linux-kernel - Re: [PATCH] ima: require signed IMA policy when UEFI secure boot is enabled

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Date:   Fri, 14 Jul 2023 09:29:04 +0800
From:   Coiby Xu <coxu@...hat.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     linux-integrity@...r.kernel.org,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        Paul Moore <paul@...l-moore.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        "open list:SECURITY SUBSYSTEM" 
        <linux-security-module@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ima: require signed IMA policy when UEFI secure boot is
 enabled

On Tue, Jul 04, 2023 at 08:57:10AM -0400, Mimi Zohar wrote:
>On Mon, 2023-07-03 at 19:54 +0800, Coiby Xu wrote:
>> With the introduction of the .machine keyring for UEFI-based systems,
>> users are able to add custom CAs keys via MOK. This allow users to sign
>> their own IMA polices. For the sake of security, mandate signed IMA
>> policy when UEFI secure boot is enabled.
>>
>> Suggested-by: Mimi Zohar <zohar@...ux.ibm.com>
>> Signed-off-by: Coiby Xu <coxu@...hat.com>
>> ---
>>  security/integrity/ima/ima_efi.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/security/integrity/ima/ima_efi.c b/security/integrity/ima/ima_efi.c
>> index 9db66fe310d4..bb2881759505 100644
>> --- a/security/integrity/ima/ima_efi.c
>> +++ b/security/integrity/ima/ima_efi.c
>> @@ -58,6 +58,9 @@ static const char * const sb_arch_rules[] = {
>>  #if !IS_ENABLED(CONFIG_MODULE_SIG)
>>  	"appraise func=MODULE_CHECK appraise_type=imasig",
>>  #endif
>> +#if IS_ENABLED(CONFIG_INTEGRITY_MACHINE_KEYRING) && IS_ENABLED(CONFIG_IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY)
>> +	"appraise func=POLICY_CHECK appraise_type=imasig",
>> +#endif /* CONFIG_INTEGRITY_MACHINE_KEYRING && IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY */
>>  	"measure func=MODULE_CHECK",
>>  	NULL
>>  };
>
>Thanks, Coiby.

You are welcome!

>
>Using IS_ENABLED() is not wrong, but unnecessary.  IS_BUILTIN()
>suffices.

Thanks for the reminding! When I was going to apply this suggestion, I
noticed ima_efi.c uses IS_ENABLED for all configuration items i.e.
CONFIG_MODULE_SIG and CONFIG_KEXEC_SIG which are all of bool type. Would
you like me to switch all IS_ENABLEs to IS_BUILTIN or still use
IS_ENABLED? While IS_BUILTIN is exclusively for bool type, it's not as
intuitive as IS_ENABLED. So it's not easy for me to make a choice.

>
>-- 
>thanks,
>
>Mimi
>

-- 
Best regards,
Coiby