xen-kernel -- x86: Disallow L3 recursive pagetable for 32-bit PV guests
The Xen Project reports:
On real hardware, a 32-bit PAE guest must leave the USER and RW bit
clear in L3 pagetable entries, but the pagetable walk behaves as if
they were set. (The L3 entries are cached in processor registers,
and don't actually form part of the pagewalk.)
When running a 32-bit PV guest on a 64-bit Xen, Xen must always OR
in the USER and RW bits for L3 updates for the guest to observe
architectural behaviour. This is unsafe in combination with
As there is no way to construct an L3 recursive pagetable in native
32-bit PAE mode, disallow this option in 32-bit PV guests.
A malicious 32-bit PV guest administrator can escalate their
privilege to that of the host.
Copyright © 2003-2005 Jacques Vidrine and contributors.
Please see the source of this document for full copyright