u2f-emulated.c

/*
 * U2F USB Emulated device.
 *
 * Copyright (c) 2020 César Belley <cesar.belley@lse.epita.fr>
 * Written by César Belley <cesar.belley@lse.epita.fr>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "qemu/osdep.h"
#include "qemu/module.h"
#include "qemu/thread.h"
#include "qemu/main-loop.h"
#include "qapi/error.h"
#include "hw/usb.h"
#include "hw/qdev-properties.h"

#include <u2f-emu/u2f-emu.h>

#include "u2f.h"

/* Counter which sync with a file */
struct synced_counter {
    /* Emulated device counter */
    struct u2f_emu_vdev_counter vdev_counter;

    /* Private attributes */
    uint32_t value;
    FILE *fp;
};

static void counter_increment(struct u2f_emu_vdev_counter *vdev_counter)
{
    struct synced_counter *counter = (struct synced_counter *)vdev_counter;
    ++counter->value;

    /* Write back */
    if (fseek(counter->fp, 0, SEEK_SET) == -1) {
        return;
    }
    fprintf(counter->fp, "%u\n", counter->value);
}

static uint32_t counter_read(struct u2f_emu_vdev_counter *vdev_counter)
{
    struct synced_counter *counter = (struct synced_counter *)vdev_counter;
    return counter->value;
}

typedef struct U2FEmulatedState U2FEmulatedState;

#define PENDING_OUT_NUM 32

struct U2FEmulatedState {
    U2FKeyState base;

    /* U2F virtual emulated device */
    u2f_emu_vdev *vdev;
    QemuMutex vdev_mutex;

    /* Properties */
    char *dir;
    char *cert;
    char *privkey;
    char *entropy;
    char *counter;
    struct synced_counter synced_counter;

    /* Pending packets received from the guest */
    uint8_t pending_out[PENDING_OUT_NUM][U2FHID_PACKET_SIZE];
    uint8_t pending_out_start;
    uint8_t pending_out_end;
    uint8_t pending_out_num;
    QemuMutex pending_out_mutex;

    /* Emulation thread and sync */
    QemuCond key_cond;
    QemuMutex key_mutex;
    QemuThread key_thread;
    bool stop_thread;
    EventNotifier notifier;
};

#define TYPE_U2F_EMULATED "u2f-emulated"
#define EMULATED_U2F_KEY(obj) \
    OBJECT_CHECK(U2FEmulatedState, (obj), TYPE_U2F_EMULATED)

static void u2f_emulated_reset(U2FEmulatedState *key)
{
    key->pending_out_start = 0;
    key->pending_out_end = 0;
    key->pending_out_num = 0;
}

static void u2f_pending_out_add(U2FEmulatedState *key,
                                const uint8_t packet[U2FHID_PACKET_SIZE])
{
    int index;

    if (key->pending_out_num >= PENDING_OUT_NUM) {
        return;
    }

    index = key->pending_out_end;
    key->pending_out_end = (index + 1) % PENDING_OUT_NUM;
    ++key->pending_out_num;

    memcpy(&key->pending_out[index], packet, U2FHID_PACKET_SIZE);
}

static uint8_t *u2f_pending_out_get(U2FEmulatedState *key)
{
    int index;

    if (key->pending_out_num == 0) {
        return NULL;
    }

    index  = key->pending_out_start;
    key->pending_out_start = (index + 1) % PENDING_OUT_NUM;
    --key->pending_out_num;

    return key->pending_out[index];
}

static void u2f_emulated_recv_from_guest(U2FKeyState *base,
                                    const uint8_t packet[U2FHID_PACKET_SIZE])
{
    U2FEmulatedState *key = EMULATED_U2F_KEY(base);

    qemu_mutex_lock(&key->pending_out_mutex);
    u2f_pending_out_add(key, packet);
    qemu_mutex_unlock(&key->pending_out_mutex);

    qemu_mutex_lock(&key->key_mutex);
    qemu_cond_signal(&key->key_cond);
    qemu_mutex_unlock(&key->key_mutex);
}

static void *u2f_emulated_thread(void* arg)
{
    U2FEmulatedState *key = arg;
    uint8_t packet[U2FHID_PACKET_SIZE];
    uint8_t *packet_out = NULL;


    while (true) {
        /* Wait signal */
        qemu_mutex_lock(&key->key_mutex);
        qemu_cond_wait(&key->key_cond, &key->key_mutex);
        qemu_mutex_unlock(&key->key_mutex);

        /* Exit thread check */
        if (key->stop_thread) {
            key->stop_thread = false;
            break;
        }

        qemu_mutex_lock(&key->pending_out_mutex);
        packet_out = u2f_pending_out_get(key);
        if (packet_out == NULL) {
            qemu_mutex_unlock(&key->pending_out_mutex);
            continue;
        }
        memcpy(packet, packet_out, U2FHID_PACKET_SIZE);
        qemu_mutex_unlock(&key->pending_out_mutex);

        qemu_mutex_lock(&key->vdev_mutex);
        u2f_emu_vdev_send(key->vdev, U2F_EMU_USB, packet,
                          U2FHID_PACKET_SIZE);

        /* Notify response */
        if (u2f_emu_vdev_has_response(key->vdev, U2F_EMU_USB)) {
            event_notifier_set(&key->notifier);
        }
        qemu_mutex_unlock(&key->vdev_mutex);
    }
    return NULL;
}

static ssize_t u2f_emulated_read(const char *path, char *buffer,
                                 size_t buffer_len)
{
    int fd;
    ssize_t ret;

    fd = qemu_open_old(path, O_RDONLY);
    if (fd < 0) {
        return -1;
    }

    ret = read(fd, buffer, buffer_len);
    close(fd);

    return ret;
}

static bool u2f_emulated_setup_counter(const char *path,
                                       struct synced_counter *counter)
{
    int fd, ret;
    FILE *fp;

    fd = qemu_open_old(path, O_RDWR);
    if (fd < 0) {
        return false;
    }
    fp = fdopen(fd, "r+");
    if (fp == NULL) {
        close(fd);
        return false;
    }
    ret = fscanf(fp, "%u", &counter->value);
    if (ret == EOF) {
        fclose(fp);
        return false;
    }
    counter->fp = fp;
    counter->vdev_counter.counter_increment = counter_increment;
    counter->vdev_counter.counter_read = counter_read;

    return true;
}

static u2f_emu_rc u2f_emulated_setup_vdev_manualy(U2FEmulatedState *key)
{
    ssize_t ret;
    char cert_pem[4096], privkey_pem[2048];
    struct u2f_emu_vdev_setup setup_info;

    /* Certificate */
    ret = u2f_emulated_read(key->cert, cert_pem, sizeof(cert_pem));
    if (ret < 0) {
        return -1;
    }

    /* Private key */
    ret = u2f_emulated_read(key->privkey, privkey_pem, sizeof(privkey_pem));
    if (ret < 0) {
        return -1;
    }

    /* Entropy */
    ret = u2f_emulated_read(key->entropy, (char *)&setup_info.entropy,
                            sizeof(setup_info.entropy));
    if (ret < 0) {
        return -1;
    }

    /* Counter */
    if (!u2f_emulated_setup_counter(key->counter, &key->synced_counter)) {
        return -1;
    }

    /* Setup */
    setup_info.certificate = cert_pem;
    setup_info.private_key = privkey_pem;
    setup_info.counter = (struct u2f_emu_vdev_counter *)&key->synced_counter;

    return u2f_emu_vdev_new(&key->vdev, &setup_info);
}

static void u2f_emulated_event_handler(EventNotifier *notifier)
{
    U2FEmulatedState *key = container_of(notifier, U2FEmulatedState, notifier);
    size_t packet_size;
    uint8_t *packet_in = NULL;

    event_notifier_test_and_clear(&key->notifier);
    qemu_mutex_lock(&key->vdev_mutex);
    while (u2f_emu_vdev_has_response(key->vdev, U2F_EMU_USB)) {
        packet_size = u2f_emu_vdev_get_response(key->vdev, U2F_EMU_USB,
                                                &packet_in);
        if (packet_size == U2FHID_PACKET_SIZE) {
            u2f_send_to_guest(&key->base, packet_in);
        }
        u2f_emu_vdev_free_response(packet_in);
    }
    qemu_mutex_unlock(&key->vdev_mutex);
}

static void u2f_emulated_realize(U2FKeyState *base, Error **errp)
{
    U2FEmulatedState *key = EMULATED_U2F_KEY(base);
    u2f_emu_rc rc;

    if (key->cert != NULL || key->privkey != NULL || key->entropy != NULL
        || key->counter != NULL) {
        if (key->cert != NULL && key->privkey != NULL
            && key->entropy != NULL && key->counter != NULL) {
            rc = u2f_emulated_setup_vdev_manualy(key);
        } else {
            error_setg(errp, "%s: cert, priv, entropy and counter "
                       "parameters must be provided to manualy configure "
                       "the emulated device", TYPE_U2F_EMULATED);
            return;
        }
    } else if (key->dir != NULL) {
        rc = u2f_emu_vdev_new_from_dir(&key->vdev, key->dir);
    } else {
        rc = u2f_emu_vdev_new_ephemeral(&key->vdev);
    }

    if (rc != U2F_EMU_OK) {
        error_setg(errp, "%s: Failed to setup the key", TYPE_U2F_EMULATED);
        return;
    }

    if (event_notifier_init(&key->notifier, false) < 0) {
        error_setg(errp, "%s: Failed to initialize notifier",
                   TYPE_U2F_EMULATED);
        return;
    }
    /* Notifier */
    event_notifier_set_handler(&key->notifier, u2f_emulated_event_handler);

    /* Synchronization */
    qemu_cond_init(&key->key_cond);
    qemu_mutex_init(&key->vdev_mutex);
    qemu_mutex_init(&key->pending_out_mutex);
    qemu_mutex_init(&key->key_mutex);
    u2f_emulated_reset(key);

    /* Thread */
    key->stop_thread = false;
    qemu_thread_create(&key->key_thread, "u2f-key", u2f_emulated_thread,
                       key, QEMU_THREAD_JOINABLE);
}

static void u2f_emulated_unrealize(U2FKeyState *base)
{
    U2FEmulatedState *key = EMULATED_U2F_KEY(base);

    /* Thread */
    key->stop_thread = true;
    qemu_cond_signal(&key->key_cond);
    qemu_thread_join(&key->key_thread);

    /* Notifier */
    event_notifier_set_handler(&key->notifier, NULL);
    event_notifier_cleanup(&key->notifier);

    /* Synchronization */
    qemu_cond_destroy(&key->key_cond);
    qemu_mutex_destroy(&key->vdev_mutex);
    qemu_mutex_destroy(&key->key_mutex);
    qemu_mutex_destroy(&key->pending_out_mutex);

    /* Vdev */
    u2f_emu_vdev_free(key->vdev);
    if (key->synced_counter.fp != NULL) {
        fclose(key->synced_counter.fp);
    }
}

static Property u2f_emulated_properties[] = {
    DEFINE_PROP_STRING("dir", U2FEmulatedState, dir),
    DEFINE_PROP_STRING("cert", U2FEmulatedState, cert),
    DEFINE_PROP_STRING("privkey", U2FEmulatedState, privkey),
    DEFINE_PROP_STRING("entropy", U2FEmulatedState, entropy),
    DEFINE_PROP_STRING("counter", U2FEmulatedState, counter),
    DEFINE_PROP_END_OF_LIST(),
};

static void u2f_emulated_class_init(ObjectClass *klass, void *data)
{
    DeviceClass *dc = DEVICE_CLASS(klass);
    U2FKeyClass *kc = U2F_KEY_CLASS(klass);

    kc->realize = u2f_emulated_realize;
    kc->unrealize = u2f_emulated_unrealize;
    kc->recv_from_guest = u2f_emulated_recv_from_guest;
    dc->desc = "QEMU U2F emulated key";
    device_class_set_props(dc, u2f_emulated_properties);
}

static const TypeInfo u2f_key_emulated_info = {
    .name = TYPE_U2F_EMULATED,
    .parent = TYPE_U2F_KEY,
    .instance_size = sizeof(U2FEmulatedState),
    .class_init = u2f_emulated_class_init
};

static void u2f_key_emulated_register_types(void)
{
    type_register_static(&u2f_key_emulated_info);
}

type_init(u2f_key_emulated_register_types)