linux-kernel - Re: [PATCH v6] ima: move APPRAISE_BOOTPARAM dependency on ARCH

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Message-ID: <20200717184019.GI2984@glitch>
Date:   Fri, 17 Jul 2020 15:40:19 -0300
From:   Bruno Meneguele <bmeneg@...hat.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-integrity@...r.kernel.org
Cc:     zohar@...ux.ibm.com, erichte@...ux.ibm.com, nayna@...ux.ibm.com,
        stable@...r.kernel.org
Subject: Re: [PATCH v6] ima: move APPRAISE_BOOTPARAM dependency on
 ARCH_POLICY to runtime

On Mon, Jul 13, 2020 at 01:48:30PM -0300, Bruno Meneguele wrote:
> The IMA_APPRAISE_BOOTPARAM config allows enabling different "ima_appraise="
> modes - log, fix, enforce - at run time, but not when IMA architecture
> specific policies are enabled.  This prevents properly labeling the
> filesystem on systems where secure boot is supported, but not enabled on the
> platform.  Only when secure boot is actually enabled should these IMA
> appraise modes be disabled.
> 
> This patch removes the compile time dependency and makes it a runtime
> decision, based on the secure boot state of that platform.
> 
> Test results as follows:
> 
> -> x86-64 with secure boot enabled
> 
> [    0.015637] Kernel command line: <...> ima_policy=appraise_tcb ima_appraise=fix
> [    0.015668] ima: Secure boot enabled: ignoring ima_appraise=fix boot parameter option
> 
> -> powerpc with secure boot disabled
> 
> [    0.000000] Kernel command line: <...> ima_policy=appraise_tcb ima_appraise=fix
> [    0.000000] Secure boot mode disabled
> 
> -> Running the system without secure boot and with both options set:
> 
> CONFIG_IMA_APPRAISE_BOOTPARAM=y
> CONFIG_IMA_ARCH_POLICY=y
> 
> Audit prompts "missing-hash" but still allow execution and, consequently,
> filesystem labeling:
> 
> type=INTEGRITY_DATA msg=audit(07/09/2020 12:30:27.778:1691) : pid=4976
> uid=root auid=root ses=2
> subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 op=appraise_data
> cause=missing-hash comm=bash name=/usr/bin/evmctl dev="dm-0" ino=493150
> res=no
> 
> Cc: stable@...r.kernel.org
> Fixes: d958083a8f64 ("x86/ima: define arch_get_ima_policy() for x86")
> Signed-off-by: Bruno Meneguele <bmeneg@...hat.com>
> ---
> v6:
>   - explictly print the bootparam being ignored to the user (Mimi)
> v5:
>   - add pr_info() to inform user the ima_appraise= boot param is being
> 	ignored due to secure boot enabled (Nayna)
>   - add some testing results to commit log
> v4:
>   - instead of change arch_policy loading code, check secure boot state at
> 	"ima_appraise=" parameter handler (Mimi)
> v3:
>   - extend secure boot arch checker to also consider trusted boot
>   - enforce IMA appraisal when secure boot is effectively enabled (Nayna)
>   - fix ima_appraise flag assignment by or'ing it (Mimi)
> v2:
>   - pr_info() message prefix correction
>  security/integrity/ima/Kconfig        | 2 +-
>  security/integrity/ima/ima_appraise.c | 6 ++++++
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> index edde88dbe576..62dc11a5af01 100644
> --- a/security/integrity/ima/Kconfig
> +++ b/security/integrity/ima/Kconfig
> @@ -232,7 +232,7 @@ config IMA_APPRAISE_REQUIRE_POLICY_SIGS
>  
>  config IMA_APPRAISE_BOOTPARAM
>  	bool "ima_appraise boot parameter"
> -	depends on IMA_APPRAISE && !IMA_ARCH_POLICY
> +	depends on IMA_APPRAISE
>  	default y
>  	help
>  	  This option enables the different "ima_appraise=" modes
> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> index a9649b04b9f1..28a59508c6bd 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -19,6 +19,12 @@
>  static int __init default_appraise_setup(char *str)
>  {
>  #ifdef CONFIG_IMA_APPRAISE_BOOTPARAM
> +	if (arch_ima_get_secureboot()) {
> +		pr_info("Secure boot enabled: ignoring ima_appraise=%s boot parameter option",
> +			str);
> +		return 1;
> +	}
> +
>  	if (strncmp(str, "off", 3) == 0)
>  		ima_appraise = 0;
>  	else if (strncmp(str, "log", 3) == 0)
> -- 
> 2.26.2
> 

Ping for review.

Many thanks.

-- 
bmeneg 
PGP Key: http://bmeneg.com/pubkey.txt

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