Comment by devttyeu
3 hours ago
The big question is whether this can break out of KVM and whether it can be microrode patched / patched in any other way.
And whether it's really real in the first place.
3 hours ago
The big question is whether this can break out of KVM and whether it can be microrode patched / patched in any other way.
And whether it's really real in the first place.
One hopes that a hypervisor would not expose hardware control registers directly in the first place, except ones deliberately designed for virtualization support.
Otherwise, the guest is running effectively at the same privilege level as the hypervisor (that's useful sometimes, but probably not intended in most applications).
Yeah, just started looking at this with my team (we run a cloud with VM instance offering on AMD so this very much caught our eye)
So far seems this is about right:
1. You need platform register access, so seems can't KVM-escape with just this
2. Big question is what about breaking Confidential SEV-SNP guests from the host?
Ok, on 2. and in general this exploit only works on pre-Zen AMD platforms as the repo states in not-so-clear terms.
Zen changed DTC (DRAM Controller) to UMC (Unified Memory Controller), UMC is programmed at boot, and one would hope they figured that locking access to it makes sense when they were adding confidential compute support; Not clear though because there is no public documentation on it, so best we can hope for is some statement from AMD/3rd party researcher saying "this won't work on Zen because X/Y/Z"
This hack is 99% giving people the control over their own computers they should already have had. Guy is a Robin Hood.
When Chris Domas left Battelle for Intel years back, shortly after hardware-fuzzing a bank of thin-clients to discover undocumented x86 instructions, I was convinced Intel was basically keeping him on the payroll to shut him up.