Restricting HOST flash access on OpenBMC
Hello,
Apologies, I have been working on this in a bit of a silo and I suspect a lot of people will be interested to know this work is going on.
The aim of my work is to provide a simple interface for the host and the BMC to talk in order for the BMC to give controlled access to the flash.
At the moment, the BMC maps the host LPC bus to point to the PNOR directly. This may be undesirable and presents security concerns. If the host can be taught to request access to the flash then the BMC could map the LPC bus into a region of its RAM and (depending on policy) writes wouldn't get propagated to the actual flash. Policy details are for later.
I developed a simple protocol to allow this exchange of information documented in the README.md file of the userspace test daemon I wrote to proof of concept this: https://github.com/cyrilbur-ibm/mboxbridge/tr
ee/newio I will no doubt move this somewhere more suitable in due course.
I chose to use the MBOX registers on the BMC as they provide a fast method of data transfer and can raise interrupts on both the host and BMC.
The aim of sharing this now is to show that the interface works and that implementation independent things can start to be integrated into skiboot and linux. Having said that, I would appreciate any feedback, I have had my head in this for quite some time please let me know if I've missed something.
The implementation is only a proof of concept, some details still need to be worked out, especially what happens on BMC reboot. I believe the interface is ok in that respect, just my implementation which is lacking.
Do try it out if you want. Of course changes need to be made to the BMC kernel as well as skiboot:
https://github.com/cyrilbur-ibm/linux/tree/newio
https://github.com/cyrilbur-ibm/skiboot/tree/newio
Thanks,
Cyril
How does this work on non-LPC platforms?
Quoted 50 lines · Cyril Bur
Hello,
Apologies, I have been working on this in a bit of a silo and I suspect a lot of people will be interested to know this work is going on.
The aim of my work is to provide a simple interface for the host and the BMC to talk in order for the BMC to give controlled access to the flash.
At the moment, the BMC maps the host LPC bus to point to the PNOR directly. This may be undesirable and presents security concerns. If the host can be taught to request access to the flash then the BMC could map the LPC bus into a region of its RAM and (depending on policy) writes wouldn't get propagated to the actual flash. Policy details are for later.
I developed a simple protocol to allow this exchange of information documented in the README.md file of the userspace test daemon I wrote to proof of concept this: https://github.com/cyrilbur-ibm/mboxbridge/tr
ee/newio I will no doubt move this somewhere more suitable in due course.I chose to use the MBOX registers on the BMC as they provide a fast method of data transfer and can raise interrupts on both the host and BMC.
The aim of sharing this now is to show that the interface works and that implementation independent things can start to be integrated into skiboot and linux. Having said that, I would appreciate any feedback, I have had my head in this for quite some time please let me know if I've missed something.
The implementation is only a proof of concept, some details still need to be worked out, especially what happens on BMC reboot. I believe the interface is ok in that respect, just my implementation which is lacking.
Do try it out if you want. Of course changes need to be made to the BMC kernel as well as skiboot:
https://github.com/cyrilbur-ibm/linux/tree/newio
https://github.com/cyrilbur-ibm/skiboot/tree/newioThanks,
Cyril
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Quoted 1 line · Rick Altherr
How does this work on non-LPC platforms?
A different mechanism such as IPMI can still be used on these.
This is basically a replacement for the code we have today which uses a backdoor into the BMC address space to directly manipulate the flash controller from the host.
That current mechanism is tricky, causes us to have at least 4 copies of the whole flash controller driver, and relies on a backdoor that we would like to close.
In the grand scheme of things, you can see this as an "accelerated" path to the flash for platforms that have an AST BMC on LPC, but you can still fallback to something like IPMI if that path isn't available.
Cheers,
Ben.
Quoted 66 lines
Quoted 63 lines · Cyril Bur
Hello,
Apologies, I have been working on this in a bit of a silo and I suspect
a lot of people will be interested to know this work is going on.The aim of my work is to provide a simple interface for the host and
the BMC to talk in order for the BMC to give controlled access to the
flash.At the moment, the BMC maps the host LPC bus to point to the PNOR directly. This may be undesirable and presents security concerns. If
the host can be taught to request access to the flash then the BMC could map the LPC bus into a region of its RAM and (depending on policy) writes wouldn't get propagated to the actual flash. Policy details are for later.I developed a simple protocol to allow this exchange of information documented in the README.md file of the userspace test daemon I wrote
to proof of concept this: https://github.com/cyrilbur-ibm/mboxbridg
e/tr
ee/newio I will no doubt move this somewhere more suitable in due course.I chose to use the MBOX registers on the BMC as they provide a fast method of data transfer and can raise interrupts on both the host and
BMC.The aim of sharing this now is to show that the interface works and that implementation independent things can start to be integrated into
skiboot and linux. Having said that, I would appreciate any feedback, I
have had my head in this for quite some time please let me know if I've
missed something.The implementation is only a proof of concept, some details still need
to be worked out, especially what happens on BMC reboot. I believe the
interface is ok in that respect, just my implementation which is lacking.Do try it out if you want. Of course changes need to be made to the BMC
kernel as well as skiboot:
https://github.com/cyrilbur-ibm/linux/tree/newio
https://github.com/cyrilbur-ibm/skiboot/tree/newioThanks,
Cyril
_______________________________________________
openbmc mailing list
[email protected]
https://lists.ozlabs.org/listinfo/openbmc