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    SubjectRe: [PATCH -tip v2 3/9] ftrace/x86: Support SAVE_REGS feature on i386
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    On Tue, 2012-06-05 at 17:24 -0400, Frank Ch. Eigler wrote:
    > Hi -
    >
    > On Tue, Jun 05, 2012 at 04:37:46PM -0400, Steven Rostedt wrote:
    > > [...]
    > > I'm not sure we really need to restore all the regs. I'll keep this for
    > > now, but for an optimization, we can just restore the ones that mcount
    > > mcount needs to.
    > >
    > > Or do you expect kprobes to change any of theses?
    >
    > That would be the way for a kprobe to modify variables/values that
    > happen to be in the registers. In systemtap, for example:
    >
    > # stap -g -e 'probe kernel.function("foo") { $bar = 1 }'
    >

    And why would we want to allow this?


    Modifying variables with probes is another way to lead to disaster. If
    the system did not intend for a variable to be a certain value, why let
    someone change it?

    What real world example leads to external sources modifying internal
    core variables? With the obvious exception of rootkits.

    -- Steve




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