Bugzilla – Bug 950704
VUL-1: CVE-2015-7970: xen: x86: Long latency populate-on-demand operation is not preemptible (XSA-150)
Last modified: 2021-01-22 08:57:29 UTC
bugbot adjusting priority
The Xen packages in SUSE Linux Enterprise are affected by XSA-150 and XSA-153 related to a DoS when the populate-on-demand option is used. Confirmed source patches were not available in time for the scheduled update. A further update to Xen will contain these fixes.
public at http://xenbits.xen.org/xsa/advisory-150.html Xen Security Advisory CVE-2015-7970 / XSA-150 version 5 x86: Long latency populate-on-demand operation is not preemptible UPDATES IN VERSION 5 ==================== Updated patch. Compared to the version in XSA-150 v4 and earlier, this patch is simpler and involves less rearrangement of the code. It is therefore thought to be less risky. However, both this version and the earlier versions have been tested, and both versions eliminate the vulnerability. Readers who have already prepared updates with, and/or deployed, the earlier patch, do not necessarily need to update. Public release. ISSUE DESCRIPTION ================= When running an HVM domain in Populate-on-Demand mode, Xen would sometimes search the domain for memory to reclaim, in response to demands for population of other pages in the same domain. This search runs without preemption. The guest can, by suitable arrangement of its memory contents, create a situation where this search is a time-consuming linear scan of the guest's address space. The scan might be triggered by the guest's own actions, or by toolstack operations such as migration. In guests affected by XSA-153, this scan might be triggered simply by memory pressure in the guest. Even guests not started in PoD mode can create PoD entries. IMPACT ====== A malicious HVM guest administrator can cause a denial of service. Specifically, prevent use of a physical CPU for a significant period. If a host watchdog (Xen or dom0) is in use, this can lead to a watchdog timeout and consequently a reboot of the host. If another, innocent, guest, is configured with a watchdog, this issue can lead to a reboot of such a guest. In guests affected by XSA-153, this vulnerability may also be triggered by an unprivileged guest user, simply by imposing a workload which generates memory pressure. VULNERABLE SYSTEMS ================== The vulnerability is exposed to any x86 HVM guest. ARM is not vulnerable. x86 PV VMs are not vulnerable. Versions of Xen from 3.4 onwards are affected. MITIGATION ========== Running only PV guests will avoid this issue. On systems not also vulnerable to XSA-153, the vulnerability can be avoided by ensuring that only trusted guest kernels are used, and that further steps are taken to prevent a guest administrator from loading code into the kernel (e.g. by disabling loadable modules etc) or from using other mechanisms which allow them to run code at kernel privilege. CREDITS ======= This is issue was disclosed by Andrew Cooper of Citrix. RESOLUTION ========== Attached is a patch which resolves the issue by limiting the long-running "sweep" operation. This patch will resolve the issue on systems where PoD is not intentionally in use. (Ie, where all HVM guests are started with memory==maxmem.) When PoD is in use, there are concerns that there may be situations -- operating systems not tested, or buggy balloon drivers, for example -- where limiting the long-running operation may cause guests to crash which may otherwise not. Therefore, the patch should be used with caution. This patch can interact badly on configurations vulnerable to XSA-153. XSA-153 is triggerable by unprivileged guest users. The patch changes the consequences from a host-wide CPU denial problem (which might be tolerated without catastrophic symptoms in some configurations) into a likely guest crash; thus it limits the scope of the consequences to the specific guest, but may worsen the severity. xsa150.patch xen-unstable, Xen 4.6.x, Xen 4.5.x, Xen 4.4.x, Xen 4.3.x $ sha256sum xsa150* 9054215f08cab48d2523efb456eb3c93ca6ac580d661f6e4f1feca115c67afa8 xsa150.patch $ DEPLOYMENT DURING EMBARGO ========================= Deployment of the patches and/or mitigations described above (or others which are substantially similar) is permitted during the embargo, even on public-facing systems with untrusted guest users and administrators. But: Distribution of updated software is prohibited (except to other members of the predisclosure list). Predisclosure list members who wish to deploy significantly different patches and/or mitigations, please contact the Xen Project Security Team. (Note: this during-embargo deployment notice is retained in post-embargo publicly released Xen Project advisories, even though it is then no longer applicable. This is to enable the community to have oversight of the Xen Project Security Team's decisionmaking.) For more information about permissible uses of embargoed information, consult the Xen Project community's agreed Security Policy: http://www.xenproject.org/security-policy.html
QA: no good reproducer available. regression testing could be done on the populate-on-demand option enabled
openSUSE-SU-2015:2249-1: An update that fixes 10 vulnerabilities is now available. Category: security (moderate) Bug References: 947165,950704,954018,954405 CVE References: CVE-2015-3259,CVE-2015-4106,CVE-2015-5154,CVE-2015-5239,CVE-2015-5307,CVE-2015-6815,CVE-2015-7311,CVE-2015-7835,CVE-2015-7970,CVE-2015-8104 Sources used: openSUSE Leap 42.1 (src): xen-4.5.2_01-6.1
openSUSE-SU-2015:2250-1: An update that fixes 5 vulnerabilities is now available. Category: security (moderate) Bug References: 947165,950704,954018,954405 CVE References: CVE-2015-5307,CVE-2015-7311,CVE-2015-7835,CVE-2015-7970,CVE-2015-8104 Sources used: openSUSE 13.2 (src): xen-4.4.3_04-33.1
SUSE-SU-2015:2306-1: An update that fixes 10 vulnerabilities is now available. Category: security (moderate) Bug References: 950703,950704,950705,950706,951845,953527,954405,956408,956411,956832 CVE References: CVE-2015-5307,CVE-2015-7504,CVE-2015-7969,CVE-2015-7970,CVE-2015-7971,CVE-2015-7972,CVE-2015-8104,CVE-2015-8339,CVE-2015-8340,CVE-2015-8345 Sources used: SUSE Linux Enterprise Server 11-SP2-LTSS (src): xen-4.1.6_08-23.1 SUSE Linux Enterprise Debuginfo 11-SP2 (src): xen-4.1.6_08-23.1
SUSE-SU-2015:2326-1: An update that solves 12 vulnerabilities and has one errata is now available. Category: security (moderate) Bug References: 947165,950703,950704,950705,950706,951845,954018,954405,956408,956409,956411,956592,956832 CVE References: CVE-2015-5307,CVE-2015-7311,CVE-2015-7504,CVE-2015-7969,CVE-2015-7970,CVE-2015-7971,CVE-2015-7972,CVE-2015-8104,CVE-2015-8339,CVE-2015-8340,CVE-2015-8341,CVE-2015-8345 Sources used: SUSE Linux Enterprise Software Development Kit 11-SP3 (src): xen-4.2.5_18-21.1 SUSE Linux Enterprise Server 11-SP3 (src): xen-4.2.5_18-21.1 SUSE Linux Enterprise Desktop 11-SP3 (src): xen-4.2.5_18-21.1 SUSE Linux Enterprise Debuginfo 11-SP3 (src): xen-4.2.5_18-21.1
SUSE-SU-2015:2328-1: An update that fixes 13 vulnerabilities is now available. Category: security (moderate) Bug References: 947165,950703,950704,950705,950706,951845,954018,954405,956408,956409,956411,956592,956832 CVE References: CVE-2015-5307,CVE-2015-7311,CVE-2015-7504,CVE-2015-7835,CVE-2015-7969,CVE-2015-7970,CVE-2015-7971,CVE-2015-7972,CVE-2015-8104,CVE-2015-8339,CVE-2015-8340,CVE-2015-8341,CVE-2015-8345 Sources used: SUSE Linux Enterprise Software Development Kit 12 (src): xen-4.4.3_06-22.15.1 SUSE Linux Enterprise Server 12 (src): xen-4.4.3_06-22.15.1 SUSE Linux Enterprise Desktop 12 (src): xen-4.4.3_06-22.15.1
released
SUSE-SU-2015:2338-1: An update that solves 13 vulnerabilities and has one errata is now available. Category: security (moderate) Bug References: 947165,950703,950704,950705,950706,951845,954018,954405,955399,956408,956409,956411,956592,956832 CVE References: CVE-2015-5307,CVE-2015-7311,CVE-2015-7504,CVE-2015-7835,CVE-2015-7969,CVE-2015-7970,CVE-2015-7971,CVE-2015-7972,CVE-2015-8104,CVE-2015-8339,CVE-2015-8340,CVE-2015-8341,CVE-2015-8345 Sources used: SUSE Linux Enterprise Software Development Kit 11-SP4 (src): xen-4.4.3_06-29.1 SUSE Linux Enterprise Server 11-SP4 (src): xen-4.4.3_06-29.1 SUSE Linux Enterprise Desktop 11-SP4 (src): xen-4.4.3_06-29.1 SUSE Linux Enterprise Debuginfo 11-SP4 (src): xen-4.4.3_06-29.1
openSUSE-SU-2016:0124-1: An update that solves 15 vulnerabilities and has one errata is now available. Category: security (important) Bug References: 947165,950704,954018,954405,956408,956409,956411,956592,956832,957988,958007,958009,958493,958523,958918,959006 CVE References: CVE-2015-5307,CVE-2015-7311,CVE-2015-7504,CVE-2015-7549,CVE-2015-7970,CVE-2015-8104,CVE-2015-8339,CVE-2015-8340,CVE-2015-8341,CVE-2015-8345,CVE-2015-8504,CVE-2015-8550,CVE-2015-8554,CVE-2015-8555,CVE-2015-8558 Sources used: openSUSE 13.1 (src): xen-4.3.4_10-53.1