Linux ioperm bitmap context switching issues

2020-07-1612:00:00

Xen Project

xenbits.xen.org

7.8 High

CVSS3

Attack Vector

LOCAL

Attack Complexity

LOW

Privileges Required

LOW

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

HIGH

Integrity Impact

HIGH

Availability Impact

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

4.6 Medium

CVSS2

Access Vector

LOCAL

Access Complexity

LOW

Authentication

NONE

Confidentiality Impact

PARTIAL

Integrity Impact

PARTIAL

Availability Impact

PARTIAL

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

0.0004 Low

EPSS

Percentile

13.4%

JSON

ISSUE DESCRIPTION

Linux 5.5 overhauled the internal state handling for the iopl() and ioperm() system calls. Unfortunately, one aspect on context switch wasn’t wired up correctly for the Xen PVOps case.

IMPACT

IO port permissions don’t get rescinded when context switching to an unprivileged task. Therefore, all userspace can use the IO ports granted to the most recently scheduled task with IO port permissions.

VULNERABLE SYSTEMS

Only x86 guests are vulnerable.
All versions of Linux from 5.5 are potentially vulnerable.
Linux is only vulnerable when running as x86 PV guest. Linux is not vulnerable when running as an x86 HVM/PVH guests.
The vulnerability can only be exploited in domains which have been granted access to IO ports by Xen. This is typically only the hardware domain, and guests configured with PCI Passthrough.