random: use the arch-specific rng in xfer_secondary_pool

If the CPU supports a hardware random number generator, use it in
xfer_secondary_pool(), where it will significantly improve things and
where we can afford it.

Also, remove the use of the arch-specific rng in
add_timer_randomness(), since the call is significantly slower than
get_cycles(), and we're much better off using it in
xfer_secondary_pool() anyway.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org

drivers/char/random.c

@@ -254,6 +254,7 @@
 #include <linux/cryptohash.h>
 #include <linux/fips.h>
 #include <linux/ptrace.h>
+#include <linux/kmemcheck.h>
 
 #ifdef CONFIG_GENERIC_HARDIRQS
 # include <linux/irq.h>
@@ -702,11 +703,7 @@ static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
 		goto out;
 
 	sample.jiffies = jiffies;
-
-	/* Use arch random value, fall back to cycles */
-	if (!arch_get_random_int(&sample.cycles))
-		sample.cycles = get_cycles();
-
+	sample.cycles = get_cycles();
 	sample.num = num;
 	mix_pool_bytes(&input_pool, &sample, sizeof(sample), NULL);
 
@@ -838,7 +835,11 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf,
  */
 static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
 {
-	__u32 tmp[OUTPUT_POOL_WORDS];
+	union {
+		__u32	tmp[OUTPUT_POOL_WORDS];
+		long	hwrand[4];
+	} u;
+	int	i;
 
 	if (r->pull && r->entropy_count < nbytes * 8 &&
 	    r->entropy_count < r->poolinfo->POOLBITS) {
@@ -849,17 +850,23 @@ static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
 		/* pull at least as many as BYTES as wakeup BITS */
 		bytes = max_t(int, bytes, random_read_wakeup_thresh / 8);
 		/* but never more than the buffer size */
-		bytes = min_t(int, bytes, sizeof(tmp));
+		bytes = min_t(int, bytes, sizeof(u.tmp));
 
 		DEBUG_ENT("going to reseed %s with %d bits "
 			  "(%d of %d requested)\n",
 			  r->name, bytes * 8, nbytes * 8, r->entropy_count);
 
-		bytes = extract_entropy(r->pull, tmp, bytes,
+		bytes = extract_entropy(r->pull, u.tmp, bytes,
 					random_read_wakeup_thresh / 8, rsvd);
-		mix_pool_bytes(r, tmp, bytes, NULL);
+		mix_pool_bytes(r, u.tmp, bytes, NULL);
 		credit_entropy_bits(r, bytes*8);
 	}
+	kmemcheck_mark_initialized(&u.hwrand, sizeof(u.hwrand));
+	for (i = 0; i < 4; i++)
+		if (arch_get_random_long(&u.hwrand[i]))
+			break;
+	if (i)
+		mix_pool_bytes(r, &u.hwrand, sizeof(u.hwrand), 0);
 }
 
 /*