am a9bce468: am 84742149: Merge "Make EntropyMixer mix in output of Hardware RNG into Linux RNG."
* commit 'a9bce46876d6f1f82727ab6922748fcc6b43c767':
Make EntropyMixer mix in output of Hardware RNG into Linux RNG.
diff --git a/services/java/com/android/server/EntropyMixer.java b/services/java/com/android/server/EntropyMixer.java
index fbb66f9..cfdbf7d 100644
--- a/services/java/com/android/server/EntropyMixer.java
+++ b/services/java/com/android/server/EntropyMixer.java
@@ -36,7 +36,8 @@
/**
* A service designed to load and periodically save "randomness"
- * for the Linux kernel.
+ * for the Linux kernel RNG and to mix in data from Hardware RNG (if present)
+ * into the Linux RNG.
*
* <p>When a Linux system starts up, the entropy pool associated with
* {@code /dev/random} may be in a fairly predictable state. Applications which
@@ -45,6 +46,13 @@
* this effect, it's helpful to carry the entropy pool information across
* shutdowns and startups.
*
+ * <p>On systems with Hardware RNG (/dev/hw_random), a block of output from HW
+ * RNG is mixed into the Linux RNG on EntropyMixer's startup and whenever
+ * EntropyMixer periodically runs to save a block of output from Linux RNG on
+ * disk. This mixing is done in a way that does not increase the Linux RNG's
+ * entropy estimate is not increased. This is to avoid having to trust/verify
+ * the quality and authenticity of the "randomness" of the HW RNG.
+ *
* <p>This class was modeled after the script in
* <a href="http://www.kernel.org/doc/man-pages/online/pages/man4/random.4.html">man
* 4 random</a>.
@@ -57,6 +65,7 @@
private static final long START_NANOTIME = System.nanoTime();
private final String randomDevice;
+ private final String hwRandomDevice;
private final String entropyFile;
/**
@@ -69,6 +78,7 @@
Slog.e(TAG, "Will not process invalid message");
return;
}
+ addHwRandomEntropy();
writeEntropy();
scheduleEntropyWriter();
}
@@ -82,18 +92,25 @@
};
public EntropyMixer(Context context) {
- this(context, getSystemDir() + "/entropy.dat", "/dev/urandom");
+ this(context, getSystemDir() + "/entropy.dat", "/dev/urandom", "/dev/hw_random");
}
/** Test only interface, not for public use */
- public EntropyMixer(Context context, String entropyFile, String randomDevice) {
+ public EntropyMixer(
+ Context context,
+ String entropyFile,
+ String randomDevice,
+ String hwRandomDevice) {
if (randomDevice == null) { throw new NullPointerException("randomDevice"); }
+ if (hwRandomDevice == null) { throw new NullPointerException("hwRandomDevice"); }
if (entropyFile == null) { throw new NullPointerException("entropyFile"); }
this.randomDevice = randomDevice;
+ this.hwRandomDevice = hwRandomDevice;
this.entropyFile = entropyFile;
loadInitialEntropy();
addDeviceSpecificEntropy();
+ addHwRandomEntropy();
writeEntropy();
scheduleEntropyWriter();
IntentFilter broadcastFilter = new IntentFilter(Intent.ACTION_SHUTDOWN);
@@ -168,6 +185,20 @@
}
}
+ /**
+ * Mixes in the output from HW RNG (if present) into the Linux RNG.
+ */
+ private void addHwRandomEntropy() {
+ try {
+ RandomBlock.fromFile(hwRandomDevice).toFile(randomDevice, false);
+ Slog.i(TAG, "Added HW RNG output to entropy pool");
+ } catch (FileNotFoundException ignored) {
+ // HW RNG not present/exposed -- ignore
+ } catch (IOException e) {
+ Slog.w(TAG, "Failed to add HW RNG output to entropy pool", e);
+ }
+ }
+
private static String getSystemDir() {
File dataDir = Environment.getDataDirectory();
File systemDir = new File(dataDir, "system");
diff --git a/services/tests/servicestests/src/com/android/server/EntropyMixerTest.java b/services/tests/servicestests/src/com/android/server/EntropyMixerTest.java
index 58d6dae..50e7a03 100644
--- a/services/tests/servicestests/src/com/android/server/EntropyMixerTest.java
+++ b/services/tests/servicestests/src/com/android/server/EntropyMixerTest.java
@@ -34,7 +34,7 @@
assertEquals(0, FileUtils.readTextFile(file, 0, null).length());
// The constructor has the side effect of writing to file
- new EntropyMixer(getContext(), "/dev/null", file.getCanonicalPath());
+ new EntropyMixer(getContext(), "/dev/null", file.getCanonicalPath(), "/dev/null");
assertTrue(FileUtils.readTextFile(file, 0, null).length() > 0);
}