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