Bug 950668 (CVE-2013-1917)

Summary:	CVE-2013-1917 kernel: xen: Xen PV DoS vulnerability with SYSENTER
Product:	[Other] Security Response	Reporter:	Petr Matousek <pmatouse>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED NOTABUG	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	dlaor, drjones, imammedo, lersek, pbonzini, security-response-team
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2013-05-13 08:01:43 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:	953569
Bug Blocks:	950673

Description Petr Matousek 2013-04-10 15:34:23 UTC

The SYSENTER instruction can be used by PV guests to accelerate system call processing. This instruction, however, leaves the EFLAGS register mostly unmodified - in particular, the NT flag doesn't get cleared. If the hypervisor subsequently uses IRET to return to the guest (which it will always do if the guest is a 32-bit one), that instruction will cause a #GP fault to be raised, but the recovery code in the hypervisor will again try to use IRET without intermediately clearing the NT flag. The #GP fault raised on this second IRET is a fatal event, causing the hypervisor to crash.

Malicious or buggy unprivileged user space can cause the entire host to crash.

The vulnerability is only exposed by 64-bit PV guests running on Intel CPUs.

Acknowledgements:

Red Hat would like to thank the Xen for reporting this issue.

Comment 1 Petr Matousek 2013-04-10 15:37:22 UTC

Statement:

Not vulnerable.

This issue did not affect the versions of the kernel-xen package as shipped with Red Hat Enterprise Linux 5 as we did not have support for sysenter for 64bit PV guests running on the Xen hypervisor (introduced in upstream changeset 16207:aeebd173c3fa).

This issue did not affect the versions of the Linux kernel as shipped with Red Hat Enterprise Linux 6 and Red Hat Enterprise MRG as we did not have support for Xen hypervisor.

Comment 3 Petr Matousek 2013-04-18 13:44:44 UTC

Created xen tracking bugs for this issue

Affects: fedora-all [bug 953569]

Comment 4 Fedora Update System 2013-05-05 02:25:11 UTC

xen-4.1.5-1.fc17 has been pushed to the Fedora 17 stable repository.  If problems still persist, please make note of it in this bug report.

Comment 5 Fedora Update System 2013-05-05 02:25:48 UTC

xen-4.2.2-1.fc18 has been pushed to the Fedora 18 stable repository.  If problems still persist, please make note of it in this bug report.