Bug 1544453 (CVE-2018-7542, xsa256) - CVE-2018-7542 xsa256 xen: x86 PVH guest without LAPIC may DoS the host (XSA-256)
Summary: CVE-2018-7542 xsa256 xen: x86 PVH guest without LAPIC may DoS the host (XSA-256)
Alias: CVE-2018-7542, xsa256
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
Whiteboard: impact=moderate,public=20180227,repor...
Keywords: Security
Depends On: 1549572
TreeView+ depends on / blocked
Reported: 2018-02-12 14:31 UTC by Adam Mariš
Modified: 2019-06-08 22:40 UTC (History)
13 users (show)

Clone Of:
Last Closed: 2019-06-08 03:39:38 UTC

Attachments (Terms of Use)

Description Adam Mariš 2018-02-12 14:31:25 UTC

So far, x86 PVH guests can be configured with or without Local APICs.
Configurations with Local APICs are identical to x86 HVM guests, and
will use as much hardware acceleration support as possible.
Configurations without Local APICs try to turn off all hardware
acceleration, and disable all software emulation.

Multiple paths in Xen assume the presence of a Local APIC without
sufficient checks, and can fall over a NULL pointer.  On Intel hardware,
the logic to turn off hardware acceleration is incomplete and leaves the
guest with full control of the real Task Priority Register.


A malicious or buggy guest may cause a hypervisor crash, resulting in
a Denial of Service (DoS) affecting the entire host.


Xen version 4.8 and onwards are vulnerable.

Only x86 systems are vulnerable.  ARM systems are not vulnerable.

Only x86 PVH guests can exploit the vulnerability.  x86 PV and HVM
guests cannot exploit the vulnerability.


Running only PV or HVM guests avoids the vulnerability.

Running all PVH guests with "apic=1" in the guest configuration file
(or equivalent thereof) also avoids the vulnerability.

External References:


Comment 2 Adam Mariš 2018-02-27 12:38:56 UTC

Name: the Xen project
Upstream: Ian Jackson (Citrix)

Comment 3 Adam Mariš 2018-02-27 12:39:36 UTC
Created xen tracking bugs for this issue:

Affects: fedora-all [bug 1549572]

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