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 */
map_switcher(void)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. */
unmap_switcher(void)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 */
lguest_address_ok(const struct lguest * lg,unsigned long addr,unsigned long len)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 */
__lgread(struct lg_cpu * cpu,void * b,unsigned long addr,unsigned bytes)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. */
__lgwrite(struct lg_cpu * cpu,unsigned long addr,const void * b,unsigned bytes)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 */
run_guest(struct lg_cpu * cpu,unsigned long __user * user)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 */
init(void)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. */
fini(void)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>");
374