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    SubjectRe: [PATCH 1/9] exec: add a global execve counter
    On Sat, Mar 10, 2012 at 4:36 PM, Linus Torvalds
    <> wrote:
    > I wonder if the number part of exec_id would even have to be 64-bit. I
    > think I can do about 10000 execves per second if I make the program a
    > small static one - and that's on a fast CPU. And it's a per-thread
    > counter, so you can't scale it with lots of CPU's. So it would take
    > something like four days to wrap. Hmm..

    Actually, using a pure counter is horrible, because even if it takes
    four days to wrap, it *will* wrap, and the attacker can just count his
    own execve's.

    If, instead, you were to use a counter that counts *independently* of
    execve's, you're much better off.

    And if you use one that is free - because the CPU implements it
    natively - you're even better off.

    IOW, why is the exec-id just the time stamp counter (on any random cpu
    - we really don't care)? That should be safe even in just 32 bits
    exactly because it's not under the control of the user.

    And it's zero cost for us to update.


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