CVE-2023-34322

For migration as well as to work around kernels unaware of L1TF (see XSA-273), PV guests may be run in shadow paging mode. Since Xen itself needs to be mapped when PV guests run, Xen and shadowed PV guests run directly the respective shadow page tables. For 64-bit PV guests this means running on the shadow of the guest root page table. In the course of dealing with shortage of memory in the shadow pool associated with a domain, shadows of page tables may be torn down. This tearing down may include the shadow root page table that the CPU in question is presently running on. While a precaution exists to supposedly prevent the tearing down of the underlying live page table, the time window covered by that precaution isn't large enough.

For migration as well as to work around kernels unaware of L1TF (see XSA-273), PV guests may be run in shadow paging mode. Since Xen itself needs to be mapped when PV guests run, Xen and shadowed PV guests run directly the respective shadow page tables. For 64-bit PV guests this means running on the shadow of the guest root page table. In the course of dealing with shortage of memory in the shadow pool associated with a domain, shadows of page tables may be torn down. This tearing down may include the shadow root page table that the CPU in question is presently running on. While a precaution exists to supposedly prevent the tearing down of the underlying live page table, the time window covered by that precaution isn't large enough.

Para la migración, así como para evitar kernels que no conocen L1TF (consulte XSA-273), los invitados PV pueden ejecutarse en modo de página oculta. Dado que el propio Xen debe mapearse cuando se ejecutan las maquinas PV de invitado, Xen y las shadowed PV de invitado ejecutan directamente las respectivas tablas de páginas ocultas. Para invitados PV de 64 bits, esto significa ejecutar en la shadow de la tabla de página raíz del invitado. Al tratar con la escasez de memoria en el shadow pool asociado con un dominio, es posible que se eliminen las tablas de páginas de shadows. Esta eliminación puede incluir la shadow de la tabla de página raíz en la que se está ejecutando actualmente la CPU en cuestión. Si bien existe una precaución para supuestamente evitar la eliminación de la tabla de las páginas activas subyacente, el período de tiempo cubierto por esa precaución no es lo suficientemente grande.