Bug 1877366 (CVE-2020-25603)

Summary: CVE-2020-25603 xen: missing memory barriers when accessing/allocating an event channel (XSA-340)
Product: [Other] Security Response Reporter: Guilherme de Almeida Suckevicz <gsuckevi>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED WONTFIX QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: 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 security flaw was found in Xen. Event channels control structures can be accessed without lock as long as the port is considered to be valid. A malicious guest may be able to cause a hypervisor crash resulting in a denial of service (DoS). An information leak and privilege escalation cannot be excluded. The highest threat from this vulnerability is to system availability.
Story Points: ---
Clone Of: Environment:
Last Closed: 2020-09-22 20:41:04 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: 1881583    
Bug Blocks: 1877386    

Description Guilherme de Almeida Suckevicz 2020-09-09 13:12:53 UTC
Event channels control structures can be accessed lockless as long as the port is considered to be valid. Such sequence is missing appropriate memory barrier (e.g smp_*mb()) to prevent both the compiler and CPU to re-order access.

Comment 1 Guilherme de Almeida Suckevicz 2020-09-09 13:20:43 UTC
Acknowledgments:

Name: the Xen project

Comment 2 Mauro Matteo Cascella 2020-09-15 08:22:29 UTC
Mitigation:

There is no known mitigation for this flaw apart from applying the patch.

Comment 4 Mauro Matteo Cascella 2020-09-15 10:19:56 UTC
Statement:

Systems running all versions of Xen are affected by this flaw. Whether a system is vulnerable will depend on the CPU and compiler used to build Xen. For all the systems, the presence and the scope of the vulnerability depends on the precise re-ordering performed by the compiler used to build Xen. x86 systems are only vulnerable if a compiler performs re-ordering. Arm systems will also be vulnerable if the CPU is able to re-order memory access.

This flaw has been rated as having a security impact of Moderate, and is not currently planned to be addressed in future updates of Red Hat Enterprise Linux 5. Red Hat Enterprise Linux 5 is now in Extended Life Phase of the support and maintenance life cycle. For additional information, refer to the Red Hat Enterprise Linux Life Cycle: https://access.redhat.com/support/policy/updates/errata/.

Comment 5 Mauro Matteo Cascella 2020-09-22 17:52:30 UTC
Created xen tracking bugs for this issue:

Affects: fedora-all [bug 1881583]

Comment 6 Product Security DevOps Team 2020-09-22 20:41:04 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-2020-25603

Comment 7 Mauro Matteo Cascella 2020-09-23 07:32:46 UTC
External References:

https://xenbits.xen.org/xsa/advisory-340.html