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 + 511) & (~511);
  39         if (mincount * LDT_ENTRY_SIZE > PAGE_SIZE)
  40                 newldt = vmalloc(mincount * LDT_ENTRY_SIZE);
  41         else
  42                 newldt = (void *)__get_free_page(GFP_KERNEL);
  43
  44         if (!newldt)
  45                 return -ENOMEM;
  46
  47         if (oldsize)
  48                 memcpy(newldt, pc->ldt, oldsize * LDT_ENTRY_SIZE);
  49         oldldt = pc->ldt;
  50         memset(newldt + oldsize * LDT_ENTRY_SIZE, 0,
  51                (mincount - oldsize) * LDT_ENTRY_SIZE);
  52
  53 #ifdef CONFIG_X86_64
  54         /* CHECKME: Do we really need this ? */
  55         wmb();
  56 #endif
  57         pc->ldt = newldt;
  58         wmb();
  59         pc->size = mincount;
  60         wmb();
  61
  62         if (reload) {
  63 #ifdef CONFIG_SMP
  64                 cpumask_t mask;
  65
  66                 preempt_disable();
  67                 load_LDT(pc);
  68                 mask = cpumask_of_cpu(smp_processor_id());
  69                 if (!cpus_equal(current->mm->cpu_vm_mask, mask))
  70                         smp_call_function(flush_ldt, NULL, 1, 1);
  71                 preempt_enable();
  72 #else
  73                 load_LDT(pc);
  74 #endif
  75         }
  76         if (oldsize) {
  77                 if (oldsize * LDT_ENTRY_SIZE > PAGE_SIZE)
  78                         vfree(oldldt);
  79                 else
  80                         put_page(virt_to_page(oldldt));
  81         }
  82         return 0;
  83 }
  84
  85 static inline int copy_ldt(mm_context_t *new, mm_context_t *old)
  86 {
  87         int err = alloc_ldt(new, old->size, 0);
  88
  89         if (err < 0)
  90                 return err;
  91         memcpy(new->ldt, old->ldt, old->size * LDT_ENTRY_SIZE);
  92         return 0;
  93 }
  94
  95 /*
  96  * we do not have to muck with descriptors here, that is
  97  * done in switch_mm() as needed.
  98  */
  99 int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
 100 {
 101         struct mm_struct *old_mm;
 102         int retval = 0;
 103
 104         mutex_init(&mm->context.lock);
 105         mm->context.size = 0;
 106         old_mm = current->mm;
 107         if (old_mm && old_mm->context.size > 0) {
 108                 mutex_lock(&old_mm->context.lock);
 109                 retval = copy_ldt(&mm->context, &old_mm->context);
 110                 mutex_unlock(&old_mm->context.lock);
 111         }
 112         return retval;
 113 }
 114
 115 /*
 116  * No need to lock the MM as we are the last user
 117  *
 118  * 64bit: Don't touch the LDT register - we're already in the next thread.
 119  */
 120 void destroy_context(struct mm_struct *mm)
 121 {
 122         if (mm->context.size) {
 123 #ifdef CONFIG_X86_32
 124                 /* CHECKME: Can this ever happen ? */
 125                 if (mm == current->active_mm)
 126                         clear_LDT();
 127 #endif
 128                 if (mm->context.size * LDT_ENTRY_SIZE > PAGE_SIZE)
 129                         vfree(mm->context.ldt);
 130                 else
 131                         put_page(virt_to_page(mm->context.ldt));
 132                 mm->context.size = 0;
 133         }
 134 }
 135
 136 static int read_ldt(void __user *ptr, unsigned long bytecount)
 137 {
 138         int err;
 139         unsigned long size;
 140         struct mm_struct *mm = current->mm;
 141
 142         if (!mm->context.size)
 143                 return 0;
 144         if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
 145                 bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
 146
 147         mutex_lock(&mm->context.lock);
 148         size = mm->context.size * LDT_ENTRY_SIZE;
 149         if (size > bytecount)
 150                 size = bytecount;
 151
 152         err = 0;
 153         if (copy_to_user(ptr, mm->context.ldt, size))
 154                 err = -EFAULT;
 155         mutex_unlock(&mm->context.lock);
 156         if (err < 0)
 157                 goto error_return;
 158         if (size != bytecount) {
 159                 /* zero-fill the rest */
 160                 if (clear_user(ptr + size, bytecount - size) != 0) {
 161                         err = -EFAULT;
 162                         goto error_return;
 163                 }
 164         }
 165         return bytecount;
 166 error_return:
 167         return err;
 168 }
 169
 170 static int read_default_ldt(void __user *ptr, unsigned long bytecount)
 171 {
 172         /* CHECKME: Can we use _one_ random number ? */
 173 #ifdef CONFIG_X86_32
 174         unsigned long size = 5 * sizeof(struct desc_struct);
 175 #else
 176         unsigned long size = 128;
 177 #endif
 178         if (bytecount > size)
 179                 bytecount = size;
 180         if (clear_user(ptr, bytecount))
 181                 return -EFAULT;
 182         return bytecount;
 183 }
 184
 185 static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
 186 {
 187         struct mm_struct *mm = current->mm;
 188         struct desc_struct ldt;
 189         int error;
 190         struct user_desc ldt_info;
 191
 192         error = -EINVAL;
 193         if (bytecount != sizeof(ldt_info))
 194                 goto out;
 195         error = -EFAULT;
 196         if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
 197                 goto out;
 198
 199         error = -EINVAL;
 200         if (ldt_info.entry_number >= LDT_ENTRIES)
 201                 goto out;
 202         if (ldt_info.contents == 3) {
 203                 if (oldmode)
 204                         goto out;
 205                 if (ldt_info.seg_not_present == 0)
 206                         goto out;
 207         }
 208
 209         mutex_lock(&mm->context.lock);
 210         if (ldt_info.entry_number >= mm->context.size) {
 211                 error = alloc_ldt(&current->mm->context,
 212                                   ldt_info.entry_number + 1, 1);
 213                 if (error < 0)
 214                         goto out_unlock;
 215         }
 216
 217         /* Allow LDTs to be cleared by the user. */
 218         if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
 219                 if (oldmode || LDT_empty(&ldt_info)) {
 220                         memset(&ldt, 0, sizeof(ldt));
 221                         goto install;
 222                 }
 223         }
 224
 225         fill_ldt(&ldt, &ldt_info);
 226         if (oldmode)
 227                 ldt.avl = 0;
 228
 229         /* Install the new entry ...  */
 230 install:
 231         write_ldt_entry(mm->context.ldt, ldt_info.entry_number, &ldt);
 232         error = 0;
 233
 234 out_unlock:
 235         mutex_unlock(&mm->context.lock);
 236 out:
 237         return error;
 238 }
 239
 240 asmlinkage int sys_modify_ldt(int func, void __user *ptr,
 241                               unsigned long bytecount)
 242 {
 243         int ret = -ENOSYS;
 244
 245         switch (func) {
 246         case 0:
 247                 ret = read_ldt(ptr, bytecount);
 248                 break;
 249         case 1:
 250                 ret = write_ldt(ptr, bytecount, 1);
 251                 break;
 252         case 2:
 253                 ret = read_default_ldt(ptr, bytecount);
 254                 break;
 255         case 0x11:
 256                 ret = write_ldt(ptr, bytecount, 0);
 257                 break;
 258         }
 259         return ret;
 260 }