Implement native method getEncryptedStoragePath()

AVmPayload_getEncryptedStoragePath will return path to encrypted storage
if present, otherwise it will return NULL pointer.

The existence of ENCRYPTEDSTORE_MOUNTPOINT path is sufficient to
determine this. This is because Microdroid manager passes this path as
the mountpoint to encryptedstore & waits for it before starting
vm_payload_service.

Bug: 254454578
Test: build succeeds
Change-Id: Ifdfe1b97f08fc2e3f84ba1e49e6ca3e25e0013fc
diff --git a/microdroid_manager/aidl/android/system/virtualization/payload/IVmPayloadService.aidl b/microdroid_manager/aidl/android/system/virtualization/payload/IVmPayloadService.aidl
index f8e7d34..3859785 100644
--- a/microdroid_manager/aidl/android/system/virtualization/payload/IVmPayloadService.aidl
+++ b/microdroid_manager/aidl/android/system/virtualization/payload/IVmPayloadService.aidl
@@ -27,6 +27,12 @@
     /** Path to the APK contents path. */
     const String VM_APK_CONTENTS_PATH = "/mnt/apk";
 
+    /**
+     * Path to the encrypted storage. Note the path will not exist if encrypted storage
+     * is not enabled.
+     */
+    const String ENCRYPTEDSTORE_MOUNTPOINT = "/mnt/encryptedstore";
+
     /** Notifies that the payload is ready to serve. */
     void notifyPayloadReady();
 
diff --git a/microdroid_manager/src/main.rs b/microdroid_manager/src/main.rs
index 4648a4e..0e45461 100644
--- a/microdroid_manager/src/main.rs
+++ b/microdroid_manager/src/main.rs
@@ -29,6 +29,7 @@
 use android_system_virtualization_payload::aidl::android::system::virtualization::payload::IVmPayloadService::{
     VM_APK_CONTENTS_PATH,
     VM_PAYLOAD_SERVICE_SOCKET_NAME,
+    ENCRYPTEDSTORE_MOUNTPOINT,
 };
 use anyhow::{anyhow, bail, ensure, Context, Error, Result};
 use apkverify::{get_public_key_der, verify, V4Signature};
@@ -86,7 +87,6 @@
 const ENCRYPTEDSTORE_BIN: &str = "/system/bin/encryptedstore";
 const ENCRYPTEDSTORE_KEY_IDENTIFIER: &str = "encryptedstore_key";
 const ENCRYPTEDSTORE_KEYSIZE: u32 = 32;
-const ENCRYPTEDSTORE_MOUNTPOINT: &str = "/mnt/encryptedstore";
 
 #[derive(thiserror::Error, Debug)]
 enum MicrodroidError {
@@ -433,6 +433,9 @@
 
     register_vm_payload_service(allow_restricted_apis, service.clone(), dice_context)?;
 
+    // Wait for encryptedstore to finish mounting the storage (if enabled) before setting
+    // microdroid_manager.init_done. Reason is init stops uneventd after that.
+    // Encryptedstore, however requires ueventd
     if let Some(mut child) = encryptedstore_child {
         let exitcode = child.wait().context("Wait for encryptedstore child")?;
         ensure!(exitcode.success(), "Unable to prepare encrypted storage. Exitcode={}", exitcode);
diff --git a/vm_payload/src/api.rs b/vm_payload/src/api.rs
index a79c0bb..28b440e 100644
--- a/vm_payload/src/api.rs
+++ b/vm_payload/src/api.rs
@@ -18,7 +18,7 @@
 #![warn(unsafe_op_in_unsafe_fn)]
 
 use android_system_virtualization_payload::aidl::android::system::virtualization::payload::IVmPayloadService::{
-    IVmPayloadService, VM_PAYLOAD_SERVICE_SOCKET_NAME, VM_APK_CONTENTS_PATH};
+    ENCRYPTEDSTORE_MOUNTPOINT, IVmPayloadService, VM_PAYLOAD_SERVICE_SOCKET_NAME, VM_APK_CONTENTS_PATH};
 use anyhow::{ensure, bail, Context, Result};
 use binder::{Strong, unstable_api::{AIBinder, new_spibinder}};
 use lazy_static::lazy_static;
@@ -28,6 +28,7 @@
 use std::ffi::CString;
 use std::fmt::Debug;
 use std::os::raw::{c_char, c_void};
+use std::path::Path;
 use std::ptr;
 use std::sync::{Mutex, atomic::{AtomicBool, Ordering}};
 
@@ -35,6 +36,8 @@
     static ref VM_APK_CONTENTS_PATH_C: CString =
         CString::new(VM_APK_CONTENTS_PATH).expect("CString::new failed");
     static ref PAYLOAD_CONNECTION: Mutex<Option<Strong<dyn IVmPayloadService>>> = Mutex::default();
+    static ref VM_ENCRYPTED_STORAGE_PATH_C: CString =
+        CString::new(ENCRYPTEDSTORE_MOUNTPOINT).expect("CString::new failed");
 }
 
 static ALREADY_NOTIFIED: AtomicBool = AtomicBool::new(false);
@@ -249,12 +252,15 @@
 /// Gets the path to the APK contents.
 #[no_mangle]
 pub extern "C" fn AVmPayload_getApkContentsPath() -> *const c_char {
-    (*VM_APK_CONTENTS_PATH_C).as_ptr()
+    VM_APK_CONTENTS_PATH_C.as_ptr()
 }
 
 /// Gets the path to the VM's encrypted storage.
 #[no_mangle]
 pub extern "C" fn AVmPayload_getEncryptedStoragePath() -> *const c_char {
-    // TODO(b/254454578): Return a real path if storage is present
-    ptr::null()
+    if Path::new(ENCRYPTEDSTORE_MOUNTPOINT).exists() {
+        VM_ENCRYPTED_STORAGE_PATH_C.as_ptr()
+    } else {
+        ptr::null()
+    }
 }