Remove WARN_ALL_UNSEEDED_RANDOM kernel config option

This config option goes way back - it used to be an internal debug
option to random.c (at that point called DEBUG_RANDOM_BOOT), then was
renamed and exposed as a config option as CONFIG_WARN_UNSEEDED_RANDOM,
and then further renamed to the current CONFIG_WARN_ALL_UNSEEDED_RANDOM.

It was all done with the best of intentions: the more limited
rate-limited reports were reporting some cases, but if you wanted to see
all the gory details, you'd enable this "ALL" option.

However, it turns out - perhaps not surprisingly - that when people
don't care about and fix the first rate-limited cases, they most
certainly don't care about any others either, and so warning about all
of them isn't actually helping anything.

And the non-ratelimited reporting causes problems, where well-meaning
people enable debug options, but the excessive flood of messages that
nobody cares about will hide actual real information when things go
wrong.

I just got a kernel bug report (which had nothing to do with randomness)
where two thirds of the the truncated dmesg was just variations of

   random: get_random_u32 called from __get_random_u32_below+0x10/0x70 with crng_init=0

and in the process early boot messages had been lost (in addition to
making the messages that _hadn't_ been lost harder to read).

The proper way to find these things for the hypothetical developer that
cares - if such a person exists - is almost certainly with boot time
tracing.  That gives you the option to get call graphs etc too, which is
likely a requirement for fixing any problems anyway.

See Documentation/trace/boottime-trace.rst for that option.

And if we for some reason do want to re-introduce actual printing of
these things, it will need to have some uniqueness filtering rather than
this "just print it all" model.

Fixes: cc1e127bfa95 ("random: remove ratelimiting for in-kernel unseeded randomness")
Acked-by: Jason Donenfeld <Jason@zx2c4.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 11 deletions

diff --git a/drivers/char/random.c b/drivers/char/random.c
index dcd002e1b890..7ff4d29911fd 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -96,8 +96,7 @@ static ATOMIC_NOTIFIER_HEAD(random_ready_notifier);
 /* Control how we warn userspace. */
 static struct ratelimit_state urandom_warning =
 	RATELIMIT_STATE_INIT_FLAGS("urandom_warning", HZ, 3, RATELIMIT_MSG_ON_RELEASE);
-static int ratelimit_disable __read_mostly =
-	IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM);
+static int ratelimit_disable __read_mostly = 0;
 module_param_named(ratelimit_disable, ratelimit_disable, int, 0644);
 MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression");
 
@@ -168,12 +167,6 @@ int __cold execute_with_initialized_rng(struct notifier_block *nb)
 	return ret;
 }
 
-#define warn_unseeded_randomness() \
-	if (IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM) && !crng_ready()) \
-		printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n", \
-				__func__, (void *)_RET_IP_, crng_init)
-
-
 /*********************************************************************
  *
  * Fast key erasure RNG, the "crng".
@@ -434,7 +427,6 @@ static void _get_random_bytes(void *buf, size_t len)
  */
 void get_random_bytes(void *buf, size_t len)
 {
-	warn_unseeded_randomness();
 	_get_random_bytes(buf, len);
 }
 EXPORT_SYMBOL(get_random_bytes);
@@ -523,8 +515,6 @@ type get_random_ ##type(void)							\
 	struct batch_ ##type *batch;						\
 	unsigned long next_gen;							\
 										\
-	warn_unseeded_randomness();						\
-										\
 	if  (!crng_ready()) {							\
 		_get_random_bytes(&ret, sizeof(ret));				\
 		return ret;							\