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 #include <asm/mmu_context.h>
  22
  23 #ifdef CONFIG_SMP /* avoids "defined but not used" warnig */
  24 static void flush_ldt(void *null)
  25 {
  26         if (current->active_mm)
  27                 load_LDT(&current->active_mm->context);
  28 }
  29 #endif
  30
  31 static int alloc_ldt(mm_context_t *pc, int mincount, int reload)
  32 {
  33         void *oldldt;
  34         void *newldt;
  35         int oldsize;
  36
  37         if (mincount <= pc->size)
  38                 return 0;
  39         oldsize = pc->size;
  40         mincount = (mincount+511)&(~511);
  41         if (mincount*LDT_ENTRY_SIZE > PAGE_SIZE)
  42                 newldt = vmalloc(mincount*LDT_ENTRY_SIZE);
  43         else
  44                 newldt = kmalloc(mincount*LDT_ENTRY_SIZE, GFP_KERNEL);
  45
  46         if (!newldt)
  47                 return -ENOMEM;
  48
  49         if (oldsize)
  50                 memcpy(newldt, pc->ldt, oldsize*LDT_ENTRY_SIZE);
  51         oldldt = pc->ldt;
  52         memset(newldt+oldsize*LDT_ENTRY_SIZE, 0, (mincount-oldsize)*LDT_ENTRY_SIZE);
  53         pc->ldt = newldt;
  54         wmb();
  55         pc->size = mincount;
  56         wmb();
  57
  58         if (reload) {
  59 #ifdef CONFIG_SMP
  60                 cpumask_t mask;
  61                 preempt_disable();
  62                 load_LDT(pc);
  63                 mask = cpumask_of_cpu(smp_processor_id());
  64                 if (!cpus_equal(current->mm->cpu_vm_mask, mask))
  65                         smp_call_function(flush_ldt, NULL, 1, 1);
  66                 preempt_enable();
  67 #else
  68                 load_LDT(pc);
  69 #endif
  70         }
  71         if (oldsize) {
  72                 if (oldsize*LDT_ENTRY_SIZE > PAGE_SIZE)
  73                         vfree(oldldt);
  74                 else
  75                         kfree(oldldt);
  76         }
  77         return 0;
  78 }
  79
  80 static inline int copy_ldt(mm_context_t *new, mm_context_t *old)
  81 {
  82         int err = alloc_ldt(new, old->size, 0);
  83         if (err < 0)
  84                 return err;
  85         memcpy(new->ldt, old->ldt, old->size*LDT_ENTRY_SIZE);
  86         return 0;
  87 }
  88
  89 /*
  90  * we do not have to muck with descriptors here, that is
  91  * done in switch_mm() as needed.
  92  */
  93 int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
  94 {
  95         struct mm_struct * old_mm;
  96         int retval = 0;
  97
  98         init_MUTEX(&mm->context.sem);
  99         mm->context.size = 0;
 100         old_mm = current->mm;
 101         if (old_mm && old_mm->context.size > 0) {
 102                 down(&old_mm->context.sem);
 103                 retval = copy_ldt(&mm->context, &old_mm->context);
 104                 up(&old_mm->context.sem);
 105         }
 106         return retval;
 107 }
 108
 109 /*
 110  * No need to lock the MM as we are the last user
 111  */
 112 void destroy_context(struct mm_struct *mm)
 113 {
 114         if (mm->context.size) {
 115                 if (mm == current->active_mm)
 116                         clear_LDT();
 117                 if (mm->context.size*LDT_ENTRY_SIZE > PAGE_SIZE)
 118                         vfree(mm->context.ldt);
 119                 else
 120                         kfree(mm->context.ldt);
 121                 mm->context.size = 0;
 122         }
 123 }
 124
 125 static int read_ldt(void __user * ptr, unsigned long bytecount)
 126 {
 127         int err;
 128         unsigned long size;
 129         struct mm_struct * mm = current->mm;
 130
 131         if (!mm->context.size)
 132                 return 0;
 133         if (bytecount > LDT_ENTRY_SIZE*LDT_ENTRIES)
 134                 bytecount = LDT_ENTRY_SIZE*LDT_ENTRIES;
 135
 136         down(&mm->context.sem);
 137         size = mm->context.size*LDT_ENTRY_SIZE;
 138         if (size > bytecount)
 139                 size = bytecount;
 140
 141         err = 0;
 142         if (copy_to_user(ptr, mm->context.ldt, size))
 143                 err = -EFAULT;
 144         up(&mm->context.sem);
 145         if (err < 0)
 146                 goto error_return;
 147         if (size != bytecount) {
 148                 /* zero-fill the rest */
 149                 if (clear_user(ptr+size, bytecount-size) != 0) {
 150                         err = -EFAULT;
 151                         goto error_return;
 152                 }
 153         }
 154         return bytecount;
 155 error_return:
 156         return err;
 157 }
 158
 159 static int read_default_ldt(void __user * ptr, unsigned long bytecount)
 160 {
 161         int err;
 162         unsigned long size;
 163         void *address;
 164
 165         err = 0;
 166         address = &default_ldt[0];
 167         size = 5*sizeof(struct desc_struct);
 168         if (size > bytecount)
 169                 size = bytecount;
 170
 171         err = size;
 172         if (copy_to_user(ptr, address, size))
 173                 err = -EFAULT;
 174
 175         return err;
 176 }
 177
 178 static int write_ldt(void __user * ptr, unsigned long bytecount, int oldmode)
 179 {
 180         struct mm_struct * mm = current->mm;
 181         __u32 entry_1, entry_2;
 182         int error;
 183         struct user_desc ldt_info;
 184
 185         error = -EINVAL;
 186         if (bytecount != sizeof(ldt_info))
 187                 goto out;
 188         error = -EFAULT;
 189         if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
 190                 goto out;
 191
 192         error = -EINVAL;
 193         if (ldt_info.entry_number >= LDT_ENTRIES)
 194                 goto out;
 195         if (ldt_info.contents == 3) {
 196                 if (oldmode)
 197                         goto out;
 198                 if (ldt_info.seg_not_present == 0)
 199                         goto out;
 200         }
 201
 202         down(&mm->context.sem);
 203         if (ldt_info.entry_number >= mm->context.size) {
 204                 error = alloc_ldt(&current->mm->context, ldt_info.entry_number+1, 1);
 205                 if (error < 0)
 206                         goto out_unlock;
 207         }
 208
 209         /* Allow LDTs to be cleared by the user. */
 210         if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
 211                 if (oldmode || LDT_empty(&ldt_info)) {
 212                         entry_1 = 0;
 213                         entry_2 = 0;
 214                         goto install;
 215                 }
 216         }
 217
 218         entry_1 = LDT_entry_a(&ldt_info);
 219         entry_2 = LDT_entry_b(&ldt_info);
 220         if (oldmode)
 221                 entry_2 &= ~(1 << 20);
 222
 223         /* Install the new entry ...  */
 224 install:
 225         write_ldt_entry(mm->context.ldt, ldt_info.entry_number, entry_1, entry_2);
 226         error = 0;
 227
 228 out_unlock:
 229         up(&mm->context.sem);
 230 out:
 231         return error;
 232 }
 233
 234 asmlinkage int sys_modify_ldt(int func, void __user *ptr, unsigned long bytecount)
 235 {
 236         int ret = -ENOSYS;
 237
 238         switch (func) {
 239         case 0:
 240                 ret = read_ldt(ptr, bytecount);
 241                 break;
 242         case 1:
 243                 ret = write_ldt(ptr, bytecount, 1);
 244                 break;
 245         case 2:
 246                 ret = read_default_ldt(ptr, bytecount);
 247                 break;
 248         case 0x11:
 249                 ret = write_ldt(ptr, bytecount, 0);
 250                 break;
 251         }
 252         return ret;
 253 }