diff mbox series

[v2,4/4] oe-selftest: Add U-Boot fitImage signing testcases

Message ID 20210326201410.13906-5-klaus@linux.vnet.ibm.com
State New
Headers show
Series u-boot: Support for SPL verified boot | expand

Commit Message

Klaus Heinrich Kiwi March 26, 2021, 8:14 p.m. UTC
Derived from the similar kernel fitImage sign testcase, the U-Boot
fitImage testcases exercises the following fitimage.FitImageTest
scenarios:

 * test_uboot_fit_image - create unsigned U-Boot fitImage
 * test_uboot_sign_fit_image - create unsigned U-Boot fitImage in
   addition to signed Kernel fitImage
 * test_sign_standalone_uboot_fit_image - Create signed U-Boot fitImage
   without a Kernel fitImage
 * test_sign_cascaded_uboot_fit_image - Create and sign U-Boot and
   Kernel fitImages

Signed-off-by: Klaus Heinrich Kiwi <klaus@linux.vnet.ibm.com>
---
 meta/lib/oeqa/selftest/cases/fitimage.py | 468 +++++++++++++++++++++++
 1 file changed, 468 insertions(+)
diff mbox series

Patch

diff --git a/meta/lib/oeqa/selftest/cases/fitimage.py b/meta/lib/oeqa/selftest/cases/fitimage.py
index 02692de822..b911fded74 100644
--- a/meta/lib/oeqa/selftest/cases/fitimage.py
+++ b/meta/lib/oeqa/selftest/cases/fitimage.py
@@ -231,6 +231,474 @@  UBOOT_MKIMAGE_SIGN_ARGS = "-c 'a smart comment'"
         result = runCmd('grep "### uboot-mkimage signing wrapper message" %s/log.do_assemble_fitimage' % tempdir, ignore_status=True)
         self.assertEqual(result.status, 0, 'UBOOT_MKIMAGE_SIGN did not work')
 
+    def test_uboot_fit_image(self):
+        """
+        Summary:     Check if Uboot FIT image and Image Tree Source
+                     (its) are built and the Image Tree Source has the
+                     correct fields.
+        Expected:    1. u-boot-fitImage and u-boot-its can be built
+                     2. The type, load address, entrypoint address and
+                     default values of U-boot image are correct in the
+                     Image Tree Source. Not all the fields are tested,
+                     only the key fields that wont vary between
+                     different architectures.
+        Product:     oe-core
+        Author:      Klaus Heinrich Kiwi <klaus@linux.vnet.ibm.com>
+                     based on work by Usama Arif <usama.arif@arm.com>
+        """
+        config = """
+# We need at least CONFIG_SPL_LOAD_FIT and CONFIG_SPL_OF_CONTROL set
+MACHINE = "qemuarm"
+UBOOT_MACHINE = "am57xx_evm_defconfig"
+SPL_BINARY = "MLO"
+
+# Enable creation of the U-Boot fitImage
+UBOOT_FITIMAGE_ENABLE = "1"
+
+# (U-boot) fitImage properties
+UBOOT_LOADADDRESS = "0x80080000"
+UBOOT_ENTRYPOINT = "0x80080000"
+UBOOT_FIT_DESC = "A model description"
+
+# Enable creation of Kernel fitImage
+KERNEL_IMAGETYPES += " fitImage "
+KERNEL_CLASSES = " kernel-fitimage"
+UBOOT_SIGN_ENABLE = "1"
+FIT_GENERATE_KEYS = "1"
+UBOOT_SIGN_KEYDIR = "${TOPDIR}/signing-keys"
+UBOOT_SIGN_KEYNAME = "oe-selftest"
+FIT_SIGN_INDIVIDUAL = "1"
+"""
+        self.write_config(config)
+
+        # The U-Boot fitImage is created as part of linux recipe
+        bitbake("virtual/kernel")
+
+        deploy_dir_image = get_bb_var('DEPLOY_DIR_IMAGE')
+        machine = get_bb_var('MACHINE')
+        fitimage_its_path = os.path.join(deploy_dir_image,
+            "u-boot-its-%s" % (machine,))
+        fitimage_path = os.path.join(deploy_dir_image,
+            "u-boot-fitImage-%s" % (machine,))
+
+        self.assertTrue(os.path.exists(fitimage_its_path),
+            "%s image tree source doesn't exist" % (fitimage_its_path))
+        self.assertTrue(os.path.exists(fitimage_path),
+            "%s FIT image doesn't exist" % (fitimage_path))
+
+        # Check that the type, load address, entrypoint address and default
+        # values for kernel and ramdisk in Image Tree Source are as expected.
+        # The order of fields in the below array is important. Not all the
+        # fields are tested, only the key fields that wont vary between
+        # different architectures.
+        its_field_check = [
+            'description = "A model description";',
+            'type = "uboot";',
+            'load = <0x80080000>;',
+            'entry = <0x80080000>;',
+            'default = "conf";',
+            'loadables = "uboot";',
+            'fdt = "fdt";'
+            ]
+
+        with open(fitimage_its_path) as its_file:
+            field_index = 0
+            for line in its_file:
+                if field_index == len(its_field_check):
+                    break
+                if its_field_check[field_index] in line:
+                    field_index +=1
+
+        if field_index != len(its_field_check): # if its equal, the test passed
+            self.assertTrue(field_index == len(its_field_check),
+                "Fields in Image Tree Source File %s did not match, error in finding %s"
+                % (fitimage_its_path, its_field_check[field_index]))
+
+    def test_uboot_sign_fit_image(self):
+        """
+        Summary:     Check if Uboot FIT image and Image Tree Source
+                     (its) are built and the Image Tree Source has the
+                     correct fields, in the scenario where the Kernel
+                     is also creating/signing it's fitImage.
+        Expected:    1. u-boot-fitImage and u-boot-its can be built
+                     2. The type, load address, entrypoint address and
+                     default values of U-boot image are correct in the
+                     Image Tree Source. Not all the fields are tested,
+                     only the key fields that wont vary between
+                     different architectures.
+        Product:     oe-core
+        Author:      Klaus Heinrich Kiwi <klaus@linux.vnet.ibm.com>
+                     based on work by Usama Arif <usama.arif@arm.com>
+        """
+        config = """
+# We need at least CONFIG_SPL_LOAD_FIT and CONFIG_SPL_OF_CONTROL set
+MACHINE = "qemuarm"
+UBOOT_MACHINE = "am57xx_evm_defconfig"
+SPL_BINARY = "MLO"
+
+# Enable creation of the U-Boot fitImage
+UBOOT_FITIMAGE_ENABLE = "1"
+
+# (U-boot) fitImage properties
+UBOOT_LOADADDRESS = "0x80080000"
+UBOOT_ENTRYPOINT = "0x80080000"
+UBOOT_FIT_DESC = "A model description"
+KERNEL_IMAGETYPES += " fitImage "
+KERNEL_CLASSES = " kernel-fitimage test-mkimage-wrapper "
+UBOOT_SIGN_ENABLE = "1"
+FIT_GENERATE_KEYS = "1"
+UBOOT_SIGN_KEYDIR = "${TOPDIR}/signing-keys"
+UBOOT_SIGN_KEYNAME = "oe-selftest"
+FIT_SIGN_INDIVIDUAL = "1"
+UBOOT_MKIMAGE_SIGN_ARGS = "-c 'a smart U-Boot comment'"
+"""
+        self.write_config(config)
+
+        # The U-Boot fitImage is created as part of linux recipe
+        bitbake("virtual/kernel")
+
+        deploy_dir_image = get_bb_var('DEPLOY_DIR_IMAGE')
+        machine = get_bb_var('MACHINE')
+        fitimage_its_path = os.path.join(deploy_dir_image,
+            "u-boot-its-%s" % (machine,))
+        fitimage_path = os.path.join(deploy_dir_image,
+            "u-boot-fitImage-%s" % (machine,))
+
+        self.assertTrue(os.path.exists(fitimage_its_path),
+            "%s image tree source doesn't exist" % (fitimage_its_path))
+        self.assertTrue(os.path.exists(fitimage_path),
+            "%s FIT image doesn't exist" % (fitimage_path))
+
+        # Check that the type, load address, entrypoint address and default
+        # values for kernel and ramdisk in Image Tree Source are as expected.
+        # The order of fields in the below array is important. Not all the
+        # fields are tested, only the key fields that wont vary between
+        # different architectures.
+        its_field_check = [
+            'description = "A model description";',
+            'type = "uboot";',
+            'load = <0x80080000>;',
+            'entry = <0x80080000>;',
+            'default = "conf";',
+            'loadables = "uboot";',
+            'fdt = "fdt";'
+            ]
+
+        with open(fitimage_its_path) as its_file:
+            field_index = 0
+            for line in its_file:
+                if field_index == len(its_field_check):
+                    break
+                if its_field_check[field_index] in line:
+                    field_index +=1
+
+        if field_index != len(its_field_check): # if its equal, the test passed
+            self.assertTrue(field_index == len(its_field_check),
+                "Fields in Image Tree Source File %s did not match, error in finding %s"
+                % (fitimage_its_path, its_field_check[field_index]))
+
+
+    def test_sign_standalone_uboot_fit_image(self):
+        """
+        Summary:     Check if U-Boot FIT image and Image Tree Source (its) are
+                     created and signed correctly for the scenario where only
+                     the U-Boot proper fitImage is being created and signed.
+        Expected:    1) U-Boot its and FIT image are built successfully
+                     2) Scanning the its file indicates signing is enabled
+                        as requested by SPL_SIGN_ENABLE (using keys generated
+                        via UBOOT_FIT_GENERATE_KEYS)
+                     3) Dumping the FIT image indicates signature values
+                        are present
+                     4) Examination of the do_uboot_assemble_fitimage
+                     runfile/logfile indicate that UBOOT_MKIMAGE, UBOOT_MKIMAGE_SIGN
+                     and SPL_MKIMAGE_SIGN_ARGS are working as expected.
+        Product:     oe-core
+        Author:      Klaus Heinrich Kiwi <klaus@linux.vnet.ibm.com> based upon
+                     work by Paul Eggleton <paul.eggleton@microsoft.com> and
+                     Usama Arif <usama.arif@arm.com>
+        """
+        config = """
+# There's no U-boot deconfig with CONFIG_FIT_SIGNATURE yet, so we need at
+# least CONFIG_SPL_LOAD_FIT and CONFIG_SPL_OF_CONTROL set
+MACHINE = "qemuarm"
+UBOOT_MACHINE = "am57xx_evm_defconfig"
+SPL_BINARY = "MLO"
+# The kernel-fitimage class is a dependency even if we're only
+# creating/signing the U-Boot fitImage
+KERNEL_CLASSES = " kernel-fitimage test-mkimage-wrapper "
+# Enable creation and signing of the U-Boot fitImage
+UBOOT_FITIMAGE_ENABLE = "1"
+SPL_SIGN_ENABLE = "1"
+SPL_SIGN_KEYNAME = "spl-oe-selftest"
+SPL_SIGN_KEYDIR = "${TOPDIR}/signing-keys"
+UBOOT_DTB_BINARY = "u-boot.dtb"
+UBOOT_ENTRYPOINT  = "0x80000000"
+UBOOT_LOADADDRESS = "0x80000000"
+UBOOT_DTB_LOADADDRESS = "0x82000000"
+UBOOT_ARCH = "arm"
+SPL_MKIMAGE_DTCOPTS = "-I dts -O dtb -p 2000"
+SPL_MKIMAGE_SIGN_ARGS = "-c 'a smart U-Boot comment'"
+UBOOT_EXTLINUX = "0"
+UBOOT_FIT_GENERATE_KEYS = "1"
+UBOOT_FIT_HASH_ALG = "sha256"
+"""
+        self.write_config(config)
+
+        # The U-Boot fitImage is created as part of linux recipe
+        bitbake("virtual/kernel")
+
+        image_type = "core-image-minimal"
+        deploy_dir_image = get_bb_var('DEPLOY_DIR_IMAGE')
+        machine = get_bb_var('MACHINE')
+        fitimage_its_path = os.path.join(deploy_dir_image,
+            "u-boot-its-%s" % (machine,))
+        fitimage_path = os.path.join(deploy_dir_image,
+            "u-boot-fitImage-%s" % (machine,))
+
+        self.assertTrue(os.path.exists(fitimage_its_path),
+            "%s image tree source doesn't exist" % (fitimage_its_path))
+        self.assertTrue(os.path.exists(fitimage_path),
+            "%s FIT image doesn't exist" % (fitimage_path))
+
+        req_itspaths = [
+            ['/', 'images', 'uboot'],
+            ['/', 'images', 'uboot', 'signature'],
+            ['/', 'images', 'fdt'],
+            ['/', 'images', 'fdt', 'signature'],
+        ]
+
+        itspath = []
+        itspaths = []
+        linect = 0
+        sigs = {}
+        with open(fitimage_its_path) as its_file:
+            linect += 1
+            for line in its_file:
+                line = line.strip()
+                if line.endswith('};'):
+                    itspath.pop()
+                elif line.endswith('{'):
+                    itspath.append(line[:-1].strip())
+                    itspaths.append(itspath[:])
+                elif itspath and itspath[-1] == 'signature':
+                    itsdotpath = '.'.join(itspath)
+                    if not itsdotpath in sigs:
+                        sigs[itsdotpath] = {}
+                    if not '=' in line or not line.endswith(';'):
+                        self.fail('Unexpected formatting in %s sigs section line %d:%s' % (fitimage_its_path, linect, line))
+                    key, value = line.split('=', 1)
+                    sigs[itsdotpath][key.rstrip()] = value.lstrip().rstrip(';')
+
+        for reqpath in req_itspaths:
+            if not reqpath in itspaths:
+                self.fail('Missing section in its file: %s' % reqpath)
+
+        reqsigvalues_image = {
+            'algo': '"sha256,rsa2048"',
+            'key-name-hint': '"spl-oe-selftest"',
+        }
+
+        for itspath, values in sigs.items():
+            reqsigvalues = reqsigvalues_image
+            for reqkey, reqvalue in reqsigvalues.items():
+                value = values.get(reqkey, None)
+                if value is None:
+                    self.fail('Missing key "%s" in its file signature section %s' % (reqkey, itspath))
+                self.assertEqual(value, reqvalue)
+
+        # Dump the image to see if it really got signed
+        bitbake("u-boot-tools-native -c addto_recipe_sysroot")
+        result = runCmd('bitbake -e u-boot-tools-native | grep ^RECIPE_SYSROOT_NATIVE=')
+        recipe_sysroot_native = result.output.split('=')[1].strip('"')
+        dumpimage_path = os.path.join(recipe_sysroot_native, 'usr', 'bin', 'dumpimage')
+        result = runCmd('%s -l %s' % (dumpimage_path, fitimage_path))
+        in_signed = None
+        signed_sections = {}
+        for line in result.output.splitlines():
+            if line.startswith((' Image')):
+                in_signed = re.search('\((.*)\)', line).groups()[0]
+            elif re.match(' \w', line):
+                in_signed = None
+            elif in_signed:
+                if not in_signed in signed_sections:
+                    signed_sections[in_signed] = {}
+                key, value = line.split(':', 1)
+                signed_sections[in_signed][key.strip()] = value.strip()
+        self.assertIn('uboot', signed_sections)
+        self.assertIn('fdt', signed_sections)
+        for signed_section, values in signed_sections.items():
+            value = values.get('Sign algo', None)
+            self.assertEqual(value, 'sha256,rsa2048:spl-oe-selftest', 'Signature algorithm for %s not expected value' % signed_section)
+            value = values.get('Sign value', None)
+            self.assertEqual(len(value), 512, 'Signature value for section %s not expected length' % signed_section)
+
+        # Check for SPL_MKIMAGE_SIGN_ARGS
+        result = runCmd('bitbake -e virtual/kernel | grep ^T=')
+        tempdir = result.output.split('=', 1)[1].strip().strip('')
+        result = runCmd('grep "a smart U-Boot comment" %s/run.do_uboot_assemble_fitimage' % tempdir, ignore_status=True)
+        self.assertEqual(result.status, 0, 'SPL_MKIMAGE_SIGN_ARGS value did not get used')
+
+        # Check for evidence of test-mkimage-wrapper class
+        result = runCmd('grep "### uboot-mkimage wrapper message" %s/log.do_uboot_assemble_fitimage' % tempdir, ignore_status=True)
+        self.assertEqual(result.status, 0, 'UBOOT_MKIMAGE did not work')
+        result = runCmd('grep "### uboot-mkimage signing wrapper message" %s/log.do_uboot_assemble_fitimage' % tempdir, ignore_status=True)
+        self.assertEqual(result.status, 0, 'UBOOT_MKIMAGE_SIGN did not work')
+
+    def test_sign_cascaded_uboot_fit_image(self):
+        """
+        Summary:     Check if U-Boot FIT image and Image Tree Source (its) are
+                     created and signed correctly for the scenario where both
+                     U-Boot proper and Kernel fitImages are being created and
+                     signed.
+        Expected:    1) U-Boot its and FIT image are built successfully
+                     2) Scanning the its file indicates signing is enabled
+                        as requested by SPL_SIGN_ENABLE (using keys generated
+                        via UBOOT_FIT_GENERATE_KEYS)
+                     3) Dumping the FIT image indicates signature values
+                        are present
+                     4) Examination of the do_uboot_assemble_fitimage
+                     runfile/logfile indicate that UBOOT_MKIMAGE, UBOOT_MKIMAGE_SIGN
+                     and SPL_MKIMAGE_SIGN_ARGS are working as expected.
+        Product:     oe-core
+        Author:      Klaus Heinrich Kiwi <klaus@linux.vnet.ibm.com> based upon
+                     work by Paul Eggleton <paul.eggleton@microsoft.com> and
+                     Usama Arif <usama.arif@arm.com>
+        """
+        config = """
+# There's no U-boot deconfig with CONFIG_FIT_SIGNATURE yet, so we need at
+# least CONFIG_SPL_LOAD_FIT and CONFIG_SPL_OF_CONTROL set
+MACHINE = "qemuarm"
+UBOOT_MACHINE = "am57xx_evm_defconfig"
+SPL_BINARY = "MLO"
+# Enable creation and signing of the U-Boot fitImage
+UBOOT_FITIMAGE_ENABLE = "1"
+SPL_SIGN_ENABLE = "1"
+SPL_SIGN_KEYNAME = "spl-cascaded-oe-selftest"
+SPL_SIGN_KEYDIR = "${TOPDIR}/signing-keys"
+UBOOT_DTB_BINARY = "u-boot.dtb"
+UBOOT_ENTRYPOINT  = "0x80000000"
+UBOOT_LOADADDRESS = "0x80000000"
+UBOOT_MKIMAGE_DTCOPTS = "-I dts -O dtb -p 2000"
+UBOOT_MKIMAGE_SIGN_ARGS = "-c 'a smart cascaded Kernel comment'"
+UBOOT_DTB_LOADADDRESS = "0x82000000"
+UBOOT_ARCH = "arm"
+SPL_MKIMAGE_DTCOPTS = "-I dts -O dtb -p 2000"
+SPL_MKIMAGE_SIGN_ARGS = "-c 'a smart cascaded U-Boot comment'"
+UBOOT_EXTLINUX = "0"
+UBOOT_FIT_GENERATE_KEYS = "1"
+UBOOT_FIT_HASH_ALG = "sha256"
+KERNEL_IMAGETYPES += " fitImage "
+KERNEL_CLASSES = " kernel-fitimage test-mkimage-wrapper "
+UBOOT_SIGN_ENABLE = "1"
+FIT_GENERATE_KEYS = "1"
+UBOOT_SIGN_KEYDIR = "${TOPDIR}/signing-keys"
+UBOOT_SIGN_KEYNAME = "kernel-oe-selftest"
+FIT_SIGN_INDIVIDUAL = "1"
+"""
+        self.write_config(config)
+
+        # The U-Boot fitImage is created as part of linux recipe
+        bitbake("virtual/kernel")
+
+        image_type = "core-image-minimal"
+        deploy_dir_image = get_bb_var('DEPLOY_DIR_IMAGE')
+        machine = get_bb_var('MACHINE')
+        fitimage_its_path = os.path.join(deploy_dir_image,
+            "u-boot-its-%s" % (machine,))
+        fitimage_path = os.path.join(deploy_dir_image,
+            "u-boot-fitImage-%s" % (machine,))
+
+        self.assertTrue(os.path.exists(fitimage_its_path),
+            "%s image tree source doesn't exist" % (fitimage_its_path))
+        self.assertTrue(os.path.exists(fitimage_path),
+            "%s FIT image doesn't exist" % (fitimage_path))
+
+        req_itspaths = [
+            ['/', 'images', 'uboot'],
+            ['/', 'images', 'uboot', 'signature'],
+            ['/', 'images', 'fdt'],
+            ['/', 'images', 'fdt', 'signature'],
+        ]
+
+        itspath = []
+        itspaths = []
+        linect = 0
+        sigs = {}
+        with open(fitimage_its_path) as its_file:
+            linect += 1
+            for line in its_file:
+                line = line.strip()
+                if line.endswith('};'):
+                    itspath.pop()
+                elif line.endswith('{'):
+                    itspath.append(line[:-1].strip())
+                    itspaths.append(itspath[:])
+                elif itspath and itspath[-1] == 'signature':
+                    itsdotpath = '.'.join(itspath)
+                    if not itsdotpath in sigs:
+                        sigs[itsdotpath] = {}
+                    if not '=' in line or not line.endswith(';'):
+                        self.fail('Unexpected formatting in %s sigs section line %d:%s' % (fitimage_its_path, linect, line))
+                    key, value = line.split('=', 1)
+                    sigs[itsdotpath][key.rstrip()] = value.lstrip().rstrip(';')
+
+        for reqpath in req_itspaths:
+            if not reqpath in itspaths:
+                self.fail('Missing section in its file: %s' % reqpath)
+
+        reqsigvalues_image = {
+            'algo': '"sha256,rsa2048"',
+            'key-name-hint': '"spl-cascaded-oe-selftest"',
+        }
+
+        for itspath, values in sigs.items():
+            reqsigvalues = reqsigvalues_image
+            for reqkey, reqvalue in reqsigvalues.items():
+                value = values.get(reqkey, None)
+                if value is None:
+                    self.fail('Missing key "%s" in its file signature section %s' % (reqkey, itspath))
+                self.assertEqual(value, reqvalue)
+
+        # Dump the image to see if it really got signed
+        bitbake("u-boot-tools-native -c addto_recipe_sysroot")
+        result = runCmd('bitbake -e u-boot-tools-native | grep ^RECIPE_SYSROOT_NATIVE=')
+        recipe_sysroot_native = result.output.split('=')[1].strip('"')
+        dumpimage_path = os.path.join(recipe_sysroot_native, 'usr', 'bin', 'dumpimage')
+        result = runCmd('%s -l %s' % (dumpimage_path, fitimage_path))
+        in_signed = None
+        signed_sections = {}
+        for line in result.output.splitlines():
+            if line.startswith((' Image')):
+                in_signed = re.search('\((.*)\)', line).groups()[0]
+            elif re.match(' \w', line):
+                in_signed = None
+            elif in_signed:
+                if not in_signed in signed_sections:
+                    signed_sections[in_signed] = {}
+                key, value = line.split(':', 1)
+                signed_sections[in_signed][key.strip()] = value.strip()
+        self.assertIn('uboot', signed_sections)
+        self.assertIn('fdt', signed_sections)
+        for signed_section, values in signed_sections.items():
+            value = values.get('Sign algo', None)
+            self.assertEqual(value, 'sha256,rsa2048:spl-cascaded-oe-selftest', 'Signature algorithm for %s not expected value' % signed_section)
+            value = values.get('Sign value', None)
+            self.assertEqual(len(value), 512, 'Signature value for section %s not expected length' % signed_section)
+
+        # Check for SPL_MKIMAGE_SIGN_ARGS
+        result = runCmd('bitbake -e virtual/kernel | grep ^T=')
+        tempdir = result.output.split('=', 1)[1].strip().strip('')
+        result = runCmd('grep "a smart cascaded U-Boot comment" %s/run.do_uboot_assemble_fitimage' % tempdir, ignore_status=True)
+        self.assertEqual(result.status, 0, 'SPL_MKIMAGE_SIGN_ARGS value did not get used')
+
+        # Check for evidence of test-mkimage-wrapper class
+        result = runCmd('grep "### uboot-mkimage wrapper message" %s/log.do_uboot_assemble_fitimage' % tempdir, ignore_status=True)
+        self.assertEqual(result.status, 0, 'UBOOT_MKIMAGE did not work')
+        result = runCmd('grep "### uboot-mkimage signing wrapper message" %s/log.do_uboot_assemble_fitimage' % tempdir, ignore_status=True)
+        self.assertEqual(result.status, 0, 'UBOOT_MKIMAGE_SIGN did not work')
+
+
+
     def test_initramfs_bundle(self):
         """
         Summary:     Verifies the content of the initramfs bundle node in the FIT Image Tree Source (its)