|Summary:||CVE-2015-7972 xen: populate-on-demand balloon size inaccuracy can crash guests on x86|
|Product:||[Other] Security Response||Reporter:||Fabio Olive Leite <fleite>|
|Component:||vulnerability||Assignee:||Red Hat Product Security <security-response-team>|
|Status:||CLOSED NOTABUG||QA Contact:|
|Version:||unspecified||CC:||ailan, drjones, imammedo, knoel, mrezanin, pbonzini, rkrcmar, security-response-team, vkuznets, xen-maint|
|Fixed In Version:||Doc Type:||Bug Fix|
|Doc Text:||Story Points:||---|
|Last Closed:||2018-03-07 10:04:48 UTC||Type:||---|
|oVirt Team:||---||RHEL 7.3 requirements from Atomic Host:|
|Cloudforms Team:||---||Target Upstream Version:|
|Bug Depends On:||1276344|
Description Fabio Olive Leite 2015-10-28 18:56:22 UTC
The design of the memory populate-on-demand (PoD) system requires that a guest's memory ballooning driver reach its memory reduction target. The target is not entirely well-defined in terms of the information visible to the appropriate parts of the system, so some unknown set of guests (but probably most guests) will fail this criterion. If the guest memory balloon driver does not free sufficient memory to reach its target, the guest will proceed to run with a nonzero number of outstanding PoD pages. When the guest or management toolstack touches such a page, the hypervisor would search the guest memory for a page containing only zeroes. If no such page is found, the guest crashes. Prior to the patch for XSA-150, the search might lock up the relevant physical cpu for a while. After the patch to XSA-150, it might crash the guest even if a suitable zero page is available. This means that in the current arrangements toolstack software must apply an adjustment to a guest's PoD target as supplied to Xen. Neither xend nor libxl do this. Guests configured with PoD might be unstable, especially under load. Mitigation: Reducing the guest's memory target, after guest startup, can cause the guest's ballon driver to eliminate the PoD discrepancy. If the guest successfully balloons down, it will no longer be vulnerable.
Comment 2 Martin Prpič 2015-10-29 13:43:34 UTC
External References: http://xenbits.xen.org/xsa/advisory-153.html
Comment 3 Martin Prpič 2015-10-29 13:51:48 UTC
Created xen tracking bugs for this issue: Affects: fedora-all [bug 1276344]
Comment 4 Fedora Update System 2015-11-08 22:21:14 UTC
xen-4.5.1-14.fc23 has been pushed to the Fedora 23 stable repository. If problems still persist, please make note of it in this bug report.
Comment 5 Fedora Update System 2015-11-10 00:22:29 UTC
xen-4.5.1-14.fc22 has been pushed to the Fedora 22 stable repository. If problems still persist, please make note of it in this bug report.
Comment 6 Fedora Update System 2015-11-10 00:50:37 UTC
xen-4.4.3-7.fc21 has been pushed to the Fedora 21 stable repository. If problems still persist, please make note of it in this bug report.