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/slab.h>
  16 #include <linux/vmalloc.h>
  17 #include <linux/uaccess.h>
  18
  19 #include <asm/ldt.h>
  20 #include <asm/desc.h>
  21 #include <asm/mmu_context.h>
  22 #include <asm/syscalls.h>
  23
  24 /* context.lock is held for us, so we don't need any locking. */
  25 static void flush_ldt(void *__mm)
  26 {
  27         struct mm_struct *mm = __mm;
  28         mm_context_t *pc;
  29
  30         if (this_cpu_read(cpu_tlbstate.loaded_mm) != mm)
  31                 return;
  32
  33         pc = &mm->context;
  34         set_ldt(pc->ldt->entries, pc->ldt->nr_entries);
  35 }
  36
  37 /* The caller must call finalize_ldt_struct on the result. LDT starts zeroed. */
  38 static struct ldt_struct *alloc_ldt_struct(unsigned int num_entries)
  39 {
  40         struct ldt_struct *new_ldt;
  41         unsigned int alloc_size;
  42
  43         if (num_entries > LDT_ENTRIES)
  44                 return NULL;
  45
  46         new_ldt = kmalloc(sizeof(struct ldt_struct), GFP_KERNEL);
  47         if (!new_ldt)
  48                 return NULL;
  49
  50         BUILD_BUG_ON(LDT_ENTRY_SIZE != sizeof(struct desc_struct));
  51         alloc_size = num_entries * LDT_ENTRY_SIZE;
  52
  53         /*
  54          * Xen is very picky: it requires a page-aligned LDT that has no
  55          * trailing nonzero bytes in any page that contains LDT descriptors.
  56          * Keep it simple: zero the whole allocation and never allocate less
  57          * than PAGE_SIZE.
  58          */
  59         if (alloc_size > PAGE_SIZE)
  60                 new_ldt->entries = vzalloc(alloc_size);
  61         else
  62                 new_ldt->entries = (void *)get_zeroed_page(GFP_KERNEL);
  63
  64         if (!new_ldt->entries) {
  65                 kfree(new_ldt);
  66                 return NULL;
  67         }
  68
  69         new_ldt->nr_entries = num_entries;
  70         return new_ldt;
  71 }
  72
  73 /* After calling this, the LDT is immutable. */
  74 static void finalize_ldt_struct(struct ldt_struct *ldt)
  75 {
  76         paravirt_alloc_ldt(ldt->entries, ldt->nr_entries);
  77 }
  78
  79 /* context.lock is held */
  80 static void install_ldt(struct mm_struct *current_mm,
  81                         struct ldt_struct *ldt)
  82 {
  83         /* Synchronizes with lockless_dereference in load_mm_ldt. */
  84         smp_store_release(&current_mm->context.ldt, ldt);
  85
  86         /* Activate the LDT for all CPUs using current_mm. */
  87         on_each_cpu_mask(mm_cpumask(current_mm), flush_ldt, current_mm, true);
  88 }
  89
  90 static void free_ldt_struct(struct ldt_struct *ldt)
  91 {
  92         if (likely(!ldt))
  93                 return;
  94
  95         paravirt_free_ldt(ldt->entries, ldt->nr_entries);
  96         if (ldt->nr_entries * LDT_ENTRY_SIZE > PAGE_SIZE)
  97                 vfree_atomic(ldt->entries);
  98         else
  99                 free_page((unsigned long)ldt->entries);
 100         kfree(ldt);
 101 }
 102
 103 /*
 104  * we do not have to muck with descriptors here, that is
 105  * done in switch_mm() as needed.
 106  */
 107 int init_new_context_ldt(struct task_struct *tsk, struct mm_struct *mm)
 108 {
 109         struct ldt_struct *new_ldt;
 110         struct mm_struct *old_mm;
 111         int retval = 0;
 112
 113         mutex_init(&mm->context.lock);
 114         old_mm = current->mm;
 115         if (!old_mm) {
 116                 mm->context.ldt = NULL;
 117                 return 0;
 118         }
 119
 120         mutex_lock(&old_mm->context.lock);
 121         if (!old_mm->context.ldt) {
 122                 mm->context.ldt = NULL;
 123                 goto out_unlock;
 124         }
 125
 126         new_ldt = alloc_ldt_struct(old_mm->context.ldt->nr_entries);
 127         if (!new_ldt) {
 128                 retval = -ENOMEM;
 129                 goto out_unlock;
 130         }
 131
 132         memcpy(new_ldt->entries, old_mm->context.ldt->entries,
 133                new_ldt->nr_entries * LDT_ENTRY_SIZE);
 134         finalize_ldt_struct(new_ldt);
 135
 136         mm->context.ldt = new_ldt;
 137
 138 out_unlock:
 139         mutex_unlock(&old_mm->context.lock);
 140         return retval;
 141 }
 142
 143 /*
 144  * No need to lock the MM as we are the last user
 145  *
 146  * 64bit: Don't touch the LDT register - we're already in the next thread.
 147  */
 148 void destroy_context_ldt(struct mm_struct *mm)
 149 {
 150         free_ldt_struct(mm->context.ldt);
 151         mm->context.ldt = NULL;
 152 }
 153
 154 static int read_ldt(void __user *ptr, unsigned long bytecount)
 155 {
 156         struct mm_struct *mm = current->mm;
 157         unsigned long entries_size;
 158         int retval;
 159
 160         mutex_lock(&mm->context.lock);
 161
 162         if (!mm->context.ldt) {
 163                 retval = 0;
 164                 goto out_unlock;
 165         }
 166
 167         if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
 168                 bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
 169
 170         entries_size = mm->context.ldt->nr_entries * LDT_ENTRY_SIZE;
 171         if (entries_size > bytecount)
 172                 entries_size = bytecount;
 173
 174         if (copy_to_user(ptr, mm->context.ldt->entries, entries_size)) {
 175                 retval = -EFAULT;
 176                 goto out_unlock;
 177         }
 178
 179         if (entries_size != bytecount) {
 180                 /* Zero-fill the rest and pretend we read bytecount bytes. */
 181                 if (clear_user(ptr + entries_size, bytecount - entries_size)) {
 182                         retval = -EFAULT;
 183                         goto out_unlock;
 184                 }
 185         }
 186         retval = bytecount;
 187
 188 out_unlock:
 189         mutex_unlock(&mm->context.lock);
 190         return retval;
 191 }
 192
 193 static int read_default_ldt(void __user *ptr, unsigned long bytecount)
 194 {
 195         /* CHECKME: Can we use _one_ random number ? */
 196 #ifdef CONFIG_X86_32
 197         unsigned long size = 5 * sizeof(struct desc_struct);
 198 #else
 199         unsigned long size = 128;
 200 #endif
 201         if (bytecount > size)
 202                 bytecount = size;
 203         if (clear_user(ptr, bytecount))
 204                 return -EFAULT;
 205         return bytecount;
 206 }
 207
 208 static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
 209 {
 210         struct mm_struct *mm = current->mm;
 211         struct ldt_struct *new_ldt, *old_ldt;
 212         unsigned int old_nr_entries, new_nr_entries;
 213         struct user_desc ldt_info;
 214         struct desc_struct ldt;
 215         int error;
 216
 217         error = -EINVAL;
 218         if (bytecount != sizeof(ldt_info))
 219                 goto out;
 220         error = -EFAULT;
 221         if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
 222                 goto out;
 223
 224         error = -EINVAL;
 225         if (ldt_info.entry_number >= LDT_ENTRIES)
 226                 goto out;
 227         if (ldt_info.contents == 3) {
 228                 if (oldmode)
 229                         goto out;
 230                 if (ldt_info.seg_not_present == 0)
 231                         goto out;
 232         }
 233
 234         if ((oldmode && !ldt_info.base_addr && !ldt_info.limit) ||
 235             LDT_empty(&ldt_info)) {
 236                 /* The user wants to clear the entry. */
 237                 memset(&ldt, 0, sizeof(ldt));
 238         } else {
 239                 if (!IS_ENABLED(CONFIG_X86_16BIT) && !ldt_info.seg_32bit) {
 240                         error = -EINVAL;
 241                         goto out;
 242                 }
 243
 244                 fill_ldt(&ldt, &ldt_info);
 245                 if (oldmode)
 246                         ldt.avl = 0;
 247         }
 248
 249         mutex_lock(&mm->context.lock);
 250
 251         old_ldt       = mm->context.ldt;
 252         old_nr_entries = old_ldt ? old_ldt->nr_entries : 0;
 253         new_nr_entries = max(ldt_info.entry_number + 1, old_nr_entries);
 254
 255         error = -ENOMEM;
 256         new_ldt = alloc_ldt_struct(new_nr_entries);
 257         if (!new_ldt)
 258                 goto out_unlock;
 259
 260         if (old_ldt)
 261                 memcpy(new_ldt->entries, old_ldt->entries, old_nr_entries * LDT_ENTRY_SIZE);
 262
 263         new_ldt->entries[ldt_info.entry_number] = ldt;
 264         finalize_ldt_struct(new_ldt);
 265
 266         install_ldt(mm, new_ldt);
 267         free_ldt_struct(old_ldt);
 268         error = 0;
 269
 270 out_unlock:
 271         mutex_unlock(&mm->context.lock);
 272 out:
 273         return error;
 274 }
 275
 276 asmlinkage int sys_modify_ldt(int func, void __user *ptr,
 277                               unsigned long bytecount)
 278 {
 279         int ret = -ENOSYS;
 280
 281         switch (func) {
 282         case 0:
 283                 ret = read_ldt(ptr, bytecount);
 284                 break;
 285         case 1:
 286                 ret = write_ldt(ptr, bytecount, 1);
 287                 break;
 288         case 2:
 289                 ret = read_default_ldt(ptr, bytecount);
 290                 break;
 291         case 0x11:
 292                 ret = write_ldt(ptr, bytecount, 0);
 293                 break;
 294         }
 295         return ret;
 296 }