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

[Dave Jones <davej@redhat.com>]

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

 > 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.
 > 
 > Things that might want to be turn-off-able include:
 >  - getrandom with GRND_RANDOM [from the getrandom threads]
 >  - Any lookup of a non-self pid [from the capsicum thread]
 >  - Any lookup of a pid outside the caller thread group [capsicum]
 >  - Various architectural things (personal wishlist), e.g.:
 >     - RDTSC and userspace HPET access
 >     - CPUID?
 >     - 32-bit GDT code segments [huge attack surface]
 >     - 64-bit GDT code segments [probably pointless]

I'm not sure there's value in disabling cpuid dev interface,
when the instruction is unprivileged.

 > I would propose a new syscall for this:
 > 
 > long restrict_userspace(int mode, int type, int value, int flags);

do the restrictions happen system-wide like in say SELinux,
or only within the calling process, like seccomp ?

	Dave