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Re: double fault -> PAGE_KERNEL flagged memory
Frank Ch. Eigler writes:
>
> zanussi wrote:
>
> > [...] What would cause a double fault would be if the vmalloc_fault
> > tried logging before the page table was updated, which would cause
> > the same vmalloc fault.
>
> Then this is analogous to the problem of calling printk from within an
> inconveniently placed kprobe. What can we do to eliminate this
> vulnerability? Can we somehow arrange to "fault in" all probe-related
> kernel-space vmalloc areas into new process' address spaces, so we don't
> encounter this unintentional and undesirable reentrancy?
>
I'll think about it, but it doesn't sound like fun. It sounds like it
might be one of those cases where you only allow a tapset to
instrument a certain area, in this case a page fault tapset to
instrument the page fault path. I can't remember, how is the
possibility of a printk() in a problematic function currently handled
in systemtap?
Tom