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 
arch_prctl(struct task_struct * task,int option,unsigned long __user * arg2)15 long 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 
SYSCALL_DEFINE2(arch_prctl,int,option,unsigned long,arg2)78 SYSCALL_DEFINE2(arch_prctl, int, option, unsigned long, arg2)
79 {
80 	return arch_prctl(current, option, (unsigned long __user *) arg2);
81 }
82 
arch_switch_to(struct task_struct * to)83 void 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 }
90