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    SubjectRe: [PATCH 4/4] x86,module: Detect CRn and DRn manipulation
    On Wed, Apr 08, 2020 at 08:46:02AM -0700, Christoph Hellwig wrote:
    > On Wed, Apr 08, 2020 at 05:44:19PM +0200, Peter Zijlstra wrote:
    > > 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@infradead.org> 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.
    >
    > Scanning all modules seems safer. While we're at it - can be move the
    > kvm bits using VMX to be always in the core kernel and just forbid
    > modules from using those instructions entirely?

    Practically speaking, no. Turning VMX on and off (literally VMXON/VMXOFF)
    could be moved to helpers in the kernel, but KVM relies on inlining all
    post-VMXON instructions (except for VMLAUNCH/VMRESUME) for performance.
    VMLAUNCH/VMRESUME have their own caveats, moving them out of KVM would be
    messy, to say the least.

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