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



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