CVE-2026-23198

Description

In the Linux kernel, the following vulnerability has been resolved:KVM: Dont clobber irqfd routing type when deassigning irqfdWhen deassigning a KVM_IRQFD, dont clobber the irqfds copy of the IRQsrouting entry as doing so breaks kvm_arch_irq_bypass_del_producer() on x86and arm64, which explicitly look for KVM_IRQ_ROUTING_MSI. Instead, tohandle a concurrent routing update, verify that the irqfd is still activebefore consuming the routing information. As evidenced by the x86 andarm64 bugs, and another bug in kvm_arch_update_irqfd_routing() (see below),clobbering the entry type without notifying arch code is surprising anderror prone.As a bonus, checking that the irqfd is active provides a convenientlocation for documenting _why_ KVM must not consume the routing entry foran irqfd that is in the process of being deassigned: once the irqfd isdeleted from the list (which happens *before* the eventfd is detached), itwill no longer receive updates via kvm_irq_routing_update(), and so KVMcould deliver an event using stale routing information (relative toKVM_SET_GSI_ROUTING returning to userspace).As an even better bonus, explicitly checking for the irqfd being activefixes a similar bug to the one the clobbering is trying to prevent: if anirqfd is deactivated, and then its routing is changed,kvm_irq_routing_update() wont invoke kvm_arch_update_irqfd_routing()(because the irqfd isnt in the list). And so if the irqfd is in bypassmode, IRQs will continue to be posted using the old routing information.As for kvm_arch_irq_bypass_del_producer(), clobbering the routing typeresults in KVM incorrectly keeping the IRQ in bypass mode, which isespecially problematic on AMD as KVM tracks IRQs that are being posted toa vCPU in a list whose lifetime is tied to the irqfd.Without the help of KASAN to detect use-after-free, the most commonsympton on AMD is a null pointer deref in amd_iommu_update_ga() due tothe memory for irqfd structure being re-allocated and zeroed, resultingin irqfd->irq_bypass_data being null when read byavic_update_iommu_vcpu_affinity(): BUG: kernel null pointer dereference, address: 0000000000000018 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 40cf2b9067 P4D 40cf2b9067 PUD 408362a067 PMD 0 Oops: Oops: 0000 [#1] SMP CPU: 6 UID: 0 PID: 40383 Comm: vfio_irq_test Tainted: G U W O 6.19.0-smp--5dddc257e6b2-irqfd #31 NONE Tainted: [U]=USER, [W]=WARN, [O]=OOT_MODULE Hardware name: Google, Inc. Arcadia_IT_80/Arcadia_IT_80, BIOS 34.78.2-0 09/05/2025 RIP: 0010:amd_iommu_update_ga+0x19/0xe0 Call Trace: avic_update_iommu_vcpu_affinity+0x3d/0x90 [kvm_amd] __avic_vcpu_load+0xf4/0x130 [kvm_amd] kvm_arch_vcpu_load+0x89/0x210 [kvm] vcpu_load+0x30/0x40 [kvm] kvm_arch_vcpu_ioctl_run+0x45/0x620 [kvm] kvm_vcpu_ioctl+0x571/0x6a0 [kvm] __se_sys_ioctl+0x6d/0xb0 do_syscall_64+0x6f/0x9d0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x46893b ---[ end trace 0000000000000000 ]---If AVIC is inhibited when the irfd is deassigned, the bug will manifest aslist corruption, e.g. on the next irqfd assignment. list_add corruption. next->prev should be prev (ffff8d474d5cd588), but was 0000000000000000. (next=ffff8d8658f86530). ------------[ cut here ]------------ kernel BUG at lib/list_debug.c:31! Oops: invalid opcode: 0000 [#1] SMP CPU: 128 UID: 0 PID: 80818 Comm: vfio_irq_test Tainted: G U W O 6.19.0-smp--f19dc4d680ba-irqfd #28 NONE Tainted: [U]=USER, [W]=WARN, [O]=OOT_MODULE Hardware name: Google, Inc. Arcadia_IT_80/Arcadia_IT_80, BIOS 34.78.2-0 09/05/2025 RIP: 0010:__list_add_valid_or_report+0x97/0xc0 Call Trace: avic_pi_update_irte+0x28e/0x2b0 [kvm_amd] kvm_pi_update_irte+0xbf/0x190 [kvm] kvm_arch_irq_bypass_add_producer+0x72/0x90 [kvm] irq_bypass_register_consumer+0xcd/0x170 [irqbypa---truncated---

Risk Information

Associated Vulnerability

Patch Details

References

https://nvd.nist.gov/vuln/detail/CVE-2023-1234
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-1234