CVE-2023-46842

Unlike 32-bit PV guests, HVM guests may switch freely between 64-bit and
other modes. This in particular means that they may set registers used to
pass 32-bit-mode hypercall arguments to values outside of the range 32-bit
code would be able to set them to. When processing of hypercalls takes a
considerable amount of time, the hypervisor may choose to invoke a
hypercall continuation. Doing so involves putting (perhaps updated)
hypercall arguments in respective registers. For guests not running in
64-bit mode this further involves a certain amount of translation of the
values. Unfortunately internal sanity checking of these translated values
assumes high halves of registers to always be clear when invoking a
hypercall. When this is found not to be the case, it triggers a consistency
check in the hypervisor and causes a crash.

Notes