arch/x86/kernel/tls.c

   1 #include <linux/kernel.h>
   2 #include <linux/errno.h>
   3 #include <linux/sched.h>
   4 #include <linux/user.h>
   5
   6 #include <asm/uaccess.h>
   7 #include <asm/desc.h>
   8 #include <asm/system.h>
   9 #include <asm/ldt.h>
  10 #include <asm/processor.h>
  11 #include <asm/proto.h>
  12
  13 /*
  14  * sys_alloc_thread_area: get a yet unused TLS descriptor index.
  15  */
  16 static int get_free_idx(void)
  17 {
  18         struct thread_struct *t = &current->thread;
  19         int idx;
  20
  21         for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
  22                 if (desc_empty(&t->tls_array[idx]))
  23                         return idx + GDT_ENTRY_TLS_MIN;
  24         return -ESRCH;
  25 }
  26
  27 static void set_tls_desc(struct task_struct *p, int idx,
  28                          const struct user_desc *info)
  29 {
  30         struct thread_struct *t = &p->thread;
  31         struct desc_struct *desc = &t->tls_array[idx - GDT_ENTRY_TLS_MIN];
  32         int cpu;
  33
  34         /*
  35          * We must not get preempted while modifying the TLS.
  36          */
  37         cpu = get_cpu();
  38
  39         if (LDT_empty(info))
  40                 desc->a = desc->b = 0;
  41         else
  42                 fill_ldt(desc, info);
  43
  44         if (t == &current->thread)
  45                 load_TLS(t, cpu);
  46
  47         put_cpu();
  48 }
  49
  50 /*
  51  * Set a given TLS descriptor:
  52  */
  53 int do_set_thread_area(struct task_struct *p, int idx,
  54                        struct user_desc __user *u_info,
  55                        int can_allocate)
  56 {
  57         struct user_desc info;
  58
  59         if (copy_from_user(&info, u_info, sizeof(info)))
  60                 return -EFAULT;
  61
  62         if (idx == -1)
  63                 idx = info.entry_number;
  64
  65         /*
  66          * index -1 means the kernel should try to find and
  67          * allocate an empty descriptor:
  68          */
  69         if (idx == -1 && can_allocate) {
  70                 idx = get_free_idx();
  71                 if (idx < 0)
  72                         return idx;
  73                 if (put_user(idx, &u_info->entry_number))
  74                         return -EFAULT;
  75         }
  76
  77         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
  78                 return -EINVAL;
  79
  80         set_tls_desc(p, idx, &info);
  81
  82         return 0;
  83 }
  84
  85 asmlinkage int sys_set_thread_area(struct user_desc __user *u_info)
  86 {
  87         return do_set_thread_area(current, -1, u_info, 1);
  88 }
  89
  90
  91 /*
  92  * Get the current Thread-Local Storage area:
  93  */
  94
  95 static void fill_user_desc(struct user_desc *info, int idx,
  96                            const struct desc_struct *desc)
  97
  98 {
  99         memset(info, 0, sizeof(*info));
 100         info->entry_number = idx;
 101         info->base_addr = get_desc_base(desc);
 102         info->limit = get_desc_limit(desc);
 103         info->seg_32bit = desc->d;
 104         info->contents = desc->type >> 2;
 105         info->read_exec_only = !(desc->type & 2);
 106         info->limit_in_pages = desc->g;
 107         info->seg_not_present = !desc->p;
 108         info->useable = desc->avl;
 109 #ifdef CONFIG_X86_64
 110         info->lm = desc->l;
 111 #endif
 112 }
 113
 114 int do_get_thread_area(struct task_struct *p, int idx,
 115                        struct user_desc __user *u_info)
 116 {
 117         struct user_desc info;
 118
 119         if (idx == -1 && get_user(idx, &u_info->entry_number))
 120                 return -EFAULT;
 121
 122         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 123                 return -EINVAL;
 124
 125         fill_user_desc(&info, idx,
 126                        &p->thread.tls_array[idx - GDT_ENTRY_TLS_MIN]);
 127
 128         if (copy_to_user(u_info, &info, sizeof(info)))
 129                 return -EFAULT;
 130         return 0;
 131 }
 132
 133 asmlinkage int sys_get_thread_area(struct user_desc __user *u_info)
 134 {
 135         return do_get_thread_area(current, -1, u_info);
 136 }