CVE-2024-42126

/// Technical description

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

powerpc: Avoid nmi_enter/nmi_exit in real mode interrupt.

nmi_enter()/nmi_exit() touches per cpu variables which can lead to kernel

crash when invoked during real mode interrupt handling (e.g. early HMI/MCE

interrupt handler) if percpu allocation comes from vmalloc area.

Early HMI/MCE handlers are called through DEFINE_INTERRUPT_HANDLER_NMI()

wrapper which invokes nmi_enter/nmi_exit calls. We don't see any issue when

percpu allocation is from the embedded first chunk. However with

CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK enabled there are chances where percpu

allocation can come from the vmalloc area.

With kernel command line "percpu_alloc=page" we can force percpu allocation

to come from vmalloc area and can see kernel crash in machine_check_early:

[ 1.215714] NIP [c000000000e49eb4] rcu_nmi_enter+0x24/0x110

[ 1.215717] LR [c0000000000461a0] machine_check_early+0xf0/0x2c0

[ 1.215719] --- interrupt: 200

[ 1

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References