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SubjectRe: [PATCH v4 5/7] s390: ap: implement PAPQ AQIC interception in kernel
On Fri, 22 Feb 2019 16:29:58 +0100
Pierre Morel <pmorel@linux.ibm.com> wrote:

> We register the AP PQAP instruction hook during the open
> of the mediated device. And unregister it on release.
>
> In the AP PQAP instruction hook, if we receive a demand to
> enable IRQs,
> - we retrieve the vfio_ap_queue based on the APQN we receive
> in REG1,
> - we retrieve the page of the guest address, (NIB), from
> register REG2
> - we the mediated device to use the VFIO pinning infratrsucture
> to pin the page of the guest address,
> - we retrieve the pointer to KVM to register the guest ISC
> and retrieve the host ISC
> - finaly we activate GISA
>
> If we receive a demand to disable IRQs,
> - we deactivate GISA
> - unregister from the GIB
> - unping the NIB
>
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
[..]
> + */
> +static void vfio_ap_free_irq(struct vfio_ap_queue *q)
> +{
> + if (!q)
> + return;
> + if (q->g_pfn)
> + vfio_unpin_pages(mdev_dev(q->matrix_mdev->mdev), &q->g_pfn, 1);
> + if (q->isc)
> + kvm_s390_gisc_unregister(q->matrix_mdev->kvm, q->isc);

Ain't isc 0 a perfectly legit isc?

> + q->nib = 0;
> + q->isc = 0;
> + q->g_pfn = 0;
> +}
> +
[..]
> @@ -109,10 +131,16 @@ static int vfio_ap_mdev_create(struct kobject *kobj, struct mdev_device *mdev)
> static int vfio_ap_mdev_remove(struct mdev_device *mdev)
> {
> struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
> + struct vfio_ap_queue *q, *qtmp;
>
> if (matrix_mdev->kvm)
> return -EBUSY;
>
> + list_for_each_entry_safe(q, qtmp, &matrix_mdev->qlist, list) {
> + q->matrix_mdev = NULL;
> + vfio_ap_mdev_reset_queue(q);
> + list_move(&q->list, &matrix_dev->free_list);

How about matrix_dev->lock? I guess you should protect free_list with
it. If not maybe a code comment would help not stumble over this.

> + }
> mutex_lock(&matrix_dev->lock);
> list_del(&matrix_mdev->node);
> mutex_unlock(&matrix_dev->lock);

[..]

> +/**
> + * vfio_ap_setirq: Enable Interruption for a APQN
> + *
> + * @dev: the device associated with the ap_queue
> + * @q: the vfio_ap_queue holding AQIC parameters
> + *
> + * Pin the NIB saved in *q
> + * Register the guest ISC to GIB interface and retrieve the
> + * host ISC to issue the host side PQAP/AQIC
> + *
> + * Response.status may be set to following Response Code in case of error:
> + * - AP_RESPONSE_INVALID_ADDRESS: vfio_pin_pages failed
> + * - AP_RESPONSE_OTHERWISE_CHANGED: Hypervizor GISA internal error
> + *
> + * Otherwise return the ap_queue_status returned by the ap_aqic()
> + */
> +static struct ap_queue_status vfio_ap_setirq(struct vfio_ap_queue *q)
> +{
> + struct ap_qirq_ctrl aqic_gisa = {};
> + struct ap_queue_status status = {};
> + struct kvm_s390_gisa *gisa;
> + struct kvm *kvm;
> + unsigned long g_pfn, h_nib, h_pfn;
> + int ret;
> +
> + kvm = q->matrix_mdev->kvm;
> + gisa = kvm->arch.gisa_int.origin;
> +
> + g_pfn = q->nib >> PAGE_SHIFT;
> + ret = vfio_pin_pages(mdev_dev(q->matrix_mdev->mdev), &g_pfn, 1,
> + IOMMU_READ | IOMMU_WRITE, &h_pfn);
> + switch (ret) {
> + case 1:
> + break;
> + case -EINVAL:
> + case -E2BIG:
> + status.response_code = AP_RESPONSE_INVALID_ADDRESS;
> + /* Fallthrough */
> + default:
> + return status;
> + }
> +
> + h_nib = (h_pfn << PAGE_SHIFT) | (q->nib & ~PAGE_MASK);
> + aqic_gisa.gisc = q->isc;
> + aqic_gisa.isc = kvm_s390_gisc_register(kvm, q->isc);
> + aqic_gisa.ir = 1;
> + aqic_gisa.gisa = gisa->next_alert >> 4;
> +
> + status = ap_aqic(q->apqn, aqic_gisa, (void *)h_nib);
> + switch (status.response_code) {
> + case AP_RESPONSE_NORMAL:
> + if (q->g_pfn)
> + vfio_unpin_pages(mdev_dev(q->matrix_mdev->mdev),
> + &q->g_pfn, 1);

Shouldn't you call kvm_s390_gisc_unregister() here.

> + q->g_pfn = g_pfn;
> + break;
> + case AP_RESPONSE_OTHERWISE_CHANGED:
> + vfio_unpin_pages(mdev_dev(q->matrix_mdev->mdev), &g_pfn, 1);

and here.

> + break;
> + case AP_RESPONSE_INVALID_GISA:
> + status.response_code = AP_RESPONSE_INVALID_ADDRESS;
> + default: /* Fall Through */
> + pr_warn("%s: apqn %04x: response: %02x\n", __func__, q->apqn,
> + status.response_code);
> + vfio_ap_free_irq(q);

This guy won't unpin g_pfn but only q->g_pfn if not zero :/

> + break;
> + }
> +
> + return status;
> +}
> +
> +/**
> + * handle_pqap: PQAP instruction callback
> + *
> + * @vcpu: The vcpu on which we received the PQAP instruction
> + *
> + * Get the general register contents to initialize internal variables.
> + * REG[0]: APQN
> + * REG[1]: IR and ISC
> + * REG[2]: NIB
> + *
> + * Response.status may be set to following Response Code:
> + * - AP_RESPONSE_Q_NOT_AVAIL: if the queue is not available
> + * - AP_RESPONSE_DECONFIGURED: if the queue is not configured
> + * - AP_RESPONSE_NORMAL (0) : in case of successs
> + * Check vfio_ap_setirq() and vfio_ap_clrirq() for other possible
> RC.
> + *
> + * Return 0 if we could handle the request inside KVM.
> + * otherwise, returns -EOPNOTSUPP to let QEMU handle the fault.
> + */
> +static int handle_pqap(struct kvm_vcpu *vcpu)
> +{
> + uint64_t status;
> + uint16_t apqn;
> + struct vfio_ap_queue *q;
> + struct ap_queue_status qstatus = {};
> + struct ap_matrix_mdev *matrix_mdev;
> +
> + /* If we do not use the AIV facility just go to userland */
> + if (!(vcpu->arch.sie_block->eca & ECA_AIV))
> + return -EOPNOTSUPP;
> +
> + apqn = vcpu->run->s.regs.gprs[0] & 0xffff;
> + matrix_mdev = vcpu->kvm->arch.crypto.vfio_private;
> + if (!matrix_mdev)
> + return -EOPNOTSUPP;
> + q = vfio_ap_get_queue(apqn, &matrix_mdev->qlist);

This get is not a 'refcount affecting get' any more...

> + if (!q) {
> + qstatus.response_code = AP_RESPONSE_Q_NOT_AVAIL;
> + goto out;
> + }
> +
> + status = vcpu->run->s.regs.gprs[1];
> +
> + /* If IR bit(16) is set we enable the interrupt */
> + if ((status >> (63 - 16)) & 0x01) {
> + q->isc = status & 0x07;
> + q->nib = vcpu->run->s.regs.gprs[2];

... and I don't see what should prevent a potential use after free here.

Regards,
Halil

> + qstatus = vfio_ap_setirq(q);
> + if (qstatus.response_code) {
> + q->nib = 0;
> + q->isc = 0;
> + }
> + } else
> + qstatus = vfio_ap_clrirq(q);
> +
> +out:
> + memcpy(&vcpu->run->s.regs.gprs[1], &qstatus, sizeof(qstatus));
> + return 0;
> +}

[..]

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