README
1This directory contains the core Android SELinux policy configuration.
2It defines the domains and types for the AOSP services and apps common to
3all devices. Device-specific policy should be placed under a
4separate device/<vendor>/<board>/sepolicy subdirectory and linked
5into the policy build as described below.
6
7Policy Generation:
8
9Additional, per device, policy files can be added into the
10policy build. These files should have each line including the
11final line terminated by a newline character (0x0A). This
12will allow files to be concatenated and processed whenever
13the m4(1) macro processor is called by the build process.
14Adding the newline will also make the intermediate text files
15easier to read when debugging build failures. The sets of file,
16service and property contexts files will automatically have a
17newline inserted between each file as these are common failure
18points.
19
20These device policy files can be configured through the use of
21the BOARD_SEPOLICY_DIRS variable. This variable should be set
22in the BoardConfig.mk file in the device or vendor directories.
23
24BOARD_SEPOLICY_DIRS contains a list of directories to search
25for additional policy files. Order matters in this list.
26For example, if you have 2 instances of widget.te files in the
27BOARD_SEPOLICY_DIRS search path, then the first one found (at the
28first search dir containing the file) will be concatenated first.
29Reviewing out/target/product/<device>/obj/ETC/sepolicy_intermediates/policy.conf
30will help sort out ordering issues.
31
32Example BoardConfig.mk Usage:
33From the Tuna device BoardConfig.mk, device/samsung/tuna/BoardConfig.mk
34
35BOARD_SEPOLICY_DIRS += device/samsung/tuna/sepolicy
36
37Additionally, OEMs can specify BOARD_SEPOLICY_M4DEFS to pass arbitrary m4
38definitions during the build. A definition consists of a string in the form
39of macro-name=value. Spaces must NOT be present. This is useful for building modular
40policies, policy generation, conditional file paths, etc. It is supported in
41the following file types:
42 * All *.te and SE Linux policy files as passed to checkpolicy
43 * file_contexts
44 * service_contexts
45 * property_contexts
46 * keys.conf
47
48Example BoardConfig.mk Usage:
49BOARD_SEPOLICY_M4DEFS += btmodule=foomatic \
50 btdevice=/dev/gps
51
52SPECIFIC POLICY FILE INFORMATION
53
54mac_permissions.xml:
55 ABOUT:
56 The mac_permissions.xml file is used for controlling the mmac solutions
57 as well as mapping a public base16 signing key with an arbitrary seinfo
58 string. Details of the files contents can be found in a comment at the
59 top of that file. The seinfo string, previously mentioned, is the same string
60 that is referenced in seapp_contexts.
61
62 It is important to note the final processed version of this file
63 is stripped of comments and whitespace. This is to preserve space on the
64 system.img. If one wishes to view it in a more human friendly format,
65 the "tidy" or "xmllint" command will assist you.
66
67 TOOLING:
68 insertkeys.py
69 Is a helper script for mapping arbitrary tags in the signature stanzas of
70 mac_permissions.xml to public keys found in pem files. This script takes
71 a mac_permissions.xml file(s) and configuration file in order to operate.
72 Details of the configuration file (keys.conf) can be found in the subsection
73 keys.conf. This tool is also responsible for stripping the comments and
74 whitespace during processing.
75
76 keys.conf
77 The keys.conf file is used for controlling the mapping of "tags" found in
78 the mac_permissions.xml signature stanzas with actual public keys found in
79 pem files. The configuration file is processed via m4.
80
81 The script allows for mapping any string contained in TARGET_BUILD_VARIANT
82 with specific path to a pem file. Typically TARGET_BUILD_VARIANT is either
83 user, eng or userdebug. Additionally, one can specify "ALL" to map a path to
84 any string specified in TARGET_BUILD_VARIANT. All tags are matched verbatim
85 and all options are matched lowercase. The options are "tolowered" automatically
86 for the user, it is convention to specify tags and options in all uppercase
87 and tags start with @. The option arguments can also use environment variables
88 via the familiar $VARIABLE syntax. This is often useful for setting a location
89 to ones release keys.
90
91 Often times, one will need to integrate an application that was signed by a separate
92 organization and may need to extract the pem file for the insertkeys/keys.conf tools.
93 Extraction of the public key in the pem format is possible via openssl. First you need
94 to unzip the apk, once it is unzipped, cd into the META_INF directory and then execute
95 openssl pkcs7 -inform DER -in CERT.RSA -out CERT.pem -outform PEM -print_certs
96 On some occasions CERT.RSA has a different name, and you will need to adjust for that.
97 After extracting the pem, you can rename it, and configure keys.conf and
98 mac_permissions.xml to pick up the change. You MUST open the generated pem file in a text
99 editor and strip out anything outside the opening and closing scissor lines. Failure to do
100 so WILL cause a compile time issue thrown by insertkeys.py
101
102 NOTE: The pem files are base64 encoded and PackageManagerService, mac_permissions.xml
103 and setool all use base16 encodings.
104