1/*
 2 * Copyright (C) 2003 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 3 * Copyright 2003 PathScale, Inc.
 4 *
 5 * Licensed under the GPL
 6 */
 7
 8#include <linux/sched.h>
 9#include <linux/sched/mm.h>
10#include <linux/syscalls.h>
11#include <linux/uaccess.h>
12#include <asm/prctl.h> /* XXX This should get the constants from libc */
13#include <os.h>
14
15long arch_prctl(struct task_struct *task, int option,
16		unsigned long __user *arg2)
17{
18	unsigned long *ptr = arg2, tmp;
19	long ret;
20	int pid = task->mm->context.id.u.pid;
21
22	/*
23	 * With ARCH_SET_FS (and ARCH_SET_GS is treated similarly to
24	 * be safe), we need to call arch_prctl on the host because
25	 * setting %fs may result in something else happening (like a
26	 * GDT or thread.fs being set instead).  So, we let the host
27	 * fiddle the registers and thread struct and restore the
28	 * registers afterwards.
29	 *
30	 * So, the saved registers are stored to the process (this
31	 * needed because a stub may have been the last thing to run),
32	 * arch_prctl is run on the host, then the registers are read
33	 * back.
34	 */
35	switch (option) {
36	case ARCH_SET_FS:
37	case ARCH_SET_GS:
38		ret = restore_registers(pid, &current->thread.regs.regs);
39		if (ret)
40			return ret;
41		break;
42	case ARCH_GET_FS:
43	case ARCH_GET_GS:
44		/*
45		 * With these two, we read to a local pointer and
46		 * put_user it to the userspace pointer that we were
47		 * given.  If addr isn't valid (because it hasn't been
48		 * faulted in or is just bogus), we want put_user to
49		 * fault it in (or return -EFAULT) instead of having
50		 * the host return -EFAULT.
51		 */
52		ptr = &tmp;
53	}
54
55	ret = os_arch_prctl(pid, option, ptr);
56	if (ret)
57		return ret;
58
59	switch (option) {
60	case ARCH_SET_FS:
61		current->thread.arch.fs = (unsigned long) ptr;
62		ret = save_registers(pid, &current->thread.regs.regs);
63		break;
64	case ARCH_SET_GS:
65		ret = save_registers(pid, &current->thread.regs.regs);
66		break;
67	case ARCH_GET_FS:
68		ret = put_user(tmp, arg2);
69		break;
70	case ARCH_GET_GS:
71		ret = put_user(tmp, arg2);
72		break;
73	}
74
75	return ret;
76}
77
78SYSCALL_DEFINE2(arch_prctl, int, option, unsigned long, arg2)
79{
80	return arch_prctl(current, option, (unsigned long __user *) arg2);
81}
82
83void arch_switch_to(struct task_struct *to)
84{
85	if ((to->thread.arch.fs == 0) || (to->mm == NULL))
86		return;
87
88	arch_prctl(to, ARCH_SET_FS, (void __user *) to->thread.arch.fs);
89}