linux-cve-announce - CVE-2023-54172: x86/hyperv: Disable IBT when hypercall page lacks ENDBR instruction

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Message-ID: <2025123021-CVE-2023-54172-bcdc@gregkh>
Date: Tue, 30 Dec 2025 13:09:40 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2023-54172: x86/hyperv: Disable IBT when hypercall page lacks ENDBR instruction

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

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

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

x86/hyperv: Disable IBT when hypercall page lacks ENDBR instruction

On hardware that supports Indirect Branch Tracking (IBT), Hyper-V VMs
with ConfigVersion 9.3 or later support IBT in the guest. However,
current versions of Hyper-V have a bug in that there's not an ENDBR64
instruction at the beginning of the hypercall page. Since hypercalls are
made with an indirect call to the hypercall page, all hypercall attempts
fail with an exception and Linux panics.

A Hyper-V fix is in progress to add ENDBR64. But guard against the Linux
panic by clearing X86_FEATURE_IBT if the hypercall page doesn't start
with ENDBR. The VM will boot and run without IBT.

If future Linux 32-bit kernels were to support IBT, additional hypercall
page hackery would be needed to make IBT work for such kernels in a
Hyper-V VM.

The Linux kernel CVE team has assigned CVE-2023-54172 to this issue.

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

	Fixed in 6.1.45 with commit 98cccbd0a19a161971bc7f7feb10577adc62c400
	Fixed in 6.4.10 with commit 73626b70b361ddda7c380e52c236aa4f2487c402
	Fixed in 6.5 with commit d5ace2a776442d80674eff9ed42e737f7dd95056

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-2023-54172
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/hyperv/hv_init.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/98cccbd0a19a161971bc7f7feb10577adc62c400
	https://git.kernel.org/stable/c/73626b70b361ddda7c380e52c236aa4f2487c402
	https://git.kernel.org/stable/c/d5ace2a776442d80674eff9ed42e737f7dd95056