Subject: CVE-2024-40944: x86/kexec: Fix bug with call depth tracking

From: Greg Kroah-Hartman <[email-masked]>

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

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

x86/kexec: Fix bug with call depth tracking

The call to cc_platform_has() triggers a fault and system crash if call depth
tracking is active because the GS segment has been reset by load_segments() and
GS_BASE is now 0 but call depth tracking uses per-CPU variables to operate.

Call cc_platform_has() earlier in the function when GS is still valid.

  [ bp: Massage. ]

The Linux kernel CVE team has assigned CVE-2024-40944 to this issue.

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

	Issue introduced in 6.2 with commit 5d8213864ade and fixed in 6.6.35 with commit d91ddd050826
	Issue introduced in 6.2 with commit 5d8213864ade and fixed in 6.9.6 with commit 2cfb464669b6
	Issue introduced in 6.2 with commit 5d8213864ade and fixed in 6.10 with commit 93c1800b3799

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-2024-40944
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/kernel/machine_kexec_64.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/d91ddd05082691e69b30744825d18ae799293258
	https://git.kernel.org/stable/c/2cfb464669b645a9b98478b74f2bcea9860dcff1
	https://git.kernel.org/stable/c/93c1800b3799f17375989b0daf76497dd3e80922