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 *null)
  24 {
  25         if (current->active_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                 cpumask_t mask;
  66
  67                 preempt_disable();
  68                 load_LDT(pc);
  69                 mask = cpumask_of_cpu(smp_processor_id());
  70                 if (!cpus_equal(current->mm->cpu_vm_mask, mask))
  71                         smp_call_function(flush_ldt, NULL, 1, 1);
  72                 preempt_enable();
  73 #else
  74                 load_LDT(pc);
  75 #endif
  76         }
  77         if (oldsize) {
  78                 if (oldsize * LDT_ENTRY_SIZE > PAGE_SIZE)
  79                         vfree(oldldt);
  80                 else
  81                         put_page(virt_to_page(oldldt));
  82         }
  83         return 0;
  84 }
  85
  86 static inline int copy_ldt(mm_context_t *new, mm_context_t *old)
  87 {
  88         int err = alloc_ldt(new, old->size, 0);
  89
  90         if (err < 0)
  91                 return err;
  92         memcpy(new->ldt, old->ldt, old->size * LDT_ENTRY_SIZE);
  93         return 0;
  94 }
  95
  96 /*
  97  * we do not have to muck with descriptors here, that is
  98  * done in switch_mm() as needed.
  99  */
 100 int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
 101 {
 102         struct mm_struct *old_mm;
 103         int retval = 0;
 104
 105         mutex_init(&mm->context.lock);
 106         mm->context.size = 0;
 107         old_mm = current->mm;
 108         if (old_mm && old_mm->context.size > 0) {
 109                 mutex_lock(&old_mm->context.lock);
 110                 retval = copy_ldt(&mm->context, &old_mm->context);
 111                 mutex_unlock(&old_mm->context.lock);
 112         }
 113         return retval;
 114 }
 115
 116 /*
 117  * No need to lock the MM as we are the last user
 118  *
 119  * 64bit: Don't touch the LDT register - we're already in the next thread.
 120  */
 121 void destroy_context(struct mm_struct *mm)
 122 {
 123         if (mm->context.size) {
 124 #ifdef CONFIG_X86_32
 125                 /* CHECKME: Can this ever happen ? */
 126                 if (mm == current->active_mm)
 127                         clear_LDT();
 128 #endif
 129                 if (mm->context.size * LDT_ENTRY_SIZE > PAGE_SIZE)
 130                         vfree(mm->context.ldt);
 131                 else
 132                         put_page(virt_to_page(mm->context.ldt));
 133                 mm->context.size = 0;
 134         }
 135 }
 136
 137 static int read_ldt(void __user *ptr, unsigned long bytecount)
 138 {
 139         int err;
 140         unsigned long size;
 141         struct mm_struct *mm = current->mm;
 142
 143         if (!mm->context.size)
 144                 return 0;
 145         if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
 146                 bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
 147
 148         mutex_lock(&mm->context.lock);
 149         size = mm->context.size * LDT_ENTRY_SIZE;
 150         if (size > bytecount)
 151                 size = bytecount;
 152
 153         err = 0;
 154         if (copy_to_user(ptr, mm->context.ldt, size))
 155                 err = -EFAULT;
 156         mutex_unlock(&mm->context.lock);
 157         if (err < 0)
 158                 goto error_return;
 159         if (size != bytecount) {
 160                 /* zero-fill the rest */
 161                 if (clear_user(ptr + size, bytecount - size) != 0) {
 162                         err = -EFAULT;
 163                         goto error_return;
 164                 }
 165         }
 166         return bytecount;
 167 error_return:
 168         return err;
 169 }
 170
 171 static int read_default_ldt(void __user *ptr, unsigned long bytecount)
 172 {
 173         /* CHECKME: Can we use _one_ random number ? */
 174 #ifdef CONFIG_X86_32
 175         unsigned long size = 5 * sizeof(struct desc_struct);
 176 #else
 177         unsigned long size = 128;
 178 #endif
 179         if (bytecount > size)
 180                 bytecount = size;
 181         if (clear_user(ptr, bytecount))
 182                 return -EFAULT;
 183         return bytecount;
 184 }
 185
 186 static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
 187 {
 188         struct mm_struct *mm = current->mm;
 189         struct desc_struct ldt;
 190         int error;
 191         struct user_desc ldt_info;
 192
 193         error = -EINVAL;
 194         if (bytecount != sizeof(ldt_info))
 195                 goto out;
 196         error = -EFAULT;
 197         if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
 198                 goto out;
 199
 200         error = -EINVAL;
 201         if (ldt_info.entry_number >= LDT_ENTRIES)
 202                 goto out;
 203         if (ldt_info.contents == 3) {
 204                 if (oldmode)
 205                         goto out;
 206                 if (ldt_info.seg_not_present == 0)
 207                         goto out;
 208         }
 209
 210         mutex_lock(&mm->context.lock);
 211         if (ldt_info.entry_number >= mm->context.size) {
 212                 error = alloc_ldt(&current->mm->context,
 213                                   ldt_info.entry_number + 1, 1);
 214                 if (error < 0)
 215                         goto out_unlock;
 216         }
 217
 218         /* Allow LDTs to be cleared by the user. */
 219         if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
 220                 if (oldmode || LDT_empty(&ldt_info)) {
 221                         memset(&ldt, 0, sizeof(ldt));
 222                         goto install;
 223                 }
 224         }
 225
 226         fill_ldt(&ldt, &ldt_info);
 227         if (oldmode)
 228                 ldt.avl = 0;
 229
 230         /* Install the new entry ...  */
 231 install:
 232         write_ldt_entry(mm->context.ldt, ldt_info.entry_number, &ldt);
 233         error = 0;
 234
 235 out_unlock:
 236         mutex_unlock(&mm->context.lock);
 237 out:
 238         return error;
 239 }
 240
 241 asmlinkage int sys_modify_ldt(int func, void __user *ptr,
 242                               unsigned long bytecount)
 243 {
 244         int ret = -ENOSYS;
 245
 246         switch (func) {
 247         case 0:
 248                 ret = read_ldt(ptr, bytecount);
 249                 break;
 250         case 1:
 251                 ret = write_ldt(ptr, bytecount, 1);
 252                 break;
 253         case 2:
 254                 ret = read_default_ldt(ptr, bytecount);
 255                 break;
 256         case 0x11:
 257                 ret = write_ldt(ptr, bytecount, 0);
 258                 break;
 259         }
 260         return ret;
 261 }