CVE-2020-27152: 
Linux Kernel vulnerability analysis and mitigation

A vulnerability was discovered in the Linux kernel before version 5.9.2, specifically in the ioapic_lazy_update_eoi function in arch/x86/kvm/ioapic.c. The vulnerability (CVE-2020-27152) was disclosed on November 6, 2020, and involves an infinite loop condition related to improper interaction between a resampler and edge triggering, also known as CID-77377064c3a9 (NVD, Ubuntu).

The vulnerability occurs in the KVM hypervisor of the Linux kernel when processing interrupts due to erroneously set IRQ state. The issue manifests as an infinite recursion loop during shutdown when the IOAPIC trigger mode is reset to edge triggered while the vfio-pci INTx is still registered with a resampler. The recursion sequence involves multiple function calls including ioapic_set_irq, ioapic_lazy_update_eoi, kvm_ioapic_update_eoi_one, and several others, creating an endless loop (Kernel Commit). The vulnerability has a CVSS v3.1 Base Score of 5.5 (Medium) with vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (NVD).

A local attacker in a guest VM could potentially exploit this vulnerability to cause a denial of service condition by crashing the host system. The vulnerability affects the system's availability but does not impact confidentiality or integrity (Ubuntu).

The vulnerability requires local access and can be exploited by a guest user in a virtual machine. It's important to note that this issue cannot occur with SR-IOV assigned devices because virtual functions do not have INTx, only MSI (Kernel Commit).

The vulnerability was fixed in Linux kernel version 5.9.2. The fix involves removing the call to kvm_ioapic_update_eoi_one from ioapic_lazy_update_eoi to break the infinite recursion loop. Various Linux distributions have released patches for their respective versions (Ubuntu).