Bug 1983988 (CVE-2021-3656)

Summary: CVE-2021-3656 kernel: SVM nested virtualization issue in KVM (VMLOAD/VMSAVE)
Product: [Other] Security Response Reporter: Mauro Matteo Cascella <mcascell>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED ERRATA QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: acaringi, adscvr, airlied, alciregi, bhu, blc, brdeoliv, bskeggs, chwhite, crwood, dhoward, dvlasenk, fhrbata, fpacheco, hdegoede, hkrzesin, jarod, jarodwilson, jeremy, jforbes, jlelli, jmaloy, jonathan, josef, jshortt, jstancek, jwboyer, kcarcia, kernel-maint, kernel-mgr, lgoncalv, linville, masami256, mchehab, mlangsdo, mlevitsk, nmurray, pbonzini, pmatouse, ptalbert, qzhao, rhandlin, rvrbovsk, security-response-team, steved, walters, williams
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: kernel 5.14-rc7 Doc Type: If docs needed, set a value
Doc Text:
A flaw was found in the KVM's AMD code for supporting SVM nested virtualization. The flaw occurs when processing the VMCB (virtual machine control block) provided by the L1 guest to spawn/handle a nested guest (L2). Due to improper validation of the "virt_ext" field, this issue could allow a malicious L1 to disable both VMLOAD/VMSAVE intercepts and VLS (Virtual VMLOAD/VMSAVE) for the L2 guest. As a result, the L2 guest would be allowed to read/write physical pages of the host, resulting in a crash of the entire system, leak of sensitive data or potential guest-to-host escape.
 Story Points: ---
Clone Of: Environment:
Last Closed: 2021-09-28 18:21:06 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: 1985423, 1985424, 1985425, 1985426, 1985427, 1985428, 1985429, 1985430, 1985431, 1985432, 1985433, 1985434, 1985435, 1985436, 1985437, 1995452    
Bug Blocks: 1983680, 1986799    

Description Mauro Matteo Cascella 2021-07-20 11:12:50 UTC 
A flaw was found in the KVM's AMD code for supporting SVM nested virtualization. The flaw occurs when processing the VMCB (virtual machine control block) provided by the L1 guest to spawn/handle a nested guest (L2). Due to improper validation of the "virt_ext" field, this issue could allow a malicious L1 to disable both VMLOAD/VMSAVE intercepts and VLS (Virtual VMLOAD/VMSAVE) for the L2 guest. As a result, the L2 guest would be allowed to read/write physical pages of the host, resulting in a crash of the entire system, leak of sensitive data or potential guest-to-host escape.

Upstream fix:
https://git.kernel.org/pub/scm/virt/kvm/kvm.git/commit/?id=c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc
Comment 5 Mauro Matteo Cascella 2021-08-02 14:03:07 UTC 
If L1 disables VMLOAD/VMSAVE intercepts, and doesn't enable Virtual VMLOAD/VMSAVE (currently not supported for the nested hypervisor), then VMLOAD/VMSAVE must operate on the L1 physical memory, which is only possible by making L0 intercept these instructions. Failure to do so allowed the nested guest to run VMLOAD/VMSAVE unintercepted, and thus read/write portions of the host physical memory.
Comment 6 Mauro Matteo Cascella 2021-08-02 15:12:41 UTC 
This bug was introduced in kernel version 4.13 while enabling the Virtual VMLOAD/VMSAVE feature:
https://github.com/torvalds/linux/commit/89c8a4984fc9
Comment 7 Mauro Matteo Cascella 2021-08-19 07:24:17 UTC 
Created kernel tracking bugs for this issue:

Affects: fedora-all [bug 1995452]
Comment 14 errata-xmlrpc 2021-09-28 14:35:01 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8.1 Extended Update Support

Via RHSA-2021:3676 https://access.redhat.com/errata/RHSA-2021:3676
Comment 15 Product Security DevOps Team 2021-09-28 18:21:06 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-2021-3656
Comment 16 errata-xmlrpc 2021-10-12 15:04:56 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7.6 Advanced Update Support
  Red Hat Enterprise Linux 7.6 Update Services for SAP Solutions
  Red Hat Enterprise Linux 7.6 Telco Extended Update Support

Via RHSA-2021:3812 https://access.redhat.com/errata/RHSA-2021:3812
Comment 17 errata-xmlrpc 2021-10-12 15:29:11 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2021:3801 https://access.redhat.com/errata/RHSA-2021:3801
Comment 18 errata-xmlrpc 2021-10-12 15:29:28 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2021:3802 https://access.redhat.com/errata/RHSA-2021:3802
Comment 20 errata-xmlrpc 2021-10-19 06:51:09 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8.2 Extended Update Support

Via RHSA-2021:3909 https://access.redhat.com/errata/RHSA-2021:3909
Comment 21 errata-xmlrpc 2021-10-19 07:03:06 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8.2 Extended Update Support

Via RHSA-2021:3904 https://access.redhat.com/errata/RHSA-2021:3904
Comment 22 errata-xmlrpc 2021-10-26 07:38:09 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7.7 Advanced Update Support
  Red Hat Enterprise Linux 7.7 Update Services for SAP Solutions
  Red Hat Enterprise Linux 7.7 Telco Extended Update Support

Via RHSA-2021:3987 https://access.redhat.com/errata/RHSA-2021:3987
Comment 23 errata-xmlrpc 2021-11-02 08:42:58 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2021:4056 https://access.redhat.com/errata/RHSA-2021:4056
Comment 24 errata-xmlrpc 2021-11-02 09:52:26 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2021:4088 https://access.redhat.com/errata/RHSA-2021:4088