linux-kernel - Re: [PATCH v2] lockdown: Only log restrictions once

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Message-ID: <2f4a1af8-adc6-4cbc-813f-4cc8e9bc75ae@huaweicloud.com>
Date: Thu, 20 Nov 2025 15:37:56 +0800
From: Xiujianfeng <xiujianfeng@...weicloud.com>
To: Daniel Tang <danielzgtg.opensource@...il.com>,
 Nicolas Bouchinet <nicolas.bouchinet@....cyber.gouv.fr>,
 Xiu Jianfeng <xiujianfeng@...wei.com>, Paul Moore <paul@...l-moore.com>
Cc: linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org,
 Nathan Lynch <nathanl@...ux.ibm.com>, Matthew Garrett <mjg59@...gle.com>,
 Kees Cook <keescook@...omium.org>, David Howells <dhowells@...hat.com>,
 James Morris <jmorris@...ei.org>
Subject: Re: [PATCH v2] lockdown: Only log restrictions once

Hi Daniel,

On 11/20/2025 2:07 AM, Daniel Tang wrote:
> KDE's lockscreen causes systemd-logind to spam dmesg about hibernation.
> systemd declined to cache /sys/power/state due to runtime changeability.
> 
> Link: https://github.com/systemd/systemd/pull/39802
> Signed-off-by: Daniel Tang <danielzgtg.opensource@...il.com>
> ---
>   security/lockdown/lockdown.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
> index cf83afa1d879..83b50de52f21 100644
> --- a/security/lockdown/lockdown.c
> +++ b/security/lockdown/lockdown.c
> @@ -58,13 +58,16 @@ early_param("lockdown", lockdown_param);
>    */
>   static int lockdown_is_locked_down(enum lockdown_reason what)
>   {
> +	static volatile unsigned long lockdown_reasons_seen;
> +	static_assert(ARRAY_SIZE(lockdown_reasons) < sizeof(lockdown_reasons_seen) * 8);
> +
>   	if (WARN(what >= LOCKDOWN_CONFIDENTIALITY_MAX,
>   		 "Invalid lockdown reason"))
>   		return -EPERM;
>   
>   	if (kernel_locked_down >= what) {
> -		if (lockdown_reasons[what])
> -			pr_notice_ratelimited("Lockdown: %s: %s is restricted; see man kernel_lockdown.7\n",
> +		if (lockdown_reasons[what] && !test_and_set_bit(what, &lockdown_reasons_seen))
> +			pr_notice("Lockdown: %s: %s is restricted; see man kernel_lockdown.7\n",
>   				  current->comm, lockdown_reasons[what]);

Currently lockdown does not support the audit function, so I believe the
logs here serve a purpose similar to auditing. Based on this, I think
this change will meaningfully degrade the quality of the logs, making it
hard for users to find out what happens when lockdown is active，
especially after a long time running.

Is it possible to adjust the printk_ratelimit & printk_ratelimit_burst
in /proc/sys/kernel/ to reduce the logs in your scenario?

Anyway, I will wait for Nicolas's comment.
>   		return -EPERM;
>   	}