linux-kernel - [PATCH 07/12] random: use the arch-specific rng in xfer_secondary

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Message-Id: <1341614704-24965-8-git-send-email-tytso@mit.edu>
Date:	Fri,  6 Jul 2012 18:44:59 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Linux Kernel Developers List <linux-kernel@...r.kernel.org>
Cc:	ewust@...ch.edu, zakir@...ch.edu, nadiah@...ucsd.edu,
	jhalderm@...ch.edu, Theodore Ts'o <tytso@....edu>,
	stable@...r.kernel.org
Subject: [PATCH 07/12] 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@....edu>
Cc: stable@...r.kernel.org
---
 drivers/char/random.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index e867409..c39bdc4 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -702,11 +702,7 @@ 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 +834,11 @@ 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 +849,22 @@ 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);
 	}
+	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);
 }
 
 /*
-- 
1.7.11.1.108.gb129051

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