}

		buffer.rewind();
		return buffer;
		}

		/**
		@@ -344,6 +464,11 @@ abstract class ApkVerityBuilder {
		return b.slice();
		}

		/** Skip the {@code ByteBuffer} position by {@code bytes}. */
		private static void skip(ByteBuffer buffer, int bytes) {
		buffer.position(buffer.position() + bytes);
		}

		/** Divides a number and round up to the closest integer. */
		private static long divideRoundup(long dividend, long divisor) {
		return (dividend + divisor - 1) / divisor;