arch/x86_64/kernel/ldt.c

   1 /*
   2  * linux/arch/x86_64/kernel/ldt.c
   3  *
   4  * Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
   5  * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
   6  * Copyright (C) 2002 Andi Kleen
   7  *
   8  * This handles calls from both 32bit and 64bit mode.
   9  */
  10
  11 #include <linux/errno.h>
  12 #include <linux/sched.h>
  13 #include <linux/string.h>
  14 #include <linux/mm.h>
  15 #include <linux/smp.h>
  16 #include <linux/smp_lock.h>
  17 #include <linux/vmalloc.h>
  18 #include <linux/slab.h>
  19
  20 #include <asm/uaccess.h>
  21 #include <asm/system.h>
  22 #include <asm/ldt.h>
  23 #include <asm/desc.h>
  24 #include <asm/proto.h>
  25
  26 #ifdef CONFIG_SMP /* avoids "defined but not used" warnig */
  27 static void flush_ldt(void *null)
  28 {
  29         if (current->active_mm)
  30                load_LDT(&current->active_mm->context);
  31 }
  32 #endif
  33
  34 static int alloc_ldt(mm_context_t *pc, unsigned mincount, int reload)
  35 {
  36         void *oldldt;
  37         void *newldt;
  38         unsigned oldsize;
  39
  40         if (mincount <= (unsigned)pc->size)
  41                 return 0;
  42         oldsize = pc->size;
  43         mincount = (mincount+511)&(~511);
  44         if (mincount*LDT_ENTRY_SIZE > PAGE_SIZE)
  45                 newldt = vmalloc(mincount*LDT_ENTRY_SIZE);
  46         else
  47                 newldt = kmalloc(mincount*LDT_ENTRY_SIZE, GFP_KERNEL);
  48
  49         if (!newldt)
  50                 return -ENOMEM;
  51
  52         if (oldsize)
  53                 memcpy(newldt, pc->ldt, oldsize*LDT_ENTRY_SIZE);
  54         oldldt = pc->ldt;
  55         memset(newldt+oldsize*LDT_ENTRY_SIZE, 0, (mincount-oldsize)*LDT_ENTRY_SIZE);
  56         wmb();
  57         pc->ldt = newldt;
  58         wmb();
  59         pc->size = mincount;
  60         wmb();
  61         if (reload) {
  62 #ifdef CONFIG_SMP
  63                 cpumask_t mask;
  64
  65                 preempt_disable();
  66                 mask = cpumask_of_cpu(smp_processor_id());
  67                 load_LDT(pc);
  68                 if (!cpus_equal(current->mm->cpu_vm_mask, mask))
  69                         smp_call_function(flush_ldt, NULL, 1, 1);
  70                 preempt_enable();
  71 #else
  72                 load_LDT(pc);
  73 #endif
  74         }
  75         if (oldsize) {
  76                 if (oldsize*LDT_ENTRY_SIZE > PAGE_SIZE)
  77                         vfree(oldldt);
  78                 else
  79                         kfree(oldldt);
  80         }
  81         return 0;
  82 }
  83
  84 static inline int copy_ldt(mm_context_t *new, mm_context_t *old)
  85 {
  86         int err = alloc_ldt(new, old->size, 0);
  87         if (err < 0)
  88                 return err;
  89         memcpy(new->ldt, old->ldt, old->size*LDT_ENTRY_SIZE);
  90         return 0;
  91 }
  92
  93 /*
  94  * we do not have to muck with descriptors here, that is
  95  * done in switch_mm() as needed.
  96  */
  97 int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
  98 {
  99         struct mm_struct * old_mm;
 100         int retval = 0;
 101
 102         init_MUTEX(&mm->context.sem);
 103         mm->context.size = 0;
 104         old_mm = current->mm;
 105         if (old_mm && old_mm->context.size > 0) {
 106                 down(&old_mm->context.sem);
 107                 retval = copy_ldt(&mm->context, &old_mm->context);
 108                 up(&old_mm->context.sem);
 109         }
 110         return retval;
 111 }
 112
 113 /*
 114  *
 115  * Don't touch the LDT register - we're already in the next thread.
 116  */
 117 void destroy_context(struct mm_struct *mm)
 118 {
 119         if (mm->context.size) {
 120                 if ((unsigned)mm->context.size*LDT_ENTRY_SIZE > PAGE_SIZE)
 121                         vfree(mm->context.ldt);
 122                 else
 123                         kfree(mm->context.ldt);
 124                 mm->context.size = 0;
 125         }
 126 }
 127
 128 static int read_ldt(void __user * ptr, unsigned long bytecount)
 129 {
 130         int err;
 131         unsigned long size;
 132         struct mm_struct * mm = current->mm;
 133
 134         if (!mm->context.size)
 135                 return 0;
 136         if (bytecount > LDT_ENTRY_SIZE*LDT_ENTRIES)
 137                 bytecount = LDT_ENTRY_SIZE*LDT_ENTRIES;
 138
 139         down(&mm->context.sem);
 140         size = mm->context.size*LDT_ENTRY_SIZE;
 141         if (size > bytecount)
 142                 size = bytecount;
 143
 144         err = 0;
 145         if (copy_to_user(ptr, mm->context.ldt, size))
 146                 err = -EFAULT;
 147         up(&mm->context.sem);
 148         if (err < 0)
 149                 goto error_return;
 150         if (size != bytecount) {
 151                 /* zero-fill the rest */
 152                 if (clear_user(ptr+size, bytecount-size) != 0) {
 153                         err = -EFAULT;
 154                         goto error_return;
 155                 }
 156         }
 157         return bytecount;
 158 error_return:
 159         return err;
 160 }
 161
 162 static int read_default_ldt(void __user * ptr, unsigned long bytecount)
 163 {
 164         /* Arbitrary number */
 165         /* x86-64 default LDT is all zeros */
 166         if (bytecount > 128)
 167                 bytecount = 128;
 168         if (clear_user(ptr, bytecount))
 169                 return -EFAULT;
 170         return bytecount;
 171 }
 172
 173 static int write_ldt(void __user * ptr, unsigned long bytecount, int oldmode)
 174 {
 175         struct task_struct *me = current;
 176         struct mm_struct * mm = me->mm;
 177         __u32 entry_1, entry_2, *lp;
 178         int error;
 179         struct user_desc ldt_info;
 180
 181         error = -EINVAL;
 182
 183         if (bytecount != sizeof(ldt_info))
 184                 goto out;
 185         error = -EFAULT;
 186         if (copy_from_user(&ldt_info, ptr, bytecount))
 187                 goto out;
 188
 189         error = -EINVAL;
 190         if (ldt_info.entry_number >= LDT_ENTRIES)
 191                 goto out;
 192         if (ldt_info.contents == 3) {
 193                 if (oldmode)
 194                         goto out;
 195                 if (ldt_info.seg_not_present == 0)
 196                         goto out;
 197         }
 198
 199         down(&mm->context.sem);
 200         if (ldt_info.entry_number >= (unsigned)mm->context.size) {
 201                 error = alloc_ldt(&current->mm->context, ldt_info.entry_number+1, 1);
 202                 if (error < 0)
 203                         goto out_unlock;
 204         }
 205
 206         lp = (__u32 *) ((ldt_info.entry_number << 3) + (char *) mm->context.ldt);
 207
 208         /* Allow LDTs to be cleared by the user. */
 209         if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
 210                 if (oldmode || LDT_empty(&ldt_info)) {
 211                         entry_1 = 0;
 212                         entry_2 = 0;
 213                         goto install;
 214                 }
 215         }
 216
 217         entry_1 = LDT_entry_a(&ldt_info);
 218         entry_2 = LDT_entry_b(&ldt_info);
 219         if (oldmode)
 220                 entry_2 &= ~(1 << 20);
 221
 222         /* Install the new entry ...  */
 223 install:
 224         *lp     = entry_1;
 225         *(lp+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 }