Android5.1系统通过包名给应用开放系统权限的方法

常用的给应用开放系统权限的方法是直接将该应用做成系统应用（即在AndroidManifest.xml文件里加上：android:sharedUserId="android.uid.system"），但是这种做法限制了应用本身的自由，也就是说经过系统签名后的系统应用只能够在对应的Android平台上安装使用，无法向其他应用一样放到Android市场里兼容所有的Android设备。

现在此介绍一种通过修改Android平台系统层代码，根据指定的应用包名给对应的应用在该平台上开放系统权限，这样既不应用应用的兼容性，又解决了应用想调用一些系统层接口而没有权限的矛盾。

该方法的核心是：在ActivityManagerService的startProcessLocked接口中把uid和gid都改为0.

需要开放系统权限的包名：

1、net.forclass.fcstudent

2、com.ckl.launcher

3、com.creative.fcstudent

修改步骤：

1、应用安装在设备上之后，点击启动必定会调用ActivityManagerService的startProcessLocked接口来开启一个新的进程，而给应用开放系统权限目的其实就是使应用能够成为超级应用，运行在系统进程中，这样我们只需要在startProcessLocked接口里面将应用的uid修改为0即可。

ActivityManagerService.java (frameworks\base\services\core\java\com\android\server\am)  final ProcessRecord startProcessLocked(String processName, ApplicationInfo info,      boolean knownToBeDead, int intentFlags, String hostingType, ComponentName hostingName,      boolean allowWhileBooting, boolean isolated, int isolatedUid, boolean keepIfLarge,      String abiOverride, String entryPoint, String[] entryPointArgs, Runnable crashHandler) {    // modified by haming patch begin, configure system permission for some special application.    if ("net.forclass.fcstudent".equals(info.packageName)        || "com.ckl.launcher".equals(info.packageName)        || "com.creative.fcstudent".equals(info.packageName)        || "com.hampoo.hampoointerfacetestdemo".equals(info.packageName)){      info.uid = 0;    }    // modified by haming patch end.    long startTime = SystemClock.elapsedRealtime();    ProcessRecord app;    ...... // 此处省略好多行    checkTime(startTime, "startProcess: stepping in to startProcess");    startProcessLocked( // 再次调用startProcessLocked重载方法        app, hostingType, hostingNameStr, abiOverride, entryPoint, entryPointArgs);    checkTime(startTime, "startProcess: done starting proc!");    return (app.pid != 0) ? app : null;  }在重载方法startProcessLocked(ProcessRecord app, String hostingType,String hostingNameStr, String abiOverride, String entryPoint, String[] entryPointArgs)里面将应用的gid也改为0：  private final void startProcessLocked(ProcessRecord app, String hostingType,      String hostingNameStr, String abiOverride, String entryPoint, String[] entryPointArgs) {    long startTime = SystemClock.elapsedRealtime();    ...... // 此处省略好多行    try {      int uid = app.uid;      int[] gids = null;      int mountExternal = Zygote.MOUNT_EXTERNAL_NONE;      if (!app.isolated) {        ...... // 此处省略好多行        // modified by haming patch begin, configure system permission for some special application.        if ("net.forclass.fcstudent".equals(app.info.packageName)          || "com.ckl.launcher".equals(app.info.packageName)          || "com.creative.fcstudent".equals(app.info.packageName)          || "com.hampoo.hampoointerfacetestdemo".equals(app.info.packageName)){          SystemProperties.set("sys.permission.enable", "true"); // 设置一个系统属性，在Zygote进行判断是否抛出异常          gids[0] = 0;          gids[1] = 0;        } else {          gids[0] = UserHandle.getSharedAppGid(UserHandle.getAppId(uid));          gids[1] = UserHandle.getUserGid(UserHandle.getUserId(uid));        }        // modified by haming patch end.      }      ...... // 此处省略好多行    } catch (RuntimeException e) {      // XXX do better error recovery.      app.setPid(0);      mBatteryStatsService.noteProcessFinish(app.processName, app.info.uid);      if (app.isolated) {        mBatteryStatsService.removeIsolatedUid(app.uid, app.info.uid);      }      Slog.e(TAG, "Failure starting process " + app.processName, e);    }  }

2、ZygoteConnection.java里的applyUidSecurityPolicy(Arguments args, Credentials peer, String peerSecurityContext)接口会对进程id进行判断，如果小于Process.SYSTEM_UID（1000）则认为是非法，而zygote是具有root权限的唯一server，所有在判断之后就可以通过读取前面设定的系统属性“sys.permission.enable”的值来决定是否抛出异常。

ZygoteConnection.java (frameworks\base\core\java\com\android\internal\os)  private static void applyUidSecurityPolicy(Arguments args, Credentials peer,      String peerSecurityContext)      throws ZygoteSecurityException {    int peerUid = peer.getUid();    if (peerUid == 0) {      // Root can do what it wants    } else if (peerUid == Process.SYSTEM_UID ) {      // System UID is restricted, except in factory test mode      String factoryTest = SystemProperties.get("ro.factorytest");      boolean uidRestricted;      /* In normal operation, SYSTEM_UID can only specify a restricted       * set of UIDs. In factory test mode, SYSTEM_UID may specify any uid.       */      uidRestricted         = !(factoryTest.equals("1") || factoryTest.equals("2"));      // modified by haming patch begin, configure system permission for some special application.      if (uidRestricted          && args.uidSpecified && (args.uid < Process.SYSTEM_UID)) {        if (!SystemProperties.getBoolean("sys.permission.enable", false)){          throw new ZygoteSecurityException(              "System UID may not launch process with UID < "              + Process.SYSTEM_UID);        } else {          SystemProperties.set("sys.permission.enable", "false");        }      }      // modified by haming patch end.    } else {      // Everything else      if (args.uidSpecified || args.gidSpecified        || args.gids != null) {        throw new ZygoteSecurityException(            "App UIDs may not specify uid's or gid's");      }    }    ...... // 此处省略好多行  }

总结

以上所述是小编给大家介绍的Android5.1系统通过包名给应用开放系统权限的方法，希望对大家有所帮助，如果大家有任何疑问欢迎给我留言！

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