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