random: Add optional continuous repetition test to entropy store based rngs

FIPS-140 requires that all random number generators implement continuous self
tests in which each extracted block of data is compared against the last block
for repetition. The ansi_cprng implements such a test, but it would be nice if
the hw rng's did the same thing. Obviously its not something thats always
needed, but it seems like it would be a nice feature to have on occasion. I've
written the below patch which allows individual entropy stores to be flagged as
desiring a continuous test to be run on them as is extracted. By default this
option is off, but is enabled in the event that fips mode is selected during
bootup.

Signed-off-by: Neil Horman <[e-mail]>
Acked-by: Matt Mackall <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

crypto/internal.h

···
 #include <linux/notifier.h>
 #include <linux/rwsem.h>
 #include <linux/slab.h>
-
-#ifdef CONFIG_CRYPTO_FIPS
-extern int fips_enabled;
-#else
-#define fips_enabled 0
-#endif
+#include <linux/fips.h>
 
 /* Crypto notification events. */
 enum {

drivers/char/random.c

···
 #include <linux/spinlock.h>
 #include <linux/percpu.h>
 #include <linux/cryptohash.h>
+#include <linux/fips.h>
 
 #ifdef CONFIG_GENERIC_HARDIRQS
 # include <linux/irq.h>
···
 	unsigned add_ptr;
 	int entropy_count;
 	int input_rotate;
+	__u8 *last_data;
 };
 
 static __u32 input_pool_data[INPUT_POOL_WORDS];
···
 {
 	ssize_t ret = 0, i;
 	__u8 tmp[EXTRACT_SIZE];
+	unsigned long flags;
 
 	xfer_secondary_pool(r, nbytes);
 	nbytes = account(r, nbytes, min, reserved);
 
 	while (nbytes) {
 		extract_buf(r, tmp);
+
+		if (r->last_data) {
+			spin_lock_irqsave(&r->lock, flags);
+			if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
+				panic("Hardware RNG duplicated output!\n");
+			memcpy(r->last_data, tmp, EXTRACT_SIZE);
+			spin_unlock_irqrestore(&r->lock, flags);
+		}
 		i = min_t(int, nbytes, EXTRACT_SIZE);
 		memcpy(buf, tmp, i);
 		nbytes -= i;
···
 	now = ktime_get_real();
 	mix_pool_bytes(r, &now, sizeof(now));
 	mix_pool_bytes(r, utsname(), sizeof(*(utsname())));
+	/* Enable continuous test in fips mode */
+	if (fips_enabled)
+		r->last_data = kmalloc(EXTRACT_SIZE, GFP_KERNEL);
 }
 
 static int rand_initialize(void)

include/linux/fips.h

···
+#ifndef _FIPS_H
+#define _FIPS_H
+
+#ifdef CONFIG_CRYPTO_FIPS
+extern int fips_enabled;
+#else
+#define fips_enabled 0
+#endif
+
+#endif