CVE-2026-64214

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

powerpc/time: Remove redundant preempt_disable|enable() calls from arch_irq_work_raise()

A kernel panic is observed when handling machine check exceptions from real mode.

BUG: Unable to handle kernel data access on read at 0xc00000006be21300 Oops: Kernel access of bad area, sig: 11 [#1] MSR: 8000000000001003 <SF,ME,RI,LE> CR: 88222248 XER: 00000005 CFAR: c00000000003ffc4 DAR: c00000006be21300 DSISR: 40000000 IRQMASK: 0 NIP [c000000000029e40] arch_irq_work_raise+0x10/0x70 LR [c00000000003ffc8] machine_check_queue_event+0xa8/0x150 Call Trace: [c0000000179d3c70] [c00000000003ff64] machine_check_queue_event+0x44/0x150 [c0000000179d3d30] [c0000000000084e0] machine_check_early_common+0x1f0/0x2c0

The crash occurs because arch_irq_work_raise() calls preempt_disable() from machine check exception (MCE) handlers running in real mode. In this context, accessing the preempt_count can fault, leading to the panic.

The preempt_disable()/preempt_enable() pair in arch_irq_work_raise() was originally added by commit 0fe1ac48bef0 (powerpc/perf_event: Fix oops due to perf_event_do_pending call) to avoid races while raising irq work from exception context.

Later, commit 471ba0e686cb (irq_work: Do not raise an IPI when queueing work on the local CPU) added preemption protection in irq_work_queue() path, while commit 20b876918c06 (irq_work: Use per cpu atomics instead of regular atomics) added equivalent protection in irq_work_queue_on() before reaching arch_irq_work_raise():

irq_work_queue() / irq_work_queue_on() -> preempt_disable() -> __irq_work_queue_local() -> irq_work_raise() -> arch_irq_work_raise()

As a result, callers other than mce_irq_work_raise() already execute with preemption disabled, making the additional preempt_disable()/preempt_enable() pair in arch_irq_work_raise() redundant.

The arch_irq_work_raise() function executes in NMI context when called from MCE handler. Hence we will not be preempted or scheduled out since we are in NMI context with MSR[EE]=0. Therefore, it is safe to remove the preempt_disable()/preempt_enable() calls from here.

Remove it to avoid accessing preempt_count from real mode context.

[Maddy: Fixed the commit title]

Weakness

The product dereferences a pointer that it expects to be valid but is NULL.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/31467b23823ffec1f6fff407f8e3ca9af8b7491a
• https://git.kernel.org/stable/c/51860e423592893cd7bfa7287d99a3aff4dc3a9d
• https://git.kernel.org/stable/c/6dcd072a5ae3aed336e4a67a7d4cc5205b240065
• https://git.kernel.org/stable/c/72d8d1c36452a4d3ee134b1da48de7518c1329f9
• https://git.kernel.org/stable/c/8079acc5ee5235a627e4586d4f42082a9000ea64
• https://git.kernel.org/stable/c/a09d07ac45e283c9861a9ceea06f56d0ba851d22