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    SubjectRe: [PATCH v3 2.6.39-rc1-tip 12/26] 12: uprobes: slot allocation for uprobes
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    On Wed, 2011-04-20 at 10:51 -0400, Frank Ch. Eigler wrote:
    > eparis wrote:
    >
    > > [...]
    > > Now how to fix the problems you were seeing. If you run a modern
    > > system with a GUI I'm willing to bet the pop-up window told you
    > > exactly how to fix your problem. [...]
    > >
    > > 1) chcon -t unconfined_execmem_t /path/to/your/binary
    > > 2) setsebool -P allow_execmem 1
    > > [...]
    > > I believe there was a question about how JIT's work with SELinux
    > > systems. They work mostly by method #1.
    >
    > Actually, that's a solution to a different problem. Here, it's not
    > particular /path/to/your/binaries that want/need selinux provileges.
    > It's a kernel-driven debugging facility that needs it temporarily for
    > arbitrary processes.
    >
    > It's not like JITs, with known binary names. It's not like GDB, which
    > simply overwrites existing instructions in the text segment. To make
    > uprobes work fast (single-step-out-of-line), one needs one or emore
    > temporary pages with unusual mapping permissions.

    I would expect that (2) would solve it, but couldn't distinguish the
    kernel-created mappings from userspace doing the same thing.
    Alternatively, you could temporarily switch your credentials around the
    mapping operation, e.g.:
    old_cred = override_creds(&init_cred);
    do_mmap_pgoff(...);
    revert_creds(old_cred);

    devtmpfs does something similar to avoid triggering permission checks on
    userspace when it is internally creating and deleting nodes.

    How is this ability to use this facility controlled?

    --
    Stephen Smalley
    National Security Agency



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