CVE-2026-89751

A moderate severity flaw was found in the Linux kernel's x86/tdx (Intel Trust Domain Extensions) guest port I/O handling. The handle_in() and handle_out() functions in arch/x86/coco/tdx/tdx.c computed the port I/O size mask as GENMASK(BITS_PER_BYTE * size, 0), which is one bit wider than intended (for example, 0x1FF instead of 0xFF for 1-byte I/O), so port I/O operations handled by the TDX guest support code could read or write one bit of data beyond the intended I/O size. Red Hat assessed this flaw as Moderate severity with a CVSS 3.1 score of 5.5 (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H): exploitation requires local access, and the established impact is to system availability, such as a kernel panic or system instability. Although the upstream description mentions potential information disclosure or data corruption, the current Red Hat assessment does not establish confidentiality or integrity impact. The vulnerable code is present in Red Hat Enterprise Linux 8 and later kernel streams and in OpenShift Container Platform releases that ship the RHEL CoreOS 9 kernel, while Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, and earlier Red Hat Enterprise Linux 8 minor streams are not affected because the vulnerable code is not present in those kernels. The fix is deferred for the affected streams because this Moderate-severity flaw has a CVSS score below 7.0 and Red Hat does not file trackers for kernel flaws at this severity; the fix will be delivered through a future scheduled kernel update, and the residual risk is limited to local availability impact on systems where the TDX guest port I/O code path is reachable.