Date: Wed, 05 Sep 2012 11:10:41 +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 15 (CVE-2012-3497) - multiple TMEM hypercall vulnerabilities -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory CVE-2012-3497 / XSA-15 version 2 multiple TMEM hypercall vulnerabilities UPDATES IN VERSION 2 ==================== Public release. Credit Matthew Daley. ISSUE DESCRIPTION ================= Several sub-operations of the Transcendent Memory (TMEM) hypercall either do not correctly validate their inputs, do not correctly validate the privilege of the calling guest, or have other security-relevant bugs. A full list of the vulnerabilities in the TMEM system is not available at present. IMPACT ====== An unprivileged guest can overwrite hypervisor owned memory with the content of their choosing allowing them to escalate their privilege to that of the host. In addition an unprivileged guest can also crash the hypervisor, leading to a Denial of Service attack. VULNERABLE SYSTEMS ================== ONLY installations where "tmem" is specified on the hypervisor command line are vulnerable. Most Xen installations do not do so. All versions of Xen from 4.0 onward which have TMEM enabled and are running guests with untrusted administrators are vulnerable. Although we consider it unlikely, we have not been able to rule out the possibility that an malicious unprivileged user could exploit these issues via a trusted TMEM-aware kernel. Therefore all administrators are advised to disable TMEM even if all guest kernels are controlled and trusted. MITIGATION ========== Only systems which have TMEM enabled at boot time are affected by this issue. By default TMEM is disabled unless it is explicitly enabled via the hypervisor command line option "tmem". TMEM has been described by its maintainers as a technology preview, and is therefore not supported by them for use in production systems. Pending a full security audit of the code, the Xen.org security team recommends that Xen users do not enable TMEM. RESOLUTION ========== Work is ongoing, by the community maintainers for TMEM, to patch the specific bugs as they are found. This includes both the multiple vulnerabilities initially reported to the Xen.org security team, and multiple further vulnerabilities which have been discovered since then during our ad-hoc code inspection. At the time of writing, a complete set of fixes even for known issues is not available. PROCESS FOR TMEM VULNERABILITIES ================================ Until TMEM has gained production maturity, the Xen.org security team intends (subject of course to the permission of anyone disclosing to us) to handle these and future TMEM vulnerabilities in public, as if they were normal non-security-related bugs. We therefore intend that currently-known vulnerabilities will be publicly disclosed on the xen-devel mailing list, as normal bug reports, at the expiry of the XSA-15 embargo. In the meantime the list below may be helpful. Xen.org security team will ensure, on expiry of the embargo, that the documentation reflects TMEM's technology preview status. CREDIT ====== Thanks to Matthew Daley for finding these vulnerabilities (and that in XSA-12) and notifying the Xen.org security team. LIST OF KNOWN VULNERABILITIES ============================= **NOTE** that this is unlikely to be a complete list of problems. **NOTE** that after publication of this advisory, after the embargo ends, the advisory will no longer be updated to extend this list of vulnerabilities. See `Process for TMEM vulnerabilities', above. Multiple tmem save-related control ops do not check for NULL clients: TMEMC_SAVE_GET_CLIENT_WEIGHT, TMEMC_SAVE_GET_CLIENT_CAP, TMEMC_SAVE_GET_CLIENT_FLAGS and TMEMC_SAVE_END do not check that the cli_id used to find the client is valid, and can hence dereference a NULL client. This allows a malicious guest to crash the host (DoS), or, in the case of TMEMC_SAVE_END, memory corruption (DoS or worse). Multiple tmem save-related control ops do not check guest output buffer pointers: The functions tmemc_save_get_next_page, tmemc_save_get_next_inv and the TMEMC_SAVE_GET_POOL_UUID subop do not check incoming guest output buffer pointers, and do not use ie. copy_to_guest. A malicious guest can crash the host or cause memory corruption (DoS / code execution). Multiple tmem ops do not check for negative pool IDs: The functions tmemc_save_get_next_page, tmemc_restore_put_page and tmemc_restore_flush_page do not check for negative pool IDs, allowing (at least) memory corruption. do_tmem_destroy_pool does not check for invalid pool IDs: The function do_tmem_destroy_pool does not check for invalid pool IDs, allowing a malicious guest to crash the host or corrupt host memory (DoS / code execution). do_tmem_control's privilege check is commented out: This allows any guest access to control stack operations (many of which themselves do not have adequate argument checking). tmh_copy_from_client and tmh_copy_to_client have an integer overflow vulnerability: This can corrupt host memory. do_tmem_get()'s bad_copy error path leaves a spinlock held: The next operation on the same object will hang the CPU. This is a host DoS. do_tmem_op has at least one error path with broken locking checks: This is a host DoS or worse. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iQEcBAEBAgAGBQJQRyVDAAoJEIP+FMlX6CvZZSEH/11RvLycH5Qm0rkmWb16iuRU s9xmGDxGr6LDGLLYenp7RDc6FU7xjFxNeMhziIWckic2f0V1UtEqxiTHViEeOsOu AQfiwrUaaSf+fwcDqt07bb6gTynxyqS+faLKpk4bq89tKK1318JlxWN2gRtEW5g9 KEo7Bt/O0hYuIJBlBWnH48OHPzGSrwVaw51NLt0oPqiWp4w3ObLRhVttKB7VWJlw OQR9hSStVWhKR68VUBd/LpTZTkX/Hn5qwhX6ltgQ10RW1n4cF2pvebiKu6CtePCl JVBJgn/4ZmaT1joJ8SpX/BONnLt0KHNrublB6vO++1m+7+lBA5qXL38gg4jl48E= =yP/R -----END PGP SIGNATURE-----
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