xref: /openbmc/linux/arch/x86/um/syscalls_64.c (revision 23c2b932)
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/uaccess.h>
10 #include <asm/prctl.h> /* XXX This should get the constants from libc */
11 #include <os.h>
12 
13 long arch_prctl(struct task_struct *task, int code, unsigned long __user *addr)
14 {
15 	unsigned long *ptr = addr, tmp;
16 	long ret;
17 	int pid = task->mm->context.id.u.pid;
18 
19 	/*
20 	 * With ARCH_SET_FS (and ARCH_SET_GS is treated similarly to
21 	 * be safe), we need to call arch_prctl on the host because
22 	 * setting %fs may result in something else happening (like a
23 	 * GDT or thread.fs being set instead).  So, we let the host
24 	 * fiddle the registers and thread struct and restore the
25 	 * registers afterwards.
26 	 *
27 	 * So, the saved registers are stored to the process (this
28 	 * needed because a stub may have been the last thing to run),
29 	 * arch_prctl is run on the host, then the registers are read
30 	 * back.
31 	 */
32 	switch (code) {
33 	case ARCH_SET_FS:
34 	case ARCH_SET_GS:
35 		ret = restore_registers(pid, &current->thread.regs.regs);
36 		if (ret)
37 			return ret;
38 		break;
39 	case ARCH_GET_FS:
40 	case ARCH_GET_GS:
41 		/*
42 		 * With these two, we read to a local pointer and
43 		 * put_user it to the userspace pointer that we were
44 		 * given.  If addr isn't valid (because it hasn't been
45 		 * faulted in or is just bogus), we want put_user to
46 		 * fault it in (or return -EFAULT) instead of having
47 		 * the host return -EFAULT.
48 		 */
49 		ptr = &tmp;
50 	}
51 
52 	ret = os_arch_prctl(pid, code, ptr);
53 	if (ret)
54 		return ret;
55 
56 	switch (code) {
57 	case ARCH_SET_FS:
58 		current->thread.arch.fs = (unsigned long) ptr;
59 		ret = save_registers(pid, &current->thread.regs.regs);
60 		break;
61 	case ARCH_SET_GS:
62 		ret = save_registers(pid, &current->thread.regs.regs);
63 		break;
64 	case ARCH_GET_FS:
65 		ret = put_user(tmp, addr);
66 		break;
67 	case ARCH_GET_GS:
68 		ret = put_user(tmp, addr);
69 		break;
70 	}
71 
72 	return ret;
73 }
74 
75 long sys_arch_prctl(int code, unsigned long addr)
76 {
77 	return arch_prctl(current, code, (unsigned long __user *) addr);
78 }
79 
80 void arch_switch_to(struct task_struct *to)
81 {
82 	if ((to->thread.arch.fs == 0) || (to->mm == NULL))
83 		return;
84 
85 	arch_prctl(to, ARCH_SET_FS, (void __user *) to->thread.arch.fs);
86 }
87