FreeBSD : xen-tools -- Unmediated PCI command register access in qemu (79f401cd-27e6-11e5-a4a5-002590263bf5)

This script is Copyright (C) 2015 Tenable Network Security, Inc.

Synopsis :

The remote FreeBSD host is missing a security-related update.

Description :

The Xen Project reports :

HVM guests are currently permitted to modify the memory and I/O decode
bits in the PCI command register of devices passed through to them.
Unless the device is an SR-IOV virtual function, after disabling one
or both of these bits subsequent accesses to the MMIO or I/O port
ranges would - on PCI Express devices - lead to Unsupported Request
responses. The treatment of such errors is platform specific.

Furthermore (at least) devices under control of the Linux pciback
driver in the host are handed to guests with the aforementioned bits
turned off. This means that such accesses can similarly lead to
Unsupported Request responses until these flags are set as needed by
the guest.

In the event that the platform surfaces aforementioned UR responses as
Non-Maskable Interrupts, and either the OS is configured to treat NMIs
as fatal or (e.g. via ACPI's APEI) the platform tells the OS to treat
these errors as fatal, the host would crash, leading to a Denial of

See also :

Solution :

Update the affected package.

Risk factor :

Medium / CVSS Base Score : 4.9

Family: FreeBSD Local Security Checks

Nessus Plugin ID: 84705 ()

Bugtraq ID:

CVE ID: CVE-2015-2756

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