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

Eric Snowberg
2024-03-12T14:05:19Z

> On Mar 11, 2024, at 8:45 PM, Randy Dunlap <rdunlap@infradead.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.