Good Day OpenBSD Team!


I previously sent this email to Mike Belopuhov (mikeb@openbsd.org), who is
listed in the HVN man page, he however said that he isn't able to assist
here, and recommended I send this email on to you guys:


I know this is a bit of a shot in the dark, but I am wondering if you could
potentially help with an OpenBSD HVN issue that I seem to be having in
OpenBSD 7.6. I got your email from the HVN man page.



A bit of background: due to changes in recent versions, it seems that
Kernel compilation flags have changed:

CMACHFLAGS+= -mretpoline-external-thunk -fcf-protection=branch

CMACHFLAGS+= -fret-clean



This activates BTI (branch target identifier) or IBT (indirect branch

tracking). The latter is the one from Intel and is activated using

-fcf-protection=branch.



To make everything work on the Dell HW, we have compiled all our own
libraries with -fcf-protection=branch.



*The problem:*

Hyper-V seems to show the same behaviour. But, a pure assumption from my
end, is that in the code for Hyper-V there is assembly code that has not
yet been adapted for BTI/IBT and thus causes a panic from the kernel's
point of view.

The main issue is the HVN network driver. The interface gets an IP and a
ping can be sent, for example, but no normal network traffic is possible.

normal network traffic is not possible.



Are there any known workarounds or patches for this problem?



Thank you very much for your help!



Warm Regards,

Adriaan Wildervanck