drivers/lguest/core.c

   1 /*P:400
   2  * This contains run_guest() which actually calls into the Host<->Guest
   3  * Switcher and analyzes the return, such as determining if the Guest wants the
   4  * Host to do something.  This file also contains useful helper routines.
   5 :*/
   6 #include <linux/module.h>
   7 #include <linux/stringify.h>
   8 #include <linux/stddef.h>
   9 #include <linux/io.h>
  10 #include <linux/mm.h>
  11 #include <linux/vmalloc.h>
  12 #include <linux/cpu.h>
  13 #include <linux/freezer.h>
  14 #include <linux/highmem.h>
  15 #include <asm/paravirt.h>
  16 #include <asm/pgtable.h>
  17 #include <asm/uaccess.h>
  18 #include <asm/poll.h>
  19 #include <asm/asm-offsets.h>
  20 #include "lg.h"
  21
  22
  23 static struct vm_struct *switcher_vma;
  24 static struct page **switcher_page;
  25
  26 /* This One Big lock protects all inter-guest data structures. */
  27 DEFINE_MUTEX(lguest_lock);
  28
  29 /*H:010
  30  * We need to set up the Switcher at a high virtual address.  Remember the
  31  * Switcher is a few hundred bytes of assembler code which actually changes the
  32  * CPU to run the Guest, and then changes back to the Host when a trap or
  33  * interrupt happens.
  34  *
  35  * The Switcher code must be at the same virtual address in the Guest as the
  36  * Host since it will be running as the switchover occurs.
  37  *
  38  * Trying to map memory at a particular address is an unusual thing to do, so
  39  * it's not a simple one-liner.
  40  */
  41 static __init int map_switcher(void)
  42 {
  43         int i, err;
  44         struct page **pagep;
  45
  46         /*
  47          * Map the Switcher in to high memory.
  48          *
  49          * It turns out that if we choose the address 0xFFC00000 (4MB under the
  50          * top virtual address), it makes setting up the page tables really
  51          * easy.
  52          */
  53
  54         /*
  55          * We allocate an array of struct page pointers.  map_vm_area() wants
  56          * this, rather than just an array of pages.
  57          */
  58         switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES,
  59                                 GFP_KERNEL);
  60         if (!switcher_page) {
  61                 err = -ENOMEM;
  62                 goto out;
  63         }
  64
  65         /*
  66          * Now we actually allocate the pages.  The Guest will see these pages,
  67          * so we make sure they're zeroed.
  68          */
  69         for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
  70                 switcher_page[i] = alloc_page(GFP_KERNEL|__GFP_ZERO);
  71                 if (!switcher_page[i]) {
  72                         err = -ENOMEM;
  73                         goto free_some_pages;
  74                 }
  75         }
  76
  77         /*
  78          * First we check that the Switcher won't overlap the fixmap area at
  79          * the top of memory.  It's currently nowhere near, but it could have
  80          * very strange effects if it ever happened.
  81          */
  82         if (SWITCHER_ADDR + (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE > FIXADDR_START){
  83                 err = -ENOMEM;
  84                 printk("lguest: mapping switcher would thwack fixmap\n");
  85                 goto free_pages;
  86         }
  87
  88         /*
  89          * Now we reserve the "virtual memory area" we want: 0xFFC00000
  90          * (SWITCHER_ADDR).  We might not get it in theory, but in practice
  91          * it's worked so far.  The end address needs +1 because __get_vm_area
  92          * allocates an extra guard page, so we need space for that.
  93          */
  94         switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
  95                                      VM_ALLOC, SWITCHER_ADDR, SWITCHER_ADDR
  96                                      + (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE);
  97         if (!switcher_vma) {
  98                 err = -ENOMEM;
  99                 printk("lguest: could not map switcher pages high\n");
 100                 goto free_pages;
 101         }
 102
 103         /*
 104          * This code actually sets up the pages we've allocated to appear at
 105          * SWITCHER_ADDR.  map_vm_area() takes the vma we allocated above, the
 106          * kind of pages we're mapping (kernel pages), and a pointer to our
 107          * array of struct pages.  It increments that pointer, but we don't
 108          * care.
 109          */
 110         pagep = switcher_page;
 111         err = map_vm_area(switcher_vma, PAGE_KERNEL_EXEC, &pagep);
 112         if (err) {
 113                 printk("lguest: map_vm_area failed: %i\n", err);
 114                 goto free_vma;
 115         }
 116
 117         /*
 118          * Now the Switcher is mapped at the right address, we can't fail!
 119          * Copy in the compiled-in Switcher code (from <arch>_switcher.S).
 120          */
 121         memcpy(switcher_vma->addr, start_switcher_text,
 122                end_switcher_text - start_switcher_text);
 123
 124         printk(KERN_INFO "lguest: mapped switcher at %p\n",
 125                switcher_vma->addr);
 126         /* And we succeeded... */
 127         return 0;
 128
 129 free_vma:
 130         vunmap(switcher_vma->addr);
 131 free_pages:
 132         i = TOTAL_SWITCHER_PAGES;
 133 free_some_pages:
 134         for (--i; i >= 0; i--)
 135                 __free_pages(switcher_page[i], 0);
 136         kfree(switcher_page);
 137 out:
 138         return err;
 139 }
 140 /*:*/
 141
 142 /* Cleaning up the mapping when the module is unloaded is almost... too easy. */
 143 static void unmap_switcher(void)
 144 {
 145         unsigned int i;
 146
 147         /* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */
 148         vunmap(switcher_vma->addr);
 149         /* Now we just need to free the pages we copied the switcher into */
 150         for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
 151                 __free_pages(switcher_page[i], 0);
 152         kfree(switcher_page);
 153 }
 154
 155 /*H:032
 156  * Dealing With Guest Memory.
 157  *
 158  * Before we go too much further into the Host, we need to grok the routines
 159  * we use to deal with Guest memory.
 160  *
 161  * When the Guest gives us (what it thinks is) a physical address, we can use
 162  * the normal copy_from_user() & copy_to_user() on the corresponding place in
 163  * the memory region allocated by the Launcher.
 164  *
 165  * But we can't trust the Guest: it might be trying to access the Launcher
 166  * code.  We have to check that the range is below the pfn_limit the Launcher
 167  * gave us.  We have to make sure that addr + len doesn't give us a false
 168  * positive by overflowing, too.
 169  */
 170 bool lguest_address_ok(const struct lguest *lg,
 171                        unsigned long addr, unsigned long len)
 172 {
 173         return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr);
 174 }
 175
 176 /*
 177  * This routine copies memory from the Guest.  Here we can see how useful the
 178  * kill_lguest() routine we met in the Launcher can be: we return a random
 179  * value (all zeroes) instead of needing to return an error.
 180  */
 181 void __lgread(struct lg_cpu *cpu, void *b, unsigned long addr, unsigned bytes)
 182 {
 183         if (!lguest_address_ok(cpu->lg, addr, bytes)
 184             || copy_from_user(b, cpu->lg->mem_base + addr, bytes) != 0) {
 185                 /* copy_from_user should do this, but as we rely on it... */
 186                 memset(b, 0, bytes);
 187                 kill_guest(cpu, "bad read address %#lx len %u", addr, bytes);
 188         }
 189 }
 190
 191 /* This is the write (copy into Guest) version. */
 192 void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b,
 193                unsigned bytes)
 194 {
 195         if (!lguest_address_ok(cpu->lg, addr, bytes)
 196             || copy_to_user(cpu->lg->mem_base + addr, b, bytes) != 0)
 197                 kill_guest(cpu, "bad write address %#lx len %u", addr, bytes);
 198 }
 199 /*:*/
 200
 201 /*H:030
 202  * Let's jump straight to the the main loop which runs the Guest.
 203  * Remember, this is called by the Launcher reading /dev/lguest, and we keep
 204  * going around and around until something interesting happens.
 205  */
 206 int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
 207 {
 208         /* We stop running once the Guest is dead. */
 209         while (!cpu->lg->dead) {
 210                 unsigned int irq;
 211                 bool more;
 212
 213                 /* First we run any hypercalls the Guest wants done. */
 214                 if (cpu->hcall)
 215                         do_hypercalls(cpu);
 216
 217                 /*
 218                  * It's possible the Guest did a NOTIFY hypercall to the
 219                  * Launcher.
 220                  */
 221                 if (cpu->pending_notify) {
 222                         /*
 223                          * Does it just needs to write to a registered
 224                          * eventfd (ie. the appropriate virtqueue thread)?
 225                          */
 226                         if (!send_notify_to_eventfd(cpu)) {
 227                                 /* OK, we tell the main Laucher. */
 228                                 if (put_user(cpu->pending_notify, user))
 229                                         return -EFAULT;
 230                                 return sizeof(cpu->pending_notify);
 231                         }
 232                 }
 233
 234                 /* Check for signals */
 235                 if (signal_pending(current))
 236                         return -ERESTARTSYS;
 237
 238                 /*
 239                  * Check if there are any interrupts which can be delivered now:
 240                  * if so, this sets up the hander to be executed when we next
 241                  * run the Guest.
 242                  */
 243                 irq = interrupt_pending(cpu, &more);
 244                 if (irq < LGUEST_IRQS)
 245                         try_deliver_interrupt(cpu, irq, more);
 246
 247                 /*
 248                  * All long-lived kernel loops need to check with this horrible
 249                  * thing called the freezer.  If the Host is trying to suspend,
 250                  * it stops us.
 251                  */
 252                 try_to_freeze();
 253
 254                 /*
 255                  * Just make absolutely sure the Guest is still alive.  One of
 256                  * those hypercalls could have been fatal, for example.
 257                  */
 258                 if (cpu->lg->dead)
 259                         break;
 260
 261                 /*
 262                  * If the Guest asked to be stopped, we sleep.  The Guest's
 263                  * clock timer will wake us.
 264                  */
 265                 if (cpu->halted) {
 266                         set_current_state(TASK_INTERRUPTIBLE);
 267                         /*
 268                          * Just before we sleep, make sure no interrupt snuck in
 269                          * which we should be doing.
 270                          */
 271                         if (interrupt_pending(cpu, &more) < LGUEST_IRQS)
 272                                 set_current_state(TASK_RUNNING);
 273                         else
 274                                 schedule();
 275                         continue;
 276                 }
 277
 278                 /*
 279                  * OK, now we're ready to jump into the Guest.  First we put up
 280                  * the "Do Not Disturb" sign:
 281                  */
 282                 local_irq_disable();
 283
 284                 /* Actually run the Guest until something happens. */
 285                 lguest_arch_run_guest(cpu);
 286
 287                 /* Now we're ready to be interrupted or moved to other CPUs */
 288                 local_irq_enable();
 289
 290                 /* Now we deal with whatever happened to the Guest. */
 291                 lguest_arch_handle_trap(cpu);
 292         }
 293
 294         /* Special case: Guest is 'dead' but wants a reboot. */
 295         if (cpu->lg->dead == ERR_PTR(-ERESTART))
 296                 return -ERESTART;
 297
 298         /* The Guest is dead => "No such file or directory" */
 299         return -ENOENT;
 300 }
 301
 302 /*H:000
 303  * Welcome to the Host!
 304  *
 305  * By this point your brain has been tickled by the Guest code and numbed by
 306  * the Launcher code; prepare for it to be stretched by the Host code.  This is
 307  * the heart.  Let's begin at the initialization routine for the Host's lg
 308  * module.
 309  */
 310 static int __init init(void)
 311 {
 312         int err;
 313
 314         /* Lguest can't run under Xen, VMI or itself.  It does Tricky Stuff. */
 315         if (paravirt_enabled()) {
 316                 printk("lguest is afraid of being a guest\n");
 317                 return -EPERM;
 318         }
 319
 320         /* First we put the Switcher up in very high virtual memory. */
 321         err = map_switcher();
 322         if (err)
 323                 goto out;
 324
 325         /* Now we set up the pagetable implementation for the Guests. */
 326         err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES);
 327         if (err)
 328                 goto unmap;
 329
 330         /* We might need to reserve an interrupt vector. */
 331         err = init_interrupts();
 332         if (err)
 333                 goto free_pgtables;
 334
 335         /* /dev/lguest needs to be registered. */
 336         err = lguest_device_init();
 337         if (err)
 338                 goto free_interrupts;
 339
 340         /* Finally we do some architecture-specific setup. */
 341         lguest_arch_host_init();
 342
 343         /* All good! */
 344         return 0;
 345
 346 free_interrupts:
 347         free_interrupts();
 348 free_pgtables:
 349         free_pagetables();
 350 unmap:
 351         unmap_switcher();
 352 out:
 353         return err;
 354 }
 355
 356 /* Cleaning up is just the same code, backwards.  With a little French. */
 357 static void __exit fini(void)
 358 {
 359         lguest_device_remove();
 360         free_interrupts();
 361         free_pagetables();
 362         unmap_switcher();
 363
 364         lguest_arch_host_fini();
 365 }
 366 /*:*/
 367
 368 /*
 369  * The Host side of lguest can be a module.  This is a nice way for people to
 370  * play with it.
 371  */
 372 module_init(init);
 373 module_exit(fini);
 374 MODULE_LICENSE("GPL");
 375 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");