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/sched.h> /* test_thread_flag(), ... */ 7 #include <linux/kdebug.h> /* oops_begin/end, ... */ 8 #include <linux/module.h> /* search_exception_table */ 9 #include <linux/bootmem.h> /* max_low_pfn */ 10 #include <linux/kprobes.h> /* NOKPROBE_SYMBOL, ... */ 11 #include <linux/mmiotrace.h> /* kmmio_handler, ... */ 12 #include <linux/perf_event.h> /* perf_sw_event */ 13 #include <linux/hugetlb.h> /* hstate_index_to_shift */ 14 #include <linux/prefetch.h> /* prefetchw */ 15 #include <linux/context_tracking.h> /* exception_enter(), ... */ 16 #include <linux/uaccess.h> /* faulthandler_disabled() */ 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_ADDR */ 22 #include <asm/vsyscall.h> /* emulate_vsyscall */ 23 #include <asm/vm86.h> /* struct vm86 */ 24 25 #define CREATE_TRACE_POINTS 26 #include <asm/trace/exceptions.h> 27 28 /* 29 * Page fault error code bits: 30 * 31 * bit 0 == 0: no page found 1: protection fault 32 * bit 1 == 0: read access 1: write access 33 * bit 2 == 0: kernel-mode access 1: user-mode access 34 * bit 3 == 1: use of reserved bit detected 35 * bit 4 == 1: fault was an instruction fetch 36 */ 37 enum x86_pf_error_code { 38 39 PF_PROT = 1 << 0, 40 PF_WRITE = 1 << 1, 41 PF_USER = 1 << 2, 42 PF_RSVD = 1 << 3, 43 PF_INSTR = 1 << 4, 44 }; 45 46 /* 47 * Returns 0 if mmiotrace is disabled, or if the fault is not 48 * handled by mmiotrace: 49 */ 50 static nokprobe_inline int 51 kmmio_fault(struct pt_regs *regs, unsigned long addr) 52 { 53 if (unlikely(is_kmmio_active())) 54 if (kmmio_handler(regs, addr) == 1) 55 return -1; 56 return 0; 57 } 58 59 static nokprobe_inline int kprobes_fault(struct pt_regs *regs) 60 { 61 int ret = 0; 62 63 /* kprobe_running() needs smp_processor_id() */ 64 if (kprobes_built_in() && !user_mode(regs)) { 65 preempt_disable(); 66 if (kprobe_running() && kprobe_fault_handler(regs, 14)) 67 ret = 1; 68 preempt_enable(); 69 } 70 71 return ret; 72 } 73 74 /* 75 * Prefetch quirks: 76 * 77 * 32-bit mode: 78 * 79 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch. 80 * Check that here and ignore it. 81 * 82 * 64-bit mode: 83 * 84 * Sometimes the CPU reports invalid exceptions on prefetch. 85 * Check that here and ignore it. 86 * 87 * Opcode checker based on code by Richard Brunner. 88 */ 89 static inline int 90 check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr, 91 unsigned char opcode, int *prefetch) 92 { 93 unsigned char instr_hi = opcode & 0xf0; 94 unsigned char instr_lo = opcode & 0x0f; 95 96 switch (instr_hi) { 97 case 0x20: 98 case 0x30: 99 /* 100 * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes. 101 * In X86_64 long mode, the CPU will signal invalid 102 * opcode if some of these prefixes are present so 103 * X86_64 will never get here anyway 104 */ 105 return ((instr_lo & 7) == 0x6); 106 #ifdef CONFIG_X86_64 107 case 0x40: 108 /* 109 * In AMD64 long mode 0x40..0x4F are valid REX prefixes 110 * Need to figure out under what instruction mode the 111 * instruction was issued. Could check the LDT for lm, 112 * but for now it's good enough to assume that long 113 * mode only uses well known segments or kernel. 114 */ 115 return (!user_mode(regs) || user_64bit_mode(regs)); 116 #endif 117 case 0x60: 118 /* 0x64 thru 0x67 are valid prefixes in all modes. */ 119 return (instr_lo & 0xC) == 0x4; 120 case 0xF0: 121 /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */ 122 return !instr_lo || (instr_lo>>1) == 1; 123 case 0x00: 124 /* Prefetch instruction is 0x0F0D or 0x0F18 */ 125 if (probe_kernel_address(instr, opcode)) 126 return 0; 127 128 *prefetch = (instr_lo == 0xF) && 129 (opcode == 0x0D || opcode == 0x18); 130 return 0; 131 default: 132 return 0; 133 } 134 } 135 136 static int 137 is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr) 138 { 139 unsigned char *max_instr; 140 unsigned char *instr; 141 int prefetch = 0; 142 143 /* 144 * If it was a exec (instruction fetch) fault on NX page, then 145 * do not ignore the fault: 146 */ 147 if (error_code & PF_INSTR) 148 return 0; 149 150 instr = (void *)convert_ip_to_linear(current, regs); 151 max_instr = instr + 15; 152 153 if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE_MAX) 154 return 0; 155 156 while (instr < max_instr) { 157 unsigned char opcode; 158 159 if (probe_kernel_address(instr, opcode)) 160 break; 161 162 instr++; 163 164 if (!check_prefetch_opcode(regs, instr, opcode, &prefetch)) 165 break; 166 } 167 return prefetch; 168 } 169 170 static void 171 force_sig_info_fault(int si_signo, int si_code, unsigned long address, 172 struct task_struct *tsk, int fault) 173 { 174 unsigned lsb = 0; 175 siginfo_t info; 176 177 info.si_signo = si_signo; 178 info.si_errno = 0; 179 info.si_code = si_code; 180 info.si_addr = (void __user *)address; 181 if (fault & VM_FAULT_HWPOISON_LARGE) 182 lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault)); 183 if (fault & VM_FAULT_HWPOISON) 184 lsb = PAGE_SHIFT; 185 info.si_addr_lsb = lsb; 186 187 force_sig_info(si_signo, &info, tsk); 188 } 189 190 DEFINE_SPINLOCK(pgd_lock); 191 LIST_HEAD(pgd_list); 192 193 #ifdef CONFIG_X86_32 194 static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address) 195 { 196 unsigned index = pgd_index(address); 197 pgd_t *pgd_k; 198 pud_t *pud, *pud_k; 199 pmd_t *pmd, *pmd_k; 200 201 pgd += index; 202 pgd_k = init_mm.pgd + index; 203 204 if (!pgd_present(*pgd_k)) 205 return NULL; 206 207 /* 208 * set_pgd(pgd, *pgd_k); here would be useless on PAE 209 * and redundant with the set_pmd() on non-PAE. As would 210 * set_pud. 211 */ 212 pud = pud_offset(pgd, address); 213 pud_k = pud_offset(pgd_k, address); 214 if (!pud_present(*pud_k)) 215 return NULL; 216 217 pmd = pmd_offset(pud, address); 218 pmd_k = pmd_offset(pud_k, address); 219 if (!pmd_present(*pmd_k)) 220 return NULL; 221 222 if (!pmd_present(*pmd)) 223 set_pmd(pmd, *pmd_k); 224 else 225 BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k)); 226 227 return pmd_k; 228 } 229 230 void vmalloc_sync_all(void) 231 { 232 unsigned long address; 233 234 if (SHARED_KERNEL_PMD) 235 return; 236 237 for (address = VMALLOC_START & PMD_MASK; 238 address >= TASK_SIZE && address < FIXADDR_TOP; 239 address += PMD_SIZE) { 240 struct page *page; 241 242 spin_lock(&pgd_lock); 243 list_for_each_entry(page, &pgd_list, lru) { 244 spinlock_t *pgt_lock; 245 pmd_t *ret; 246 247 /* the pgt_lock only for Xen */ 248 pgt_lock = &pgd_page_get_mm(page)->page_table_lock; 249 250 spin_lock(pgt_lock); 251 ret = vmalloc_sync_one(page_address(page), address); 252 spin_unlock(pgt_lock); 253 254 if (!ret) 255 break; 256 } 257 spin_unlock(&pgd_lock); 258 } 259 } 260 261 /* 262 * 32-bit: 263 * 264 * Handle a fault on the vmalloc or module mapping area 265 */ 266 static noinline int vmalloc_fault(unsigned long address) 267 { 268 unsigned long pgd_paddr; 269 pmd_t *pmd_k; 270 pte_t *pte_k; 271 272 /* Make sure we are in vmalloc area: */ 273 if (!(address >= VMALLOC_START && address < VMALLOC_END)) 274 return -1; 275 276 WARN_ON_ONCE(in_nmi()); 277 278 /* 279 * Synchronize this task's top level page-table 280 * with the 'reference' page table. 281 * 282 * Do _not_ use "current" here. We might be inside 283 * an interrupt in the middle of a task switch.. 284 */ 285 pgd_paddr = read_cr3(); 286 pmd_k = vmalloc_sync_one(__va(pgd_paddr), address); 287 if (!pmd_k) 288 return -1; 289 290 pte_k = pte_offset_kernel(pmd_k, address); 291 if (!pte_present(*pte_k)) 292 return -1; 293 294 return 0; 295 } 296 NOKPROBE_SYMBOL(vmalloc_fault); 297 298 /* 299 * Did it hit the DOS screen memory VA from vm86 mode? 300 */ 301 static inline void 302 check_v8086_mode(struct pt_regs *regs, unsigned long address, 303 struct task_struct *tsk) 304 { 305 #ifdef CONFIG_VM86 306 unsigned long bit; 307 308 if (!v8086_mode(regs) || !tsk->thread.vm86) 309 return; 310 311 bit = (address - 0xA0000) >> PAGE_SHIFT; 312 if (bit < 32) 313 tsk->thread.vm86->screen_bitmap |= 1 << bit; 314 #endif 315 } 316 317 static bool low_pfn(unsigned long pfn) 318 { 319 return pfn < max_low_pfn; 320 } 321 322 static void dump_pagetable(unsigned long address) 323 { 324 pgd_t *base = __va(read_cr3()); 325 pgd_t *pgd = &base[pgd_index(address)]; 326 pmd_t *pmd; 327 pte_t *pte; 328 329 #ifdef CONFIG_X86_PAE 330 printk("*pdpt = %016Lx ", pgd_val(*pgd)); 331 if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd)) 332 goto out; 333 #endif 334 pmd = pmd_offset(pud_offset(pgd, address), address); 335 printk(KERN_CONT "*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd)); 336 337 /* 338 * We must not directly access the pte in the highpte 339 * case if the page table is located in highmem. 340 * And let's rather not kmap-atomic the pte, just in case 341 * it's allocated already: 342 */ 343 if (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_large(*pmd)) 344 goto out; 345 346 pte = pte_offset_kernel(pmd, address); 347 printk("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte)); 348 out: 349 printk("\n"); 350 } 351 352 #else /* CONFIG_X86_64: */ 353 354 void vmalloc_sync_all(void) 355 { 356 sync_global_pgds(VMALLOC_START & PGDIR_MASK, VMALLOC_END, 0); 357 } 358 359 /* 360 * 64-bit: 361 * 362 * Handle a fault on the vmalloc area 363 * 364 * This assumes no large pages in there. 365 */ 366 static noinline int vmalloc_fault(unsigned long address) 367 { 368 pgd_t *pgd, *pgd_ref; 369 pud_t *pud, *pud_ref; 370 pmd_t *pmd, *pmd_ref; 371 pte_t *pte, *pte_ref; 372 373 /* Make sure we are in vmalloc area: */ 374 if (!(address >= VMALLOC_START && address < VMALLOC_END)) 375 return -1; 376 377 WARN_ON_ONCE(in_nmi()); 378 379 /* 380 * Copy kernel mappings over when needed. This can also 381 * happen within a race in page table update. In the later 382 * case just flush: 383 */ 384 pgd = pgd_offset(current->active_mm, address); 385 pgd_ref = pgd_offset_k(address); 386 if (pgd_none(*pgd_ref)) 387 return -1; 388 389 if (pgd_none(*pgd)) { 390 set_pgd(pgd, *pgd_ref); 391 arch_flush_lazy_mmu_mode(); 392 } else { 393 BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref)); 394 } 395 396 /* 397 * Below here mismatches are bugs because these lower tables 398 * are shared: 399 */ 400 401 pud = pud_offset(pgd, address); 402 pud_ref = pud_offset(pgd_ref, address); 403 if (pud_none(*pud_ref)) 404 return -1; 405 406 if (pud_none(*pud) || pud_page_vaddr(*pud) != pud_page_vaddr(*pud_ref)) 407 BUG(); 408 409 pmd = pmd_offset(pud, address); 410 pmd_ref = pmd_offset(pud_ref, address); 411 if (pmd_none(*pmd_ref)) 412 return -1; 413 414 if (pmd_none(*pmd) || pmd_page(*pmd) != pmd_page(*pmd_ref)) 415 BUG(); 416 417 pte_ref = pte_offset_kernel(pmd_ref, address); 418 if (!pte_present(*pte_ref)) 419 return -1; 420 421 pte = pte_offset_kernel(pmd, address); 422 423 /* 424 * Don't use pte_page here, because the mappings can point 425 * outside mem_map, and the NUMA hash lookup cannot handle 426 * that: 427 */ 428 if (!pte_present(*pte) || pte_pfn(*pte) != pte_pfn(*pte_ref)) 429 BUG(); 430 431 return 0; 432 } 433 NOKPROBE_SYMBOL(vmalloc_fault); 434 435 #ifdef CONFIG_CPU_SUP_AMD 436 static const char errata93_warning[] = 437 KERN_ERR 438 "******* Your BIOS seems to not contain a fix for K8 errata #93\n" 439 "******* Working around it, but it may cause SEGVs or burn power.\n" 440 "******* Please consider a BIOS update.\n" 441 "******* Disabling USB legacy in the BIOS may also help.\n"; 442 #endif 443 444 /* 445 * No vm86 mode in 64-bit mode: 446 */ 447 static inline void 448 check_v8086_mode(struct pt_regs *regs, unsigned long address, 449 struct task_struct *tsk) 450 { 451 } 452 453 static int bad_address(void *p) 454 { 455 unsigned long dummy; 456 457 return probe_kernel_address((unsigned long *)p, dummy); 458 } 459 460 static void dump_pagetable(unsigned long address) 461 { 462 pgd_t *base = __va(read_cr3() & PHYSICAL_PAGE_MASK); 463 pgd_t *pgd = base + pgd_index(address); 464 pud_t *pud; 465 pmd_t *pmd; 466 pte_t *pte; 467 468 if (bad_address(pgd)) 469 goto bad; 470 471 printk("PGD %lx ", pgd_val(*pgd)); 472 473 if (!pgd_present(*pgd)) 474 goto out; 475 476 pud = pud_offset(pgd, address); 477 if (bad_address(pud)) 478 goto bad; 479 480 printk("PUD %lx ", pud_val(*pud)); 481 if (!pud_present(*pud) || pud_large(*pud)) 482 goto out; 483 484 pmd = pmd_offset(pud, address); 485 if (bad_address(pmd)) 486 goto bad; 487 488 printk("PMD %lx ", pmd_val(*pmd)); 489 if (!pmd_present(*pmd) || pmd_large(*pmd)) 490 goto out; 491 492 pte = pte_offset_kernel(pmd, address); 493 if (bad_address(pte)) 494 goto bad; 495 496 printk("PTE %lx", pte_val(*pte)); 497 out: 498 printk("\n"); 499 return; 500 bad: 501 printk("BAD\n"); 502 } 503 504 #endif /* CONFIG_X86_64 */ 505 506 /* 507 * Workaround for K8 erratum #93 & buggy BIOS. 508 * 509 * BIOS SMM functions are required to use a specific workaround 510 * to avoid corruption of the 64bit RIP register on C stepping K8. 511 * 512 * A lot of BIOS that didn't get tested properly miss this. 513 * 514 * The OS sees this as a page fault with the upper 32bits of RIP cleared. 515 * Try to work around it here. 516 * 517 * Note we only handle faults in kernel here. 518 * Does nothing on 32-bit. 519 */ 520 static int is_errata93(struct pt_regs *regs, unsigned long address) 521 { 522 #if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD) 523 if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD 524 || boot_cpu_data.x86 != 0xf) 525 return 0; 526 527 if (address != regs->ip) 528 return 0; 529 530 if ((address >> 32) != 0) 531 return 0; 532 533 address |= 0xffffffffUL << 32; 534 if ((address >= (u64)_stext && address <= (u64)_etext) || 535 (address >= MODULES_VADDR && address <= MODULES_END)) { 536 printk_once(errata93_warning); 537 regs->ip = address; 538 return 1; 539 } 540 #endif 541 return 0; 542 } 543 544 /* 545 * Work around K8 erratum #100 K8 in compat mode occasionally jumps 546 * to illegal addresses >4GB. 547 * 548 * We catch this in the page fault handler because these addresses 549 * are not reachable. Just detect this case and return. Any code 550 * segment in LDT is compatibility mode. 551 */ 552 static int is_errata100(struct pt_regs *regs, unsigned long address) 553 { 554 #ifdef CONFIG_X86_64 555 if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32)) 556 return 1; 557 #endif 558 return 0; 559 } 560 561 static int is_f00f_bug(struct pt_regs *regs, unsigned long address) 562 { 563 #ifdef CONFIG_X86_F00F_BUG 564 unsigned long nr; 565 566 /* 567 * Pentium F0 0F C7 C8 bug workaround: 568 */ 569 if (boot_cpu_has_bug(X86_BUG_F00F)) { 570 nr = (address - idt_descr.address) >> 3; 571 572 if (nr == 6) { 573 do_invalid_op(regs, 0); 574 return 1; 575 } 576 } 577 #endif 578 return 0; 579 } 580 581 static const char nx_warning[] = KERN_CRIT 582 "kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n"; 583 static const char smep_warning[] = KERN_CRIT 584 "unable to execute userspace code (SMEP?) (uid: %d)\n"; 585 586 static void 587 show_fault_oops(struct pt_regs *regs, unsigned long error_code, 588 unsigned long address) 589 { 590 if (!oops_may_print()) 591 return; 592 593 if (error_code & PF_INSTR) { 594 unsigned int level; 595 pgd_t *pgd; 596 pte_t *pte; 597 598 pgd = __va(read_cr3() & PHYSICAL_PAGE_MASK); 599 pgd += pgd_index(address); 600 601 pte = lookup_address_in_pgd(pgd, address, &level); 602 603 if (pte && pte_present(*pte) && !pte_exec(*pte)) 604 printk(nx_warning, from_kuid(&init_user_ns, current_uid())); 605 if (pte && pte_present(*pte) && pte_exec(*pte) && 606 (pgd_flags(*pgd) & _PAGE_USER) && 607 (__read_cr4() & X86_CR4_SMEP)) 608 printk(smep_warning, from_kuid(&init_user_ns, current_uid())); 609 } 610 611 printk(KERN_ALERT "BUG: unable to handle kernel "); 612 if (address < PAGE_SIZE) 613 printk(KERN_CONT "NULL pointer dereference"); 614 else 615 printk(KERN_CONT "paging request"); 616 617 printk(KERN_CONT " at %p\n", (void *) address); 618 printk(KERN_ALERT "IP:"); 619 printk_address(regs->ip); 620 621 dump_pagetable(address); 622 } 623 624 static noinline void 625 pgtable_bad(struct pt_regs *regs, unsigned long error_code, 626 unsigned long address) 627 { 628 struct task_struct *tsk; 629 unsigned long flags; 630 int sig; 631 632 flags = oops_begin(); 633 tsk = current; 634 sig = SIGKILL; 635 636 printk(KERN_ALERT "%s: Corrupted page table at address %lx\n", 637 tsk->comm, address); 638 dump_pagetable(address); 639 640 tsk->thread.cr2 = address; 641 tsk->thread.trap_nr = X86_TRAP_PF; 642 tsk->thread.error_code = error_code; 643 644 if (__die("Bad pagetable", regs, error_code)) 645 sig = 0; 646 647 oops_end(flags, regs, sig); 648 } 649 650 static noinline void 651 no_context(struct pt_regs *regs, unsigned long error_code, 652 unsigned long address, int signal, int si_code) 653 { 654 struct task_struct *tsk = current; 655 unsigned long flags; 656 int sig; 657 658 /* Are we prepared to handle this kernel fault? */ 659 if (fixup_exception(regs)) { 660 /* 661 * Any interrupt that takes a fault gets the fixup. This makes 662 * the below recursive fault logic only apply to a faults from 663 * task context. 664 */ 665 if (in_interrupt()) 666 return; 667 668 /* 669 * Per the above we're !in_interrupt(), aka. task context. 670 * 671 * In this case we need to make sure we're not recursively 672 * faulting through the emulate_vsyscall() logic. 673 */ 674 if (current_thread_info()->sig_on_uaccess_error && signal) { 675 tsk->thread.trap_nr = X86_TRAP_PF; 676 tsk->thread.error_code = error_code | PF_USER; 677 tsk->thread.cr2 = address; 678 679 /* XXX: hwpoison faults will set the wrong code. */ 680 force_sig_info_fault(signal, si_code, address, tsk, 0); 681 } 682 683 /* 684 * Barring that, we can do the fixup and be happy. 685 */ 686 return; 687 } 688 689 /* 690 * 32-bit: 691 * 692 * Valid to do another page fault here, because if this fault 693 * had been triggered by is_prefetch fixup_exception would have 694 * handled it. 695 * 696 * 64-bit: 697 * 698 * Hall of shame of CPU/BIOS bugs. 699 */ 700 if (is_prefetch(regs, error_code, address)) 701 return; 702 703 if (is_errata93(regs, address)) 704 return; 705 706 /* 707 * Oops. The kernel tried to access some bad page. We'll have to 708 * terminate things with extreme prejudice: 709 */ 710 flags = oops_begin(); 711 712 show_fault_oops(regs, error_code, address); 713 714 if (task_stack_end_corrupted(tsk)) 715 printk(KERN_EMERG "Thread overran stack, or stack corrupted\n"); 716 717 tsk->thread.cr2 = address; 718 tsk->thread.trap_nr = X86_TRAP_PF; 719 tsk->thread.error_code = error_code; 720 721 sig = SIGKILL; 722 if (__die("Oops", regs, error_code)) 723 sig = 0; 724 725 /* Executive summary in case the body of the oops scrolled away */ 726 printk(KERN_DEFAULT "CR2: %016lx\n", address); 727 728 oops_end(flags, regs, sig); 729 } 730 731 /* 732 * Print out info about fatal segfaults, if the show_unhandled_signals 733 * sysctl is set: 734 */ 735 static inline void 736 show_signal_msg(struct pt_regs *regs, unsigned long error_code, 737 unsigned long address, struct task_struct *tsk) 738 { 739 if (!unhandled_signal(tsk, SIGSEGV)) 740 return; 741 742 if (!printk_ratelimit()) 743 return; 744 745 printk("%s%s[%d]: segfault at %lx ip %p sp %p error %lx", 746 task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG, 747 tsk->comm, task_pid_nr(tsk), address, 748 (void *)regs->ip, (void *)regs->sp, error_code); 749 750 print_vma_addr(KERN_CONT " in ", regs->ip); 751 752 printk(KERN_CONT "\n"); 753 } 754 755 static void 756 __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, 757 unsigned long address, int si_code) 758 { 759 struct task_struct *tsk = current; 760 761 /* User mode accesses just cause a SIGSEGV */ 762 if (error_code & PF_USER) { 763 /* 764 * It's possible to have interrupts off here: 765 */ 766 local_irq_enable(); 767 768 /* 769 * Valid to do another page fault here because this one came 770 * from user space: 771 */ 772 if (is_prefetch(regs, error_code, address)) 773 return; 774 775 if (is_errata100(regs, address)) 776 return; 777 778 #ifdef CONFIG_X86_64 779 /* 780 * Instruction fetch faults in the vsyscall page might need 781 * emulation. 782 */ 783 if (unlikely((error_code & PF_INSTR) && 784 ((address & ~0xfff) == VSYSCALL_ADDR))) { 785 if (emulate_vsyscall(regs, address)) 786 return; 787 } 788 #endif 789 /* Kernel addresses are always protection faults: */ 790 if (address >= TASK_SIZE) 791 error_code |= PF_PROT; 792 793 if (likely(show_unhandled_signals)) 794 show_signal_msg(regs, error_code, address, tsk); 795 796 tsk->thread.cr2 = address; 797 tsk->thread.error_code = error_code; 798 tsk->thread.trap_nr = X86_TRAP_PF; 799 800 force_sig_info_fault(SIGSEGV, si_code, address, tsk, 0); 801 802 return; 803 } 804 805 if (is_f00f_bug(regs, address)) 806 return; 807 808 no_context(regs, error_code, address, SIGSEGV, si_code); 809 } 810 811 static noinline void 812 bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, 813 unsigned long address) 814 { 815 __bad_area_nosemaphore(regs, error_code, address, SEGV_MAPERR); 816 } 817 818 static void 819 __bad_area(struct pt_regs *regs, unsigned long error_code, 820 unsigned long address, int si_code) 821 { 822 struct mm_struct *mm = current->mm; 823 824 /* 825 * Something tried to access memory that isn't in our memory map.. 826 * Fix it, but check if it's kernel or user first.. 827 */ 828 up_read(&mm->mmap_sem); 829 830 __bad_area_nosemaphore(regs, error_code, address, si_code); 831 } 832 833 static noinline void 834 bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address) 835 { 836 __bad_area(regs, error_code, address, SEGV_MAPERR); 837 } 838 839 static noinline void 840 bad_area_access_error(struct pt_regs *regs, unsigned long error_code, 841 unsigned long address) 842 { 843 __bad_area(regs, error_code, address, SEGV_ACCERR); 844 } 845 846 static void 847 do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address, 848 unsigned int fault) 849 { 850 struct task_struct *tsk = current; 851 int code = BUS_ADRERR; 852 853 /* Kernel mode? Handle exceptions or die: */ 854 if (!(error_code & PF_USER)) { 855 no_context(regs, error_code, address, SIGBUS, BUS_ADRERR); 856 return; 857 } 858 859 /* User-space => ok to do another page fault: */ 860 if (is_prefetch(regs, error_code, address)) 861 return; 862 863 tsk->thread.cr2 = address; 864 tsk->thread.error_code = error_code; 865 tsk->thread.trap_nr = X86_TRAP_PF; 866 867 #ifdef CONFIG_MEMORY_FAILURE 868 if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) { 869 printk(KERN_ERR 870 "MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n", 871 tsk->comm, tsk->pid, address); 872 code = BUS_MCEERR_AR; 873 } 874 #endif 875 force_sig_info_fault(SIGBUS, code, address, tsk, fault); 876 } 877 878 static noinline void 879 mm_fault_error(struct pt_regs *regs, unsigned long error_code, 880 unsigned long address, unsigned int fault) 881 { 882 if (fatal_signal_pending(current) && !(error_code & PF_USER)) { 883 no_context(regs, error_code, address, 0, 0); 884 return; 885 } 886 887 if (fault & VM_FAULT_OOM) { 888 /* Kernel mode? Handle exceptions or die: */ 889 if (!(error_code & PF_USER)) { 890 no_context(regs, error_code, address, 891 SIGSEGV, SEGV_MAPERR); 892 return; 893 } 894 895 /* 896 * We ran out of memory, call the OOM killer, and return the 897 * userspace (which will retry the fault, or kill us if we got 898 * oom-killed): 899 */ 900 pagefault_out_of_memory(); 901 } else { 902 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON| 903 VM_FAULT_HWPOISON_LARGE)) 904 do_sigbus(regs, error_code, address, fault); 905 else if (fault & VM_FAULT_SIGSEGV) 906 bad_area_nosemaphore(regs, error_code, address); 907 else 908 BUG(); 909 } 910 } 911 912 static int spurious_fault_check(unsigned long error_code, pte_t *pte) 913 { 914 if ((error_code & PF_WRITE) && !pte_write(*pte)) 915 return 0; 916 917 if ((error_code & PF_INSTR) && !pte_exec(*pte)) 918 return 0; 919 920 return 1; 921 } 922 923 /* 924 * Handle a spurious fault caused by a stale TLB entry. 925 * 926 * This allows us to lazily refresh the TLB when increasing the 927 * permissions of a kernel page (RO -> RW or NX -> X). Doing it 928 * eagerly is very expensive since that implies doing a full 929 * cross-processor TLB flush, even if no stale TLB entries exist 930 * on other processors. 931 * 932 * Spurious faults may only occur if the TLB contains an entry with 933 * fewer permission than the page table entry. Non-present (P = 0) 934 * and reserved bit (R = 1) faults are never spurious. 935 * 936 * There are no security implications to leaving a stale TLB when 937 * increasing the permissions on a page. 938 * 939 * Returns non-zero if a spurious fault was handled, zero otherwise. 940 * 941 * See Intel Developer's Manual Vol 3 Section 4.10.4.3, bullet 3 942 * (Optional Invalidation). 943 */ 944 static noinline int 945 spurious_fault(unsigned long error_code, unsigned long address) 946 { 947 pgd_t *pgd; 948 pud_t *pud; 949 pmd_t *pmd; 950 pte_t *pte; 951 int ret; 952 953 /* 954 * Only writes to RO or instruction fetches from NX may cause 955 * spurious faults. 956 * 957 * These could be from user or supervisor accesses but the TLB 958 * is only lazily flushed after a kernel mapping protection 959 * change, so user accesses are not expected to cause spurious 960 * faults. 961 */ 962 if (error_code != (PF_WRITE | PF_PROT) 963 && error_code != (PF_INSTR | PF_PROT)) 964 return 0; 965 966 pgd = init_mm.pgd + pgd_index(address); 967 if (!pgd_present(*pgd)) 968 return 0; 969 970 pud = pud_offset(pgd, address); 971 if (!pud_present(*pud)) 972 return 0; 973 974 if (pud_large(*pud)) 975 return spurious_fault_check(error_code, (pte_t *) pud); 976 977 pmd = pmd_offset(pud, address); 978 if (!pmd_present(*pmd)) 979 return 0; 980 981 if (pmd_large(*pmd)) 982 return spurious_fault_check(error_code, (pte_t *) pmd); 983 984 pte = pte_offset_kernel(pmd, address); 985 if (!pte_present(*pte)) 986 return 0; 987 988 ret = spurious_fault_check(error_code, pte); 989 if (!ret) 990 return 0; 991 992 /* 993 * Make sure we have permissions in PMD. 994 * If not, then there's a bug in the page tables: 995 */ 996 ret = spurious_fault_check(error_code, (pte_t *) pmd); 997 WARN_ONCE(!ret, "PMD has incorrect permission bits\n"); 998 999 return ret; 1000 } 1001 NOKPROBE_SYMBOL(spurious_fault); 1002 1003 int show_unhandled_signals = 1; 1004 1005 static inline int 1006 access_error(unsigned long error_code, struct vm_area_struct *vma) 1007 { 1008 if (error_code & PF_WRITE) { 1009 /* write, present and write, not present: */ 1010 if (unlikely(!(vma->vm_flags & VM_WRITE))) 1011 return 1; 1012 return 0; 1013 } 1014 1015 /* read, present: */ 1016 if (unlikely(error_code & PF_PROT)) 1017 return 1; 1018 1019 /* read, not present: */ 1020 if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))) 1021 return 1; 1022 1023 return 0; 1024 } 1025 1026 static int fault_in_kernel_space(unsigned long address) 1027 { 1028 return address >= TASK_SIZE_MAX; 1029 } 1030 1031 static inline bool smap_violation(int error_code, struct pt_regs *regs) 1032 { 1033 if (!IS_ENABLED(CONFIG_X86_SMAP)) 1034 return false; 1035 1036 if (!static_cpu_has(X86_FEATURE_SMAP)) 1037 return false; 1038 1039 if (error_code & PF_USER) 1040 return false; 1041 1042 if (!user_mode(regs) && (regs->flags & X86_EFLAGS_AC)) 1043 return false; 1044 1045 return true; 1046 } 1047 1048 /* 1049 * This routine handles page faults. It determines the address, 1050 * and the problem, and then passes it off to one of the appropriate 1051 * routines. 1052 * 1053 * This function must have noinline because both callers 1054 * {,trace_}do_page_fault() have notrace on. Having this an actual function 1055 * guarantees there's a function trace entry. 1056 */ 1057 static noinline void 1058 __do_page_fault(struct pt_regs *regs, unsigned long error_code, 1059 unsigned long address) 1060 { 1061 struct vm_area_struct *vma; 1062 struct task_struct *tsk; 1063 struct mm_struct *mm; 1064 int fault, major = 0; 1065 unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE; 1066 1067 tsk = current; 1068 mm = tsk->mm; 1069 1070 /* 1071 * Detect and handle instructions that would cause a page fault for 1072 * both a tracked kernel page and a userspace page. 1073 */ 1074 if (kmemcheck_active(regs)) 1075 kmemcheck_hide(regs); 1076 prefetchw(&mm->mmap_sem); 1077 1078 if (unlikely(kmmio_fault(regs, address))) 1079 return; 1080 1081 /* 1082 * We fault-in kernel-space virtual memory on-demand. The 1083 * 'reference' page table is init_mm.pgd. 1084 * 1085 * NOTE! We MUST NOT take any locks for this case. We may 1086 * be in an interrupt or a critical region, and should 1087 * only copy the information from the master page table, 1088 * nothing more. 1089 * 1090 * This verifies that the fault happens in kernel space 1091 * (error_code & 4) == 0, and that the fault was not a 1092 * protection error (error_code & 9) == 0. 1093 */ 1094 if (unlikely(fault_in_kernel_space(address))) { 1095 if (!(error_code & (PF_RSVD | PF_USER | PF_PROT))) { 1096 if (vmalloc_fault(address) >= 0) 1097 return; 1098 1099 if (kmemcheck_fault(regs, address, error_code)) 1100 return; 1101 } 1102 1103 /* Can handle a stale RO->RW TLB: */ 1104 if (spurious_fault(error_code, address)) 1105 return; 1106 1107 /* kprobes don't want to hook the spurious faults: */ 1108 if (kprobes_fault(regs)) 1109 return; 1110 /* 1111 * Don't take the mm semaphore here. If we fixup a prefetch 1112 * fault we could otherwise deadlock: 1113 */ 1114 bad_area_nosemaphore(regs, error_code, address); 1115 1116 return; 1117 } 1118 1119 /* kprobes don't want to hook the spurious faults: */ 1120 if (unlikely(kprobes_fault(regs))) 1121 return; 1122 1123 if (unlikely(error_code & PF_RSVD)) 1124 pgtable_bad(regs, error_code, address); 1125 1126 if (unlikely(smap_violation(error_code, regs))) { 1127 bad_area_nosemaphore(regs, error_code, address); 1128 return; 1129 } 1130 1131 /* 1132 * If we're in an interrupt, have no user context or are running 1133 * in a region with pagefaults disabled then we must not take the fault 1134 */ 1135 if (unlikely(faulthandler_disabled() || !mm)) { 1136 bad_area_nosemaphore(regs, error_code, address); 1137 return; 1138 } 1139 1140 /* 1141 * It's safe to allow irq's after cr2 has been saved and the 1142 * vmalloc fault has been handled. 1143 * 1144 * User-mode registers count as a user access even for any 1145 * potential system fault or CPU buglet: 1146 */ 1147 if (user_mode(regs)) { 1148 local_irq_enable(); 1149 error_code |= PF_USER; 1150 flags |= FAULT_FLAG_USER; 1151 } else { 1152 if (regs->flags & X86_EFLAGS_IF) 1153 local_irq_enable(); 1154 } 1155 1156 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address); 1157 1158 if (error_code & PF_WRITE) 1159 flags |= FAULT_FLAG_WRITE; 1160 1161 /* 1162 * When running in the kernel we expect faults to occur only to 1163 * addresses in user space. All other faults represent errors in 1164 * the kernel and should generate an OOPS. Unfortunately, in the 1165 * case of an erroneous fault occurring in a code path which already 1166 * holds mmap_sem we will deadlock attempting to validate the fault 1167 * against the address space. Luckily the kernel only validly 1168 * references user space from well defined areas of code, which are 1169 * listed in the exceptions table. 1170 * 1171 * As the vast majority of faults will be valid we will only perform 1172 * the source reference check when there is a possibility of a 1173 * deadlock. Attempt to lock the address space, if we cannot we then 1174 * validate the source. If this is invalid we can skip the address 1175 * space check, thus avoiding the deadlock: 1176 */ 1177 if (unlikely(!down_read_trylock(&mm->mmap_sem))) { 1178 if ((error_code & PF_USER) == 0 && 1179 !search_exception_tables(regs->ip)) { 1180 bad_area_nosemaphore(regs, error_code, address); 1181 return; 1182 } 1183 retry: 1184 down_read(&mm->mmap_sem); 1185 } else { 1186 /* 1187 * The above down_read_trylock() might have succeeded in 1188 * which case we'll have missed the might_sleep() from 1189 * down_read(): 1190 */ 1191 might_sleep(); 1192 } 1193 1194 vma = find_vma(mm, address); 1195 if (unlikely(!vma)) { 1196 bad_area(regs, error_code, address); 1197 return; 1198 } 1199 if (likely(vma->vm_start <= address)) 1200 goto good_area; 1201 if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) { 1202 bad_area(regs, error_code, address); 1203 return; 1204 } 1205 if (error_code & PF_USER) { 1206 /* 1207 * Accessing the stack below %sp is always a bug. 1208 * The large cushion allows instructions like enter 1209 * and pusha to work. ("enter $65535, $31" pushes 1210 * 32 pointers and then decrements %sp by 65535.) 1211 */ 1212 if (unlikely(address + 65536 + 32 * sizeof(unsigned long) < regs->sp)) { 1213 bad_area(regs, error_code, address); 1214 return; 1215 } 1216 } 1217 if (unlikely(expand_stack(vma, address))) { 1218 bad_area(regs, error_code, address); 1219 return; 1220 } 1221 1222 /* 1223 * Ok, we have a good vm_area for this memory access, so 1224 * we can handle it.. 1225 */ 1226 good_area: 1227 if (unlikely(access_error(error_code, vma))) { 1228 bad_area_access_error(regs, error_code, address); 1229 return; 1230 } 1231 1232 /* 1233 * If for any reason at all we couldn't handle the fault, 1234 * make sure we exit gracefully rather than endlessly redo 1235 * the fault. Since we never set FAULT_FLAG_RETRY_NOWAIT, if 1236 * we get VM_FAULT_RETRY back, the mmap_sem has been unlocked. 1237 */ 1238 fault = handle_mm_fault(mm, vma, address, flags); 1239 major |= fault & VM_FAULT_MAJOR; 1240 1241 /* 1242 * If we need to retry the mmap_sem has already been released, 1243 * and if there is a fatal signal pending there is no guarantee 1244 * that we made any progress. Handle this case first. 1245 */ 1246 if (unlikely(fault & VM_FAULT_RETRY)) { 1247 /* Retry at most once */ 1248 if (flags & FAULT_FLAG_ALLOW_RETRY) { 1249 flags &= ~FAULT_FLAG_ALLOW_RETRY; 1250 flags |= FAULT_FLAG_TRIED; 1251 if (!fatal_signal_pending(tsk)) 1252 goto retry; 1253 } 1254 1255 /* User mode? Just return to handle the fatal exception */ 1256 if (flags & FAULT_FLAG_USER) 1257 return; 1258 1259 /* Not returning to user mode? Handle exceptions or die: */ 1260 no_context(regs, error_code, address, SIGBUS, BUS_ADRERR); 1261 return; 1262 } 1263 1264 up_read(&mm->mmap_sem); 1265 if (unlikely(fault & VM_FAULT_ERROR)) { 1266 mm_fault_error(regs, error_code, address, fault); 1267 return; 1268 } 1269 1270 /* 1271 * Major/minor page fault accounting. If any of the events 1272 * returned VM_FAULT_MAJOR, we account it as a major fault. 1273 */ 1274 if (major) { 1275 tsk->maj_flt++; 1276 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, address); 1277 } else { 1278 tsk->min_flt++; 1279 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, address); 1280 } 1281 1282 check_v8086_mode(regs, address, tsk); 1283 } 1284 NOKPROBE_SYMBOL(__do_page_fault); 1285 1286 dotraplinkage void notrace 1287 do_page_fault(struct pt_regs *regs, unsigned long error_code) 1288 { 1289 unsigned long address = read_cr2(); /* Get the faulting address */ 1290 enum ctx_state prev_state; 1291 1292 /* 1293 * We must have this function tagged with __kprobes, notrace and call 1294 * read_cr2() before calling anything else. To avoid calling any kind 1295 * of tracing machinery before we've observed the CR2 value. 1296 * 1297 * exception_{enter,exit}() contain all sorts of tracepoints. 1298 */ 1299 1300 prev_state = exception_enter(); 1301 __do_page_fault(regs, error_code, address); 1302 exception_exit(prev_state); 1303 } 1304 NOKPROBE_SYMBOL(do_page_fault); 1305 1306 #ifdef CONFIG_TRACING 1307 static nokprobe_inline void 1308 trace_page_fault_entries(unsigned long address, struct pt_regs *regs, 1309 unsigned long error_code) 1310 { 1311 if (user_mode(regs)) 1312 trace_page_fault_user(address, regs, error_code); 1313 else 1314 trace_page_fault_kernel(address, regs, error_code); 1315 } 1316 1317 dotraplinkage void notrace 1318 trace_do_page_fault(struct pt_regs *regs, unsigned long error_code) 1319 { 1320 /* 1321 * The exception_enter and tracepoint processing could 1322 * trigger another page faults (user space callchain 1323 * reading) and destroy the original cr2 value, so read 1324 * the faulting address now. 1325 */ 1326 unsigned long address = read_cr2(); 1327 enum ctx_state prev_state; 1328 1329 prev_state = exception_enter(); 1330 trace_page_fault_entries(address, regs, error_code); 1331 __do_page_fault(regs, error_code, address); 1332 exception_exit(prev_state); 1333 } 1334 NOKPROBE_SYMBOL(trace_do_page_fault); 1335 #endif /* CONFIG_TRACING */ 1336