Date: Wed, 24 Jul 2013 14:00:46 +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@....org> Subject: Xen Security Advisory 60 (CVE-2013-2212) - Excessive time to disable caching with HVM guests with PCI passthrough -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory CVE-2013-2212 / XSA-60 version 5 Excessive time to disable caching with HVM guests with PCI passthrough UPDATES IN VERSION 5 ==================== Corrected credit. ISSUE DESCRIPTION ================= HVM guests are able to manipulate their physical address space such that processing a subsequent request by that guest to disable caches takes an extended amount of time changing the cachability of the memory pages assigned to this guest. This applies only when the guest has been granted access to some memory mapped I/O region (typically by way of assigning a passthrough PCI device). This can cause the CPU which processes the request to become unavailable, possibly causing the hypervisor or a guest kernel (including the domain 0 one) to halt itself ("panic"). For reference, as long as no patch implementing an approved alternative solution is available (there's only a draft violating certain requirements set by Intel's documentation), the problematic code is the function vmx_set_uc_mode() (in that it calls ept_change_entry_emt_with_range() with the full guest GFN range, which the guest has control over, but which also would be a problem with sufficiently large but not malicious guests). IMPACT ====== A malicious domain, given access to a device with memory mapped I/O regions, can cause the host to become unresponsive for a period of time, potentially leading to a DoS affecting the whole system. VULNERABLE SYSTEMS ================== Xen version 3.3 onwards is vulnerable. Only systems using the Intel variant of Hardware Assisted Paging (aka EPT) are vulnerable. MITIGATION ========== This issue can be avoided by not assigning PCI devices to untrusted guests, or by running HVM guests with shadow mode paging (through adding "hap=0" to the domain configuration file). CREDITS ======= Zhenzhong Duan found the issue as a bug, which on examination by the Xenproject.org Security Team turned out to be a security problem. RESOLUTION ========== There is currently no resolution to this issue. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iQEcBAEBAgAGBQJR7932AAoJEIP+FMlX6CvZ8pUIAJFFqtelnwQ58gEM3XYmbBdo FXF9xPiykqCbRzSfbVohmSj3vmORUsI22m8kk1fsJmSayJr9P8nJaYLqdr4/tcMf gqDLqBFWiOf+O48ULFaPf7eDBnVUzYQXBAcEEkfInjenvYgclTmdMQUbFGCtr+/O 6BI8Y0NU6K5Nawu7n3VZK7j6D7VniwyNnIfgApK+k2PLdb9r9m4GQdQVulYOSw8h 8H49C3D6c1L6m63he6c3NiyjfLZbFZbcqZuJPMMM5IR/J025Om6Kxyxcmx4wCCog nnyOPjCalPe9zOdsQlOEbrvH/UV/4U1EzkiWR2hRLbOS9bFJ2YweQxhvn7k/TVk= =rRXP -----END PGP SIGNATURE-----
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