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hw/usb: Add U2F key passthru mode 

This patch adds the U2F key pass-through mode.

The pass-through mode consists of passing all requests made from the
guest to the physical security key connected to the host machine and
vice versa.

In addition, the dedicated pass-through allows to have a U2F security key
shared on several guests which is not possible with a simple host device
assignment pass-through.

The pass-through mode is associated with a device inheriting from
u2f-key base.

To work, it needs the path to a U2F hidraw, obtained from the Qemu
command line, and passed by the user:

    qemu -usb -device u2f-passthru,hidraw=/dev/hidrawX

Autoscan and U2F compatibility checking features are given at the end
of the patch series.

Signed-off-by: César Belley <cesar.belley@lse.epita.fr>
Message-id: 20200826114209.28821-6-cesar.belley@lse.epita.fr
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
This commit is contained in:
César Belley 2020-08-26 13:42:02 +02:00 committed by Gerd Hoffmann
parent bb014a810b
commit 299976b050
1 changed files with 423 additions and 0 deletions
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hw/usb/u2f-passthru.c Normal file
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/*
* U2F USB Passthru 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/main-loop.h"
#include "qemu/error-report.h"
#include "qapi/error.h"
#include "hw/qdev-properties.h"
#include "hw/usb.h"
#include "migration/vmstate.h"
#include "u2f.h"
#define NONCE_SIZE 8
#define BROADCAST_CID 0xFFFFFFFF
#define TRANSACTION_TIMEOUT 120000
struct transaction {
uint32_t cid;
uint16_t resp_bcnt;
uint16_t resp_size;
/* Nonce for broadcast isolation */
uint8_t nonce[NONCE_SIZE];
};
typedef struct U2FPassthruState U2FPassthruState;
#define CURRENT_TRANSACTIONS_NUM 4
struct U2FPassthruState {
U2FKeyState base;
/* Host device */
char *hidraw;
int hidraw_fd;
/* Current Transactions */
struct transaction current_transactions[CURRENT_TRANSACTIONS_NUM];
uint8_t current_transactions_start;
uint8_t current_transactions_end;
uint8_t current_transactions_num;
/* Transaction time checking */
int64_t last_transaction_time;
QEMUTimer timer;
};
#define TYPE_U2F_PASSTHRU "u2f-passthru"
#define PASSTHRU_U2F_KEY(obj) \
OBJECT_CHECK(U2FPassthruState, (obj), TYPE_U2F_PASSTHRU)
/* Init packet sizes */
#define PACKET_INIT_HEADER_SIZE 7
#define PACKET_INIT_DATA_SIZE (U2FHID_PACKET_SIZE - PACKET_INIT_HEADER_SIZE)
/* Cont packet sizes */
#define PACKET_CONT_HEADER_SIZE 5
#define PACKET_CONT_DATA_SIZE (U2FHID_PACKET_SIZE - PACKET_CONT_HEADER_SIZE)
struct packet_init {
uint32_t cid;
uint8_t cmd;
uint8_t bcnth;
uint8_t bcntl;
uint8_t data[PACKET_INIT_DATA_SIZE];
} QEMU_PACKED;
static inline uint32_t packet_get_cid(const void *packet)
{
return *((uint32_t *)packet);
}
static inline bool packet_is_init(const void *packet)
{
return ((uint8_t *)packet)[4] & (1 << 7);
}
static inline uint16_t packet_init_get_bcnt(
const struct packet_init *packet_init)
{
uint16_t bcnt = 0;
bcnt |= packet_init->bcnth << 8;
bcnt |= packet_init->bcntl;
return bcnt;
}
static void u2f_passthru_reset(U2FPassthruState *key)
{
timer_del(&key->timer);
qemu_set_fd_handler(key->hidraw_fd, NULL, NULL, key);
key->last_transaction_time = 0;
key->current_transactions_start = 0;
key->current_transactions_end = 0;
key->current_transactions_num = 0;
}
static void u2f_timeout_check(void *opaque)
{
U2FPassthruState *key = opaque;
int64_t time = qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL);
if (time > key->last_transaction_time + TRANSACTION_TIMEOUT) {
u2f_passthru_reset(key);
} else {
timer_mod(&key->timer, time + TRANSACTION_TIMEOUT / 4);
}
}
static int u2f_transaction_get_index(U2FPassthruState *key, uint32_t cid)
{
for (int i = 0; i < key->current_transactions_num; ++i) {
int index = (key->current_transactions_start + i)
% CURRENT_TRANSACTIONS_NUM;
if (cid == key->current_transactions[index].cid) {
return index;
}
}
return -1;
}
static struct transaction *u2f_transaction_get(U2FPassthruState *key,
uint32_t cid)
{
int index = u2f_transaction_get_index(key, cid);
if (index < 0) {
return NULL;
}
return &key->current_transactions[index];
}
static struct transaction *u2f_transaction_get_from_nonce(U2FPassthruState *key,
const uint8_t nonce[NONCE_SIZE])
{
for (int i = 0; i < key->current_transactions_num; ++i) {
int index = (key->current_transactions_start + i)
% CURRENT_TRANSACTIONS_NUM;
if (key->current_transactions[index].cid == BROADCAST_CID
&& memcmp(nonce, key->current_transactions[index].nonce,
NONCE_SIZE) == 0) {
return &key->current_transactions[index];
}
}
return NULL;
}
static void u2f_transaction_close(U2FPassthruState *key, uint32_t cid)
{
int index, next_index;
index = u2f_transaction_get_index(key, cid);
if (index < 0) {
return;
}
next_index = (index + 1) % CURRENT_TRANSACTIONS_NUM;
/* Rearrange to ensure the oldest is at the start position */
while (next_index != key->current_transactions_end) {
memcpy(&key->current_transactions[index],
&key->current_transactions[next_index],
sizeof(struct transaction));
index = next_index;
next_index = (index + 1) % CURRENT_TRANSACTIONS_NUM;
}
key->current_transactions_end = index;
--key->current_transactions_num;
if (key->current_transactions_num == 0) {
u2f_passthru_reset(key);
}
}
static void u2f_transaction_add(U2FPassthruState *key, uint32_t cid,
const uint8_t nonce[NONCE_SIZE])
{
uint8_t index;
struct transaction *transaction;
if (key->current_transactions_num >= CURRENT_TRANSACTIONS_NUM) {
/* Close the oldest transaction */
index = key->current_transactions_start;
transaction = &key->current_transactions[index];
u2f_transaction_close(key, transaction->cid);
}
/* Index */
index = key->current_transactions_end;
key->current_transactions_end = (index + 1) % CURRENT_TRANSACTIONS_NUM;
++key->current_transactions_num;
/* Transaction */
transaction = &key->current_transactions[index];
transaction->cid = cid;
transaction->resp_bcnt = 0;
transaction->resp_size = 0;
/* Nonce */
if (nonce != NULL) {
memcpy(transaction->nonce, nonce, NONCE_SIZE);
}
}
static void u2f_passthru_read(void *opaque);
static void u2f_transaction_start(U2FPassthruState *key,
const struct packet_init *packet_init)
{
int64_t time;
/* Transaction */
if (packet_init->cid == BROADCAST_CID) {
u2f_transaction_add(key, packet_init->cid, packet_init->data);
} else {
u2f_transaction_add(key, packet_init->cid, NULL);
}
/* Time */
time = qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL);
if (key->last_transaction_time == 0) {
qemu_set_fd_handler(key->hidraw_fd, u2f_passthru_read, NULL, key);
timer_init_ms(&key->timer, QEMU_CLOCK_VIRTUAL, u2f_timeout_check, key);
timer_mod(&key->timer, time + TRANSACTION_TIMEOUT / 4);
}
key->last_transaction_time = time;
}
static void u2f_passthru_recv_from_host(U2FPassthruState *key,
const uint8_t packet[U2FHID_PACKET_SIZE])
{
struct transaction *transaction;
uint32_t cid;
/* Retrieve transaction */
cid = packet_get_cid(packet);
if (cid == BROADCAST_CID) {
struct packet_init *packet_init;
if (!packet_is_init(packet)) {
return;
}
packet_init = (struct packet_init *)packet;
transaction = u2f_transaction_get_from_nonce(key, packet_init->data);
} else {
transaction = u2f_transaction_get(key, cid);
}
/* Ignore no started transaction */
if (transaction == NULL) {
return;
}
if (packet_is_init(packet)) {
struct packet_init *packet_init = (struct packet_init *)packet;
transaction->resp_bcnt = packet_init_get_bcnt(packet_init);
transaction->resp_size = PACKET_INIT_DATA_SIZE;
if (packet_init->cid == BROADCAST_CID) {
/* Nonce checking for legitimate response */
if (memcmp(transaction->nonce, packet_init->data, NONCE_SIZE)
!= 0) {
return;
}
}
} else {
transaction->resp_size += PACKET_CONT_DATA_SIZE;
}
/* Transaction end check */
if (transaction->resp_size >= transaction->resp_bcnt) {
u2f_transaction_close(key, cid);
}
u2f_send_to_guest(&key->base, packet);
}
static void u2f_passthru_read(void *opaque)
{
U2FPassthruState *key = opaque;
U2FKeyState *base = &key->base;
uint8_t packet[2 * U2FHID_PACKET_SIZE];
int ret;
/* Full size base queue check */
if (base->pending_in_num >= U2FHID_PENDING_IN_NUM) {
return;
}
ret = read(key->hidraw_fd, packet, sizeof(packet));
if (ret < 0) {
/* Detach */
if (base->dev.attached) {
usb_device_detach(&base->dev);
u2f_passthru_reset(key);
}
return;
}
if (ret != U2FHID_PACKET_SIZE) {
return;
}
u2f_passthru_recv_from_host(key, packet);
}
static void u2f_passthru_recv_from_guest(U2FKeyState *base,
const uint8_t packet[U2FHID_PACKET_SIZE])
{
U2FPassthruState *key = PASSTHRU_U2F_KEY(base);
uint8_t host_packet[U2FHID_PACKET_SIZE + 1];
ssize_t written;
if (packet_is_init(packet)) {
u2f_transaction_start(key, (struct packet_init *)packet);
}
host_packet[0] = 0;
memcpy(host_packet + 1, packet, U2FHID_PACKET_SIZE);
written = write(key->hidraw_fd, host_packet, sizeof(host_packet));
if (written != sizeof(host_packet)) {
error_report("%s: Bad written size (req 0x%zu, val 0x%zd)",
TYPE_U2F_PASSTHRU, sizeof(host_packet), written);
}
}
static void u2f_passthru_unrealize(U2FKeyState *base)
{
U2FPassthruState *key = PASSTHRU_U2F_KEY(base);
u2f_passthru_reset(key);
qemu_close(key->hidraw_fd);
}
static void u2f_passthru_realize(U2FKeyState *base, Error **errp)
{
U2FPassthruState *key = PASSTHRU_U2F_KEY(base);
int fd;
if (key->hidraw == NULL) {
error_setg(errp, "%s: Missing hidraw", TYPE_U2F_PASSTHRU);
return;
}
fd = qemu_open(key->hidraw, O_RDWR);
if (fd < 0) {
error_setg(errp, "%s: Failed to open %s", TYPE_U2F_PASSTHRU,
key->hidraw);
return;
}
key->hidraw_fd = fd;
u2f_passthru_reset(key);
}
static int u2f_passthru_post_load(void *opaque, int version_id)
{
U2FPassthruState *key = opaque;
u2f_passthru_reset(key);
return 0;
}
static const VMStateDescription u2f_passthru_vmstate = {
.name = "u2f-key-passthru",
.version_id = 1,
.minimum_version_id = 1,
.post_load = u2f_passthru_post_load,
.fields = (VMStateField[]) {
VMSTATE_U2F_KEY(base, U2FPassthruState),
VMSTATE_END_OF_LIST()
}
};
static Property u2f_passthru_properties[] = {
DEFINE_PROP_STRING("hidraw", U2FPassthruState, hidraw),
DEFINE_PROP_END_OF_LIST(),
};
static void u2f_passthru_class_init(ObjectClass *klass, void *data)
{
DeviceClass *dc = DEVICE_CLASS(klass);
U2FKeyClass *kc = U2F_KEY_CLASS(klass);
kc->realize = u2f_passthru_realize;
kc->unrealize = u2f_passthru_unrealize;
kc->recv_from_guest = u2f_passthru_recv_from_guest;
dc->desc = "QEMU U2F passthrough key";
dc->vmsd = &u2f_passthru_vmstate;
device_class_set_props(dc, u2f_passthru_properties);
}
static const TypeInfo u2f_key_passthru_info = {
.name = TYPE_U2F_PASSTHRU,
.parent = TYPE_U2F_KEY,
.instance_size = sizeof(U2FPassthruState),
.class_init = u2f_passthru_class_init
};
static void u2f_key_passthru_register_types(void)
{
type_register_static(&u2f_key_passthru_info);
}
type_init(u2f_key_passthru_register_types)