xref: /kernel/linux/linux-5.10/arch/x86/um/ldt.c

/*
 * 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;

	BUILD_BUG_ON(sizeof(*desc) % sizeof(long));

	res = syscall_stub_data(mm_idp, (unsigned long *)desc,
				sizeof(*desc) / sizeof(long),
				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);
}