title: x86/AMD: Debug Mask handling
description:
[This CNA information record relates to multiple CVEs; the
text explains which aspects/vulnerabilities correspond to which CVE.]
AMD CPUs since ~2014 have extensions to normal x86 debugging functionality.
Xen supports guests using these extensions.
Unfortunately there are errors in Xen's handling of the guest state, leading
to denials of service.
1) CVE-2023-34327 - An HVM vCPU can end up operating in the context of
a previous vCPUs debug mask state.
2) CVE-2023-34328 - A PV vCPU can place a breakpoint over the live GDT.
This allows the PV vCPU to exploit XSA-156 / CVE-2015-8104 and lock
up the CPU entirely.
affected:
{
defaultStatus: unknown
product: Xen
vendor: Xen
versions:
status: unknown, version: consult Xen advisory XSA-444
}
workarounds: For CVE-2023-34327, HVM VMs which can see the DBEXT feature are not
susceptible to running in the wrong state.  By default, VMs will see the
DBEXT feature on capable hardware, and when not explicitly levelled for
migration compatibility.
For CVE-2023-34328, PV VMs which cannot see the DBEXT feature cannot
leverage the vulnerability.