[PATCH] ima: add a knob ima= to make IMA be able to be disabled

[Baoquan He]

CC kexec list.

On 05/16/25 at 07:39am, Baoquan He wrote:
> Kdump kernel doesn't need IMA functionality, and enabling IMA will cost
> extra memory. It would be very helpful to allow IMA to be disabled for
> kdump kernel.
> 
> And Coiby also mentioned that for kdump kernel incorrect ima-policy loaded
> by systemd could cause kdump kernel hang, and it's possible the booting
> process may be stopped by a strict, albeit syntax-correct policy and users
> can't log into the system to fix the policy. In these cases, allowing to
> disable IMA is very helpful too for kdump kernel.
> 
> Hence add a knob ima=on|off here to allow people to disable IMA in kdump
> kenrel if needed.
> 
> Signed-off-by: Baoquan He <bhe at redhat.com>
> ---
>  .../admin-guide/kernel-parameters.txt         |  5 +++++
>  security/integrity/ima/ima_main.c             | 22 +++++++++++++++++++
>  2 files changed, 27 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index d9fd26b95b34..762fb6ddcc24 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2202,6 +2202,11 @@
>  			different crypto accelerators. This option can be used
>  			to achieve best performance for particular HW.
>  
> +	ima=		[IMA] Enable or disable IMA
> +			Format: { "off" | "on" }
> +			Default: "on"
> +			Note that this is only useful for kdump kernel.
> +
>  	init=		[KNL]
>  			Format: <full_path>
>  			Run specified binary instead of /sbin/init as init
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index f3e7ac513db3..07af5c6af138 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -27,6 +27,7 @@
>  #include <linux/fs.h>
>  #include <linux/iversion.h>
>  #include <linux/evm.h>
> +#include <linux/crash_dump.h>
>  
>  #include "ima.h"
>  
> @@ -38,11 +39,27 @@ int ima_appraise;
>  
>  int __ro_after_init ima_hash_algo = HASH_ALGO_SHA1;
>  static int hash_setup_done;
> +static int ima_disabled;
>  
>  static struct notifier_block ima_lsm_policy_notifier = {
>  	.notifier_call = ima_lsm_policy_change,
>  };
>  
> +static int __init ima_setup(char *str)
> +{
> +	if (strncmp(str, "off", 3) == 0)
> +		ima_disabled = 1;
> +	else if (strncmp(str, "on", 2) == 0)
> +		ima_disabled = 0;
> +	else
> +		pr_err("Invalid ima setup option: \"%s\" , please specify ima=on|off.", str);
> +
> +	return 1;
> +}
> +__setup("ima=", ima_setup);
> +
> +
> +
>  static int __init hash_setup(char *str)
>  {
>  	struct ima_template_desc *template_desc = ima_template_desc_current();
> @@ -1184,6 +1201,11 @@ static int __init init_ima(void)
>  {
>  	int error;
>  
> +	if (ima_disabled && is_kdump_kernel()) {
> +		pr_info("IMA functionality is disabled");
> +		return 0;
> +	}
> +
>  	ima_appraise_parse_cmdline();
>  	ima_init_template_list();
>  	hash_setup(CONFIG_IMA_DEFAULT_HASH);
> -- 
> 2.41.0
>