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