On 04/10/20 01:27, Suravee Suthikulpanit wrote:
> The function amd_ir_set_vcpu_affinity makes use of the parameter struct
> amd_iommu_pi_data.prev_ga_tag to determine if it should delete struct
> amd_iommu_pi_data from a list when not running in AVIC mode.
>
> However, prev_ga_tag is initialized only when AVIC is enabled. The non-zero
> uninitialized value can cause unintended code path, which ends up making
> use of the struct vcpu_svm.ir_list and ir_list_lock without being
> initialized (since they are intended only for the AVIC case).
>
> This triggers NULL pointer dereference bug in the function vm_ir_list_del
> with the following call trace:
>
> svm_update_pi_irte+0x3c2/0x550 [kvm_amd]
> ? proc_create_single_data+0x41/0x50
> kvm_arch_irq_bypass_add_producer+0x40/0x60 [kvm]
> __connect+0x5f/0xb0 [irqbypass]
> irq_bypass_register_producer+0xf8/0x120 [irqbypass]
> vfio_msi_set_vector_signal+0x1de/0x2d0 [vfio_pci]
> vfio_msi_set_block+0x77/0xe0 [vfio_pci]
> vfio_pci_set_msi_trigger+0x25c/0x2f0 [vfio_pci]
> vfio_pci_set_irqs_ioctl+0x88/0xb0 [vfio_pci]
> vfio_pci_ioctl+0x2ea/0xed0 [vfio_pci]
> ? alloc_file_pseudo+0xa5/0x100
> vfio_device_fops_unl_ioctl+0x26/0x30 [vfio]
> ? vfio_device_fops_unl_ioctl+0x26/0x30 [vfio]
> __x64_sys_ioctl+0x96/0xd0
> do_syscall_64+0x37/0x80
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Therefore, initialize prev_ga_tag to zero before use. This should be safe
> because ga_tag value 0 is invalid (see function avic_vm_init).
>
> Fixes: dfa20099e26e ("KVM: SVM: Refactor AVIC vcpu initialization into avic_init_vcpu()")
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> ---
> arch/x86/kvm/svm/avic.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
> index ac830cd50830..381d22daa4ac 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -868,6 +868,7 @@ int svm_update_pi_irte(struct kvm *kvm, unsigned int host_irq,
> * - Tell IOMMU to use legacy mode for this interrupt.
> * - Retrieve ga_tag of prior interrupt remapping data.
> */
> + pi.prev_ga_tag = 0;
> pi.is_guest_mode = false;
> ret = irq_set_vcpu_affinity(host_irq, &pi);
>
>
Queued (with Cc: stable), thanks.
Paolo
