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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2020.0873 Xen: Load Value Injection (LVI) speculative side channel 11 March 2020 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Xen Publisher: Xen Operating System: Windows UNIX variants (UNIX, Linux, OSX) Impact/Access: Access Privileged Data -- Existing Account Resolution: Patch/Upgrade CVE Names: CVE-2020-0551 Reference: ESB-2020.0869 Original Bulletin: http://xenbits.xen.org/xsa/advisory-315.html Comment: Xen notes: "Only Intel based processors are potentially affected. Processors from other manufacturers (e.g. AMD) are not believed to be vulnerable." - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2020-0551 / XSA-315 Load Value Injection (LVI) speculative side channel ISSUE DESCRIPTION ================= This is very closely related to the Microarchitectural Data Sampling vulnerabilities from May 2019. Please see https://xenbits.xen.org/xsa/advisory-297.html for details about MDS. A new way of using the micro-architectural details behind MDS has been identified. Instead of simply trying to sample data from a different privilege context, an attacker can arrange for poisoned data to be consumed (speculatively) in a victim context. This expands the range of tools by which an attacker can manipulate speculation in the victim context to leak data via a side channel. For more details, see: https://software.intel.com/security-software-guidance/insights/deep-dive-load-value-injection IMPACT ====== An attacker, which could include a malicious untrusted user process on a trusted guest, or an untrusted guest, can potentially cause a victim context (process, or guest, or guest kernel, or hypervisor) to leak secrets available to it. VULNERABLE SYSTEMS ================== Systems running all versions of Xen are affected. Only x86 processors are vulnerable. ARM processors are not believed to be vulnerable. Only Intel based processors are potentially affected. Processors from other manufacturers (e.g. AMD) are not believed to be vulnerable. Please consult the Intel Security Advisory for details on the affected processors. MITIGATION ========== Xen does not support the use of SGX (Software Guard Extensions). Outside of the SGX enclave case, the attacker has a limited ability to control the paging behaviour in the victim context. Therefore, it is not believed that there is a practical way to attack a victim context which is not an SGX enclave. Furthermore, preexisting work (including fixes for MDS, SMAP hardening for user pointers) and in-progress work (core scheduling for SMT systems) all raise the bar further for an attacker. There are no known LVI gadgets within Xen. As a result, we have decided not to make any changes to default configurations of Xen. Systems with untrusted PV guests, and whose host administrators are worried about potential LVI gadgets, might wish to consider changing the VM to be HVM instead, or make use of PV-Shim, to limit the scope of a potential attack. NOTE REGARDING PAGE MODIFICATION LOGGING ======================================== Included for completeness, rather than due to being a realistic concern: On Intel Broadwell and later systems, Xen uses Page Modification Logging to accelerate logdirty tracking on migration. The use of this does put the guest kernel at a higher risk of being attacked, due to the use of EPT Access/Dirty bits used behind the scenes. Userspace shouldn't be able to influence when a migration occurs, but booting Xen with `ept=no-ad` will mitigate this concern by causing Xen to fall back to software logdirty tracking. RESOLUTION ========== There is no complete resolution available. In general, administrators of Xen systems are recommended to take no action in response to this vulnerability. If potential LVI gadgets are discovered in Xen, they will be addressed on a case by case basis, in the same way as Spectre v1 hardening. NOTE REGARDING LACK OF EMBARGO ============================== Despite an attempt to organise predisclosure, the discoverers ultimately did not authorise a predisclosure. - -----BEGIN PGP SIGNATURE----- iQFABAEBCAAqFiEEI+MiLBRfRHX6gGCng/4UyVfoK9kFAl5nyAsMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZposH/0ZH/AXAFND2aBRdxKoWZtWyAaxrI0NPRz/H+AEZ CKtoV7E0HmwCSucxJOCe95yv/shKYSqoG4mMkxT+6v1gH7Hv/2dbl12G0Nlo5lyq LSkbvyLwCa1ceL6xa5qanx0GkJL+tiOP3EPDBKpO5Lqok5WS/uXQRwIequArPLNi S4xmE0oKv/yOXRRe2BhnAp6+lY/U6kuMxVNEXF5/6p3/31tnZhabkLJp5N2yl5Ts OEVjwnzEYRgi5npes1TW6PkPA5p0L4rq/oiVPvTqJsNWRkCmHvR2uRXDc1cI/9gs wnam4wTVF2tOXZ8/+n+XvUVUPeLAqzncv2D8+RWkX8pKu18= =DFQP - -----END PGP SIGNATURE----- - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. The mailing list you are subscribed to is maintained within your organisation, so if you do not wish to continue receiving these bulletins you should contact your local IT manager. If you do not know who that is, please send an email to auscert@auscert.org.au and we will forward your request to the appropriate person. NOTE: Third Party Rights This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. The decision to follow or act on information or advice contained in this security bulletin is the responsibility of each user or organisation, and should be considered in accordance with your organisation's site policies and procedures. AusCERT takes no responsibility for consequences which may arise from following or acting on information or advice contained in this security bulletin. NOTE: This is only the original release of the security bulletin. It may not be updated when updates to the original are made. If downloading at a later date, it is recommended that the bulletin is retrieved directly from the author's website to ensure that the information is still current. Contact information for the authors of the original document is included in the Security Bulletin above. If you have any questions or need further information, please contact them directly. Previous advisories and external security bulletins can be retrieved from: https://www.auscert.org.au/bulletins/ =========================================================================== Australian Computer Emergency Response Team The University of Queensland Brisbane Qld 4072 Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for member emergencies only. =========================================================================== -----BEGIN PGP SIGNATURE----- Comment: http://www.auscert.org.au/render.html?it=1967 iQIVAwUBXmh7b2aOgq3Tt24GAQiRhw/+O0wmdEzvBi1XVQed/LFyWO5SNfzApcIt 9vJyUscT3nyke79BMREB2b5oewEwkPTU21AsilCtOTejs7ohP2JVcYbGGB7rS3IV bAjU556C9Vk03Yq/qf9CtupVL229FUZ3yL8qz4Q58hOaCrrYEL+x5Sr7eQcawN7X dFd5PRzUb4BB4TeqY9oWGwP52aYBck1mMe8BnlpFaa/q3kMlhM5TBmtYFtb8pwsE VYlBQ8HjT/2YeT9698AqZW0WX6Qxz/RRx/yFsS/3UJcnbMSasqQIi3DvzjLzMCtf Zv3cfrCbBZhkgeuM+bmWvevh1wHH6i90QFQDPloUqUYMYXj9XZ5sye1OW4/kxOSw xh8qBfUVGs+W1NEMv+GtEnsycXJBa5gxbjG4lKSVD4dW8ClhbkKTAarYd8NuecMr KuBzYKPH+ogzU87QklUgdN7uZGaGE+Ow5DjL32PfVT5se80PxRqgpmj6ycqAfN5j Y0eXcIBo1zOCE5iSnj19H2z3Kcuv+Gmm/OFXU48Klxwsclh4Q1hPo8LseqNH3jTg jBAJPAmTLP0goUFn7Z2eiMswYP90lZ+qiTnAdInxGko83aR1iaIebkOZW6wMajGC tJeKg1iR1vSY7vbnJQLq000S692QIPYbDoTVLXINQ3WtSied6rSrIlofS6NRbcQb WA6s2tJ4op4= =s4jW -----END PGP SIGNATURE-----