arch/x86/um/ldt.c - linux - Git at Google

 /*
  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  * Licensed under the GPL
  */

 #include <linux/mm.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/syscalls.h>
 #include <linux/uaccess.h>
 #include <asm/unistd.h>
 #include <os.h>
 #include <skas.h>
 #include <sysdep/tls.h>

 static inline int modify_ldt (int func, void *ptr, unsigned long bytecount)
 {
 	return syscall(__NR_modify_ldt, func, ptr, bytecount);
 }

 static long write_ldt_entry(struct mm_id *mm_idp, int func,
 		     struct user_desc *desc, void **addr, int done)
 {
 	long res;
 	void *stub_addr;
 	res = syscall_stub_data(mm_idp, (unsigned long *)desc,
 				(sizeof(*desc) + sizeof(long) - 1) &
 				    ~(sizeof(long) - 1),
 				addr, &stub_addr);
 	if (!res) {
 		unsigned long args[] = { func,
 					 (unsigned long)stub_addr,
 					 sizeof(*desc),
 					 0, 0, 0 };
 		res = run_syscall_stub(mm_idp, __NR_modify_ldt, args,
 				       0, addr, done);
 	}

 	return res;
 }

 /*
  * In skas mode, we hold our own ldt data in UML.
  * Thus, the code implementing sys_modify_ldt_skas
  * is very similar to (and mostly stolen from) sys_modify_ldt
  * for arch/i386/kernel/ldt.c
  * The routines copied and modified in part are:
  * - read_ldt
  * - read_default_ldt
  * - write_ldt
  * - sys_modify_ldt_skas
  */

 static int read_ldt(void __user * ptr, unsigned long bytecount)
 {
 	int i, err = 0;
 	unsigned long size;
 	uml_ldt_t *ldt = &current->mm->context.arch.ldt;

 	if (!ldt->entry_count)
 		goto out;
 	if (bytecount > LDT_ENTRY_SIZE*LDT_ENTRIES)
 		bytecount = LDT_ENTRY_SIZE*LDT_ENTRIES;
 	err = bytecount;

 	mutex_lock(&ldt->lock);
 	if (ldt->entry_count <= LDT_DIRECT_ENTRIES) {
 		size = LDT_ENTRY_SIZE*LDT_DIRECT_ENTRIES;
 		if (size > bytecount)
 			size = bytecount;
 		if (copy_to_user(ptr, ldt->u.entries, size))
 			err = -EFAULT;
 		bytecount -= size;
 		ptr += size;
 	}
 	else {
 		for (i=0; i<ldt->entry_count/LDT_ENTRIES_PER_PAGE && bytecount;
 		     i++) {
 			size = PAGE_SIZE;
 			if (size > bytecount)
 				size = bytecount;
 			if (copy_to_user(ptr, ldt->u.pages[i], size)) {
 				err = -EFAULT;
 				break;
 			}
 			bytecount -= size;
 			ptr += size;
 		}
 	}
 	mutex_unlock(&ldt->lock);

 	if (bytecount == 0 || err == -EFAULT)
 		goto out;

 	if (clear_user(ptr, bytecount))
 		err = -EFAULT;

 out:
 	return err;
 }

 static int read_default_ldt(void __user * ptr, unsigned long bytecount)
 {
 	int err;

 	if (bytecount > 5*LDT_ENTRY_SIZE)
 		bytecount = 5*LDT_ENTRY_SIZE;

 	err = bytecount;
 	/*
 	 * UML doesn't support lcall7 and lcall27.
 	 * So, we don't really have a default ldt, but emulate
 	 * an empty ldt of common host default ldt size.
 	 */
 	if (clear_user(ptr, bytecount))
 		err = -EFAULT;

 	return err;
 }

 static int write_ldt(void __user * ptr, unsigned long bytecount, int func)
 {
 	uml_ldt_t *ldt = &current->mm->context.arch.ldt;
 	struct mm_id * mm_idp = &current->mm->context.id;
 	int i, err;
 	struct user_desc ldt_info;
 	struct ldt_entry entry0, *ldt_p;
 	void *addr = NULL;

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

 	err = -EINVAL;
 	if (ldt_info.entry_number >= LDT_ENTRIES)
 		goto out;
 	if (ldt_info.contents == 3) {
 		if (func == 1)
 			goto out;
 		if (ldt_info.seg_not_present == 0)
 			goto out;
 	}

 	mutex_lock(&ldt->lock);

 	err = write_ldt_entry(mm_idp, func, &ldt_info, &addr, 1);
 	if (err)
 		goto out_unlock;

 	if (ldt_info.entry_number >= ldt->entry_count &&
 	    ldt_info.entry_number >= LDT_DIRECT_ENTRIES) {
 		for (i=ldt->entry_count/LDT_ENTRIES_PER_PAGE;
 		     i*LDT_ENTRIES_PER_PAGE <= ldt_info.entry_number;
 		     i++) {
 			if (i == 0)
 				memcpy(&entry0, ldt->u.entries,
 				       sizeof(entry0));
 			ldt->u.pages[i] = (struct ldt_entry *)
 				__get_free_page(GFP_KERNEL|__GFP_ZERO);
 			if (!ldt->u.pages[i]) {
 				err = -ENOMEM;
 				/* Undo the change in host */
 				memset(&ldt_info, 0, sizeof(ldt_info));
 				write_ldt_entry(mm_idp, 1, &ldt_info, &addr, 1);
 				goto out_unlock;
 			}
 			if (i == 0) {
 				memcpy(ldt->u.pages[0], &entry0,
 				       sizeof(entry0));
 				memcpy(ldt->u.pages[0]+1, ldt->u.entries+1,
 				       sizeof(entry0)*(LDT_DIRECT_ENTRIES-1));
 			}
 			ldt->entry_count = (i + 1) * LDT_ENTRIES_PER_PAGE;
 		}
 	}
 	if (ldt->entry_count <= ldt_info.entry_number)
 		ldt->entry_count = ldt_info.entry_number + 1;

 	if (ldt->entry_count <= LDT_DIRECT_ENTRIES)
 		ldt_p = ldt->u.entries + ldt_info.entry_number;
 	else
 		ldt_p = ldt->u.pages[ldt_info.entry_number/LDT_ENTRIES_PER_PAGE] +
 			ldt_info.entry_number%LDT_ENTRIES_PER_PAGE;

 	if (ldt_info.base_addr == 0 && ldt_info.limit == 0 &&
 	   (func == 1 || LDT_empty(&ldt_info))) {
 		ldt_p->a = 0;
 		ldt_p->b = 0;
 	}
 	else{
 		if (func == 1)
 			ldt_info.useable = 0;
 		ldt_p->a = LDT_entry_a(&ldt_info);
 		ldt_p->b = LDT_entry_b(&ldt_info);
 	}
 	err = 0;

 out_unlock:
 	mutex_unlock(&ldt->lock);
 out:
 	return err;
 }

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

 	switch (func) {
 		case 0:
 			ret = read_ldt(ptr, bytecount);
 			break;
 		case 1:
 		case 0x11:
 			ret = write_ldt(ptr, bytecount, func);
 			break;
 		case 2:
 			ret = read_default_ldt(ptr, bytecount);
 			break;
 	}
 	return ret;
 }

 static DEFINE_SPINLOCK(host_ldt_lock);
 static short dummy_list[9] = {0, -1};
 static short * host_ldt_entries = NULL;

 static void ldt_get_host_info(void)
 {
 	long ret;
 	struct ldt_entry * ldt;
 	short *tmp;
 	int i, size, k, order;

 	spin_lock(&host_ldt_lock);

 	if (host_ldt_entries != NULL) {
 		spin_unlock(&host_ldt_lock);
 		return;
 	}
 	host_ldt_entries = dummy_list+1;

 	spin_unlock(&host_ldt_lock);

 	for (i = LDT_PAGES_MAX-1, order=0; i; i>>=1, order++)
 		;

 	ldt = (struct ldt_entry *)
 	      __get_free_pages(GFP_KERNEL|__GFP_ZERO, order);
 	if (ldt == NULL) {
 		printk(KERN_ERR "ldt_get_host_info: couldn't allocate buffer "
 		       "for host ldt\n");
 		return;
 	}

 	ret = modify_ldt(0, ldt, (1<<order)*PAGE_SIZE);
 	if (ret < 0) {
 		printk(KERN_ERR "ldt_get_host_info: couldn't read host ldt\n");
 		goto out_free;
 	}
 	if (ret == 0) {
 		/* default_ldt is active, simply write an empty entry 0 */
 		host_ldt_entries = dummy_list;
 		goto out_free;
 	}

 	for (i=0, size=0; i<ret/LDT_ENTRY_SIZE; i++) {
 		if (ldt[i].a != 0 || ldt[i].b != 0)
 			size++;
 	}

 	if (size < ARRAY_SIZE(dummy_list))
 		host_ldt_entries = dummy_list;
 	else {
 		size = (size + 1) * sizeof(dummy_list[0]);
 		tmp = kmalloc(size, GFP_KERNEL);
 		if (tmp == NULL) {
 			printk(KERN_ERR "ldt_get_host_info: couldn't allocate "
 			       "host ldt list\n");
 			goto out_free;
 		}
 		host_ldt_entries = tmp;
 	}

 	for (i=0, k=0; i<ret/LDT_ENTRY_SIZE; i++) {
 		if (ldt[i].a != 0 || ldt[i].b != 0)
 			host_ldt_entries[k++] = i;
 	}
 	host_ldt_entries[k] = -1;

 out_free:
 	free_pages((unsigned long)ldt, order);
 }

 long init_new_ldt(struct mm_context *new_mm, struct mm_context *from_mm)
 {
 	struct user_desc desc;
 	short * num_p;
 	int i;
 	long page, err=0;
 	void *addr = NULL;


 	mutex_init(&new_mm->arch.ldt.lock);

 	if (!from_mm) {
 		memset(&desc, 0, sizeof(desc));
 		/*
 		 * Now we try to retrieve info about the ldt, we
 		 * inherited from the host. All ldt-entries found
 		 * will be reset in the following loop
 		 */
 		ldt_get_host_info();
 		for (num_p=host_ldt_entries; *num_p != -1; num_p++) {
 			desc.entry_number = *num_p;
 			err = write_ldt_entry(&new_mm->id, 1, &desc,
 					      &addr, *(num_p + 1) == -1);
 			if (err)
 				break;
 		}
 		new_mm->arch.ldt.entry_count = 0;

 		goto out;
 	}

 	/*
 	 * Our local LDT is used to supply the data for
 	 * modify_ldt(READLDT), if PTRACE_LDT isn't available,
 	 * i.e., we have to use the stub for modify_ldt, which
 	 * can't handle the big read buffer of up to 64kB.
 	 */
 	mutex_lock(&from_mm->arch.ldt.lock);
 	if (from_mm->arch.ldt.entry_count <= LDT_DIRECT_ENTRIES)
 		memcpy(new_mm->arch.ldt.u.entries, from_mm->arch.ldt.u.entries,
 		       sizeof(new_mm->arch.ldt.u.entries));
 	else {
 		i = from_mm->arch.ldt.entry_count / LDT_ENTRIES_PER_PAGE;
 		while (i-->0) {
 			page = __get_free_page(GFP_KERNEL|__GFP_ZERO);
 			if (!page) {
 				err = -ENOMEM;
 				break;
 			}
 			new_mm->arch.ldt.u.pages[i] =
 				(struct ldt_entry *) page;
 			memcpy(new_mm->arch.ldt.u.pages[i],
 			       from_mm->arch.ldt.u.pages[i], PAGE_SIZE);
 		}
 	}
 	new_mm->arch.ldt.entry_count = from_mm->arch.ldt.entry_count;
 	mutex_unlock(&from_mm->arch.ldt.lock);

     out:
 	return err;
 }


 void free_ldt(struct mm_context *mm)
 {
 	int i;

 	if (mm->arch.ldt.entry_count > LDT_DIRECT_ENTRIES) {
 		i = mm->arch.ldt.entry_count / LDT_ENTRIES_PER_PAGE;
 		while (i-- > 0)
 			free_page((long) mm->arch.ldt.u.pages[i]);
 	}
 	mm->arch.ldt.entry_count = 0;
 }

 SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr ,
 		unsigned long , bytecount)
 {
 	/* See non-um modify_ldt() for why we do this cast */
 	return (unsigned int)do_modify_ldt_skas(func, ptr, bytecount);
 }
	/*
	* Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
	* Licensed under the GPL
	*/

	#include <linux/mm.h>
	#include <linux/sched.h>
	#include <linux/slab.h>
	#include <linux/syscalls.h>
	#include <linux/uaccess.h>
	#include <asm/unistd.h>
	#include <os.h>
	#include <skas.h>
	#include <sysdep/tls.h>

	static inline int modify_ldt (int func, void *ptr, unsigned long bytecount)
	{
	return syscall(__NR_modify_ldt, func, ptr, bytecount);
	}

	static long write_ldt_entry(struct mm_id *mm_idp, int func,
	struct user_desc desc, void *addr, int done)
	{
	long res;
	void *stub_addr;
	res = syscall_stub_data(mm_idp, (unsigned long *)desc,
	(sizeof(*desc) + sizeof(long) - 1) &
	~(sizeof(long) - 1),
	addr, &stub_addr);
	if (!res) {
	unsigned long args[] = { func,
	(unsigned long)stub_addr,
	sizeof(*desc),
	0, 0, 0 };
	res = run_syscall_stub(mm_idp, __NR_modify_ldt, args,
	0, addr, done);
	}

	return res;
	}

	/*
	* In skas mode, we hold our own ldt data in UML.
	* Thus, the code implementing sys_modify_ldt_skas
	* is very similar to (and mostly stolen from) sys_modify_ldt
	* for arch/i386/kernel/ldt.c
	* The routines copied and modified in part are:
	* - read_ldt
	* - read_default_ldt
	* - write_ldt
	* - sys_modify_ldt_skas
	*/

	static int read_ldt(void __user * ptr, unsigned long bytecount)
	{
	int i, err = 0;
	unsigned long size;
	uml_ldt_t *ldt = &current->mm->context.arch.ldt;

	if (!ldt->entry_count)
	goto out;
	if (bytecount > LDT_ENTRY_SIZE*LDT_ENTRIES)
	bytecount = LDT_ENTRY_SIZE*LDT_ENTRIES;
	err = bytecount;

	mutex_lock(&ldt->lock);
	if (ldt->entry_count <= LDT_DIRECT_ENTRIES) {
	size = LDT_ENTRY_SIZE*LDT_DIRECT_ENTRIES;
	if (size > bytecount)
	size = bytecount;
	if (copy_to_user(ptr, ldt->u.entries, size))
	err = -EFAULT;
	bytecount -= size;
	ptr += size;
	}
	else {
	for (i=0; i<ldt->entry_count/LDT_ENTRIES_PER_PAGE && bytecount;
	i++) {
	size = PAGE_SIZE;
	if (size > bytecount)
	size = bytecount;
	if (copy_to_user(ptr, ldt->u.pages[i], size)) {
	err = -EFAULT;
	break;
	}
	bytecount -= size;
	ptr += size;
	}
	}
	mutex_unlock(&ldt->lock);

	if (bytecount == 0 \|\| err == -EFAULT)
	goto out;

	if (clear_user(ptr, bytecount))
	err = -EFAULT;

	out:
	return err;
	}

	static int read_default_ldt(void __user * ptr, unsigned long bytecount)
	{
	int err;

	if (bytecount > 5*LDT_ENTRY_SIZE)
	bytecount = 5*LDT_ENTRY_SIZE;

	err = bytecount;
	/*
	* UML doesn't support lcall7 and lcall27.
	* So, we don't really have a default ldt, but emulate
	* an empty ldt of common host default ldt size.
	*/
	if (clear_user(ptr, bytecount))
	err = -EFAULT;

	return err;
	}

	static int write_ldt(void __user * ptr, unsigned long bytecount, int func)
	{
	uml_ldt_t *ldt = &current->mm->context.arch.ldt;
	struct mm_id * mm_idp = &current->mm->context.id;
	int i, err;
	struct user_desc ldt_info;
	struct ldt_entry entry0, *ldt_p;
	void *addr = NULL;

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

	err = -EINVAL;
	if (ldt_info.entry_number >= LDT_ENTRIES)
	goto out;
	if (ldt_info.contents == 3) {
	if (func == 1)
	goto out;
	if (ldt_info.seg_not_present == 0)
	goto out;
	}

	mutex_lock(&ldt->lock);

	err = write_ldt_entry(mm_idp, func, &ldt_info, &addr, 1);
	if (err)
	goto out_unlock;

	if (ldt_info.entry_number >= ldt->entry_count &&
	ldt_info.entry_number >= LDT_DIRECT_ENTRIES) {
	for (i=ldt->entry_count/LDT_ENTRIES_PER_PAGE;
	i*LDT_ENTRIES_PER_PAGE <= ldt_info.entry_number;
	i++) {
	if (i == 0)
	memcpy(&entry0, ldt->u.entries,
	sizeof(entry0));
	ldt->u.pages[i] = (struct ldt_entry *)
	__get_free_page(GFP_KERNEL\|__GFP_ZERO);
	if (!ldt->u.pages[i]) {
	err = -ENOMEM;
	/* Undo the change in host */
	memset(&ldt_info, 0, sizeof(ldt_info));
	write_ldt_entry(mm_idp, 1, &ldt_info, &addr, 1);
	goto out_unlock;
	}
	if (i == 0) {
	memcpy(ldt->u.pages[0], &entry0,
	sizeof(entry0));
	memcpy(ldt->u.pages[0]+1, ldt->u.entries+1,
	sizeof(entry0)*(LDT_DIRECT_ENTRIES-1));
	}
	ldt->entry_count = (i + 1) * LDT_ENTRIES_PER_PAGE;
	}
	}
	if (ldt->entry_count <= ldt_info.entry_number)
	ldt->entry_count = ldt_info.entry_number + 1;

	if (ldt->entry_count <= LDT_DIRECT_ENTRIES)
	ldt_p = ldt->u.entries + ldt_info.entry_number;
	else
	ldt_p = ldt->u.pages[ldt_info.entry_number/LDT_ENTRIES_PER_PAGE] +
	ldt_info.entry_number%LDT_ENTRIES_PER_PAGE;

	if (ldt_info.base_addr == 0 && ldt_info.limit == 0 &&
	(func == 1 \|\| LDT_empty(&ldt_info))) {
	ldt_p->a = 0;
	ldt_p->b = 0;
	}
	else{
	if (func == 1)
	ldt_info.useable = 0;
	ldt_p->a = LDT_entry_a(&ldt_info);
	ldt_p->b = LDT_entry_b(&ldt_info);
	}
	err = 0;

	out_unlock:
	mutex_unlock(&ldt->lock);
	out:
	return err;
	}

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

	switch (func) {
	case 0:
	ret = read_ldt(ptr, bytecount);
	break;
	case 1:
	case 0x11:
	ret = write_ldt(ptr, bytecount, func);
	break;
	case 2:
	ret = read_default_ldt(ptr, bytecount);
	break;
	}
	return ret;
	}

	static DEFINE_SPINLOCK(host_ldt_lock);
	static short dummy_list[9] = {0, -1};
	static short * host_ldt_entries = NULL;

	static void ldt_get_host_info(void)
	{
	long ret;
	struct ldt_entry * ldt;
	short *tmp;
	int i, size, k, order;

	spin_lock(&host_ldt_lock);

	if (host_ldt_entries != NULL) {
	spin_unlock(&host_ldt_lock);
	return;
	}
	host_ldt_entries = dummy_list+1;

	spin_unlock(&host_ldt_lock);

	for (i = LDT_PAGES_MAX-1, order=0; i; i>>=1, order++)
	;

	ldt = (struct ldt_entry *)
	__get_free_pages(GFP_KERNEL\|__GFP_ZERO, order);
	if (ldt == NULL) {
	printk(KERN_ERR "ldt_get_host_info: couldn't allocate buffer "
	"for host ldt\n");
	return;
	}

	ret = modify_ldt(0, ldt, (1<<order)*PAGE_SIZE);
	if (ret < 0) {
	printk(KERN_ERR "ldt_get_host_info: couldn't read host ldt\n");
	goto out_free;
	}
	if (ret == 0) {
	/* default_ldt is active, simply write an empty entry 0 */
	host_ldt_entries = dummy_list;
	goto out_free;
	}

	for (i=0, size=0; i<ret/LDT_ENTRY_SIZE; i++) {
	if (ldt[i].a != 0 \|\| ldt[i].b != 0)
	size++;
	}

	if (size < ARRAY_SIZE(dummy_list))
	host_ldt_entries = dummy_list;
	else {
	size = (size + 1) * sizeof(dummy_list[0]);
	tmp = kmalloc(size, GFP_KERNEL);
	if (tmp == NULL) {
	printk(KERN_ERR "ldt_get_host_info: couldn't allocate "
	"host ldt list\n");
	goto out_free;
	}
	host_ldt_entries = tmp;
	}

	for (i=0, k=0; i<ret/LDT_ENTRY_SIZE; i++) {
	if (ldt[i].a != 0 \|\| ldt[i].b != 0)
	host_ldt_entries[k++] = i;
	}
	host_ldt_entries[k] = -1;

	out_free:
	free_pages((unsigned long)ldt, order);
	}

	long init_new_ldt(struct mm_context new_mm, struct mm_context from_mm)
	{
	struct user_desc desc;
	short * num_p;
	int i;
	long page, err=0;
	void *addr = NULL;


	mutex_init(&new_mm->arch.ldt.lock);

	if (!from_mm) {
	memset(&desc, 0, sizeof(desc));
	/*
	* Now we try to retrieve info about the ldt, we
	* inherited from the host. All ldt-entries found
	* will be reset in the following loop
	*/
	ldt_get_host_info();
	for (num_p=host_ldt_entries; *num_p != -1; num_p++) {
	desc.entry_number = *num_p;
	err = write_ldt_entry(&new_mm->id, 1, &desc,
	&addr, *(num_p + 1) == -1);
	if (err)
	break;
	}
	new_mm->arch.ldt.entry_count = 0;

	goto out;
	}

	/*
	* Our local LDT is used to supply the data for
	* modify_ldt(READLDT), if PTRACE_LDT isn't available,
	* i.e., we have to use the stub for modify_ldt, which
	* can't handle the big read buffer of up to 64kB.
	*/
	mutex_lock(&from_mm->arch.ldt.lock);
	if (from_mm->arch.ldt.entry_count <= LDT_DIRECT_ENTRIES)
	memcpy(new_mm->arch.ldt.u.entries, from_mm->arch.ldt.u.entries,
	sizeof(new_mm->arch.ldt.u.entries));
	else {
	i = from_mm->arch.ldt.entry_count / LDT_ENTRIES_PER_PAGE;
	while (i-->0) {
	page = __get_free_page(GFP_KERNEL\|__GFP_ZERO);
	if (!page) {
	err = -ENOMEM;
	break;
	}
	new_mm->arch.ldt.u.pages[i] =
	(struct ldt_entry *) page;
	memcpy(new_mm->arch.ldt.u.pages[i],
	from_mm->arch.ldt.u.pages[i], PAGE_SIZE);
	}
	}
	new_mm->arch.ldt.entry_count = from_mm->arch.ldt.entry_count;
	mutex_unlock(&from_mm->arch.ldt.lock);

	out:
	return err;
	}


	void free_ldt(struct mm_context *mm)
	{
	int i;

	if (mm->arch.ldt.entry_count > LDT_DIRECT_ENTRIES) {
	i = mm->arch.ldt.entry_count / LDT_ENTRIES_PER_PAGE;
	while (i-- > 0)
	free_page((long) mm->arch.ldt.u.pages[i]);
	}
	mm->arch.ldt.entry_count = 0;
	}

	SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr ,
	unsigned long , bytecount)
	{
	/* See non-um modify_ldt() for why we do this cast */
	return (unsigned int)do_modify_ldt_skas(func, ptr, bytecount);
	}