drivers/lguest/lguest_user.c

   1 /*P:200 This contains all the /dev/lguest code, whereby the userspace launcher
   2  * controls and communicates with the Guest.  For example, the first write will
   3  * tell us the Guest's memory layout, pagetable, entry point and kernel address
   4  * offset.  A read will run the Guest until something happens, such as a signal
   5  * or the Guest doing a NOTIFY out to the Launcher. :*/
   6 #include <linux/uaccess.h>
   7 #include <linux/miscdevice.h>
   8 #include <linux/fs.h>
   9 #include "lg.h"
  10
  11 /*L:055 When something happens, the Waker process needs a way to stop the
  12  * kernel running the Guest and return to the Launcher.  So the Waker writes
  13  * LHREQ_BREAK and the value "1" to /dev/lguest to do this.  Once the Launcher
  14  * has done whatever needs attention, it writes LHREQ_BREAK and "0" to release
  15  * the Waker. */
  16 static int break_guest_out(struct lguest *lg, const unsigned long __user *input)
  17 {
  18         unsigned long on;
  19
  20         /* Fetch whether they're turning break on or off. */
  21         if (get_user(on, input) != 0)
  22                 return -EFAULT;
  23
  24         if (on) {
  25                 lg->break_out = 1;
  26                 /* Pop it out of the Guest (may be running on different CPU) */
  27                 wake_up_process(lg->tsk);
  28                 /* Wait for them to reset it */
  29                 return wait_event_interruptible(lg->break_wq, !lg->break_out);
  30         } else {
  31                 lg->break_out = 0;
  32                 wake_up(&lg->break_wq);
  33                 return 0;
  34         }
  35 }
  36
  37 /*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
  38  * number to /dev/lguest. */
  39 static int user_send_irq(struct lguest *lg, const unsigned long __user *input)
  40 {
  41         unsigned long irq;
  42
  43         if (get_user(irq, input) != 0)
  44                 return -EFAULT;
  45         if (irq >= LGUEST_IRQS)
  46                 return -EINVAL;
  47         /* Next time the Guest runs, the core code will see if it can deliver
  48          * this interrupt. */
  49         set_bit(irq, lg->irqs_pending);
  50         return 0;
  51 }
  52
  53 /*L:040 Once our Guest is initialized, the Launcher makes it run by reading
  54  * from /dev/lguest. */
  55 static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
  56 {
  57         struct lguest *lg = file->private_data;
  58
  59         /* You must write LHREQ_INITIALIZE first! */
  60         if (!lg)
  61                 return -EINVAL;
  62
  63         /* If you're not the task which owns the Guest, go away. */
  64         if (current != lg->tsk)
  65                 return -EPERM;
  66
  67         /* If the guest is already dead, we indicate why */
  68         if (lg->dead) {
  69                 size_t len;
  70
  71                 /* lg->dead either contains an error code, or a string. */
  72                 if (IS_ERR(lg->dead))
  73                         return PTR_ERR(lg->dead);
  74
  75                 /* We can only return as much as the buffer they read with. */
  76                 len = min(size, strlen(lg->dead)+1);
  77                 if (copy_to_user(user, lg->dead, len) != 0)
  78                         return -EFAULT;
  79                 return len;
  80         }
  81
  82         /* If we returned from read() last time because the Guest notified,
  83          * clear the flag. */
  84         if (lg->pending_notify)
  85                 lg->pending_notify = 0;
  86
  87         /* Run the Guest until something interesting happens. */
  88         return run_guest(lg, (unsigned long __user *)user);
  89 }
  90
  91 /*L:020 The initialization write supplies 4 pointer sized (32 or 64 bit)
  92  * values (in addition to the LHREQ_INITIALIZE value).  These are:
  93  *
  94  * base: The start of the Guest-physical memory inside the Launcher memory.
  95  *
  96  * pfnlimit: The highest (Guest-physical) page number the Guest should be
  97  * allowed to access.  The Guest memory lives inside the Launcher, so it sets
  98  * this to ensure the Guest can only reach its own memory.
  99  *
 100  * pgdir: The (Guest-physical) address of the top of the initial Guest
 101  * pagetables (which are set up by the Launcher).
 102  *
 103  * start: The first instruction to execute ("eip" in x86-speak).
 104  */
 105 static int initialize(struct file *file, const unsigned long __user *input)
 106 {
 107         /* "struct lguest" contains everything we (the Host) know about a
 108          * Guest. */
 109         struct lguest *lg;
 110         int err;
 111         unsigned long args[4];
 112
 113         /* We grab the Big Lguest lock, which protects against multiple
 114          * simultaneous initializations. */
 115         mutex_lock(&lguest_lock);
 116         /* You can't initialize twice!  Close the device and start again... */
 117         if (file->private_data) {
 118                 err = -EBUSY;
 119                 goto unlock;
 120         }
 121
 122         if (copy_from_user(args, input, sizeof(args)) != 0) {
 123                 err = -EFAULT;
 124                 goto unlock;
 125         }
 126
 127         lg = kzalloc(sizeof(*lg), GFP_KERNEL);
 128         if (!lg) {
 129                 err = -ENOMEM;
 130                 goto unlock;
 131         }
 132
 133         /* Populate the easy fields of our "struct lguest" */
 134         lg->mem_base = (void __user *)(long)args[0];
 135         lg->pfn_limit = args[1];
 136
 137         /* We need a complete page for the Guest registers: they are accessible
 138          * to the Guest and we can only grant it access to whole pages. */
 139         lg->regs_page = get_zeroed_page(GFP_KERNEL);
 140         if (!lg->regs_page) {
 141                 err = -ENOMEM;
 142                 goto release_guest;
 143         }
 144         /* We actually put the registers at the bottom of the page. */
 145         lg->regs = (void *)lg->regs_page + PAGE_SIZE - sizeof(*lg->regs);
 146
 147         /* Initialize the Guest's shadow page tables, using the toplevel
 148          * address the Launcher gave us.  This allocates memory, so can
 149          * fail. */
 150         err = init_guest_pagetable(lg, args[2]);
 151         if (err)
 152                 goto free_regs;
 153
 154         /* Now we initialize the Guest's registers, handing it the start
 155          * address. */
 156         lguest_arch_setup_regs(lg, args[3]);
 157
 158         /* The timer for lguest's clock needs initialization. */
 159         init_clockdev(lg);
 160
 161         /* We keep a pointer to the Launcher task (ie. current task) for when
 162          * other Guests want to wake this one (inter-Guest I/O). */
 163         lg->tsk = current;
 164         /* We need to keep a pointer to the Launcher's memory map, because if
 165          * the Launcher dies we need to clean it up.  If we don't keep a
 166          * reference, it is destroyed before close() is called. */
 167         lg->mm = get_task_mm(lg->tsk);
 168
 169         /* Initialize the queue for the waker to wait on */
 170         init_waitqueue_head(&lg->break_wq);
 171
 172         /* We remember which CPU's pages this Guest used last, for optimization
 173          * when the same Guest runs on the same CPU twice. */
 174         lg->last_pages = NULL;
 175
 176         /* We keep our "struct lguest" in the file's private_data. */
 177         file->private_data = lg;
 178
 179         mutex_unlock(&lguest_lock);
 180
 181         /* And because this is a write() call, we return the length used. */
 182         return sizeof(args);
 183
 184 free_regs:
 185         free_page(lg->regs_page);
 186 release_guest:
 187         kfree(lg);
 188 unlock:
 189         mutex_unlock(&lguest_lock);
 190         return err;
 191 }
 192
 193 /*L:010 The first operation the Launcher does must be a write.  All writes
 194  * start with an unsigned long number: for the first write this must be
 195  * LHREQ_INITIALIZE to set up the Guest.  After that the Launcher can use
 196  * writes of other values to send interrupts. */
 197 static ssize_t write(struct file *file, const char __user *in,
 198                      size_t size, loff_t *off)
 199 {
 200         /* Once the guest is initialized, we hold the "struct lguest" in the
 201          * file private data. */
 202         struct lguest *lg = file->private_data;
 203         const unsigned long __user *input = (const unsigned long __user *)in;
 204         unsigned long req;
 205
 206         if (get_user(req, input) != 0)
 207                 return -EFAULT;
 208         input++;
 209
 210         /* If you haven't initialized, you must do that first. */
 211         if (req != LHREQ_INITIALIZE && !lg)
 212                 return -EINVAL;
 213
 214         /* Once the Guest is dead, all you can do is read() why it died. */
 215         if (lg && lg->dead)
 216                 return -ENOENT;
 217
 218         /* If you're not the task which owns the Guest, you can only break */
 219         if (lg && current != lg->tsk && req != LHREQ_BREAK)
 220                 return -EPERM;
 221
 222         switch (req) {
 223         case LHREQ_INITIALIZE:
 224                 return initialize(file, input);
 225         case LHREQ_IRQ:
 226                 return user_send_irq(lg, input);
 227         case LHREQ_BREAK:
 228                 return break_guest_out(lg, input);
 229         default:
 230                 return -EINVAL;
 231         }
 232 }
 233
 234 /*L:060 The final piece of interface code is the close() routine.  It reverses
 235  * everything done in initialize().  This is usually called because the
 236  * Launcher exited.
 237  *
 238  * Note that the close routine returns 0 or a negative error number: it can't
 239  * really fail, but it can whine.  I blame Sun for this wart, and K&R C for
 240  * letting them do it. :*/
 241 static int close(struct inode *inode, struct file *file)
 242 {
 243         struct lguest *lg = file->private_data;
 244
 245         /* If we never successfully initialized, there's nothing to clean up */
 246         if (!lg)
 247                 return 0;
 248
 249         /* We need the big lock, to protect from inter-guest I/O and other
 250          * Launchers initializing guests. */
 251         mutex_lock(&lguest_lock);
 252         /* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
 253         hrtimer_cancel(&lg->hrt);
 254         /* Free up the shadow page tables for the Guest. */
 255         free_guest_pagetable(lg);
 256         /* Now all the memory cleanups are done, it's safe to release the
 257          * Launcher's memory management structure. */
 258         mmput(lg->mm);
 259         /* If lg->dead doesn't contain an error code it will be NULL or a
 260          * kmalloc()ed string, either of which is ok to hand to kfree(). */
 261         if (!IS_ERR(lg->dead))
 262                 kfree(lg->dead);
 263         /* We can free up the register page we allocated. */
 264         free_page(lg->regs_page);
 265         /* We clear the entire structure, which also marks it as free for the
 266          * next user. */
 267         memset(lg, 0, sizeof(*lg));
 268         /* Release lock and exit. */
 269         mutex_unlock(&lguest_lock);
 270
 271         return 0;
 272 }
 273
 274 /*L:000
 275  * Welcome to our journey through the Launcher!
 276  *
 277  * The Launcher is the Host userspace program which sets up, runs and services
 278  * the Guest.  In fact, many comments in the Drivers which refer to "the Host"
 279  * doing things are inaccurate: the Launcher does all the device handling for
 280  * the Guest, but the Guest can't know that.
 281  *
 282  * Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we
 283  * shall see more of that later.
 284  *
 285  * We begin our understanding with the Host kernel interface which the Launcher
 286  * uses: reading and writing a character device called /dev/lguest.  All the
 287  * work happens in the read(), write() and close() routines: */
 288 static struct file_operations lguest_fops = {
 289         .owner   = THIS_MODULE,
 290         .release = close,
 291         .write   = write,
 292         .read    = read,
 293 };
 294
 295 /* This is a textbook example of a "misc" character device.  Populate a "struct
 296  * miscdevice" and register it with misc_register(). */
 297 static struct miscdevice lguest_dev = {
 298         .minor  = MISC_DYNAMIC_MINOR,
 299         .name   = "lguest",
 300         .fops   = &lguest_fops,
 301 };
 302
 303 int __init lguest_device_init(void)
 304 {
 305         return misc_register(&lguest_dev);
 306 }
 307
 308 void __exit lguest_device_remove(void)
 309 {
 310         misc_deregister(&lguest_dev);
 311 }