arch/x86/kernel/ldt.c

   1 /*
   2  * Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
   3  * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
   4  * Copyright (C) 2002 Andi Kleen
   5  *
   6  * This handles calls from both 32bit and 64bit mode.
   7  */
   8
   9 #include <linux/errno.h>
  10 #include <linux/gfp.h>
  11 #include <linux/sched.h>
  12 #include <linux/string.h>
  13 #include <linux/mm.h>
  14 #include <linux/smp.h>
  15 #include <linux/vmalloc.h>
  16 #include <linux/uaccess.h>
  17
  18 #include <asm/system.h>
  19 #include <asm/ldt.h>
  20 #include <asm/desc.h>
  21 #include <asm/mmu_context.h>
  22 #include <asm/syscalls.h>
  23
  24 #ifdef CONFIG_SMP
  25 static void flush_ldt(void *current_mm)
  26 {
  27         if (current->active_mm == current_mm)
  28                 load_LDT(&current->active_mm->context);
  29 }
  30 #endif
  31
  32 static int alloc_ldt(mm_context_t *pc, int mincount, int reload)
  33 {
  34         void *oldldt, *newldt;
  35         int oldsize;
  36
  37         if (mincount <= pc->size)
  38                 return 0;
  39         oldsize = pc->size;
  40         mincount = (mincount + (PAGE_SIZE / LDT_ENTRY_SIZE - 1)) &
  41                         (~(PAGE_SIZE / LDT_ENTRY_SIZE - 1));
  42         if (mincount * LDT_ENTRY_SIZE > PAGE_SIZE)
  43                 newldt = vmalloc(mincount * LDT_ENTRY_SIZE);
  44         else
  45                 newldt = (void *)__get_free_page(GFP_KERNEL);
  46
  47         if (!newldt)
  48                 return -ENOMEM;
  49
  50         if (oldsize)
  51                 memcpy(newldt, pc->ldt, oldsize * LDT_ENTRY_SIZE);
  52         oldldt = pc->ldt;
  53         memset(newldt + oldsize * LDT_ENTRY_SIZE, 0,
  54                (mincount - oldsize) * LDT_ENTRY_SIZE);
  55
  56         paravirt_alloc_ldt(newldt, mincount);
  57
  58 #ifdef CONFIG_X86_64
  59         /* CHECKME: Do we really need this ? */
  60         wmb();
  61 #endif
  62         pc->ldt = newldt;
  63         wmb();
  64         pc->size = mincount;
  65         wmb();
  66
  67         if (reload) {
  68 #ifdef CONFIG_SMP
  69                 preempt_disable();
  70                 load_LDT(pc);
  71                 if (!cpumask_equal(mm_cpumask(current->mm),
  72                                    cpumask_of(smp_processor_id())))
  73                         smp_call_function(flush_ldt, current->mm, 1);
  74                 preempt_enable();
  75 #else
  76                 load_LDT(pc);
  77 #endif
  78         }
  79         if (oldsize) {
  80                 paravirt_free_ldt(oldldt, oldsize);
  81                 if (oldsize * LDT_ENTRY_SIZE > PAGE_SIZE)
  82                         vfree(oldldt);
  83                 else
  84                         put_page(virt_to_page(oldldt));
  85         }
  86         return 0;
  87 }
  88
  89 static inline int copy_ldt(mm_context_t *new, mm_context_t *old)
  90 {
  91         int err = alloc_ldt(new, old->size, 0);
  92         int i;
  93
  94         if (err < 0)
  95                 return err;
  96
  97         for (i = 0; i < old->size; i++)
  98                 write_ldt_entry(new->ldt, i, old->ldt + i * LDT_ENTRY_SIZE);
  99         return 0;
 100 }
 101
 102 /*
 103  * we do not have to muck with descriptors here, that is
 104  * done in switch_mm() as needed.
 105  */
 106 int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
 107 {
 108         struct mm_struct *old_mm;
 109         int retval = 0;
 110
 111         mutex_init(&mm->context.lock);
 112         mm->context.size = 0;
 113         old_mm = current->mm;
 114         if (old_mm && old_mm->context.size > 0) {
 115                 mutex_lock(&old_mm->context.lock);
 116                 retval = copy_ldt(&mm->context, &old_mm->context);
 117                 mutex_unlock(&old_mm->context.lock);
 118         }
 119         return retval;
 120 }
 121
 122 /*
 123  * No need to lock the MM as we are the last user
 124  *
 125  * 64bit: Don't touch the LDT register - we're already in the next thread.
 126  */
 127 void destroy_context(struct mm_struct *mm)
 128 {
 129         if (mm->context.size) {
 130 #ifdef CONFIG_X86_32
 131                 /* CHECKME: Can this ever happen ? */
 132                 if (mm == current->active_mm)
 133                         clear_LDT();
 134 #endif
 135                 paravirt_free_ldt(mm->context.ldt, mm->context.size);
 136                 if (mm->context.size * LDT_ENTRY_SIZE > PAGE_SIZE)
 137                         vfree(mm->context.ldt);
 138                 else
 139                         put_page(virt_to_page(mm->context.ldt));
 140                 mm->context.size = 0;
 141         }
 142 }
 143
 144 static int read_ldt(void __user *ptr, unsigned long bytecount)
 145 {
 146         int err;
 147         unsigned long size;
 148         struct mm_struct *mm = current->mm;
 149
 150         if (!mm->context.size)
 151                 return 0;
 152         if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
 153                 bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
 154
 155         mutex_lock(&mm->context.lock);
 156         size = mm->context.size * LDT_ENTRY_SIZE;
 157         if (size > bytecount)
 158                 size = bytecount;
 159
 160         err = 0;
 161         if (copy_to_user(ptr, mm->context.ldt, size))
 162                 err = -EFAULT;
 163         mutex_unlock(&mm->context.lock);
 164         if (err < 0)
 165                 goto error_return;
 166         if (size != bytecount) {
 167                 /* zero-fill the rest */
 168                 if (clear_user(ptr + size, bytecount - size) != 0) {
 169                         err = -EFAULT;
 170                         goto error_return;
 171                 }
 172         }
 173         return bytecount;
 174 error_return:
 175         return err;
 176 }
 177
 178 static int read_default_ldt(void __user *ptr, unsigned long bytecount)
 179 {
 180         /* CHECKME: Can we use _one_ random number ? */
 181 #ifdef CONFIG_X86_32
 182         unsigned long size = 5 * sizeof(struct desc_struct);
 183 #else
 184         unsigned long size = 128;
 185 #endif
 186         if (bytecount > size)
 187                 bytecount = size;
 188         if (clear_user(ptr, bytecount))
 189                 return -EFAULT;
 190         return bytecount;
 191 }
 192
 193 static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
 194 {
 195         struct mm_struct *mm = current->mm;
 196         struct desc_struct ldt;
 197         int error;
 198         struct user_desc ldt_info;
 199
 200         error = -EINVAL;
 201         if (bytecount != sizeof(ldt_info))
 202                 goto out;
 203         error = -EFAULT;
 204         if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
 205                 goto out;
 206
 207         error = -EINVAL;
 208         if (ldt_info.entry_number >= LDT_ENTRIES)
 209                 goto out;
 210         if (ldt_info.contents == 3) {
 211                 if (oldmode)
 212                         goto out;
 213                 if (ldt_info.seg_not_present == 0)
 214                         goto out;
 215         }
 216
 217         mutex_lock(&mm->context.lock);
 218         if (ldt_info.entry_number >= mm->context.size) {
 219                 error = alloc_ldt(&current->mm->context,
 220                                   ldt_info.entry_number + 1, 1);
 221                 if (error < 0)
 222                         goto out_unlock;
 223         }
 224
 225         /* Allow LDTs to be cleared by the user. */
 226         if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
 227                 if (oldmode || LDT_empty(&ldt_info)) {
 228                         memset(&ldt, 0, sizeof(ldt));
 229                         goto install;
 230                 }
 231         }
 232
 233         fill_ldt(&ldt, &ldt_info);
 234         if (oldmode)
 235                 ldt.avl = 0;
 236
 237         /* Install the new entry ...  */
 238 install:
 239         write_ldt_entry(mm->context.ldt, ldt_info.entry_number, &ldt);
 240         error = 0;
 241
 242 out_unlock:
 243         mutex_unlock(&mm->context.lock);
 244 out:
 245         return error;
 246 }
 247
 248 asmlinkage int sys_modify_ldt(int func, void __user *ptr,
 249                               unsigned long bytecount)
 250 {
 251         int ret = -ENOSYS;
 252
 253         switch (func) {
 254         case 0:
 255                 ret = read_ldt(ptr, bytecount);
 256                 break;
 257         case 1:
 258                 ret = write_ldt(ptr, bytecount, 1);
 259                 break;
 260         case 2:
 261                 ret = read_default_ldt(ptr, bytecount);
 262                 break;
 263         case 0x11:
 264                 ret = write_ldt(ptr, bytecount, 0);
 265                 break;
 266         }
 267         return ret;
 268 }