// SPDX-License-Identifier: GPL-2.0-only
/*
 * Implementation of the Xen vTPM device frontend
 *
 * Author:  Daniel De Graaf <dgdegra@tycho.nsa.gov>
 */
#include <linux/errno.h>
#include <linux/err.h>
#include <linux/interrupt.h>
#include <linux/freezer.h>
#include <xen/xen.h>
#include <xen/events.h>
#include <xen/interface/io/tpmif.h>
#include <xen/grant_table.h>
#include <xen/xenbus.h>
#include <xen/page.h>
#include "tpm.h"
#include <xen/platform_pci.h>

struct tpm_private {
        struct tpm_chip *chip;
        struct xenbus_device *dev;

        struct vtpm_shared_page *shr;

        unsigned int evtchn;
        int ring_ref;
        domid_t backend_id;
        int irq;
        wait_queue_head_t read_queue;
};

enum status_bits {
        VTPM_STATUS_RUNNING  = 0x1,
        VTPM_STATUS_IDLE     = 0x2,
        VTPM_STATUS_RESULT   = 0x4,
        VTPM_STATUS_CANCELED = 0x8,
};

static bool wait_for_tpm_stat_cond(struct tpm_chip *chip, u8 mask,
                                        bool check_cancel, bool *canceled)
{
        u8 status = chip->ops->status(chip);

        *canceled = false;
        if ((status & mask) == mask)
                return true;
        if (check_cancel && chip->ops->req_canceled(chip, status)) {
                *canceled = true;
                return true;
        }
        return false;
}

static int wait_for_tpm_stat(struct tpm_chip *chip, u8 mask,
                unsigned long timeout, wait_queue_head_t *queue,
                bool check_cancel)
{
        unsigned long stop;
        long rc;
        u8 status;
        bool canceled = false;

        /* check current status */
        status = chip->ops->status(chip);
        if ((status & mask) == mask)
                return 0;

        stop = jiffies + timeout;

        if (chip->flags & TPM_CHIP_FLAG_IRQ) {
again:
                timeout = stop - jiffies;
                if ((long)timeout <= 0)
                        return -ETIME;
                rc = wait_event_interruptible_timeout(*queue,
                        wait_for_tpm_stat_cond(chip, mask, check_cancel,
                                               &canceled),
                        timeout);
                if (rc > 0) {
                        if (canceled)
                                return -ECANCELED;
                        return 0;
                }
                if (rc == -ERESTARTSYS && freezing(current)) {
                        clear_thread_flag(TIF_SIGPENDING);
                        goto again;
                }
        } else {
                do {
                        tpm_msleep(TPM_TIMEOUT);
                        status = chip->ops->status(chip);
                        if ((status & mask) == mask)
                                return 0;
                } while (time_before(jiffies, stop));
        }
        return -ETIME;
}

static u8 vtpm_status(struct tpm_chip *chip)
{
        struct tpm_private *priv = dev_get_drvdata(&chip->dev);
        switch (priv->shr->state) {
        case VTPM_STATE_IDLE:
                return VTPM_STATUS_IDLE | VTPM_STATUS_CANCELED;
        case VTPM_STATE_FINISH:
                return VTPM_STATUS_IDLE | VTPM_STATUS_RESULT;
        case VTPM_STATE_SUBMIT:
        case VTPM_STATE_CANCEL: /* cancel requested, not yet canceled */
                return VTPM_STATUS_RUNNING;
        default:
                return 0;
        }
}

static bool vtpm_req_canceled(struct tpm_chip *chip, u8 status)
{
        return status & VTPM_STATUS_CANCELED;
}

static void vtpm_cancel(struct tpm_chip *chip)
{
        struct tpm_private *priv = dev_get_drvdata(&chip->dev);
        priv->shr->state = VTPM_STATE_CANCEL;
        wmb();
        notify_remote_via_evtchn(priv->evtchn);
}

static size_t shr_data_offset(struct vtpm_shared_page *shr)
{
        return struct_size(shr, extra_pages, shr->nr_extra_pages);
}

static int vtpm_send(struct tpm_chip *chip, u8 *buf, size_t bufsiz,
                     size_t count)
{
        struct tpm_private *priv = dev_get_drvdata(&chip->dev);
        struct vtpm_shared_page *shr = priv->shr;
        size_t offset = shr_data_offset(shr);

        u32 ordinal;
        unsigned long duration;

        if (offset > PAGE_SIZE)
                return -EINVAL;

        if (offset + count > PAGE_SIZE)
                return -EINVAL;

        /* Wait for completion of any existing command or cancellation */
        if (wait_for_tpm_stat(chip, VTPM_STATUS_IDLE, chip->timeout_c,
                        &priv->read_queue, true) < 0) {
                vtpm_cancel(chip);
                return -ETIME;
        }

        memcpy(offset + (u8 *)shr, buf, count);
        shr->length = count;
        barrier();
        shr->state = VTPM_STATE_SUBMIT;
        wmb();
        notify_remote_via_evtchn(priv->evtchn);

        ordinal = be32_to_cpu(((struct tpm_header *)buf)->ordinal);
        duration = tpm_calc_ordinal_duration(chip, ordinal);

        if (wait_for_tpm_stat(chip, VTPM_STATUS_IDLE, duration,
                        &priv->read_queue, true) < 0) {
                /* got a signal or timeout, try to cancel */
                vtpm_cancel(chip);
                return -ETIME;
        }

        return 0;
}

static int vtpm_recv(struct tpm_chip *chip, u8 *buf, size_t count)
{
        struct tpm_private *priv = dev_get_drvdata(&chip->dev);
        struct vtpm_shared_page *shr = priv->shr;
        size_t offset = shr_data_offset(shr);
        size_t length = shr->length;

        if (shr->state == VTPM_STATE_IDLE)
                return -ECANCELED;

        /* In theory the wait at the end of _send makes this one unnecessary */
        if (wait_for_tpm_stat(chip, VTPM_STATUS_RESULT, chip->timeout_c,
                        &priv->read_queue, true) < 0) {
                vtpm_cancel(chip);
                return -ETIME;
        }

        if (offset > PAGE_SIZE)
                return -EIO;

        if (offset + length > PAGE_SIZE)
                length = PAGE_SIZE - offset;

        if (length > count)
                length = count;

        memcpy(buf, offset + (u8 *)shr, length);

        return length;
}

static const struct tpm_class_ops tpm_vtpm = {
        .status = vtpm_status,
        .recv = vtpm_recv,
        .send = vtpm_send,
        .cancel = vtpm_cancel,
        .req_complete_mask = VTPM_STATUS_IDLE | VTPM_STATUS_RESULT,
        .req_complete_val  = VTPM_STATUS_IDLE | VTPM_STATUS_RESULT,
        .req_canceled      = vtpm_req_canceled,
};

static irqreturn_t tpmif_interrupt(int dummy, void *dev_id)
{
        struct tpm_private *priv = dev_id;

        switch (priv->shr->state) {
        case VTPM_STATE_IDLE:
        case VTPM_STATE_FINISH:
                wake_up_interruptible(&priv->read_queue);
                break;
        case VTPM_STATE_SUBMIT:
        case VTPM_STATE_CANCEL:
        default:
                break;
        }
        return IRQ_HANDLED;
}

static int setup_chip(struct device *dev, struct tpm_private *priv)
{
        struct tpm_chip *chip;

        chip = tpmm_chip_alloc(dev, &tpm_vtpm);
        if (IS_ERR(chip))
                return PTR_ERR(chip);

        init_waitqueue_head(&priv->read_queue);

        priv->chip = chip;
        dev_set_drvdata(&chip->dev, priv);

        return 0;
}

/* caller must clean up in case of errors */
static int setup_ring(struct xenbus_device *dev, struct tpm_private *priv)
{
        struct xenbus_transaction xbt;
        const char *message = NULL;
        int rv;

        rv = xenbus_setup_ring(dev, GFP_KERNEL, (void **)&priv->shr, 1,
                               &priv->ring_ref);
        if (rv < 0)
                return rv;

        rv = xenbus_alloc_evtchn(dev, &priv->evtchn);
        if (rv)
                return rv;

        rv = bind_evtchn_to_irqhandler(priv->evtchn, tpmif_interrupt, 0,
                                       "tpmif", priv);
        if (rv <= 0) {
                xenbus_dev_fatal(dev, rv, "allocating TPM irq");
                return rv;
        }
        priv->irq = rv;

 again:
        rv = xenbus_transaction_start(&xbt);
        if (rv) {
                xenbus_dev_fatal(dev, rv, "starting transaction");
                return rv;
        }

        rv = xenbus_printf(xbt, dev->nodename,
                        "ring-ref", "%u", priv->ring_ref);
        if (rv) {
                message = "writing ring-ref";
                goto abort_transaction;
        }

        rv = xenbus_printf(xbt, dev->nodename, "event-channel", "%u",
                        priv->evtchn);
        if (rv) {
                message = "writing event-channel";
                goto abort_transaction;
        }

        rv = xenbus_printf(xbt, dev->nodename, "feature-protocol-v2", "1");
        if (rv) {
                message = "writing feature-protocol-v2";
                goto abort_transaction;
        }

        rv = xenbus_transaction_end(xbt, 0);
        if (rv == -EAGAIN)
                goto again;
        if (rv) {
                xenbus_dev_fatal(dev, rv, "completing transaction");
                return rv;
        }

        xenbus_switch_state(dev, XenbusStateInitialised);

        return 0;

 abort_transaction:
        xenbus_transaction_end(xbt, 1);
        if (message)
                xenbus_dev_error(dev, rv, "%s", message);

        return rv;
}

static void ring_free(struct tpm_private *priv)
{
        if (!priv)
                return;

        xenbus_teardown_ring((void **)&priv->shr, 1, &priv->ring_ref);

        if (priv->irq)
                unbind_from_irqhandler(priv->irq, priv);

        kfree(priv);
}

static int tpmfront_probe(struct xenbus_device *dev,
                const struct xenbus_device_id *id)
{
        struct tpm_private *priv;
        int rv;

        priv = kzalloc_obj(*priv);
        if (!priv) {
                xenbus_dev_fatal(dev, -ENOMEM, "allocating priv structure");
                return -ENOMEM;
        }

        rv = setup_chip(&dev->dev, priv);
        if (rv) {
                kfree(priv);
                return rv;
        }

        rv = setup_ring(dev, priv);
        if (rv) {
                ring_free(priv);
                return rv;
        }

        tpm_get_timeouts(priv->chip);

        return tpm_chip_register(priv->chip);
}

static void tpmfront_remove(struct xenbus_device *dev)
{
        struct tpm_chip *chip = dev_get_drvdata(&dev->dev);
        struct tpm_private *priv = dev_get_drvdata(&chip->dev);
        tpm_chip_unregister(chip);
        ring_free(priv);
        dev_set_drvdata(&chip->dev, NULL);
}

static int tpmfront_resume(struct xenbus_device *dev)
{
        /* A suspend/resume/migrate will interrupt a vTPM anyway */
        tpmfront_remove(dev);
        return tpmfront_probe(dev, NULL);
}

static void backend_changed(struct xenbus_device *dev,
                enum xenbus_state backend_state)
{
        switch (backend_state) {
        case XenbusStateInitialised:
        case XenbusStateConnected:
                if (dev->state == XenbusStateConnected)
                        break;

                if (!xenbus_read_unsigned(dev->otherend, "feature-protocol-v2",
                                          0)) {
                        xenbus_dev_fatal(dev, -EINVAL,
                                        "vTPM protocol 2 required");
                        return;
                }
                xenbus_switch_state(dev, XenbusStateConnected);
                break;

        case XenbusStateClosing:
        case XenbusStateClosed:
                device_unregister(&dev->dev);
                xenbus_frontend_closed(dev);
                break;
        default:
                break;
        }
}

static const struct xenbus_device_id tpmfront_ids[] = {
        { "vtpm" },
        { "" }
};
MODULE_ALIAS("xen:vtpm");

static struct xenbus_driver tpmfront_driver = {
        .ids = tpmfront_ids,
        .probe = tpmfront_probe,
        .remove = tpmfront_remove,
        .resume = tpmfront_resume,
        .otherend_changed = backend_changed,
};

static int __init xen_tpmfront_init(void)
{
        if (!xen_domain())
                return -ENODEV;

        if (!xen_has_pv_devices())
                return -ENODEV;

        return xenbus_register_frontend(&tpmfront_driver);
}
module_init(xen_tpmfront_init);

static void __exit xen_tpmfront_exit(void)
{
        xenbus_unregister_driver(&tpmfront_driver);
}
module_exit(xen_tpmfront_exit);

MODULE_AUTHOR("Daniel De Graaf <dgdegra@tycho.nsa.gov>");
MODULE_DESCRIPTION("Xen vTPM Driver");
MODULE_LICENSE("GPL");