1 /* 2 * Copyright (C) 1995 Linus Torvalds 3 * Copyright (C) 2001, 2002 Andi Kleen, SuSE Labs. 4 * Copyright (C) 2008-2009, Red Hat Inc., Ingo Molnar 5 */ 6 #include <linux/magic.h> /* STACK_END_MAGIC */ 7 #include <linux/sched.h> /* test_thread_flag(), ... */ 8 #include <linux/kdebug.h> /* oops_begin/end, ... */ 9 #include <linux/module.h> /* search_exception_table */ 10 #include <linux/bootmem.h> /* max_low_pfn */ 11 #include <linux/kprobes.h> /* __kprobes, ... */ 12 #include <linux/mmiotrace.h> /* kmmio_handler, ... */ 13 #include <linux/perf_event.h> /* perf_sw_event */ 14 #include <linux/hugetlb.h> /* hstate_index_to_shift */ 15 #include <linux/prefetch.h> /* prefetchw */ 16 #include <linux/context_tracking.h> /* exception_enter(), ... */ 17 18 #include <asm/traps.h> /* dotraplinkage, ... */ 19 #include <asm/pgalloc.h> /* pgd_*(), ... */ 20 #include <asm/kmemcheck.h> /* kmemcheck_*(), ... */ 21 #include <asm/fixmap.h> /* VSYSCALL_START */ 22 23 #define CREATE_TRACE_POINTS 24 #include <asm/trace/exceptions.h> 25 26 /* 27 * Page fault error code bits: 28 * 29 * bit 0 == 0: no page found 1: protection fault 30 * bit 1 == 0: read access 1: write access 31 * bit 2 == 0: kernel-mode access 1: user-mode access 32 * bit 3 == 1: use of reserved bit detected 33 * bit 4 == 1: fault was an instruction fetch 34 */ 35 enum x86_pf_error_code { 36 37 PF_PROT = 1 << 0, 38 PF_WRITE = 1 << 1, 39 PF_USER = 1 << 2, 40 PF_RSVD = 1 << 3, 41 PF_INSTR = 1 << 4, 42 }; 43 44 /* 45 * Returns 0 if mmiotrace is disabled, or if the fault is not 46 * handled by mmiotrace: 47 */ 48 static inline int __kprobes 49 kmmio_fault(struct pt_regs *regs, unsigned long addr) 50 { 51 if (unlikely(is_kmmio_active())) 52 if (kmmio_handler(regs, addr) == 1) 53 return -1; 54 return 0; 55 } 56 57 static inline int __kprobes kprobes_fault(struct pt_regs *regs) 58 { 59 int ret = 0; 60 61 /* kprobe_running() needs smp_processor_id() */ 62 if (kprobes_built_in() && !user_mode_vm(regs)) { 63 preempt_disable(); 64 if (kprobe_running() && kprobe_fault_handler(regs, 14)) 65 ret = 1; 66 preempt_enable(); 67 } 68 69 return ret; 70 } 71 72 /* 73 * Prefetch quirks: 74 * 75 * 32-bit mode: 76 * 77 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch. 78 * Check that here and ignore it. 79 * 80 * 64-bit mode: 81 * 82 * Sometimes the CPU reports invalid exceptions on prefetch. 83 * Check that here and ignore it. 84 * 85 * Opcode checker based on code by Richard Brunner. 86 */ 87 static inline int 88 check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr, 89 unsigned char opcode, int *prefetch) 90 { 91 unsigned char instr_hi = opcode & 0xf0; 92 unsigned char instr_lo = opcode & 0x0f; 93 94 switch (instr_hi) { 95 case 0x20: 96 case 0x30: 97 /* 98 * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes. 99 * In X86_64 long mode, the CPU will signal invalid 100 * opcode if some of these prefixes are present so 101 * X86_64 will never get here anyway 102 */ 103 return ((instr_lo & 7) == 0x6); 104 #ifdef CONFIG_X86_64 105 case 0x40: 106 /* 107 * In AMD64 long mode 0x40..0x4F are valid REX prefixes 108 * Need to figure out under what instruction mode the 109 * instruction was issued. Could check the LDT for lm, 110 * but for now it's good enough to assume that long 111 * mode only uses well known segments or kernel. 112 */ 113 return (!user_mode(regs) || user_64bit_mode(regs)); 114 #endif 115 case 0x60: 116 /* 0x64 thru 0x67 are valid prefixes in all modes. */ 117 return (instr_lo & 0xC) == 0x4; 118 case 0xF0: 119 /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */ 120 return !instr_lo || (instr_lo>>1) == 1; 121 case 0x00: 122 /* Prefetch instruction is 0x0F0D or 0x0F18 */ 123 if (probe_kernel_address(instr, opcode)) 124 return 0; 125 126 *prefetch = (instr_lo == 0xF) && 127 (opcode == 0x0D || opcode == 0x18); 128 return 0; 129 default: 130 return 0; 131 } 132 } 133 134 static int 135 is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr) 136 { 137 unsigned char *max_instr; 138 unsigned char *instr; 139 int prefetch = 0; 140 141 /* 142 * If it was a exec (instruction fetch) fault on NX page, then 143 * do not ignore the fault: 144 */ 145 if (error_code & PF_INSTR) 146 return 0; 147 148 instr = (void *)convert_ip_to_linear(current, regs); 149 max_instr = instr + 15; 150 151 if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE) 152 return 0; 153 154 while (instr < max_instr) { 155 unsigned char opcode; 156 157 if (probe_kernel_address(instr, opcode)) 158 break; 159 160 instr++; 161 162 if (!check_prefetch_opcode(regs, instr, opcode, &prefetch)) 163 break; 164 } 165 return prefetch; 166 } 167 168 static void 169 force_sig_info_fault(int si_signo, int si_code, unsigned long address, 170 struct task_struct *tsk, int fault) 171 { 172 unsigned lsb = 0; 173 siginfo_t info; 174 175 info.si_signo = si_signo; 176 info.si_errno = 0; 177 info.si_code = si_code; 178 info.si_addr = (void __user *)address; 179 if (fault & VM_FAULT_HWPOISON_LARGE) 180 lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault)); 181 if (fault & VM_FAULT_HWPOISON) 182 lsb = PAGE_SHIFT; 183 info.si_addr_lsb = lsb; 184 185 force_sig_info(si_signo, &info, tsk); 186 } 187 188 DEFINE_SPINLOCK(pgd_lock); 189 LIST_HEAD(pgd_list); 190 191 #ifdef CONFIG_X86_32 192 static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address) 193 { 194 unsigned index = pgd_index(address); 195 pgd_t *pgd_k; 196 pud_t *pud, *pud_k; 197 pmd_t *pmd, *pmd_k; 198 199 pgd += index; 200 pgd_k = init_mm.pgd + index; 201 202 if (!pgd_present(*pgd_k)) 203 return NULL; 204 205 /* 206 * set_pgd(pgd, *pgd_k); here would be useless on PAE 207 * and redundant with the set_pmd() on non-PAE. As would 208 * set_pud. 209 */ 210 pud = pud_offset(pgd, address); 211 pud_k = pud_offset(pgd_k, address); 212 if (!pud_present(*pud_k)) 213 return NULL; 214 215 pmd = pmd_offset(pud, address); 216 pmd_k = pmd_offset(pud_k, address); 217 if (!pmd_present(*pmd_k)) 218 return NULL; 219 220 if (!pmd_present(*pmd)) 221 set_pmd(pmd, *pmd_k); 222 else 223 BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k)); 224 225 return pmd_k; 226 } 227 228 void vmalloc_sync_all(void) 229 { 230 unsigned long address; 231 232 if (SHARED_KERNEL_PMD) 233 return; 234 235 for (address = VMALLOC_START & PMD_MASK; 236 address >= TASK_SIZE && address < FIXADDR_TOP; 237 address += PMD_SIZE) { 238 struct page *page; 239 240 spin_lock(&pgd_lock); 241 list_for_each_entry(page, &pgd_list, lru) { 242 spinlock_t *pgt_lock; 243 pmd_t *ret; 244 245 /* the pgt_lock only for Xen */ 246 pgt_lock = &pgd_page_get_mm(page)->page_table_lock; 247 248 spin_lock(pgt_lock); 249 ret = vmalloc_sync_one(page_address(page), address); 250 spin_unlock(pgt_lock); 251 252 if (!ret) 253 break; 254 } 255 spin_unlock(&pgd_lock); 256 } 257 } 258 259 /* 260 * 32-bit: 261 * 262 * Handle a fault on the vmalloc or module mapping area 263 */ 264 static noinline __kprobes int vmalloc_fault(unsigned long address) 265 { 266 unsigned long pgd_paddr; 267 pmd_t *pmd_k; 268 pte_t *pte_k; 269 270 /* Make sure we are in vmalloc area: */ 271 if (!(address >= VMALLOC_START && address < VMALLOC_END)) 272 return -1; 273 274 WARN_ON_ONCE(in_nmi()); 275 276 /* 277 * Synchronize this task's top level page-table 278 * with the 'reference' page table. 279 * 280 * Do _not_ use "current" here. We might be inside 281 * an interrupt in the middle of a task switch.. 282 */ 283 pgd_paddr = read_cr3(); 284 pmd_k = vmalloc_sync_one(__va(pgd_paddr), address); 285 if (!pmd_k) 286 return -1; 287 288 pte_k = pte_offset_kernel(pmd_k, address); 289 if (!pte_present(*pte_k)) 290 return -1; 291 292 return 0; 293 } 294 295 /* 296 * Did it hit the DOS screen memory VA from vm86 mode? 297 */ 298 static inline void 299 check_v8086_mode(struct pt_regs *regs, unsigned long address, 300 struct task_struct *tsk) 301 { 302 unsigned long bit; 303 304 if (!v8086_mode(regs)) 305 return; 306 307 bit = (address - 0xA0000) >> PAGE_SHIFT; 308 if (bit < 32) 309 tsk->thread.screen_bitmap |= 1 << bit; 310 } 311 312 static bool low_pfn(unsigned long pfn) 313 { 314 return pfn < max_low_pfn; 315 } 316 317 static void dump_pagetable(unsigned long address) 318 { 319 pgd_t *base = __va(read_cr3()); 320 pgd_t *pgd = &base[pgd_index(address)]; 321 pmd_t *pmd; 322 pte_t *pte; 323 324 #ifdef CONFIG_X86_PAE 325 printk("*pdpt = %016Lx ", pgd_val(*pgd)); 326 if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd)) 327 goto out; 328 #endif 329 pmd = pmd_offset(pud_offset(pgd, address), address); 330 printk(KERN_CONT "*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd)); 331 332 /* 333 * We must not directly access the pte in the highpte 334 * case if the page table is located in highmem. 335 * And let's rather not kmap-atomic the pte, just in case 336 * it's allocated already: 337 */ 338 if (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_large(*pmd)) 339 goto out; 340 341 pte = pte_offset_kernel(pmd, address); 342 printk("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte)); 343 out: 344 printk("\n"); 345 } 346 347 #else /* CONFIG_X86_64: */ 348 349 void vmalloc_sync_all(void) 350 { 351 sync_global_pgds(VMALLOC_START & PGDIR_MASK, VMALLOC_END); 352 } 353 354 /* 355 * 64-bit: 356 * 357 * Handle a fault on the vmalloc area 358 * 359 * This assumes no large pages in there. 360 */ 361 static noinline __kprobes int vmalloc_fault(unsigned long address) 362 { 363 pgd_t *pgd, *pgd_ref; 364 pud_t *pud, *pud_ref; 365 pmd_t *pmd, *pmd_ref; 366 pte_t *pte, *pte_ref; 367 368 /* Make sure we are in vmalloc area: */ 369 if (!(address >= VMALLOC_START && address < VMALLOC_END)) 370 return -1; 371 372 WARN_ON_ONCE(in_nmi()); 373 374 /* 375 * Copy kernel mappings over when needed. This can also 376 * happen within a race in page table update. In the later 377 * case just flush: 378 */ 379 pgd = pgd_offset(current->active_mm, address); 380 pgd_ref = pgd_offset_k(address); 381 if (pgd_none(*pgd_ref)) 382 return -1; 383 384 if (pgd_none(*pgd)) { 385 set_pgd(pgd, *pgd_ref); 386 arch_flush_lazy_mmu_mode(); 387 } else { 388 BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref)); 389 } 390 391 /* 392 * Below here mismatches are bugs because these lower tables 393 * are shared: 394 */ 395 396 pud = pud_offset(pgd, address); 397 pud_ref = pud_offset(pgd_ref, address); 398 if (pud_none(*pud_ref)) 399 return -1; 400 401 if (pud_none(*pud) || pud_page_vaddr(*pud) != pud_page_vaddr(*pud_ref)) 402 BUG(); 403 404 pmd = pmd_offset(pud, address); 405 pmd_ref = pmd_offset(pud_ref, address); 406 if (pmd_none(*pmd_ref)) 407 return -1; 408 409 if (pmd_none(*pmd) || pmd_page(*pmd) != pmd_page(*pmd_ref)) 410 BUG(); 411 412 pte_ref = pte_offset_kernel(pmd_ref, address); 413 if (!pte_present(*pte_ref)) 414 return -1; 415 416 pte = pte_offset_kernel(pmd, address); 417 418 /* 419 * Don't use pte_page here, because the mappings can point 420 * outside mem_map, and the NUMA hash lookup cannot handle 421 * that: 422 */ 423 if (!pte_present(*pte) || pte_pfn(*pte) != pte_pfn(*pte_ref)) 424 BUG(); 425 426 return 0; 427 } 428 429 #ifdef CONFIG_CPU_SUP_AMD 430 static const char errata93_warning[] = 431 KERN_ERR 432 "******* Your BIOS seems to not contain a fix for K8 errata #93\n" 433 "******* Working around it, but it may cause SEGVs or burn power.\n" 434 "******* Please consider a BIOS update.\n" 435 "******* Disabling USB legacy in the BIOS may also help.\n"; 436 #endif 437 438 /* 439 * No vm86 mode in 64-bit mode: 440 */ 441 static inline void 442 check_v8086_mode(struct pt_regs *regs, unsigned long address, 443 struct task_struct *tsk) 444 { 445 } 446 447 static int bad_address(void *p) 448 { 449 unsigned long dummy; 450 451 return probe_kernel_address((unsigned long *)p, dummy); 452 } 453 454 static void dump_pagetable(unsigned long address) 455 { 456 pgd_t *base = __va(read_cr3() & PHYSICAL_PAGE_MASK); 457 pgd_t *pgd = base + pgd_index(address); 458 pud_t *pud; 459 pmd_t *pmd; 460 pte_t *pte; 461 462 if (bad_address(pgd)) 463 goto bad; 464 465 printk("PGD %lx ", pgd_val(*pgd)); 466 467 if (!pgd_present(*pgd)) 468 goto out; 469 470 pud = pud_offset(pgd, address); 471 if (bad_address(pud)) 472 goto bad; 473 474 printk("PUD %lx ", pud_val(*pud)); 475 if (!pud_present(*pud) || pud_large(*pud)) 476 goto out; 477 478 pmd = pmd_offset(pud, address); 479 if (bad_address(pmd)) 480 goto bad; 481 482 printk("PMD %lx ", pmd_val(*pmd)); 483 if (!pmd_present(*pmd) || pmd_large(*pmd)) 484 goto out; 485 486 pte = pte_offset_kernel(pmd, address); 487 if (bad_address(pte)) 488 goto bad; 489 490 printk("PTE %lx", pte_val(*pte)); 491 out: 492 printk("\n"); 493 return; 494 bad: 495 printk("BAD\n"); 496 } 497 498 #endif /* CONFIG_X86_64 */ 499 500 /* 501 * Workaround for K8 erratum #93 & buggy BIOS. 502 * 503 * BIOS SMM functions are required to use a specific workaround 504 * to avoid corruption of the 64bit RIP register on C stepping K8. 505 * 506 * A lot of BIOS that didn't get tested properly miss this. 507 * 508 * The OS sees this as a page fault with the upper 32bits of RIP cleared. 509 * Try to work around it here. 510 * 511 * Note we only handle faults in kernel here. 512 * Does nothing on 32-bit. 513 */ 514 static int is_errata93(struct pt_regs *regs, unsigned long address) 515 { 516 #if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD) 517 if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD 518 || boot_cpu_data.x86 != 0xf) 519 return 0; 520 521 if (address != regs->ip) 522 return 0; 523 524 if ((address >> 32) != 0) 525 return 0; 526 527 address |= 0xffffffffUL << 32; 528 if ((address >= (u64)_stext && address <= (u64)_etext) || 529 (address >= MODULES_VADDR && address <= MODULES_END)) { 530 printk_once(errata93_warning); 531 regs->ip = address; 532 return 1; 533 } 534 #endif 535 return 0; 536 } 537 538 /* 539 * Work around K8 erratum #100 K8 in compat mode occasionally jumps 540 * to illegal addresses >4GB. 541 * 542 * We catch this in the page fault handler because these addresses 543 * are not reachable. Just detect this case and return. Any code 544 * segment in LDT is compatibility mode. 545 */ 546 static int is_errata100(struct pt_regs *regs, unsigned long address) 547 { 548 #ifdef CONFIG_X86_64 549 if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32)) 550 return 1; 551 #endif 552 return 0; 553 } 554 555 static int is_f00f_bug(struct pt_regs *regs, unsigned long address) 556 { 557 #ifdef CONFIG_X86_F00F_BUG 558 unsigned long nr; 559 560 /* 561 * Pentium F0 0F C7 C8 bug workaround: 562 */ 563 if (boot_cpu_has_bug(X86_BUG_F00F)) { 564 nr = (address - idt_descr.address) >> 3; 565 566 if (nr == 6) { 567 do_invalid_op(regs, 0); 568 return 1; 569 } 570 } 571 #endif 572 return 0; 573 } 574 575 static const char nx_warning[] = KERN_CRIT 576 "kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n"; 577 578 static void 579 show_fault_oops(struct pt_regs *regs, unsigned long error_code, 580 unsigned long address) 581 { 582 if (!oops_may_print()) 583 return; 584 585 if (error_code & PF_INSTR) { 586 unsigned int level; 587 588 pte_t *pte = lookup_address(address, &level); 589 590 if (pte && pte_present(*pte) && !pte_exec(*pte)) 591 printk(nx_warning, from_kuid(&init_user_ns, current_uid())); 592 } 593 594 printk(KERN_ALERT "BUG: unable to handle kernel "); 595 if (address < PAGE_SIZE) 596 printk(KERN_CONT "NULL pointer dereference"); 597 else 598 printk(KERN_CONT "paging request"); 599 600 printk(KERN_CONT " at %p\n", (void *) address); 601 printk(KERN_ALERT "IP:"); 602 printk_address(regs->ip); 603 604 dump_pagetable(address); 605 } 606 607 static noinline void 608 pgtable_bad(struct pt_regs *regs, unsigned long error_code, 609 unsigned long address) 610 { 611 struct task_struct *tsk; 612 unsigned long flags; 613 int sig; 614 615 flags = oops_begin(); 616 tsk = current; 617 sig = SIGKILL; 618 619 printk(KERN_ALERT "%s: Corrupted page table at address %lx\n", 620 tsk->comm, address); 621 dump_pagetable(address); 622 623 tsk->thread.cr2 = address; 624 tsk->thread.trap_nr = X86_TRAP_PF; 625 tsk->thread.error_code = error_code; 626 627 if (__die("Bad pagetable", regs, error_code)) 628 sig = 0; 629 630 oops_end(flags, regs, sig); 631 } 632 633 static noinline void 634 no_context(struct pt_regs *regs, unsigned long error_code, 635 unsigned long address, int signal, int si_code) 636 { 637 struct task_struct *tsk = current; 638 unsigned long *stackend; 639 unsigned long flags; 640 int sig; 641 642 /* Are we prepared to handle this kernel fault? */ 643 if (fixup_exception(regs)) { 644 /* 645 * Any interrupt that takes a fault gets the fixup. This makes 646 * the below recursive fault logic only apply to a faults from 647 * task context. 648 */ 649 if (in_interrupt()) 650 return; 651 652 /* 653 * Per the above we're !in_interrupt(), aka. task context. 654 * 655 * In this case we need to make sure we're not recursively 656 * faulting through the emulate_vsyscall() logic. 657 */ 658 if (current_thread_info()->sig_on_uaccess_error && signal) { 659 tsk->thread.trap_nr = X86_TRAP_PF; 660 tsk->thread.error_code = error_code | PF_USER; 661 tsk->thread.cr2 = address; 662 663 /* XXX: hwpoison faults will set the wrong code. */ 664 force_sig_info_fault(signal, si_code, address, tsk, 0); 665 } 666 667 /* 668 * Barring that, we can do the fixup and be happy. 669 */ 670 return; 671 } 672 673 /* 674 * 32-bit: 675 * 676 * Valid to do another page fault here, because if this fault 677 * had been triggered by is_prefetch fixup_exception would have 678 * handled it. 679 * 680 * 64-bit: 681 * 682 * Hall of shame of CPU/BIOS bugs. 683 */ 684 if (is_prefetch(regs, error_code, address)) 685 return; 686 687 if (is_errata93(regs, address)) 688 return; 689 690 /* 691 * Oops. The kernel tried to access some bad page. We'll have to 692 * terminate things with extreme prejudice: 693 */ 694 flags = oops_begin(); 695 696 show_fault_oops(regs, error_code, address); 697 698 stackend = end_of_stack(tsk); 699 if (tsk != &init_task && *stackend != STACK_END_MAGIC) 700 printk(KERN_EMERG "Thread overran stack, or stack corrupted\n"); 701 702 tsk->thread.cr2 = address; 703 tsk->thread.trap_nr = X86_TRAP_PF; 704 tsk->thread.error_code = error_code; 705 706 sig = SIGKILL; 707 if (__die("Oops", regs, error_code)) 708 sig = 0; 709 710 /* Executive summary in case the body of the oops scrolled away */ 711 printk(KERN_DEFAULT "CR2: %016lx\n", address); 712 713 oops_end(flags, regs, sig); 714 } 715 716 /* 717 * Print out info about fatal segfaults, if the show_unhandled_signals 718 * sysctl is set: 719 */ 720 static inline void 721 show_signal_msg(struct pt_regs *regs, unsigned long error_code, 722 unsigned long address, struct task_struct *tsk) 723 { 724 if (!unhandled_signal(tsk, SIGSEGV)) 725 return; 726 727 if (!printk_ratelimit()) 728 return; 729 730 printk("%s%s[%d]: segfault at %lx ip %p sp %p error %lx", 731 task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG, 732 tsk->comm, task_pid_nr(tsk), address, 733 (void *)regs->ip, (void *)regs->sp, error_code); 734 735 print_vma_addr(KERN_CONT " in ", regs->ip); 736 737 printk(KERN_CONT "\n"); 738 } 739 740 static void 741 __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, 742 unsigned long address, int si_code) 743 { 744 struct task_struct *tsk = current; 745 746 /* User mode accesses just cause a SIGSEGV */ 747 if (error_code & PF_USER) { 748 /* 749 * It's possible to have interrupts off here: 750 */ 751 local_irq_enable(); 752 753 /* 754 * Valid to do another page fault here because this one came 755 * from user space: 756 */ 757 if (is_prefetch(regs, error_code, address)) 758 return; 759 760 if (is_errata100(regs, address)) 761 return; 762 763 #ifdef CONFIG_X86_64 764 /* 765 * Instruction fetch faults in the vsyscall page might need 766 * emulation. 767 */ 768 if (unlikely((error_code & PF_INSTR) && 769 ((address & ~0xfff) == VSYSCALL_START))) { 770 if (emulate_vsyscall(regs, address)) 771 return; 772 } 773 #endif 774 /* Kernel addresses are always protection faults: */ 775 if (address >= TASK_SIZE) 776 error_code |= PF_PROT; 777 778 if (likely(show_unhandled_signals)) 779 show_signal_msg(regs, error_code, address, tsk); 780 781 tsk->thread.cr2 = address; 782 tsk->thread.error_code = error_code; 783 tsk->thread.trap_nr = X86_TRAP_PF; 784 785 force_sig_info_fault(SIGSEGV, si_code, address, tsk, 0); 786 787 return; 788 } 789 790 if (is_f00f_bug(regs, address)) 791 return; 792 793 no_context(regs, error_code, address, SIGSEGV, si_code); 794 } 795 796 static noinline void 797 bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, 798 unsigned long address) 799 { 800 __bad_area_nosemaphore(regs, error_code, address, SEGV_MAPERR); 801 } 802 803 static void 804 __bad_area(struct pt_regs *regs, unsigned long error_code, 805 unsigned long address, int si_code) 806 { 807 struct mm_struct *mm = current->mm; 808 809 /* 810 * Something tried to access memory that isn't in our memory map.. 811 * Fix it, but check if it's kernel or user first.. 812 */ 813 up_read(&mm->mmap_sem); 814 815 __bad_area_nosemaphore(regs, error_code, address, si_code); 816 } 817 818 static noinline void 819 bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address) 820 { 821 __bad_area(regs, error_code, address, SEGV_MAPERR); 822 } 823 824 static noinline void 825 bad_area_access_error(struct pt_regs *regs, unsigned long error_code, 826 unsigned long address) 827 { 828 __bad_area(regs, error_code, address, SEGV_ACCERR); 829 } 830 831 static void 832 do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address, 833 unsigned int fault) 834 { 835 struct task_struct *tsk = current; 836 struct mm_struct *mm = tsk->mm; 837 int code = BUS_ADRERR; 838 839 up_read(&mm->mmap_sem); 840 841 /* Kernel mode? Handle exceptions or die: */ 842 if (!(error_code & PF_USER)) { 843 no_context(regs, error_code, address, SIGBUS, BUS_ADRERR); 844 return; 845 } 846 847 /* User-space => ok to do another page fault: */ 848 if (is_prefetch(regs, error_code, address)) 849 return; 850 851 tsk->thread.cr2 = address; 852 tsk->thread.error_code = error_code; 853 tsk->thread.trap_nr = X86_TRAP_PF; 854 855 #ifdef CONFIG_MEMORY_FAILURE 856 if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) { 857 printk(KERN_ERR 858 "MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n", 859 tsk->comm, tsk->pid, address); 860 code = BUS_MCEERR_AR; 861 } 862 #endif 863 force_sig_info_fault(SIGBUS, code, address, tsk, fault); 864 } 865 866 static noinline void 867 mm_fault_error(struct pt_regs *regs, unsigned long error_code, 868 unsigned long address, unsigned int fault) 869 { 870 if (fatal_signal_pending(current) && !(error_code & PF_USER)) { 871 up_read(¤t->mm->mmap_sem); 872 no_context(regs, error_code, address, 0, 0); 873 return; 874 } 875 876 if (fault & VM_FAULT_OOM) { 877 /* Kernel mode? Handle exceptions or die: */ 878 if (!(error_code & PF_USER)) { 879 up_read(¤t->mm->mmap_sem); 880 no_context(regs, error_code, address, 881 SIGSEGV, SEGV_MAPERR); 882 return; 883 } 884 885 up_read(¤t->mm->mmap_sem); 886 887 /* 888 * We ran out of memory, call the OOM killer, and return the 889 * userspace (which will retry the fault, or kill us if we got 890 * oom-killed): 891 */ 892 pagefault_out_of_memory(); 893 } else { 894 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON| 895 VM_FAULT_HWPOISON_LARGE)) 896 do_sigbus(regs, error_code, address, fault); 897 else 898 BUG(); 899 } 900 } 901 902 static int spurious_fault_check(unsigned long error_code, pte_t *pte) 903 { 904 if ((error_code & PF_WRITE) && !pte_write(*pte)) 905 return 0; 906 907 if ((error_code & PF_INSTR) && !pte_exec(*pte)) 908 return 0; 909 910 return 1; 911 } 912 913 /* 914 * Handle a spurious fault caused by a stale TLB entry. 915 * 916 * This allows us to lazily refresh the TLB when increasing the 917 * permissions of a kernel page (RO -> RW or NX -> X). Doing it 918 * eagerly is very expensive since that implies doing a full 919 * cross-processor TLB flush, even if no stale TLB entries exist 920 * on other processors. 921 * 922 * There are no security implications to leaving a stale TLB when 923 * increasing the permissions on a page. 924 */ 925 static noinline __kprobes int 926 spurious_fault(unsigned long error_code, unsigned long address) 927 { 928 pgd_t *pgd; 929 pud_t *pud; 930 pmd_t *pmd; 931 pte_t *pte; 932 int ret; 933 934 /* Reserved-bit violation or user access to kernel space? */ 935 if (error_code & (PF_USER | PF_RSVD)) 936 return 0; 937 938 pgd = init_mm.pgd + pgd_index(address); 939 if (!pgd_present(*pgd)) 940 return 0; 941 942 pud = pud_offset(pgd, address); 943 if (!pud_present(*pud)) 944 return 0; 945 946 if (pud_large(*pud)) 947 return spurious_fault_check(error_code, (pte_t *) pud); 948 949 pmd = pmd_offset(pud, address); 950 if (!pmd_present(*pmd)) 951 return 0; 952 953 if (pmd_large(*pmd)) 954 return spurious_fault_check(error_code, (pte_t *) pmd); 955 956 pte = pte_offset_kernel(pmd, address); 957 if (!pte_present(*pte)) 958 return 0; 959 960 ret = spurious_fault_check(error_code, pte); 961 if (!ret) 962 return 0; 963 964 /* 965 * Make sure we have permissions in PMD. 966 * If not, then there's a bug in the page tables: 967 */ 968 ret = spurious_fault_check(error_code, (pte_t *) pmd); 969 WARN_ONCE(!ret, "PMD has incorrect permission bits\n"); 970 971 return ret; 972 } 973 974 int show_unhandled_signals = 1; 975 976 static inline int 977 access_error(unsigned long error_code, struct vm_area_struct *vma) 978 { 979 if (error_code & PF_WRITE) { 980 /* write, present and write, not present: */ 981 if (unlikely(!(vma->vm_flags & VM_WRITE))) 982 return 1; 983 return 0; 984 } 985 986 /* read, present: */ 987 if (unlikely(error_code & PF_PROT)) 988 return 1; 989 990 /* read, not present: */ 991 if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))) 992 return 1; 993 994 return 0; 995 } 996 997 static int fault_in_kernel_space(unsigned long address) 998 { 999 return address >= TASK_SIZE_MAX; 1000 } 1001 1002 static inline bool smap_violation(int error_code, struct pt_regs *regs) 1003 { 1004 if (!IS_ENABLED(CONFIG_X86_SMAP)) 1005 return false; 1006 1007 if (!static_cpu_has(X86_FEATURE_SMAP)) 1008 return false; 1009 1010 if (error_code & PF_USER) 1011 return false; 1012 1013 if (!user_mode_vm(regs) && (regs->flags & X86_EFLAGS_AC)) 1014 return false; 1015 1016 return true; 1017 } 1018 1019 /* 1020 * This routine handles page faults. It determines the address, 1021 * and the problem, and then passes it off to one of the appropriate 1022 * routines. 1023 */ 1024 static void __kprobes 1025 __do_page_fault(struct pt_regs *regs, unsigned long error_code) 1026 { 1027 struct vm_area_struct *vma; 1028 struct task_struct *tsk; 1029 unsigned long address; 1030 struct mm_struct *mm; 1031 int fault; 1032 unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE; 1033 1034 tsk = current; 1035 mm = tsk->mm; 1036 1037 /* Get the faulting address: */ 1038 address = read_cr2(); 1039 1040 /* 1041 * Detect and handle instructions that would cause a page fault for 1042 * both a tracked kernel page and a userspace page. 1043 */ 1044 if (kmemcheck_active(regs)) 1045 kmemcheck_hide(regs); 1046 prefetchw(&mm->mmap_sem); 1047 1048 if (unlikely(kmmio_fault(regs, address))) 1049 return; 1050 1051 /* 1052 * We fault-in kernel-space virtual memory on-demand. The 1053 * 'reference' page table is init_mm.pgd. 1054 * 1055 * NOTE! We MUST NOT take any locks for this case. We may 1056 * be in an interrupt or a critical region, and should 1057 * only copy the information from the master page table, 1058 * nothing more. 1059 * 1060 * This verifies that the fault happens in kernel space 1061 * (error_code & 4) == 0, and that the fault was not a 1062 * protection error (error_code & 9) == 0. 1063 */ 1064 if (unlikely(fault_in_kernel_space(address))) { 1065 if (!(error_code & (PF_RSVD | PF_USER | PF_PROT))) { 1066 if (vmalloc_fault(address) >= 0) 1067 return; 1068 1069 if (kmemcheck_fault(regs, address, error_code)) 1070 return; 1071 } 1072 1073 /* Can handle a stale RO->RW TLB: */ 1074 if (spurious_fault(error_code, address)) 1075 return; 1076 1077 /* kprobes don't want to hook the spurious faults: */ 1078 if (kprobes_fault(regs)) 1079 return; 1080 /* 1081 * Don't take the mm semaphore here. If we fixup a prefetch 1082 * fault we could otherwise deadlock: 1083 */ 1084 bad_area_nosemaphore(regs, error_code, address); 1085 1086 return; 1087 } 1088 1089 /* kprobes don't want to hook the spurious faults: */ 1090 if (unlikely(kprobes_fault(regs))) 1091 return; 1092 1093 if (unlikely(error_code & PF_RSVD)) 1094 pgtable_bad(regs, error_code, address); 1095 1096 if (unlikely(smap_violation(error_code, regs))) { 1097 bad_area_nosemaphore(regs, error_code, address); 1098 return; 1099 } 1100 1101 /* 1102 * If we're in an interrupt, have no user context or are running 1103 * in an atomic region then we must not take the fault: 1104 */ 1105 if (unlikely(in_atomic() || !mm)) { 1106 bad_area_nosemaphore(regs, error_code, address); 1107 return; 1108 } 1109 1110 /* 1111 * It's safe to allow irq's after cr2 has been saved and the 1112 * vmalloc fault has been handled. 1113 * 1114 * User-mode registers count as a user access even for any 1115 * potential system fault or CPU buglet: 1116 */ 1117 if (user_mode_vm(regs)) { 1118 local_irq_enable(); 1119 error_code |= PF_USER; 1120 flags |= FAULT_FLAG_USER; 1121 } else { 1122 if (regs->flags & X86_EFLAGS_IF) 1123 local_irq_enable(); 1124 } 1125 1126 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address); 1127 1128 if (error_code & PF_WRITE) 1129 flags |= FAULT_FLAG_WRITE; 1130 1131 /* 1132 * When running in the kernel we expect faults to occur only to 1133 * addresses in user space. All other faults represent errors in 1134 * the kernel and should generate an OOPS. Unfortunately, in the 1135 * case of an erroneous fault occurring in a code path which already 1136 * holds mmap_sem we will deadlock attempting to validate the fault 1137 * against the address space. Luckily the kernel only validly 1138 * references user space from well defined areas of code, which are 1139 * listed in the exceptions table. 1140 * 1141 * As the vast majority of faults will be valid we will only perform 1142 * the source reference check when there is a possibility of a 1143 * deadlock. Attempt to lock the address space, if we cannot we then 1144 * validate the source. If this is invalid we can skip the address 1145 * space check, thus avoiding the deadlock: 1146 */ 1147 if (unlikely(!down_read_trylock(&mm->mmap_sem))) { 1148 if ((error_code & PF_USER) == 0 && 1149 !search_exception_tables(regs->ip)) { 1150 bad_area_nosemaphore(regs, error_code, address); 1151 return; 1152 } 1153 retry: 1154 down_read(&mm->mmap_sem); 1155 } else { 1156 /* 1157 * The above down_read_trylock() might have succeeded in 1158 * which case we'll have missed the might_sleep() from 1159 * down_read(): 1160 */ 1161 might_sleep(); 1162 } 1163 1164 vma = find_vma(mm, address); 1165 if (unlikely(!vma)) { 1166 bad_area(regs, error_code, address); 1167 return; 1168 } 1169 if (likely(vma->vm_start <= address)) 1170 goto good_area; 1171 if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) { 1172 bad_area(regs, error_code, address); 1173 return; 1174 } 1175 if (error_code & PF_USER) { 1176 /* 1177 * Accessing the stack below %sp is always a bug. 1178 * The large cushion allows instructions like enter 1179 * and pusha to work. ("enter $65535, $31" pushes 1180 * 32 pointers and then decrements %sp by 65535.) 1181 */ 1182 if (unlikely(address + 65536 + 32 * sizeof(unsigned long) < regs->sp)) { 1183 bad_area(regs, error_code, address); 1184 return; 1185 } 1186 } 1187 if (unlikely(expand_stack(vma, address))) { 1188 bad_area(regs, error_code, address); 1189 return; 1190 } 1191 1192 /* 1193 * Ok, we have a good vm_area for this memory access, so 1194 * we can handle it.. 1195 */ 1196 good_area: 1197 if (unlikely(access_error(error_code, vma))) { 1198 bad_area_access_error(regs, error_code, address); 1199 return; 1200 } 1201 1202 /* 1203 * If for any reason at all we couldn't handle the fault, 1204 * make sure we exit gracefully rather than endlessly redo 1205 * the fault: 1206 */ 1207 fault = handle_mm_fault(mm, vma, address, flags); 1208 1209 /* 1210 * If we need to retry but a fatal signal is pending, handle the 1211 * signal first. We do not need to release the mmap_sem because it 1212 * would already be released in __lock_page_or_retry in mm/filemap.c. 1213 */ 1214 if (unlikely((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))) 1215 return; 1216 1217 if (unlikely(fault & VM_FAULT_ERROR)) { 1218 mm_fault_error(regs, error_code, address, fault); 1219 return; 1220 } 1221 1222 /* 1223 * Major/minor page fault accounting is only done on the 1224 * initial attempt. If we go through a retry, it is extremely 1225 * likely that the page will be found in page cache at that point. 1226 */ 1227 if (flags & FAULT_FLAG_ALLOW_RETRY) { 1228 if (fault & VM_FAULT_MAJOR) { 1229 tsk->maj_flt++; 1230 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, 1231 regs, address); 1232 } else { 1233 tsk->min_flt++; 1234 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, 1235 regs, address); 1236 } 1237 if (fault & VM_FAULT_RETRY) { 1238 /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk 1239 * of starvation. */ 1240 flags &= ~FAULT_FLAG_ALLOW_RETRY; 1241 flags |= FAULT_FLAG_TRIED; 1242 goto retry; 1243 } 1244 } 1245 1246 check_v8086_mode(regs, address, tsk); 1247 1248 up_read(&mm->mmap_sem); 1249 } 1250 1251 dotraplinkage void __kprobes 1252 do_page_fault(struct pt_regs *regs, unsigned long error_code) 1253 { 1254 enum ctx_state prev_state; 1255 1256 prev_state = exception_enter(); 1257 __do_page_fault(regs, error_code); 1258 exception_exit(prev_state); 1259 } 1260 1261 static void trace_page_fault_entries(struct pt_regs *regs, 1262 unsigned long error_code) 1263 { 1264 if (user_mode(regs)) 1265 trace_page_fault_user(read_cr2(), regs, error_code); 1266 else 1267 trace_page_fault_kernel(read_cr2(), regs, error_code); 1268 } 1269 1270 dotraplinkage void __kprobes 1271 trace_do_page_fault(struct pt_regs *regs, unsigned long error_code) 1272 { 1273 enum ctx_state prev_state; 1274 1275 prev_state = exception_enter(); 1276 trace_page_fault_entries(regs, error_code); 1277 __do_page_fault(regs, error_code); 1278 exception_exit(prev_state); 1279 } 1280