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 memory size, pagetable, entry point and kernel address offset.
   4  * A read will run the Guest until a signal is pending (-EINTR), or the Guest
   5  * does a DMA out to the Launcher.  Writes are also used to get a DMA buffer
   6  * registered by the Guest and to send the Guest an interrupt. :*/
   7 #include <linux/uaccess.h>
   8 #include <linux/miscdevice.h>
   9 #include <linux/fs.h>
  10 #include "lg.h"
  11
  12 /*L:030 setup_regs() doesn't really belong in this file, but it gives us an
  13  * early glimpse deeper into the Host so it's worth having here.
  14  *
  15  * Most of the Guest's registers are left alone: we used get_zeroed_page() to
  16  * allocate the structure, so they will be 0. */
  17 static void setup_regs(struct lguest_regs *regs, unsigned long start)
  18 {
  19         /* There are four "segment" registers which the Guest needs to boot:
  20          * The "code segment" register (cs) refers to the kernel code segment
  21          * __KERNEL_CS, and the "data", "extra" and "stack" segment registers
  22          * refer to the kernel data segment __KERNEL_DS.
  23          *
  24          * The privilege level is packed into the lower bits.  The Guest runs
  25          * at privilege level 1 (GUEST_PL).*/
  26         regs->ds = regs->es = regs->ss = __KERNEL_DS|GUEST_PL;
  27         regs->cs = __KERNEL_CS|GUEST_PL;
  28
  29         /* The "eflags" register contains miscellaneous flags.  Bit 1 (0x002)
  30          * is supposed to always be "1".  Bit 9 (0x200) controls whether
  31          * interrupts are enabled.  We always leave interrupts enabled while
  32          * running the Guest. */
  33         regs->eflags = 0x202;
  34
  35         /* The "Extended Instruction Pointer" register says where the Guest is
  36          * running. */
  37         regs->eip = start;
  38
  39         /* %esi points to our boot information, at physical address 0, so don't
  40          * touch it. */
  41 }
  42
  43 /*L:310 To send DMA into the Guest, the Launcher needs to be able to ask for a
  44  * DMA buffer.  This is done by writing LHREQ_GETDMA and the key to
  45  * /dev/lguest. */
  46 static long user_get_dma(struct lguest *lg, const u32 __user *input)
  47 {
  48         unsigned long key, udma, irq;
  49
  50         /* Fetch the key they wrote to us. */
  51         if (get_user(key, input) != 0)
  52                 return -EFAULT;
  53         /* Look for a free Guest DMA buffer bound to that key. */
  54         udma = get_dma_buffer(lg, key, &irq);
  55         if (!udma)
  56                 return -ENOENT;
  57
  58         /* We need to tell the Launcher what interrupt the Guest expects after
  59          * the buffer is filled.  We stash it in udma->used_len. */
  60         lgwrite_u32(lg, udma + offsetof(struct lguest_dma, used_len), irq);
  61
  62         /* The (guest-physical) address of the DMA buffer is returned from
  63          * the write(). */
  64         return udma;
  65 }
  66
  67 /*L:315 To force the Guest to stop running and return to the Launcher, the
  68  * Waker sets writes LHREQ_BREAK and the value "1" to /dev/lguest.  The
  69  * Launcher then writes LHREQ_BREAK and "0" to release the Waker. */
  70 static int break_guest_out(struct lguest *lg, const u32 __user *input)
  71 {
  72         unsigned long on;
  73
  74         /* Fetch whether they're turning break on or off.. */
  75         if (get_user(on, input) != 0)
  76                 return -EFAULT;
  77
  78         if (on) {
  79                 lg->break_out = 1;
  80                 /* Pop it out (may be running on different CPU) */
  81                 wake_up_process(lg->tsk);
  82                 /* Wait for them to reset it */
  83                 return wait_event_interruptible(lg->break_wq, !lg->break_out);
  84         } else {
  85                 lg->break_out = 0;
  86                 wake_up(&lg->break_wq);
  87                 return 0;
  88         }
  89 }
  90
  91 /*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
  92  * number to /dev/lguest. */
  93 static int user_send_irq(struct lguest *lg, const u32 __user *input)
  94 {
  95         u32 irq;
  96
  97         if (get_user(irq, input) != 0)
  98                 return -EFAULT;
  99         if (irq >= LGUEST_IRQS)
 100                 return -EINVAL;
 101         /* Next time the Guest runs, the core code will see if it can deliver
 102          * this interrupt. */
 103         set_bit(irq, lg->irqs_pending);
 104         return 0;
 105 }
 106
 107 /*L:040 Once our Guest is initialized, the Launcher makes it run by reading
 108  * from /dev/lguest. */
 109 static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
 110 {
 111         struct lguest *lg = file->private_data;
 112
 113         /* You must write LHREQ_INITIALIZE first! */
 114         if (!lg)
 115                 return -EINVAL;
 116
 117         /* If you're not the task which owns the guest, go away. */
 118         if (current != lg->tsk)
 119                 return -EPERM;
 120
 121         /* If the guest is already dead, we indicate why */
 122         if (lg->dead) {
 123                 size_t len;
 124
 125                 /* lg->dead either contains an error code, or a string. */
 126                 if (IS_ERR(lg->dead))
 127                         return PTR_ERR(lg->dead);
 128
 129                 /* We can only return as much as the buffer they read with. */
 130                 len = min(size, strlen(lg->dead)+1);
 131                 if (copy_to_user(user, lg->dead, len) != 0)
 132                         return -EFAULT;
 133                 return len;
 134         }
 135
 136         /* If we returned from read() last time because the Guest sent DMA,
 137          * clear the flag. */
 138         if (lg->dma_is_pending)
 139                 lg->dma_is_pending = 0;
 140
 141         /* Run the Guest until something interesting happens. */
 142         return run_guest(lg, (unsigned long __user *)user);
 143 }
 144
 145 /*L:020 The initialization write supplies 4 32-bit values (in addition to the
 146  * 32-bit LHREQ_INITIALIZE value).  These are:
 147  *
 148  * pfnlimit: The highest (Guest-physical) page number the Guest should be
 149  * allowed to access.  The Launcher has to live in Guest memory, so it sets
 150  * this to ensure the Guest can't reach it.
 151  *
 152  * pgdir: The (Guest-physical) address of the top of the initial Guest
 153  * pagetables (which are set up by the Launcher).
 154  *
 155  * start: The first instruction to execute ("eip" in x86-speak).
 156  *
 157  * page_offset: The PAGE_OFFSET constant in the Guest kernel.  We should
 158  * probably wean the code off this, but it's a very useful constant!  Any
 159  * address above this is within the Guest kernel, and any kernel address can
 160  * quickly converted from physical to virtual by adding PAGE_OFFSET.  It's
 161  * 0xC0000000 (3G) by default, but it's configurable at kernel build time.
 162  */
 163 static int initialize(struct file *file, const u32 __user *input)
 164 {
 165         /* "struct lguest" contains everything we (the Host) know about a
 166          * Guest. */
 167         struct lguest *lg;
 168         int err, i;
 169         u32 args[4];
 170
 171         /* We grab the Big Lguest lock, which protects the global array
 172          * "lguests" and multiple simultaneous initializations. */
 173         mutex_lock(&lguest_lock);
 174         /* You can't initialize twice!  Close the device and start again... */
 175         if (file->private_data) {
 176                 err = -EBUSY;
 177                 goto unlock;
 178         }
 179
 180         if (copy_from_user(args, input, sizeof(args)) != 0) {
 181                 err = -EFAULT;
 182                 goto unlock;
 183         }
 184
 185         /* Find an unused guest. */
 186         i = find_free_guest();
 187         if (i < 0) {
 188                 err = -ENOSPC;
 189                 goto unlock;
 190         }
 191         /* OK, we have an index into the "lguest" array: "lg" is a convenient
 192          * pointer. */
 193         lg = &lguests[i];
 194
 195         /* Populate the easy fields of our "struct lguest" */
 196         lg->guestid = i;
 197         lg->pfn_limit = args[0];
 198         lg->page_offset = args[3];
 199
 200         /* We need a complete page for the Guest registers: they are accessible
 201          * to the Guest and we can only grant it access to whole pages. */
 202         lg->regs_page = get_zeroed_page(GFP_KERNEL);
 203         if (!lg->regs_page) {
 204                 err = -ENOMEM;
 205                 goto release_guest;
 206         }
 207         /* We actually put the registers at the bottom of the page. */
 208         lg->regs = (void *)lg->regs_page + PAGE_SIZE - sizeof(*lg->regs);
 209
 210         /* Initialize the Guest's shadow page tables, using the toplevel
 211          * address the Launcher gave us.  This allocates memory, so can
 212          * fail. */
 213         err = init_guest_pagetable(lg, args[1]);
 214         if (err)
 215                 goto free_regs;
 216
 217         /* Now we initialize the Guest's registers, handing it the start
 218          * address. */
 219         setup_regs(lg->regs, args[2]);
 220
 221         /* There are a couple of GDT entries the Guest expects when first
 222          * booting. */
 223         setup_guest_gdt(lg);
 224
 225         /* The timer for lguest's clock needs initialization. */
 226         init_clockdev(lg);
 227
 228         /* We keep a pointer to the Launcher task (ie. current task) for when
 229          * other Guests want to wake this one (inter-Guest I/O). */
 230         lg->tsk = current;
 231         /* We need to keep a pointer to the Launcher's memory map, because if
 232          * the Launcher dies we need to clean it up.  If we don't keep a
 233          * reference, it is destroyed before close() is called. */
 234         lg->mm = get_task_mm(lg->tsk);
 235
 236         /* Initialize the queue for the waker to wait on */
 237         init_waitqueue_head(&lg->break_wq);
 238
 239         /* We remember which CPU's pages this Guest used last, for optimization
 240          * when the same Guest runs on the same CPU twice. */
 241         lg->last_pages = NULL;
 242
 243         /* We keep our "struct lguest" in the file's private_data. */
 244         file->private_data = lg;
 245
 246         mutex_unlock(&lguest_lock);
 247
 248         /* And because this is a write() call, we return the length used. */
 249         return sizeof(args);
 250
 251 free_regs:
 252         free_page(lg->regs_page);
 253 release_guest:
 254         memset(lg, 0, sizeof(*lg));
 255 unlock:
 256         mutex_unlock(&lguest_lock);
 257         return err;
 258 }
 259
 260 /*L:010 The first operation the Launcher does must be a write.  All writes
 261  * start with a 32 bit number: for the first write this must be
 262  * LHREQ_INITIALIZE to set up the Guest.  After that the Launcher can use
 263  * writes of other values to get DMA buffers and send interrupts. */
 264 static ssize_t write(struct file *file, const char __user *input,
 265                      size_t size, loff_t *off)
 266 {
 267         /* Once the guest is initialized, we hold the "struct lguest" in the
 268          * file private data. */
 269         struct lguest *lg = file->private_data;
 270         u32 req;
 271
 272         if (get_user(req, input) != 0)
 273                 return -EFAULT;
 274         input += sizeof(req);
 275
 276         /* If you haven't initialized, you must do that first. */
 277         if (req != LHREQ_INITIALIZE && !lg)
 278                 return -EINVAL;
 279
 280         /* Once the Guest is dead, all you can do is read() why it died. */
 281         if (lg && lg->dead)
 282                 return -ENOENT;
 283
 284         /* If you're not the task which owns the Guest, you can only break */
 285         if (lg && current != lg->tsk && req != LHREQ_BREAK)
 286                 return -EPERM;
 287
 288         switch (req) {
 289         case LHREQ_INITIALIZE:
 290                 return initialize(file, (const u32 __user *)input);
 291         case LHREQ_GETDMA:
 292                 return user_get_dma(lg, (const u32 __user *)input);
 293         case LHREQ_IRQ:
 294                 return user_send_irq(lg, (const u32 __user *)input);
 295         case LHREQ_BREAK:
 296                 return break_guest_out(lg, (const u32 __user *)input);
 297         default:
 298                 return -EINVAL;
 299         }
 300 }
 301
 302 /*L:060 The final piece of interface code is the close() routine.  It reverses
 303  * everything done in initialize().  This is usually called because the
 304  * Launcher exited.
 305  *
 306  * Note that the close routine returns 0 or a negative error number: it can't
 307  * really fail, but it can whine.  I blame Sun for this wart, and K&R C for
 308  * letting them do it. :*/
 309 static int close(struct inode *inode, struct file *file)
 310 {
 311         struct lguest *lg = file->private_data;
 312
 313         /* If we never successfully initialized, there's nothing to clean up */
 314         if (!lg)
 315                 return 0;
 316
 317         /* We need the big lock, to protect from inter-guest I/O and other
 318          * Launchers initializing guests. */
 319         mutex_lock(&lguest_lock);
 320         /* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
 321         hrtimer_cancel(&lg->hrt);
 322         /* Free any DMA buffers the Guest had bound. */
 323         release_all_dma(lg);
 324         /* Free up the shadow page tables for the Guest. */
 325         free_guest_pagetable(lg);
 326         /* Now all the memory cleanups are done, it's safe to release the
 327          * Launcher's memory management structure. */
 328         mmput(lg->mm);
 329         /* If lg->dead doesn't contain an error code it will be NULL or a
 330          * kmalloc()ed string, either of which is ok to hand to kfree(). */
 331         if (!IS_ERR(lg->dead))
 332                 kfree(lg->dead);
 333         /* We can free up the register page we allocated. */
 334         free_page(lg->regs_page);
 335         /* We clear the entire structure, which also marks it as free for the
 336          * next user. */
 337         memset(lg, 0, sizeof(*lg));
 338         /* Release lock and exit. */
 339         mutex_unlock(&lguest_lock);
 340
 341         return 0;
 342 }
 343
 344 /*L:000
 345  * Welcome to our journey through the Launcher!
 346  *
 347  * The Launcher is the Host userspace program which sets up, runs and services
 348  * the Guest.  In fact, many comments in the Drivers which refer to "the Host"
 349  * doing things are inaccurate: the Launcher does all the device handling for
 350  * the Guest.  The Guest can't tell what's done by the the Launcher and what by
 351  * the Host.
 352  *
 353  * Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we
 354  * shall see more of that later.
 355  *
 356  * We begin our understanding with the Host kernel interface which the Launcher
 357  * uses: reading and writing a character device called /dev/lguest.  All the
 358  * work happens in the read(), write() and close() routines: */
 359 static struct file_operations lguest_fops = {
 360         .owner   = THIS_MODULE,
 361         .release = close,
 362         .write   = write,
 363         .read    = read,
 364 };
 365
 366 /* This is a textbook example of a "misc" character device.  Populate a "struct
 367  * miscdevice" and register it with misc_register(). */
 368 static struct miscdevice lguest_dev = {
 369         .minor  = MISC_DYNAMIC_MINOR,
 370         .name   = "lguest",
 371         .fops   = &lguest_fops,
 372 };
 373
 374 int __init lguest_device_init(void)
 375 {
 376         return misc_register(&lguest_dev);
 377 }
 378
 379 void __exit lguest_device_remove(void)
 380 {
 381         misc_deregister(&lguest_dev);
 382 }