Bug 1518659 (CVE-2017-17565, xsa251) - CVE-2017-17565 xsa251 xen: improper bug check in x86 log-dirty handling (XSA-251)
Summary: CVE-2017-17565 xsa251 xen: improper bug check in x86 log-dirty handling (XSA-...
Status: CLOSED NOTABUG
Alias: CVE-2017-17565, xsa251
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
URL:
Whiteboard: impact=moderate,public=20171212,repor...
Keywords: Security
Depends On: 1525018
Blocks:
TreeView+ depends on / blocked
 
Reported: 2017-11-29 12:26 UTC by Adam Mariš
Modified: 2019-06-08 22:31 UTC (History)
13 users (show)

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Clone Of:
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Last Closed: 2019-06-08 03:32:29 UTC


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Description Adam Mariš 2017-11-29 12:26:35 UTC
ISSUE DESCRIPTION
=================

Memory sharing, available to x86 HVM guests only, uses a special value
in the global machine to physical address translation table (M2P).  PV
guests have full control over M2P entries corresponding to pages they
own.  A bug check (specifically, an assertion that an M2P entry is not
the special "shared" indicator) was insufficiently qualified, and as a
consequence is triggerable by PV guests in log-dirty mode
(e.g. because of being live migrated).

IMPACT
======

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

VULNERABLE SYSTEMS
==================

Xen versions 4.0 and later are affected.  Xen versions 3.4 and earlier
are not affected.

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

x86 HVM guests cannot exploit this vulnerability.

Only x86 PV guests can exploit this vulnerability, and only when being
run in shadow mode.  PV guests are typically run in shadow mode for live
migration, as well as for features like VM snapshot.

Note that save / restore does *not* use shadow mode, and so does not
expose this vulnerability.  Some downstreams also  include a "non-live
migration" feature, which also does not use shadow mode (and thus does
not expose this vulnerability).

MITIGATION
==========

Running only HVM guests avoids the vulnerability.

Avoiding live migration of x86 PV guests also avoids the vulnerability.

External References:

http://xenbits.xen.org/xsa/advisory-251.html

Comment 2 Adam Mariš 2017-12-12 13:14:34 UTC
Acknowledgments:

Name: the Xen project
Upstream: Jan Beulich (SUSE)

Comment 3 Adam Mariš 2017-12-12 13:16:17 UTC
Created xen tracking bugs for this issue:

Affects: fedora-all [bug 1525018]


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