Xen Security Advisory XSA-274 Linux: Uninitialized state in PV syscall return path ISSUE DESCRIPTION ================= Linux has a `failsafe` callback, invoked by Xen under certain conditions. Normally in this failsafe callback, error_entry is paired with error_exit; and error_entry uses %ebx to communicate to error_exit whether to use the user or kernel return path. Unfortunately, on 64-bit PV Xen on x86, error_exit is called without error_entry being called first, leaving %ebx with an invalid value. IMPACT ====== A rogue user-space program could crash a guest kernel. Privilege escalation cannot be ruled out. VULNERABLE SYSTEMS ================== Only 64-bit x86 PV Linux systems are vulnerable. All versions of Linux are vulnerable. MITIGATION ========== Switching to HVM or PVH guests will mitigate this issue. CREDITS ======= This issue was discovered by M. Vefa Bicakci, and recognized as a security issue by Andy Lutorminski. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. NB this patch has not been accepted into Linux upstream yet. An updated advisory will be sent if the fix upstreamed looks significantly different. xsa274-linux-4.17.patch Linux 4.17 $ sha256sum xsa274* 0c30cb13d1d573f446c8cb8d4824ffad8ef9149a7589a19ef9bcc83c07bddcf5 xsa274-linux-4.17.patch $ NOTE ON THE LACK OF EMBARGO =========================== The patch for this issue was published on linux-kernel without being first reported to the XenProject Security Team.
Acknowledgments: Name: M. Vefa Bicakci, the Xen project Upstream: Andy Lutorminski
Created xen tracking bugs for this issue: Affects: fedora-all [bug 1608560]
This bug is now closed. Further updates for individual products will be reflected on the CVE page(s): https://access.redhat.com/security/cve/cve-2018-14678
Statement: This issue only affects guests running as Xen paravirtualized (PV) guests. Starting with Red Hat Enterprise Linux 7 onwards running Red Hat Enterprise Linux installations as Xen PV guests is not supported.