LoongArch: Fix address space mismatch in kexec command line lookup

Overview

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.

Affected

• Linux >= 4a03b2ac06a5bcae29371866d9d11f5bfd4c9188 < 3b71f51fa3a247921408879eab2ddee82da8a980
• Linux >= 4a03b2ac06a5bcae29371866d9d11f5bfd4c9188 < eaa908d8d523b0ab75dab5ebd6662e70af5e5d7e
• Linux >= 4a03b2ac06a5bcae29371866d9d11f5bfd4c9188 < a94d6726ec8680a2b0c453fc782a543f68a1ea06
• Linux >= 4a03b2ac06a5bcae29371866d9d11f5bfd4c9188 < 7a54e0cbaad4a5a09e7cc7a4f05d181048e98ca7
• Linux >= 4a03b2ac06a5bcae29371866d9d11f5bfd4c9188 < 485ed44db5694d8d2e5027f63ad608e705286f30
• Linux 6.1

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.