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 <linux/slab.h>
  16 #include <asm/paravirt.h>
  17 #include <asm/pgtable.h>
  18 #include <asm/uaccess.h>
  19 #include <asm/poll.h>
  20 #include <asm/asm-offsets.h>
  21 #include "lg.h"
  22
  23
  24 static struct vm_struct *switcher_vma;
  25 static struct page **switcher_page;
  26
  27 /* This One Big lock protects all inter-guest data structures. */
  28 DEFINE_MUTEX(lguest_lock);
  29
  30 /*H:010
  31  * We need to set up the Switcher at a high virtual address.  Remember the
  32  * Switcher is a few hundred bytes of assembler code which actually changes the
  33  * CPU to run the Guest, and then changes back to the Host when a trap or
  34  * interrupt happens.
  35  *
  36  * The Switcher code must be at the same virtual address in the Guest as the
  37  * Host since it will be running as the switchover occurs.
  38  *
  39  * Trying to map memory at a particular address is an unusual thing to do, so
  40  * it's not a simple one-liner.
  41  */
  42 static __init int map_switcher(void)
  43 {
  44         int i, err;
  45         struct page **pagep;
  46
  47         /*
  48          * Map the Switcher in to high memory.
  49          *
  50          * It turns out that if we choose the address 0xFFC00000 (4MB under the
  51          * top virtual address), it makes setting up the page tables really
  52          * easy.
  53          */
  54
  55         /*
  56          * We allocate an array of struct page pointers.  map_vm_area() wants
  57          * this, rather than just an array of pages.
  58          */
  59         switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES,
  60                                 GFP_KERNEL);
  61         if (!switcher_page) {
  62                 err = -ENOMEM;
  63                 goto out;
  64         }
  65
  66         /*
  67          * Now we actually allocate the pages.  The Guest will see these pages,
  68          * so we make sure they're zeroed.
  69          */
  70         for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
  71                 switcher_page[i] = alloc_page(GFP_KERNEL|__GFP_ZERO);
  72                 if (!switcher_page[i]) {
  73                         err = -ENOMEM;
  74                         goto free_some_pages;
  75                 }
  76         }
  77
  78         /*
  79          * First we check that the Switcher won't overlap the fixmap area at
  80          * the top of memory.  It's currently nowhere near, but it could have
  81          * very strange effects if it ever happened.
  82          */
  83         if (SWITCHER_ADDR + (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE > FIXADDR_START){
  84                 err = -ENOMEM;
  85                 printk("lguest: mapping switcher would thwack fixmap\n");
  86                 goto free_pages;
  87         }
  88
  89         /*
  90          * Now we reserve the "virtual memory area" we want: 0xFFC00000
  91          * (SWITCHER_ADDR).  We might not get it in theory, but in practice
  92          * it's worked so far.  The end address needs +1 because __get_vm_area
  93          * allocates an extra guard page, so we need space for that.
  94          */
  95         switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
  96                                      VM_ALLOC, SWITCHER_ADDR, SWITCHER_ADDR
  97                                      + (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE);
  98         if (!switcher_vma) {
  99                 err = -ENOMEM;
 100                 printk("lguest: could not map switcher pages high\n");
 101                 goto free_pages;
 102         }
 103
 104         /*
 105          * This code actually sets up the pages we've allocated to appear at
 106          * SWITCHER_ADDR.  map_vm_area() takes the vma we allocated above, the
 107          * kind of pages we're mapping (kernel pages), and a pointer to our
 108          * array of struct pages.  It increments that pointer, but we don't
 109          * care.
 110          */
 111         pagep = switcher_page;
 112         err = map_vm_area(switcher_vma, PAGE_KERNEL_EXEC, &pagep);
 113         if (err) {
 114                 printk("lguest: map_vm_area failed: %i\n", err);
 115                 goto free_vma;
 116         }
 117
 118         /*
 119          * Now the Switcher is mapped at the right address, we can't fail!
 120          * Copy in the compiled-in Switcher code (from x86/switcher_32.S).
 121          */
 122         memcpy(switcher_vma->addr, start_switcher_text,
 123                end_switcher_text - start_switcher_text);
 124
 125         printk(KERN_INFO "lguest: mapped switcher at %p\n",
 126                switcher_vma->addr);
 127         /* And we succeeded... */
 128         return 0;
 129
 130 free_vma:
 131         vunmap(switcher_vma->addr);
 132 free_pages:
 133         i = TOTAL_SWITCHER_PAGES;
 134 free_some_pages:
 135         for (--i; i >= 0; i--)
 136                 __free_pages(switcher_page[i], 0);
 137         kfree(switcher_page);
 138 out:
 139         return err;
 140 }
 141 /*:*/
 142
 143 /* Cleaning up the mapping when the module is unloaded is almost... too easy. */
 144 static void unmap_switcher(void)
 145 {
 146         unsigned int i;
 147
 148         /* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */
 149         vunmap(switcher_vma->addr);
 150         /* Now we just need to free the pages we copied the switcher into */
 151         for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
 152                 __free_pages(switcher_page[i], 0);
 153         kfree(switcher_page);
 154 }
 155
 156 /*H:032
 157  * Dealing With Guest Memory.
 158  *
 159  * Before we go too much further into the Host, we need to grok the routines
 160  * we use to deal with Guest memory.
 161  *
 162  * When the Guest gives us (what it thinks is) a physical address, we can use
 163  * the normal copy_from_user() & copy_to_user() on the corresponding place in
 164  * the memory region allocated by the Launcher.
 165  *
 166  * But we can't trust the Guest: it might be trying to access the Launcher
 167  * code.  We have to check that the range is below the pfn_limit the Launcher
 168  * gave us.  We have to make sure that addr + len doesn't give us a false
 169  * positive by overflowing, too.
 170  */
 171 bool lguest_address_ok(const struct lguest *lg,
 172                        unsigned long addr, unsigned long len)
 173 {
 174         return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr);
 175 }
 176
 177 /*
 178  * This routine copies memory from the Guest.  Here we can see how useful the
 179  * kill_lguest() routine we met in the Launcher can be: we return a random
 180  * value (all zeroes) instead of needing to return an error.
 181  */
 182 void __lgread(struct lg_cpu *cpu, void *b, unsigned long addr, unsigned bytes)
 183 {
 184         if (!lguest_address_ok(cpu->lg, addr, bytes)
 185             || copy_from_user(b, cpu->lg->mem_base + addr, bytes) != 0) {
 186                 /* copy_from_user should do this, but as we rely on it... */
 187                 memset(b, 0, bytes);
 188                 kill_guest(cpu, "bad read address %#lx len %u", addr, bytes);
 189         }
 190 }
 191
 192 /* This is the write (copy into Guest) version. */
 193 void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b,
 194                unsigned bytes)
 195 {
 196         if (!lguest_address_ok(cpu->lg, addr, bytes)
 197             || copy_to_user(cpu->lg->mem_base + addr, b, bytes) != 0)
 198                 kill_guest(cpu, "bad write address %#lx len %u", addr, bytes);
 199 }
 200 /*:*/
 201
 202 /*H:030
 203  * Let's jump straight to the the main loop which runs the Guest.
 204  * Remember, this is called by the Launcher reading /dev/lguest, and we keep
 205  * going around and around until something interesting happens.
 206  */
 207 int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
 208 {
 209         /* We stop running once the Guest is dead. */
 210         while (!cpu->lg->dead) {
 211                 unsigned int irq;
 212                 bool more;
 213
 214                 /* First we run any hypercalls the Guest wants done. */
 215                 if (cpu->hcall)
 216                         do_hypercalls(cpu);
 217
 218                 /*
 219                  * It's possible the Guest did a NOTIFY hypercall to the
 220                  * Launcher.
 221                  */
 222                 if (cpu->pending_notify) {
 223                         /*
 224                          * Does it just needs to write to a registered
 225                          * eventfd (ie. the appropriate virtqueue thread)?
 226                          */
 227                         if (!send_notify_to_eventfd(cpu)) {
 228                                 /* OK, we tell the main Laucher. */
 229                                 if (put_user(cpu->pending_notify, user))
 230                                         return -EFAULT;
 231                                 return sizeof(cpu->pending_notify);
 232                         }
 233                 }
 234
 235                 /*
 236                  * All long-lived kernel loops need to check with this horrible
 237                  * thing called the freezer.  If the Host is trying to suspend,
 238                  * it stops us.
 239                  */
 240                 try_to_freeze();
 241
 242                 /* Check for signals */
 243                 if (signal_pending(current))
 244                         return -ERESTARTSYS;
 245
 246                 /*
 247                  * Check if there are any interrupts which can be delivered now:
 248                  * if so, this sets up the hander to be executed when we next
 249                  * run the Guest.
 250                  */
 251                 irq = interrupt_pending(cpu, &more);
 252                 if (irq < LGUEST_IRQS)
 253                         try_deliver_interrupt(cpu, irq, more);
 254
 255                 /*
 256                  * Just make absolutely sure the Guest is still alive.  One of
 257                  * those hypercalls could have been fatal, for example.
 258                  */
 259                 if (cpu->lg->dead)
 260                         break;
 261
 262                 /*
 263                  * If the Guest asked to be stopped, we sleep.  The Guest's
 264                  * clock timer will wake us.
 265                  */
 266                 if (cpu->halted) {
 267                         set_current_state(TASK_INTERRUPTIBLE);
 268                         /*
 269                          * Just before we sleep, make sure no interrupt snuck in
 270                          * which we should be doing.
 271                          */
 272                         if (interrupt_pending(cpu, &more) < LGUEST_IRQS)
 273                                 set_current_state(TASK_RUNNING);
 274                         else
 275                                 schedule();
 276                         continue;
 277                 }
 278
 279                 /*
 280                  * OK, now we're ready to jump into the Guest.  First we put up
 281                  * the "Do Not Disturb" sign:
 282                  */
 283                 local_irq_disable();
 284
 285                 /* Actually run the Guest until something happens. */
 286                 lguest_arch_run_guest(cpu);
 287
 288                 /* Now we're ready to be interrupted or moved to other CPUs */
 289                 local_irq_enable();
 290
 291                 /* Now we deal with whatever happened to the Guest. */
 292                 lguest_arch_handle_trap(cpu);
 293         }
 294
 295         /* Special case: Guest is 'dead' but wants a reboot. */
 296         if (cpu->lg->dead == ERR_PTR(-ERESTART))
 297                 return -ERESTART;
 298
 299         /* The Guest is dead => "No such file or directory" */
 300         return -ENOENT;
 301 }
 302
 303 /*H:000
 304  * Welcome to the Host!
 305  *
 306  * By this point your brain has been tickled by the Guest code and numbed by
 307  * the Launcher code; prepare for it to be stretched by the Host code.  This is
 308  * the heart.  Let's begin at the initialization routine for the Host's lg
 309  * module.
 310  */
 311 static int __init init(void)
 312 {
 313         int err;
 314
 315         /* Lguest can't run under Xen, VMI or itself.  It does Tricky Stuff. */
 316         if (get_kernel_rpl() != 0) {
 317                 printk("lguest is afraid of being a guest\n");
 318                 return -EPERM;
 319         }
 320
 321         /* First we put the Switcher up in very high virtual memory. */
 322         err = map_switcher();
 323         if (err)
 324                 goto out;
 325
 326         /* Now we set up the pagetable implementation for the Guests. */
 327         err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES);
 328         if (err)
 329                 goto unmap;
 330
 331         /* We might need to reserve an interrupt vector. */
 332         err = init_interrupts();
 333         if (err)
 334                 goto free_pgtables;
 335
 336         /* /dev/lguest needs to be registered. */
 337         err = lguest_device_init();
 338         if (err)
 339                 goto free_interrupts;
 340
 341         /* Finally we do some architecture-specific setup. */
 342         lguest_arch_host_init();
 343
 344         /* All good! */
 345         return 0;
 346
 347 free_interrupts:
 348         free_interrupts();
 349 free_pgtables:
 350         free_pagetables();
 351 unmap:
 352         unmap_switcher();
 353 out:
 354         return err;
 355 }
 356
 357 /* Cleaning up is just the same code, backwards.  With a little French. */
 358 static void __exit fini(void)
 359 {
 360         lguest_device_remove();
 361         free_interrupts();
 362         free_pagetables();
 363         unmap_switcher();
 364
 365         lguest_arch_host_fini();
 366 }
 367 /*:*/
 368
 369 /*
 370  * The Host side of lguest can be a module.  This is a nice way for people to
 371  * play with it.
 372  */
 373 module_init(init);
 374 module_exit(fini);
 375 MODULE_LICENSE("GPL");
 376 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");