Memory protection in RTEMS

[Gedare Bloom]

On Thu, Apr 2, 2015 at 11:47 AM, Tomasz Gregorek
<tomasz.gregorek at gmail.com> wrote:
> 2015-04-02 17:38 GMT+02:00 Gedare Bloom <gedare at rtems.org>:
>>
>> On Thu, Apr 2, 2015 at 11:19 AM, Tomasz Gregorek
>> <tomasz.gregorek at gmail.com> wrote:
>> > Hi Gedare
>> >
>> > Thank you for your comments, they answer my question.
>> >
>> > We will look at other RTOSes this time.
>> >
>> OK, I'd be happy to hear what you find or settle on. It's a topic that
>> I have continued interest in working on for RTEMS.
>
>
> I'll let you know.
> So far I've seen some commercial RTOS with MPU. At the moment we consider
> even Linux so you can say that the selection process is at early stage.
>
Great. If you need hard RT you must avoid Linux. Even soft RT is iffy
there. The only feasible way to do real-time memory protection is with
a region-based approach using MPU/segmentation like I wrote on my
blog, or to write some custom hardware mechanisms and roll-your-own.
Anything else seems unlikely to me to achieve RT guarantees.

Good luck!
Gedare

> Tomasz
>
>>
>> Gedare
>>
>> > Thanks
>> > Tomasz
>> >
>> > 2015-04-02 17:01 GMT+02:00 Gedare Bloom <gedare at rtems.org>:
>> >>
>> >> Hi Tomasz,
>> >>
>> >> It is possible to implement some memory protection between threads. As
>> >> you noticed, RTEMS is a SASOS with "one process" when viewed from the
>> >> POSIX interface. Generalizing memory protection in such a system is
>> >> hard. The most common approach I know of is to provide separate
>> >> protection domains for each thread stack. In theory, you could create
>> >> a protection domain for the RTEMS "kernel", but I'm not aware of
>> >> anyone that has tried hard to do that. You may also look for the "Zero
>> >> Kernel" work some folks did as a research project at Univ of Idaho I
>> >> think it was.
>> >>
>> >> If you want memory protection, you'd have to tailor it to your
>> >> specific application requirements and set-up the MMU/MPU to do it.
>> >> Final note: Since there is no notion of privilege in RTEMS, any thread
>> >> can always disable or modify the protection domains since priviliged
>> >> registers and instructions are available. Thus, while you may add
>> >> memory protection, it would not be for a complete security solution.
>> >>
>> >> Gedare
>> >>
>> >> On Thu, Apr 2, 2015 at 10:04 AM, Tomasz Gregorek
>> >> <tomasz.gregorek at gmail.com> wrote:
>> >> > Hi
>> >> >
>> >> > We are investigating possible OSes for a new product where one of the
>> >> > requirements is memory protection between processes.
>> >> >
>> >> > Does RTEMS supports memory protection? If not than is it planned to
>> >> > implement memory protection?
>> >> >
>> >> > This is what I found so far:
>> >> >
>> >> > RTEMS is single process, multiple threads and as such have everything
>> >> > in
>> >> > single memory space.
>> >> > http://comments.gmane.org/gmane.os.rtems.user/19858
>> >> >
>> >> > Gedare's blog with his implementation of memory protection from
>> >> > 2011/2012.
>> >> >
>> >> > http://gedare-csphd.blogspot.be/2011/12/rtems-memory-protection-api.html
>> >> > but it seems that this code didn't get to the main.
>> >> >
>> >> > Project "MMU Support" by Aanjhan Ranganathan from 6 years ago:
>> >> > https://devel.rtems.org/wiki/Projects/MMU_Support
>> >> >
>> >> > Source code configures MMUs but it seems it do it to enable cache
>> >> > only,
>> >> > not
>> >> > the memory protection. Though I did only simple search through the
>> >> > code.
>> >> > There are exception handlers for some architectures/CPUs but only for
>> >> > few if
>> >> > not for only one.
>> >> >
>> >> > Best regards
>> >> > Tomasz Gregorek
>> >> >
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>> >> > users at rtems.org
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>> >
>> >
>
>