linux-kernel - Re: [PATCH v2] ima: add a knob ima= to make IMA be able to be disabled

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Message-ID: <c1ad06ef84170633bdcc7f49b06d646ddbbdc763.camel@linux.ibm.com>
Date: Thu, 12 Jun 2025 06:59:44 -0400
From: Mimi Zohar <zohar@...ux.ibm.com>
To: Baoquan He <bhe@...hat.com>, linux-integrity@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, coxu@...hat.com, piliu@...hat.com,
        pmenzel@...gen.mpg.de, chenste@...ux.microsoft.com
Subject: Re: [PATCH v2] ima: add a knob ima= to make IMA be able to be
 disabled

Hi Baoquan,

As discussed
https://lore.kernel.org/linux-integrity/aC6ezNcUZ%2FulKgpv@MiWiFi-R3L-srv/ the
Subject line should indicate disabling IMA is limited to kdump.

On Wed, 2025-06-11 at 16:25 +0800, 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.
> 
> Hence add a knob ima=on|off here to allow turning IMA off in kdump
> kernel if needed.
> 
> Note that this IMA disabling is only limited to kdump kernel, please don't
> abuse it in other kernel and thus serious consequences are caused.

Remove the word 'only', here, and in other places.

> 
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
> v1->v2:
> - Improve patch log and doc description;
> - Make slight adjustment in code; 
> These are all made according to Mimi's great suggestions. 
> 
>  .../admin-guide/kernel-parameters.txt         |  5 ++++
>  security/integrity/ima/ima_main.c             | 26 +++++++++++++++++++
>  2 files changed, 31 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index b3d62f4c370a..1de67b9c20b4 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2214,6 +2214,11 @@
>  			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 limited to kdump kernel.

Remove the word 'only' ->  Note that disabling IMA is limited to kdump kernel.

> +
>  	indirect_target_selection= [X86,Intel] Mitigation control for Indirect
>  			Target Selection(ITS) bug in Intel CPUs. Updated
>  			microcode is also required for a fix in IBPB.
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index f99ab1a3b0f0..c38f3881d72f 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 +39,30 @@ int ima_appraise;
>  
>  int __ro_after_init ima_hash_algo = HASH_ALGO_SHA1;
>  static int hash_setup_done;
> +static int ima_disabled __ro_after_init;
>  
>  static struct notifier_block ima_lsm_policy_notifier = {
>  	.notifier_call = ima_lsm_policy_change,
>  };
>  
> +static int __init ima_setup(char *str)
> +{
> +	if (!is_kdump_kernel()) {
> +		pr_info("Warning: ima setup option only permitted in kdump");
> +		return 1;
> +	}
> +
> +	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();
> @@ -1186,6 +1206,12 @@ static int __init init_ima(void)
>  {
>  	int error;
>  
> +	/*Note that turning IMA off is only limited to kdump kernel.*/

Remove the word "only"  -> Note that turning IMA off is intentionally limited to
kdump kernel."

> +	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);

Mimi