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