linux-cve-announce - CVE-2022-50720: x86/apic: Don't disable x2APIC if locked

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Message-ID: <2025122417-CVE-2022-50720-0297@gregkh>
Date: Wed, 24 Dec 2025 13:26:19 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2022-50720: x86/apic: Don't disable x2APIC if locked

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

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

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

x86/apic: Don't disable x2APIC if locked

The APIC supports two modes, legacy APIC (or xAPIC), and Extended APIC
(or x2APIC).  X2APIC mode is mostly compatible with legacy APIC, but
it disables the memory-mapped APIC interface in favor of one that uses
MSRs.  The APIC mode is controlled by the EXT bit in the APIC MSR.

The MMIO/xAPIC interface has some problems, most notably the APIC LEAK
[1].  This bug allows an attacker to use the APIC MMIO interface to
extract data from the SGX enclave.

Introduce support for a new feature that will allow the BIOS to lock
the APIC in x2APIC mode.  If the APIC is locked in x2APIC mode and the
kernel tries to disable the APIC or revert to legacy APIC mode a GP
fault will occur.

Introduce support for a new MSR (IA32_XAPIC_DISABLE_STATUS) and handle
the new locked mode when the LEGACY_XAPIC_DISABLED bit is set by
preventing the kernel from trying to disable the x2APIC.

On platforms with the IA32_XAPIC_DISABLE_STATUS MSR, if SGX or TDX are
enabled the LEGACY_XAPIC_DISABLED will be set by the BIOS.  If
legacy APIC is required, then it SGX and TDX need to be disabled in the
BIOS.

[1]: https://aepicleak.com/aepicleak.pdf

The Linux kernel CVE team has assigned CVE-2022-50720 to this issue.

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

	Fixed in 5.19.17 with commit 05785ba834f23272f9d23427ae4a80ac505a5296
	Fixed in 6.0.3 with commit dd1241e00addbf0b95f6cd6ce32152692820657e
	Fixed in 6.1 with commit b8d1d163604bd1e600b062fb00de5dc42baa355f

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-2022-50720
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:
	Documentation/admin-guide/kernel-parameters.txt
	arch/x86/Kconfig
	arch/x86/include/asm/cpu.h
	arch/x86/include/asm/msr-index.h
	arch/x86/kernel/apic/apic.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/05785ba834f23272f9d23427ae4a80ac505a5296
	https://git.kernel.org/stable/c/dd1241e00addbf0b95f6cd6ce32152692820657e
	https://git.kernel.org/stable/c/b8d1d163604bd1e600b062fb00de5dc42baa355f