| Summary: | <app-emulation/xen-4.7.3: PKRU and BND* leakage between vCPU-s | ||
|---|---|---|---|
| Product: | Gentoo Security | Reporter: | Christopher Díaz Riveros (RETIRED) <chrisadr> |
| Component: | Vulnerabilities | Assignee: | Gentoo Security <security> |
| Status: | RESOLVED FIXED | ||
| Severity: | minor | CC: | xen |
| Priority: | Normal | ||
| Version: | unspecified | ||
| Hardware: | All | ||
| OS: | Linux | ||
| URL: | https://xenbits.xen.org/xsa/advisory-220.html | ||
| Whiteboard: | B3 [noglsa cve] | ||
| Package list: | Runtime testing required: | --- | |
| Bug Depends on: | 624128 | ||
| Bug Blocks: | |||
commit 7a8fc554850ee501e1ad705b4154874adf102947 Author: Yixun Lan <dlan@gentoo.org> Date: Wed Jul 12 15:15:52 2017 +0800 app-emulation/xen: security bump fix XSA-217,218,219,220,221,222,223,224,225 Gentoo-Bug: 624112,624114,624116,624118,624120,624122,624124,624126,624130 Package-Manager: Portage-2.3.6, Repoman-2.3.2 :100644 100644 6534404116c... 49df2654a33... M app-emulation/xen/Manifest :000000 100644 00000000000... f66bd1b70f8... A app-emulation/xen/xen-4.7.3.ebuild :000000 100644 00000000000... bf73951bc39... A app-emulation/xen/xen-4.8.1-r2.ebuild Thank you Yixun Lan Arches please let us know when all is stable Added to an existing GLSA Request. Maintainer(s), please drop the vulnerable version(s). GLSA Vote: No Cleanup will occur in another bug. |
From $URL: ISSUE DESCRIPTION ================= Memory Protection Extensions (MPX) and Protection Key (PKU) are features in newer processors, whose state is intended to be per-thread and context switched along with all other XSAVE state. Xen's vCPU context switch code would save and restore the state only if the guest had set the relevant XSTATE enable bits. However, surprisingly, the use of these features is not dependent (PKU) or may not be dependent (MPX) on having the relevant XSTATE bits enabled. VMs which use MPX or PKU, and context switch the state manually rather than via XSAVE, will have the state leak between vCPUs (possibly, between vCPUs in different guests). This in turn corrupts state in the destination vCPU, and hence may lead to weakened protections Experimentally, MPX appears not to make any interaction with BND* state if BNDCFGS.EN is set but XCR0.BND{CSR,REGS} are clear. However, the SDM is not clear in this case; therefore MPX is included in this advisory as a precaution. IMPACT ====== There is an information leak, of control information mentioning pointers into guest address space; this may weaken address space randomisation and make other attacks easier. When an innocent guest acquires leaked state, it will run with incorrect protection state. This could weaken the protection intended by the MPX or PKU features, making other attacks easier which would otherwise be excluded; and the incorrect state could also cause a denial of service by preventing legitimate accesses. VULNERABLE SYSTEMS ================== Xen 4.4 and earlier are not vulnerable, as they do not use or expose MPX or PKU to guests. Xen 4.5 and later expose MPX to guests. Xen 4.7 and later expose PKU to guests. Therefore, Xen 4.5 and later are vulnerable. Only x86 hardware implementing the MPX or PKU features is vulnerable. At the time of writing, these are Intel Skylake (and later) processors for MPX, and Intel Skylake Server (and later) processors for PKU. ARM hardware is not vulnerable. The vulnerability is only exposed to HVM guests. PV guests cannot exploit the vulnerability. Vulnerable guest operating systems - ---------------------------------- Guests which use XSAVE for context switching PKU and MPX state are not vulnerable to inbound corruption caused by another malicious domain. With respect to PKU, the remaining outbound information leak is of no conceivable consequence. And, experimentally, MPX does not appear to have a real vulnerability, even though the CPU documentation is not clear. Therefore we think that these guests (those which use XSAVE) are not vulnerable. Linux uses XSAVE, so is therefore not vulnerable. MITIGATION ========== Passing "pku=0" on the hypervisor command line will avoid the PKU vulnerability (by not advertising the feature to guests). There is no corresponding option for the probably-theoretical MPX vulnerability. CREDITS ======= This issue was discovered by Andrew Cooper of Citrix. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa220.patch xen-unstable xsa220-4.8.patch Xen 4.8 xsa220-4.7.patch Xen 4.7 xsa220-4.6.patch Xen 4.6 xsa220-4.5.patch Xen 4.5 $ sha256sum xsa220* 8b86d9a284c0b14717467e672e63aebfc2bce201658493a54c64fb7c1863ce49 xsa220.patch 4b53ad5748313fb92c68eac1160b00d1bf7310019657028122a455855334252b xsa220-4.5.patch befe5ca5321d903428fc496abeee3a3b5eb0cee27a382e20d3caf8cc7bdfced2 xsa220-4.6.patch 555fa741348909943393aaf73571bc7817b30eafcff73dbfcd73911113db5d7f xsa220-4.7.patch 7a41ad9c6f9d46536abae051c517456bdfa3564278e98f80222a904df749fb0c xsa220-4.8.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.