In the Linux kernel, the following vulnerability has been resolved: KVM: s390: Fix IRQ injection with SIGP Stop and Store Status When… (CVE-2026-98930)

The vulnerability in the Linux kernel's KVM s390 module concerns the __inject_sigp_stop() function used for Stop and Store Status operations. When called while the virtual CPU (vCPU) is running, the interrupt is marked as pending and the status is stored by the thread performing the KVM_RUN IOCTL. If the vCPU is stopped, the status is stored immediately. Storing the status involves writing into userspace, which might fault. This operation was previously done while holding a spinlock, which is problematic. The fix returns -EWOULDBLOCK from __inject_sigp_stop() to indicate deferral and adds a flag to indicate when status storage is needed, allowing the actual store to occur outside the spinlock. Additionally, kvm_s390_set_irq_state() was refactored for improved resource management.

The vulnerability could cause faults or instability in the kernel due to unsafe memory operations while holding a spinlock. This could potentially lead to kernel crashes or undefined behavior in the KVM s390 virtualization environment. No known exploits in the wild have been reported.

A fix has been implemented in the Linux kernel to address this issue by deferring the Store Status operation outside the spinlock context. Users should update to the fixed kernel version once available. No additional mitigation steps are indicated.