From: H. Peter Anvin <hpa@linux.intel.com>
Date: Mon, 17 Mar 2014 23:36:29 +0000 (-0700)
Subject: random: If we have arch_get_random_seed*(), try it before blocking
X-Git-Tag: firefly_0821_release~176^2~4142^2~1
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=331c6490c7f10dcf263712e313b7c0bc7fb6d77a;p=firefly-linux-kernel-4.4.55.git

random: If we have arch_get_random_seed*(), try it before blocking

If we have arch_get_random_seed*(), try to use it for emergency refill
of the entropy pool before giving up and blocking on /dev/random.  It
may or may not work in the moment, but if it does work, it will give
the user better service than blocking will.

Reviewed-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---

diff --git a/drivers/char/random.c b/drivers/char/random.c
index a4bea7775e0f..c35cee268e13 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1294,6 +1294,34 @@ void rand_initialize_disk(struct gendisk *disk)
 }
 #endif
 
+/*
+ * Attempt an emergency refill using arch_get_random_seed_long().
+ *
+ * As with add_interrupt_randomness() be paranoid and only
+ * credit the output as 50% entropic.
+ */
+static int arch_random_refill(void)
+{
+	const unsigned int nlongs = 64;	/* Arbitrary number */
+	unsigned int n = 0;
+	unsigned int i;
+	unsigned long buf[nlongs];
+
+	for (i = 0; i < nlongs; i++) {
+		if (arch_get_random_seed_long(&buf[n]))
+			n++;
+	}
+
+	if (n) {
+		unsigned int rand_bytes = n * sizeof(unsigned long);
+
+		mix_pool_bytes(&input_pool, buf, rand_bytes, NULL);
+		credit_entropy_bits(&input_pool, rand_bytes*4);
+	}
+
+	return n;
+}
+
 static ssize_t
 random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 {
@@ -1312,8 +1340,13 @@ random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 				  ENTROPY_BITS(&input_pool));
 		if (n > 0)
 			return n;
+
 		/* Pool is (near) empty.  Maybe wait and retry. */
 
+		/* First try an emergency refill */
+		if (arch_random_refill())
+			continue;
+
 		if (file->f_flags & O_NONBLOCK)
 			return -EAGAIN;