[PATCH] lib: random: add CONFIG_INSECURE logging of seeds

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

clocksource_srand() can be called after events that take a varying
amount of time to extract some entropy. To get an idea about how much
entropy we are getting out, add a CONFIG_INSECURE-guarded debug print
that prints the seeds out as-is.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 lib/random.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/lib/random.c b/lib/random.c
index 889d314e0fad..632f361c4627 100644
--- a/lib/random.c
+++ b/lib/random.c
@@ -11,6 +11,8 @@
  *     CONFIG_ALLOW_PRNG_FALLBACK set, which will emit a warning at runtime.
  */
 
+#define pr_fmt(fmt) "random: " fmt
+
 #include <common.h>
 #include <stdlib.h>
 #include <linux/hw_random.h>
@@ -75,6 +77,12 @@ void randbuf_r(u64 *x, void *buf, size_t len)
  */
 void srand_xor(u64 entropy)
 {
+	/* The PRNG shouldn't be used for crypto anyway, but still let's not
+	 * divulge the whole state in secure configurations.
+	 */
+	if (IS_ENABLED(CONFIG_INSECURE))
+		pr_debug("PRNG seeded with %llu\n", entropy);
+
 	prng_state ^= entropy;
 	/* Ensure prng_state is never zero */
 	prng_state += !prng_state;
-- 
2.39.5