Re: [RFC 0/2] ima: evm: Add kernel cmdline options to disable IMA/EVM

Casey Schaufler
2024-12-18T17:03:01Z

On 12/17/2024 10:41 PM, Song Liu wrote:
>> On Dec 17, 2024, at 3:33 PM, Song Liu <songliubraving@meta.com> wrote:
> [...]
>
>>>> +
>>>> found = true;
>>>> }
>>>> }
>>>> @@ -386,7 +389,7 @@ static void __init ordered_lsm_parse(const char *order, const char *origin)
>>>>
>>>> /* LSM_ORDER_LAST is always last. */
>>>> for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
>>>> - if (lsm->order == LSM_ORDER_LAST)
>>>> + if (lsm->order == LSM_ORDER_LAST && is_enabled(lsm))
>>>> append_ordered_lsm(lsm, " last");
>> Before this change, lsm with order==LSM_ORDER_LAST is always considered
>> enabled, which is a bug (if I understand you and Casey correctly).
> According to commit 42994ee3cd7298b27698daa6848ed7168e72d056, LSMs with
> order LSM_ORDER_LAST is expected to be always enabled:
>
> "Similarly to LSM_ORDER_FIRST, LSMs with LSM_ORDER_LAST are always enabled
> and put at the end of the LSM list, if selected in the kernel
> configuration. "
>
> Roberto, it feels weird to have two "last and always on" LSMs (ima and evm)
> I guess this is not the expected behavior? At least, it appears to be a
> surprise for Paul and Casey.

I can't speak for Paul, but having multiple "first" and "last" entries
comes as no surprise to me. We should probably have used LSM_ORDER_EARLY
and LSM_ORDER_LATE instead of LSM_ORDER_FIRST and LSM_ORDER_LAST. As for
"always on", I recall that being an artifact of compatibility for the
security= boot option.

> I will send patch that allow enable/disable ima and evm with lsm= cmdline.
> We can further discuss the topic with the patch.
>
> Thanks,
> Song
>
>