Re: [RFC PATCH 00/56] Dynamic mitigations

Josh Poimboeuf
2025-10-15T16:02:22Z

On Wed, Oct 15, 2025 at 03:51:01PM +0000, Kaplan, David wrote:
> > On Wed, Oct 15, 2025 at 01:53:31PM +0000, Kaplan, David wrote:
> > > > If `root` is capable of setting `mitigations=off` via this interface,
> > > > doesn't that somewhat defeat the purpose of denying `/proc/kcore`
> > > > access in lockdown confidentiality mode? Assuming one is running on a
> > > > CPU with some form of side-channel memory read vulnerability (which they
> > > > very likely are), they can turn off all mitigations, then read kernel
> > > > memory via one of those exploits.
> > > >
> > > > There should be a one-way switch to allow denying all further writes to
> > > > this interface, so that once the system's mitigations are set properly,
> > > > any further attempts to change them until the next reboot can be
> > > > prevented.
> > > >
> > >
> > > That's a good idea, there could be a separate mitigation_lock file
> > > perhaps that once written to 1 denies any further changes.
> >
> > Wouldn't the enablement of lockdown mode effectively function as that
> > one way switch?
> >
>
> I'm not too familiar with lockdown mode, but that gets enabled (with
> right cmdline options) during boot right? I guess the question is
> would we want to allow any window for userspace to reconfigure things
> and then lock things down, or say that if you enable lockdown then
> this interface is completely disabled and you need to specify your
> mitigation options on the cmdline only.

Yeah, I would say the latter, otherwise it defeats the point of lockdown
mode. Note that lockdown mode can also be enabled at runtime.

--
Josh