[thirdparty/linux.git] / arch / x86 / kernel / ldt.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
 * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
 * Copyright (C) 2002 Andi Kleen
 *
 * This handles calls from both 32bit and 64bit mode.
 *
 * Lock order:
 *	contex.ldt_usr_sem
 *	  mmap_sem
 *	    context.lock
 */

#include <linux/errno.h>
#include <linux/gfp.h>
#include <linux/sched.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/syscalls.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/uaccess.h>

#include <asm/ldt.h>
#include <asm/tlb.h>
#include <asm/desc.h>
#include <asm/mmu_context.h>
#include <asm/syscalls.h>

static void refresh_ldt_segments(void)
{
#ifdef CONFIG_X86_64
	unsigned short sel;

	/*
	 * Make sure that the cached DS and ES descriptors match the updated
	 * LDT.
	 */
	savesegment(ds, sel);
	if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT)
		loadsegment(ds, sel);

	savesegment(es, sel);
	if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT)
		loadsegment(es, sel);
#endif
}

/* context.lock is held by the task which issued the smp function call */
static void flush_ldt(void *__mm)
{
	struct mm_struct *mm = __mm;

	if (this_cpu_read(cpu_tlbstate.loaded_mm) != mm)
		return;

	load_mm_ldt(mm);

	refresh_ldt_segments();
}

/* The caller must call finalize_ldt_struct on the result. LDT starts zeroed. */
static struct ldt_struct *alloc_ldt_struct(unsigned int num_entries)
{
	struct ldt_struct *new_ldt;
	unsigned int alloc_size;

	if (num_entries > LDT_ENTRIES)
		return NULL;

	new_ldt = kmalloc(sizeof(struct ldt_struct), GFP_KERNEL);
	if (!new_ldt)
		return NULL;

	BUILD_BUG_ON(LDT_ENTRY_SIZE != sizeof(struct desc_struct));
	alloc_size = num_entries * LDT_ENTRY_SIZE;

	/*
	 * Xen is very picky: it requires a page-aligned LDT that has no
	 * trailing nonzero bytes in any page that contains LDT descriptors.
	 * Keep it simple: zero the whole allocation and never allocate less
	 * than PAGE_SIZE.
	 */
	if (alloc_size > PAGE_SIZE)
		new_ldt->entries = vzalloc(alloc_size);
	else
		new_ldt->entries = (void *)get_zeroed_page(GFP_KERNEL);

	if (!new_ldt->entries) {
		kfree(new_ldt);
		return NULL;
	}

	/* The new LDT isn't aliased for PTI yet. */
	new_ldt->slot = -1;

	new_ldt->nr_entries = num_entries;
	return new_ldt;
}

/*
 * If PTI is enabled, this maps the LDT into the kernelmode and
 * usermode tables for the given mm.
 *
 * There is no corresponding unmap function.  Even if the LDT is freed, we
 * leave the PTEs around until the slot is reused or the mm is destroyed.
 * This is harmless: the LDT is always in ordinary memory, and no one will
 * access the freed slot.
 *
 * If we wanted to unmap freed LDTs, we'd also need to do a flush to make
 * it useful, and the flush would slow down modify_ldt().
 */
static int
map_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt, int slot)
{
#ifdef CONFIG_PAGE_TABLE_ISOLATION
	bool is_vmalloc, had_top_level_entry;
	unsigned long va;
	spinlock_t *ptl;
	pgd_t *pgd;
	int i;

	if (!static_cpu_has(X86_FEATURE_PTI))
		return 0;

	/*
	 * Any given ldt_struct should have map_ldt_struct() called at most
	 * once.
	 */
	WARN_ON(ldt->slot != -1);

	/*
	 * Did we already have the top level entry allocated?  We can't
	 * use pgd_none() for this because it doens't do anything on
	 * 4-level page table kernels.
	 */
	pgd = pgd_offset(mm, LDT_BASE_ADDR);
	had_top_level_entry = (pgd->pgd != 0);

	is_vmalloc = is_vmalloc_addr(ldt->entries);

	for (i = 0; i * PAGE_SIZE < ldt->nr_entries * LDT_ENTRY_SIZE; i++) {
		unsigned long offset = i << PAGE_SHIFT;
		const void *src = (char *)ldt->entries + offset;
		unsigned long pfn;
		pte_t pte, *ptep;

		va = (unsigned long)ldt_slot_va(slot) + offset;
		pfn = is_vmalloc ? vmalloc_to_pfn(src) :
			page_to_pfn(virt_to_page(src));
		/*
		 * Treat the PTI LDT range as a *userspace* range.
		 * get_locked_pte() will allocate all needed pagetables
		 * and account for them in this mm.
		 */
		ptep = get_locked_pte(mm, va, &ptl);
		if (!ptep)
			return -ENOMEM;
		pte = pfn_pte(pfn, __pgprot(__PAGE_KERNEL & ~_PAGE_GLOBAL));
		set_pte_at(mm, va, ptep, pte);
		pte_unmap_unlock(ptep, ptl);
	}

	if (mm->context.ldt) {
		/*
		 * We already had an LDT.  The top-level entry should already
		 * have been allocated and synchronized with the usermode
		 * tables.
		 */
		WARN_ON(!had_top_level_entry);
		if (static_cpu_has(X86_FEATURE_PTI))
			WARN_ON(!kernel_to_user_pgdp(pgd)->pgd);
	} else {
		/*
		 * This is the first time we're mapping an LDT for this process.
		 * Sync the pgd to the usermode tables.
		 */
		WARN_ON(had_top_level_entry);
		if (static_cpu_has(X86_FEATURE_PTI)) {
			WARN_ON(kernel_to_user_pgdp(pgd)->pgd);
			set_pgd(kernel_to_user_pgdp(pgd), *pgd);
		}
	}

	va = (unsigned long)ldt_slot_va(slot);
	flush_tlb_mm_range(mm, va, va + LDT_SLOT_STRIDE, 0);

	ldt->slot = slot;
#endif
	return 0;
}

static void free_ldt_pgtables(struct mm_struct *mm)
{
#ifdef CONFIG_PAGE_TABLE_ISOLATION
	struct mmu_gather tlb;
	unsigned long start = LDT_BASE_ADDR;
	unsigned long end = start + (1UL << PGDIR_SHIFT);

	if (!static_cpu_has(X86_FEATURE_PTI))
		return;

	tlb_gather_mmu(&tlb, mm, start, end);
	free_pgd_range(&tlb, start, end, start, end);
	tlb_finish_mmu(&tlb, start, end);
#endif
}

/* After calling this, the LDT is immutable. */
static void finalize_ldt_struct(struct ldt_struct *ldt)
{
	paravirt_alloc_ldt(ldt->entries, ldt->nr_entries);
}

static void install_ldt(struct mm_struct *mm, struct ldt_struct *ldt)
{
	mutex_lock(&mm->context.lock);

	/* Synchronizes with READ_ONCE in load_mm_ldt. */
	smp_store_release(&mm->context.ldt, ldt);

	/* Activate the LDT for all CPUs using currents mm. */
	on_each_cpu_mask(mm_cpumask(mm), flush_ldt, mm, true);

	mutex_unlock(&mm->context.lock);
}

static void free_ldt_struct(struct ldt_struct *ldt)
{
	if (likely(!ldt))
		return;

	paravirt_free_ldt(ldt->entries, ldt->nr_entries);
	if (ldt->nr_entries * LDT_ENTRY_SIZE > PAGE_SIZE)
		vfree_atomic(ldt->entries);
	else
		free_page((unsigned long)ldt->entries);
	kfree(ldt);
}

/*
 * Called on fork from arch_dup_mmap(). Just copy the current LDT state,
 * the new task is not running, so nothing can be installed.
 */
int ldt_dup_context(struct mm_struct *old_mm, struct mm_struct *mm)
{
	struct ldt_struct *new_ldt;
	int retval = 0;

	if (!old_mm)
		return 0;

	mutex_lock(&old_mm->context.lock);
	if (!old_mm->context.ldt)
		goto out_unlock;

	new_ldt = alloc_ldt_struct(old_mm->context.ldt->nr_entries);
	if (!new_ldt) {
		retval = -ENOMEM;
		goto out_unlock;
	}

	memcpy(new_ldt->entries, old_mm->context.ldt->entries,
	       new_ldt->nr_entries * LDT_ENTRY_SIZE);
	finalize_ldt_struct(new_ldt);

	retval = map_ldt_struct(mm, new_ldt, 0);
	if (retval) {
		free_ldt_pgtables(mm);
		free_ldt_struct(new_ldt);
		goto out_unlock;
	}
	mm->context.ldt = new_ldt;

out_unlock:
	mutex_unlock(&old_mm->context.lock);
	return retval;
}

/*
 * No need to lock the MM as we are the last user
 *
 * 64bit: Don't touch the LDT register - we're already in the next thread.
 */
void destroy_context_ldt(struct mm_struct *mm)
{
	free_ldt_struct(mm->context.ldt);
	mm->context.ldt = NULL;
}

void ldt_arch_exit_mmap(struct mm_struct *mm)
{
	free_ldt_pgtables(mm);
}

static int read_ldt(void __user *ptr, unsigned long bytecount)
{
	struct mm_struct *mm = current->mm;
	unsigned long entries_size;
	int retval;

	down_read(&mm->context.ldt_usr_sem);

	if (!mm->context.ldt) {
		retval = 0;
		goto out_unlock;
	}

	if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
		bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;

	entries_size = mm->context.ldt->nr_entries * LDT_ENTRY_SIZE;
	if (entries_size > bytecount)
		entries_size = bytecount;

	if (copy_to_user(ptr, mm->context.ldt->entries, entries_size)) {
		retval = -EFAULT;
		goto out_unlock;
	}

	if (entries_size != bytecount) {
		/* Zero-fill the rest and pretend we read bytecount bytes. */
		if (clear_user(ptr + entries_size, bytecount - entries_size)) {
			retval = -EFAULT;
			goto out_unlock;
		}
	}
	retval = bytecount;

out_unlock:
	up_read(&mm->context.ldt_usr_sem);
	return retval;
}

static int read_default_ldt(void __user *ptr, unsigned long bytecount)
{
	/* CHECKME: Can we use _one_ random number ? */
#ifdef CONFIG_X86_32
	unsigned long size = 5 * sizeof(struct desc_struct);
#else
	unsigned long size = 128;
#endif
	if (bytecount > size)
		bytecount = size;
	if (clear_user(ptr, bytecount))
		return -EFAULT;
	return bytecount;
}

static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
{
	struct mm_struct *mm = current->mm;
	struct ldt_struct *new_ldt, *old_ldt;
	unsigned int old_nr_entries, new_nr_entries;
	struct user_desc ldt_info;
	struct desc_struct ldt;
	int error;

	error = -EINVAL;
	if (bytecount != sizeof(ldt_info))
		goto out;
	error = -EFAULT;
	if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
		goto out;

	error = -EINVAL;
	if (ldt_info.entry_number >= LDT_ENTRIES)
		goto out;
	if (ldt_info.contents == 3) {
		if (oldmode)
			goto out;
		if (ldt_info.seg_not_present == 0)
			goto out;
	}

	if ((oldmode && !ldt_info.base_addr && !ldt_info.limit) ||
	    LDT_empty(&ldt_info)) {
		/* The user wants to clear the entry. */
		memset(&ldt, 0, sizeof(ldt));
	} else {
		if (!IS_ENABLED(CONFIG_X86_16BIT) && !ldt_info.seg_32bit) {
			error = -EINVAL;
			goto out;
		}

		fill_ldt(&ldt, &ldt_info);
		if (oldmode)
			ldt.avl = 0;
	}

	if (down_write_killable(&mm->context.ldt_usr_sem))
		return -EINTR;

	old_ldt       = mm->context.ldt;
	old_nr_entries = old_ldt ? old_ldt->nr_entries : 0;
	new_nr_entries = max(ldt_info.entry_number + 1, old_nr_entries);

	error = -ENOMEM;
	new_ldt = alloc_ldt_struct(new_nr_entries);
	if (!new_ldt)
		goto out_unlock;

	if (old_ldt)
		memcpy(new_ldt->entries, old_ldt->entries, old_nr_entries * LDT_ENTRY_SIZE);

	new_ldt->entries[ldt_info.entry_number] = ldt;
	finalize_ldt_struct(new_ldt);

	/*
	 * If we are using PTI, map the new LDT into the userspace pagetables.
	 * If there is already an LDT, use the other slot so that other CPUs
	 * will continue to use the old LDT until install_ldt() switches
	 * them over to the new LDT.
	 */
	error = map_ldt_struct(mm, new_ldt, old_ldt ? !old_ldt->slot : 0);
	if (error) {
		free_ldt_struct(old_ldt);
		goto out_unlock;
	}

	install_ldt(mm, new_ldt);
	free_ldt_struct(old_ldt);
	error = 0;

out_unlock:
	up_write(&mm->context.ldt_usr_sem);
out:
	return error;
}

SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr ,
		unsigned long , bytecount)
{
	int ret = -ENOSYS;

	switch (func) {
	case 0:
		ret = read_ldt(ptr, bytecount);
		break;
	case 1:
		ret = write_ldt(ptr, bytecount, 1);
		break;
	case 2:
		ret = read_default_ldt(ptr, bytecount);
		break;
	case 0x11:
		ret = write_ldt(ptr, bytecount, 0);
		break;
	}
	/*
	 * The SYSCALL_DEFINE() macros give us an 'unsigned long'
	 * return type, but tht ABI for sys_modify_ldt() expects
	 * 'int'.  This cast gives us an int-sized value in %rax
	 * for the return code.  The 'unsigned' is necessary so
	 * the compiler does not try to sign-extend the negative
	 * return codes into the high half of the register when
	 * taking the value from int->long.
	 */
	return (unsigned int)ret;
}
Commit	Line	Data
b2441318	1	// SPDX-License-Identifier: GPL-2.0
1da177e4	2	/*
1da177e4 LT	3	* Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
	4	* Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
	5	* Copyright (C) 2002 Andi Kleen
78aa1f66	6	*
1da177e4	7	* This handles calls from both 32bit and 64bit mode.
c2b3496b PZ	8	*
	9	* Lock order:
	10	* contex.ldt_usr_sem
	11	* mmap_sem
	12	* context.lock
1da177e4 LT	13	*/
	14
	15	#include <linux/errno.h>
5a0e3ad6	16	#include <linux/gfp.h>
1da177e4 LT	17	#include <linux/sched.h>
	18	#include <linux/string.h>
	19	#include <linux/mm.h>
	20	#include <linux/smp.h>
da20ab35	21	#include <linux/syscalls.h>
37868fe1	22	#include <linux/slab.h>
1da177e4	23	#include <linux/vmalloc.h>
423a5405	24	#include <linux/uaccess.h>
1da177e4	25
1da177e4	26	#include <asm/ldt.h>
f55f0501	27	#include <asm/tlb.h>
1da177e4	28	#include <asm/desc.h>
70f5088d	29	#include <asm/mmu_context.h>
bbc1f698	30	#include <asm/syscalls.h>
1da177e4	31
a6323757 AL	32	static 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
c2b3496b	51	/* context.lock is held by the task which issued the smp function call */
3d28ebce	52	static void flush_ldt(void *__mm)
1da177e4	53	{
3d28ebce	54	struct mm_struct *mm = __mm;
37868fe1	55
3d28ebce	56	if (this_cpu_read(cpu_tlbstate.loaded_mm) != mm)
37868fe1 AL	57	return;
37868fe1 AL	58
f55f0501	59	load_mm_ldt(mm);
a6323757 AL	60
a6323757 AL	61	refresh_ldt_segments();
1da177e4	62	}
1da177e4	63
37868fe1	64	/* The caller must call finalize_ldt_struct on the result. LDT starts zeroed. */
bbf79d21	65	static struct ldt_struct *alloc_ldt_struct(unsigned int num_entries)
1da177e4	66	{
37868fe1	67	struct ldt_struct *new_ldt;
990e9dc3	68	unsigned int alloc_size;
37868fe1	69
bbf79d21	70	if (num_entries > LDT_ENTRIES)
37868fe1 AL	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));
bbf79d21	78	alloc_size = num_entries * LDT_ENTRY_SIZE;
37868fe1 AL	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);
1da177e4	88	else
f454b478	89	new_ldt->entries = (void *)get_zeroed_page(GFP_KERNEL);
1da177e4	90
37868fe1 AL	91	if (!new_ldt->entries) {
	92	kfree(new_ldt);
	93	return NULL;
	94	}
77e463d1	95
f55f0501 AL	96	/* The new LDT isn't aliased for PTI yet. */
	97	new_ldt->slot = -1;
	98
bbf79d21	99	new_ldt->nr_entries = num_entries;
37868fe1 AL	100	return new_ldt;
37868fe1 AL	101	}
38ffbe66	102
f55f0501 AL	103	/*
	104	* If PTI is enabled, this maps the LDT into the kernelmode and
	105	* usermode tables for the given mm.
	106	*
	107	* There is no corresponding unmap function. Even if the LDT is freed, we
	108	* leave the PTEs around until the slot is reused or the mm is destroyed.
	109	* This is harmless: the LDT is always in ordinary memory, and no one will
	110	* access the freed slot.
	111	*
	112	* If we wanted to unmap freed LDTs, we'd also need to do a flush to make
	113	* it useful, and the flush would slow down modify_ldt().
	114	*/
	115	static int
	116	map_ldt_struct(struct mm_struct mm, struct ldt_struct ldt, int slot)
	117	{
	118	#ifdef CONFIG_PAGE_TABLE_ISOLATION
	119	bool is_vmalloc, had_top_level_entry;
	120	unsigned long va;
	121	spinlock_t *ptl;
	122	pgd_t *pgd;
	123	int i;
	124
	125	if (!static_cpu_has(X86_FEATURE_PTI))
	126	return 0;
	127
	128	/*
	129	* Any given ldt_struct should have map_ldt_struct() called at most
	130	* once.
	131	*/
	132	WARN_ON(ldt->slot != -1);
	133
	134	/*
	135	* Did we already have the top level entry allocated? We can't
	136	* use pgd_none() for this because it doens't do anything on
	137	* 4-level page table kernels.
	138	*/
	139	pgd = pgd_offset(mm, LDT_BASE_ADDR);
	140	had_top_level_entry = (pgd->pgd != 0);
	141
	142	is_vmalloc = is_vmalloc_addr(ldt->entries);
	143
	144	for (i = 0; i * PAGE_SIZE < ldt->nr_entries * LDT_ENTRY_SIZE; i++) {
	145	unsigned long offset = i << PAGE_SHIFT;
	146	const void src = (char )ldt->entries + offset;
	147	unsigned long pfn;
	148	pte_t pte, *ptep;
	149
	150	va = (unsigned long)ldt_slot_va(slot) + offset;
	151	pfn = is_vmalloc ? vmalloc_to_pfn(src) :
	152	page_to_pfn(virt_to_page(src));
	153	/*
	154	* Treat the PTI LDT range as a userspace range.
	155	* get_locked_pte() will allocate all needed pagetables
	156	* and account for them in this mm.
	157	*/
	158	ptep = get_locked_pte(mm, va, &ptl);
	159	if (!ptep)
	160	return -ENOMEM;
	161	pte = pfn_pte(pfn, __pgprot(__PAGE_KERNEL & ~_PAGE_GLOBAL));
	162	set_pte_at(mm, va, ptep, pte);
	163	pte_unmap_unlock(ptep, ptl);
	164	}
	165
	166	if (mm->context.ldt) {
167	/*
168	* We already had an LDT. The top-level entry should already
169	* have been allocated and synchronized with the usermode
170	* tables.
171	*/
172	WARN_ON(!had_top_level_entry);
173	if (static_cpu_has(X86_FEATURE_PTI))
174	WARN_ON(!kernel_to_user_pgdp(pgd)->pgd);
175	} else {
176	/*
177	* This is the first time we're mapping an LDT for this process.
178	* Sync the pgd to the usermode tables.
179	*/
180	WARN_ON(had_top_level_entry);
181	if (static_cpu_has(X86_FEATURE_PTI)) {
182	WARN_ON(kernel_to_user_pgdp(pgd)->pgd);
183	set_pgd(kernel_to_user_pgdp(pgd), *pgd);
184	}
185	}
186
187	va = (unsigned long)ldt_slot_va(slot);
188	flush_tlb_mm_range(mm, va, va + LDT_SLOT_STRIDE, 0);
189
190	ldt->slot = slot;
191	#endif
192	return 0;
193	}
194
195	static void free_ldt_pgtables(struct mm_struct *mm)
196	{
197	#ifdef CONFIG_PAGE_TABLE_ISOLATION
198	struct mmu_gather tlb;
199	unsigned long start = LDT_BASE_ADDR;
200	unsigned long end = start + (1UL << PGDIR_SHIFT);
201
202	if (!static_cpu_has(X86_FEATURE_PTI))
203	return;
204
205	tlb_gather_mmu(&tlb, mm, start, end);
206	free_pgd_range(&tlb, start, end, start, end);
207	tlb_finish_mmu(&tlb, start, end);
208	#endif
209	}
210
37868fe1 AL	211	/* After calling this, the LDT is immutable. */
	212	static void finalize_ldt_struct(struct ldt_struct *ldt)
	213	{
bbf79d21	214	paravirt_alloc_ldt(ldt->entries, ldt->nr_entries);
1da177e4 LT	215	}
1da177e4 LT	216
c2b3496b	217	static void install_ldt(struct mm_struct mm, struct ldt_struct ldt)
1da177e4	218	{
c2b3496b PZ	219	mutex_lock(&mm->context.lock);
c2b3496b PZ	220
3382290e	221	/* Synchronizes with READ_ONCE in load_mm_ldt. */
c2b3496b	222	smp_store_release(&mm->context.ldt, ldt);
37868fe1	223
c2b3496b PZ	224	/* Activate the LDT for all CPUs using currents mm. */
	225	on_each_cpu_mask(mm_cpumask(mm), flush_ldt, mm, true);
	226
	227	mutex_unlock(&mm->context.lock);
37868fe1	228	}
78aa1f66	229
37868fe1 AL	230	static void free_ldt_struct(struct ldt_struct *ldt)
	231	{
	232	if (likely(!ldt))
	233	return;
38ffbe66	234
bbf79d21 BP	235	paravirt_free_ldt(ldt->entries, ldt->nr_entries);
bbf79d21 BP	236	if (ldt->nr_entries * LDT_ENTRY_SIZE > PAGE_SIZE)
8d5341a6	237	vfree_atomic(ldt->entries);
37868fe1	238	else
f454b478	239	free_page((unsigned long)ldt->entries);
37868fe1	240	kfree(ldt);
1da177e4 LT	241	}
	242
	243	/*
a4828f81 TG	244	* Called on fork from arch_dup_mmap(). Just copy the current LDT state,
a4828f81 TG	245	* the new task is not running, so nothing can be installed.
1da177e4	246	*/
a4828f81	247	int ldt_dup_context(struct mm_struct old_mm, struct mm_struct mm)
1da177e4	248	{
37868fe1	249	struct ldt_struct *new_ldt;
1da177e4 LT	250	int retval = 0;
1da177e4 LT	251
a4828f81	252	if (!old_mm)
37868fe1	253	return 0;
37868fe1 AL	254
37868fe1 AL	255	mutex_lock(&old_mm->context.lock);
a4828f81	256	if (!old_mm->context.ldt)
37868fe1	257	goto out_unlock;
37868fe1	258
bbf79d21	259	new_ldt = alloc_ldt_struct(old_mm->context.ldt->nr_entries);
37868fe1 AL	260	if (!new_ldt) {
	261	retval = -ENOMEM;
	262	goto out_unlock;
	263	}
	264
	265	memcpy(new_ldt->entries, old_mm->context.ldt->entries,
bbf79d21	266	new_ldt->nr_entries * LDT_ENTRY_SIZE);
37868fe1 AL	267	finalize_ldt_struct(new_ldt);
37868fe1 AL	268
f55f0501 AL	269	retval = map_ldt_struct(mm, new_ldt, 0);
	270	if (retval) {
	271	free_ldt_pgtables(mm);
	272	free_ldt_struct(new_ldt);
	273	goto out_unlock;
	274	}
37868fe1 AL	275	mm->context.ldt = new_ldt;
	276
	277	out_unlock:
	278	mutex_unlock(&old_mm->context.lock);
1da177e4 LT	279	return retval;
	280	}
	281
	282	/*
77e463d1 TG	283	* No need to lock the MM as we are the last user
	284	*
	285	* 64bit: Don't touch the LDT register - we're already in the next thread.
1da177e4	286	*/
39a0526f	287	void destroy_context_ldt(struct mm_struct *mm)
1da177e4	288	{
37868fe1 AL	289	free_ldt_struct(mm->context.ldt);
37868fe1 AL	290	mm->context.ldt = NULL;
1da177e4 LT	291	}
1da177e4 LT	292
f55f0501 AL	293	void ldt_arch_exit_mmap(struct mm_struct *mm)
	294	{
	295	free_ldt_pgtables(mm);
	296	}
	297
78aa1f66	298	static int read_ldt(void __user *ptr, unsigned long bytecount)
1da177e4	299	{
78aa1f66	300	struct mm_struct *mm = current->mm;
bbf79d21 BP	301	unsigned long entries_size;
bbf79d21 BP	302	int retval;
1da177e4	303
c2b3496b	304	down_read(&mm->context.ldt_usr_sem);
37868fe1 AL	305
	306	if (!mm->context.ldt) {
	307	retval = 0;
	308	goto out_unlock;
	309	}
	310
78aa1f66 TG	311	if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
78aa1f66 TG	312	bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
1da177e4	313
bbf79d21 BP	314	entries_size = mm->context.ldt->nr_entries * LDT_ENTRY_SIZE;
	315	if (entries_size > bytecount)
	316	entries_size = bytecount;
1da177e4	317
bbf79d21	318	if (copy_to_user(ptr, mm->context.ldt->entries, entries_size)) {
37868fe1 AL	319	retval = -EFAULT;
	320	goto out_unlock;
	321	}
	322
bbf79d21	323	if (entries_size != bytecount) {
37868fe1	324	/* Zero-fill the rest and pretend we read bytecount bytes. */
bbf79d21	325	if (clear_user(ptr + entries_size, bytecount - entries_size)) {
37868fe1 AL	326	retval = -EFAULT;
37868fe1 AL	327	goto out_unlock;
1da177e4 LT	328	}
1da177e4 LT	329	}
37868fe1 AL	330	retval = bytecount;
	331
	332	out_unlock:
c2b3496b	333	up_read(&mm->context.ldt_usr_sem);
37868fe1	334	return retval;
1da177e4 LT	335	}
1da177e4 LT	336
78aa1f66	337	static int read_default_ldt(void __user *ptr, unsigned long bytecount)
1da177e4	338	{
77e463d1 TG	339	/* CHECKME: Can we use _one_ random number ? */
	340	#ifdef CONFIG_X86_32
	341	unsigned long size = 5 * sizeof(struct desc_struct);
	342	#else
	343	unsigned long size = 128;
	344	#endif
	345	if (bytecount > size)
	346	bytecount = size;
1da177e4 LT	347	if (clear_user(ptr, bytecount))
1da177e4 LT	348	return -EFAULT;
78aa1f66	349	return bytecount;
1da177e4 LT	350	}
1da177e4 LT	351
78aa1f66	352	static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
1da177e4	353	{
70f5088d	354	struct mm_struct *mm = current->mm;
990e9dc3	355	struct ldt_struct new_ldt, old_ldt;
bbf79d21	356	unsigned int old_nr_entries, new_nr_entries;
990e9dc3	357	struct user_desc ldt_info;
5af72502	358	struct desc_struct ldt;
1da177e4	359	int error;
1da177e4 LT	360
1da177e4 LT	361	error = -EINVAL;
1da177e4 LT	362	if (bytecount != sizeof(ldt_info))
1da177e4 LT	363	goto out;
78aa1f66	364	error = -EFAULT;
70f5088d	365	if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
1da177e4 LT	366	goto out;
	367
	368	error = -EINVAL;
	369	if (ldt_info.entry_number >= LDT_ENTRIES)
	370	goto out;
	371	if (ldt_info.contents == 3) {
	372	if (oldmode)
	373	goto out;
	374	if (ldt_info.seg_not_present == 0)
	375	goto out;
	376	}
	377
37868fe1 AL	378	if ((oldmode && !ldt_info.base_addr && !ldt_info.limit) \|\|
	379	LDT_empty(&ldt_info)) {
	380	/* The user wants to clear the entry. */
	381	memset(&ldt, 0, sizeof(ldt));
	382	} else {
	383	if (!IS_ENABLED(CONFIG_X86_16BIT) && !ldt_info.seg_32bit) {
	384	error = -EINVAL;
	385	goto out;
1da177e4	386	}
37868fe1 AL	387
	388	fill_ldt(&ldt, &ldt_info);
	389	if (oldmode)
	390	ldt.avl = 0;
1da177e4 LT	391	}
1da177e4 LT	392
c2b3496b PZ	393	if (down_write_killable(&mm->context.ldt_usr_sem))
c2b3496b PZ	394	return -EINTR;
37868fe1	395
bbf79d21 BP	396	old_ldt = mm->context.ldt;
	397	old_nr_entries = old_ldt ? old_ldt->nr_entries : 0;
	398	new_nr_entries = max(ldt_info.entry_number + 1, old_nr_entries);
37868fe1 AL	399
37868fe1 AL	400	error = -ENOMEM;
bbf79d21	401	new_ldt = alloc_ldt_struct(new_nr_entries);
37868fe1	402	if (!new_ldt)
34273f41	403	goto out_unlock;
34273f41	404
37868fe1	405	if (old_ldt)
bbf79d21 BP	406	memcpy(new_ldt->entries, old_ldt->entries, old_nr_entries * LDT_ENTRY_SIZE);
bbf79d21 BP	407
37868fe1 AL	408	new_ldt->entries[ldt_info.entry_number] = ldt;
37868fe1 AL	409	finalize_ldt_struct(new_ldt);
1da177e4	410
f55f0501 AL	411	/*
	412	* If we are using PTI, map the new LDT into the userspace pagetables.
	413	* If there is already an LDT, use the other slot so that other CPUs
	414	* will continue to use the old LDT until install_ldt() switches
	415	* them over to the new LDT.
	416	*/
	417	error = map_ldt_struct(mm, new_ldt, old_ldt ? !old_ldt->slot : 0);
	418	if (error) {
	419	free_ldt_struct(old_ldt);
	420	goto out_unlock;
	421	}
	422
37868fe1 AL	423	install_ldt(mm, new_ldt);
37868fe1 AL	424	free_ldt_struct(old_ldt);
1da177e4 LT	425	error = 0;
	426
	427	out_unlock:
c2b3496b	428	up_write(&mm->context.ldt_usr_sem);
1da177e4 LT	429	out:
	430	return error;
	431	}
	432
da20ab35 DH	433	SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr ,
da20ab35 DH	434	unsigned long , bytecount)
1da177e4 LT	435	{
	436	int ret = -ENOSYS;
	437
	438	switch (func) {
	439	case 0:
	440	ret = read_ldt(ptr, bytecount);
	441	break;
	442	case 1:
	443	ret = write_ldt(ptr, bytecount, 1);
	444	break;
	445	case 2:
	446	ret = read_default_ldt(ptr, bytecount);
	447	break;
	448	case 0x11:
	449	ret = write_ldt(ptr, bytecount, 0);
	450	break;
	451	}
da20ab35 DH	452	/*
	453	* The SYSCALL_DEFINE() macros give us an 'unsigned long'
	454	* return type, but tht ABI for sys_modify_ldt() expects
	455	* 'int'. This cast gives us an int-sized value in %rax
	456	* for the return code. The 'unsigned' is necessary so
	457	* the compiler does not try to sign-extend the negative
	458	* return codes into the high half of the register when
	459	* taking the value from int->long.
	460	*/
	461	return (unsigned int)ret;
1da177e4	462	}