[PATCH v7 7/8] IMA: define a builtin critical data measurement policy

[Tyler Hicks]

On 2020-12-09 11:42:11, Tushar Sugandhi wrote:
> From: Lakshmi Ramasubramanian <nramas at linux.microsoft.com>
> 
> Define a new critical data builtin policy to allow measuring
> early kernel integrity critical data before a custom IMA policy
> is loaded.
> 
> Add critical data to built-in IMA rules if the kernel command line
> contains "ima_policy=critical_data".
> 
> Update the documentation on kernel parameters to document
> the new critical data builtin policy.
> 
> Signed-off-by: Lakshmi Ramasubramanian <nramas at linux.microsoft.com>

Reviewed-by: Tyler Hicks <tyhicks at linux.microsoft.com>

Tyler

> ---
>  Documentation/admin-guide/kernel-parameters.txt |  5 ++++-
>  security/integrity/ima/ima_policy.c             | 12 ++++++++++++
>  2 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 526d65d8573a..6034d75c3ca0 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1746,7 +1746,7 @@
>  	ima_policy=	[IMA]
>  			The builtin policies to load during IMA setup.
>  			Format: "tcb | appraise_tcb | secure_boot |
> -				 fail_securely"
> +				 fail_securely | critical_data"
>  
>  			The "tcb" policy measures all programs exec'd, files
>  			mmap'd for exec, and all files opened with the read
> @@ -1765,6 +1765,9 @@
>  			filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
>  			flag.
>  
> +			The "critical_data" policy measures kernel integrity
> +			critical data.
> +
>  	ima_tcb		[IMA] Deprecated.  Use ima_policy= instead.
>  			Load a policy which meets the needs of the Trusted
>  			Computing Base.  This means IMA will measure all
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index 7486d09a3f60..37ca16a9e65f 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -206,6 +206,10 @@ static struct ima_rule_entry secure_boot_rules[] __ro_after_init = {
>  	 .flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
>  };
>  
> +static struct ima_rule_entry critical_data_rules[] __ro_after_init = {
> +	{.action = MEASURE, .func = CRITICAL_DATA, .flags = IMA_FUNC},
> +};
> +
>  /* An array of architecture specific rules */
>  static struct ima_rule_entry *arch_policy_entry __ro_after_init;
>  
> @@ -228,6 +232,7 @@ __setup("ima_tcb", default_measure_policy_setup);
>  
>  static bool ima_use_appraise_tcb __initdata;
>  static bool ima_use_secure_boot __initdata;
> +static bool ima_use_critical_data __initdata;
>  static bool ima_fail_unverifiable_sigs __ro_after_init;
>  static int __init policy_setup(char *str)
>  {
> @@ -242,6 +247,8 @@ static int __init policy_setup(char *str)
>  			ima_use_appraise_tcb = true;
>  		else if (strcmp(p, "secure_boot") == 0)
>  			ima_use_secure_boot = true;
> +		else if (strcmp(p, "critical_data") == 0)
> +			ima_use_critical_data = true;
>  		else if (strcmp(p, "fail_securely") == 0)
>  			ima_fail_unverifiable_sigs = true;
>  		else
> @@ -875,6 +882,11 @@ void __init ima_init_policy(void)
>  			  ARRAY_SIZE(default_appraise_rules),
>  			  IMA_DEFAULT_POLICY);
>  
> +	if (ima_use_critical_data)
> +		add_rules(critical_data_rules,
> +			  ARRAY_SIZE(critical_data_rules),
> +			  IMA_DEFAULT_POLICY);
> +
>  	ima_update_policy_flag();
>  }
>  
> -- 
> 2.17.1
>