Re: [PATCH 4/4] x86,module: Detect CRn and DRn manipulation

[Jessica Yu]

+++ Peter Zijlstra [08/04/20 17:44 +0200]:
> On Wed, Apr 08, 2020 at 09:27:26AM -0400, Steven Rostedt wrote:
> > On Tue, 07 Apr 2020 13:02:40 +0200
> > Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> > > +		if (insn_is_mov_CRn(&insn) || insn_is_mov_DRn(&insn)) {
> > > +			pr_err("Module writes to CRn or DRn, please use the proper accessors: %s\n", mod->name);
> > > +			return -ENOEXEC;
> > > +		}
> > > +
> >
> > Something like this should be done for all modules, not just out of tree
> > modules.
>
> I'm all for it; but people were worried scanning all modules was too
> expensive (I don't really believe it is, module loading just can't be a
> hot-path). Also, in-tree modules are audited a lot more than out of tree
> magic voodoo crap.

The intention of the original patches was to do the text scan to catch
a handful of out-of-tree hypervisor modules - but now that
decode_module() is being generalized to more cases, I don't mind
scanning all modules.

Thanks,

Jessica