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！