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_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 
ldt_slot_va(int slot)37 static inline void *ldt_slot_va(int slot)
38 {
39 	return (void *)(LDT_BASE_ADDR + LDT_SLOT_STRIDE * slot);
40 }
41 
load_mm_ldt(struct mm_struct * mm)42 void 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 (static_cpu_has(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 
switch_ldt(struct mm_struct * prev,struct mm_struct * next)90 void 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 
refresh_ldt_segments(void)116 static 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 */
flush_ldt(void * __mm)136 static 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. */
alloc_ldt_struct(unsigned int num_entries)149 static 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(sizeof(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_PAGE_TABLE_ISOLATION
188 
do_sanity_check(struct mm_struct * mm,bool had_kernel_mapping,bool had_user_mapping)189 static 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 
pgd_to_pmd_walk(pgd_t * pgd,unsigned long va)215 static 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 
map_ldt_struct_to_user(struct mm_struct * mm)234 static 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 
sanity_check_ldt_mapping(struct mm_struct * mm)247 static 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 
map_ldt_struct_to_user(struct mm_struct * mm)264 static 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 
sanity_check_ldt_mapping(struct mm_struct * mm)272 static 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  */
287 static int
map_ldt_struct(struct mm_struct * mm,struct ldt_struct * ldt,int slot)288 map_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 
unmap_ldt_struct(struct mm_struct * mm,struct ldt_struct * ldt)349 static 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 		pte_clear(mm, va, ptep);
371 		pte_unmap_unlock(ptep, ptl);
372 	}
373 
374 	va = (unsigned long)ldt_slot_va(ldt->slot);
375 	flush_tlb_mm_range(mm, va, va + nr_pages * PAGE_SIZE, PAGE_SHIFT, false);
376 }
377 
378 #else /* !CONFIG_PAGE_TABLE_ISOLATION */
379 
380 static int
map_ldt_struct(struct mm_struct * mm,struct ldt_struct * ldt,int slot)381 map_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt, int slot)
382 {
383 	return 0;
384 }
385 
unmap_ldt_struct(struct mm_struct * mm,struct ldt_struct * ldt)386 static void unmap_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt)
387 {
388 }
389 #endif /* CONFIG_PAGE_TABLE_ISOLATION */
390 
free_ldt_pgtables(struct mm_struct * mm)391 static void free_ldt_pgtables(struct mm_struct *mm)
392 {
393 #ifdef CONFIG_PAGE_TABLE_ISOLATION
394 	struct mmu_gather tlb;
395 	unsigned long start = LDT_BASE_ADDR;
396 	unsigned long end = LDT_END_ADDR;
397 
398 	if (!boot_cpu_has(X86_FEATURE_PTI))
399 		return;
400 
401 	/*
402 	 * Although free_pgd_range() is intended for freeing user
403 	 * page-tables, it also works out for kernel mappings on x86.
404 	 * We use tlb_gather_mmu_fullmm() to avoid confusing the
405 	 * range-tracking logic in __tlb_adjust_range().
406 	 */
407 	tlb_gather_mmu_fullmm(&tlb, mm);
408 	free_pgd_range(&tlb, start, end, start, end);
409 	tlb_finish_mmu(&tlb);
410 #endif
411 }
412 
413 /* After calling this, the LDT is immutable. */
finalize_ldt_struct(struct ldt_struct * ldt)414 static void finalize_ldt_struct(struct ldt_struct *ldt)
415 {
416 	paravirt_alloc_ldt(ldt->entries, ldt->nr_entries);
417 }
418 
install_ldt(struct mm_struct * mm,struct ldt_struct * ldt)419 static void install_ldt(struct mm_struct *mm, struct ldt_struct *ldt)
420 {
421 	mutex_lock(&mm->context.lock);
422 
423 	/* Synchronizes with READ_ONCE in load_mm_ldt. */
424 	smp_store_release(&mm->context.ldt, ldt);
425 
426 	/* Activate the LDT for all CPUs using currents mm. */
427 	on_each_cpu_mask(mm_cpumask(mm), flush_ldt, mm, true);
428 
429 	mutex_unlock(&mm->context.lock);
430 }
431 
free_ldt_struct(struct ldt_struct * ldt)432 static void free_ldt_struct(struct ldt_struct *ldt)
433 {
434 	if (likely(!ldt))
435 		return;
436 
437 	paravirt_free_ldt(ldt->entries, ldt->nr_entries);
438 	if (ldt->nr_entries * LDT_ENTRY_SIZE > PAGE_SIZE)
439 		vfree_atomic(ldt->entries);
440 	else
441 		free_page((unsigned long)ldt->entries);
442 	kfree(ldt);
443 }
444 
445 /*
446  * Called on fork from arch_dup_mmap(). Just copy the current LDT state,
447  * the new task is not running, so nothing can be installed.
448  */
ldt_dup_context(struct mm_struct * old_mm,struct mm_struct * mm)449 int ldt_dup_context(struct mm_struct *old_mm, struct mm_struct *mm)
450 {
451 	struct ldt_struct *new_ldt;
452 	int retval = 0;
453 
454 	if (!old_mm)
455 		return 0;
456 
457 	mutex_lock(&old_mm->context.lock);
458 	if (!old_mm->context.ldt)
459 		goto out_unlock;
460 
461 	new_ldt = alloc_ldt_struct(old_mm->context.ldt->nr_entries);
462 	if (!new_ldt) {
463 		retval = -ENOMEM;
464 		goto out_unlock;
465 	}
466 
467 	memcpy(new_ldt->entries, old_mm->context.ldt->entries,
468 	       new_ldt->nr_entries * LDT_ENTRY_SIZE);
469 	finalize_ldt_struct(new_ldt);
470 
471 	retval = map_ldt_struct(mm, new_ldt, 0);
472 	if (retval) {
473 		free_ldt_pgtables(mm);
474 		free_ldt_struct(new_ldt);
475 		goto out_unlock;
476 	}
477 	mm->context.ldt = new_ldt;
478 
479 out_unlock:
480 	mutex_unlock(&old_mm->context.lock);
481 	return retval;
482 }
483 
484 /*
485  * No need to lock the MM as we are the last user
486  *
487  * 64bit: Don't touch the LDT register - we're already in the next thread.
488  */
destroy_context_ldt(struct mm_struct * mm)489 void destroy_context_ldt(struct mm_struct *mm)
490 {
491 	free_ldt_struct(mm->context.ldt);
492 	mm->context.ldt = NULL;
493 }
494 
ldt_arch_exit_mmap(struct mm_struct * mm)495 void ldt_arch_exit_mmap(struct mm_struct *mm)
496 {
497 	free_ldt_pgtables(mm);
498 }
499 
read_ldt(void __user * ptr,unsigned long bytecount)500 static int read_ldt(void __user *ptr, unsigned long bytecount)
501 {
502 	struct mm_struct *mm = current->mm;
503 	unsigned long entries_size;
504 	int retval;
505 
506 	down_read(&mm->context.ldt_usr_sem);
507 
508 	if (!mm->context.ldt) {
509 		retval = 0;
510 		goto out_unlock;
511 	}
512 
513 	if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
514 		bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
515 
516 	entries_size = mm->context.ldt->nr_entries * LDT_ENTRY_SIZE;
517 	if (entries_size > bytecount)
518 		entries_size = bytecount;
519 
520 	if (copy_to_user(ptr, mm->context.ldt->entries, entries_size)) {
521 		retval = -EFAULT;
522 		goto out_unlock;
523 	}
524 
525 	if (entries_size != bytecount) {
526 		/* Zero-fill the rest and pretend we read bytecount bytes. */
527 		if (clear_user(ptr + entries_size, bytecount - entries_size)) {
528 			retval = -EFAULT;
529 			goto out_unlock;
530 		}
531 	}
532 	retval = bytecount;
533 
534 out_unlock:
535 	up_read(&mm->context.ldt_usr_sem);
536 	return retval;
537 }
538 
read_default_ldt(void __user * ptr,unsigned long bytecount)539 static int read_default_ldt(void __user *ptr, unsigned long bytecount)
540 {
541 	/* CHECKME: Can we use _one_ random number ? */
542 #ifdef CONFIG_X86_32
543 	unsigned long size = 5 * sizeof(struct desc_struct);
544 #else
545 	unsigned long size = 128;
546 #endif
547 	if (bytecount > size)
548 		bytecount = size;
549 	if (clear_user(ptr, bytecount))
550 		return -EFAULT;
551 	return bytecount;
552 }
553 
allow_16bit_segments(void)554 static bool allow_16bit_segments(void)
555 {
556 	if (!IS_ENABLED(CONFIG_X86_16BIT))
557 		return false;
558 
559 #ifdef CONFIG_XEN_PV
560 	/*
561 	 * Xen PV does not implement ESPFIX64, which means that 16-bit
562 	 * segments will not work correctly.  Until either Xen PV implements
563 	 * ESPFIX64 and can signal this fact to the guest or unless someone
564 	 * provides compelling evidence that allowing broken 16-bit segments
565 	 * is worthwhile, disallow 16-bit segments under Xen PV.
566 	 */
567 	if (xen_pv_domain()) {
568 		pr_info_once("Warning: 16-bit segments do not work correctly in a Xen PV guest\n");
569 		return false;
570 	}
571 #endif
572 
573 	return true;
574 }
575 
write_ldt(void __user * ptr,unsigned long bytecount,int oldmode)576 static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
577 {
578 	struct mm_struct *mm = current->mm;
579 	struct ldt_struct *new_ldt, *old_ldt;
580 	unsigned int old_nr_entries, new_nr_entries;
581 	struct user_desc ldt_info;
582 	struct desc_struct ldt;
583 	int error;
584 
585 	error = -EINVAL;
586 	if (bytecount != sizeof(ldt_info))
587 		goto out;
588 	error = -EFAULT;
589 	if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
590 		goto out;
591 
592 	error = -EINVAL;
593 	if (ldt_info.entry_number >= LDT_ENTRIES)
594 		goto out;
595 	if (ldt_info.contents == 3) {
596 		if (oldmode)
597 			goto out;
598 		if (ldt_info.seg_not_present == 0)
599 			goto out;
600 	}
601 
602 	if ((oldmode && !ldt_info.base_addr && !ldt_info.limit) ||
603 	    LDT_empty(&ldt_info)) {
604 		/* The user wants to clear the entry. */
605 		memset(&ldt, 0, sizeof(ldt));
606 	} else {
607 		if (!ldt_info.seg_32bit && !allow_16bit_segments()) {
608 			error = -EINVAL;
609 			goto out;
610 		}
611 
612 		fill_ldt(&ldt, &ldt_info);
613 		if (oldmode)
614 			ldt.avl = 0;
615 	}
616 
617 	if (down_write_killable(&mm->context.ldt_usr_sem))
618 		return -EINTR;
619 
620 	old_ldt       = mm->context.ldt;
621 	old_nr_entries = old_ldt ? old_ldt->nr_entries : 0;
622 	new_nr_entries = max(ldt_info.entry_number + 1, old_nr_entries);
623 
624 	error = -ENOMEM;
625 	new_ldt = alloc_ldt_struct(new_nr_entries);
626 	if (!new_ldt)
627 		goto out_unlock;
628 
629 	if (old_ldt)
630 		memcpy(new_ldt->entries, old_ldt->entries, old_nr_entries * LDT_ENTRY_SIZE);
631 
632 	new_ldt->entries[ldt_info.entry_number] = ldt;
633 	finalize_ldt_struct(new_ldt);
634 
635 	/*
636 	 * If we are using PTI, map the new LDT into the userspace pagetables.
637 	 * If there is already an LDT, use the other slot so that other CPUs
638 	 * will continue to use the old LDT until install_ldt() switches
639 	 * them over to the new LDT.
640 	 */
641 	error = map_ldt_struct(mm, new_ldt, old_ldt ? !old_ldt->slot : 0);
642 	if (error) {
643 		/*
644 		 * This only can fail for the first LDT setup. If an LDT is
645 		 * already installed then the PTE page is already
646 		 * populated. Mop up a half populated page table.
647 		 */
648 		if (!WARN_ON_ONCE(old_ldt))
649 			free_ldt_pgtables(mm);
650 		free_ldt_struct(new_ldt);
651 		goto out_unlock;
652 	}
653 
654 	install_ldt(mm, new_ldt);
655 	unmap_ldt_struct(mm, old_ldt);
656 	free_ldt_struct(old_ldt);
657 	error = 0;
658 
659 out_unlock:
660 	up_write(&mm->context.ldt_usr_sem);
661 out:
662 	return error;
663 }
664 
SYSCALL_DEFINE3(modify_ldt,int,func,void __user *,ptr,unsigned long,bytecount)665 SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr ,
666 		unsigned long , bytecount)
667 {
668 	int ret = -ENOSYS;
669 
670 	switch (func) {
671 	case 0:
672 		ret = read_ldt(ptr, bytecount);
673 		break;
674 	case 1:
675 		ret = write_ldt(ptr, bytecount, 1);
676 		break;
677 	case 2:
678 		ret = read_default_ldt(ptr, bytecount);
679 		break;
680 	case 0x11:
681 		ret = write_ldt(ptr, bytecount, 0);
682 		break;
683 	}
684 	/*
685 	 * The SYSCALL_DEFINE() macros give us an 'unsigned long'
686 	 * return type, but tht ABI for sys_modify_ldt() expects
687 	 * 'int'.  This cast gives us an int-sized value in %rax
688 	 * for the return code.  The 'unsigned' is necessary so
689 	 * the compiler does not try to sign-extend the negative
690 	 * return codes into the high half of the register when
691 	 * taking the value from int->long.
692 	 */
693 	return (unsigned int)ret;
694 }
695