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xenXen ProjectXSA-279
HistoryNov 20, 2018 - 12:00 p.m.

x86: DoS from attempting to use INVPCID with a non-canonical addresses

2018-11-2012:00:00
Xen Project
xenbits.xen.org
346

4.7 Medium

CVSS2

Attack Vector

LOCAL

Attack Complexity

MEDIUM

Authentication

NONE

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

COMPLETE

AV:L/AC:M/Au:N/C:N/I:N/A:C

5.6 Medium

CVSS3

Attack Vector

LOCAL

Attack Complexity

HIGH

Privileges Required

LOW

User Interaction

NONE

Scope

CHANGED

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

HIGH

CVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:N/A:H

0.974 High

EPSS

Percentile

99.9%

ISSUE DESCRIPTION

The INVPCID instruction raises #GP[0] if an attempt is made to invalidate a non-canonical address. Older flushing mechanisms such as INVLPG tolerate this without error, and perform no action.
There is one guest accessible path in Xen where a non-canonical address was passed into the TLB flushing code. This previously had no ill effect, but became vulnerable with the introduction of PCID to reduce the performance hit from the Meltdown mitigations.

IMPACT

A buggy or malicious PV guest can crash the host.

VULNERABLE SYSTEMS

Only hardware which supports the INVPCID instruction is vulnerable. This is available on Intel Haswell processors and later. AMD x86 processors are not known to support this instruction, and ARM processors are entirely unaffected.
Only versions of Xen with PCID support are vulnerable. Support first appeared in Xen 4.11 but was backported to the stable trees as part of the Meltdown (XSA-254 / CVE-2017-5754) fixes. Xen 4.10.2, 4.9.3, 4.8.4 as well as the stable-4.7 and 4.6 branches are vulnerable.
The vulnerability is only exposed to 64-bit PV guests. 32-bit PV guests, as well as HVM/PVH guests cannot exploit the vulnerability.

4.7 Medium

CVSS2

Attack Vector

LOCAL

Attack Complexity

MEDIUM

Authentication

NONE

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

COMPLETE

AV:L/AC:M/Au:N/C:N/I:N/A:C

5.6 Medium

CVSS3

Attack Vector

LOCAL

Attack Complexity

HIGH

Privileges Required

LOW

User Interaction

NONE

Scope

CHANGED

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

HIGH

CVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:N/A:H

0.974 High

EPSS

Percentile

99.9%