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SubjectRe: [PATCH 11/16] IB uverbs: add mthca mmap support
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    Michael> Roland, I think VM_DONTCOPY is needed here.

Michael> If a process forks, we must prevent the child from
Michael> accessing the parent's hardware page. Otherwise the child
Michael> can corrupt the parent's queues since the hardware wont
Michael> be able to distinguish between parent and child.

Michael> Does this make sense?

This is true, but there are a number of pieces that are required
before fork will work for processes using userspace verbs. One of the
ingredients that's missing is adding something like PROT_DONTCOPY for
mprotect(). Once that's in place, an app can use that on the
doorbell page before forking.

I don't consider this attack by children of a process very serious,
since a process can always fork, munmap the doorbell page in the child
process, and then fork the untrusted child into yet another child.

- R.
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