1 files changed, 61 insertions, 1 deletions

diff --git a/drivers/char/random.c b/drivers/char/random.c
index d3beed084c0a..c2f7de9dc543 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1732,6 +1732,56 @@ void get_random_bytes(void *buf, int nbytes)
 }
 EXPORT_SYMBOL(get_random_bytes);
 
+
+/*
+ * Each time the timer fires, we expect that we got an unpredictable
+ * jump in the cycle counter. Even if the timer is running on another
+ * CPU, the timer activity will be touching the stack of the CPU that is
+ * generating entropy..
+ *
+ * Note that we don't re-arm the timer in the timer itself - we are
+ * happy to be scheduled away, since that just makes the load more
+ * complex, but we do not want the timer to keep ticking unless the
+ * entropy loop is running.
+ *
+ * So the re-arming always happens in the entropy loop itself.
+ */
+static void entropy_timer(struct timer_list *t)
+{
+	credit_entropy_bits(&input_pool, 1);
+}
+
+/*
+ * If we have an actual cycle counter, see if we can
+ * generate enough entropy with timing noise
+ */
+static void try_to_generate_entropy(void)
+{
+	struct {
+		unsigned long now;
+		struct timer_list timer;
+	} stack;
+
+	stack.now = random_get_entropy();
+
+	/* Slow counter - or none. Don't even bother */
+	if (stack.now == random_get_entropy())
+		return;
+
+	timer_setup_on_stack(&stack.timer, entropy_timer, 0);
+	while (!crng_ready()) {
+		if (!timer_pending(&stack.timer))
+			mod_timer(&stack.timer, jiffies+1);
+		mix_pool_bytes(&input_pool, &stack.now, sizeof(stack.now));
+		schedule();
+		stack.now = random_get_entropy();
+	}
+
+	del_timer_sync(&stack.timer);
+	destroy_timer_on_stack(&stack.timer);
+	mix_pool_bytes(&input_pool, &stack.now, sizeof(stack.now));
+}
+
 /*
  * Wait for the urandom pool to be seeded and thus guaranteed to supply
  * cryptographically secure random numbers. This applies to: the /dev/urandom
@@ -1746,7 +1796,17 @@ int wait_for_random_bytes(void)
 {
 	if (likely(crng_ready()))
 		return 0;
-	return wait_event_interruptible(crng_init_wait, crng_ready());
+
+	do {
+		int ret;
+		ret = wait_event_interruptible_timeout(crng_init_wait, crng_ready(), HZ);
+		if (ret)
+			return ret > 0 ? 0 : ret;
+
+		try_to_generate_entropy();
+	} while (!crng_ready());
+
+	return 0;
 }
 EXPORT_SYMBOL(wait_for_random_bytes);