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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 <[email protected]>
5 * Copyright (C) 2002 Andi Kleen
6 *
7 * This handles calls from both 32bit and 64bit mode.
8 *
9 * Lock order:
10 * context.ldt_usr_sem
11 * mmap_lock
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/pgtable_areas.h>
31
32#include <xen/xen.h>
33
34/* This is a multiple of PAGE_SIZE. */
35#define LDT_SLOT_STRIDE (LDT_ENTRIES * LDT_ENTRY_SIZE)
36
37static inline void *ldt_slot_va(int slot)
38{
39 return (void *)(LDT_BASE_ADDR + LDT_SLOT_STRIDE * slot);
40}
41
42void load_mm_ldt(struct mm_struct *mm)
43{
44 struct ldt_struct *ldt;
45
46 /* READ_ONCE synchronizes with smp_store_release */
47 ldt = READ_ONCE(mm->context.ldt);
48
49 /*
50 * Any change to mm->context.ldt is followed by an IPI to all
51 * CPUs with the mm active. The LDT will not be freed until
52 * after the IPI is handled by all such CPUs. This means that
53 * if the ldt_struct changes before we return, the values we see
54 * will be safe, and the new values will be loaded before we run
55 * any user code.
56 *
57 * NB: don't try to convert this to use RCU without extreme care.
58 * We would still need IRQs off, because we don't want to change
59 * the local LDT after an IPI loaded a newer value than the one
60 * that we can see.
61 */
62
63 if (unlikely(ldt)) {
64 if (cpu_feature_enabled(X86_FEATURE_PTI)) {
65 if (WARN_ON_ONCE((unsigned long)ldt->slot > 1)) {
66 /*
67 * Whoops -- either the new LDT isn't mapped
68 * (if slot == -1) or is mapped into a bogus
69 * slot (if slot > 1).
70 */
71 clear_LDT();
72 return;
73 }
74
75 /*
76 * If page table isolation is enabled, ldt->entries
77 * will not be mapped in the userspace pagetables.
78 * Tell the CPU to access the LDT through the alias
79 * at ldt_slot_va(ldt->slot).
80 */
81 set_ldt(ldt_slot_va(ldt->slot), ldt->nr_entries);
82 } else {
83 set_ldt(ldt->entries, ldt->nr_entries);
84 }
85 } else {
86 clear_LDT();
87 }
88}
89
90void switch_ldt(struct mm_struct *prev, struct mm_struct *next)
91{
92 /*
93 * Load the LDT if either the old or new mm had an LDT.
94 *
95 * An mm will never go from having an LDT to not having an LDT. Two
96 * mms never share an LDT, so we don't gain anything by checking to
97 * see whether the LDT changed. There's also no guarantee that
98 * prev->context.ldt actually matches LDTR, but, if LDTR is non-NULL,
99 * then prev->context.ldt will also be non-NULL.
100 *
101 * If we really cared, we could optimize the case where prev == next
102 * and we're exiting lazy mode. Most of the time, if this happens,
103 * we don't actually need to reload LDTR, but modify_ldt() is mostly
104 * used by legacy code and emulators where we don't need this level of
105 * performance.
106 *
107 * This uses | instead of || because it generates better code.
108 */
109 if (unlikely((unsigned long)prev->context.ldt |
110 (unsigned long)next->context.ldt))
111 load_mm_ldt(next);
112
113 DEBUG_LOCKS_WARN_ON(preemptible());
114}
115
116static void refresh_ldt_segments(void)
117{
118#ifdef CONFIG_X86_64
119 unsigned short sel;
120
121 /*
122 * Make sure that the cached DS and ES descriptors match the updated
123 * LDT.
124 */
125 savesegment(ds, sel);
126 if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT)
127 loadsegment(ds, sel);
128
129 savesegment(es, sel);
130 if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT)
131 loadsegment(es, sel);
132#endif
133}
134
135/* context.lock is held by the task which issued the smp function call */
136static void flush_ldt(void *__mm)
137{
138 struct mm_struct *mm = __mm;
139
140 if (this_cpu_read(cpu_tlbstate.loaded_mm) != mm)
141 return;
142
143 load_mm_ldt(mm);
144
145 refresh_ldt_segments();
146}
147
148/* The caller must call finalize_ldt_struct on the result. LDT starts zeroed. */
149static struct ldt_struct *alloc_ldt_struct(unsigned int num_entries)
150{
151 struct ldt_struct *new_ldt;
152 unsigned int alloc_size;
153
154 if (num_entries > LDT_ENTRIES)
155 return NULL;
156
157 new_ldt = kmalloc_obj(struct ldt_struct, GFP_KERNEL_ACCOUNT);
158 if (!new_ldt)
159 return NULL;
160
161 BUILD_BUG_ON(LDT_ENTRY_SIZE != sizeof(struct desc_struct));
162 alloc_size = num_entries * LDT_ENTRY_SIZE;
163
164 /*
165 * Xen is very picky: it requires a page-aligned LDT that has no
166 * trailing nonzero bytes in any page that contains LDT descriptors.
167 * Keep it simple: zero the whole allocation and never allocate less
168 * than PAGE_SIZE.
169 */
170 if (alloc_size > PAGE_SIZE)
171 new_ldt->entries = __vmalloc(alloc_size, GFP_KERNEL_ACCOUNT | __GFP_ZERO);
172 else
173 new_ldt->entries = (void *)get_zeroed_page(GFP_KERNEL_ACCOUNT);
174
175 if (!new_ldt->entries) {
176 kfree(new_ldt);
177 return NULL;
178 }
179
180 /* The new LDT isn't aliased for PTI yet. */
181 new_ldt->slot = -1;
182
183 new_ldt->nr_entries = num_entries;
184 return new_ldt;
185}
186
187#ifdef CONFIG_MITIGATION_PAGE_TABLE_ISOLATION
188
189static void do_sanity_check(struct mm_struct *mm,
190 bool had_kernel_mapping,
191 bool had_user_mapping)
192{
193 if (mm->context.ldt) {
194 /*
195 * We already had an LDT. The top-level entry should already
196 * have been allocated and synchronized with the usermode
197 * tables.
198 */
199 WARN_ON(!had_kernel_mapping);
200 if (boot_cpu_has(X86_FEATURE_PTI))
201 WARN_ON(!had_user_mapping);
202 } else {
203 /*
204 * This is the first time we're mapping an LDT for this process.
205 * Sync the pgd to the usermode tables.
206 */
207 WARN_ON(had_kernel_mapping);
208 if (boot_cpu_has(X86_FEATURE_PTI))
209 WARN_ON(had_user_mapping);
210 }
211}
212
213#ifdef CONFIG_X86_PAE
214
215static pmd_t *pgd_to_pmd_walk(pgd_t *pgd, unsigned long va)
216{
217 p4d_t *p4d;
218 pud_t *pud;
219
220 if (pgd->pgd == 0)
221 return NULL;
222
223 p4d = p4d_offset(pgd, va);
224 if (p4d_none(*p4d))
225 return NULL;
226
227 pud = pud_offset(p4d, va);
228 if (pud_none(*pud))
229 return NULL;
230
231 return pmd_offset(pud, va);
232}
233
234static void map_ldt_struct_to_user(struct mm_struct *mm)
235{
236 pgd_t *k_pgd = pgd_offset(mm, LDT_BASE_ADDR);
237 pgd_t *u_pgd = kernel_to_user_pgdp(k_pgd);
238 pmd_t *k_pmd, *u_pmd;
239
240 k_pmd = pgd_to_pmd_walk(k_pgd, LDT_BASE_ADDR);
241 u_pmd = pgd_to_pmd_walk(u_pgd, LDT_BASE_ADDR);
242
243 if (boot_cpu_has(X86_FEATURE_PTI) && !mm->context.ldt)
244 set_pmd(u_pmd, *k_pmd);
245}
246
247static void sanity_check_ldt_mapping(struct mm_struct *mm)
248{
249 pgd_t *k_pgd = pgd_offset(mm, LDT_BASE_ADDR);
250 pgd_t *u_pgd = kernel_to_user_pgdp(k_pgd);
251 bool had_kernel, had_user;
252 pmd_t *k_pmd, *u_pmd;
253
254 k_pmd = pgd_to_pmd_walk(k_pgd, LDT_BASE_ADDR);
255 u_pmd = pgd_to_pmd_walk(u_pgd, LDT_BASE_ADDR);
256 had_kernel = (k_pmd->pmd != 0);
257 had_user = (u_pmd->pmd != 0);
258
259 do_sanity_check(mm, had_kernel, had_user);
260}
261
262#else /* !CONFIG_X86_PAE */
263
264static void map_ldt_struct_to_user(struct mm_struct *mm)
265{
266 pgd_t *pgd = pgd_offset(mm, LDT_BASE_ADDR);
267
268 if (boot_cpu_has(X86_FEATURE_PTI) && !mm->context.ldt)
269 set_pgd(kernel_to_user_pgdp(pgd), *pgd);
270}
271
272static void sanity_check_ldt_mapping(struct mm_struct *mm)
273{
274 pgd_t *pgd = pgd_offset(mm, LDT_BASE_ADDR);
275 bool had_kernel = (pgd->pgd != 0);
276 bool had_user = (kernel_to_user_pgdp(pgd)->pgd != 0);
277
278 do_sanity_check(mm, had_kernel, had_user);
279}
280
281#endif /* CONFIG_X86_PAE */
282
283/*
284 * If PTI is enabled, this maps the LDT into the kernelmode and
285 * usermode tables for the given mm.
286 */
287static int
288map_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt, int slot)
289{
290 unsigned long va;
291 bool is_vmalloc;
292 spinlock_t *ptl;
293 int i, nr_pages;
294
295 if (!boot_cpu_has(X86_FEATURE_PTI))
296 return 0;
297
298 /*
299 * Any given ldt_struct should have map_ldt_struct() called at most
300 * once.
301 */
302 WARN_ON(ldt->slot != -1);
303
304 /* Check if the current mappings are sane */
305 sanity_check_ldt_mapping(mm);
306
307 is_vmalloc = is_vmalloc_addr(ldt->entries);
308
309 nr_pages = DIV_ROUND_UP(ldt->nr_entries * LDT_ENTRY_SIZE, PAGE_SIZE);
310
311 for (i = 0; i < nr_pages; i++) {
312 unsigned long offset = i << PAGE_SHIFT;
313 const void *src = (char *)ldt->entries + offset;
314 unsigned long pfn;
315 pgprot_t pte_prot;
316 pte_t pte, *ptep;
317
318 va = (unsigned long)ldt_slot_va(slot) + offset;
319 pfn = is_vmalloc ? vmalloc_to_pfn(src) :
320 page_to_pfn(virt_to_page(src));
321 /*
322 * Treat the PTI LDT range as a *userspace* range.
323 * get_locked_pte() will allocate all needed pagetables
324 * and account for them in this mm.
325 */
326 ptep = get_locked_pte(mm, va, &ptl);
327 if (!ptep)
328 return -ENOMEM;
329 /*
330 * Map it RO so the easy to find address is not a primary
331 * target via some kernel interface which misses a
332 * permission check.
333 */
334 pte_prot = __pgprot(__PAGE_KERNEL_RO & ~_PAGE_GLOBAL);
335 /* Filter out unsuppored __PAGE_KERNEL* bits: */
336 pgprot_val(pte_prot) &= __supported_pte_mask;
337 pte = pfn_pte(pfn, pte_prot);
338 set_pte_at(mm, va, ptep, pte);
339 pte_unmap_unlock(ptep, ptl);
340 }
341
342 /* Propagate LDT mapping to the user page-table */
343 map_ldt_struct_to_user(mm);
344
345 ldt->slot = slot;
346 return 0;
347}
348
349static void unmap_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt)
350{
351 unsigned long va;
352 int i, nr_pages;
353
354 if (!ldt)
355 return;
356
357 /* LDT map/unmap is only required for PTI */
358 if (!boot_cpu_has(X86_FEATURE_PTI))
359 return;
360
361 nr_pages = DIV_ROUND_UP(ldt->nr_entries * LDT_ENTRY_SIZE, PAGE_SIZE);
362
363 for (i = 0; i < nr_pages; i++) {
364 unsigned long offset = i << PAGE_SHIFT;
365 spinlock_t *ptl;
366 pte_t *ptep;
367
368 va = (unsigned long)ldt_slot_va(ldt->slot) + offset;
369 ptep = get_locked_pte(mm, va, &ptl);
370 if (!WARN_ON_ONCE(!ptep)) {
371 pte_clear(mm, va, ptep);
372 pte_unmap_unlock(ptep, ptl);
373 }
374 }
375
376 va = (unsigned long)ldt_slot_va(ldt->slot);
377 flush_tlb_mm_range(mm, va, va + nr_pages * PAGE_SIZE, PAGE_SHIFT, false);
378}
379
380#else /* !CONFIG_MITIGATION_PAGE_TABLE_ISOLATION */
381
382static int
383map_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt, int slot)
384{
385 return 0;
386}
387
388static void unmap_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt)
389{
390}
391#endif /* CONFIG_MITIGATION_PAGE_TABLE_ISOLATION */
392
393static void free_ldt_pgtables(struct mm_struct *mm)
394{
395#ifdef CONFIG_MITIGATION_PAGE_TABLE_ISOLATION
396 struct mmu_gather tlb;
397 unsigned long start = LDT_BASE_ADDR;
398 unsigned long end = LDT_END_ADDR;
399
400 if (!boot_cpu_has(X86_FEATURE_PTI))
401 return;
402
403 /*
404 * Although free_pgd_range() is intended for freeing user
405 * page-tables, it also works out for kernel mappings on x86.
406 * We use tlb_gather_mmu_fullmm() to avoid confusing the
407 * range-tracking logic in __tlb_adjust_range().
408 */
409 tlb_gather_mmu_fullmm(&tlb, mm);
410 free_pgd_range(&tlb, start, end, start, end);
411 tlb_finish_mmu(&tlb);
412#endif
413}
414
415/* After calling this, the LDT is immutable. */
416static void finalize_ldt_struct(struct ldt_struct *ldt)
417{
418 paravirt_alloc_ldt(ldt->entries, ldt->nr_entries);
419}
420
421static void install_ldt(struct mm_struct *mm, struct ldt_struct *ldt)
422{
423 mutex_lock(&mm->context.lock);
424
425 /* Synchronizes with READ_ONCE in load_mm_ldt. */
426 smp_store_release(&mm->context.ldt, ldt);
427
428 /* Activate the LDT for all CPUs using currents mm. */
429 on_each_cpu_mask(mm_cpumask(mm), flush_ldt, mm, true);
430
431 mutex_unlock(&mm->context.lock);
432}
433
434static void free_ldt_struct(struct ldt_struct *ldt)
435{
436 if (likely(!ldt))
437 return;
438
439 paravirt_free_ldt(ldt->entries, ldt->nr_entries);
440 if (ldt->nr_entries * LDT_ENTRY_SIZE > PAGE_SIZE)
441 vfree_atomic(ldt->entries);
442 else
443 free_page((unsigned long)ldt->entries);
444 kfree(ldt);
445}
446
447/*
448 * Called on fork from arch_dup_mmap(). Just copy the current LDT state,
449 * the new task is not running, so nothing can be installed.
450 */
451int ldt_dup_context(struct mm_struct *old_mm, struct mm_struct *mm)
452{
453 struct ldt_struct *new_ldt;
454 int retval = 0;
455
456 if (!old_mm)
457 return 0;
458
459 mutex_lock(&old_mm->context.lock);
460 if (!old_mm->context.ldt)
461 goto out_unlock;
462
463 new_ldt = alloc_ldt_struct(old_mm->context.ldt->nr_entries);
464 if (!new_ldt) {
465 retval = -ENOMEM;
466 goto out_unlock;
467 }
468
469 memcpy(new_ldt->entries, old_mm->context.ldt->entries,
470 new_ldt->nr_entries * LDT_ENTRY_SIZE);
471 finalize_ldt_struct(new_ldt);
472
473 retval = map_ldt_struct(mm, new_ldt, 0);
474 if (retval) {
475 free_ldt_pgtables(mm);
476 free_ldt_struct(new_ldt);
477 goto out_unlock;
478 }
479 mm->context.ldt = new_ldt;
480
481out_unlock:
482 mutex_unlock(&old_mm->context.lock);
483 return retval;
484}
485
486/*
487 * No need to lock the MM as we are the last user
488 *
489 * 64bit: Don't touch the LDT register - we're already in the next thread.
490 */
491void destroy_context_ldt(struct mm_struct *mm)
492{
493 free_ldt_struct(mm->context.ldt);
494 mm->context.ldt = NULL;
495}
496
497void ldt_arch_exit_mmap(struct mm_struct *mm)
498{
499 free_ldt_pgtables(mm);
500}
501
502static int read_ldt(void __user *ptr, unsigned long bytecount)
503{
504 struct mm_struct *mm = current->mm;
505 unsigned long entries_size;
506 int retval;
507
508 down_read(&mm->context.ldt_usr_sem);
509
510 if (!mm->context.ldt) {
511 retval = 0;
512 goto out_unlock;
513 }
514
515 if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
516 bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
517
518 entries_size = mm->context.ldt->nr_entries * LDT_ENTRY_SIZE;
519 if (entries_size > bytecount)
520 entries_size = bytecount;
521
522 if (copy_to_user(ptr, mm->context.ldt->entries, entries_size)) {
523 retval = -EFAULT;
524 goto out_unlock;
525 }
526
527 if (entries_size != bytecount) {
528 /* Zero-fill the rest and pretend we read bytecount bytes. */
529 if (clear_user(ptr + entries_size, bytecount - entries_size)) {
530 retval = -EFAULT;
531 goto out_unlock;
532 }
533 }
534 retval = bytecount;
535
536out_unlock:
537 up_read(&mm->context.ldt_usr_sem);
538 return retval;
539}
540
541static int read_default_ldt(void __user *ptr, unsigned long bytecount)
542{
543 /* CHECKME: Can we use _one_ random number ? */
544#ifdef CONFIG_X86_32
545 unsigned long size = 5 * sizeof(struct desc_struct);
546#else
547 unsigned long size = 128;
548#endif
549 if (bytecount > size)
550 bytecount = size;
551 if (clear_user(ptr, bytecount))
552 return -EFAULT;
553 return bytecount;
554}
555
556static bool allow_16bit_segments(void)
557{
558 if (!IS_ENABLED(CONFIG_X86_16BIT))
559 return false;
560
561#ifdef CONFIG_XEN_PV
562 /*
563 * Xen PV does not implement ESPFIX64, which means that 16-bit
564 * segments will not work correctly. Until either Xen PV implements
565 * ESPFIX64 and can signal this fact to the guest or unless someone
566 * provides compelling evidence that allowing broken 16-bit segments
567 * is worthwhile, disallow 16-bit segments under Xen PV.
568 */
569 if (xen_pv_domain()) {
570 pr_info_once("Warning: 16-bit segments do not work correctly in a Xen PV guest\n");
571 return false;
572 }
573#endif
574
575 return true;
576}
577
578static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
579{
580 struct mm_struct *mm = current->mm;
581 struct ldt_struct *new_ldt, *old_ldt;
582 unsigned int old_nr_entries, new_nr_entries;
583 struct user_desc ldt_info;
584 struct desc_struct ldt;
585 int error;
586
587 error = -EINVAL;
588 if (bytecount != sizeof(ldt_info))
589 goto out;
590 error = -EFAULT;
591 if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
592 goto out;
593
594 error = -EINVAL;
595 if (ldt_info.entry_number >= LDT_ENTRIES)
596 goto out;
597 if (ldt_info.contents == 3) {
598 if (oldmode)
599 goto out;
600 if (ldt_info.seg_not_present == 0)
601 goto out;
602 }
603
604 if ((oldmode && !ldt_info.base_addr && !ldt_info.limit) ||
605 LDT_empty(&ldt_info)) {
606 /* The user wants to clear the entry. */
607 memset(&ldt, 0, sizeof(ldt));
608 } else {
609 if (!ldt_info.seg_32bit && !allow_16bit_segments()) {
610 error = -EINVAL;
611 goto out;
612 }
613
614 fill_ldt(&ldt, &ldt_info);
615 if (oldmode)
616 ldt.avl = 0;
617 }
618
619 if (down_write_killable(&mm->context.ldt_usr_sem))
620 return -EINTR;
621
622 old_ldt = mm->context.ldt;
623 old_nr_entries = old_ldt ? old_ldt->nr_entries : 0;
624 new_nr_entries = max(ldt_info.entry_number + 1, old_nr_entries);
625
626 error = -ENOMEM;
627 new_ldt = alloc_ldt_struct(new_nr_entries);
628 if (!new_ldt)
629 goto out_unlock;
630
631 if (old_ldt)
632 memcpy(new_ldt->entries, old_ldt->entries, old_nr_entries * LDT_ENTRY_SIZE);
633
634 new_ldt->entries[ldt_info.entry_number] = ldt;
635 finalize_ldt_struct(new_ldt);
636
637 /*
638 * If we are using PTI, map the new LDT into the userspace pagetables.
639 * If there is already an LDT, use the other slot so that other CPUs
640 * will continue to use the old LDT until install_ldt() switches
641 * them over to the new LDT.
642 */
643 error = map_ldt_struct(mm, new_ldt, old_ldt ? !old_ldt->slot : 0);
644 if (error) {
645 /*
646 * This only can fail for the first LDT setup. If an LDT is
647 * already installed then the PTE page is already
648 * populated. Mop up a half populated page table.
649 */
650 if (!WARN_ON_ONCE(old_ldt))
651 free_ldt_pgtables(mm);
652 free_ldt_struct(new_ldt);
653 goto out_unlock;
654 }
655
656 install_ldt(mm, new_ldt);
657 unmap_ldt_struct(mm, old_ldt);
658 free_ldt_struct(old_ldt);
659 error = 0;
660
661out_unlock:
662 up_write(&mm->context.ldt_usr_sem);
663out:
664 return error;
665}
666
667SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr ,
668 unsigned long , bytecount)
669{
670 int ret = -ENOSYS;
671
672 switch (func) {
673 case 0:
674 ret = read_ldt(ptr, bytecount);
675 break;
676 case 1:
677 ret = write_ldt(ptr, bytecount, 1);
678 break;
679 case 2:
680 ret = read_default_ldt(ptr, bytecount);
681 break;
682 case 0x11:
683 ret = write_ldt(ptr, bytecount, 0);
684 break;
685 }
686 /*
687 * The SYSCALL_DEFINE() macros give us an 'unsigned long'
688 * return type, but the ABI for sys_modify_ldt() expects
689 * 'int'. This cast gives us an int-sized value in %rax
690 * for the return code. The 'unsigned' is necessary so
691 * the compiler does not try to sign-extend the negative
692 * return codes into the high half of the register when
693 * taking the value from int->long.
694 */
695 return (unsigned int)ret;
696}