Re: General flags to turn things off (getrandom, pid lookup, etc)

On Jul 27, 2014 5:06 PM, "Theodore Ts'o" [off-list ref] wrote:

On Fri, Jul 25, 2014 at 11:30:48AM -0700, Andy Lutomirski wrote:

quoted

There is recent interest in having a way to turn generally-available
kernel features off.  Maybe we should add a good one so we can stop
bikeshedding and avoid proliferating dumb interfaces.

I believe the seccomp infrastructure (which is already upstream)
should be able to do most of what you want, at least with respect to
features which are exposed via system calls (which was most of your
list).

Seccomp can't really restrict lookups of non-self pids.  In fact, this
feature idea started out as a response to a patch adding a kind of
nasty seccomp feature to make it sort of possible.

I agree that that seccomp can turn off GRND_RANDOM, but how is it
supposed to do it in such a way that the filtered software will fall
back to something sensible?  -ENOSYS?  -EPERM?  Something else?

I think that -ENOSYS is clearly wrong, but standardizing this would be
nice.  Admittedly, adding something fancy like this for GRND_RANDOM
may not be appropriate.

--Andy

It won't cover x86 specific things like restricting RDTSC or CPUID
(and as far as I know you can't intercept the CPUID instruction), but
I'm not sure it matters.  I don't really see the point, myself.

                                         - Ted