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 #include <linux/regset.h>
   6
   7 #include <asm/uaccess.h>
   8 #include <asm/desc.h>
   9 #include <asm/system.h>
  10 #include <asm/ldt.h>
  11 #include <asm/processor.h>
  12 #include <asm/proto.h>
  13 #include <asm/syscalls.h>
  14
  15 #include "tls.h"
  16
  17 /*
  18  * sys_alloc_thread_area: get a yet unused TLS descriptor index.
  19  */
  20 static int get_free_idx(void)
  21 {
  22         struct thread_struct *t = &current->thread;
  23         int idx;
  24
  25         for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
  26                 if (desc_empty(&t->tls_array[idx]))
  27                         return idx + GDT_ENTRY_TLS_MIN;
  28         return -ESRCH;
  29 }
  30
  31 static bool tls_desc_okay(const struct user_desc *info)
  32 {
  33         if (LDT_empty(info))
  34                 return true;
  35
  36         /*
  37          * espfix is required for 16-bit data segments, but espfix
  38          * only works for LDT segments.
  39          */
  40         if (!info->seg_32bit)
  41                 return false;
  42
  43         /* Only allow data segments in the TLS array. */
  44         if (info->contents > 1)
  45                 return false;
  46
  47         /*
  48          * Non-present segments with DPL 3 present an interesting attack
  49          * surface.  The kernel should handle such segments correctly,
  50          * but TLS is very difficult to protect in a sandbox, so prevent
  51          * such segments from being created.
  52          *
  53          * If userspace needs to remove a TLS entry, it can still delete
  54          * it outright.
  55          */
  56         if (info->seg_not_present)
  57                 return false;
  58
  59         return true;
  60 }
  61
  62 static void set_tls_desc(struct task_struct *p, int idx,
  63                          const struct user_desc *info, int n)
  64 {
  65         struct thread_struct *t = &p->thread;
  66         struct desc_struct *desc = &t->tls_array[idx - GDT_ENTRY_TLS_MIN];
  67         int cpu;
  68
  69         /*
  70          * We must not get preempted while modifying the TLS.
  71          */
  72         cpu = get_cpu();
  73
  74         while (n-- > 0) {
  75                 if (LDT_empty(info))
  76                         desc->a = desc->b = 0;
  77                 else
  78                         fill_ldt(desc, info);
  79                 ++info;
  80                 ++desc;
  81         }
  82
  83         if (t == &current->thread)
  84                 load_TLS(t, cpu);
  85
  86         put_cpu();
  87 }
  88
  89 /*
  90  * Set a given TLS descriptor:
  91  */
  92 int do_set_thread_area(struct task_struct *p, int idx,
  93                        struct user_desc __user *u_info,
  94                        int can_allocate)
  95 {
  96         struct user_desc info;
  97
  98         if (copy_from_user(&info, u_info, sizeof(info)))
  99                 return -EFAULT;
 100
 101         if (!tls_desc_okay(&info))
 102                 return -EINVAL;
 103
 104         if (idx == -1)
 105                 idx = info.entry_number;
 106
 107         /*
 108          * index -1 means the kernel should try to find and
 109          * allocate an empty descriptor:
 110          */
 111         if (idx == -1 && can_allocate) {
 112                 idx = get_free_idx();
 113                 if (idx < 0)
 114                         return idx;
 115                 if (put_user(idx, &u_info->entry_number))
 116                         return -EFAULT;
 117         }
 118
 119         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 120                 return -EINVAL;
 121
 122         set_tls_desc(p, idx, &info, 1);
 123
 124         return 0;
 125 }
 126
 127 asmlinkage int sys_set_thread_area(struct user_desc __user *u_info)
 128 {
 129         int ret = do_set_thread_area(current, -1, u_info, 1);
 130         asmlinkage_protect(1, ret, u_info);
 131         return ret;
 132 }
 133
 134
 135 /*
 136  * Get the current Thread-Local Storage area:
 137  */
 138
 139 static void fill_user_desc(struct user_desc *info, int idx,
 140                            const struct desc_struct *desc)
 141
 142 {
 143         memset(info, 0, sizeof(*info));
 144         info->entry_number = idx;
 145         info->base_addr = get_desc_base(desc);
 146         info->limit = get_desc_limit(desc);
 147         info->seg_32bit = desc->d;
 148         info->contents = desc->type >> 2;
 149         info->read_exec_only = !(desc->type & 2);
 150         info->limit_in_pages = desc->g;
 151         info->seg_not_present = !desc->p;
 152         info->useable = desc->avl;
 153 #ifdef CONFIG_X86_64
 154         info->lm = desc->l;
 155 #endif
 156 }
 157
 158 int do_get_thread_area(struct task_struct *p, int idx,
 159                        struct user_desc __user *u_info)
 160 {
 161         struct user_desc info;
 162
 163         if (idx == -1 && get_user(idx, &u_info->entry_number))
 164                 return -EFAULT;
 165
 166         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 167                 return -EINVAL;
 168
 169         fill_user_desc(&info, idx,
 170                        &p->thread.tls_array[idx - GDT_ENTRY_TLS_MIN]);
 171
 172         if (copy_to_user(u_info, &info, sizeof(info)))
 173                 return -EFAULT;
 174         return 0;
 175 }
 176
 177 asmlinkage int sys_get_thread_area(struct user_desc __user *u_info)
 178 {
 179         int ret = do_get_thread_area(current, -1, u_info);
 180         asmlinkage_protect(1, ret, u_info);
 181         return ret;
 182 }
 183
 184 int regset_tls_active(struct task_struct *target,
 185                       const struct user_regset *regset)
 186 {
 187         struct thread_struct *t = &target->thread;
 188         int n = GDT_ENTRY_TLS_ENTRIES;
 189         while (n > 0 && desc_empty(&t->tls_array[n - 1]))
 190                 --n;
 191         return n;
 192 }
 193
 194 int regset_tls_get(struct task_struct *target, const struct user_regset *regset,
 195                    unsigned int pos, unsigned int count,
 196                    void *kbuf, void __user *ubuf)
 197 {
 198         const struct desc_struct *tls;
 199
 200         if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
 201             (pos % sizeof(struct user_desc)) != 0 ||
 202             (count % sizeof(struct user_desc)) != 0)
 203                 return -EINVAL;
 204
 205         pos /= sizeof(struct user_desc);
 206         count /= sizeof(struct user_desc);
 207
 208         tls = &target->thread.tls_array[pos];
 209
 210         if (kbuf) {
 211                 struct user_desc *info = kbuf;
 212                 while (count-- > 0)
 213                         fill_user_desc(info++, GDT_ENTRY_TLS_MIN + pos++,
 214                                        tls++);
 215         } else {
 216                 struct user_desc __user *u_info = ubuf;
 217                 while (count-- > 0) {
 218                         struct user_desc info;
 219                         fill_user_desc(&info, GDT_ENTRY_TLS_MIN + pos++, tls++);
 220                         if (__copy_to_user(u_info++, &info, sizeof(info)))
 221                                 return -EFAULT;
 222                 }
 223         }
 224
 225         return 0;
 226 }
 227
 228 int regset_tls_set(struct task_struct *target, const struct user_regset *regset,
 229                    unsigned int pos, unsigned int count,
 230                    const void *kbuf, const void __user *ubuf)
 231 {
 232         struct user_desc infobuf[GDT_ENTRY_TLS_ENTRIES];
 233         const struct user_desc *info;
 234         int i;
 235
 236         if (pos >= GDT_ENTRY_TLS_ENTRIES * sizeof(struct user_desc) ||
 237             (pos % sizeof(struct user_desc)) != 0 ||
 238             (count % sizeof(struct user_desc)) != 0)
 239                 return -EINVAL;
 240
 241         if (kbuf)
 242                 info = kbuf;
 243         else if (__copy_from_user(infobuf, ubuf, count))
 244                 return -EFAULT;
 245         else
 246                 info = infobuf;
 247
 248         for (i = 0; i < count / sizeof(struct user_desc); i++)
 249                 if (!tls_desc_okay(info + i))
 250                         return -EINVAL;
 251
 252         set_tls_desc(target,
 253                      GDT_ENTRY_TLS_MIN + (pos / sizeof(struct user_desc)),
 254                      info, count / sizeof(struct user_desc));
 255
 256         return 0;
 257 }