CVE-2026-23287

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

irqchip/sifive-plic: Fix frozen interrupt due to affinity setting

PLIC ignores interrupt completion message for disabled interrupt, explained

by the specification:

The PLIC signals it has completed executing an interrupt handler by

writing the interrupt ID it received from the claim to the

claim/complete register. The PLIC does not check whether the completion

ID is the same as the last claim ID for that target. If the completion

ID does not match an interrupt source that is currently enabled for

the target, the completion is silently ignored.

This caused problems in the past, because an interrupt can be disabled

while still being handled and plic_irq_eoi() had no effect. That was fixed

by checking if the interrupt is disabled, and if so enable it, before

sending the completion message. That check is done with irqd_irq_disabled().

However, that is not sufficient because the enable bit for the handling

hart can be zero despite irqd_irq_disabled(d) being false. This can happen

when affinity setting is changed while a hart is still handling the

interrupt.

This problem is easily reproducible by dumping a large file to uart (which

generates lots of interrupts) and at the same time keep changing the uart

interrupt's affinity setting. The uart port becomes frozen almost

instantaneously.

Fix this by checking PLIC's enable bit instead of irqd_irq_disabled().