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xenXen ProjectXSA-348
HistoryDec 15, 2020 - 12:00 p.m.

undue recursion in x86 HVM context switch code

2020-12-1512:00:00
Xen Project
xenbits.xen.org
26

0.001 Low

EPSS

Percentile

18.2%

ISSUE DESCRIPTION

When they require assistance from the device model, x86 HVM guests must be temporarily de-scheduled. The device model will signal Xen when it has completed its operation, via an event channel, so that the relevant vCPU is rescheduled.
If the device model were to signal Xen without having actually completed the operation, the de-schedule / re-schedule cycle would repeat. If, in addition, Xen is resignalled very quickly, the re-schedule may occur before the de-schedule was fully complete, triggering a shortcut. This potentially repeating process uses ordinary recursive function calls, so could result a stack overflow.

IMPACT

A malicious or buggy stubdomain serving a HVM guest can cause Xen to crash, resulting in a Denial of Service (DoS) to the entire host.

VULNERABLE SYSTEMS

All Xen versions are vulnerable.
Only x86 systems are affected. Arm systems are not affected.
Only x86 stubdomains serving HVM guests can exploit the vulnerability.

CPENameOperatorVersion
xeneqany