| 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 = ¤t->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(int size) |
| 38 | { |
| 39 | struct ldt_struct *new_ldt; |
| 40 | 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(¤t_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(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 desc_struct ldt; |
| 211 | int error; |
| 212 | struct user_desc ldt_info; |
| 213 | int oldsize, newsize; |
| 214 | struct ldt_struct *new_ldt, *old_ldt; |
| 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((int)(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 | } |