[PATCH 6.18 418/752] Remove WARN_ALL_UNSEEDED_RANDOM kernel config option

Sasha Levin
2026-02-28T17:53:58Z

From: Linus Torvalds <torvalds@linux-foundation.org>

[ Upstream commit 7dff99b354601dd01829e1511711846e04340a69 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/char/random.c | 12 +-----------
kernel/configs/debug.config | 1 -
lib/Kconfig.debug | 27 ---------------------------
3 files changed, 1 insertion(+), 39 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 4ba5f0c4c8b24..f344f67c83f4e 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; \
diff --git a/kernel/configs/debug.config b/kernel/configs/debug.config
index e81327d2cd639..1d5d8b0396e95 100644
--- a/kernel/configs/debug.config
+++ b/kernel/configs/debug.config
@@ -29,7 +29,6 @@ CONFIG_SECTION_MISMATCH_WARN_ONLY=y
# CONFIG_UBSAN_ALIGNMENT is not set
# CONFIG_UBSAN_DIV_ZERO is not set
# CONFIG_UBSAN_TRAP is not set
-# CONFIG_WARN_ALL_UNSEEDED_RANDOM is not set
CONFIG_DEBUG_FS=y
CONFIG_DEBUG_FS_ALLOW_ALL=y
CONFIG_DEBUG_IRQFLAGS=y
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 713cc94caa02e..88fa610e83840 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1684,33 +1684,6 @@ config STACKTRACE
It is also used by various kernel debugging features that require
stack trace generation.

-config WARN_ALL_UNSEEDED_RANDOM
- bool "Warn for all uses of unseeded randomness"
- default n
- help
- Some parts of the kernel contain bugs relating to their use of
- cryptographically secure random numbers before it's actually possible
- to generate those numbers securely. This setting ensures that these
- flaws don't go unnoticed, by enabling a message, should this ever
- occur. This will allow people with obscure setups to know when things
- are going wrong, so that they might contact developers about fixing
- it.
-
- Unfortunately, on some models of some architectures getting
- a fully seeded CRNG is extremely difficult, and so this can
- result in dmesg getting spammed for a surprisingly long
- time. This is really bad from a security perspective, and
- so architecture maintainers really need to do what they can
- to get the CRNG seeded sooner after the system is booted.
- However, since users cannot do anything actionable to
- address this, by default this option is disabled.
-
- Say Y here if you want to receive warnings for all uses of
- unseeded randomness. This will be of use primarily for
- those developers interested in improving the security of
- Linux kernels running on their architecture (or
- subarchitecture).
-
config DEBUG_KOBJECT
bool "kobject debugging"
depends on DEBUG_KERNEL
--
2.51.0