arch/x86/um/syscalls_64.c

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