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Linux/arch/x86/kernel/ldt.c

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  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/vmalloc.h>
 16 #include <linux/uaccess.h>
 17 
 18 #include <asm/ldt.h>
 19 #include <asm/desc.h>
 20 #include <asm/mmu_context.h>
 21 #include <asm/syscalls.h>
 22 
 23 #ifdef CONFIG_SMP
 24 static void flush_ldt(void *current_mm)
 25 {
 26         if (current->active_mm == current_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, *newldt;
 34         int oldsize;
 35 
 36         if (mincount <= pc->size)
 37                 return 0;
 38         oldsize = pc->size;
 39         mincount = (mincount + (PAGE_SIZE / LDT_ENTRY_SIZE - 1)) &
 40                         (~(PAGE_SIZE / LDT_ENTRY_SIZE - 1));
 41         if (mincount * LDT_ENTRY_SIZE > PAGE_SIZE)
 42                 newldt = vmalloc(mincount * LDT_ENTRY_SIZE);
 43         else
 44                 newldt = (void *)__get_free_page(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,
 53                (mincount - oldsize) * LDT_ENTRY_SIZE);
 54 
 55         paravirt_alloc_ldt(newldt, mincount);
 56 
 57 #ifdef CONFIG_X86_64
 58         /* CHECKME: Do we really need this ? */
 59         wmb();
 60 #endif
 61         pc->ldt = newldt;
 62         wmb();
 63         pc->size = mincount;
 64         wmb();
 65 
 66         if (reload) {
 67 #ifdef CONFIG_SMP
 68                 preempt_disable();
 69                 load_LDT(pc);
 70                 if (!cpumask_equal(mm_cpumask(current->mm),
 71                                    cpumask_of(smp_processor_id())))
 72                         smp_call_function(flush_ldt, current->mm, 1);
 73                 preempt_enable();
 74 #else
 75                 load_LDT(pc);
 76 #endif
 77         }
 78         if (oldsize) {
 79                 paravirt_free_ldt(oldldt, oldsize);
 80                 if (oldsize * LDT_ENTRY_SIZE > PAGE_SIZE)
 81                         vfree(oldldt);
 82                 else
 83                         put_page(virt_to_page(oldldt));
 84         }
 85         return 0;
 86 }
 87 
 88 static inline int copy_ldt(mm_context_t *new, mm_context_t *old)
 89 {
 90         int err = alloc_ldt(new, old->size, 0);
 91         int i;
 92 
 93         if (err < 0)
 94                 return err;
 95 
 96         for (i = 0; i < old->size; i++)
 97                 write_ldt_entry(new->ldt, i, old->ldt + i * LDT_ENTRY_SIZE);
 98         return 0;
 99 }
100 
101 /*
102  * we do not have to muck with descriptors here, that is
103  * done in switch_mm() as needed.
104  */
105 int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
106 {
107         struct mm_struct *old_mm;
108         int retval = 0;
109 
110         mutex_init(&mm->context.lock);
111         mm->context.size = 0;
112         old_mm = current->mm;
113         if (old_mm && old_mm->context.size > 0) {
114                 mutex_lock(&old_mm->context.lock);
115                 retval = copy_ldt(&mm->context, &old_mm->context);
116                 mutex_unlock(&old_mm->context.lock);
117         }
118         return retval;
119 }
120 
121 /*
122  * No need to lock the MM as we are the last user
123  *
124  * 64bit: Don't touch the LDT register - we're already in the next thread.
125  */
126 void destroy_context(struct mm_struct *mm)
127 {
128         if (mm->context.size) {
129 #ifdef CONFIG_X86_32
130                 /* CHECKME: Can this ever happen ? */
131                 if (mm == current->active_mm)
132                         clear_LDT();
133 #endif
134                 paravirt_free_ldt(mm->context.ldt, mm->context.size);
135                 if (mm->context.size * LDT_ENTRY_SIZE > PAGE_SIZE)
136                         vfree(mm->context.ldt);
137                 else
138                         put_page(virt_to_page(mm->context.ldt));
139                 mm->context.size = 0;
140         }
141 }
142 
143 static int read_ldt(void __user *ptr, unsigned long bytecount)
144 {
145         int err;
146         unsigned long size;
147         struct mm_struct *mm = current->mm;
148 
149         if (!mm->context.size)
150                 return 0;
151         if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
152                 bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
153 
154         mutex_lock(&mm->context.lock);
155         size = mm->context.size * LDT_ENTRY_SIZE;
156         if (size > bytecount)
157                 size = bytecount;
158 
159         err = 0;
160         if (copy_to_user(ptr, mm->context.ldt, size))
161                 err = -EFAULT;
162         mutex_unlock(&mm->context.lock);
163         if (err < 0)
164                 goto error_return;
165         if (size != bytecount) {
166                 /* zero-fill the rest */
167                 if (clear_user(ptr + size, bytecount - size) != 0) {
168                         err = -EFAULT;
169                         goto error_return;
170                 }
171         }
172         return bytecount;
173 error_return:
174         return err;
175 }
176 
177 static int read_default_ldt(void __user *ptr, unsigned long bytecount)
178 {
179         /* CHECKME: Can we use _one_ random number ? */
180 #ifdef CONFIG_X86_32
181         unsigned long size = 5 * sizeof(struct desc_struct);
182 #else
183         unsigned long size = 128;
184 #endif
185         if (bytecount > size)
186                 bytecount = size;
187         if (clear_user(ptr, bytecount))
188                 return -EFAULT;
189         return bytecount;
190 }
191 
192 static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
193 {
194         struct mm_struct *mm = current->mm;
195         struct desc_struct ldt;
196         int error;
197         struct user_desc ldt_info;
198 
199         error = -EINVAL;
200         if (bytecount != sizeof(ldt_info))
201                 goto out;
202         error = -EFAULT;
203         if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
204                 goto out;
205 
206         error = -EINVAL;
207         if (ldt_info.entry_number >= LDT_ENTRIES)
208                 goto out;
209         if (ldt_info.contents == 3) {
210                 if (oldmode)
211                         goto out;
212                 if (ldt_info.seg_not_present == 0)
213                         goto out;
214         }
215 
216         mutex_lock(&mm->context.lock);
217         if (ldt_info.entry_number >= mm->context.size) {
218                 error = alloc_ldt(&current->mm->context,
219                                   ldt_info.entry_number + 1, 1);
220                 if (error < 0)
221                         goto out_unlock;
222         }
223 
224         /* Allow LDTs to be cleared by the user. */
225         if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
226                 if (oldmode || LDT_empty(&ldt_info)) {
227                         memset(&ldt, 0, sizeof(ldt));
228                         goto install;
229                 }
230         }
231 
232         if (!IS_ENABLED(CONFIG_X86_16BIT) && !ldt_info.seg_32bit) {
233                 error = -EINVAL;
234                 goto out_unlock;
235         }
236 
237         fill_ldt(&ldt, &ldt_info);
238         if (oldmode)
239                 ldt.avl = 0;
240 
241         /* Install the new entry ...  */
242 install:
243         write_ldt_entry(mm->context.ldt, ldt_info.entry_number, &ldt);
244         error = 0;
245 
246 out_unlock:
247         mutex_unlock(&mm->context.lock);
248 out:
249         return error;
250 }
251 
252 asmlinkage int sys_modify_ldt(int func, void __user *ptr,
253                               unsigned long bytecount)
254 {
255         int ret = -ENOSYS;
256 
257         switch (func) {
258         case 0:
259                 ret = read_ldt(ptr, bytecount);
260                 break;
261         case 1:
262                 ret = write_ldt(ptr, bytecount, 1);
263                 break;
264         case 2:
265                 ret = read_default_ldt(ptr, bytecount);
266                 break;
267         case 0x11:
268                 ret = write_ldt(ptr, bytecount, 0);
269                 break;
270         }
271         return ret;
272 }
273 

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