Re: Linux Firmware Signing

[Mimi Zohar <zohar@linux.vnet.ibm.com>]

On Tue, 2015-09-01 at 20:08 -0700, Kees Cook wrote:
> On Tue, Sep 1, 2015 at 4:43 PM, Luis R. Rodriguez <mcgrof@suse.com> wrote:
> > On Mon, Aug 31, 2015 at 10:18:55AM -0400, Mimi Zohar wrote:
> >> > > eBPF/seccomp
> >
> > OK I knew nothing about this but I just looked into it, here are my notes:
> >
> >   * old BPF - how far do we want to go? This goes so far as to parsing
> >     user passed void __user *arg data through ioctls which typically
> >     gets copy_from_user()'d and eventually gets BPF_PROG_RUN().
> >
> >   * eBPF:
> >                              seccomp() & prctl_set_seccomp()
> >                                         |
> >                                         V
> >                              do_seccomp()
> >                                         |
> >                                         V
> >                              seccomp_set_mode_filter()
> >                                         |
> >                                         V
> >                              seccomp_prepare_user_filter()
> >                                         |
> >                                         V
> >         bpf_prog_create_from_user() (seccomp) \
> >         bpf_prog_create()                      > bpf_prepare_filter()
> >         sk_attach_filter()                    /
> >
> >     All approaches come from user passed data, nothing fd based.
> >
> >     For both old BPF and eBPF then:
> >
> >     If we wanted to be paranoid I suppose the Machine Owner Key (MOK)
> >     Paul had mentioned up could be used to vet for passed filters, or
> >     a new interface to enable fd based filters. This really would limit
> >     the dynamic nature of these features though.
> >
> >     eBPF / secccomp would not be the only place in the kernel that would have
> >     issues with user passed data, we have tons of places the same applies so
> >     implicating the old BPF / eBPF / seccomp approaches can easily implicate
> >     many other areas of the kernel, that's pretty huge but from the looks of
> >     it below you seem to enable that to be a possibility for us to consider.
> 
> At the time (LSS 2014?) I argued that seccomp policies come from
> binaries, which are already being measured. And that policies only
> further restrict a process, so there seems to be to be little risk in
> continuing to leave them unmeasured.

What do you mean by "measured"?  Who is doing the measurement?  Could
someone detect a change in measurement?

Mimi