linux-kernel - Re: [PATCH 0/2] Allow individual features to be locked down

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Message-ID: <efcca734-2c80-43e3-b347-2af39f811502@suse.com>
Date: Tue, 13 May 2025 14:10:54 +0300
From: Nikolay Borisov <nik.borisov@...e.com>
To: Paul Moore <paul@...l-moore.com>, Dan Williams <dan.j.williams@...el.com>
Cc: linux-security-module@...r.kernel.org, serge@...lyn.com, kees@...nel.org,
 linux-kernel@...r.kernel.org, kirill.shutemov@...ux.intel.com,
 linux-coco@...ts.linux.dev
Subject: Re: [PATCH 0/2] Allow individual features to be locked down



On 5/13/25 01:01, Paul Moore wrote:
> On Mon, May 12, 2025 at 5:41 PM Dan Williams <dan.j.williams@...el.com> wrote:
>> Dan Williams wrote:
>>> Paul Moore wrote:
>>>> On Fri, Mar 21, 2025 at 6:24 AM Nikolay Borisov <nik.borisov@...e.com> wrote:
>>>>>
>>>>> This simple change allows usecases where someone might want to  lock only specific
>>>>> feature at a finer granularity than integrity/confidentiality levels allows.
>>>>> The first likely user of this is the CoCo subsystem where certain features will be
>>>>> disabled.
>>>>>
>>>>> Nikolay Borisov (2):
>>>>>    lockdown: Switch implementation to using bitmap
>>>>>    lockdown/kunit: Introduce kunit tests
>>>>
>>>> Hi Nikolay,
>>>>
>>>> Thanks for the patches!  With the merge window opening in a few days,
>>>> it is too late to consider this for the upcoming merge window so
>>>> realistically this patchset is two weeks out and I'm hopeful we'll
>>>> have a dedicated Lockdown maintainer by then so I'm going to defer the
>>>> ultimate decision on acceptance to them.
>>>
>>> The patches in this thread proposed to selectively disable /dev/mem
>>> independent of all the other lockdown mitigations. That goal can be
>>> achieved with more precision with this proposed patch:
>>>
>>> http://lore.kernel.org/67f5b75c37143_71fe2949b@dwillia2-xfh.jf.intel.com.notmuch
>>
>> Just wanted to circle back here and repair the damage I caused to the
>> momentum of this "lockdown feature bitmap" proposal. It turns out that
>> devmem maintainers are not looking to add yet more arch-specific hacks
>> [1].
>>
>>      "Restricting /dev/mem further is a good idea, but it would be nice
>>       if that could be done without adding yet another special case."
>>
>> security_locked_down() is already plumbed into all the places that
>> confidential VMs may need to manage userspace access to confidential /
>> private memory.
>>
>> I considered registering a new "coco-LSM" to hook
>> security_locked_down(), but that immediately raises the next question of
>> how does userspace discover what is currently locked_down. So just teach
>> the native lockdown LSM how to be more fine-grained rather than
>> complicate the situation with a new LSM.
> 
> Historically Linus has bristled at LSMs with alternative
> security_locked_down() implementations/security-models, therefore I'd
> probably give a nod to refining the existing Lockdown approach over a
> new LSM.
> 
> Related update, there are new Lockdown maintainers coming, there is
> just an issue of sorting out some email addresses first.  Hopefully
> we'll see something on-list soon.
> 


So I guess the most sensible way forward will be to resend these 2 
patches after the new maintainer has been officially announced?