Bug 1880137 (CVE-2020-25596)

Summary:	CVE-2020-25596 xen: x86 pv guest kernel DoS via SYSENTER (XSA-339)
Product:	[Other] Security Response	Reporter:	Guilherme de Almeida Suckevicz <gsuckevi>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED NOTABUG	QA Contact:
Severity:	low	Docs Contact:
Priority:	low
Version:	unspecified	CC:	acaringi, ailan, bhu, bmasney, brdeoliv, dhoward, drjones, dvlasenk, fhrbata, hkrzesin, imammedo, jforbes, jshortt, jstancek, knoel, m.a.young, mrezanin, nmurray, pbonzini, ptalbert, robinlee.sysu, rvrbovsk, security-response-team, vkuznets, xen-maint
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:	A flaw was found in Xen. One of Xen's sanitization paths injects a #GP fault and incorrectly delivers it twice to the guest. This flaw allows malicious or buggy user space to crash the guest kernel, resulting in a VM denial of service.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2020-09-22 20:41:38 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	1881617
Bug Blocks:	1877386

Description Guilherme de Almeida Suckevicz 2020-09-17 18:26:21 UTC

The SYSENTER instruction leaves various state sanitization activities to software. One of Xen's sanitization paths injects a #GP fault, and incorrectly delivers it twice to the guest. This causes the guest kernel to observe a kernel-privilege #GP fault (typically fatal) rather than a user-privilege #GP fault (usually converted into SIGSEGV/etc).

Comment 1 Guilherme de Almeida Suckevicz 2020-09-17 18:26:27 UTC

Acknowledgments:

Name: the Xen project

Comment 3 Mauro Matteo Cascella 2020-09-18 16:15:11 UTC

Mitigation:

Running only x86 PVH/HVM guests avoids the vulnerability.

Comment 4 Mauro Matteo Cascella 2020-09-22 18:27:27 UTC

Created xen tracking bugs for this issue:

Affects: fedora-all [bug 1881617]

Comment 5 Product Security DevOps Team 2020-09-22 20:41:38 UTC

This bug is now closed. Further updates for individual products will be reflected on the CVE page(s):

https://access.redhat.com/security/cve/cve-2020-25596

Comment 6 Mauro Matteo Cascella 2020-09-23 07:37:03 UTC

External References:

https://xenbits.xen.org/xsa/advisory-339.html

Comment 7 RaTasha Tillery-Smith 2020-09-29 19:15:40 UTC

Statement:

All Xen versions from 3.2 onward are vulnerable. Red Hat Enterprise Linux 5 is not affected by this flaw, as it shipped in an older version of Xen.