Don't create vendor_init in microdroid

vendor_init is a subcontext of init which is responsible for handling
the vendor-defined services and vendor-defined actions. This is mainly
to enforce the Treble architecture in which the vendor components are
provided with a less-privileged context than the system components
because they are less-trusted.

However, in case of microdroid, both the system and the vendor
partitions are from the same entity. As VMs don't have direct access to
any of the underlying hardware, the vendor partition is targeting the
virtual platform, not the real hw platform. There really is no need for
the discrimination.

This CL disables the creation of the vendor_init subcontext when init
runs in microdroid.

Bug: 201363575
Test: atest MicrodroidHostTestCases
Change-Id: Ie5e47d84e9e245565239b4f2159e8182b457699d

init/mount_namespace.cpp

@@ -82,11 +82,6 @@ static bool IsApexUpdatable() {
     return updatable;
 }
 
-static bool IsMicrodroid() {
-    static bool is_microdroid = android::base::GetProperty("ro.hardware", "") == "microdroid";
-    return is_microdroid;
-}
-
 // In case we have two sets of APEXes (non-updatable, updatable), we need two separate mount
 // namespaces.
 static bool NeedsTwoMountNamespaces() {

init/subcontext.cpp

@@ -44,6 +44,7 @@
 #endif
 
 using android::base::GetExecutablePath;
+using android::base::GetProperty;
 using android::base::Join;
 using android::base::Socketpair;
 using android::base::Split;
@@ -337,6 +338,11 @@ Result<std::vector<std::string>> Subcontext::ExpandArgs(const std::vector<std::s
 }
 
 void InitializeSubcontext() {
+    if (IsMicrodroid()) {
+        LOG(INFO) << "Not using subcontext for microdroid";
+        return;
+    }
+
     if (SelinuxGetVendorAndroidVersion() >= __ANDROID_API_P__) {
         subcontext.reset(
                 new Subcontext(std::vector<std::string>{"/vendor", "/odm"}, kVendorContext));

init/util.cpp

@@ -757,5 +757,10 @@ void SetDefaultMountNamespaceReady() {
     is_default_mount_namespace_ready = true;
 }
 
+bool IsMicrodroid() {
+    static bool is_microdroid = android::base::GetProperty("ro.hardware", "") == "microdroid";
+    return is_microdroid;
+}
+
 }  // namespace init
 }  // namespace android

init/util.h

@@ -103,5 +103,7 @@ bool IsRecoveryMode();
 
 bool IsDefaultMountNamespaceReady();
 void SetDefaultMountNamespaceReady();
+
+bool IsMicrodroid();
 }  // namespace init
 }  // namespace android