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 <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
  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
  78 SYSCALL_DEFINE2(arch_prctl, int, option, unsigned long, arg2)
  79 {
  80         return arch_prctl(current, option, (unsigned long __user *) arg2);
  81 }
  82
  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 }