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

Song Liu
2024-12-18T17:07:06Z

Hi Mimi,

Thanks for your comments!

> On Dec 18, 2024, at 3:02 AM, Mimi Zohar <zohar@linux.ibm.com> wrote:
>
> On Tue, 2024-12-17 at 13:29 -0800, Casey Schaufler wrote:
>> On 12/17/2024 12:25 PM, Song Liu wrote:
>>> While reading and testing LSM code, I found IMA/EVM consume per inode
>>> storage even when they are not in use. Add options to diable them in
>>> kernel command line. The logic and syntax is mostly borrowed from an
>>> old serious [1].
>>
>> Why not omit ima and evm from the lsm= parameter?
>
> Casey, Paul, always enabling IMA & EVM as the last LSMs, if configured, were the
> conditions for making IMA and EVM LSMs. Up to that point, only when an inode
> was in policy did it consume any memory (rbtree). I'm pretty sure you remember
> the rather heated discussion(s).

I didn't know about this history until today. I apologize if this
RFC/PATCH is moving to the direction against the original agreement.
I didn't mean to break any agreement.

My motivation is actually the per inode memory consumption of IMA
and EVM. Once enabled, EVM appends a whole struct evm_iint_cache to
each inode via i_security. IMA is better on memory consumption, as
it only adds a pointer to i_security.

It appears to me that a way to disable IMA and EVM at boot time can
be useful, especially for distro kernels. But I guess there are
reasons to not allow this (thus the earlier agreement). Could you
please share your thoughts on this?

Thanks,
Song