From: Marc Zyngier Date: Mon, 15 Jun 2026 18:16:25 +0000 (+0100) Subject: KVM: arm64: vgic: Handle race between interrupt affinity change and LPI disabling X-Git-Tag: v7.2-rc4~28^2~5^2~20 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7258770e5814f15e8308ebda82ac9acf6964ba8e;p=thirdparty%2Fkernel%2Flinux.git KVM: arm64: vgic: Handle race between interrupt affinity change and LPI disabling Hyunwoo Kim reports some really bad races should the following situation occur: - LPI-I is pending in vcpu-B's AP list - vcpu-A writes to vcpu-B's RD to disable its LPIs - vcpu-C moves I from B to C If the last two race nicely enough, vgic_prune_ap_list() can drop the irq and AP list locks, reacquire them, and in the interval the irq has been freed. UAF follows. The fix is two-fold: - Before dropping the irq and ap_list locks, take a reference on the irq - Do not try to handle migration of the pending bit: there is no expectation that this state is retained, as per the architecture With that, we're sure that the interrupt is still around, and we safely remove it from the AP list as it has no target at this stage (unless another interrupt fires, but that's another story). Reported-by: Hyunwoo Kim Tested-by: Hyunwoo Kim Link: https://lore.kernel.org/r/ailsCnyoS82r_QRz@v4bel Link: https://patch.msgid.link/20260615181625.3029352-1-maz@kernel.org Fixes: 5dd4b924e390a ("KVM: arm/arm64: vgic: Add refcounting for IRQs") Signed-off-by: Marc Zyngier Cc: stable@vger.kernel.org --- diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c index 5a4768d8cd4f3..70a161383e5a6 100644 --- a/arch/arm64/kvm/vgic/vgic.c +++ b/arch/arm64/kvm/vgic/vgic.c @@ -203,6 +203,7 @@ void vgic_flush_pending_lpis(struct kvm_vcpu *vcpu) list_for_each_entry_safe(irq, tmp, &vgic_cpu->ap_list_head, ap_list) { if (irq_is_lpi(vcpu->kvm, irq->intid)) { raw_spin_lock(&irq->irq_lock); + irq->pending_latch = false; list_del(&irq->ap_list); irq->vcpu = NULL; raw_spin_unlock(&irq->irq_lock); @@ -792,7 +793,11 @@ retry: continue; } - /* This interrupt looks like it has to be migrated. */ + /* + * This interrupt looks like it has to be migrated, + * make sure it is kept alive while locks are dropped. + */ + vgic_get_irq_ref(irq); raw_spin_unlock(&irq->irq_lock); raw_spin_unlock(&vgic_cpu->ap_list_lock); @@ -836,6 +841,8 @@ retry: raw_spin_unlock(&vcpuB->arch.vgic_cpu.ap_list_lock); raw_spin_unlock(&vcpuA->arch.vgic_cpu.ap_list_lock); + deleted_lpis |= vgic_put_irq_norelease(vcpu->kvm, irq); + if (target_vcpu_needs_kick) { kvm_make_request(KVM_REQ_IRQ_PENDING, target_vcpu); kvm_vcpu_kick(target_vcpu);