（三十七）探索platform.xml

前言：最近工作涉及到platform.xml的修改，其中涉及的条目还是挺多的，就着周末有时间梳理一下。

扩展阅读：

1.doze模式： https://developer.android.com/training/monitoring-device-state/doze-standby?hl=zh-cn

2. https://blog.csdn.net/licaomengRICE/article/details/48735957

1. platform.xml存放位置

platform.xml其实是将aosp中的配置文件直接拷贝到手机目录中

1.1 手机存放位置

如下所示，手机中所存放的位置是位于/system/etc/permissions下

1.2 aosp中位置

在aosp中是放在framework/base/data/etc/下的

2. platform.xml内容

摘自小米mix 2:

3. platform.xml内容梳理

关键tag:

• 
  
• 
  

3.1 警告部分

说明这个文件是处理普通用户和系统权限之间映射的，如果擅自改动，会造成大的安全漏洞。

3.2 权限映射

将低等级的groups id和权限名称相关联。通过指定这样的映射，表明了一个授予了给定权限的应用进程将附带这所给的group id运行，因此它可以执行这个群组所允许的读写和执行操作。

有个例外：

3.3 分配权限

:有些用户比较特殊，它们是系统核心用户，Android会分配特定的高级权限来允许它们来完成一些高级的操作。比如，shell用户有很多权限，这是因为开发者需要比较开放的环境来和system进行交互。

shell用户的权限有时候需要adb root/adb remount才能享受，对应的需要userdebug或者root版本，user版本下shell命令还是有所限制的。

3.4 库

:应用可以链接到的库，可以理解为应用可以调用到的jar？

3.5 省电优化白名单

: 这个对应于手机中的省电优化设置，用这个tag配置在这张表中就代表该应用不受省电优化显示，可以在后台访问网络。对应应用在原生设置中的电源菜单也是灰显，不可设置优化的。

这个tag也和doze mode有些关系

可以使用命令查看：adb shell dumpsys deviceidle whitelist

chiron:/system/etc/permissions $ dumpsys deviceidle whitelist
system-excidle,com.android.providers.downloads,10012
system-excidle,com.qualcomm.qti.telephonyservice,1001
system-excidle,com.qualcomm.qti.radioconfiginterface,1001
system-excidle,com.android.cellbroadcastreceiver,10007
system-excidle,com.qualcomm.qti.ims,1001
system-excidle,com.android.shell,2000
system,com.android.providers.downloads,10012
system,com.qualcomm.qti.telephonyservice,1001
system,com.qualcomm.qti.radioconfiginterface,1001
system,com.android.cellbroadcastreceiver,10007
system,com.qualcomm.qti.ims,1001
system,com.android.shell,2000
user,com.android.cts.priv.ctsshim,10009
user,com.qualcomm.qti.auth.sampleextauthservice,10077
user,com.miui.contentextension,10113
user,com.unionpay.tsmservice.mi,10086

3.6 数据白名单

3.7 系统应用白名单

设置是系统应用，可以看它的AndroidManifest.xml：

这表明了设置uid是1000，并且是核心应用。

3.8 系统应用黑名单

4. platform.xml对应的解析代码

xml肯定是需要解析才能用的，/frameworks/core/java/com/android/server/SystemConfig.java 这个SystemConfig就是来解析platform.xml，然后供一个个系统接口用作返回值的依据。

    void readPermissions(File libraryDir, int permissionFlag) {
        // Read permissions from given directory.
        if (!libraryDir.exists() || !libraryDir.isDirectory()) {
            if (permissionFlag == ALLOW_ALL) {
                Slog.w(TAG, "No directory " + libraryDir + ", skipping");
            }
            return;
        }
        if (!libraryDir.canRead()) {
            Slog.w(TAG, "Directory " + libraryDir + " cannot be read");
            return;
        }

        // Iterate over the files in the directory and scan .xml files
        File platformFile = null;
        for (File f : libraryDir.listFiles()) {
            // We'll read platform.xml last
            if (f.getPath().endsWith("etc/permissions/platform.xml")) {
                platformFile = f;
                continue;
            }

            if (!f.getPath().endsWith(".xml")) {
                Slog.i(TAG, "Non-xml file " + f + " in " + libraryDir + " directory, ignoring");
                continue;
            }
            if (!f.canRead()) {
                Slog.w(TAG, "Permissions library file " + f + " cannot be read");
                continue;
            }

            readPermissionsFromXml(f, permissionFlag);
        }

        // Read platform permissions last so it will take precedence
        if (platformFile != null) {
            readPermissionsFromXml(platformFile, permissionFlag);
        }
    }

    private void readPermissionsFromXml(File permFile, int permissionFlag) {
        FileReader permReader = null;
        try {
            permReader = new FileReader(permFile);
        } catch (FileNotFoundException e) {
            Slog.w(TAG, "Couldn't find or open permissions file " + permFile);
            return;
        }

        final boolean lowRam = ActivityManager.isLowRamDeviceStatic();

        try {
            XmlPullParser parser = Xml.newPullParser();
            parser.setInput(permReader);

            int type;
            while ((type=parser.next()) != parser.START_TAG
                       && type != parser.END_DOCUMENT) {
                ;
            }

            if (type != parser.START_TAG) {
                throw new XmlPullParserException("No start tag found");
            }

            if (!parser.getName().equals("permissions") && !parser.getName().equals("config")) {
                throw new XmlPullParserException("Unexpected start tag in " + permFile
                        + ": found " + parser.getName() + ", expected 'permissions' or 'config'");
            }

            boolean allowAll = permissionFlag == ALLOW_ALL;
            boolean allowLibs = (permissionFlag & ALLOW_LIBS) != 0;
            boolean allowFeatures = (permissionFlag & ALLOW_FEATURES) != 0;
            boolean allowPermissions = (permissionFlag & ALLOW_PERMISSIONS) != 0;
            boolean allowAppConfigs = (permissionFlag & ALLOW_APP_CONFIGS) != 0;
            boolean allowPrivappPermissions = (permissionFlag & ALLOW_PRIVAPP_PERMISSIONS) != 0;
            boolean allowApiWhitelisting = (permissionFlag & ALLOW_HIDDENAPI_WHITELISTING) != 0;
            while (true) {
                XmlUtils.nextElement(parser);
                if (parser.getEventType() == XmlPullParser.END_DOCUMENT) {
                    break;
                }

                String name = parser.getName();
                if ("group".equals(name) && allowAll) {
                    String gidStr = parser.getAttributeValue(null, "gid");
                    if (gidStr != null) {
                        int gid = android.os.Process.getGidForName(gidStr);
                        mGlobalGids = appendInt(mGlobalGids, gid);
                    } else {
                        Slog.w(TAG, " without gid in " + permFile + " at "
                                + parser.getPositionDescription());
                    }

                    XmlUtils.skipCurrentTag(parser);
                    continue;
                } else if ("permission".equals(name) && allowPermissions) {
                    String perm = parser.getAttributeValue(null, "name");
                    if (perm == null) {
                        Slog.w(TAG, " without name in " + permFile + " at "
                                + parser.getPositionDescription());
                        XmlUtils.skipCurrentTag(parser);
                        continue;
                    }
                    perm = perm.intern();
                    readPermission(parser, perm);

                } else if ("assign-permission".equals(name) && allowPermissions) {
                    String perm = parser.getAttributeValue(null, "name");
                    if (perm == null) {
                        Slog.w(TAG, " without name in " + permFile + " at "
                                + parser.getPositionDescription());
                        XmlUtils.skipCurrentTag(parser);
                        continue;
                    }
                    String uidStr = parser.getAttributeValue(null, "uid");
                    if (uidStr == null) {
                        Slog.w(TAG, " without uid in " + permFile + " at "
                                + parser.getPositionDescription());
                        XmlUtils.skipCurrentTag(parser);
                        continue;
                    }
                    int uid = Process.getUidForName(uidStr);
                    if (uid < 0) {
                        Slog.w(TAG, " with unknown uid \""
                                + uidStr + "  in " + permFile + " at "
                                + parser.getPositionDescription());
                        XmlUtils.skipCurrentTag(parser);
                        continue;
                    }
                    perm = perm.intern();
                    ArraySet perms = mSystemPermissions.get(uid);
                    if (perms == null) {
                        perms = new ArraySet();
                        mSystemPermissions.put(uid, perms);
                    }
                    perms.add(perm);
                    XmlUtils.skipCurrentTag(parser);

                } else if ("library".equals(name) && allowLibs) {
                    String lname = parser.getAttributeValue(null, "name");
                    String lfile = parser.getAttributeValue(null, "file");
                    if (lname == null) {
                        Slog.w(TAG, " without name in " + permFile + " at "
                                + parser.getPositionDescription());
                    } else if (lfile == null) {
                        Slog.w(TAG, " without file in " + permFile + " at "
                                + parser.getPositionDescription());
                    } else {
                        //Log.i(TAG, "Got library " + lname + " in " + lfile);
                        mSharedLibraries.put(lname, lfile);
                    }
                    XmlUtils.skipCurrentTag(parser);
                    continue;

                } else if ("feature".equals(name) && allowFeatures) {
                    String fname = parser.getAttributeValue(null, "name");
                    int fversion = XmlUtils.readIntAttribute(parser, "version", 0);
                    boolean allowed;
                    if (!lowRam) {
                        allowed = true;
                    } else {
                        String notLowRam = parser.getAttributeValue(null, "notLowRam");
                        allowed = !"true".equals(notLowRam);
                    }
                    if (fname == null) {
                        Slog.w(TAG, " without name in " + permFile + " at "
                                + parser.getPositionDescription());
                    } else if (allowed) {
                        addFeature(fname, fversion);
                    }
                    XmlUtils.skipCurrentTag(parser);
                    continue;

                } else if ("unavailable-feature".equals(name) && allowFeatures) {
                    String fname = parser.getAttributeValue(null, "name");
                    if (fname == null) {
                        Slog.w(TAG, " without name in " + permFile + " at "
                                + parser.getPositionDescription());
                    } else {
                        mUnavailableFeatures.add(fname);
                    }
                    XmlUtils.skipCurrentTag(parser);
                    continue;

                } else if ("allow-in-power-save-except-idle".equals(name) && allowAll) {
                    String pkgname = parser.getAttributeValue(null, "package");
                    if (pkgname == null) {
                        Slog.w(TAG, " without package in "
                                + permFile + " at " + parser.getPositionDescription());
                    } else {
                        mAllowInPowerSaveExceptIdle.add(pkgname);
                    }
                    XmlUtils.skipCurrentTag(parser);
                    continue;

                } else if ("allow-in-power-save".equals(name) && allowAll) {
                    String pkgname = parser.getAttributeValue(null, "package");
                    if (pkgname == null) {
                        Slog.w(TAG, " without package in " + permFile + " at "
                                + parser.getPositionDescription());
                    } else {
                        mAllowInPowerSave.add(pkgname);
                    }
                    XmlUtils.skipCurrentTag(parser);
                    continue;

                } else if ("allow-in-data-usage-save".equals(name) && allowAll) {
                    String pkgname = parser.getAttributeValue(null, "package");
                    if (pkgname == null) {
                        Slog.w(TAG, " without package in " + permFile
                                + " at " + parser.getPositionDescription());
                    } else {
                        mAllowInDataUsageSave.add(pkgname);
                    }
                    XmlUtils.skipCurrentTag(parser);
                    continue;

                } else if ("allow-unthrottled-location".equals(name) && allowAll) {
                    String pkgname = parser.getAttributeValue(null, "package");
                    if (pkgname == null) {
                        Slog.w(TAG, " without package in "
                            + permFile + " at " + parser.getPositionDescription());
                    } else {
                        mAllowUnthrottledLocation.add(pkgname);
                    }
                    XmlUtils.skipCurrentTag(parser);
                    continue;

                } else if ("allow-implicit-broadcast".equals(name) && allowAll) {
                    String action = parser.getAttributeValue(null, "action");
                    if (action == null) {
                        Slog.w(TAG, " without action in " + permFile
                                + " at " + parser.getPositionDescription());
                    } else {
                        mAllowImplicitBroadcasts.add(action);
                    }
                    XmlUtils.skipCurrentTag(parser);
                    continue;

                } else if ("app-link".equals(name) && allowAppConfigs) {
                    String pkgname = parser.getAttributeValue(null, "package");
                    if (pkgname == null) {
                        Slog.w(TAG, " without package in " + permFile + " at "
                                + parser.getPositionDescription());
                    } else {
                        mLinkedApps.add(pkgname);
                    }
                    XmlUtils.skipCurrentTag(parser);
                } else if ("system-user-whitelisted-app".equals(name) && allowAppConfigs) {
                    String pkgname = parser.getAttributeValue(null, "package");
                    if (pkgname == null) {
                        Slog.w(TAG, " without package in " + permFile
                                + " at " + parser.getPositionDescription());
                    } else {
                        mSystemUserWhitelistedApps.add(pkgname);
                    }
                    XmlUtils.skipCurrentTag(parser);
                } else if ("system-user-blacklisted-app".equals(name) && allowAppConfigs) {
                    String pkgname = parser.getAttributeValue(null, "package");
                    if (pkgname == null) {
                        Slog.w(TAG, " without service in "
                                + permFile + " at " + parser.getPositionDescription());
                    } else {
                        ComponentName cn = ComponentName.unflattenFromString(serviceName);
                        if (cn == null) {
                            Slog.w(TAG,
                                    " with invalid service name "
                                    + serviceName + " in "+ permFile
                                    + " at " + parser.getPositionDescription());
                        } else {
                            mBackupTransportWhitelist.add(cn);
                        }
                    }
                    XmlUtils.skipCurrentTag(parser);
                } else if ("disabled-until-used-preinstalled-carrier-associated-app".equals(name)
                        && allowAppConfigs) {
                    String pkgname = parser.getAttributeValue(null, "package");
                    String carrierPkgname = parser.getAttributeValue(null, "carrierAppPackage");
                    if (pkgname == null || carrierPkgname == null) {
                        Slog.w(TAG, " associatedPkgs =
                                mDisabledUntilUsedPreinstalledCarrierAssociatedApps.get(
                                        carrierPkgname);
                        if (associatedPkgs == null) {
                            associatedPkgs = new ArrayList<>();
                            mDisabledUntilUsedPreinstalledCarrierAssociatedApps.put(
                                    carrierPkgname, associatedPkgs);
                        }
                        associatedPkgs.add(pkgname);
                    }
                    XmlUtils.skipCurrentTag(parser);
                } else if ("privapp-permissions".equals(name) && allowPrivappPermissions) {
                    readPrivAppPermissions(parser);
                } else if ("hidden-api-whitelisted-app".equals(name) && allowApiWhitelisting) {
                    String pkgname = parser.getAttributeValue(null, "package");
                    if (pkgname == null) {
                        Slog.w(TAG, " without package in " + permFile
                                + " at " + parser.getPositionDescription());
                    } else {
                        mHiddenApiPackageWhitelist.add(pkgname);
                    }
                    XmlUtils.skipCurrentTag(parser);
                } else {
                    XmlUtils.skipCurrentTag(parser);
                    continue;
                }
            }
        } catch (XmlPullParserException e) {
            Slog.w(TAG, "Got exception parsing permissions.", e);
        } catch (IOException e) {
            Slog.w(TAG, "Got exception parsing permissions.", e);
        } finally {
            IoUtils.closeQuietly(permReader);
        }

        // Some devices can be field-converted to FBE, so offer to splice in
        // those features if not already defined by the static config
        if (StorageManager.isFileEncryptedNativeOnly()) {
            addFeature(PackageManager.FEATURE_FILE_BASED_ENCRYPTION, 0);
            addFeature(PackageManager.FEATURE_SECURELY_REMOVES_USERS, 0);
        }

        if (ActivityManager.isLowRamDeviceStatic()) {
            addFeature(PackageManager.FEATURE_RAM_LOW, 0);
        } else {
            addFeature(PackageManager.FEATURE_RAM_NORMAL, 0);
        }

        for (String featureName : mUnavailableFeatures) {
            removeFeature(featureName);
        }
    }

    private void addFeature(String name, int version) {
        FeatureInfo fi = mAvailableFeatures.get(name);
        if (fi == null) {
            fi = new FeatureInfo();
            fi.name = name;
            fi.version = version;
            mAvailableFeatures.put(name, fi);
        } else {
            fi.version = Math.max(fi.version, version);
        }
    }

    private void removeFeature(String name) {
        if (mAvailableFeatures.remove(name) != null) {
            Slog.d(TAG, "Removed unavailable feature " + name);
        }
    }

    void readPermission(XmlPullParser parser, String name)
            throws IOException, XmlPullParserException {
        if (mPermissions.containsKey(name)) {
            throw new IllegalStateException("Duplicate permission definition for " + name);
        }

        final boolean perUser = XmlUtils.readBooleanAttribute(parser, "perUser", false);
        final PermissionEntry perm = new PermissionEntry(name, perUser);
        mPermissions.put(name, perm);

        int outerDepth = parser.getDepth();
        int type;
        while ((type=parser.next()) != XmlPullParser.END_DOCUMENT
               && (type != XmlPullParser.END_TAG
                       || parser.getDepth() > outerDepth)) {
            if (type == XmlPullParser.END_TAG
                    || type == XmlPullParser.TEXT) {
                continue;
            }

            String tagName = parser.getName();
            if ("group".equals(tagName)) {
                String gidStr = parser.getAttributeValue(null, "gid");
                if (gidStr != null) {
                    int gid = Process.getGidForName(gidStr);
                    perm.gids = appendInt(perm.gids, gid);
                } else {
                    Slog.w(TAG, " without gid at "
                            + parser.getPositionDescription());
                }
            }
            XmlUtils.skipCurrentTag(parser);
        }
    }

5. 总结

整篇博客其实对platform.xml的分析还是比较肤浅的，了解的稍微好一点，后续接着对应的系统调用看下配置各项属性真正的作用才算真正的对这个xml有所了解吧。