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 if (pmd_huge(*pmd_k)) 291 return 0; 292 293 pte_k = pte_offset_kernel(pmd_k, address); 294 if (!pte_present(*pte_k)) 295 return -1; 296 297 return 0; 298 } 299 NOKPROBE_SYMBOL(vmalloc_fault); 300 301 /* 302 * Did it hit the DOS screen memory VA from vm86 mode? 303 */ 304 static inline void 305 check_v8086_mode(struct pt_regs *regs, unsigned long address, 306 struct task_struct *tsk) 307 { 308 #ifdef CONFIG_VM86 309 unsigned long bit; 310 311 if (!v8086_mode(regs) || !tsk->thread.vm86) 312 return; 313 314 bit = (address - 0xA0000) >> PAGE_SHIFT; 315 if (bit < 32) 316 tsk->thread.vm86->screen_bitmap |= 1 << bit; 317 #endif 318 } 319 320 static bool low_pfn(unsigned long pfn) 321 { 322 return pfn < max_low_pfn; 323 } 324 325 static void dump_pagetable(unsigned long address) 326 { 327 pgd_t *base = __va(read_cr3()); 328 pgd_t *pgd = &base[pgd_index(address)]; 329 pmd_t *pmd; 330 pte_t *pte; 331 332 #ifdef CONFIG_X86_PAE 333 printk("*pdpt = %016Lx ", pgd_val(*pgd)); 334 if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd)) 335 goto out; 336 #endif 337 pmd = pmd_offset(pud_offset(pgd, address), address); 338 printk(KERN_CONT "*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd)); 339 340 /* 341 * We must not directly access the pte in the highpte 342 * case if the page table is located in highmem. 343 * And let's rather not kmap-atomic the pte, just in case 344 * it's allocated already: 345 */ 346 if (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_large(*pmd)) 347 goto out; 348 349 pte = pte_offset_kernel(pmd, address); 350 printk("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte)); 351 out: 352 printk("\n"); 353 } 354 355 #else /* CONFIG_X86_64: */ 356 357 void vmalloc_sync_all(void) 358 { 359 sync_global_pgds(VMALLOC_START & PGDIR_MASK, VMALLOC_END, 0); 360 } 361 362 /* 363 * 64-bit: 364 * 365 * Handle a fault on the vmalloc area 366 */ 367 static noinline int vmalloc_fault(unsigned long address) 368 { 369 pgd_t *pgd, *pgd_ref; 370 pud_t *pud, *pud_ref; 371 pmd_t *pmd, *pmd_ref; 372 pte_t *pte, *pte_ref; 373 374 /* Make sure we are in vmalloc area: */ 375 if (!(address >= VMALLOC_START && address < VMALLOC_END)) 376 return -1; 377 378 WARN_ON_ONCE(in_nmi()); 379 380 /* 381 * Copy kernel mappings over when needed. This can also 382 * happen within a race in page table update. In the later 383 * case just flush: 384 */ 385 pgd = pgd_offset(current->active_mm, address); 386 pgd_ref = pgd_offset_k(address); 387 if (pgd_none(*pgd_ref)) 388 return -1; 389 390 if (pgd_none(*pgd)) { 391 set_pgd(pgd, *pgd_ref); 392 arch_flush_lazy_mmu_mode(); 393 } else { 394 BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref)); 395 } 396 397 /* 398 * Below here mismatches are bugs because these lower tables 399 * are shared: 400 */ 401 402 pud = pud_offset(pgd, address); 403 pud_ref = pud_offset(pgd_ref, address); 404 if (pud_none(*pud_ref)) 405 return -1; 406 407 if (pud_none(*pud) || pud_pfn(*pud) != pud_pfn(*pud_ref)) 408 BUG(); 409 410 if (pud_huge(*pud)) 411 return 0; 412 413 pmd = pmd_offset(pud, address); 414 pmd_ref = pmd_offset(pud_ref, address); 415 if (pmd_none(*pmd_ref)) 416 return -1; 417 418 if (pmd_none(*pmd) || pmd_pfn(*pmd) != pmd_pfn(*pmd_ref)) 419 BUG(); 420 421 if (pmd_huge(*pmd)) 422 return 0; 423 424 pte_ref = pte_offset_kernel(pmd_ref, address); 425 if (!pte_present(*pte_ref)) 426 return -1; 427 428 pte = pte_offset_kernel(pmd, address); 429 430 /* 431 * Don't use pte_page here, because the mappings can point 432 * outside mem_map, and the NUMA hash lookup cannot handle 433 * that: 434 */ 435 if (!pte_present(*pte) || pte_pfn(*pte) != pte_pfn(*pte_ref)) 436 BUG(); 437 438 return 0; 439 } 440 NOKPROBE_SYMBOL(vmalloc_fault); 441 442 #ifdef CONFIG_CPU_SUP_AMD 443 static const char errata93_warning[] = 444 KERN_ERR 445 "******* Your BIOS seems to not contain a fix for K8 errata #93\n" 446 "******* Working around it, but it may cause SEGVs or burn power.\n" 447 "******* Please consider a BIOS update.\n" 448 "******* Disabling USB legacy in the BIOS may also help.\n"; 449 #endif 450 451 /* 452 * No vm86 mode in 64-bit mode: 453 */ 454 static inline void 455 check_v8086_mode(struct pt_regs *regs, unsigned long address, 456 struct task_struct *tsk) 457 { 458 } 459 460 static int bad_address(void *p) 461 { 462 unsigned long dummy; 463 464 return probe_kernel_address((unsigned long *)p, dummy); 465 } 466 467 static void dump_pagetable(unsigned long address) 468 { 469 pgd_t *base = __va(read_cr3() & PHYSICAL_PAGE_MASK); 470 pgd_t *pgd = base + pgd_index(address); 471 pud_t *pud; 472 pmd_t *pmd; 473 pte_t *pte; 474 475 if (bad_address(pgd)) 476 goto bad; 477 478 printk("PGD %lx ", pgd_val(*pgd)); 479 480 if (!pgd_present(*pgd)) 481 goto out; 482 483 pud = pud_offset(pgd, address); 484 if (bad_address(pud)) 485 goto bad; 486 487 printk("PUD %lx ", pud_val(*pud)); 488 if (!pud_present(*pud) || pud_large(*pud)) 489 goto out; 490 491 pmd = pmd_offset(pud, address); 492 if (bad_address(pmd)) 493 goto bad; 494 495 printk("PMD %lx ", pmd_val(*pmd)); 496 if (!pmd_present(*pmd) || pmd_large(*pmd)) 497 goto out; 498 499 pte = pte_offset_kernel(pmd, address); 500 if (bad_address(pte)) 501 goto bad; 502 503 printk("PTE %lx", pte_val(*pte)); 504 out: 505 printk("\n"); 506 return; 507 bad: 508 printk("BAD\n"); 509 } 510 511 #endif /* CONFIG_X86_64 */ 512 513 /* 514 * Workaround for K8 erratum #93 & buggy BIOS. 515 * 516 * BIOS SMM functions are required to use a specific workaround 517 * to avoid corruption of the 64bit RIP register on C stepping K8. 518 * 519 * A lot of BIOS that didn't get tested properly miss this. 520 * 521 * The OS sees this as a page fault with the upper 32bits of RIP cleared. 522 * Try to work around it here. 523 * 524 * Note we only handle faults in kernel here. 525 * Does nothing on 32-bit. 526 */ 527 static int is_errata93(struct pt_regs *regs, unsigned long address) 528 { 529 #if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD) 530 if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD 531 || boot_cpu_data.x86 != 0xf) 532 return 0; 533 534 if (address != regs->ip) 535 return 0; 536 537 if ((address >> 32) != 0) 538 return 0; 539 540 address |= 0xffffffffUL << 32; 541 if ((address >= (u64)_stext && address <= (u64)_etext) || 542 (address >= MODULES_VADDR && address <= MODULES_END)) { 543 printk_once(errata93_warning); 544 regs->ip = address; 545 return 1; 546 } 547 #endif 548 return 0; 549 } 550 551 /* 552 * Work around K8 erratum #100 K8 in compat mode occasionally jumps 553 * to illegal addresses >4GB. 554 * 555 * We catch this in the page fault handler because these addresses 556 * are not reachable. Just detect this case and return. Any code 557 * segment in LDT is compatibility mode. 558 */ 559 static int is_errata100(struct pt_regs *regs, unsigned long address) 560 { 561 #ifdef CONFIG_X86_64 562 if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32)) 563 return 1; 564 #endif 565 return 0; 566 } 567 568 static int is_f00f_bug(struct pt_regs *regs, unsigned long address) 569 { 570 #ifdef CONFIG_X86_F00F_BUG 571 unsigned long nr; 572 573 /* 574 * Pentium F0 0F C7 C8 bug workaround: 575 */ 576 if (boot_cpu_has_bug(X86_BUG_F00F)) { 577 nr = (address - idt_descr.address) >> 3; 578 579 if (nr == 6) { 580 do_invalid_op(regs, 0); 581 return 1; 582 } 583 } 584 #endif 585 return 0; 586 } 587 588 static const char nx_warning[] = KERN_CRIT 589 "kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n"; 590 static const char smep_warning[] = KERN_CRIT 591 "unable to execute userspace code (SMEP?) (uid: %d)\n"; 592 593 static void 594 show_fault_oops(struct pt_regs *regs, unsigned long error_code, 595 unsigned long address) 596 { 597 if (!oops_may_print()) 598 return; 599 600 if (error_code & PF_INSTR) { 601 unsigned int level; 602 pgd_t *pgd; 603 pte_t *pte; 604 605 pgd = __va(read_cr3() & PHYSICAL_PAGE_MASK); 606 pgd += pgd_index(address); 607 608 pte = lookup_address_in_pgd(pgd, address, &level); 609 610 if (pte && pte_present(*pte) && !pte_exec(*pte)) 611 printk(nx_warning, from_kuid(&init_user_ns, current_uid())); 612 if (pte && pte_present(*pte) && pte_exec(*pte) && 613 (pgd_flags(*pgd) & _PAGE_USER) && 614 (__read_cr4() & X86_CR4_SMEP)) 615 printk(smep_warning, from_kuid(&init_user_ns, current_uid())); 616 } 617 618 printk(KERN_ALERT "BUG: unable to handle kernel "); 619 if (address < PAGE_SIZE) 620 printk(KERN_CONT "NULL pointer dereference"); 621 else 622 printk(KERN_CONT "paging request"); 623 624 printk(KERN_CONT " at %p\n", (void *) address); 625 printk(KERN_ALERT "IP:"); 626 printk_address(regs->ip); 627 628 dump_pagetable(address); 629 } 630 631 static noinline void 632 pgtable_bad(struct pt_regs *regs, unsigned long error_code, 633 unsigned long address) 634 { 635 struct task_struct *tsk; 636 unsigned long flags; 637 int sig; 638 639 flags = oops_begin(); 640 tsk = current; 641 sig = SIGKILL; 642 643 printk(KERN_ALERT "%s: Corrupted page table at address %lx\n", 644 tsk->comm, address); 645 dump_pagetable(address); 646 647 tsk->thread.cr2 = address; 648 tsk->thread.trap_nr = X86_TRAP_PF; 649 tsk->thread.error_code = error_code; 650 651 if (__die("Bad pagetable", regs, error_code)) 652 sig = 0; 653 654 oops_end(flags, regs, sig); 655 } 656 657 static noinline void 658 no_context(struct pt_regs *regs, unsigned long error_code, 659 unsigned long address, int signal, int si_code) 660 { 661 struct task_struct *tsk = current; 662 unsigned long flags; 663 int sig; 664 665 /* Are we prepared to handle this kernel fault? */ 666 if (fixup_exception(regs)) { 667 /* 668 * Any interrupt that takes a fault gets the fixup. This makes 669 * the below recursive fault logic only apply to a faults from 670 * task context. 671 */ 672 if (in_interrupt()) 673 return; 674 675 /* 676 * Per the above we're !in_interrupt(), aka. task context. 677 * 678 * In this case we need to make sure we're not recursively 679 * faulting through the emulate_vsyscall() logic. 680 */ 681 if (current_thread_info()->sig_on_uaccess_error && signal) { 682 tsk->thread.trap_nr = X86_TRAP_PF; 683 tsk->thread.error_code = error_code | PF_USER; 684 tsk->thread.cr2 = address; 685 686 /* XXX: hwpoison faults will set the wrong code. */ 687 force_sig_info_fault(signal, si_code, address, tsk, 0); 688 } 689 690 /* 691 * Barring that, we can do the fixup and be happy. 692 */ 693 return; 694 } 695 696 /* 697 * 32-bit: 698 * 699 * Valid to do another page fault here, because if this fault 700 * had been triggered by is_prefetch fixup_exception would have 701 * handled it. 702 * 703 * 64-bit: 704 * 705 * Hall of shame of CPU/BIOS bugs. 706 */ 707 if (is_prefetch(regs, error_code, address)) 708 return; 709 710 if (is_errata93(regs, address)) 711 return; 712 713 /* 714 * Oops. The kernel tried to access some bad page. We'll have to 715 * terminate things with extreme prejudice: 716 */ 717 flags = oops_begin(); 718 719 show_fault_oops(regs, error_code, address); 720 721 if (task_stack_end_corrupted(tsk)) 722 printk(KERN_EMERG "Thread overran stack, or stack corrupted\n"); 723 724 tsk->thread.cr2 = address; 725 tsk->thread.trap_nr = X86_TRAP_PF; 726 tsk->thread.error_code = error_code; 727 728 sig = SIGKILL; 729 if (__die("Oops", regs, error_code)) 730 sig = 0; 731 732 /* Executive summary in case the body of the oops scrolled away */ 733 printk(KERN_DEFAULT "CR2: %016lx\n", address); 734 735 oops_end(flags, regs, sig); 736 } 737 738 /* 739 * Print out info about fatal segfaults, if the show_unhandled_signals 740 * sysctl is set: 741 */ 742 static inline void 743 show_signal_msg(struct pt_regs *regs, unsigned long error_code, 744 unsigned long address, struct task_struct *tsk) 745 { 746 if (!unhandled_signal(tsk, SIGSEGV)) 747 return; 748 749 if (!printk_ratelimit()) 750 return; 751 752 printk("%s%s[%d]: segfault at %lx ip %p sp %p error %lx", 753 task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG, 754 tsk->comm, task_pid_nr(tsk), address, 755 (void *)regs->ip, (void *)regs->sp, error_code); 756 757 print_vma_addr(KERN_CONT " in ", regs->ip); 758 759 printk(KERN_CONT "\n"); 760 } 761 762 static void 763 __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, 764 unsigned long address, int si_code) 765 { 766 struct task_struct *tsk = current; 767 768 /* User mode accesses just cause a SIGSEGV */ 769 if (error_code & PF_USER) { 770 /* 771 * It's possible to have interrupts off here: 772 */ 773 local_irq_enable(); 774 775 /* 776 * Valid to do another page fault here because this one came 777 * from user space: 778 */ 779 if (is_prefetch(regs, error_code, address)) 780 return; 781 782 if (is_errata100(regs, address)) 783 return; 784 785 #ifdef CONFIG_X86_64 786 /* 787 * Instruction fetch faults in the vsyscall page might need 788 * emulation. 789 */ 790 if (unlikely((error_code & PF_INSTR) && 791 ((address & ~0xfff) == VSYSCALL_ADDR))) { 792 if (emulate_vsyscall(regs, address)) 793 return; 794 } 795 #endif 796 /* Kernel addresses are always protection faults: */ 797 if (address >= TASK_SIZE) 798 error_code |= PF_PROT; 799 800 if (likely(show_unhandled_signals)) 801 show_signal_msg(regs, error_code, address, tsk); 802 803 tsk->thread.cr2 = address; 804 tsk->thread.error_code = error_code; 805 tsk->thread.trap_nr = X86_TRAP_PF; 806 807 force_sig_info_fault(SIGSEGV, si_code, address, tsk, 0); 808 809 return; 810 } 811 812 if (is_f00f_bug(regs, address)) 813 return; 814 815 no_context(regs, error_code, address, SIGSEGV, si_code); 816 } 817 818 static noinline void 819 bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, 820 unsigned long address) 821 { 822 __bad_area_nosemaphore(regs, error_code, address, SEGV_MAPERR); 823 } 824 825 static void 826 __bad_area(struct pt_regs *regs, unsigned long error_code, 827 unsigned long address, int si_code) 828 { 829 struct mm_struct *mm = current->mm; 830 831 /* 832 * Something tried to access memory that isn't in our memory map.. 833 * Fix it, but check if it's kernel or user first.. 834 */ 835 up_read(&mm->mmap_sem); 836 837 __bad_area_nosemaphore(regs, error_code, address, si_code); 838 } 839 840 static noinline void 841 bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address) 842 { 843 __bad_area(regs, error_code, address, SEGV_MAPERR); 844 } 845 846 static noinline void 847 bad_area_access_error(struct pt_regs *regs, unsigned long error_code, 848 unsigned long address) 849 { 850 __bad_area(regs, error_code, address, SEGV_ACCERR); 851 } 852 853 static void 854 do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address, 855 unsigned int fault) 856 { 857 struct task_struct *tsk = current; 858 int code = BUS_ADRERR; 859 860 /* Kernel mode? Handle exceptions or die: */ 861 if (!(error_code & PF_USER)) { 862 no_context(regs, error_code, address, SIGBUS, BUS_ADRERR); 863 return; 864 } 865 866 /* User-space => ok to do another page fault: */ 867 if (is_prefetch(regs, error_code, address)) 868 return; 869 870 tsk->thread.cr2 = address; 871 tsk->thread.error_code = error_code; 872 tsk->thread.trap_nr = X86_TRAP_PF; 873 874 #ifdef CONFIG_MEMORY_FAILURE 875 if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) { 876 printk(KERN_ERR 877 "MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n", 878 tsk->comm, tsk->pid, address); 879 code = BUS_MCEERR_AR; 880 } 881 #endif 882 force_sig_info_fault(SIGBUS, code, address, tsk, fault); 883 } 884 885 static noinline void 886 mm_fault_error(struct pt_regs *regs, unsigned long error_code, 887 unsigned long address, unsigned int fault) 888 { 889 if (fatal_signal_pending(current) && !(error_code & PF_USER)) { 890 no_context(regs, error_code, address, 0, 0); 891 return; 892 } 893 894 if (fault & VM_FAULT_OOM) { 895 /* Kernel mode? Handle exceptions or die: */ 896 if (!(error_code & PF_USER)) { 897 no_context(regs, error_code, address, 898 SIGSEGV, SEGV_MAPERR); 899 return; 900 } 901 902 /* 903 * We ran out of memory, call the OOM killer, and return the 904 * userspace (which will retry the fault, or kill us if we got 905 * oom-killed): 906 */ 907 pagefault_out_of_memory(); 908 } else { 909 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON| 910 VM_FAULT_HWPOISON_LARGE)) 911 do_sigbus(regs, error_code, address, fault); 912 else if (fault & VM_FAULT_SIGSEGV) 913 bad_area_nosemaphore(regs, error_code, address); 914 else 915 BUG(); 916 } 917 } 918 919 static int spurious_fault_check(unsigned long error_code, pte_t *pte) 920 { 921 if ((error_code & PF_WRITE) && !pte_write(*pte)) 922 return 0; 923 924 if ((error_code & PF_INSTR) && !pte_exec(*pte)) 925 return 0; 926 927 return 1; 928 } 929 930 /* 931 * Handle a spurious fault caused by a stale TLB entry. 932 * 933 * This allows us to lazily refresh the TLB when increasing the 934 * permissions of a kernel page (RO -> RW or NX -> X). Doing it 935 * eagerly is very expensive since that implies doing a full 936 * cross-processor TLB flush, even if no stale TLB entries exist 937 * on other processors. 938 * 939 * Spurious faults may only occur if the TLB contains an entry with 940 * fewer permission than the page table entry. Non-present (P = 0) 941 * and reserved bit (R = 1) faults are never spurious. 942 * 943 * There are no security implications to leaving a stale TLB when 944 * increasing the permissions on a page. 945 * 946 * Returns non-zero if a spurious fault was handled, zero otherwise. 947 * 948 * See Intel Developer's Manual Vol 3 Section 4.10.4.3, bullet 3 949 * (Optional Invalidation). 950 */ 951 static noinline int 952 spurious_fault(unsigned long error_code, unsigned long address) 953 { 954 pgd_t *pgd; 955 pud_t *pud; 956 pmd_t *pmd; 957 pte_t *pte; 958 int ret; 959 960 /* 961 * Only writes to RO or instruction fetches from NX may cause 962 * spurious faults. 963 * 964 * These could be from user or supervisor accesses but the TLB 965 * is only lazily flushed after a kernel mapping protection 966 * change, so user accesses are not expected to cause spurious 967 * faults. 968 */ 969 if (error_code != (PF_WRITE | PF_PROT) 970 && error_code != (PF_INSTR | PF_PROT)) 971 return 0; 972 973 pgd = init_mm.pgd + pgd_index(address); 974 if (!pgd_present(*pgd)) 975 return 0; 976 977 pud = pud_offset(pgd, address); 978 if (!pud_present(*pud)) 979 return 0; 980 981 if (pud_large(*pud)) 982 return spurious_fault_check(error_code, (pte_t *) pud); 983 984 pmd = pmd_offset(pud, address); 985 if (!pmd_present(*pmd)) 986 return 0; 987 988 if (pmd_large(*pmd)) 989 return spurious_fault_check(error_code, (pte_t *) pmd); 990 991 pte = pte_offset_kernel(pmd, address); 992 if (!pte_present(*pte)) 993 return 0; 994 995 ret = spurious_fault_check(error_code, pte); 996 if (!ret) 997 return 0; 998 999 /* 1000 * Make sure we have permissions in PMD. 1001 * If not, then there's a bug in the page tables: 1002 */ 1003 ret = spurious_fault_check(error_code, (pte_t *) pmd); 1004 WARN_ONCE(!ret, "PMD has incorrect permission bits\n"); 1005 1006 return ret; 1007 } 1008 NOKPROBE_SYMBOL(spurious_fault); 1009 1010 int show_unhandled_signals = 1; 1011 1012 static inline int 1013 access_error(unsigned long error_code, struct vm_area_struct *vma) 1014 { 1015 if (error_code & PF_WRITE) { 1016 /* write, present and write, not present: */ 1017 if (unlikely(!(vma->vm_flags & VM_WRITE))) 1018 return 1; 1019 return 0; 1020 } 1021 1022 /* read, present: */ 1023 if (unlikely(error_code & PF_PROT)) 1024 return 1; 1025 1026 /* read, not present: */ 1027 if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))) 1028 return 1; 1029 1030 return 0; 1031 } 1032 1033 static int fault_in_kernel_space(unsigned long address) 1034 { 1035 return address >= TASK_SIZE_MAX; 1036 } 1037 1038 static inline bool smap_violation(int error_code, struct pt_regs *regs) 1039 { 1040 if (!IS_ENABLED(CONFIG_X86_SMAP)) 1041 return false; 1042 1043 if (!static_cpu_has(X86_FEATURE_SMAP)) 1044 return false; 1045 1046 if (error_code & PF_USER) 1047 return false; 1048 1049 if (!user_mode(regs) && (regs->flags & X86_EFLAGS_AC)) 1050 return false; 1051 1052 return true; 1053 } 1054 1055 /* 1056 * This routine handles page faults. It determines the address, 1057 * and the problem, and then passes it off to one of the appropriate 1058 * routines. 1059 * 1060 * This function must have noinline because both callers 1061 * {,trace_}do_page_fault() have notrace on. Having this an actual function 1062 * guarantees there's a function trace entry. 1063 */ 1064 static noinline void 1065 __do_page_fault(struct pt_regs *regs, unsigned long error_code, 1066 unsigned long address) 1067 { 1068 struct vm_area_struct *vma; 1069 struct task_struct *tsk; 1070 struct mm_struct *mm; 1071 int fault, major = 0; 1072 unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE; 1073 1074 tsk = current; 1075 mm = tsk->mm; 1076 1077 /* 1078 * Detect and handle instructions that would cause a page fault for 1079 * both a tracked kernel page and a userspace page. 1080 */ 1081 if (kmemcheck_active(regs)) 1082 kmemcheck_hide(regs); 1083 prefetchw(&mm->mmap_sem); 1084 1085 if (unlikely(kmmio_fault(regs, address))) 1086 return; 1087 1088 /* 1089 * We fault-in kernel-space virtual memory on-demand. The 1090 * 'reference' page table is init_mm.pgd. 1091 * 1092 * NOTE! We MUST NOT take any locks for this case. We may 1093 * be in an interrupt or a critical region, and should 1094 * only copy the information from the master page table, 1095 * nothing more. 1096 * 1097 * This verifies that the fault happens in kernel space 1098 * (error_code & 4) == 0, and that the fault was not a 1099 * protection error (error_code & 9) == 0. 1100 */ 1101 if (unlikely(fault_in_kernel_space(address))) { 1102 if (!(error_code & (PF_RSVD | PF_USER | PF_PROT))) { 1103 if (vmalloc_fault(address) >= 0) 1104 return; 1105 1106 if (kmemcheck_fault(regs, address, error_code)) 1107 return; 1108 } 1109 1110 /* Can handle a stale RO->RW TLB: */ 1111 if (spurious_fault(error_code, address)) 1112 return; 1113 1114 /* kprobes don't want to hook the spurious faults: */ 1115 if (kprobes_fault(regs)) 1116 return; 1117 /* 1118 * Don't take the mm semaphore here. If we fixup a prefetch 1119 * fault we could otherwise deadlock: 1120 */ 1121 bad_area_nosemaphore(regs, error_code, address); 1122 1123 return; 1124 } 1125 1126 /* kprobes don't want to hook the spurious faults: */ 1127 if (unlikely(kprobes_fault(regs))) 1128 return; 1129 1130 if (unlikely(error_code & PF_RSVD)) 1131 pgtable_bad(regs, error_code, address); 1132 1133 if (unlikely(smap_violation(error_code, regs))) { 1134 bad_area_nosemaphore(regs, error_code, address); 1135 return; 1136 } 1137 1138 /* 1139 * If we're in an interrupt, have no user context or are running 1140 * in a region with pagefaults disabled then we must not take the fault 1141 */ 1142 if (unlikely(faulthandler_disabled() || !mm)) { 1143 bad_area_nosemaphore(regs, error_code, address); 1144 return; 1145 } 1146 1147 /* 1148 * It's safe to allow irq's after cr2 has been saved and the 1149 * vmalloc fault has been handled. 1150 * 1151 * User-mode registers count as a user access even for any 1152 * potential system fault or CPU buglet: 1153 */ 1154 if (user_mode(regs)) { 1155 local_irq_enable(); 1156 error_code |= PF_USER; 1157 flags |= FAULT_FLAG_USER; 1158 } else { 1159 if (regs->flags & X86_EFLAGS_IF) 1160 local_irq_enable(); 1161 } 1162 1163 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address); 1164 1165 if (error_code & PF_WRITE) 1166 flags |= FAULT_FLAG_WRITE; 1167 1168 /* 1169 * When running in the kernel we expect faults to occur only to 1170 * addresses in user space. All other faults represent errors in 1171 * the kernel and should generate an OOPS. Unfortunately, in the 1172 * case of an erroneous fault occurring in a code path which already 1173 * holds mmap_sem we will deadlock attempting to validate the fault 1174 * against the address space. Luckily the kernel only validly 1175 * references user space from well defined areas of code, which are 1176 * listed in the exceptions table. 1177 * 1178 * As the vast majority of faults will be valid we will only perform 1179 * the source reference check when there is a possibility of a 1180 * deadlock. Attempt to lock the address space, if we cannot we then 1181 * validate the source. If this is invalid we can skip the address 1182 * space check, thus avoiding the deadlock: 1183 */ 1184 if (unlikely(!down_read_trylock(&mm->mmap_sem))) { 1185 if ((error_code & PF_USER) == 0 && 1186 !search_exception_tables(regs->ip)) { 1187 bad_area_nosemaphore(regs, error_code, address); 1188 return; 1189 } 1190 retry: 1191 down_read(&mm->mmap_sem); 1192 } else { 1193 /* 1194 * The above down_read_trylock() might have succeeded in 1195 * which case we'll have missed the might_sleep() from 1196 * down_read(): 1197 */ 1198 might_sleep(); 1199 } 1200 1201 vma = find_vma(mm, address); 1202 if (unlikely(!vma)) { 1203 bad_area(regs, error_code, address); 1204 return; 1205 } 1206 if (likely(vma->vm_start <= address)) 1207 goto good_area; 1208 if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) { 1209 bad_area(regs, error_code, address); 1210 return; 1211 } 1212 if (error_code & PF_USER) { 1213 /* 1214 * Accessing the stack below %sp is always a bug. 1215 * The large cushion allows instructions like enter 1216 * and pusha to work. ("enter $65535, $31" pushes 1217 * 32 pointers and then decrements %sp by 65535.) 1218 */ 1219 if (unlikely(address + 65536 + 32 * sizeof(unsigned long) < regs->sp)) { 1220 bad_area(regs, error_code, address); 1221 return; 1222 } 1223 } 1224 if (unlikely(expand_stack(vma, address))) { 1225 bad_area(regs, error_code, address); 1226 return; 1227 } 1228 1229 /* 1230 * Ok, we have a good vm_area for this memory access, so 1231 * we can handle it.. 1232 */ 1233 good_area: 1234 if (unlikely(access_error(error_code, vma))) { 1235 bad_area_access_error(regs, error_code, address); 1236 return; 1237 } 1238 1239 /* 1240 * If for any reason at all we couldn't handle the fault, 1241 * make sure we exit gracefully rather than endlessly redo 1242 * the fault. Since we never set FAULT_FLAG_RETRY_NOWAIT, if 1243 * we get VM_FAULT_RETRY back, the mmap_sem has been unlocked. 1244 */ 1245 fault = handle_mm_fault(mm, vma, address, flags); 1246 major |= fault & VM_FAULT_MAJOR; 1247 1248 /* 1249 * If we need to retry the mmap_sem has already been released, 1250 * and if there is a fatal signal pending there is no guarantee 1251 * that we made any progress. Handle this case first. 1252 */ 1253 if (unlikely(fault & VM_FAULT_RETRY)) { 1254 /* Retry at most once */ 1255 if (flags & FAULT_FLAG_ALLOW_RETRY) { 1256 flags &= ~FAULT_FLAG_ALLOW_RETRY; 1257 flags |= FAULT_FLAG_TRIED; 1258 if (!fatal_signal_pending(tsk)) 1259 goto retry; 1260 } 1261 1262 /* User mode? Just return to handle the fatal exception */ 1263 if (flags & FAULT_FLAG_USER) 1264 return; 1265 1266 /* Not returning to user mode? Handle exceptions or die: */ 1267 no_context(regs, error_code, address, SIGBUS, BUS_ADRERR); 1268 return; 1269 } 1270 1271 up_read(&mm->mmap_sem); 1272 if (unlikely(fault & VM_FAULT_ERROR)) { 1273 mm_fault_error(regs, error_code, address, fault); 1274 return; 1275 } 1276 1277 /* 1278 * Major/minor page fault accounting. If any of the events 1279 * returned VM_FAULT_MAJOR, we account it as a major fault. 1280 */ 1281 if (major) { 1282 tsk->maj_flt++; 1283 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, address); 1284 } else { 1285 tsk->min_flt++; 1286 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, address); 1287 } 1288 1289 check_v8086_mode(regs, address, tsk); 1290 } 1291 NOKPROBE_SYMBOL(__do_page_fault); 1292 1293 dotraplinkage void notrace 1294 do_page_fault(struct pt_regs *regs, unsigned long error_code) 1295 { 1296 unsigned long address = read_cr2(); /* Get the faulting address */ 1297 enum ctx_state prev_state; 1298 1299 /* 1300 * We must have this function tagged with __kprobes, notrace and call 1301 * read_cr2() before calling anything else. To avoid calling any kind 1302 * of tracing machinery before we've observed the CR2 value. 1303 * 1304 * exception_{enter,exit}() contain all sorts of tracepoints. 1305 */ 1306 1307 prev_state = exception_enter(); 1308 __do_page_fault(regs, error_code, address); 1309 exception_exit(prev_state); 1310 } 1311 NOKPROBE_SYMBOL(do_page_fault); 1312 1313 #ifdef CONFIG_TRACING 1314 static nokprobe_inline void 1315 trace_page_fault_entries(unsigned long address, struct pt_regs *regs, 1316 unsigned long error_code) 1317 { 1318 if (user_mode(regs)) 1319 trace_page_fault_user(address, regs, error_code); 1320 else 1321 trace_page_fault_kernel(address, regs, error_code); 1322 } 1323 1324 dotraplinkage void notrace 1325 trace_do_page_fault(struct pt_regs *regs, unsigned long error_code) 1326 { 1327 /* 1328 * The exception_enter and tracepoint processing could 1329 * trigger another page faults (user space callchain 1330 * reading) and destroy the original cr2 value, so read 1331 * the faulting address now. 1332 */ 1333 unsigned long address = read_cr2(); 1334 enum ctx_state prev_state; 1335 1336 prev_state = exception_enter(); 1337 trace_page_fault_entries(address, regs, error_code); 1338 __do_page_fault(regs, error_code, address); 1339 exception_exit(prev_state); 1340 } 1341 NOKPROBE_SYMBOL(trace_do_page_fault); 1342 #endif /* CONFIG_TRACING */ 1343