From 5744a0927df22f46e4b7f134b3dfb405fdfcf6ce Mon Sep 17 00:00:00 2001
From: Jeremy Cline <jeremy@jcline.org>
Date: Wed, 2 May 2018 15:16:29 -0400
Subject: [PATCH 1/2] Revert "random: use a different mixing algorithm for
 add_device_randomness()"

This reverts commit 89b59f050347d376c2ace8b1ceb908a218cfdc2e.

Signed-off-by: Jeremy Cline <jeremy@jcline.org>
---
 drivers/char/random.c | 55 ++++---------------------------------------
 1 file changed, 4 insertions(+), 51 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 8f4e11842c60..aa5b04af86c6 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -831,10 +831,6 @@ static void numa_crng_init(void)
 static void numa_crng_init(void) {}
 #endif
 
-/*
- * crng_fast_load() can be called by code in the interrupt service
- * path.  So we can't afford to dilly-dally.
- */
 static int crng_fast_load(const char *cp, size_t len)
 {
 	unsigned long flags;
@@ -861,51 +857,6 @@ static int crng_fast_load(const char *cp, size_t len)
 	return 1;
 }
 
-/*
- * crng_slow_load() is called by add_device_randomness, which has two
- * attributes.  (1) We can't trust the buffer passed to it is
- * guaranteed to be unpredictable (so it might not have any entropy at
- * all), and (2) it doesn't have the performance constraints of
- * crng_fast_load().
- *
- * So we do something more comprehensive which is guaranteed to touch
- * all of the primary_crng's state, and which uses a LFSR with a
- * period of 255 as part of the mixing algorithm.  Finally, we do
- * *not* advance crng_init_cnt since buffer we may get may be something
- * like a fixed DMI table (for example), which might very well be
- * unique to the machine, but is otherwise unvarying.
- */
-static int crng_slow_load(const char *cp, size_t len)
-{
-	unsigned long		flags;
-	static unsigned char	lfsr = 1;
-	unsigned char		tmp;
-	unsigned		i, max = CHACHA20_KEY_SIZE;
-	const char *		src_buf = cp;
-	char *			dest_buf = (char *) &primary_crng.state[4];
-
-	if (!spin_trylock_irqsave(&primary_crng.lock, flags))
-		return 0;
-	if (crng_init != 0) {
-		spin_unlock_irqrestore(&primary_crng.lock, flags);
-		return 0;
-	}
-	if (len > max)
-		max = len;
-
-	for (i = 0; i < max ; i++) {
-		tmp = lfsr;
-		lfsr >>= 1;
-		if (tmp & 1)
-			lfsr ^= 0xE1;
-		tmp = dest_buf[i % CHACHA20_KEY_SIZE];
-		dest_buf[i % CHACHA20_KEY_SIZE] ^= src_buf[i % len] ^ lfsr;
-		lfsr += (tmp << 3) | (tmp >> 5);
-	}
-	spin_unlock_irqrestore(&primary_crng.lock, flags);
-	return 1;
-}
-
 static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
 {
 	unsigned long	flags;
@@ -1089,8 +1040,10 @@ void add_device_randomness(const void *buf, unsigned int size)
 	unsigned long time = random_get_entropy() ^ jiffies;
 	unsigned long flags;
 
-	if (!crng_ready() && size)
-		crng_slow_load(buf, size);
+	if (!crng_ready()) {
+		crng_fast_load(buf, size);
+		return;
+	}
 
 	trace_add_device_randomness(size, _RET_IP_);
 	spin_lock_irqsave(&input_pool.lock, flags);
-- 
2.17.0

From e1b1b5b62740b0e6ea8258a4eb81b2a336538fed Mon Sep 17 00:00:00 2001
From: Jeremy Cline <jeremy@jcline.org>
Date: Wed, 2 May 2018 15:18:03 -0400
Subject: [PATCH 2/2] Revert "random: fix crng_ready() test"

This reverts commit cd8d7a5778a4abf76ee8fe8f1bfcf78976029f8d.

Signed-off-by: Jeremy Cline <jeremy@jcline.org>
---
 drivers/char/random.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index aa5b04af86c6..ef05cc685b74 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -428,7 +428,7 @@ struct crng_state primary_crng = {
  * its value (from 0->1->2).
  */
 static int crng_init = 0;
-#define crng_ready() (likely(crng_init > 1))
+#define crng_ready() (likely(crng_init > 0))
 static int crng_init_cnt = 0;
 static unsigned long crng_global_init_time = 0;
 #define CRNG_INIT_CNT_THRESH (2*CHACHA20_KEY_SIZE)
@@ -838,7 +838,7 @@ static int crng_fast_load(const char *cp, size_t len)
 
 	if (!spin_trylock_irqsave(&primary_crng.lock, flags))
 		return 0;
-	if (crng_init != 0) {
+	if (crng_ready()) {
 		spin_unlock_irqrestore(&primary_crng.lock, flags);
 		return 0;
 	}
@@ -913,7 +913,7 @@ static void _extract_crng(struct crng_state *crng,
 {
 	unsigned long v, flags;
 
-	if (crng_ready() &&
+	if (crng_init > 1 &&
 	    (time_after(crng_global_init_time, crng->init_time) ||
 	     time_after(jiffies, crng->init_time + CRNG_RESEED_INTERVAL)))
 		crng_reseed(crng, crng == &primary_crng ? &input_pool : NULL);
@@ -1200,7 +1200,7 @@ void add_interrupt_randomness(int irq, int irq_flags)
 	fast_mix(fast_pool);
 	add_interrupt_bench(cycles);
 
-	if (unlikely(crng_init == 0)) {
+	if (!crng_ready()) {
 		if ((fast_pool->count >= 64) &&
 		    crng_fast_load((char *) fast_pool->pool,
 				   sizeof(fast_pool->pool))) {
@@ -2269,7 +2269,7 @@ void add_hwgenerator_randomness(const char *buffer, size_t count,
 {
 	struct entropy_store *poolp = &input_pool;
 
-	if (unlikely(crng_init == 0)) {
+	if (!crng_ready()) {
 		crng_fast_load(buffer, count);
 		return;
 	}
-- 
2.17.0