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
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. */
unmap_switcher(void)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 */
lguest_address_ok(const struct lguest * lg,unsigned long addr,unsigned long len)173 bool lguest_address_ok(const struct lguest *lg,
174 unsigned long addr, unsigned long len)
175 {
176 return addr+len <= lg->pfn_limit * PAGE_SIZE && (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 */
__lgread(struct lg_cpu * cpu,void * b,unsigned long addr,unsigned bytes)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. */
__lgwrite(struct lg_cpu * cpu,unsigned long addr,const void * b,unsigned bytes)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 */
run_guest(struct lg_cpu * cpu,unsigned long __user * user)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 */
init(void)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. */
fini(void)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>");
371