double fault -> PAGE_KERNEL flagged memory

[Mathieu Desnoyers]

* Roland McGrath (roland@redhat.com) wrote:
> > 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?
> 
> What's the reason for using vmalloc then?  Why not use kmalloc that doesn't
> need page table changes?
> 

kmalloc needs contiguous pages of memory. It can be problematic in a system
where the memory is fragmented and the requested allocation size is big.

Mathieu

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