CVE-2022-42332

x86 shadow plus log-dirty mode use-after-free In environments where host
assisted address translation is necessary but Hardware Assisted Paging
(HAP) is unavailable, Xen will run guests in so called shadow mode. Shadow
mode maintains a pool of memory used for both shadow page tables as well as
auxiliary data structures. To migrate or snapshot guests, Xen additionally
runs them in so called log-dirty mode. The data structures needed by the
log-dirty tracking are part of aformentioned auxiliary data. In order to
keep error handling efforts within reasonable bounds, for operations which
may require memory allocations shadow mode logic ensures up front that
enough memory is available for the worst case requirements. Unfortunately,
while page table memory is properly accounted for on the code path
requiring the potential establishing of new shadows, demands by the
log-dirty infrastructure were not taken into consideration. As a result,
just established shadow page tables could be freed again immediately, while
other code is still accessing them on the assumption that they would remain
allocated.

Bugs

• <http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1033297&gt;

Notes