Date: Tue, 20 Jun 2017 12:00:06 +0000 From: Xen.org security team <security@....org> To: xen-announce@...ts.xen.org, xen-devel@...ts.xen.org, xen-users@...ts.xen.org, oss-security@...ts.openwall.com CC: Xen.org security team <security-team-members@....org> Subject: Xen Security Advisory 217 - page transfer may allow PV guest to elevate privilege -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory XSA-217 version 2 page transfer may allow PV guest to elevate privilege UPDATES IN VERSION 2 ==================== Public release. ISSUE DESCRIPTION ================= Domains controlling other domains are permitted to map pages owned by the domain being controlled. If the controlling domain unmaps such a page without flushing the TLB, and if soon after the domain being controlled transfers this page to another PV domain (via GNTTABOP_transfer or, indirectly, XENMEM_exchange), and that third domain uses the page as a page table, the controlling domain will have write access to a live page table until the applicable TLB entry is flushed or evicted. Note that the domain being controlled is necessarily HVM, while the controlling domain is PV. IMPACT ====== A malicious pair of guests may be able to access all of system memory, allowing for all of privilege escalation, host crashes, and information leaks. VULNERABLE SYSTEMS ================== All Xen versions are vulnerable. Only x86 systems are affected. ARM systems are not vulnerable. Only systems where an attacker can control both a PV and an HVM guest are vulnerable. This must be presumed to include systems containing HVM domains with service domains such as stub domain device models. Systems containing only PV guests are not vulnerable. Systems containing only HVM domains serviced by dom0 device model processes are not vulnerable. Note that with libxl, xl, and libvirt, HVM domains use dom0 device model processes by default. MITIGATION ========== There is no mitigation for this vulnerability. Switching from stub device models to dom0 process device models is not recommended as a mitigation, as in practice the vulnerability is likely to be hard to exploit through this route; whereas dom0 process device models may have unknown vulnerabilities. CREDITS ======= This issue was discovered by Jann Horn of Google Project Zero. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa217.patch xen-unstable, Xen 4.8.x, Xen 4.7.x, Xen 4.6.x xsa217-4.5.patch Xen 4.5.x $ sha256sum xsa217* 3e896412389d8e59e417ea7bb3d5b47a20de27b8eae0420c98071ce4b17d219c xsa217.patch 4e555cf47faf5e8d2bba4ff8a31fbe72fb11a6c0e3b286f23b26e684a1809705 xsa217-4.5.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 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQEbBAEBCAAGBQJZSQ3LAAoJEIP+FMlX6CvZe2MH90dkMpagV2W3Q0uzwo3GT4tv VmrsM5O5oSCvJBpgRk397Nr6jbPfUOdH8LqHSuNjoU4vYThNqM8mTT0mqW0MKniK didfWFyXIjHuBIBaye2r+mFWQ5AFH9B4vp3XT65k+vgq6GTIlRmV8H/bGdeCE4kT 6ht+ZLzc9XAvOy46pxAw0nz51QkknX4DXC0JTJW77aqKFz3H9+LKS015MLPxBvwj JFgmGIgLHR9lsMIGHScLLFibzTE1cDGF9u0I2DLHpWsDMaZN6kJfq8xblEtq58EE goth3SydPXPq4UuLfRMQMHX+pCxCdh9bwz82qThSmMFY7h/kPbw340D9+bBZIw== =/qch -----END PGP SIGNATURE----- Download attachment "xsa217.patch" of type "application/octet-stream" (1384 bytes) Download attachment "xsa217-4.5.patch" of type "application/octet-stream" (1356 bytes)
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