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

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Message-ID: <CAHC9VhRyKtyROAwTSdRv+UmLSwat-Vxiu-BqM+1DwnYv2r1ejA@mail.gmail.com>
Date: Tue, 13 May 2025 19:07:44 -0400
From: Paul Moore <paul@...l-moore.com>
To: Nikolay Borisov <nik.borisov@...e.com>
Cc: Dan Williams <dan.j.williams@...el.com>, 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 Tue, May 13, 2025 at 7:10 AM Nikolay Borisov <nik.borisov@...e.com> wrote:
> 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?

Possibly, or at least bump the thread to get it some fresh attention.

-- 
paul-moore.com