CVE-2026-23287: irqchip/sifive-plic: Fix frozen interrupt due to affinity setting
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 plicirqeoi() 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 irqdirqdisabled().
However, that is not sufficient because the enable bit for the handling hart can be zero despite irqdirqdisabled(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 irqdirqdisabled().
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
debian/linuxto a version that resolves this vulnerability.Fixed in 6.1.176-1Fixed in 6.1.190-1Fixed in 6.12.107-1Fixed in 6.12.113-1Fixed in 7.2.12-1Fixed in 7.2.13-1 - Upgrade
Upgrade
ubuntu/linux-aws-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1061.64~22.04.1 - Upgrade
Upgrade
ubuntu/linux-azure-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1063.71~22.04.1 - Upgrade
Upgrade
ubuntu/linux-azure-fde-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1062.69~22.04.1 - Upgrade
Upgrade
ubuntu/linux-gcp-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1064.72~22.04.1 - Upgrade
Upgrade
ubuntu/linux-hwe-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-136.136~22.04.1 - Upgrade
Upgrade
ubuntu/linux-ibm-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1061.62~22.04.1 - Upgrade
Upgrade
ubuntu/linux-lowlatency-hwe-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-136.136.2~22.04.1 - Upgrade
Upgrade
ubuntu/linux-nvidia-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1059.62~22.04.1 - Upgrade
Upgrade
ubuntu/linux-oracle-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1058.61~22.04.1 - Upgrade
Upgrade
ubuntu/linux-riscv-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-136.136~22.04.3 - Upgrade
Upgrade
ubuntu/linux-realtime-6.8to a version that resolves this vulnerability.Fixed in 6.8.1-1056.57~22.04.2 - Upgrade
Upgrade
ubuntu/linuxto a version that resolves this vulnerability.Fixed in 6.8.0-136.136 - Upgrade
Upgrade
ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 6.8.0-1061.64 - Upgrade
Upgrade
ubuntu/linux-azureto a version that resolves this vulnerability.Fixed in 6.8.0-1063.71 - Upgrade
Upgrade
ubuntu/linux-azure-fdeto a version that resolves this vulnerability.Fixed in 6.8.0-1062.69 - Upgrade
Upgrade
ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 6.8.0-1064.72 - Upgrade
Upgrade
ubuntu/linux-gketo a version that resolves this vulnerability.Fixed in 6.8.0-1059.67 - Upgrade
Upgrade
ubuntu/linux-gkeopto a version that resolves this vulnerability.Fixed in 6.8.0-1046.50 - Upgrade
Upgrade
ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 6.8.0-1061.62 - Upgrade
Upgrade
ubuntu/linux-lowlatencyto a version that resolves this vulnerability.Fixed in 6.8.0-136.136.2 - Upgrade
Upgrade
ubuntu/linux-nvidiato a version that resolves this vulnerability.Fixed in 6.8.0-1059.62 - Upgrade
Upgrade
ubuntu/linux-nvidia-lowlatencyto a version that resolves this vulnerability.Fixed in 6.8.0-1059.62.1 - Upgrade
Upgrade
ubuntu/linux-nvidia-tegrato a version that resolves this vulnerability.Fixed in 6.8.0-1030.31 - Upgrade
Upgrade
ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 6.8.0-1058.61 - Upgrade
Upgrade
ubuntu/linux-raspito a version that resolves this vulnerability.Fixed in 6.8.0-1061.65 - Upgrade
Upgrade
ubuntu/linux-xilinxto a version that resolves this vulnerability.Fixed in 6.8.0-1033.34 - Upgrade
Upgrade
ubuntu/linux-bluefieldto a version that resolves this vulnerability.Fixed in 6.8.0-1028.33 - Upgrade
Upgrade
ubuntu/linux-raspi-realtimeto a version that resolves this vulnerability.Fixed in 6.8.0-2050.52 - Upgrade
Upgrade
ubuntu/linux-realtimeto a version that resolves this vulnerability.Fixed in 6.8.1-1056.57 - Upgrade
Upgrade
ubuntu/linux-aws-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1061.64+fips1 - Upgrade
Upgrade
ubuntu/linux-azure-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1063.71+fips2 - Upgrade
Upgrade
ubuntu/linux-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-136.136+fips2 - Upgrade
Upgrade
ubuntu/linux-gcp-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1064.72+fips1 - Configuration
Before plic_irq_eoi() sends the interrupt completion message, check the PLIC enable bit for the interrupt and enable the interrupt if it is disabled.
SiFive PLIC interrupt handling PLIC interrupt enable bit = enabled before sending the completion message
Event History
Frequently Asked Questions
Which systems are exposed to this issue?
Systems using the Linux kernel SiFive PLIC interrupt controller are exposed when an interrupt's CPU affinity can be changed while a hart is still handling that interrupt. In that state, the handling hart's enable bit can be cleared even though the IRQ is not marked disabled.
What access does an attacker need?
The CVSS vector indicates local access with low privileges is required. No user interaction is required.
What is the practical impact?
A completion message can be silently ignored by the PLIC when the interrupt source is not enabled for the target handling it. This can leave an interrupt frozen and cause a high availability impact; the CVSS vector lists no confidentiality or integrity impact.
How can this be remediated?
Update to a Linux kernel release that includes the resolved SiFive PLIC affinity-handling fix. The provided stable-kernel references identify commits associated with the fix.