arch/x86/kernel/ldt.c - arm/linux - Git at Google

 // 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.
  */

 #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/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/uaccess.h>

 #include <asm/ldt.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 for us, so we don't need any locking. */
 static void flush_ldt(void *__mm)
 {
 	struct mm_struct *mm = __mm;
 	mm_context_t *pc;

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

 	pc = &mm->context;
 	set_ldt(pc->ldt->entries, pc->ldt->nr_entries);

 	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;
 	}

 	new_ldt->nr_entries = num_entries;
 	return new_ldt;
 }

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

 /* context.lock is held */
 static void install_ldt(struct mm_struct *current_mm,
 			struct ldt_struct *ldt)
 {
 	/* Synchronizes with lockless_dereference in load_mm_ldt. */
 	smp_store_release(&current_mm->context.ldt, ldt);

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

 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);
 }

 /*
  * we do not have to muck with descriptors here, that is
  * done in switch_mm() as needed.
  */
 int init_new_context_ldt(struct task_struct *tsk, struct mm_struct *mm)
 {
 	struct ldt_struct *new_ldt;
 	struct mm_struct *old_mm;
 	int retval = 0;

 	mutex_init(&mm->context.lock);
 	old_mm = current->mm;
 	if (!old_mm) {
 		mm->context.ldt = NULL;
 		return 0;
 	}

 	mutex_lock(&old_mm->context.lock);
 	if (!old_mm->context.ldt) {
 		mm->context.ldt = NULL;
 		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);

 	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;
 }

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

 	mutex_lock(&mm->context.lock);

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

 	mutex_lock(&mm->context.lock);

 	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);

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

 out_unlock:
 	mutex_unlock(&mm->context.lock);
 out:
 	return error;
 }

 asmlinkage int sys_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;
 	}
 	return ret;
 }
	// 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.
	*/

	#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/slab.h>
	#include <linux/vmalloc.h>
	#include <linux/uaccess.h>

	#include <asm/ldt.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 for us, so we don't need any locking. */
	static void flush_ldt(void *__mm)
	{
	struct mm_struct *mm = __mm;
	mm_context_t *pc;

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

	pc = &mm->context;
	set_ldt(pc->ldt->entries, pc->ldt->nr_entries);

	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;
	}

	new_ldt->nr_entries = num_entries;
	return new_ldt;
	}

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

	/* context.lock is held */
	static void install_ldt(struct mm_struct *current_mm,
	struct ldt_struct *ldt)
	{
	/* Synchronizes with lockless_dereference in load_mm_ldt. */
	smp_store_release(&current_mm->context.ldt, ldt);

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

	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);
	}

	/*
	* we do not have to muck with descriptors here, that is
	* done in switch_mm() as needed.
	*/
	int init_new_context_ldt(struct task_struct tsk, struct mm_struct mm)
	{
	struct ldt_struct *new_ldt;
	struct mm_struct *old_mm;
	int retval = 0;

	mutex_init(&mm->context.lock);
	old_mm = current->mm;
	if (!old_mm) {
	mm->context.ldt = NULL;
	return 0;
	}

	mutex_lock(&old_mm->context.lock);
	if (!old_mm->context.ldt) {
	mm->context.ldt = NULL;
	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);

	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;
	}

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

	mutex_lock(&mm->context.lock);

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

	mutex_lock(&mm->context.lock);

	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);

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

	out_unlock:
	mutex_unlock(&mm->context.lock);
	out:
	return error;
	}

	asmlinkage int sys_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;
	}
	return ret;
	}