| 1 | // SPDX-License-Identifier: GPL-2.0 |
| 2 | /* |
| 3 | * Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds |
| 4 | * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com> |
| 5 | * Copyright (C) 2002 Andi Kleen |
| 6 | * |
| 7 | * This handles calls from both 32bit and 64bit mode. |
| 8 | * |
| 9 | * Lock order: |
| 10 | * contex.ldt_usr_sem |
| 11 | * mmap_lock |
| 12 | * context.lock |
| 13 | */ |
| 14 | |
| 15 | #include <linux/errno.h> |
| 16 | #include <linux/gfp.h> |
| 17 | #include <linux/sched.h> |
| 18 | #include <linux/string.h> |
| 19 | #include <linux/mm.h> |
| 20 | #include <linux/smp.h> |
| 21 | #include <linux/syscalls.h> |
| 22 | #include <linux/slab.h> |
| 23 | #include <linux/vmalloc.h> |
| 24 | #include <linux/uaccess.h> |
| 25 | |
| 26 | #include <asm/ldt.h> |
| 27 | #include <asm/tlb.h> |
| 28 | #include <asm/desc.h> |
| 29 | #include <asm/mmu_context.h> |
| 30 | #include <asm/pgtable_areas.h> |
| 31 | |
| 32 | #include <xen/xen.h> |
| 33 | |
| 34 | /* This is a multiple of PAGE_SIZE. */ |
| 35 | #define LDT_SLOT_STRIDE (LDT_ENTRIES * LDT_ENTRY_SIZE) |
| 36 | |
| 37 | static inline void *ldt_slot_va(int slot) |
| 38 | { |
| 39 | return (void *)(LDT_BASE_ADDR + LDT_SLOT_STRIDE * slot); |
| 40 | } |
| 41 | |
| 42 | void load_mm_ldt(struct mm_struct *mm) |
| 43 | { |
| 44 | struct ldt_struct *ldt; |
| 45 | |
| 46 | /* READ_ONCE synchronizes with smp_store_release */ |
| 47 | ldt = READ_ONCE(mm->context.ldt); |
| 48 | |
| 49 | /* |
| 50 | * Any change to mm->context.ldt is followed by an IPI to all |
| 51 | * CPUs with the mm active. The LDT will not be freed until |
| 52 | * after the IPI is handled by all such CPUs. This means that, |
| 53 | * if the ldt_struct changes before we return, the values we see |
| 54 | * will be safe, and the new values will be loaded before we run |
| 55 | * any user code. |
| 56 | * |
| 57 | * NB: don't try to convert this to use RCU without extreme care. |
| 58 | * We would still need IRQs off, because we don't want to change |
| 59 | * the local LDT after an IPI loaded a newer value than the one |
| 60 | * that we can see. |
| 61 | */ |
| 62 | |
| 63 | if (unlikely(ldt)) { |
| 64 | if (static_cpu_has(X86_FEATURE_PTI)) { |
| 65 | if (WARN_ON_ONCE((unsigned long)ldt->slot > 1)) { |
| 66 | /* |
| 67 | * Whoops -- either the new LDT isn't mapped |
| 68 | * (if slot == -1) or is mapped into a bogus |
| 69 | * slot (if slot > 1). |
| 70 | */ |
| 71 | clear_LDT(); |
| 72 | return; |
| 73 | } |
| 74 | |
| 75 | /* |
| 76 | * If page table isolation is enabled, ldt->entries |
| 77 | * will not be mapped in the userspace pagetables. |
| 78 | * Tell the CPU to access the LDT through the alias |
| 79 | * at ldt_slot_va(ldt->slot). |
| 80 | */ |
| 81 | set_ldt(ldt_slot_va(ldt->slot), ldt->nr_entries); |
| 82 | } else { |
| 83 | set_ldt(ldt->entries, ldt->nr_entries); |
| 84 | } |
| 85 | } else { |
| 86 | clear_LDT(); |
| 87 | } |
| 88 | } |
| 89 | |
| 90 | void switch_ldt(struct mm_struct *prev, struct mm_struct *next) |
| 91 | { |
| 92 | /* |
| 93 | * Load the LDT if either the old or new mm had an LDT. |
| 94 | * |
| 95 | * An mm will never go from having an LDT to not having an LDT. Two |
| 96 | * mms never share an LDT, so we don't gain anything by checking to |
| 97 | * see whether the LDT changed. There's also no guarantee that |
| 98 | * prev->context.ldt actually matches LDTR, but, if LDTR is non-NULL, |
| 99 | * then prev->context.ldt will also be non-NULL. |
| 100 | * |
| 101 | * If we really cared, we could optimize the case where prev == next |
| 102 | * and we're exiting lazy mode. Most of the time, if this happens, |
| 103 | * we don't actually need to reload LDTR, but modify_ldt() is mostly |
| 104 | * used by legacy code and emulators where we don't need this level of |
| 105 | * performance. |
| 106 | * |
| 107 | * This uses | instead of || because it generates better code. |
| 108 | */ |
| 109 | if (unlikely((unsigned long)prev->context.ldt | |
| 110 | (unsigned long)next->context.ldt)) |
| 111 | load_mm_ldt(next); |
| 112 | |
| 113 | DEBUG_LOCKS_WARN_ON(preemptible()); |
| 114 | } |
| 115 | |
| 116 | static void refresh_ldt_segments(void) |
| 117 | { |
| 118 | #ifdef CONFIG_X86_64 |
| 119 | unsigned short sel; |
| 120 | |
| 121 | /* |
| 122 | * Make sure that the cached DS and ES descriptors match the updated |
| 123 | * LDT. |
| 124 | */ |
| 125 | savesegment(ds, sel); |
| 126 | if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT) |
| 127 | loadsegment(ds, sel); |
| 128 | |
| 129 | savesegment(es, sel); |
| 130 | if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT) |
| 131 | loadsegment(es, sel); |
| 132 | #endif |
| 133 | } |
| 134 | |
| 135 | /* context.lock is held by the task which issued the smp function call */ |
| 136 | static void flush_ldt(void *__mm) |
| 137 | { |
| 138 | struct mm_struct *mm = __mm; |
| 139 | |
| 140 | if (this_cpu_read(cpu_tlbstate.loaded_mm) != mm) |
| 141 | return; |
| 142 | |
| 143 | load_mm_ldt(mm); |
| 144 | |
| 145 | refresh_ldt_segments(); |
| 146 | } |
| 147 | |
| 148 | /* The caller must call finalize_ldt_struct on the result. LDT starts zeroed. */ |
| 149 | static struct ldt_struct *alloc_ldt_struct(unsigned int num_entries) |
| 150 | { |
| 151 | struct ldt_struct *new_ldt; |
| 152 | unsigned int alloc_size; |
| 153 | |
| 154 | if (num_entries > LDT_ENTRIES) |
| 155 | return NULL; |
| 156 | |
| 157 | new_ldt = kmalloc(sizeof(struct ldt_struct), GFP_KERNEL_ACCOUNT); |
| 158 | if (!new_ldt) |
| 159 | return NULL; |
| 160 | |
| 161 | BUILD_BUG_ON(LDT_ENTRY_SIZE != sizeof(struct desc_struct)); |
| 162 | alloc_size = num_entries * LDT_ENTRY_SIZE; |
| 163 | |
| 164 | /* |
| 165 | * Xen is very picky: it requires a page-aligned LDT that has no |
| 166 | * trailing nonzero bytes in any page that contains LDT descriptors. |
| 167 | * Keep it simple: zero the whole allocation and never allocate less |
| 168 | * than PAGE_SIZE. |
| 169 | */ |
| 170 | if (alloc_size > PAGE_SIZE) |
| 171 | new_ldt->entries = __vmalloc(alloc_size, GFP_KERNEL_ACCOUNT | __GFP_ZERO); |
| 172 | else |
| 173 | new_ldt->entries = (void *)get_zeroed_page(GFP_KERNEL_ACCOUNT); |
| 174 | |
| 175 | if (!new_ldt->entries) { |
| 176 | kfree(new_ldt); |
| 177 | return NULL; |
| 178 | } |
| 179 | |
| 180 | /* The new LDT isn't aliased for PTI yet. */ |
| 181 | new_ldt->slot = -1; |
| 182 | |
| 183 | new_ldt->nr_entries = num_entries; |
| 184 | return new_ldt; |
| 185 | } |
| 186 | |
| 187 | #ifdef CONFIG_PAGE_TABLE_ISOLATION |
| 188 | |
| 189 | static void do_sanity_check(struct mm_struct *mm, |
| 190 | bool had_kernel_mapping, |
| 191 | bool had_user_mapping) |
| 192 | { |
| 193 | if (mm->context.ldt) { |
| 194 | /* |
| 195 | * We already had an LDT. The top-level entry should already |
| 196 | * have been allocated and synchronized with the usermode |
| 197 | * tables. |
| 198 | */ |
| 199 | WARN_ON(!had_kernel_mapping); |
| 200 | if (boot_cpu_has(X86_FEATURE_PTI)) |
| 201 | WARN_ON(!had_user_mapping); |
| 202 | } else { |
| 203 | /* |
| 204 | * This is the first time we're mapping an LDT for this process. |
| 205 | * Sync the pgd to the usermode tables. |
| 206 | */ |
| 207 | WARN_ON(had_kernel_mapping); |
| 208 | if (boot_cpu_has(X86_FEATURE_PTI)) |
| 209 | WARN_ON(had_user_mapping); |
| 210 | } |
| 211 | } |
| 212 | |
| 213 | #ifdef CONFIG_X86_PAE |
| 214 | |
| 215 | static pmd_t *pgd_to_pmd_walk(pgd_t *pgd, unsigned long va) |
| 216 | { |
| 217 | p4d_t *p4d; |
| 218 | pud_t *pud; |
| 219 | |
| 220 | if (pgd->pgd == 0) |
| 221 | return NULL; |
| 222 | |
| 223 | p4d = p4d_offset(pgd, va); |
| 224 | if (p4d_none(*p4d)) |
| 225 | return NULL; |
| 226 | |
| 227 | pud = pud_offset(p4d, va); |
| 228 | if (pud_none(*pud)) |
| 229 | return NULL; |
| 230 | |
| 231 | return pmd_offset(pud, va); |
| 232 | } |
| 233 | |
| 234 | static void map_ldt_struct_to_user(struct mm_struct *mm) |
| 235 | { |
| 236 | pgd_t *k_pgd = pgd_offset(mm, LDT_BASE_ADDR); |
| 237 | pgd_t *u_pgd = kernel_to_user_pgdp(k_pgd); |
| 238 | pmd_t *k_pmd, *u_pmd; |
| 239 | |
| 240 | k_pmd = pgd_to_pmd_walk(k_pgd, LDT_BASE_ADDR); |
| 241 | u_pmd = pgd_to_pmd_walk(u_pgd, LDT_BASE_ADDR); |
| 242 | |
| 243 | if (boot_cpu_has(X86_FEATURE_PTI) && !mm->context.ldt) |
| 244 | set_pmd(u_pmd, *k_pmd); |
| 245 | } |
| 246 | |
| 247 | static void sanity_check_ldt_mapping(struct mm_struct *mm) |
| 248 | { |
| 249 | pgd_t *k_pgd = pgd_offset(mm, LDT_BASE_ADDR); |
| 250 | pgd_t *u_pgd = kernel_to_user_pgdp(k_pgd); |
| 251 | bool had_kernel, had_user; |
| 252 | pmd_t *k_pmd, *u_pmd; |
| 253 | |
| 254 | k_pmd = pgd_to_pmd_walk(k_pgd, LDT_BASE_ADDR); |
| 255 | u_pmd = pgd_to_pmd_walk(u_pgd, LDT_BASE_ADDR); |
| 256 | had_kernel = (k_pmd->pmd != 0); |
| 257 | had_user = (u_pmd->pmd != 0); |
| 258 | |
| 259 | do_sanity_check(mm, had_kernel, had_user); |
| 260 | } |
| 261 | |
| 262 | #else /* !CONFIG_X86_PAE */ |
| 263 | |
| 264 | static void map_ldt_struct_to_user(struct mm_struct *mm) |
| 265 | { |
| 266 | pgd_t *pgd = pgd_offset(mm, LDT_BASE_ADDR); |
| 267 | |
| 268 | if (boot_cpu_has(X86_FEATURE_PTI) && !mm->context.ldt) |
| 269 | set_pgd(kernel_to_user_pgdp(pgd), *pgd); |
| 270 | } |
| 271 | |
| 272 | static void sanity_check_ldt_mapping(struct mm_struct *mm) |
| 273 | { |
| 274 | pgd_t *pgd = pgd_offset(mm, LDT_BASE_ADDR); |
| 275 | bool had_kernel = (pgd->pgd != 0); |
| 276 | bool had_user = (kernel_to_user_pgdp(pgd)->pgd != 0); |
| 277 | |
| 278 | do_sanity_check(mm, had_kernel, had_user); |
| 279 | } |
| 280 | |
| 281 | #endif /* CONFIG_X86_PAE */ |
| 282 | |
| 283 | /* |
| 284 | * If PTI is enabled, this maps the LDT into the kernelmode and |
| 285 | * usermode tables for the given mm. |
| 286 | */ |
| 287 | static int |
| 288 | map_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt, int slot) |
| 289 | { |
| 290 | unsigned long va; |
| 291 | bool is_vmalloc; |
| 292 | spinlock_t *ptl; |
| 293 | int i, nr_pages; |
| 294 | |
| 295 | if (!boot_cpu_has(X86_FEATURE_PTI)) |
| 296 | return 0; |
| 297 | |
| 298 | /* |
| 299 | * Any given ldt_struct should have map_ldt_struct() called at most |
| 300 | * once. |
| 301 | */ |
| 302 | WARN_ON(ldt->slot != -1); |
| 303 | |
| 304 | /* Check if the current mappings are sane */ |
| 305 | sanity_check_ldt_mapping(mm); |
| 306 | |
| 307 | is_vmalloc = is_vmalloc_addr(ldt->entries); |
| 308 | |
| 309 | nr_pages = DIV_ROUND_UP(ldt->nr_entries * LDT_ENTRY_SIZE, PAGE_SIZE); |
| 310 | |
| 311 | for (i = 0; i < nr_pages; i++) { |
| 312 | unsigned long offset = i << PAGE_SHIFT; |
| 313 | const void *src = (char *)ldt->entries + offset; |
| 314 | unsigned long pfn; |
| 315 | pgprot_t pte_prot; |
| 316 | pte_t pte, *ptep; |
| 317 | |
| 318 | va = (unsigned long)ldt_slot_va(slot) + offset; |
| 319 | pfn = is_vmalloc ? vmalloc_to_pfn(src) : |
| 320 | page_to_pfn(virt_to_page(src)); |
| 321 | /* |
| 322 | * Treat the PTI LDT range as a *userspace* range. |
| 323 | * get_locked_pte() will allocate all needed pagetables |
| 324 | * and account for them in this mm. |
| 325 | */ |
| 326 | ptep = get_locked_pte(mm, va, &ptl); |
| 327 | if (!ptep) |
| 328 | return -ENOMEM; |
| 329 | /* |
| 330 | * Map it RO so the easy to find address is not a primary |
| 331 | * target via some kernel interface which misses a |
| 332 | * permission check. |
| 333 | */ |
| 334 | pte_prot = __pgprot(__PAGE_KERNEL_RO & ~_PAGE_GLOBAL); |
| 335 | /* Filter out unsuppored __PAGE_KERNEL* bits: */ |
| 336 | pgprot_val(pte_prot) &= __supported_pte_mask; |
| 337 | pte = pfn_pte(pfn, pte_prot); |
| 338 | set_pte_at(mm, va, ptep, pte); |
| 339 | pte_unmap_unlock(ptep, ptl); |
| 340 | } |
| 341 | |
| 342 | /* Propagate LDT mapping to the user page-table */ |
| 343 | map_ldt_struct_to_user(mm); |
| 344 | |
| 345 | ldt->slot = slot; |
| 346 | return 0; |
| 347 | } |
| 348 | |
| 349 | static void unmap_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt) |
| 350 | { |
| 351 | unsigned long va; |
| 352 | int i, nr_pages; |
| 353 | |
| 354 | if (!ldt) |
| 355 | return; |
| 356 | |
| 357 | /* LDT map/unmap is only required for PTI */ |
| 358 | if (!boot_cpu_has(X86_FEATURE_PTI)) |
| 359 | return; |
| 360 | |
| 361 | nr_pages = DIV_ROUND_UP(ldt->nr_entries * LDT_ENTRY_SIZE, PAGE_SIZE); |
| 362 | |
| 363 | for (i = 0; i < nr_pages; i++) { |
| 364 | unsigned long offset = i << PAGE_SHIFT; |
| 365 | spinlock_t *ptl; |
| 366 | pte_t *ptep; |
| 367 | |
| 368 | va = (unsigned long)ldt_slot_va(ldt->slot) + offset; |
| 369 | ptep = get_locked_pte(mm, va, &ptl); |
| 370 | pte_clear(mm, va, ptep); |
| 371 | pte_unmap_unlock(ptep, ptl); |
| 372 | } |
| 373 | |
| 374 | va = (unsigned long)ldt_slot_va(ldt->slot); |
| 375 | flush_tlb_mm_range(mm, va, va + nr_pages * PAGE_SIZE, PAGE_SHIFT, false); |
| 376 | } |
| 377 | |
| 378 | #else /* !CONFIG_PAGE_TABLE_ISOLATION */ |
| 379 | |
| 380 | static int |
| 381 | map_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt, int slot) |
| 382 | { |
| 383 | return 0; |
| 384 | } |
| 385 | |
| 386 | static void unmap_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt) |
| 387 | { |
| 388 | } |
| 389 | #endif /* CONFIG_PAGE_TABLE_ISOLATION */ |
| 390 | |
| 391 | static void free_ldt_pgtables(struct mm_struct *mm) |
| 392 | { |
| 393 | #ifdef CONFIG_PAGE_TABLE_ISOLATION |
| 394 | struct mmu_gather tlb; |
| 395 | unsigned long start = LDT_BASE_ADDR; |
| 396 | unsigned long end = LDT_END_ADDR; |
| 397 | |
| 398 | if (!boot_cpu_has(X86_FEATURE_PTI)) |
| 399 | return; |
| 400 | |
| 401 | /* |
| 402 | * Although free_pgd_range() is intended for freeing user |
| 403 | * page-tables, it also works out for kernel mappings on x86. |
| 404 | * We use tlb_gather_mmu_fullmm() to avoid confusing the |
| 405 | * range-tracking logic in __tlb_adjust_range(). |
| 406 | */ |
| 407 | tlb_gather_mmu_fullmm(&tlb, mm); |
| 408 | free_pgd_range(&tlb, start, end, start, end); |
| 409 | tlb_finish_mmu(&tlb); |
| 410 | #endif |
| 411 | } |
| 412 | |
| 413 | /* After calling this, the LDT is immutable. */ |
| 414 | static void finalize_ldt_struct(struct ldt_struct *ldt) |
| 415 | { |
| 416 | paravirt_alloc_ldt(ldt->entries, ldt->nr_entries); |
| 417 | } |
| 418 | |
| 419 | static void install_ldt(struct mm_struct *mm, struct ldt_struct *ldt) |
| 420 | { |
| 421 | mutex_lock(&mm->context.lock); |
| 422 | |
| 423 | /* Synchronizes with READ_ONCE in load_mm_ldt. */ |
| 424 | smp_store_release(&mm->context.ldt, ldt); |
| 425 | |
| 426 | /* Activate the LDT for all CPUs using currents mm. */ |
| 427 | on_each_cpu_mask(mm_cpumask(mm), flush_ldt, mm, true); |
| 428 | |
| 429 | mutex_unlock(&mm->context.lock); |
| 430 | } |
| 431 | |
| 432 | static void free_ldt_struct(struct ldt_struct *ldt) |
| 433 | { |
| 434 | if (likely(!ldt)) |
| 435 | return; |
| 436 | |
| 437 | paravirt_free_ldt(ldt->entries, ldt->nr_entries); |
| 438 | if (ldt->nr_entries * LDT_ENTRY_SIZE > PAGE_SIZE) |
| 439 | vfree_atomic(ldt->entries); |
| 440 | else |
| 441 | free_page((unsigned long)ldt->entries); |
| 442 | kfree(ldt); |
| 443 | } |
| 444 | |
| 445 | /* |
| 446 | * Called on fork from arch_dup_mmap(). Just copy the current LDT state, |
| 447 | * the new task is not running, so nothing can be installed. |
| 448 | */ |
| 449 | int ldt_dup_context(struct mm_struct *old_mm, struct mm_struct *mm) |
| 450 | { |
| 451 | struct ldt_struct *new_ldt; |
| 452 | int retval = 0; |
| 453 | |
| 454 | if (!old_mm) |
| 455 | return 0; |
| 456 | |
| 457 | mutex_lock(&old_mm->context.lock); |
| 458 | if (!old_mm->context.ldt) |
| 459 | goto out_unlock; |
| 460 | |
| 461 | new_ldt = alloc_ldt_struct(old_mm->context.ldt->nr_entries); |
| 462 | if (!new_ldt) { |
| 463 | retval = -ENOMEM; |
| 464 | goto out_unlock; |
| 465 | } |
| 466 | |
| 467 | memcpy(new_ldt->entries, old_mm->context.ldt->entries, |
| 468 | new_ldt->nr_entries * LDT_ENTRY_SIZE); |
| 469 | finalize_ldt_struct(new_ldt); |
| 470 | |
| 471 | retval = map_ldt_struct(mm, new_ldt, 0); |
| 472 | if (retval) { |
| 473 | free_ldt_pgtables(mm); |
| 474 | free_ldt_struct(new_ldt); |
| 475 | goto out_unlock; |
| 476 | } |
| 477 | mm->context.ldt = new_ldt; |
| 478 | |
| 479 | out_unlock: |
| 480 | mutex_unlock(&old_mm->context.lock); |
| 481 | return retval; |
| 482 | } |
| 483 | |
| 484 | /* |
| 485 | * No need to lock the MM as we are the last user |
| 486 | * |
| 487 | * 64bit: Don't touch the LDT register - we're already in the next thread. |
| 488 | */ |
| 489 | void destroy_context_ldt(struct mm_struct *mm) |
| 490 | { |
| 491 | free_ldt_struct(mm->context.ldt); |
| 492 | mm->context.ldt = NULL; |
| 493 | } |
| 494 | |
| 495 | void ldt_arch_exit_mmap(struct mm_struct *mm) |
| 496 | { |
| 497 | free_ldt_pgtables(mm); |
| 498 | } |
| 499 | |
| 500 | static int read_ldt(void __user *ptr, unsigned long bytecount) |
| 501 | { |
| 502 | struct mm_struct *mm = current->mm; |
| 503 | unsigned long entries_size; |
| 504 | int retval; |
| 505 | |
| 506 | down_read(&mm->context.ldt_usr_sem); |
| 507 | |
| 508 | if (!mm->context.ldt) { |
| 509 | retval = 0; |
| 510 | goto out_unlock; |
| 511 | } |
| 512 | |
| 513 | if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES) |
| 514 | bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES; |
| 515 | |
| 516 | entries_size = mm->context.ldt->nr_entries * LDT_ENTRY_SIZE; |
| 517 | if (entries_size > bytecount) |
| 518 | entries_size = bytecount; |
| 519 | |
| 520 | if (copy_to_user(ptr, mm->context.ldt->entries, entries_size)) { |
| 521 | retval = -EFAULT; |
| 522 | goto out_unlock; |
| 523 | } |
| 524 | |
| 525 | if (entries_size != bytecount) { |
| 526 | /* Zero-fill the rest and pretend we read bytecount bytes. */ |
| 527 | if (clear_user(ptr + entries_size, bytecount - entries_size)) { |
| 528 | retval = -EFAULT; |
| 529 | goto out_unlock; |
| 530 | } |
| 531 | } |
| 532 | retval = bytecount; |
| 533 | |
| 534 | out_unlock: |
| 535 | up_read(&mm->context.ldt_usr_sem); |
| 536 | return retval; |
| 537 | } |
| 538 | |
| 539 | static int read_default_ldt(void __user *ptr, unsigned long bytecount) |
| 540 | { |
| 541 | /* CHECKME: Can we use _one_ random number ? */ |
| 542 | #ifdef CONFIG_X86_32 |
| 543 | unsigned long size = 5 * sizeof(struct desc_struct); |
| 544 | #else |
| 545 | unsigned long size = 128; |
| 546 | #endif |
| 547 | if (bytecount > size) |
| 548 | bytecount = size; |
| 549 | if (clear_user(ptr, bytecount)) |
| 550 | return -EFAULT; |
| 551 | return bytecount; |
| 552 | } |
| 553 | |
| 554 | static bool allow_16bit_segments(void) |
| 555 | { |
| 556 | if (!IS_ENABLED(CONFIG_X86_16BIT)) |
| 557 | return false; |
| 558 | |
| 559 | #ifdef CONFIG_XEN_PV |
| 560 | /* |
| 561 | * Xen PV does not implement ESPFIX64, which means that 16-bit |
| 562 | * segments will not work correctly. Until either Xen PV implements |
| 563 | * ESPFIX64 and can signal this fact to the guest or unless someone |
| 564 | * provides compelling evidence that allowing broken 16-bit segments |
| 565 | * is worthwhile, disallow 16-bit segments under Xen PV. |
| 566 | */ |
| 567 | if (xen_pv_domain()) { |
| 568 | pr_info_once("Warning: 16-bit segments do not work correctly in a Xen PV guest\n"); |
| 569 | return false; |
| 570 | } |
| 571 | #endif |
| 572 | |
| 573 | return true; |
| 574 | } |
| 575 | |
| 576 | static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode) |
| 577 | { |
| 578 | struct mm_struct *mm = current->mm; |
| 579 | struct ldt_struct *new_ldt, *old_ldt; |
| 580 | unsigned int old_nr_entries, new_nr_entries; |
| 581 | struct user_desc ldt_info; |
| 582 | struct desc_struct ldt; |
| 583 | int error; |
| 584 | |
| 585 | error = -EINVAL; |
| 586 | if (bytecount != sizeof(ldt_info)) |
| 587 | goto out; |
| 588 | error = -EFAULT; |
| 589 | if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info))) |
| 590 | goto out; |
| 591 | |
| 592 | error = -EINVAL; |
| 593 | if (ldt_info.entry_number >= LDT_ENTRIES) |
| 594 | goto out; |
| 595 | if (ldt_info.contents == 3) { |
| 596 | if (oldmode) |
| 597 | goto out; |
| 598 | if (ldt_info.seg_not_present == 0) |
| 599 | goto out; |
| 600 | } |
| 601 | |
| 602 | if ((oldmode && !ldt_info.base_addr && !ldt_info.limit) || |
| 603 | LDT_empty(&ldt_info)) { |
| 604 | /* The user wants to clear the entry. */ |
| 605 | memset(&ldt, 0, sizeof(ldt)); |
| 606 | } else { |
| 607 | if (!ldt_info.seg_32bit && !allow_16bit_segments()) { |
| 608 | error = -EINVAL; |
| 609 | goto out; |
| 610 | } |
| 611 | |
| 612 | fill_ldt(&ldt, &ldt_info); |
| 613 | if (oldmode) |
| 614 | ldt.avl = 0; |
| 615 | } |
| 616 | |
| 617 | if (down_write_killable(&mm->context.ldt_usr_sem)) |
| 618 | return -EINTR; |
| 619 | |
| 620 | old_ldt = mm->context.ldt; |
| 621 | old_nr_entries = old_ldt ? old_ldt->nr_entries : 0; |
| 622 | new_nr_entries = max(ldt_info.entry_number + 1, old_nr_entries); |
| 623 | |
| 624 | error = -ENOMEM; |
| 625 | new_ldt = alloc_ldt_struct(new_nr_entries); |
| 626 | if (!new_ldt) |
| 627 | goto out_unlock; |
| 628 | |
| 629 | if (old_ldt) |
| 630 | memcpy(new_ldt->entries, old_ldt->entries, old_nr_entries * LDT_ENTRY_SIZE); |
| 631 | |
| 632 | new_ldt->entries[ldt_info.entry_number] = ldt; |
| 633 | finalize_ldt_struct(new_ldt); |
| 634 | |
| 635 | /* |
| 636 | * If we are using PTI, map the new LDT into the userspace pagetables. |
| 637 | * If there is already an LDT, use the other slot so that other CPUs |
| 638 | * will continue to use the old LDT until install_ldt() switches |
| 639 | * them over to the new LDT. |
| 640 | */ |
| 641 | error = map_ldt_struct(mm, new_ldt, old_ldt ? !old_ldt->slot : 0); |
| 642 | if (error) { |
| 643 | /* |
| 644 | * This only can fail for the first LDT setup. If an LDT is |
| 645 | * already installed then the PTE page is already |
| 646 | * populated. Mop up a half populated page table. |
| 647 | */ |
| 648 | if (!WARN_ON_ONCE(old_ldt)) |
| 649 | free_ldt_pgtables(mm); |
| 650 | free_ldt_struct(new_ldt); |
| 651 | goto out_unlock; |
| 652 | } |
| 653 | |
| 654 | install_ldt(mm, new_ldt); |
| 655 | unmap_ldt_struct(mm, old_ldt); |
| 656 | free_ldt_struct(old_ldt); |
| 657 | error = 0; |
| 658 | |
| 659 | out_unlock: |
| 660 | up_write(&mm->context.ldt_usr_sem); |
| 661 | out: |
| 662 | return error; |
| 663 | } |
| 664 | |
| 665 | SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr , |
| 666 | unsigned long , bytecount) |
| 667 | { |
| 668 | int ret = -ENOSYS; |
| 669 | |
| 670 | switch (func) { |
| 671 | case 0: |
| 672 | ret = read_ldt(ptr, bytecount); |
| 673 | break; |
| 674 | case 1: |
| 675 | ret = write_ldt(ptr, bytecount, 1); |
| 676 | break; |
| 677 | case 2: |
| 678 | ret = read_default_ldt(ptr, bytecount); |
| 679 | break; |
| 680 | case 0x11: |
| 681 | ret = write_ldt(ptr, bytecount, 0); |
| 682 | break; |
| 683 | } |
| 684 | /* |
| 685 | * The SYSCALL_DEFINE() macros give us an 'unsigned long' |
| 686 | * return type, but tht ABI for sys_modify_ldt() expects |
| 687 | * 'int'. This cast gives us an int-sized value in %rax |
| 688 | * for the return code. The 'unsigned' is necessary so |
| 689 | * the compiler does not try to sign-extend the negative |
| 690 | * return codes into the high half of the register when |
| 691 | * taking the value from int->long. |
| 692 | */ |
| 693 | return (unsigned int)ret; |
| 694 | } |