CVE-2026-89751: x86/tdx: Fix off-by-one in port I/O handling

CVE-2026-89751: x86/tdx: Fix off-by-one in port I/O handling

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

x86/tdx: Fix off-by-one in port I/O handling

handle_in() and handle_out() in arch/x86/coco/tdx/tdx.c use:

    u64 mask = GENMASK(BITS_PER_BYTE * size, 0);

GENMASK(h, l) includes bit h. For size=1 (INB), this produces
GENMASK(8, 0) = 0x1FF (9 bits) instead of GENMASK(7, 0) = 0xFF (8
bits). The mask is one bit too wide for all I/O sizes.

Fix the mask calculation.

The Linux kernel CVE team has assigned CVE-2026-89751 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.19 with commit 03149948832a078f759022ed5b92e722d8d23c26 and fixed in 6.12.109 with commit 222b7005e4519f633b4cd666226256abbab46a1a
	Issue introduced in 5.19 with commit 03149948832a078f759022ed5b92e722d8d23c26 and fixed in 6.18.50 with commit c4a22154870813d10aa0b4c734a574c726f9d4b0
	Issue introduced in 5.19 with commit 03149948832a078f759022ed5b92e722d8d23c26 and fixed in 7.2.4 with commit bb45f705c4440dd3c689328319b88dd28770bbb8
	Issue introduced in 5.19 with commit 03149948832a078f759022ed5b92e722d8d23c26 and fixed in 7.3-rc1 with commit 0f63e656b1c679d32ac595de29d10c03efca6a25

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-89751
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	arch/x86/coco/tdx/tdx.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/222b7005e4519f633b4cd666226256abbab46a1a
	https://git.kernel.org/stable/c/c4a22154870813d10aa0b4c734a574c726f9d4b0
	https://git.kernel.org/stable/c/bb45f705c4440dd3c689328319b88dd28770bbb8
	https://git.kernel.org/stable/c/0f63e656b1c679d32ac595de29d10c03efca6a25