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    SubjectRe: [PATCH] New phys_addr() syscall
    Tony Cook writes:
    > On Mon, 20 Jul 1998, Richard Gooch wrote:
    >
    > > Just so I'm clear on this: I'm in no way saying that phys_addr(2)
    > > combined with mlock(2) is the proper way to do this. I just wanted to
    > > point out that you *could*, if you wanted. Sigh. Maybe I shouldn't
    > > have mentioned that aspect at all.
    >
    > I'm wondering if phys_addr(2) could be used in combination with
    > mlock(2) to fragment physical memory.
    >
    > Could an attacker:
    >
    > for() {
    > allocate a large block of memory and page it in (memset(base, 1, size))
    > scan the block with phys_addr(2) looking for blocks matching a pattern
    > (eg. every second block)
    > mlock those blocks
    > }

    Yes, it's true that you could misuse phys_addr(2) this way. On the
    other hand your attack relies on mlock(2) privileges in the first
    place. This option is not available to non-root processes. If I want
    to bring a machine to its knees, and I have root access, I'm not going
    to bother with fragmenting memory. I'll just run halt(8)!

    So far all the "security problems" I've seen raised about phys_addr(2)
    are in fact just problems with existing facilities being abused. The
    phys_addr(2) syscall confers no extra benefits/privileges other than
    convenience.

    > This simple version could be easily defeated with ulimit, but is it
    > possible a more sophisticated version wouldn't be?

    Show me a way of abusing phys_addr(2) which doesn't rely on root
    privileges and can't be done without phys_addr(2) (note that I can
    write an unprivileged programme which will punish your machine with
    resorting to phys_addr(2) at all).

    Please, everyone. I'm convinced that phys_addr(2) "abuse" is a
    non-issue. Show me *how* phys_addr(2) can lead to attacks that you
    otherwise couldn't do.

    Regards,

    Richard....

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