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

From: Dave Jones
Date: Fri Jul 25 2014 - 16:15:59 EST

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 ?


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