1 files changed, 28 insertions, 0 deletions

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 315feb1f59f3..df3358ab5b99 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -125,11 +125,20 @@
  * The current exported interfaces for gathering environmental noise
  * from the devices are:
  *
+ *      void add_device_randomness(const void *buf, unsigned int size);
  *      void add_input_randomness(unsigned int type, unsigned int code,
  *                                unsigned int value);
  *      void add_interrupt_randomness(int irq, int irq_flags);
  *      void add_disk_randomness(struct gendisk *disk);
  *
+ * add_device_randomness() is for adding data to the random pool that
+ * is likely to differ between two devices (or possibly even per boot).
+ * This would be things like MAC addresses or serial numbers, or the
+ * read-out of the RTC. This does *not* add any actual entropy to the
+ * pool, but it initializes the pool to different values for devices
+ * that might otherwise be identical and have very little entropy
+ * available to them (particularly common in the embedded world).
+ *
  * add_input_randomness() uses the input layer interrupt timing, as well as
  * the event type information from the hardware.
  *
@@ -646,6 +655,25 @@ static void set_timer_rand_state(unsigned int irq,
 }
 #endif
 
+/*
+ * Add device- or boot-specific data to the input and nonblocking
+ * pools to help initialize them to unique values.
+ *
+ * None of this adds any entropy, it is meant to avoid the
+ * problem of the nonblocking pool having similar initial state
+ * across largely identical devices.
+ */
+void add_device_randomness(const void *buf, unsigned int size)
+{
+        unsigned long time = get_cycles() ^ jiffies;
+
+        mix_pool_bytes(&input_pool, buf, size, NULL);
+        mix_pool_bytes(&input_pool, &time, sizeof(time), NULL);
+        mix_pool_bytes(&nonblocking_pool, buf, size, NULL);
+        mix_pool_bytes(&nonblocking_pool, &time, sizeof(time), NULL);
+}
+EXPORT_SYMBOL(add_device_randomness);
+
 static struct timer_rand_state input_timer_state;
 
 /*