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/sched/signal.h>
  12 #include <linux/vmalloc.h>
  13 #include <linux/cpu.h>
  14 #include <linux/freezer.h>
  15 #include <linux/highmem.h>
  16 #include <linux/slab.h>
  17 #include <asm/paravirt.h>
  18 #include <asm/pgtable.h>
  19 #include <linux/uaccess.h>
  20 #include <asm/poll.h>
  21 #include <asm/asm-offsets.h>
  22 #include "lg.h"
  23
  24 unsigned long switcher_addr;
  25 struct page **lg_switcher_pages;
  26 static struct vm_struct *switcher_text_vma;
  27 static struct vm_struct *switcher_stacks_vma;
  28
  29 /* This One Big lock protects all inter-guest data structures. */
  30 DEFINE_MUTEX(lguest_lock);
  31
  32 /*H:010
  33  * We need to set up the Switcher at a high virtual address.  Remember the
  34  * Switcher is a few hundred bytes of assembler code which actually changes the
  35  * CPU to run the Guest, and then changes back to the Host when a trap or
  36  * interrupt happens.
  37  *
  38  * The Switcher code must be at the same virtual address in the Guest as the
  39  * Host since it will be running as the switchover occurs.
  40  *
  41  * Trying to map memory at a particular address is an unusual thing to do, so
  42  * it's not a simple one-liner.
  43  */
  44 static __init int map_switcher(void)
  45 {
  46         int i, err;
  47
  48         /*
  49          * Map the Switcher in to high memory.
  50          *
  51          * It turns out that if we choose the address 0xFFC00000 (4MB under the
  52          * top virtual address), it makes setting up the page tables really
  53          * easy.
  54          */
  55
  56         /* We assume Switcher text fits into a single page. */
  57         if (end_switcher_text - start_switcher_text > PAGE_SIZE) {
  58                 printk(KERN_ERR "lguest: switcher text too large (%zu)\n",
  59                        end_switcher_text - start_switcher_text);
  60                 return -EINVAL;
  61         }
  62
  63         /*
  64          * We allocate an array of struct page pointers.  map_vm_area() wants
  65          * this, rather than just an array of pages.
  66          */
  67         lg_switcher_pages = kmalloc(sizeof(lg_switcher_pages[0])
  68                                     * TOTAL_SWITCHER_PAGES,
  69                                     GFP_KERNEL);
  70         if (!lg_switcher_pages) {
  71                 err = -ENOMEM;
  72                 goto out;
  73         }
  74
  75         /*
  76          * Now we actually allocate the pages.  The Guest will see these pages,
  77          * so we make sure they're zeroed.
  78          */
  79         for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
  80                 lg_switcher_pages[i] = alloc_page(GFP_KERNEL|__GFP_ZERO);
  81                 if (!lg_switcher_pages[i]) {
  82                         err = -ENOMEM;
  83                         goto free_some_pages;
  84                 }
  85         }
  86
  87         /*
  88          * Copy in the compiled-in Switcher code (from x86/switcher_32.S).
  89          * It goes in the first page, which we map in momentarily.
  90          */
  91         memcpy(kmap(lg_switcher_pages[0]), start_switcher_text,
  92                end_switcher_text - start_switcher_text);
  93         kunmap(lg_switcher_pages[0]);
  94
  95         /*
  96          * We place the Switcher underneath the fixmap area, which is the
  97          * highest virtual address we can get.  This is important, since we
  98          * tell the Guest it can't access this memory, so we want its ceiling
  99          * as high as possible.
 100          */
 101         switcher_addr = FIXADDR_START - TOTAL_SWITCHER_PAGES*PAGE_SIZE;
 102
 103         /*
 104          * Now we reserve the "virtual memory area"s we want.  We might
 105          * not get them in theory, but in practice it's worked so far.
 106          *
 107          * We want the switcher text to be read-only and executable, and
 108          * the stacks to be read-write and non-executable.
 109          */
 110         switcher_text_vma = __get_vm_area(PAGE_SIZE, VM_ALLOC|VM_NO_GUARD,
 111                                           switcher_addr,
 112                                           switcher_addr + PAGE_SIZE);
 113
 114         if (!switcher_text_vma) {
 115                 err = -ENOMEM;
 116                 printk("lguest: could not map switcher pages high\n");
 117                 goto free_pages;
 118         }
 119
 120         switcher_stacks_vma = __get_vm_area(SWITCHER_STACK_PAGES * PAGE_SIZE,
 121                                             VM_ALLOC|VM_NO_GUARD,
 122                                             switcher_addr + PAGE_SIZE,
 123                                             switcher_addr + TOTAL_SWITCHER_PAGES * PAGE_SIZE);
 124         if (!switcher_stacks_vma) {
 125                 err = -ENOMEM;
 126                 printk("lguest: could not map switcher pages high\n");
 127                 goto free_text_vma;
 128         }
 129
 130         /*
 131          * This code actually sets up the pages we've allocated to appear at
 132          * switcher_addr.  map_vm_area() takes the vma we allocated above, the
 133          * kind of pages we're mapping (kernel text pages and kernel writable
 134          * pages respectively), and a pointer to our array of struct pages.
 135          */
 136         err = map_vm_area(switcher_text_vma, PAGE_KERNEL_RX, lg_switcher_pages);
 137         if (err) {
 138                 printk("lguest: text map_vm_area failed: %i\n", err);
 139                 goto free_vmas;
 140         }
 141
 142         err = map_vm_area(switcher_stacks_vma, PAGE_KERNEL,
 143                           lg_switcher_pages + SWITCHER_TEXT_PAGES);
 144         if (err) {
 145                 printk("lguest: stacks map_vm_area failed: %i\n", err);
 146                 goto free_vmas;
 147         }
 148
 149         /*
 150          * Now the Switcher is mapped at the right address, we can't fail!
 151          */
 152         printk(KERN_INFO "lguest: mapped switcher at %p\n",
 153                switcher_text_vma->addr);
 154         /* And we succeeded... */
 155         return 0;
 156
 157 free_vmas:
 158         /* Undoes map_vm_area and __get_vm_area */
 159         vunmap(switcher_stacks_vma->addr);
 160 free_text_vma:
 161         vunmap(switcher_text_vma->addr);
 162 free_pages:
 163         i = TOTAL_SWITCHER_PAGES;
 164 free_some_pages:
 165         for (--i; i >= 0; i--)
 166                 __free_pages(lg_switcher_pages[i], 0);
 167         kfree(lg_switcher_pages);
 168 out:
 169         return err;
 170 }
 171 /*:*/
 172
 173 /* Cleaning up the mapping when the module is unloaded is almost... too easy. */
 174 static void unmap_switcher(void)
 175 {
 176         unsigned int i;
 177
 178         /* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */
 179         vunmap(switcher_text_vma->addr);
 180         vunmap(switcher_stacks_vma->addr);
 181         /* Now we just need to free the pages we copied the switcher into */
 182         for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
 183                 __free_pages(lg_switcher_pages[i], 0);
 184         kfree(lg_switcher_pages);
 185 }
 186
 187 /*H:032
 188  * Dealing With Guest Memory.
 189  *
 190  * Before we go too much further into the Host, we need to grok the routines
 191  * we use to deal with Guest memory.
 192  *
 193  * When the Guest gives us (what it thinks is) a physical address, we can use
 194  * the normal copy_from_user() & copy_to_user() on the corresponding place in
 195  * the memory region allocated by the Launcher.
 196  *
 197  * But we can't trust the Guest: it might be trying to access the Launcher
 198  * code.  We have to check that the range is below the pfn_limit the Launcher
 199  * gave us.  We have to make sure that addr + len doesn't give us a false
 200  * positive by overflowing, too.
 201  */
 202 bool lguest_address_ok(const struct lguest *lg,
 203                        unsigned long addr, unsigned long len)
 204 {
 205         return addr+len <= lg->pfn_limit * PAGE_SIZE && (addr+len >= addr);
 206 }
 207
 208 /*
 209  * This routine copies memory from the Guest.  Here we can see how useful the
 210  * kill_lguest() routine we met in the Launcher can be: we return a random
 211  * value (all zeroes) instead of needing to return an error.
 212  */
 213 void __lgread(struct lg_cpu *cpu, void *b, unsigned long addr, unsigned bytes)
 214 {
 215         if (!lguest_address_ok(cpu->lg, addr, bytes)
 216             || copy_from_user(b, cpu->lg->mem_base + addr, bytes) != 0) {
 217                 /* copy_from_user should do this, but as we rely on it... */
 218                 memset(b, 0, bytes);
 219                 kill_guest(cpu, "bad read address %#lx len %u", addr, bytes);
 220         }
 221 }
 222
 223 /* This is the write (copy into Guest) version. */
 224 void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b,
 225                unsigned bytes)
 226 {
 227         if (!lguest_address_ok(cpu->lg, addr, bytes)
 228             || copy_to_user(cpu->lg->mem_base + addr, b, bytes) != 0)
 229                 kill_guest(cpu, "bad write address %#lx len %u", addr, bytes);
 230 }
 231 /*:*/
 232
 233 /*H:030
 234  * Let's jump straight to the the main loop which runs the Guest.
 235  * Remember, this is called by the Launcher reading /dev/lguest, and we keep
 236  * going around and around until something interesting happens.
 237  */
 238 int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
 239 {
 240         /* If the launcher asked for a register with LHREQ_GETREG */
 241         if (cpu->reg_read) {
 242                 if (put_user(*cpu->reg_read, user))
 243                         return -EFAULT;
 244                 cpu->reg_read = NULL;
 245                 return sizeof(*cpu->reg_read);
 246         }
 247
 248         /* We stop running once the Guest is dead. */
 249         while (!cpu->lg->dead) {
 250                 unsigned int irq;
 251                 bool more;
 252
 253                 /* First we run any hypercalls the Guest wants done. */
 254                 if (cpu->hcall)
 255                         do_hypercalls(cpu);
 256
 257                 /* Do we have to tell the Launcher about a trap? */
 258                 if (cpu->pending.trap) {
 259                         if (copy_to_user(user, &cpu->pending,
 260                                          sizeof(cpu->pending)))
 261                                 return -EFAULT;
 262                         return sizeof(cpu->pending);
 263                 }
 264
 265                 /*
 266                  * All long-lived kernel loops need to check with this horrible
 267                  * thing called the freezer.  If the Host is trying to suspend,
 268                  * it stops us.
 269                  */
 270                 try_to_freeze();
 271
 272                 /* Check for signals */
 273                 if (signal_pending(current))
 274                         return -ERESTARTSYS;
 275
 276                 /*
 277                  * Check if there are any interrupts which can be delivered now:
 278                  * if so, this sets up the hander to be executed when we next
 279                  * run the Guest.
 280                  */
 281                 irq = interrupt_pending(cpu, &more);
 282                 if (irq < LGUEST_IRQS)
 283                         try_deliver_interrupt(cpu, irq, more);
 284
 285                 /*
 286                  * Just make absolutely sure the Guest is still alive.  One of
 287                  * those hypercalls could have been fatal, for example.
 288                  */
 289                 if (cpu->lg->dead)
 290                         break;
 291
 292                 /*
 293                  * If the Guest asked to be stopped, we sleep.  The Guest's
 294                  * clock timer will wake us.
 295                  */
 296                 if (cpu->halted) {
 297                         set_current_state(TASK_INTERRUPTIBLE);
 298                         /*
 299                          * Just before we sleep, make sure no interrupt snuck in
 300                          * which we should be doing.
 301                          */
 302                         if (interrupt_pending(cpu, &more) < LGUEST_IRQS)
 303                                 set_current_state(TASK_RUNNING);
 304                         else
 305                                 schedule();
 306                         continue;
 307                 }
 308
 309                 /*
 310                  * OK, now we're ready to jump into the Guest.  First we put up
 311                  * the "Do Not Disturb" sign:
 312                  */
 313                 local_irq_disable();
 314
 315                 /* Actually run the Guest until something happens. */
 316                 lguest_arch_run_guest(cpu);
 317
 318                 /* Now we're ready to be interrupted or moved to other CPUs */
 319                 local_irq_enable();
 320
 321                 /* Now we deal with whatever happened to the Guest. */
 322                 lguest_arch_handle_trap(cpu);
 323         }
 324
 325         /* Special case: Guest is 'dead' but wants a reboot. */
 326         if (cpu->lg->dead == ERR_PTR(-ERESTART))
 327                 return -ERESTART;
 328
 329         /* The Guest is dead => "No such file or directory" */
 330         return -ENOENT;
 331 }
 332
 333 /*H:000
 334  * Welcome to the Host!
 335  *
 336  * By this point your brain has been tickled by the Guest code and numbed by
 337  * the Launcher code; prepare for it to be stretched by the Host code.  This is
 338  * the heart.  Let's begin at the initialization routine for the Host's lg
 339  * module.
 340  */
 341 static int __init init(void)
 342 {
 343         int err;
 344
 345         /* Lguest can't run under Xen, VMI or itself.  It does Tricky Stuff. */
 346         if (get_kernel_rpl() != 0) {
 347                 printk("lguest is afraid of being a guest\n");
 348                 return -EPERM;
 349         }
 350
 351         /* First we put the Switcher up in very high virtual memory. */
 352         err = map_switcher();
 353         if (err)
 354                 goto out;
 355
 356         /* We might need to reserve an interrupt vector. */
 357         err = init_interrupts();
 358         if (err)
 359                 goto unmap;
 360
 361         /* /dev/lguest needs to be registered. */
 362         err = lguest_device_init();
 363         if (err)
 364                 goto free_interrupts;
 365
 366         /* Finally we do some architecture-specific setup. */
 367         lguest_arch_host_init();
 368
 369         /* All good! */
 370         return 0;
 371
 372 free_interrupts:
 373         free_interrupts();
 374 unmap:
 375         unmap_switcher();
 376 out:
 377         return err;
 378 }
 379
 380 /* Cleaning up is just the same code, backwards.  With a little French. */
 381 static void __exit fini(void)
 382 {
 383         lguest_device_remove();
 384         free_interrupts();
 385         unmap_switcher();
 386
 387         lguest_arch_host_fini();
 388 }
 389 /*:*/
 390
 391 /*
 392  * The Host side of lguest can be a module.  This is a nice way for people to
 393  * play with it.
 394  */
 395 module_init(init);
 396 module_exit(fini);
 397 MODULE_LICENSE("GPL");
 398 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");