Date: Tue, 23 Feb 2021 16:37:07 +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 366 v2 (CVE-2021-27379) - missed flush in XSA-321 backport -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2021-27379 / XSA-366 version 2 missed flush in XSA-321 backport UPDATES IN VERSION 2 ==================== CVE assigned. Fixed erroneous reference to XSA-320; should have read XSA-321. ISSUE DESCRIPTION ================= An oversight was made when backporting XSA-321, leading entries in the IOMMU not being properly updated under certain circumstances. IMPACT ====== A malicious guest may be able to retain read/write DMA access to frames returned to Xen's free pool, and later reused for another purpose. Host crashes (leading to a Denial of Service) and privilege escalation cannot be ruled out. VULNERABLE SYSTEMS ================== Xen versions up to 4.11, from at least 3.2 onwards, are affected. Xen versions 4.12 and newer are not affected. Only x86 Intel systems are affected. x86 AMD as well as Arm systems are not affected. Only x86 HVM guests using hardware assisted paging (HAP), having a passed through PCI device assigned, and having page table sharing enabled can leverage the vulnerability. Note that page table sharing will be enabled (by default) only if Xen considers IOMMU and CPU large page size support compatible. MITIGATION ========== Suppressing the use of page table sharing will avoid the vulnerability (command line option "iommu=no-sharept"). Suppressing the use of large HAP pages will avoid the vulnerability (command line options "hap_2mb=no hap_1gb=no"). Not passing through PCI devices to HVM guests will avoid the vulnerability. CREDITS ======= This issue was reported as a bug by M. Vefa Bicakci, and recognized as a security issue by Roger Pau Monne of Citrix. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. Note that patches for released versions are generally prepared to apply to the stable branches, and may not apply cleanly to the most recent release tarball. Downstreams are encouraged to update to the tip of the stable branch before applying these patches. xsa366-4.11.patch Xen 4.11.x $ sha256sum xsa366* 3131c9487b9446655e2e21df4ccf1e003bec471881396d7b2b1a0939f5cbae96 xsa366.meta 8c8c18ca8425e6167535c3cf774ffeb9dcb4572e81c8d2ff4a73fefede2d4d94 xsa366-4.11.patch $ NOTE REGARDING LACK OF EMBARGO ============================== This was reported and debugged publicly, before the security implications were apparent. -----BEGIN PGP SIGNATURE----- iQE/BAEBCAAqFiEEI+MiLBRfRHX6gGCng/4UyVfoK9kFAmA1Lx4MHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZXRkH+MsCFrh/HOCaqzbdlT46sZBSS3B7wMjaCt4WtB8z MKxRY013/MMi7xbOhMvLE/qEtT8cdkOykxac9WjMnAPk2NQE3L3uRvoWsS8cYLa6 39RklCw0o/0YTsiY4bB5X1jI+8dBZxt4QPYl1YQqsLOHTlSJFix2Vm6w/K8+BZt9 ceS58GEoAawwlkVXdSH2115rSVRoBUZqgHCkPIc6eOjAmXCPL++8uUToWWhiROWD Ic0STLsf/Rt44G71rPh8GoFdncIBULcPlp1LbxCUEzRVhdmeb1/shs79vsIk0Z3l c2oHzypyS15p/kdQbulGTXDFq933C4ELtjrY/HwPumJSdg== =er6n -----END PGP SIGNATURE----- Download attachment "xsa366.meta" of type "application/octet-stream" (338 bytes) Download attachment "xsa366-4.11.patch" of type "application/octet-stream" (1512 bytes)
Powered by blists - more mailing lists
Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.