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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
4 * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
5 * Copyright (C) 2002 Andi Kleen
6 *
7 * This handles calls from both 32bit and 64bit mode.
8 *
9 * Lock order:
10 * contex.ldt_usr_sem
11 * mmap_sem
12 * context.lock
13 */
14
15#include <linux/errno.h>
16#include <linux/gfp.h>
17#include <linux/sched.h>
18#include <linux/string.h>
19#include <linux/mm.h>
20#include <linux/smp.h>
21#include <linux/syscalls.h>
22#include <linux/slab.h>
23#include <linux/vmalloc.h>
24#include <linux/uaccess.h>
25
26#include <asm/ldt.h>
27#include <asm/tlb.h>
28#include <asm/desc.h>
29#include <asm/mmu_context.h>
30#include <asm/syscalls.h>
31
32static void refresh_ldt_segments(void)
33{
34#ifdef CONFIG_X86_64
35 unsigned short sel;
36
37 /*
38 * Make sure that the cached DS and ES descriptors match the updated
39 * LDT.
40 */
41 savesegment(ds, sel);
42 if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT)
43 loadsegment(ds, sel);
44
45 savesegment(es, sel);
46 if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT)
47 loadsegment(es, sel);
48#endif
49}
50
51/* context.lock is held by the task which issued the smp function call */
52static void flush_ldt(void *__mm)
53{
54 struct mm_struct *mm = __mm;
55
56 if (this_cpu_read(cpu_tlbstate.loaded_mm) != mm)
57 return;
58
59 load_mm_ldt(mm);
60
61 refresh_ldt_segments();
62}
63
64/* The caller must call finalize_ldt_struct on the result. LDT starts zeroed. */
65static struct ldt_struct *alloc_ldt_struct(unsigned int num_entries)
66{
67 struct ldt_struct *new_ldt;
68 unsigned int alloc_size;
69
70 if (num_entries > LDT_ENTRIES)
71 return NULL;
72
73 new_ldt = kmalloc(sizeof(struct ldt_struct), GFP_KERNEL);
74 if (!new_ldt)
75 return NULL;
76
77 BUILD_BUG_ON(LDT_ENTRY_SIZE != sizeof(struct desc_struct));
78 alloc_size = num_entries * LDT_ENTRY_SIZE;
79
80 /*
81 * Xen is very picky: it requires a page-aligned LDT that has no
82 * trailing nonzero bytes in any page that contains LDT descriptors.
83 * Keep it simple: zero the whole allocation and never allocate less
84 * than PAGE_SIZE.
85 */
86 if (alloc_size > PAGE_SIZE)
87 new_ldt->entries = vzalloc(alloc_size);
88 else
89 new_ldt->entries = (void *)get_zeroed_page(GFP_KERNEL);
90
91 if (!new_ldt->entries) {
92 kfree(new_ldt);
93 return NULL;
94 }
95
96 /* The new LDT isn't aliased for PTI yet. */
97 new_ldt->slot = -1;
98
99 new_ldt->nr_entries = num_entries;
100 return new_ldt;
101}
102
103#ifdef CONFIG_PAGE_TABLE_ISOLATION
104
105static void do_sanity_check(struct mm_struct *mm,
106 bool had_kernel_mapping,
107 bool had_user_mapping)
108{
109 if (mm->context.ldt) {
110 /*
111 * We already had an LDT. The top-level entry should already
112 * have been allocated and synchronized with the usermode
113 * tables.
114 */
115 WARN_ON(!had_kernel_mapping);
116 if (boot_cpu_has(X86_FEATURE_PTI))
117 WARN_ON(!had_user_mapping);
118 } else {
119 /*
120 * This is the first time we're mapping an LDT for this process.
121 * Sync the pgd to the usermode tables.
122 */
123 WARN_ON(had_kernel_mapping);
124 if (boot_cpu_has(X86_FEATURE_PTI))
125 WARN_ON(had_user_mapping);
126 }
127}
128
129#ifdef CONFIG_X86_PAE
130
131static pmd_t *pgd_to_pmd_walk(pgd_t *pgd, unsigned long va)
132{
133 p4d_t *p4d;
134 pud_t *pud;
135
136 if (pgd->pgd == 0)
137 return NULL;
138
139 p4d = p4d_offset(pgd, va);
140 if (p4d_none(*p4d))
141 return NULL;
142
143 pud = pud_offset(p4d, va);
144 if (pud_none(*pud))
145 return NULL;
146
147 return pmd_offset(pud, va);
148}
149
150static void map_ldt_struct_to_user(struct mm_struct *mm)
151{
152 pgd_t *k_pgd = pgd_offset(mm, LDT_BASE_ADDR);
153 pgd_t *u_pgd = kernel_to_user_pgdp(k_pgd);
154 pmd_t *k_pmd, *u_pmd;
155
156 k_pmd = pgd_to_pmd_walk(k_pgd, LDT_BASE_ADDR);
157 u_pmd = pgd_to_pmd_walk(u_pgd, LDT_BASE_ADDR);
158
159 if (boot_cpu_has(X86_FEATURE_PTI) && !mm->context.ldt)
160 set_pmd(u_pmd, *k_pmd);
161}
162
163static void sanity_check_ldt_mapping(struct mm_struct *mm)
164{
165 pgd_t *k_pgd = pgd_offset(mm, LDT_BASE_ADDR);
166 pgd_t *u_pgd = kernel_to_user_pgdp(k_pgd);
167 bool had_kernel, had_user;
168 pmd_t *k_pmd, *u_pmd;
169
170 k_pmd = pgd_to_pmd_walk(k_pgd, LDT_BASE_ADDR);
171 u_pmd = pgd_to_pmd_walk(u_pgd, LDT_BASE_ADDR);
172 had_kernel = (k_pmd->pmd != 0);
173 had_user = (u_pmd->pmd != 0);
174
175 do_sanity_check(mm, had_kernel, had_user);
176}
177
178#else /* !CONFIG_X86_PAE */
179
180static void map_ldt_struct_to_user(struct mm_struct *mm)
181{
182 pgd_t *pgd = pgd_offset(mm, LDT_BASE_ADDR);
183
184 if (boot_cpu_has(X86_FEATURE_PTI) && !mm->context.ldt)
185 set_pgd(kernel_to_user_pgdp(pgd), *pgd);
186}
187
188static void sanity_check_ldt_mapping(struct mm_struct *mm)
189{
190 pgd_t *pgd = pgd_offset(mm, LDT_BASE_ADDR);
191 bool had_kernel = (pgd->pgd != 0);
192 bool had_user = (kernel_to_user_pgdp(pgd)->pgd != 0);
193
194 do_sanity_check(mm, had_kernel, had_user);
195}
196
197#endif /* CONFIG_X86_PAE */
198
199/*
200 * If PTI is enabled, this maps the LDT into the kernelmode and
201 * usermode tables for the given mm.
202 */
203static int
204map_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt, int slot)
205{
206 unsigned long va;
207 bool is_vmalloc;
208 spinlock_t *ptl;
209 int i, nr_pages;
210
211 if (!boot_cpu_has(X86_FEATURE_PTI))
212 return 0;
213
214 /*
215 * Any given ldt_struct should have map_ldt_struct() called at most
216 * once.
217 */
218 WARN_ON(ldt->slot != -1);
219
220 /* Check if the current mappings are sane */
221 sanity_check_ldt_mapping(mm);
222
223 is_vmalloc = is_vmalloc_addr(ldt->entries);
224
225 nr_pages = DIV_ROUND_UP(ldt->nr_entries * LDT_ENTRY_SIZE, PAGE_SIZE);
226
227 for (i = 0; i < nr_pages; i++) {
228 unsigned long offset = i << PAGE_SHIFT;
229 const void *src = (char *)ldt->entries + offset;
230 unsigned long pfn;
231 pgprot_t pte_prot;
232 pte_t pte, *ptep;
233
234 va = (unsigned long)ldt_slot_va(slot) + offset;
235 pfn = is_vmalloc ? vmalloc_to_pfn(src) :
236 page_to_pfn(virt_to_page(src));
237 /*
238 * Treat the PTI LDT range as a *userspace* range.
239 * get_locked_pte() will allocate all needed pagetables
240 * and account for them in this mm.
241 */
242 ptep = get_locked_pte(mm, va, &ptl);
243 if (!ptep)
244 return -ENOMEM;
245 /*
246 * Map it RO so the easy to find address is not a primary
247 * target via some kernel interface which misses a
248 * permission check.
249 */
250 pte_prot = __pgprot(__PAGE_KERNEL_RO & ~_PAGE_GLOBAL);
251 /* Filter out unsuppored __PAGE_KERNEL* bits: */
252 pgprot_val(pte_prot) &= __supported_pte_mask;
253 pte = pfn_pte(pfn, pte_prot);
254 set_pte_at(mm, va, ptep, pte);
255 pte_unmap_unlock(ptep, ptl);
256 }
257
258 /* Propagate LDT mapping to the user page-table */
259 map_ldt_struct_to_user(mm);
260
261 ldt->slot = slot;
262 return 0;
263}
264
265static void unmap_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt)
266{
267 unsigned long va;
268 int i, nr_pages;
269
270 if (!ldt)
271 return;
272
273 /* LDT map/unmap is only required for PTI */
274 if (!boot_cpu_has(X86_FEATURE_PTI))
275 return;
276
277 nr_pages = DIV_ROUND_UP(ldt->nr_entries * LDT_ENTRY_SIZE, PAGE_SIZE);
278
279 for (i = 0; i < nr_pages; i++) {
280 unsigned long offset = i << PAGE_SHIFT;
281 spinlock_t *ptl;
282 pte_t *ptep;
283
284 va = (unsigned long)ldt_slot_va(ldt->slot) + offset;
285 ptep = get_locked_pte(mm, va, &ptl);
286 pte_clear(mm, va, ptep);
287 pte_unmap_unlock(ptep, ptl);
288 }
289
290 va = (unsigned long)ldt_slot_va(ldt->slot);
291 flush_tlb_mm_range(mm, va, va + nr_pages * PAGE_SIZE, PAGE_SHIFT, false);
292}
293
294#else /* !CONFIG_PAGE_TABLE_ISOLATION */
295
296static int
297map_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt, int slot)
298{
299 return 0;
300}
301
302static void unmap_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt)
303{
304}
305#endif /* CONFIG_PAGE_TABLE_ISOLATION */
306
307static void free_ldt_pgtables(struct mm_struct *mm)
308{
309#ifdef CONFIG_PAGE_TABLE_ISOLATION
310 struct mmu_gather tlb;
311 unsigned long start = LDT_BASE_ADDR;
312 unsigned long end = LDT_END_ADDR;
313
314 if (!boot_cpu_has(X86_FEATURE_PTI))
315 return;
316
317 tlb_gather_mmu(&tlb, mm, start, end);
318 free_pgd_range(&tlb, start, end, start, end);
319 tlb_finish_mmu(&tlb, start, end);
320#endif
321}
322
323/* After calling this, the LDT is immutable. */
324static void finalize_ldt_struct(struct ldt_struct *ldt)
325{
326 paravirt_alloc_ldt(ldt->entries, ldt->nr_entries);
327}
328
329static void install_ldt(struct mm_struct *mm, struct ldt_struct *ldt)
330{
331 mutex_lock(&mm->context.lock);
332
333 /* Synchronizes with READ_ONCE in load_mm_ldt. */
334 smp_store_release(&mm->context.ldt, ldt);
335
336 /* Activate the LDT for all CPUs using currents mm. */
337 on_each_cpu_mask(mm_cpumask(mm), flush_ldt, mm, true);
338
339 mutex_unlock(&mm->context.lock);
340}
341
342static void free_ldt_struct(struct ldt_struct *ldt)
343{
344 if (likely(!ldt))
345 return;
346
347 paravirt_free_ldt(ldt->entries, ldt->nr_entries);
348 if (ldt->nr_entries * LDT_ENTRY_SIZE > PAGE_SIZE)
349 vfree_atomic(ldt->entries);
350 else
351 free_page((unsigned long)ldt->entries);
352 kfree(ldt);
353}
354
355/*
356 * Called on fork from arch_dup_mmap(). Just copy the current LDT state,
357 * the new task is not running, so nothing can be installed.
358 */
359int ldt_dup_context(struct mm_struct *old_mm, struct mm_struct *mm)
360{
361 struct ldt_struct *new_ldt;
362 int retval = 0;
363
364 if (!old_mm)
365 return 0;
366
367 mutex_lock(&old_mm->context.lock);
368 if (!old_mm->context.ldt)
369 goto out_unlock;
370
371 new_ldt = alloc_ldt_struct(old_mm->context.ldt->nr_entries);
372 if (!new_ldt) {
373 retval = -ENOMEM;
374 goto out_unlock;
375 }
376
377 memcpy(new_ldt->entries, old_mm->context.ldt->entries,
378 new_ldt->nr_entries * LDT_ENTRY_SIZE);
379 finalize_ldt_struct(new_ldt);
380
381 retval = map_ldt_struct(mm, new_ldt, 0);
382 if (retval) {
383 free_ldt_pgtables(mm);
384 free_ldt_struct(new_ldt);
385 goto out_unlock;
386 }
387 mm->context.ldt = new_ldt;
388
389out_unlock:
390 mutex_unlock(&old_mm->context.lock);
391 return retval;
392}
393
394/*
395 * No need to lock the MM as we are the last user
396 *
397 * 64bit: Don't touch the LDT register - we're already in the next thread.
398 */
399void destroy_context_ldt(struct mm_struct *mm)
400{
401 free_ldt_struct(mm->context.ldt);
402 mm->context.ldt = NULL;
403}
404
405void ldt_arch_exit_mmap(struct mm_struct *mm)
406{
407 free_ldt_pgtables(mm);
408}
409
410static int read_ldt(void __user *ptr, unsigned long bytecount)
411{
412 struct mm_struct *mm = current->mm;
413 unsigned long entries_size;
414 int retval;
415
416 down_read(&mm->context.ldt_usr_sem);
417
418 if (!mm->context.ldt) {
419 retval = 0;
420 goto out_unlock;
421 }
422
423 if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
424 bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
425
426 entries_size = mm->context.ldt->nr_entries * LDT_ENTRY_SIZE;
427 if (entries_size > bytecount)
428 entries_size = bytecount;
429
430 if (copy_to_user(ptr, mm->context.ldt->entries, entries_size)) {
431 retval = -EFAULT;
432 goto out_unlock;
433 }
434
435 if (entries_size != bytecount) {
436 /* Zero-fill the rest and pretend we read bytecount bytes. */
437 if (clear_user(ptr + entries_size, bytecount - entries_size)) {
438 retval = -EFAULT;
439 goto out_unlock;
440 }
441 }
442 retval = bytecount;
443
444out_unlock:
445 up_read(&mm->context.ldt_usr_sem);
446 return retval;
447}
448
449static int read_default_ldt(void __user *ptr, unsigned long bytecount)
450{
451 /* CHECKME: Can we use _one_ random number ? */
452#ifdef CONFIG_X86_32
453 unsigned long size = 5 * sizeof(struct desc_struct);
454#else
455 unsigned long size = 128;
456#endif
457 if (bytecount > size)
458 bytecount = size;
459 if (clear_user(ptr, bytecount))
460 return -EFAULT;
461 return bytecount;
462}
463
464static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
465{
466 struct mm_struct *mm = current->mm;
467 struct ldt_struct *new_ldt, *old_ldt;
468 unsigned int old_nr_entries, new_nr_entries;
469 struct user_desc ldt_info;
470 struct desc_struct ldt;
471 int error;
472
473 error = -EINVAL;
474 if (bytecount != sizeof(ldt_info))
475 goto out;
476 error = -EFAULT;
477 if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
478 goto out;
479
480 error = -EINVAL;
481 if (ldt_info.entry_number >= LDT_ENTRIES)
482 goto out;
483 if (ldt_info.contents == 3) {
484 if (oldmode)
485 goto out;
486 if (ldt_info.seg_not_present == 0)
487 goto out;
488 }
489
490 if ((oldmode && !ldt_info.base_addr && !ldt_info.limit) ||
491 LDT_empty(&ldt_info)) {
492 /* The user wants to clear the entry. */
493 memset(&ldt, 0, sizeof(ldt));
494 } else {
495 if (!IS_ENABLED(CONFIG_X86_16BIT) && !ldt_info.seg_32bit) {
496 error = -EINVAL;
497 goto out;
498 }
499
500 fill_ldt(&ldt, &ldt_info);
501 if (oldmode)
502 ldt.avl = 0;
503 }
504
505 if (down_write_killable(&mm->context.ldt_usr_sem))
506 return -EINTR;
507
508 old_ldt = mm->context.ldt;
509 old_nr_entries = old_ldt ? old_ldt->nr_entries : 0;
510 new_nr_entries = max(ldt_info.entry_number + 1, old_nr_entries);
511
512 error = -ENOMEM;
513 new_ldt = alloc_ldt_struct(new_nr_entries);
514 if (!new_ldt)
515 goto out_unlock;
516
517 if (old_ldt)
518 memcpy(new_ldt->entries, old_ldt->entries, old_nr_entries * LDT_ENTRY_SIZE);
519
520 new_ldt->entries[ldt_info.entry_number] = ldt;
521 finalize_ldt_struct(new_ldt);
522
523 /*
524 * If we are using PTI, map the new LDT into the userspace pagetables.
525 * If there is already an LDT, use the other slot so that other CPUs
526 * will continue to use the old LDT until install_ldt() switches
527 * them over to the new LDT.
528 */
529 error = map_ldt_struct(mm, new_ldt, old_ldt ? !old_ldt->slot : 0);
530 if (error) {
531 /*
532 * This only can fail for the first LDT setup. If an LDT is
533 * already installed then the PTE page is already
534 * populated. Mop up a half populated page table.
535 */
536 if (!WARN_ON_ONCE(old_ldt))
537 free_ldt_pgtables(mm);
538 free_ldt_struct(new_ldt);
539 goto out_unlock;
540 }
541
542 install_ldt(mm, new_ldt);
543 unmap_ldt_struct(mm, old_ldt);
544 free_ldt_struct(old_ldt);
545 error = 0;
546
547out_unlock:
548 up_write(&mm->context.ldt_usr_sem);
549out:
550 return error;
551}
552
553SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr ,
554 unsigned long , bytecount)
555{
556 int ret = -ENOSYS;
557
558 switch (func) {
559 case 0:
560 ret = read_ldt(ptr, bytecount);
561 break;
562 case 1:
563 ret = write_ldt(ptr, bytecount, 1);
564 break;
565 case 2:
566 ret = read_default_ldt(ptr, bytecount);
567 break;
568 case 0x11:
569 ret = write_ldt(ptr, bytecount, 0);
570 break;
571 }
572 /*
573 * The SYSCALL_DEFINE() macros give us an 'unsigned long'
574 * return type, but tht ABI for sys_modify_ldt() expects
575 * 'int'. This cast gives us an int-sized value in %rax
576 * for the return code. The 'unsigned' is necessary so
577 * the compiler does not try to sign-extend the negative
578 * return codes into the high half of the register when
579 * taking the value from int->long.
580 */
581 return (unsigned int)ret;
582}
1/*
2 * Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
3 * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
4 * Copyright (C) 2002 Andi Kleen
5 *
6 * This handles calls from both 32bit and 64bit mode.
7 */
8
9#include <linux/errno.h>
10#include <linux/gfp.h>
11#include <linux/sched.h>
12#include <linux/string.h>
13#include <linux/mm.h>
14#include <linux/smp.h>
15#include <linux/vmalloc.h>
16#include <linux/uaccess.h>
17
18#include <asm/system.h>
19#include <asm/ldt.h>
20#include <asm/desc.h>
21#include <asm/mmu_context.h>
22#include <asm/syscalls.h>
23
24#ifdef CONFIG_SMP
25static void flush_ldt(void *current_mm)
26{
27 if (current->active_mm == current_mm)
28 load_LDT(¤t->active_mm->context);
29}
30#endif
31
32static int alloc_ldt(mm_context_t *pc, int mincount, int reload)
33{
34 void *oldldt, *newldt;
35 int oldsize;
36
37 if (mincount <= pc->size)
38 return 0;
39 oldsize = pc->size;
40 mincount = (mincount + (PAGE_SIZE / LDT_ENTRY_SIZE - 1)) &
41 (~(PAGE_SIZE / LDT_ENTRY_SIZE - 1));
42 if (mincount * LDT_ENTRY_SIZE > PAGE_SIZE)
43 newldt = vmalloc(mincount * LDT_ENTRY_SIZE);
44 else
45 newldt = (void *)__get_free_page(GFP_KERNEL);
46
47 if (!newldt)
48 return -ENOMEM;
49
50 if (oldsize)
51 memcpy(newldt, pc->ldt, oldsize * LDT_ENTRY_SIZE);
52 oldldt = pc->ldt;
53 memset(newldt + oldsize * LDT_ENTRY_SIZE, 0,
54 (mincount - oldsize) * LDT_ENTRY_SIZE);
55
56 paravirt_alloc_ldt(newldt, mincount);
57
58#ifdef CONFIG_X86_64
59 /* CHECKME: Do we really need this ? */
60 wmb();
61#endif
62 pc->ldt = newldt;
63 wmb();
64 pc->size = mincount;
65 wmb();
66
67 if (reload) {
68#ifdef CONFIG_SMP
69 preempt_disable();
70 load_LDT(pc);
71 if (!cpumask_equal(mm_cpumask(current->mm),
72 cpumask_of(smp_processor_id())))
73 smp_call_function(flush_ldt, current->mm, 1);
74 preempt_enable();
75#else
76 load_LDT(pc);
77#endif
78 }
79 if (oldsize) {
80 paravirt_free_ldt(oldldt, oldsize);
81 if (oldsize * LDT_ENTRY_SIZE > PAGE_SIZE)
82 vfree(oldldt);
83 else
84 put_page(virt_to_page(oldldt));
85 }
86 return 0;
87}
88
89static inline int copy_ldt(mm_context_t *new, mm_context_t *old)
90{
91 int err = alloc_ldt(new, old->size, 0);
92 int i;
93
94 if (err < 0)
95 return err;
96
97 for (i = 0; i < old->size; i++)
98 write_ldt_entry(new->ldt, i, old->ldt + i * LDT_ENTRY_SIZE);
99 return 0;
100}
101
102/*
103 * we do not have to muck with descriptors here, that is
104 * done in switch_mm() as needed.
105 */
106int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
107{
108 struct mm_struct *old_mm;
109 int retval = 0;
110
111 mutex_init(&mm->context.lock);
112 mm->context.size = 0;
113 old_mm = current->mm;
114 if (old_mm && old_mm->context.size > 0) {
115 mutex_lock(&old_mm->context.lock);
116 retval = copy_ldt(&mm->context, &old_mm->context);
117 mutex_unlock(&old_mm->context.lock);
118 }
119 return retval;
120}
121
122/*
123 * No need to lock the MM as we are the last user
124 *
125 * 64bit: Don't touch the LDT register - we're already in the next thread.
126 */
127void destroy_context(struct mm_struct *mm)
128{
129 if (mm->context.size) {
130#ifdef CONFIG_X86_32
131 /* CHECKME: Can this ever happen ? */
132 if (mm == current->active_mm)
133 clear_LDT();
134#endif
135 paravirt_free_ldt(mm->context.ldt, mm->context.size);
136 if (mm->context.size * LDT_ENTRY_SIZE > PAGE_SIZE)
137 vfree(mm->context.ldt);
138 else
139 put_page(virt_to_page(mm->context.ldt));
140 mm->context.size = 0;
141 }
142}
143
144static int read_ldt(void __user *ptr, unsigned long bytecount)
145{
146 int err;
147 unsigned long size;
148 struct mm_struct *mm = current->mm;
149
150 if (!mm->context.size)
151 return 0;
152 if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
153 bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
154
155 mutex_lock(&mm->context.lock);
156 size = mm->context.size * LDT_ENTRY_SIZE;
157 if (size > bytecount)
158 size = bytecount;
159
160 err = 0;
161 if (copy_to_user(ptr, mm->context.ldt, size))
162 err = -EFAULT;
163 mutex_unlock(&mm->context.lock);
164 if (err < 0)
165 goto error_return;
166 if (size != bytecount) {
167 /* zero-fill the rest */
168 if (clear_user(ptr + size, bytecount - size) != 0) {
169 err = -EFAULT;
170 goto error_return;
171 }
172 }
173 return bytecount;
174error_return:
175 return err;
176}
177
178static int read_default_ldt(void __user *ptr, unsigned long bytecount)
179{
180 /* CHECKME: Can we use _one_ random number ? */
181#ifdef CONFIG_X86_32
182 unsigned long size = 5 * sizeof(struct desc_struct);
183#else
184 unsigned long size = 128;
185#endif
186 if (bytecount > size)
187 bytecount = size;
188 if (clear_user(ptr, bytecount))
189 return -EFAULT;
190 return bytecount;
191}
192
193static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
194{
195 struct mm_struct *mm = current->mm;
196 struct desc_struct ldt;
197 int error;
198 struct user_desc ldt_info;
199
200 error = -EINVAL;
201 if (bytecount != sizeof(ldt_info))
202 goto out;
203 error = -EFAULT;
204 if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
205 goto out;
206
207 error = -EINVAL;
208 if (ldt_info.entry_number >= LDT_ENTRIES)
209 goto out;
210 if (ldt_info.contents == 3) {
211 if (oldmode)
212 goto out;
213 if (ldt_info.seg_not_present == 0)
214 goto out;
215 }
216
217 mutex_lock(&mm->context.lock);
218 if (ldt_info.entry_number >= mm->context.size) {
219 error = alloc_ldt(¤t->mm->context,
220 ldt_info.entry_number + 1, 1);
221 if (error < 0)
222 goto out_unlock;
223 }
224
225 /* Allow LDTs to be cleared by the user. */
226 if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
227 if (oldmode || LDT_empty(&ldt_info)) {
228 memset(&ldt, 0, sizeof(ldt));
229 goto install;
230 }
231 }
232
233 fill_ldt(&ldt, &ldt_info);
234 if (oldmode)
235 ldt.avl = 0;
236
237 /* Install the new entry ... */
238install:
239 write_ldt_entry(mm->context.ldt, ldt_info.entry_number, &ldt);
240 error = 0;
241
242out_unlock:
243 mutex_unlock(&mm->context.lock);
244out:
245 return error;
246}
247
248asmlinkage int sys_modify_ldt(int func, void __user *ptr,
249 unsigned long bytecount)
250{
251 int ret = -ENOSYS;
252
253 switch (func) {
254 case 0:
255 ret = read_ldt(ptr, bytecount);
256 break;
257 case 1:
258 ret = write_ldt(ptr, bytecount, 1);
259 break;
260 case 2:
261 ret = read_default_ldt(ptr, bytecount);
262 break;
263 case 0x11:
264 ret = write_ldt(ptr, bytecount, 0);
265 break;
266 }
267 return ret;
268}