CVE-2026-68435: LoongArch: Fix address space mismatch in kexec command line lookup

CVE-2026-68435: LoongArch: Fix address space mismatch in kexec command line lookup

[Greg Kroah-Hartman]

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

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

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

LoongArch: Fix address space mismatch in kexec command line lookup

When searching the loaded segments for the "kexec" command line marker,
the kexec_load(2) path (file_mode == 0) passes the user-space segment
buffer straight to strncmp() through a bogus (char __user *) cast. This
dereferences a user pointer in kernel context, which is wrong and is
flagged by sparse:

  arch/loongarch/kernel/machine_kexec.c:84:51: sparse: incorrect type in
  argument 2 (different address spaces) @@ expected char const * @@ got
  char [noderef] __user *

Here copy the marker-sized prefix of each segment into a small on-stack
buffer with copy_from_user() before comparing, and skip segments that
fault. The subsequent copy_from_user() that stages the full command line
into the safe area is left unchanged.

The Linux kernel CVE team has assigned CVE-2026-68435 to this issue.


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

	Issue introduced in 6.1 with commit 4a03b2ac06a5bcae29371866d9d11f5bfd4c9188 and fixed in 6.18.42 with commit a94d6726ec8680a2b0c453fc782a543f68a1ea06
	Issue introduced in 6.1 with commit 4a03b2ac06a5bcae29371866d9d11f5bfd4c9188 and fixed in 7.1.6 with commit 7a54e0cbaad4a5a09e7cc7a4f05d181048e98ca7
	Issue introduced in 6.1 with commit 4a03b2ac06a5bcae29371866d9d11f5bfd4c9188 and fixed in 7.2-rc5 with commit 485ed44db5694d8d2e5027f63ad608e705286f30

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-2026-68435
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/loongarch/kernel/machine_kexec.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/a94d6726ec8680a2b0c453fc782a543f68a1ea06
	https://git.kernel.org/stable/c/7a54e0cbaad4a5a09e7cc7a4f05d181048e98ca7
	https://git.kernel.org/stable/c/485ed44db5694d8d2e5027f63ad608e705286f30