linux-kernel - Re: [PATCH RFC 8/8] clavis: Introduce new LSM called clavis

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Message-ID: <C9A0995A-2390-486F-99EF-89098E78021A@oracle.com>
Date: Tue, 12 Mar 2024 14:04:42 +0000
From: Eric Snowberg <eric.snowberg@...cle.com>
To: Randy Dunlap <rdunlap@...radead.org>
CC: "open list:SECURITY SUBSYSTEM" <linux-security-module@...r.kernel.org>,
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Subject: Re: [PATCH RFC 8/8] clavis: Introduce new LSM called clavis



> On Mar 11, 2024, at 8:45 PM, Randy Dunlap <rdunlap@...radead.org> wrote:
> 
> On 3/11/24 09:11, Eric Snowberg wrote:
>> In the future it is envisioned this LSM could be enhanced to provide
>> access control for UEFI Secure Boot Advanced Targeting (SBAT).  Using
>> the same clavis= boot param and storing the additional contents within
>> the new RT UEFI var, SBAT restrictions could be maintained across kexec.
> 
> What does "RT" mean here?

I will define it in the next round.  It stands for Run-Time.

>> +
>> +Clavis is a Linux Security Module that provides mandatory access control to
>> +system kernel keys (i.e. builtin, secondary, machine and platform). These
>> +restrictions will prohit keys from being used for validation. Upon boot, the
> 
>                     prohibit

I will fix this spelling error and all the others you identified below.

> 
>> +Clavis LSM is provided a key id as a boot param.  This single key is then
>> +used as the root of trust for any access control modifications made going
>> +forward. Access control updates must be signed and validated by this key.
>> +
>> +Clavis has its own keyring.  All ACL updates are applied through this keyring.
>> +The update must be signed by the single root of trust key.
>> +
>> +When enabled, all system keys are prohibited from being used until an ACL is
>> +added for it. There is two exceptions to this rule, builtin keys may be used
> 
> What is     "it"?  The predecessor seems to be "all system keys" (plural).

The word "for" should be "to" above.  The sentence should be:

When enabled, all system keys are prohibited from being used until an ACL is
added to it.

>> +
>> +The Clavis LSM contains a system keyring call .clavis.  It contains a single
>> +asymmetric key that is use to validate anything added to it.  This key can only
>> +be added during boot and must be a preexisting system kernel key.  If the
>> +clavis= boot param is not used, the keyring does not exist and the feature
>> +can not be used until the next power on reset.
> 
> So just a reboot won't cause it to be used?  Must be power off/on?

A reboot would too.  I will rework this sentence.  I just want to show that doing a kexec 
can not be used to make changes to the root of trust.

>> diff --git a/security/security.c b/security/security.c
>> index 4cb832b00c40..d1da60a1b7a4 100644
>> --- a/security/security.c
>> +++ b/security/security.c
> 
>> @@ -5313,6 +5314,19 @@ void security_key_post_create_or_update(struct key *keyring, struct key *key,
>> call_void_hook(key_post_create_or_update, keyring, key, payload,
>>       payload_len, flags, create);
>> }
>> +
>> +/**
>> + * security_key_verify_signature - verify signature
>> + * @key: key
>> + * @public_key_signature: signature
> 
> Above should be "@sig:".

I will fix that too.  Thanks for your review.