Re: [PATCH V31 19/25] x86/mmiotrace: Lock down the testmmiotrace module

[Matthew Garrett]

On Wed, Mar 27, 2019 at 8:57 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> On Tue, 26 Mar 2019 11:27:35 -0700
> Matthew Garrett <matthewgarrett@xxxxxxxxxx> wrote:
>
> > From: David Howells <dhowells@xxxxxxxxxx>
> >
> > The testmmiotrace module shouldn't be permitted when the kernel is locked
> > down as it can be used to arbitrarily read and write MMIO space. This is
> > a runtime check rather than buildtime in order to allow configurations
> > where the same kernel may be run in both locked down or permissive modes
> > depending on local policy.
> >
>
> Acked-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
>
> I'm curious. Should there be a mode to lockdown the tracefs directory
> too? As that can expose addresses.

That sounds like a reasonable thing to do in the confidentiality mode,
I don't think it'd be necessary in the integrity mode.