arch/i386/kernel/ldt.c

   1 /*
   2  * linux/kernel/ldt.c
   3  *
   4  * Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
   5  * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
   6  */
   7
   8 #include <linux/errno.h>
   9 #include <linux/sched.h>
  10 #include <linux/string.h>
  11 #include <linux/mm.h>
  12 #include <linux/smp.h>
  13 #include <linux/smp_lock.h>
  14 #include <linux/vmalloc.h>
  15 #include <linux/slab.h>
  16
  17 #include <asm/uaccess.h>
  18 #include <asm/system.h>
  19 #include <asm/ldt.h>
  20 #include <asm/desc.h>
  21
  22 #ifdef CONFIG_SMP /* avoids "defined but not used" warnig */
  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;
  33         void *newldt;
  34         int oldsize;
  35
  36         if (mincount <= pc->size)
  37                 return 0;
  38         oldsize = pc->size;
  39         mincount = (mincount+511)&(~511);
  40         if (mincount*LDT_ENTRY_SIZE > PAGE_SIZE)
  41                 newldt = vmalloc(mincount*LDT_ENTRY_SIZE);
  42         else
  43                 newldt = kmalloc(mincount*LDT_ENTRY_SIZE, 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, (mincount-oldsize)*LDT_ENTRY_SIZE);
  52         pc->ldt = newldt;
  53         wmb();
  54         pc->size = mincount;
  55         wmb();
  56
  57         if (reload) {
  58 #ifdef CONFIG_SMP
  59                 cpumask_t mask;
  60                 preempt_disable();
  61                 load_LDT(pc);
  62                 mask = cpumask_of_cpu(smp_processor_id());
  63                 if (!cpus_equal(current->mm->cpu_vm_mask, mask))
  64                         smp_call_function(flush_ldt, NULL, 1, 1);
  65                 preempt_enable();
  66 #else
  67                 load_LDT(pc);
  68 #endif
  69         }
  70         if (oldsize) {
  71                 if (oldsize*LDT_ENTRY_SIZE > PAGE_SIZE)
  72                         vfree(oldldt);
  73                 else
  74                         kfree(oldldt);
  75         }
  76         return 0;
  77 }
  78
  79 static inline int copy_ldt(mm_context_t *new, mm_context_t *old)
  80 {
  81         int err = alloc_ldt(new, old->size, 0);
  82         if (err < 0)
  83                 return err;
  84         memcpy(new->ldt, old->ldt, old->size*LDT_ENTRY_SIZE);
  85         return 0;
  86 }
  87
  88 /*
  89  * we do not have to muck with descriptors here, that is
  90  * done in switch_mm() as needed.
  91  */
  92 int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
  93 {
  94         struct mm_struct * old_mm;
  95         int retval = 0;
  96
  97         init_MUTEX(&mm->context.sem);
  98         mm->context.size = 0;
  99         old_mm = current->mm;
 100         if (old_mm && old_mm->context.size > 0) {
 101                 down(&old_mm->context.sem);
 102                 retval = copy_ldt(&mm->context, &old_mm->context);
 103                 up(&old_mm->context.sem);
 104         }
 105         return retval;
 106 }
 107
 108 /*
 109  * No need to lock the MM as we are the last user
 110  */
 111 void destroy_context(struct mm_struct *mm)
 112 {
 113         if (mm->context.size) {
 114                 if (mm == current->active_mm)
 115                         clear_LDT();
 116                 if (mm->context.size*LDT_ENTRY_SIZE > PAGE_SIZE)
 117                         vfree(mm->context.ldt);
 118                 else
 119                         kfree(mm->context.ldt);
 120                 mm->context.size = 0;
 121         }
 122 }
 123
 124 static int read_ldt(void __user * ptr, unsigned long bytecount)
 125 {
 126         int err;
 127         unsigned long size;
 128         struct mm_struct * mm = current->mm;
 129
 130         if (!mm->context.size)
 131                 return 0;
 132         if (bytecount > LDT_ENTRY_SIZE*LDT_ENTRIES)
 133                 bytecount = LDT_ENTRY_SIZE*LDT_ENTRIES;
 134
 135         down(&mm->context.sem);
 136         size = mm->context.size*LDT_ENTRY_SIZE;
 137         if (size > bytecount)
 138                 size = bytecount;
 139
 140         err = 0;
 141         if (copy_to_user(ptr, mm->context.ldt, size))
 142                 err = -EFAULT;
 143         up(&mm->context.sem);
 144         if (err < 0)
 145                 goto error_return;
 146         if (size != bytecount) {
 147                 /* zero-fill the rest */
 148                 if (clear_user(ptr+size, bytecount-size) != 0) {
 149                         err = -EFAULT;
 150                         goto error_return;
 151                 }
 152         }
 153         return bytecount;
 154 error_return:
 155         return err;
 156 }
 157
 158 static int read_default_ldt(void __user * ptr, unsigned long bytecount)
 159 {
 160         int err;
 161         unsigned long size;
 162         void *address;
 163
 164         err = 0;
 165         address = &default_ldt[0];
 166         size = 5*sizeof(struct desc_struct);
 167         if (size > bytecount)
 168                 size = bytecount;
 169
 170         err = size;
 171         if (copy_to_user(ptr, address, size))
 172                 err = -EFAULT;
 173
 174         return err;
 175 }
 176
 177 static int write_ldt(void __user * ptr, unsigned long bytecount, int oldmode)
 178 {
 179         struct mm_struct * mm = current->mm;
 180         __u32 entry_1, entry_2, *lp;
 181         int error;
 182         struct user_desc ldt_info;
 183
 184         error = -EINVAL;
 185         if (bytecount != sizeof(ldt_info))
 186                 goto out;
 187         error = -EFAULT;
 188         if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
 189                 goto out;
 190
 191         error = -EINVAL;
 192         if (ldt_info.entry_number >= LDT_ENTRIES)
 193                 goto out;
 194         if (ldt_info.contents == 3) {
 195                 if (oldmode)
 196                         goto out;
 197                 if (ldt_info.seg_not_present == 0)
 198                         goto out;
 199         }
 200
 201         down(&mm->context.sem);
 202         if (ldt_info.entry_number >= mm->context.size) {
 203                 error = alloc_ldt(&current->mm->context, ldt_info.entry_number+1, 1);
 204                 if (error < 0)
 205                         goto out_unlock;
 206         }
 207
 208         lp = (__u32 *) ((ldt_info.entry_number << 3) + (char *) mm->context.ldt);
 209
 210         /* Allow LDTs to be cleared by the user. */
 211         if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
 212                 if (oldmode || LDT_empty(&ldt_info)) {
 213                         entry_1 = 0;
 214                         entry_2 = 0;
 215                         goto install;
 216                 }
 217         }
 218
 219         entry_1 = LDT_entry_a(&ldt_info);
 220         entry_2 = LDT_entry_b(&ldt_info);
 221         if (oldmode)
 222                 entry_2 &= ~(1 << 20);
 223
 224         /* Install the new entry ...  */
 225 install:
 226         *lp     = entry_1;
 227         *(lp+1) = entry_2;
 228         error = 0;
 229
 230 out_unlock:
 231         up(&mm->context.sem);
 232 out:
 233         return error;
 234 }
 235
 236 asmlinkage int sys_modify_ldt(int func, void __user *ptr, unsigned long bytecount)
 237 {
 238         int ret = -ENOSYS;
 239
 240         switch (func) {
 241         case 0:
 242                 ret = read_ldt(ptr, bytecount);
 243                 break;
 244         case 1:
 245                 ret = write_ldt(ptr, bytecount, 1);
 246                 break;
 247         case 2:
 248                 ret = read_default_ldt(ptr, bytecount);
 249                 break;
 250         case 0x11:
 251                 ret = write_ldt(ptr, bytecount, 0);
 252                 break;
 253         }
 254         return ret;
 255 }