Fix some minor issues with fixed load address in chromium linker.

- Fix address space leak in modern linker. If wanted address can no
longer be mapped at (which is possible), linker falls back to usual aslr
loading without sharing relro's. There was a missing call to munmap, so
that this chunk of 192MB remained dangling. Legacy linker handles this
correctly, see InternalElfLoader::ReserveAddressSpace at crazy_linker
lib.

- Fix needless call to GetRandomBaseLoadAddress in child processes.
Method ensureInitializedLocked uses mInBrowserProcess to determine if it
needs to generate an address for library loading. mInBrowserProcess is
initialized with 'true', so we had a useless mmap of 192MB in every
child process.

Change-Id: I918e9a35bf5179a79a3676e4a50f3c6e7677933c
Bug: 1108740
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2315019Reviewed-by: Benoit L <lizeb@chromium.org>
Commit-Queue: Benoit L <lizeb@chromium.org>
Auto-Submit: Igor Eremeev <myrth@yandex-team.ru>
Cr-Commit-Position: refs/heads/master@{#791213}

base/android/java/src/org/chromium/base/library_loader/Linker.java

@@ -256,9 +256,9 @@ public abstract class Linker {
     public final void disableSharedRelros() {
         if (DEBUG) Log.i(TAG, "disableSharedRelros() called");
         synchronized (sLock) {
+            mInBrowserProcess = false;
             ensureInitializedLocked();
             assert mState == State.INITIALIZED; // Not after the library has been loaded.
-            mInBrowserProcess = false;
             mWaitForSharedRelros = false;
         }
     }
@@ -358,10 +358,11 @@ public abstract class Linker {
     public final void initServiceProcess(long baseLoadAddress) {
         if (DEBUG) Log.i(TAG, "initServiceProcess(0x%x) called", baseLoadAddress);
         synchronized (sLock) {
+            mInBrowserProcess = false;
+
             ensureInitializedLocked();
             assert mState == State.INITIALIZED;
 
-            mInBrowserProcess = false;
             mWaitForSharedRelros = true;
             mBaseLoadAddress = baseLoadAddress;
         }

base/android/linker/modern_linker_jni.cc

@@ -116,6 +116,7 @@ ScopedAnonymousMmap ScopedAnonymousMmap::ReserveAtAddress(void* address,
 
   if (actual_address && actual_address != address) {
     LOG_ERROR("Failed to obtain fixed address for load");
+    munmap(actual_address, size);
     return {};
   }