test/py/tests/test_vboot.py

# SPDX-License-Identifier:	GPL-2.0+
# Copyright (c) 2016, Google Inc.
#
# U-Boot Verified Boot Test

"""
This tests verified boot in the following ways:

For image verification:
- Create FIT (unsigned) with mkimage
- Check that verification shows that no keys are verified
- Sign image
- Check that verification shows that a key is now verified

For configuration verification:
- Corrupt signature and check for failure
- Create FIT (with unsigned configuration) with mkimage
- Check that image verification works
- Sign the FIT and mark the key as 'required' for verification
- Check that image verification works
- Corrupt the signature
- Check that image verification no-longer works

Tests run with both SHA1 and SHA256 hashing.
"""

import struct
import pytest
import u_boot_utils as util
import vboot_forge

TESTDATA = [
    ['sha1', '', False],
    ['sha1', '-pss', False],
    ['sha256', '', False],
    ['sha256', '-pss', False],
    ['sha256', '-pss', True],
]

@pytest.mark.boardspec('sandbox')
@pytest.mark.buildconfigspec('fit_signature')
@pytest.mark.requiredtool('dtc')
@pytest.mark.requiredtool('fdtget')
@pytest.mark.requiredtool('fdtput')
@pytest.mark.requiredtool('openssl')
@pytest.mark.parametrize("sha_algo,padding,required", TESTDATA)
def test_vboot(u_boot_console, sha_algo, padding, required):
    """Test verified boot signing with mkimage and verification with 'bootm'.

    This works using sandbox only as it needs to update the device tree used
    by U-Boot to hold public keys from the signing process.

    The SHA1 and SHA256 tests are combined into a single test since the
    key-generation process is quite slow and we want to avoid doing it twice.
    """
    def dtc(dts):
        """Run the device tree compiler to compile a .dts file

        The output file will be the same as the input file but with a .dtb
        extension.

        Args:
            dts: Device tree file to compile.
        """
        dtb = dts.replace('.dts', '.dtb')
        util.run_and_log(cons, 'dtc %s %s%s -O dtb '
                         '-o %s%s' % (dtc_args, datadir, dts, tmpdir, dtb))

    def run_bootm(sha_algo, test_type, expect_string, boots):
        """Run a 'bootm' command U-Boot.

        This always starts a fresh U-Boot instance since the device tree may
        contain a new public key.

        Args:
            test_type: A string identifying the test type.
            expect_string: A string which is expected in the output.
            sha_algo: Either 'sha1' or 'sha256', to select the algorithm to
                    use.
            boots: A boolean that is True if Linux should boot and False if
                    we are expected to not boot
        """
        cons.restart_uboot()
        with cons.log.section('Verified boot %s %s' % (sha_algo, test_type)):
            output = cons.run_command_list(
                ['host load hostfs - 100 %stest.fit' % tmpdir,
                 'fdt addr 100',
                 'bootm 100'])
        assert expect_string in ''.join(output)
        if boots:
            assert 'sandbox: continuing, as we cannot run' in ''.join(output)
        else:
            assert('sandbox: continuing, as we cannot run'
                   not in ''.join(output))

    def make_fit(its):
        """Make a new FIT from the .its source file.

        This runs 'mkimage -f' to create a new FIT.

        Args:
            its: Filename containing .its source.
        """
        util.run_and_log(cons, [mkimage, '-D', dtc_args, '-f',
                                '%s%s' % (datadir, its), fit])

    def sign_fit(sha_algo):
        """Sign the FIT

        Signs the FIT and writes the signature into it. It also writes the
        public key into the dtb.

        Args:
            sha_algo: Either 'sha1' or 'sha256', to select the algorithm to
                    use.
        """
        cons.log.action('%s: Sign images' % sha_algo)
        util.run_and_log(cons, [mkimage, '-F', '-k', tmpdir, '-K', dtb,
                                '-r', fit])

    def replace_fit_totalsize(size):
        """Replace FIT header's totalsize with something greater.

        The totalsize must be less than or equal to FIT_SIGNATURE_MAX_SIZE.
        If the size is greater, the signature verification should return false.

        Args:
            size: The new totalsize of the header

        Returns:
            prev_size: The previous totalsize read from the header
        """
        total_size = 0
        with open(fit, 'r+b') as handle:
            handle.seek(4)
            total_size = handle.read(4)
            handle.seek(4)
            handle.write(struct.pack(">I", size))
        return struct.unpack(">I", total_size)[0]

    def create_rsa_pair(name):
        """Generate a new RSA key paid and certificate

        Args:
            name: Name of of the key (e.g. 'dev')
        """
        public_exponent = 65537
        util.run_and_log(cons, 'openssl genpkey -algorithm RSA -out %s%s.key '
                     '-pkeyopt rsa_keygen_bits:2048 '
                     '-pkeyopt rsa_keygen_pubexp:%d' %
                     (tmpdir, name, public_exponent))

        # Create a certificate containing the public key
        util.run_and_log(cons, 'openssl req -batch -new -x509 -key %s%s.key '
                         '-out %s%s.crt' % (tmpdir, name, tmpdir, name))

    def test_with_algo(sha_algo, padding):
        """Test verified boot with the given hash algorithm.

        This is the main part of the test code. The same procedure is followed
        for both hashing algorithms.

        Args:
            sha_algo: Either 'sha1' or 'sha256', to select the algorithm to
                    use.
        """
        # Compile our device tree files for kernel and U-Boot. These are
        # regenerated here since mkimage will modify them (by adding a
        # public key) below.
        dtc('sandbox-kernel.dts')
        dtc('sandbox-u-boot.dts')

        # Build the FIT, but don't sign anything yet
        cons.log.action('%s: Test FIT with signed images' % sha_algo)
        make_fit('sign-images-%s%s.its' % (sha_algo, padding))
        run_bootm(sha_algo, 'unsigned images', 'dev-', True)

        # Sign images with our dev keys
        sign_fit(sha_algo)
        run_bootm(sha_algo, 'signed images', 'dev+', True)

        # Create a fresh .dtb without the public keys
        dtc('sandbox-u-boot.dts')

        cons.log.action('%s: Test FIT with signed configuration' % sha_algo)
        make_fit('sign-configs-%s%s.its' % (sha_algo, padding))
        run_bootm(sha_algo, 'unsigned config', '%s+ OK' % sha_algo, True)

        # Sign images with our dev keys
        sign_fit(sha_algo)
        run_bootm(sha_algo, 'signed config', 'dev+', True)

        cons.log.action('%s: Check signed config on the host' % sha_algo)

        util.run_and_log(cons, [fit_check_sign, '-f', fit, '-k', dtb])

        # Make sure that U-Boot checks that the config is in the list of hashed
        # nodes. If it isn't, a security bypass is possible.
        with open(fit, 'rb') as fd:
            root, strblock = vboot_forge.read_fdt(fd)
        root, strblock = vboot_forge.manipulate(root, strblock)
        with open(fit, 'w+b') as fd:
            vboot_forge.write_fdt(root, strblock, fd)
        util.run_and_log_expect_exception(
            cons, [fit_check_sign, '-f', fit, '-k', dtb],
            1, 'Failed to verify required signature')

        run_bootm(sha_algo, 'forged config', 'Bad Data Hash', False)

        # Create a new properly signed fit and replace header bytes
        make_fit('sign-configs-%s%s.its' % (sha_algo, padding))
        sign_fit(sha_algo)
        bcfg = u_boot_console.config.buildconfig
        max_size = int(bcfg.get('config_fit_signature_max_size', 0x10000000), 0)
        existing_size = replace_fit_totalsize(max_size + 1)
        run_bootm(sha_algo, 'Signed config with bad hash', 'Bad Data Hash',
                  False)
        cons.log.action('%s: Check overflowed FIT header totalsize' % sha_algo)

        # Replace with existing header bytes
        replace_fit_totalsize(existing_size)
        run_bootm(sha_algo, 'signed config', 'dev+', True)
        cons.log.action('%s: Check default FIT header totalsize' % sha_algo)

        # Increment the first byte of the signature, which should cause failure
        sig = util.run_and_log(cons, 'fdtget -t bx %s %s value' %
                               (fit, sig_node))
        byte_list = sig.split()
        byte = int(byte_list[0], 16)
        byte_list[0] = '%x' % (byte + 1)
        sig = ' '.join(byte_list)
        util.run_and_log(cons, 'fdtput -t bx %s %s value %s' %
                         (fit, sig_node, sig))

        run_bootm(sha_algo, 'Signed config with bad hash', 'Bad Data Hash',
                  False)

        cons.log.action('%s: Check bad config on the host' % sha_algo)
        util.run_and_log_expect_exception(
            cons, [fit_check_sign, '-f', fit, '-k', dtb],
            1, 'Failed to verify required signature')

    def test_required_key(sha_algo, padding):
        """Test verified boot with the given hash algorithm.

        This function tests if U-Boot rejects an image when a required key isn't
        used to sign a FIT.

        Args:
            sha_algo: Either 'sha1' or 'sha256', to select the algorithm to use
        """
        # Compile our device tree files for kernel and U-Boot. These are
        # regenerated here since mkimage will modify them (by adding a
        # public key) below.
        dtc('sandbox-kernel.dts')
        dtc('sandbox-u-boot.dts')

        cons.log.action('%s: Test FIT with configs images' % sha_algo)

        # Build the FIT with prod key (keys required) and sign it. This puts the
        # signature into sandbox-u-boot.dtb, marked 'required'
        make_fit('sign-configs-%s%s-prod.its' % (sha_algo, padding))
        sign_fit(sha_algo)

        # Build the FIT with dev key (keys NOT required). This adds the
        # signature into sandbox-u-boot.dtb, NOT marked 'required'.
        make_fit('sign-configs-%s%s.its' % (sha_algo, padding))
        sign_fit(sha_algo)

        # So now sandbox-u-boot.dtb two signatures, for the prod and dev keys.
        # Only the prod key is set as 'required'. But FIT we just built has
        # a dev signature only (sign_fit() overwrites the FIT).
        # Try to boot the FIT with dev key. This FIT should not be accepted by
        # U-Boot because the prod key is required.
        run_bootm(sha_algo, 'required key', '', False)

    cons = u_boot_console
    tmpdir = cons.config.result_dir + '/'
    datadir = cons.config.source_dir + '/test/py/tests/vboot/'
    fit = '%stest.fit' % tmpdir
    mkimage = cons.config.build_dir + '/tools/mkimage'
    fit_check_sign = cons.config.build_dir + '/tools/fit_check_sign'
    dtc_args = '-I dts -O dtb -i %s' % tmpdir
    dtb = '%ssandbox-u-boot.dtb' % tmpdir
    sig_node = '/configurations/conf-1/signature'

    create_rsa_pair('dev')
    create_rsa_pair('prod')

    # Create a number kernel image with zeroes
    with open('%stest-kernel.bin' % tmpdir, 'w') as fd:
        fd.write(500 * chr(0))

    try:
        # We need to use our own device tree file. Remember to restore it
        # afterwards.
        old_dtb = cons.config.dtb
        cons.config.dtb = dtb
        if required:
            test_required_key(sha_algo, padding)
        else:
            test_with_algo(sha_algo, padding)
    finally:
        # Go back to the original U-Boot with the correct dtb.
        cons.config.dtb = old_dtb
        cons.restart_uboot()