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    SubjectRe: [RFC] Tracepoint proposal

    Takashi Nishiie wrote:
    > Hi
    > Hiramatsu wrote:
    >> One reason why we need markers or other in-the-middle-of-function
    >> trace point is that some events happen inside functions, not it's
    >> interface.
    > Each kernel sub-system seems to have its own way of dealing with
    > debugging statements. Some of these methods include 'dprintk',
    > 'pr_debug', 'dev_debug', 'DEBUGP'. I think that these functions are
    > the tracepoints that has been availably mounted without setting up
    > the tool set of the outside. I think whether mounting that unites
    > these functions can be done if kernel marker and tracepoint are used.

    Sure, I think those functions covers each partially, but some requirements
    are different.

    dynamic printk
    - stored in a section
    - dynamic activation
    - formatted message (multiple messages for each activation group)
    - export basic types
    - variadic function
    - low frequently called
    - module support

    - stored in a section
    - dynamic activation
    - formatted string (single format for each marker)
    - export basic types
    - variadic function
    - low-high frequently called
    - module support

    - stored in a section
    - dynamic activation
    - no message
    - export kernel structure
    - arguments depending on points
    - high frequently called
    - no module support (kernel use only)

    > By the way, isn't there problem on security?
    > What kprobe, jprobe, and kernel marker, etc. offer looks like what
    > the framework of Linux Security Module had offered before. Gotten
    > kprobe, jprobe, and kernel marker, etc. should not be exported to the
    > userland for security because it becomes the hotbed of rootkits. Users
    > such as kprobe, jprobe, and kernel marker should not be Loadable Kernel
    > Module. I think that there are some solutions in LTTng about this
    > security problem. However, will the environment to be able to operate
    > SystemTap be really secure?
    >  At least, kernel commandline option to invalidate all of kprobe,
    > jprobe, and kernel marker, etc. because of the batch might be
    > necessary.

    Please, set CONFIG_MODULES=no.
    If your system really really needs to be hardened, please
    don't make kernel module loadable. Otherwise, any kernel module
    can modify any kernel code. So, I think it's not a problem of
    any specific functionality.

    Anyway, I think selinux will give you more flexible way to
    restrict who can load what modules.

    Thank you,

    Masami Hiramatsu

    Software Engineer
    Hitachi Computer Products (America) Inc.
    Software Solutions Division


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