GSoc-2017: Platforms - Microkernelizing Linux, help needed

José Roberto Teixeira jrctbr at ...9...
Thu Mar 2 04:23:52 CET 2017

Hi, Norman,

I think this explanation you gave would fit greatly in the Genode site
documentation. It would help a lot if the documentation had some guidance
on where to start, essential reading (like Tanenbaum's book on Operating
Systems), etc. Personally it would be great because I work with systems
development (Java, etc) but have a lot of interest on microkernels and such
areas are far from each other. I already programmed in C and enjoy
optimizing things. A high level path on what should be read by people with
some programming background could attract more help.

I think microkernels have a fantastic potential and particularly this
project. The inherent security, the concept of delegation of responsibility
of sharing resources through other microkernels, the reduction on the
trusted code base by an order of magnitude and the consequence of making it
auditable is a revolution. Once it begin being used in some distribution
with only the essential it will get momentum.

By the way, some time ago I saw some discussion here about how to make this
effort more visible. I remember it ended because the focus of the project
was about developing the framework. I understand and agree with that, but
if/when the idea comes back, I suggest considering releasing a very basic
server installation: essential GNU tools, TCP/IP stack, login through SSH,
a compiler, etc. The problem would be the drivers. But to counter that, you
could release the ISO at least for Raspberry Pi which is a fixed hardware
and is very widespread. It could be used as a home server by hobbyists as a
firewall (where security is paramount), as a file server, etc. Or, maybe by
handling the work of a dedicated server that don't need to withstand great
loads. To call more attention, it should run starting at Raspberry Pi 1
model B, which has 512MB. About this last requirement (to run on Raspberry
Pi 1), I don't remember very well, but I think running Samba, Apache and a
firewall (which is built in Linux TCP/IP stack) should not exhaust the
memory, so I think it's possible.

Sorry for having digressed. ;)

Best regards,

José Roberto

2017-03-01 12:58 GMT-03:00 Sky Liu <blackskygg at ...9...>:

> Hi Norman,
> Thanks for the detailed suggestions with so much patience. I'm a
> practitioner, so I really appreciate details, and I'll check out the stuff
> that you've mentioned and try to get started ASAP.
> BTW, do you have any suggestions on small related tasks that I can take in
> prior to my formal application for the GSoC project? I think committing
> small patches would be a great starting point to getting familiar with the
> Genode codebase.
> Best Regards,
> Zhongze Liu.
> 2017-03-01 19:37 GMT+08:00 Norman Feske <norman.feske at ...1...>:
>> Hello Sky Liu,
>> thank you for your interest in Genode!
>> > I'm a college student majoring Information Security in HUST, and I'm
>> > interested in genode's GSoC project on microkernelizaing the Linux
>> > kernel. I've been quite interested in microkernel OSs and
>> > virtualization, with limited experiences working on xen and the linux
>> > kernel. and have been in the MINIX community for a short time, so I was
>> > attracted by this challenge at the first sight.
>> >
>> > However, I'm still new to the genode project. So I'll appreciate it if I
>> > could get from you some suggestions on where to get started. :)
>> The best way to start exploring Genode is the "Genode Foundations" book,
>> which you can download here:
>> I recommend you to at follow the getting-started section, and skim over
>> the Chapter 3 (Architecture) and Section 4.7 (Component compositions) to
>> get a tangible feeling for Genode.
>> To practically tackle the "microkernelization of Linux", there are
>> actually two approaches. (1) The first approach is to enable Genode to
>> access devices of the Linux system you are working on. This is
>> convenient, but it bears the risk that a device driver (running in a
>> Genode component) may interfere with the Linux kernel, crashing the
>> system. The other approach (2) is booting a custom-made Linux system +
>> Genode's core as init process in Qemu. The latter approach would be
>> equivalent to how we work with the various microkernels.
>> Depending on your interests, you may quickly dive in into the actual
>> Genode code (1) or work on a custom run environment for Linux-based
>> Genode system (2) first.
>> Regarding the actual topic, the overall challenge is allowing Genode's
>> device drivers access to the hardware that is normally accessed by the
>> Linux kernel only. From Linux' point of view, Genode appears as a
>> user-level device driver. So one piece of the puzzle is to gain a good
>> understanding of Linux' user-level device-driver support. From Genode's
>> perspective, device hardware is accessed through the IO_MEM, IO_PORT,
>> and IRQ services of Genode's core component. So in principle, the topic
>> comes down to implementing these services for the 'base-linux' version
>> of core by using Linux' interfaces for user-level device drivers.
>> There are several stages:
>> 1. By implementing the IO_PORT service, Genode components can interact
>>    with simple port-I/O-devices such as the PIT timer. The
>>    implementation should by straight-forward: When running core at
>>    I/O privilege level (IOPL) 3, core can execute the regular
>>    'inb', 'outb', etc. instructions. A simple test component could
>>    request a Genode IO_PORT session for, let's say, the PIT, program
>>    the PIT as a running counter, and repeatedly read the current
>>    counter value.
>> 2. Non-trivial devices need access to memory-mapped I/O registers.
>>    Core's IO_MEM service makes such registers available to its
>>    clients as a dataspace (the concept is explained in the book).
>>    On Linux, dataspaces are represented as memory-mapped files, passed
>>    from core to the driver component by passing a file descriptor, and
>>    attached to the driver's address space via 'mmap'. Consequently,
>>    the problem comes down to core obtaining a file descriptor for
>>    a given physical address region. Here the challenge is to find
>>    a suitable Linux kernel mechanism that hands out portions of
>>    physical memory as a file descriptor.
>>    With the principle support for memory-mapped I/O and port I/O
>>    in place, it should be possible to run the VESA framebuffer driver.
>> 3. Most drivers use device interrupts. To use those drivers, core's
>>    IRQ service needs to be implemented. Again, this calls for an
>>    investigation of Linux' user-level device driver support.
>> 4. Direct memory access. Many drivers use DMA to let the device
>>    write directly into memory. For this to work, the driver must
>>    supply the targeted memory address to the device. On systems
>>    without IOMMU, this is the physical bus address. In order to
>>    use DMA on Genode/Linux, DMA buffers need to be allocated as
>>    contiguous physical memory and their physical addresses must
>>    become known to the user-level driver component. In systems with
>>    IOMMU, the device-physical addresses a virtualized. So there is
>>    more freedom. But the details ultimately depends on the Linux
>>    handling of IOMMUs.
>> 5. In Genode, PCI devices are managed by the so-called platform
>>    driver. When a regular device driver needs access to a certain
>>    device, it does not use core's IO_MEM, IO_PORT, and IRQ services
>>    directly but it requests a platform session. A platform session is
>>    like a virtual bus where one or multiple devices are present,
>>    depending on the platform driver's policy. The platform session
>>    makes the device resources of those devices available to the
>>    client (the device driver). Under the hood, the platform driver
>>    opens IO_MEM/IO_PORT/IRQ sessions at core.
>>    In order to use Genode's existing arsenal of device drivers on
>>    Linux, we need either a platform-driver version specifically adapted
>>    for Linux (when re-using the Linux PCI driver), or investigate a way
>>    to use our regular platform driver (including the PCI driver)
>>    directly (this would be pretty cool!).
>> I hope that the level of detail does not frighten you. We certainly
>> don't expect you to complete all these stages. E.g., if completing stage
>> 1 to 3, there would already be demonstratable results. Stage 4 certainly
>> requires an investigation into the ways about the interplay of the IOMMU
>> handling of the kernel with user-level device drivers. Stage 5 also has
>> a atrong design aspect to it.
>> It goes without saying that we won't leave you on your own. :-)
>> Cheers
>> Norman
>> --
>> Dr.-Ing. Norman Feske
>> Genode Labs
>> ·
>> Genode Labs GmbH · Amtsgericht Dresden · HRB 28424 · Sitz Dresden
>> Geschäftsführer: Dr.-Ing. Norman Feske, Christian Helmuth
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