Messages in this thread | | | Date | Sat, 14 Oct 2017 14:22:10 +0000 (UTC) | From | Mathieu Desnoyers <> | Subject | Re: [RFC PATCH for 4.15 09/14] Provide cpu_opv system call |
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----- On Oct 13, 2017, at 10:50 AM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:
> ----- On Oct 13, 2017, at 9:57 AM, One Thousand Gnomes > gnomes@lxorguk.ukuu.org.uk wrote: > >>> A maximum limit of 16 operations per cpu_opv syscall invocation is >>> enforced, so user-space cannot generate a too long preempt-off critical >>> section. >> >> Except that all the operations could be going to mmapped I/O space and if >> I pick the right targets could take quite a long time to complete. > > We could check whether a struct page belongs to mmapped I/O space, and return > EINVAL in that case. > >> It's >> still only 16 operations - But 160ms is a lot worse than 10ms. In fact >> with compare_iter I could make it much much worse still as I get 2 x >> TMP_BUFLEN x 16 x worst case latency in my attack. That's enough to screw >> up plenty of things. > > Would a check that ensures the page is not mmapped I/O space be sufficient > to take care of this ? If happen to know which API I need to look for, it > would be welcome.
I think is_zone_device_page() is what I was looking for.
Let me know if I missed something,
Thanks,
Mathieu
> Thanks, > > Mathieu > > >> >> Alan > > -- > Mathieu Desnoyers > EfficiOS Inc. > http://www.efficios.com
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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