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SubjectRe: [PATCH 01/24] Add the ability to lock down access to the running kernel image
On April 11, 2018 8:09 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Wed, Apr 11, 2018 at 9:24 AM, David Howells dhowells@redhat.com wrote:
>
> > Provide a single call to allow kernel code to determine whether the system
> >
> > should be locked down, thereby disallowing various accesses that might
> >
> > allow the running kernel image to be changed, including:
> >
> > - /dev/mem and similar
> > - Loading of unauthorised modules
> > - Fiddling with MSR registers
> > - Suspend to disk managed by the kernel
> > - Use of device DMA
>
> So what I stlll absolutely detest about this series is that I think
>
> many of these things should simply be done as separate config options.
>
> For example, if the distro is sure that it doesn't need /dev/mem, then
>
> why the hell is this tied to "lockdown" that then may have to be
>
> disabled because other changes may not be acceptable (eg people may
>
> need that device DMA, or whatever).
>
> If that /dev/mem access prevention was just instead done as an even
>
> stricter mode of the existing CONFIG_STRICT_DEVMEM, it could just be
>
> enabled unconditionally.

CONFIG_DEVMEM=n

>
> So none of these patches raise my hackles per se. But what continues
>
> to makes me very very uncomfortable is how this is all tied together.
>
> Why is this one magical mode that then - because it has such a big
>
> impact - has to be enabled/disabled as a single magical mode and with
>
> very odd rules?
>
> I think a lot of people would be happier if this wasn't so incestuous
>
> and mixing together independent things under one name, and one flag.
>
> I think a lot of the secure boot problems were exacerbated by that mixup.
>
> So I would seriously ask that the distros that have been using these
>
> patches look at which parts of lockdown they could make unconditional
>
> (because it doesn't break machines), and which ones need that escape
>
> clause.
>
> Linus
>

​Jordan

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