Bug 1643116 (CVE-2018-18883)

Summary: CVE-2018-18883 xen: Nested VT-x usable even when disabled
Product: [Other] Security Response Reporter: Andrej Nemec <anemec>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED NOTABUG QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: ailan, drjones, imammedo, jforbes, knoel, m.a.young, mrezanin, pbonzini, rkrcmar, robinlee.sysu, vkuznets, xen-maint
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Last Closed: 2019-06-10 10:41:05 UTC Type: ---
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 1643118    
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Description Andrej Nemec 2018-10-25 14:16:07 UTC
When running HVM guests, virtual extensions are enabled in hardware because
Xen is using them.  As a result, a guest can blindly execute the
virtualisation instructions, and will exit to Xen for processing.

In the case that the guest hasn't followed the correct (virtual) configuration
procedure, it shouldn't be able to use the instructions, and Xen should
respond with #UD exception.  When nested virtualisation is disabled for the
guest, it is not permitted to complete the configuration procedure.

Unfortunately, when nested virtualisation is intended to be disabled for the
guest, an incorrect default value leads Xen to believe that the configuration
procedure has already been completed.

References:

https://seclists.org/oss-sec/2018/q4/98

Comment 1 Andrej Nemec 2018-10-25 14:16:37 UTC
Created xen tracking bugs for this issue:

Affects: fedora-all [bug 1643118]