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Linux/arch/x86/um/ldt.c

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  1 /*
  2  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  3  * Licensed under the GPL
  4  */
  5 
  6 #include <linux/mm.h>
  7 #include <linux/sched.h>
  8 #include <linux/slab.h>
  9 #include <linux/syscalls.h>
 10 #include <linux/uaccess.h>
 11 #include <asm/unistd.h>
 12 #include <os.h>
 13 #include <skas.h>
 14 #include <sysdep/tls.h>
 15 
 16 static inline int modify_ldt (int func, void *ptr, unsigned long bytecount)
 17 {
 18         return syscall(__NR_modify_ldt, func, ptr, bytecount);
 19 }
 20 
 21 static long write_ldt_entry(struct mm_id *mm_idp, int func,
 22                      struct user_desc *desc, void **addr, int done)
 23 {
 24         long res;
 25         void *stub_addr;
 26         res = syscall_stub_data(mm_idp, (unsigned long *)desc,
 27                                 (sizeof(*desc) + sizeof(long) - 1) &
 28                                     ~(sizeof(long) - 1),
 29                                 addr, &stub_addr);
 30         if (!res) {
 31                 unsigned long args[] = { func,
 32                                          (unsigned long)stub_addr,
 33                                          sizeof(*desc),
 34                                          0, 0, 0 };
 35                 res = run_syscall_stub(mm_idp, __NR_modify_ldt, args,
 36                                        0, addr, done);
 37         }
 38 
 39         return res;
 40 }
 41 
 42 /*
 43  * In skas mode, we hold our own ldt data in UML.
 44  * Thus, the code implementing sys_modify_ldt_skas
 45  * is very similar to (and mostly stolen from) sys_modify_ldt
 46  * for arch/i386/kernel/ldt.c
 47  * The routines copied and modified in part are:
 48  * - read_ldt
 49  * - read_default_ldt
 50  * - write_ldt
 51  * - sys_modify_ldt_skas
 52  */
 53 
 54 static int read_ldt(void __user * ptr, unsigned long bytecount)
 55 {
 56         int i, err = 0;
 57         unsigned long size;
 58         uml_ldt_t *ldt = &current->mm->context.arch.ldt;
 59 
 60         if (!ldt->entry_count)
 61                 goto out;
 62         if (bytecount > LDT_ENTRY_SIZE*LDT_ENTRIES)
 63                 bytecount = LDT_ENTRY_SIZE*LDT_ENTRIES;
 64         err = bytecount;
 65 
 66         mutex_lock(&ldt->lock);
 67         if (ldt->entry_count <= LDT_DIRECT_ENTRIES) {
 68                 size = LDT_ENTRY_SIZE*LDT_DIRECT_ENTRIES;
 69                 if (size > bytecount)
 70                         size = bytecount;
 71                 if (copy_to_user(ptr, ldt->u.entries, size))
 72                         err = -EFAULT;
 73                 bytecount -= size;
 74                 ptr += size;
 75         }
 76         else {
 77                 for (i=0; i<ldt->entry_count/LDT_ENTRIES_PER_PAGE && bytecount;
 78                      i++) {
 79                         size = PAGE_SIZE;
 80                         if (size > bytecount)
 81                                 size = bytecount;
 82                         if (copy_to_user(ptr, ldt->u.pages[i], size)) {
 83                                 err = -EFAULT;
 84                                 break;
 85                         }
 86                         bytecount -= size;
 87                         ptr += size;
 88                 }
 89         }
 90         mutex_unlock(&ldt->lock);
 91 
 92         if (bytecount == 0 || err == -EFAULT)
 93                 goto out;
 94 
 95         if (clear_user(ptr, bytecount))
 96                 err = -EFAULT;
 97 
 98 out:
 99         return err;
100 }
101 
102 static int read_default_ldt(void __user * ptr, unsigned long bytecount)
103 {
104         int err;
105 
106         if (bytecount > 5*LDT_ENTRY_SIZE)
107                 bytecount = 5*LDT_ENTRY_SIZE;
108 
109         err = bytecount;
110         /*
111          * UML doesn't support lcall7 and lcall27.
112          * So, we don't really have a default ldt, but emulate
113          * an empty ldt of common host default ldt size.
114          */
115         if (clear_user(ptr, bytecount))
116                 err = -EFAULT;
117 
118         return err;
119 }
120 
121 static int write_ldt(void __user * ptr, unsigned long bytecount, int func)
122 {
123         uml_ldt_t *ldt = &current->mm->context.arch.ldt;
124         struct mm_id * mm_idp = &current->mm->context.id;
125         int i, err;
126         struct user_desc ldt_info;
127         struct ldt_entry entry0, *ldt_p;
128         void *addr = NULL;
129 
130         err = -EINVAL;
131         if (bytecount != sizeof(ldt_info))
132                 goto out;
133         err = -EFAULT;
134         if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
135                 goto out;
136 
137         err = -EINVAL;
138         if (ldt_info.entry_number >= LDT_ENTRIES)
139                 goto out;
140         if (ldt_info.contents == 3) {
141                 if (func == 1)
142                         goto out;
143                 if (ldt_info.seg_not_present == 0)
144                         goto out;
145         }
146 
147         mutex_lock(&ldt->lock);
148 
149         err = write_ldt_entry(mm_idp, func, &ldt_info, &addr, 1);
150         if (err)
151                 goto out_unlock;
152 
153         if (ldt_info.entry_number >= ldt->entry_count &&
154             ldt_info.entry_number >= LDT_DIRECT_ENTRIES) {
155                 for (i=ldt->entry_count/LDT_ENTRIES_PER_PAGE;
156                      i*LDT_ENTRIES_PER_PAGE <= ldt_info.entry_number;
157                      i++) {
158                         if (i == 0)
159                                 memcpy(&entry0, ldt->u.entries,
160                                        sizeof(entry0));
161                         ldt->u.pages[i] = (struct ldt_entry *)
162                                 __get_free_page(GFP_KERNEL|__GFP_ZERO);
163                         if (!ldt->u.pages[i]) {
164                                 err = -ENOMEM;
165                                 /* Undo the change in host */
166                                 memset(&ldt_info, 0, sizeof(ldt_info));
167                                 write_ldt_entry(mm_idp, 1, &ldt_info, &addr, 1);
168                                 goto out_unlock;
169                         }
170                         if (i == 0) {
171                                 memcpy(ldt->u.pages[0], &entry0,
172                                        sizeof(entry0));
173                                 memcpy(ldt->u.pages[0]+1, ldt->u.entries+1,
174                                        sizeof(entry0)*(LDT_DIRECT_ENTRIES-1));
175                         }
176                         ldt->entry_count = (i + 1) * LDT_ENTRIES_PER_PAGE;
177                 }
178         }
179         if (ldt->entry_count <= ldt_info.entry_number)
180                 ldt->entry_count = ldt_info.entry_number + 1;
181 
182         if (ldt->entry_count <= LDT_DIRECT_ENTRIES)
183                 ldt_p = ldt->u.entries + ldt_info.entry_number;
184         else
185                 ldt_p = ldt->u.pages[ldt_info.entry_number/LDT_ENTRIES_PER_PAGE] +
186                         ldt_info.entry_number%LDT_ENTRIES_PER_PAGE;
187 
188         if (ldt_info.base_addr == 0 && ldt_info.limit == 0 &&
189            (func == 1 || LDT_empty(&ldt_info))) {
190                 ldt_p->a = 0;
191                 ldt_p->b = 0;
192         }
193         else{
194                 if (func == 1)
195                         ldt_info.useable = 0;
196                 ldt_p->a = LDT_entry_a(&ldt_info);
197                 ldt_p->b = LDT_entry_b(&ldt_info);
198         }
199         err = 0;
200 
201 out_unlock:
202         mutex_unlock(&ldt->lock);
203 out:
204         return err;
205 }
206 
207 static long do_modify_ldt_skas(int func, void __user *ptr,
208                                unsigned long bytecount)
209 {
210         int ret = -ENOSYS;
211 
212         switch (func) {
213                 case 0:
214                         ret = read_ldt(ptr, bytecount);
215                         break;
216                 case 1:
217                 case 0x11:
218                         ret = write_ldt(ptr, bytecount, func);
219                         break;
220                 case 2:
221                         ret = read_default_ldt(ptr, bytecount);
222                         break;
223         }
224         return ret;
225 }
226 
227 static DEFINE_SPINLOCK(host_ldt_lock);
228 static short dummy_list[9] = {0, -1};
229 static short * host_ldt_entries = NULL;
230 
231 static void ldt_get_host_info(void)
232 {
233         long ret;
234         struct ldt_entry * ldt;
235         short *tmp;
236         int i, size, k, order;
237 
238         spin_lock(&host_ldt_lock);
239 
240         if (host_ldt_entries != NULL) {
241                 spin_unlock(&host_ldt_lock);
242                 return;
243         }
244         host_ldt_entries = dummy_list+1;
245 
246         spin_unlock(&host_ldt_lock);
247 
248         for (i = LDT_PAGES_MAX-1, order=0; i; i>>=1, order++)
249                 ;
250 
251         ldt = (struct ldt_entry *)
252               __get_free_pages(GFP_KERNEL|__GFP_ZERO, order);
253         if (ldt == NULL) {
254                 printk(KERN_ERR "ldt_get_host_info: couldn't allocate buffer "
255                        "for host ldt\n");
256                 return;
257         }
258 
259         ret = modify_ldt(0, ldt, (1<<order)*PAGE_SIZE);
260         if (ret < 0) {
261                 printk(KERN_ERR "ldt_get_host_info: couldn't read host ldt\n");
262                 goto out_free;
263         }
264         if (ret == 0) {
265                 /* default_ldt is active, simply write an empty entry 0 */
266                 host_ldt_entries = dummy_list;
267                 goto out_free;
268         }
269 
270         for (i=0, size=0; i<ret/LDT_ENTRY_SIZE; i++) {
271                 if (ldt[i].a != 0 || ldt[i].b != 0)
272                         size++;
273         }
274 
275         if (size < ARRAY_SIZE(dummy_list))
276                 host_ldt_entries = dummy_list;
277         else {
278                 size = (size + 1) * sizeof(dummy_list[0]);
279                 tmp = kmalloc(size, GFP_KERNEL);
280                 if (tmp == NULL) {
281                         printk(KERN_ERR "ldt_get_host_info: couldn't allocate "
282                                "host ldt list\n");
283                         goto out_free;
284                 }
285                 host_ldt_entries = tmp;
286         }
287 
288         for (i=0, k=0; i<ret/LDT_ENTRY_SIZE; i++) {
289                 if (ldt[i].a != 0 || ldt[i].b != 0)
290                         host_ldt_entries[k++] = i;
291         }
292         host_ldt_entries[k] = -1;
293 
294 out_free:
295         free_pages((unsigned long)ldt, order);
296 }
297 
298 long init_new_ldt(struct mm_context *new_mm, struct mm_context *from_mm)
299 {
300         struct user_desc desc;
301         short * num_p;
302         int i;
303         long page, err=0;
304         void *addr = NULL;
305 
306 
307         mutex_init(&new_mm->arch.ldt.lock);
308 
309         if (!from_mm) {
310                 memset(&desc, 0, sizeof(desc));
311                 /*
312                  * Now we try to retrieve info about the ldt, we
313                  * inherited from the host. All ldt-entries found
314                  * will be reset in the following loop
315                  */
316                 ldt_get_host_info();
317                 for (num_p=host_ldt_entries; *num_p != -1; num_p++) {
318                         desc.entry_number = *num_p;
319                         err = write_ldt_entry(&new_mm->id, 1, &desc,
320                                               &addr, *(num_p + 1) == -1);
321                         if (err)
322                                 break;
323                 }
324                 new_mm->arch.ldt.entry_count = 0;
325 
326                 goto out;
327         }
328 
329         /*
330          * Our local LDT is used to supply the data for
331          * modify_ldt(READLDT), if PTRACE_LDT isn't available,
332          * i.e., we have to use the stub for modify_ldt, which
333          * can't handle the big read buffer of up to 64kB.
334          */
335         mutex_lock(&from_mm->arch.ldt.lock);
336         if (from_mm->arch.ldt.entry_count <= LDT_DIRECT_ENTRIES)
337                 memcpy(new_mm->arch.ldt.u.entries, from_mm->arch.ldt.u.entries,
338                        sizeof(new_mm->arch.ldt.u.entries));
339         else {
340                 i = from_mm->arch.ldt.entry_count / LDT_ENTRIES_PER_PAGE;
341                 while (i-->0) {
342                         page = __get_free_page(GFP_KERNEL|__GFP_ZERO);
343                         if (!page) {
344                                 err = -ENOMEM;
345                                 break;
346                         }
347                         new_mm->arch.ldt.u.pages[i] =
348                                 (struct ldt_entry *) page;
349                         memcpy(new_mm->arch.ldt.u.pages[i],
350                                from_mm->arch.ldt.u.pages[i], PAGE_SIZE);
351                 }
352         }
353         new_mm->arch.ldt.entry_count = from_mm->arch.ldt.entry_count;
354         mutex_unlock(&from_mm->arch.ldt.lock);
355 
356     out:
357         return err;
358 }
359 
360 
361 void free_ldt(struct mm_context *mm)
362 {
363         int i;
364 
365         if (mm->arch.ldt.entry_count > LDT_DIRECT_ENTRIES) {
366                 i = mm->arch.ldt.entry_count / LDT_ENTRIES_PER_PAGE;
367                 while (i-- > 0)
368                         free_page((long) mm->arch.ldt.u.pages[i]);
369         }
370         mm->arch.ldt.entry_count = 0;
371 }
372 
373 SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr ,
374                 unsigned long , bytecount)
375 {
376         /* See non-um modify_ldt() for why we do this cast */
377         return (unsigned int)do_modify_ldt_skas(func, ptr, bytecount);
378 }
379 

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