linux-kernel - Re: [RFC][PATCH v3 04/10] ima: Add digest_cache_measure/appraise boot-time built-in policies

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Message-Id: <D3Z3S9Z6B4BC.2OSFJZYTZOPZD@kernel.org>
Date: Fri, 06 Sep 2024 12:45:02 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Roberto Sassu" <roberto.sassu@...weicloud.com>, <corbet@....net>,
 <zohar@...ux.ibm.com>, <dmitry.kasatkin@...il.com>,
 <eric.snowberg@...cle.com>, <paul@...l-moore.com>, <jmorris@...ei.org>,
 <serge@...lyn.com>
Cc: <linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>,
 <linux-integrity@...r.kernel.org>, <linux-security-module@...r.kernel.org>,
 <wufan@...ux.microsoft.com>, <pbrobinson@...il.com>, <zbyszek@...waw.pl>,
 <hch@....de>, <mjg59@...f.ucam.org>, <pmatilai@...hat.com>,
 <jannh@...gle.com>, <dhowells@...hat.com>, <jikos@...nel.org>,
 <mkoutny@...e.com>, <ppavlu@...e.com>, <petr.vorel@...il.com>,
 <mzerqung@...inter.de>, <kgold@...ux.ibm.com>, "Roberto Sassu"
 <roberto.sassu@...wei.com>
Subject: Re: [RFC][PATCH v3 04/10] ima: Add digest_cache_measure/appraise
 boot-time built-in policies

On Thu Sep 5, 2024 at 6:25 PM EEST, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@...wei.com>
>
> Specify the 'digest_cache_measure' boot-time policy with 'ima_policy=' in
> the kernel command line to add the following rule at the beginning of the
> IMA policy, before other rules:
>
> measure func=DIGEST_LIST_CHECK pcr=12
>
> which will measure digest lists into PCR 12 (or the value in
> CONFIG_IMA_DIGEST_CACHE_MEASURE_PCR_IDX).
>
> Specify 'digest_cache_appraise' to add the following rule at the beginning,
> before other rules:
>
> appraise func=DIGEST_LIST_CHECK appraise_type=imasig|modsig
>
> which will appraise digest lists with IMA signatures or module-style
> appended signatures.
>
> Adding those rule at the beginning rather than at the end is necessary to
> ensure that digest lists are measured and appraised in the initial ram
> disk, which would be otherwise prevented by the dont_ rules.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> ---
>  .../admin-guide/kernel-parameters.txt         | 10 +++++-
>  security/integrity/ima/Kconfig                | 10 ++++++
>  security/integrity/ima/ima_policy.c           | 35 +++++++++++++++++++
>  3 files changed, 54 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 09126bb8cc9f..afaaf125a237 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2077,7 +2077,8 @@
>  	ima_policy=	[IMA]
>  			The builtin policies to load during IMA setup.
>  			Format: "tcb | appraise_tcb | secure_boot |
> -				 fail_securely | critical_data"
> +				 fail_securely | critical_data |
> +				 digest_cache_measure | digest_cache_appraise"
>  
>  			The "tcb" policy measures all programs exec'd, files
>  			mmap'd for exec, and all files opened with the read
> @@ -2099,6 +2100,13 @@
>  			The "critical_data" policy measures kernel integrity
>  			critical data.
>  
> +			The "digest_cache_measure" policy measures digest lists
> +			into PCR 12 (can be changed with kernel config).
> +
> +			The "digest_cache_appraise" policy appraises digest
> +			lists with IMA signatures or module-style appended
> +			signatures.
> +
>  	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

Must be updated as a separate commit as kernel-parameters.txt not
part of IMA. Consider it as a different subsystem in this context.

BR, Jarkko