1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Copyright (C) 1995 Linus Torvalds 4 * Copyright (C) 2001, 2002 Andi Kleen, SuSE Labs. 5 * Copyright (C) 2008-2009, Red Hat Inc., Ingo Molnar 6 */ 7 #include <linux/sched.h> /* test_thread_flag(), ... */ 8 #include <linux/sched/task_stack.h> /* task_stack_*(), ... */ 9 #include <linux/kdebug.h> /* oops_begin/end, ... */ 10 #include <linux/extable.h> /* search_exception_tables */ 11 #include <linux/memblock.h> /* max_low_pfn */ 12 #include <linux/kfence.h> /* kfence_handle_page_fault */ 13 #include <linux/kprobes.h> /* NOKPROBE_SYMBOL, ... */ 14 #include <linux/mmiotrace.h> /* kmmio_handler, ... */ 15 #include <linux/perf_event.h> /* perf_sw_event */ 16 #include <linux/hugetlb.h> /* hstate_index_to_shift */ 17 #include <linux/prefetch.h> /* prefetchw */ 18 #include <linux/context_tracking.h> /* exception_enter(), ... */ 19 #include <linux/uaccess.h> /* faulthandler_disabled() */ 20 #include <linux/efi.h> /* efi_crash_gracefully_on_page_fault()*/ 21 #include <linux/mm_types.h> 22 23 #include <asm/cpufeature.h> /* boot_cpu_has, ... */ 24 #include <asm/traps.h> /* dotraplinkage, ... */ 25 #include <asm/fixmap.h> /* VSYSCALL_ADDR */ 26 #include <asm/vsyscall.h> /* emulate_vsyscall */ 27 #include <asm/vm86.h> /* struct vm86 */ 28 #include <asm/mmu_context.h> /* vma_pkey() */ 29 #include <asm/efi.h> /* efi_crash_gracefully_on_page_fault()*/ 30 #include <asm/desc.h> /* store_idt(), ... */ 31 #include <asm/cpu_entry_area.h> /* exception stack */ 32 #include <asm/pgtable_areas.h> /* VMALLOC_START, ... */ 33 #include <asm/kvm_para.h> /* kvm_handle_async_pf */ 34 #include <asm/vdso.h> /* fixup_vdso_exception() */ 35 36 #define CREATE_TRACE_POINTS 37 #include <asm/trace/exceptions.h> 38 39 /* 40 * Returns 0 if mmiotrace is disabled, or if the fault is not 41 * handled by mmiotrace: 42 */ 43 static nokprobe_inline int 44 kmmio_fault(struct pt_regs *regs, unsigned long addr) 45 { 46 if (unlikely(is_kmmio_active())) 47 if (kmmio_handler(regs, addr) == 1) 48 return -1; 49 return 0; 50 } 51 52 /* 53 * Prefetch quirks: 54 * 55 * 32-bit mode: 56 * 57 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch. 58 * Check that here and ignore it. This is AMD erratum #91. 59 * 60 * 64-bit mode: 61 * 62 * Sometimes the CPU reports invalid exceptions on prefetch. 63 * Check that here and ignore it. 64 * 65 * Opcode checker based on code by Richard Brunner. 66 */ 67 static inline int 68 check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr, 69 unsigned char opcode, int *prefetch) 70 { 71 unsigned char instr_hi = opcode & 0xf0; 72 unsigned char instr_lo = opcode & 0x0f; 73 74 switch (instr_hi) { 75 case 0x20: 76 case 0x30: 77 /* 78 * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes. 79 * In X86_64 long mode, the CPU will signal invalid 80 * opcode if some of these prefixes are present so 81 * X86_64 will never get here anyway 82 */ 83 return ((instr_lo & 7) == 0x6); 84 #ifdef CONFIG_X86_64 85 case 0x40: 86 /* 87 * In 64-bit mode 0x40..0x4F are valid REX prefixes 88 */ 89 return (!user_mode(regs) || user_64bit_mode(regs)); 90 #endif 91 case 0x60: 92 /* 0x64 thru 0x67 are valid prefixes in all modes. */ 93 return (instr_lo & 0xC) == 0x4; 94 case 0xF0: 95 /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */ 96 return !instr_lo || (instr_lo>>1) == 1; 97 case 0x00: 98 /* Prefetch instruction is 0x0F0D or 0x0F18 */ 99 if (get_kernel_nofault(opcode, instr)) 100 return 0; 101 102 *prefetch = (instr_lo == 0xF) && 103 (opcode == 0x0D || opcode == 0x18); 104 return 0; 105 default: 106 return 0; 107 } 108 } 109 110 static bool is_amd_k8_pre_npt(void) 111 { 112 struct cpuinfo_x86 *c = &boot_cpu_data; 113 114 return unlikely(IS_ENABLED(CONFIG_CPU_SUP_AMD) && 115 c->x86_vendor == X86_VENDOR_AMD && 116 c->x86 == 0xf && c->x86_model < 0x40); 117 } 118 119 static int 120 is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr) 121 { 122 unsigned char *max_instr; 123 unsigned char *instr; 124 int prefetch = 0; 125 126 /* Erratum #91 affects AMD K8, pre-NPT CPUs */ 127 if (!is_amd_k8_pre_npt()) 128 return 0; 129 130 /* 131 * If it was a exec (instruction fetch) fault on NX page, then 132 * do not ignore the fault: 133 */ 134 if (error_code & X86_PF_INSTR) 135 return 0; 136 137 instr = (void *)convert_ip_to_linear(current, regs); 138 max_instr = instr + 15; 139 140 /* 141 * This code has historically always bailed out if IP points to a 142 * not-present page (e.g. due to a race). No one has ever 143 * complained about this. 144 */ 145 pagefault_disable(); 146 147 while (instr < max_instr) { 148 unsigned char opcode; 149 150 if (user_mode(regs)) { 151 if (get_user(opcode, instr)) 152 break; 153 } else { 154 if (get_kernel_nofault(opcode, instr)) 155 break; 156 } 157 158 instr++; 159 160 if (!check_prefetch_opcode(regs, instr, opcode, &prefetch)) 161 break; 162 } 163 164 pagefault_enable(); 165 return prefetch; 166 } 167 168 DEFINE_SPINLOCK(pgd_lock); 169 LIST_HEAD(pgd_list); 170 171 #ifdef CONFIG_X86_32 172 static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address) 173 { 174 unsigned index = pgd_index(address); 175 pgd_t *pgd_k; 176 p4d_t *p4d, *p4d_k; 177 pud_t *pud, *pud_k; 178 pmd_t *pmd, *pmd_k; 179 180 pgd += index; 181 pgd_k = init_mm.pgd + index; 182 183 if (!pgd_present(*pgd_k)) 184 return NULL; 185 186 /* 187 * set_pgd(pgd, *pgd_k); here would be useless on PAE 188 * and redundant with the set_pmd() on non-PAE. As would 189 * set_p4d/set_pud. 190 */ 191 p4d = p4d_offset(pgd, address); 192 p4d_k = p4d_offset(pgd_k, address); 193 if (!p4d_present(*p4d_k)) 194 return NULL; 195 196 pud = pud_offset(p4d, address); 197 pud_k = pud_offset(p4d_k, address); 198 if (!pud_present(*pud_k)) 199 return NULL; 200 201 pmd = pmd_offset(pud, address); 202 pmd_k = pmd_offset(pud_k, address); 203 204 if (pmd_present(*pmd) != pmd_present(*pmd_k)) 205 set_pmd(pmd, *pmd_k); 206 207 if (!pmd_present(*pmd_k)) 208 return NULL; 209 else 210 BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k)); 211 212 return pmd_k; 213 } 214 215 /* 216 * Handle a fault on the vmalloc or module mapping area 217 * 218 * This is needed because there is a race condition between the time 219 * when the vmalloc mapping code updates the PMD to the point in time 220 * where it synchronizes this update with the other page-tables in the 221 * system. 222 * 223 * In this race window another thread/CPU can map an area on the same 224 * PMD, finds it already present and does not synchronize it with the 225 * rest of the system yet. As a result v[mz]alloc might return areas 226 * which are not mapped in every page-table in the system, causing an 227 * unhandled page-fault when they are accessed. 228 */ 229 static noinline int vmalloc_fault(unsigned long address) 230 { 231 unsigned long pgd_paddr; 232 pmd_t *pmd_k; 233 pte_t *pte_k; 234 235 /* Make sure we are in vmalloc area: */ 236 if (!(address >= VMALLOC_START && address < VMALLOC_END)) 237 return -1; 238 239 /* 240 * Synchronize this task's top level page-table 241 * with the 'reference' page table. 242 * 243 * Do _not_ use "current" here. We might be inside 244 * an interrupt in the middle of a task switch.. 245 */ 246 pgd_paddr = read_cr3_pa(); 247 pmd_k = vmalloc_sync_one(__va(pgd_paddr), address); 248 if (!pmd_k) 249 return -1; 250 251 if (pmd_large(*pmd_k)) 252 return 0; 253 254 pte_k = pte_offset_kernel(pmd_k, address); 255 if (!pte_present(*pte_k)) 256 return -1; 257 258 return 0; 259 } 260 NOKPROBE_SYMBOL(vmalloc_fault); 261 262 void arch_sync_kernel_mappings(unsigned long start, unsigned long end) 263 { 264 unsigned long addr; 265 266 for (addr = start & PMD_MASK; 267 addr >= TASK_SIZE_MAX && addr < VMALLOC_END; 268 addr += PMD_SIZE) { 269 struct page *page; 270 271 spin_lock(&pgd_lock); 272 list_for_each_entry(page, &pgd_list, lru) { 273 spinlock_t *pgt_lock; 274 275 /* the pgt_lock only for Xen */ 276 pgt_lock = &pgd_page_get_mm(page)->page_table_lock; 277 278 spin_lock(pgt_lock); 279 vmalloc_sync_one(page_address(page), addr); 280 spin_unlock(pgt_lock); 281 } 282 spin_unlock(&pgd_lock); 283 } 284 } 285 286 static bool low_pfn(unsigned long pfn) 287 { 288 return pfn < max_low_pfn; 289 } 290 291 static void dump_pagetable(unsigned long address) 292 { 293 pgd_t *base = __va(read_cr3_pa()); 294 pgd_t *pgd = &base[pgd_index(address)]; 295 p4d_t *p4d; 296 pud_t *pud; 297 pmd_t *pmd; 298 pte_t *pte; 299 300 #ifdef CONFIG_X86_PAE 301 pr_info("*pdpt = %016Lx ", pgd_val(*pgd)); 302 if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd)) 303 goto out; 304 #define pr_pde pr_cont 305 #else 306 #define pr_pde pr_info 307 #endif 308 p4d = p4d_offset(pgd, address); 309 pud = pud_offset(p4d, address); 310 pmd = pmd_offset(pud, address); 311 pr_pde("*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd)); 312 #undef pr_pde 313 314 /* 315 * We must not directly access the pte in the highpte 316 * case if the page table is located in highmem. 317 * And let's rather not kmap-atomic the pte, just in case 318 * it's allocated already: 319 */ 320 if (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_large(*pmd)) 321 goto out; 322 323 pte = pte_offset_kernel(pmd, address); 324 pr_cont("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte)); 325 out: 326 pr_cont("\n"); 327 } 328 329 #else /* CONFIG_X86_64: */ 330 331 #ifdef CONFIG_CPU_SUP_AMD 332 static const char errata93_warning[] = 333 KERN_ERR 334 "******* Your BIOS seems to not contain a fix for K8 errata #93\n" 335 "******* Working around it, but it may cause SEGVs or burn power.\n" 336 "******* Please consider a BIOS update.\n" 337 "******* Disabling USB legacy in the BIOS may also help.\n"; 338 #endif 339 340 static int bad_address(void *p) 341 { 342 unsigned long dummy; 343 344 return get_kernel_nofault(dummy, (unsigned long *)p); 345 } 346 347 static void dump_pagetable(unsigned long address) 348 { 349 pgd_t *base = __va(read_cr3_pa()); 350 pgd_t *pgd = base + pgd_index(address); 351 p4d_t *p4d; 352 pud_t *pud; 353 pmd_t *pmd; 354 pte_t *pte; 355 356 if (bad_address(pgd)) 357 goto bad; 358 359 pr_info("PGD %lx ", pgd_val(*pgd)); 360 361 if (!pgd_present(*pgd)) 362 goto out; 363 364 p4d = p4d_offset(pgd, address); 365 if (bad_address(p4d)) 366 goto bad; 367 368 pr_cont("P4D %lx ", p4d_val(*p4d)); 369 if (!p4d_present(*p4d) || p4d_large(*p4d)) 370 goto out; 371 372 pud = pud_offset(p4d, address); 373 if (bad_address(pud)) 374 goto bad; 375 376 pr_cont("PUD %lx ", pud_val(*pud)); 377 if (!pud_present(*pud) || pud_large(*pud)) 378 goto out; 379 380 pmd = pmd_offset(pud, address); 381 if (bad_address(pmd)) 382 goto bad; 383 384 pr_cont("PMD %lx ", pmd_val(*pmd)); 385 if (!pmd_present(*pmd) || pmd_large(*pmd)) 386 goto out; 387 388 pte = pte_offset_kernel(pmd, address); 389 if (bad_address(pte)) 390 goto bad; 391 392 pr_cont("PTE %lx", pte_val(*pte)); 393 out: 394 pr_cont("\n"); 395 return; 396 bad: 397 pr_info("BAD\n"); 398 } 399 400 #endif /* CONFIG_X86_64 */ 401 402 /* 403 * Workaround for K8 erratum #93 & buggy BIOS. 404 * 405 * BIOS SMM functions are required to use a specific workaround 406 * to avoid corruption of the 64bit RIP register on C stepping K8. 407 * 408 * A lot of BIOS that didn't get tested properly miss this. 409 * 410 * The OS sees this as a page fault with the upper 32bits of RIP cleared. 411 * Try to work around it here. 412 * 413 * Note we only handle faults in kernel here. 414 * Does nothing on 32-bit. 415 */ 416 static int is_errata93(struct pt_regs *regs, unsigned long address) 417 { 418 #if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD) 419 if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD 420 || boot_cpu_data.x86 != 0xf) 421 return 0; 422 423 if (user_mode(regs)) 424 return 0; 425 426 if (address != regs->ip) 427 return 0; 428 429 if ((address >> 32) != 0) 430 return 0; 431 432 address |= 0xffffffffUL << 32; 433 if ((address >= (u64)_stext && address <= (u64)_etext) || 434 (address >= MODULES_VADDR && address <= MODULES_END)) { 435 printk_once(errata93_warning); 436 regs->ip = address; 437 return 1; 438 } 439 #endif 440 return 0; 441 } 442 443 /* 444 * Work around K8 erratum #100 K8 in compat mode occasionally jumps 445 * to illegal addresses >4GB. 446 * 447 * We catch this in the page fault handler because these addresses 448 * are not reachable. Just detect this case and return. Any code 449 * segment in LDT is compatibility mode. 450 */ 451 static int is_errata100(struct pt_regs *regs, unsigned long address) 452 { 453 #ifdef CONFIG_X86_64 454 if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32)) 455 return 1; 456 #endif 457 return 0; 458 } 459 460 /* Pentium F0 0F C7 C8 bug workaround: */ 461 static int is_f00f_bug(struct pt_regs *regs, unsigned long error_code, 462 unsigned long address) 463 { 464 #ifdef CONFIG_X86_F00F_BUG 465 if (boot_cpu_has_bug(X86_BUG_F00F) && !(error_code & X86_PF_USER) && 466 idt_is_f00f_address(address)) { 467 handle_invalid_op(regs); 468 return 1; 469 } 470 #endif 471 return 0; 472 } 473 474 static void show_ldttss(const struct desc_ptr *gdt, const char *name, u16 index) 475 { 476 u32 offset = (index >> 3) * sizeof(struct desc_struct); 477 unsigned long addr; 478 struct ldttss_desc desc; 479 480 if (index == 0) { 481 pr_alert("%s: NULL\n", name); 482 return; 483 } 484 485 if (offset + sizeof(struct ldttss_desc) >= gdt->size) { 486 pr_alert("%s: 0x%hx -- out of bounds\n", name, index); 487 return; 488 } 489 490 if (copy_from_kernel_nofault(&desc, (void *)(gdt->address + offset), 491 sizeof(struct ldttss_desc))) { 492 pr_alert("%s: 0x%hx -- GDT entry is not readable\n", 493 name, index); 494 return; 495 } 496 497 addr = desc.base0 | (desc.base1 << 16) | ((unsigned long)desc.base2 << 24); 498 #ifdef CONFIG_X86_64 499 addr |= ((u64)desc.base3 << 32); 500 #endif 501 pr_alert("%s: 0x%hx -- base=0x%lx limit=0x%x\n", 502 name, index, addr, (desc.limit0 | (desc.limit1 << 16))); 503 } 504 505 static void 506 show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long address) 507 { 508 if (!oops_may_print()) 509 return; 510 511 if (error_code & X86_PF_INSTR) { 512 unsigned int level; 513 pgd_t *pgd; 514 pte_t *pte; 515 516 pgd = __va(read_cr3_pa()); 517 pgd += pgd_index(address); 518 519 pte = lookup_address_in_pgd(pgd, address, &level); 520 521 if (pte && pte_present(*pte) && !pte_exec(*pte)) 522 pr_crit("kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n", 523 from_kuid(&init_user_ns, current_uid())); 524 if (pte && pte_present(*pte) && pte_exec(*pte) && 525 (pgd_flags(*pgd) & _PAGE_USER) && 526 (__read_cr4() & X86_CR4_SMEP)) 527 pr_crit("unable to execute userspace code (SMEP?) (uid: %d)\n", 528 from_kuid(&init_user_ns, current_uid())); 529 } 530 531 if (address < PAGE_SIZE && !user_mode(regs)) 532 pr_alert("BUG: kernel NULL pointer dereference, address: %px\n", 533 (void *)address); 534 else 535 pr_alert("BUG: unable to handle page fault for address: %px\n", 536 (void *)address); 537 538 pr_alert("#PF: %s %s in %s mode\n", 539 (error_code & X86_PF_USER) ? "user" : "supervisor", 540 (error_code & X86_PF_INSTR) ? "instruction fetch" : 541 (error_code & X86_PF_WRITE) ? "write access" : 542 "read access", 543 user_mode(regs) ? "user" : "kernel"); 544 pr_alert("#PF: error_code(0x%04lx) - %s\n", error_code, 545 !(error_code & X86_PF_PROT) ? "not-present page" : 546 (error_code & X86_PF_RSVD) ? "reserved bit violation" : 547 (error_code & X86_PF_PK) ? "protection keys violation" : 548 "permissions violation"); 549 550 if (!(error_code & X86_PF_USER) && user_mode(regs)) { 551 struct desc_ptr idt, gdt; 552 u16 ldtr, tr; 553 554 /* 555 * This can happen for quite a few reasons. The more obvious 556 * ones are faults accessing the GDT, or LDT. Perhaps 557 * surprisingly, if the CPU tries to deliver a benign or 558 * contributory exception from user code and gets a page fault 559 * during delivery, the page fault can be delivered as though 560 * it originated directly from user code. This could happen 561 * due to wrong permissions on the IDT, GDT, LDT, TSS, or 562 * kernel or IST stack. 563 */ 564 store_idt(&idt); 565 566 /* Usable even on Xen PV -- it's just slow. */ 567 native_store_gdt(&gdt); 568 569 pr_alert("IDT: 0x%lx (limit=0x%hx) GDT: 0x%lx (limit=0x%hx)\n", 570 idt.address, idt.size, gdt.address, gdt.size); 571 572 store_ldt(ldtr); 573 show_ldttss(&gdt, "LDTR", ldtr); 574 575 store_tr(tr); 576 show_ldttss(&gdt, "TR", tr); 577 } 578 579 dump_pagetable(address); 580 } 581 582 static noinline void 583 pgtable_bad(struct pt_regs *regs, unsigned long error_code, 584 unsigned long address) 585 { 586 struct task_struct *tsk; 587 unsigned long flags; 588 int sig; 589 590 flags = oops_begin(); 591 tsk = current; 592 sig = SIGKILL; 593 594 printk(KERN_ALERT "%s: Corrupted page table at address %lx\n", 595 tsk->comm, address); 596 dump_pagetable(address); 597 598 if (__die("Bad pagetable", regs, error_code)) 599 sig = 0; 600 601 oops_end(flags, regs, sig); 602 } 603 604 static void sanitize_error_code(unsigned long address, 605 unsigned long *error_code) 606 { 607 /* 608 * To avoid leaking information about the kernel page 609 * table layout, pretend that user-mode accesses to 610 * kernel addresses are always protection faults. 611 * 612 * NB: This means that failed vsyscalls with vsyscall=none 613 * will have the PROT bit. This doesn't leak any 614 * information and does not appear to cause any problems. 615 */ 616 if (address >= TASK_SIZE_MAX) 617 *error_code |= X86_PF_PROT; 618 } 619 620 static void set_signal_archinfo(unsigned long address, 621 unsigned long error_code) 622 { 623 struct task_struct *tsk = current; 624 625 tsk->thread.trap_nr = X86_TRAP_PF; 626 tsk->thread.error_code = error_code | X86_PF_USER; 627 tsk->thread.cr2 = address; 628 } 629 630 static noinline void 631 page_fault_oops(struct pt_regs *regs, unsigned long error_code, 632 unsigned long address) 633 { 634 unsigned long flags; 635 int sig; 636 637 if (user_mode(regs)) { 638 /* 639 * Implicit kernel access from user mode? Skip the stack 640 * overflow and EFI special cases. 641 */ 642 goto oops; 643 } 644 645 #ifdef CONFIG_VMAP_STACK 646 /* 647 * Stack overflow? During boot, we can fault near the initial 648 * stack in the direct map, but that's not an overflow -- check 649 * that we're in vmalloc space to avoid this. 650 */ 651 if (is_vmalloc_addr((void *)address) && 652 (((unsigned long)current->stack - 1 - address < PAGE_SIZE) || 653 address - ((unsigned long)current->stack + THREAD_SIZE) < PAGE_SIZE)) { 654 unsigned long stack = __this_cpu_ist_top_va(DF) - sizeof(void *); 655 /* 656 * We're likely to be running with very little stack space 657 * left. It's plausible that we'd hit this condition but 658 * double-fault even before we get this far, in which case 659 * we're fine: the double-fault handler will deal with it. 660 * 661 * We don't want to make it all the way into the oops code 662 * and then double-fault, though, because we're likely to 663 * break the console driver and lose most of the stack dump. 664 */ 665 asm volatile ("movq %[stack], %%rsp\n\t" 666 "call handle_stack_overflow\n\t" 667 "1: jmp 1b" 668 : ASM_CALL_CONSTRAINT 669 : "D" ("kernel stack overflow (page fault)"), 670 "S" (regs), "d" (address), 671 [stack] "rm" (stack)); 672 unreachable(); 673 } 674 #endif 675 676 /* 677 * Buggy firmware could access regions which might page fault. If 678 * this happens, EFI has a special OOPS path that will try to 679 * avoid hanging the system. 680 */ 681 if (IS_ENABLED(CONFIG_EFI)) 682 efi_crash_gracefully_on_page_fault(address); 683 684 /* Only not-present faults should be handled by KFENCE. */ 685 if (!(error_code & X86_PF_PROT) && 686 kfence_handle_page_fault(address, error_code & X86_PF_WRITE, regs)) 687 return; 688 689 oops: 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 if (task_stack_end_corrupted(current)) 699 printk(KERN_EMERG "Thread overran stack, or stack corrupted\n"); 700 701 sig = SIGKILL; 702 if (__die("Oops", regs, error_code)) 703 sig = 0; 704 705 /* Executive summary in case the body of the oops scrolled away */ 706 printk(KERN_DEFAULT "CR2: %016lx\n", address); 707 708 oops_end(flags, regs, sig); 709 } 710 711 static noinline void 712 kernelmode_fixup_or_oops(struct pt_regs *regs, unsigned long error_code, 713 unsigned long address, int signal, int si_code) 714 { 715 WARN_ON_ONCE(user_mode(regs)); 716 717 /* Are we prepared to handle this kernel fault? */ 718 if (fixup_exception(regs, X86_TRAP_PF, error_code, address)) { 719 /* 720 * Any interrupt that takes a fault gets the fixup. This makes 721 * the below recursive fault logic only apply to a faults from 722 * task context. 723 */ 724 if (in_interrupt()) 725 return; 726 727 /* 728 * Per the above we're !in_interrupt(), aka. task context. 729 * 730 * In this case we need to make sure we're not recursively 731 * faulting through the emulate_vsyscall() logic. 732 */ 733 if (current->thread.sig_on_uaccess_err && signal) { 734 sanitize_error_code(address, &error_code); 735 736 set_signal_archinfo(address, error_code); 737 738 /* XXX: hwpoison faults will set the wrong code. */ 739 force_sig_fault(signal, si_code, (void __user *)address); 740 } 741 742 /* 743 * Barring that, we can do the fixup and be happy. 744 */ 745 return; 746 } 747 748 /* 749 * AMD erratum #91 manifests as a spurious page fault on a PREFETCH 750 * instruction. 751 */ 752 if (is_prefetch(regs, error_code, address)) 753 return; 754 755 page_fault_oops(regs, error_code, address); 756 } 757 758 /* 759 * Print out info about fatal segfaults, if the show_unhandled_signals 760 * sysctl is set: 761 */ 762 static inline void 763 show_signal_msg(struct pt_regs *regs, unsigned long error_code, 764 unsigned long address, struct task_struct *tsk) 765 { 766 const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG; 767 768 if (!unhandled_signal(tsk, SIGSEGV)) 769 return; 770 771 if (!printk_ratelimit()) 772 return; 773 774 printk("%s%s[%d]: segfault at %lx ip %px sp %px error %lx", 775 loglvl, tsk->comm, task_pid_nr(tsk), address, 776 (void *)regs->ip, (void *)regs->sp, error_code); 777 778 print_vma_addr(KERN_CONT " in ", regs->ip); 779 780 printk(KERN_CONT "\n"); 781 782 show_opcodes(regs, loglvl); 783 } 784 785 /* 786 * The (legacy) vsyscall page is the long page in the kernel portion 787 * of the address space that has user-accessible permissions. 788 */ 789 static bool is_vsyscall_vaddr(unsigned long vaddr) 790 { 791 return unlikely((vaddr & PAGE_MASK) == VSYSCALL_ADDR); 792 } 793 794 static void 795 __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, 796 unsigned long address, u32 pkey, int si_code) 797 { 798 struct task_struct *tsk = current; 799 800 if (!user_mode(regs)) { 801 kernelmode_fixup_or_oops(regs, error_code, address, pkey, si_code); 802 return; 803 } 804 805 if (!(error_code & X86_PF_USER)) { 806 /* Implicit user access to kernel memory -- just oops */ 807 page_fault_oops(regs, error_code, address); 808 return; 809 } 810 811 /* 812 * User mode accesses just cause a SIGSEGV. 813 * It's possible to have interrupts off here: 814 */ 815 local_irq_enable(); 816 817 /* 818 * Valid to do another page fault here because this one came 819 * from user space: 820 */ 821 if (is_prefetch(regs, error_code, address)) 822 return; 823 824 if (is_errata100(regs, address)) 825 return; 826 827 sanitize_error_code(address, &error_code); 828 829 if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address)) 830 return; 831 832 if (likely(show_unhandled_signals)) 833 show_signal_msg(regs, error_code, address, tsk); 834 835 set_signal_archinfo(address, error_code); 836 837 if (si_code == SEGV_PKUERR) 838 force_sig_pkuerr((void __user *)address, pkey); 839 else 840 force_sig_fault(SIGSEGV, si_code, (void __user *)address); 841 842 local_irq_disable(); 843 } 844 845 static noinline void 846 bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, 847 unsigned long address) 848 { 849 __bad_area_nosemaphore(regs, error_code, address, 0, SEGV_MAPERR); 850 } 851 852 static void 853 __bad_area(struct pt_regs *regs, unsigned long error_code, 854 unsigned long address, u32 pkey, int si_code) 855 { 856 struct mm_struct *mm = current->mm; 857 /* 858 * Something tried to access memory that isn't in our memory map.. 859 * Fix it, but check if it's kernel or user first.. 860 */ 861 mmap_read_unlock(mm); 862 863 __bad_area_nosemaphore(regs, error_code, address, pkey, si_code); 864 } 865 866 static noinline void 867 bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address) 868 { 869 __bad_area(regs, error_code, address, 0, SEGV_MAPERR); 870 } 871 872 static inline bool bad_area_access_from_pkeys(unsigned long error_code, 873 struct vm_area_struct *vma) 874 { 875 /* This code is always called on the current mm */ 876 bool foreign = false; 877 878 if (!cpu_feature_enabled(X86_FEATURE_OSPKE)) 879 return false; 880 if (error_code & X86_PF_PK) 881 return true; 882 /* this checks permission keys on the VMA: */ 883 if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE), 884 (error_code & X86_PF_INSTR), foreign)) 885 return true; 886 return false; 887 } 888 889 static noinline void 890 bad_area_access_error(struct pt_regs *regs, unsigned long error_code, 891 unsigned long address, struct vm_area_struct *vma) 892 { 893 /* 894 * This OSPKE check is not strictly necessary at runtime. 895 * But, doing it this way allows compiler optimizations 896 * if pkeys are compiled out. 897 */ 898 if (bad_area_access_from_pkeys(error_code, vma)) { 899 /* 900 * A protection key fault means that the PKRU value did not allow 901 * access to some PTE. Userspace can figure out what PKRU was 902 * from the XSAVE state. This function captures the pkey from 903 * the vma and passes it to userspace so userspace can discover 904 * which protection key was set on the PTE. 905 * 906 * If we get here, we know that the hardware signaled a X86_PF_PK 907 * fault and that there was a VMA once we got in the fault 908 * handler. It does *not* guarantee that the VMA we find here 909 * was the one that we faulted on. 910 * 911 * 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4); 912 * 2. T1 : set PKRU to deny access to pkey=4, touches page 913 * 3. T1 : faults... 914 * 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5); 915 * 5. T1 : enters fault handler, takes mmap_lock, etc... 916 * 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really 917 * faulted on a pte with its pkey=4. 918 */ 919 u32 pkey = vma_pkey(vma); 920 921 __bad_area(regs, error_code, address, pkey, SEGV_PKUERR); 922 } else { 923 __bad_area(regs, error_code, address, 0, SEGV_ACCERR); 924 } 925 } 926 927 static void 928 do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address, 929 vm_fault_t fault) 930 { 931 /* Kernel mode? Handle exceptions or die: */ 932 if (!user_mode(regs)) { 933 kernelmode_fixup_or_oops(regs, error_code, address, SIGBUS, BUS_ADRERR); 934 return; 935 } 936 937 /* User-space => ok to do another page fault: */ 938 if (is_prefetch(regs, error_code, address)) 939 return; 940 941 sanitize_error_code(address, &error_code); 942 943 if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address)) 944 return; 945 946 set_signal_archinfo(address, error_code); 947 948 #ifdef CONFIG_MEMORY_FAILURE 949 if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) { 950 struct task_struct *tsk = current; 951 unsigned lsb = 0; 952 953 pr_err( 954 "MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n", 955 tsk->comm, tsk->pid, address); 956 if (fault & VM_FAULT_HWPOISON_LARGE) 957 lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault)); 958 if (fault & VM_FAULT_HWPOISON) 959 lsb = PAGE_SHIFT; 960 force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb); 961 return; 962 } 963 #endif 964 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address); 965 } 966 967 static int spurious_kernel_fault_check(unsigned long error_code, pte_t *pte) 968 { 969 if ((error_code & X86_PF_WRITE) && !pte_write(*pte)) 970 return 0; 971 972 if ((error_code & X86_PF_INSTR) && !pte_exec(*pte)) 973 return 0; 974 975 return 1; 976 } 977 978 /* 979 * Handle a spurious fault caused by a stale TLB entry. 980 * 981 * This allows us to lazily refresh the TLB when increasing the 982 * permissions of a kernel page (RO -> RW or NX -> X). Doing it 983 * eagerly is very expensive since that implies doing a full 984 * cross-processor TLB flush, even if no stale TLB entries exist 985 * on other processors. 986 * 987 * Spurious faults may only occur if the TLB contains an entry with 988 * fewer permission than the page table entry. Non-present (P = 0) 989 * and reserved bit (R = 1) faults are never spurious. 990 * 991 * There are no security implications to leaving a stale TLB when 992 * increasing the permissions on a page. 993 * 994 * Returns non-zero if a spurious fault was handled, zero otherwise. 995 * 996 * See Intel Developer's Manual Vol 3 Section 4.10.4.3, bullet 3 997 * (Optional Invalidation). 998 */ 999 static noinline int 1000 spurious_kernel_fault(unsigned long error_code, unsigned long address) 1001 { 1002 pgd_t *pgd; 1003 p4d_t *p4d; 1004 pud_t *pud; 1005 pmd_t *pmd; 1006 pte_t *pte; 1007 int ret; 1008 1009 /* 1010 * Only writes to RO or instruction fetches from NX may cause 1011 * spurious faults. 1012 * 1013 * These could be from user or supervisor accesses but the TLB 1014 * is only lazily flushed after a kernel mapping protection 1015 * change, so user accesses are not expected to cause spurious 1016 * faults. 1017 */ 1018 if (error_code != (X86_PF_WRITE | X86_PF_PROT) && 1019 error_code != (X86_PF_INSTR | X86_PF_PROT)) 1020 return 0; 1021 1022 pgd = init_mm.pgd + pgd_index(address); 1023 if (!pgd_present(*pgd)) 1024 return 0; 1025 1026 p4d = p4d_offset(pgd, address); 1027 if (!p4d_present(*p4d)) 1028 return 0; 1029 1030 if (p4d_large(*p4d)) 1031 return spurious_kernel_fault_check(error_code, (pte_t *) p4d); 1032 1033 pud = pud_offset(p4d, address); 1034 if (!pud_present(*pud)) 1035 return 0; 1036 1037 if (pud_large(*pud)) 1038 return spurious_kernel_fault_check(error_code, (pte_t *) pud); 1039 1040 pmd = pmd_offset(pud, address); 1041 if (!pmd_present(*pmd)) 1042 return 0; 1043 1044 if (pmd_large(*pmd)) 1045 return spurious_kernel_fault_check(error_code, (pte_t *) pmd); 1046 1047 pte = pte_offset_kernel(pmd, address); 1048 if (!pte_present(*pte)) 1049 return 0; 1050 1051 ret = spurious_kernel_fault_check(error_code, pte); 1052 if (!ret) 1053 return 0; 1054 1055 /* 1056 * Make sure we have permissions in PMD. 1057 * If not, then there's a bug in the page tables: 1058 */ 1059 ret = spurious_kernel_fault_check(error_code, (pte_t *) pmd); 1060 WARN_ONCE(!ret, "PMD has incorrect permission bits\n"); 1061 1062 return ret; 1063 } 1064 NOKPROBE_SYMBOL(spurious_kernel_fault); 1065 1066 int show_unhandled_signals = 1; 1067 1068 static inline int 1069 access_error(unsigned long error_code, struct vm_area_struct *vma) 1070 { 1071 /* This is only called for the current mm, so: */ 1072 bool foreign = false; 1073 1074 /* 1075 * Read or write was blocked by protection keys. This is 1076 * always an unconditional error and can never result in 1077 * a follow-up action to resolve the fault, like a COW. 1078 */ 1079 if (error_code & X86_PF_PK) 1080 return 1; 1081 1082 /* 1083 * SGX hardware blocked the access. This usually happens 1084 * when the enclave memory contents have been destroyed, like 1085 * after a suspend/resume cycle. In any case, the kernel can't 1086 * fix the cause of the fault. Handle the fault as an access 1087 * error even in cases where no actual access violation 1088 * occurred. This allows userspace to rebuild the enclave in 1089 * response to the signal. 1090 */ 1091 if (unlikely(error_code & X86_PF_SGX)) 1092 return 1; 1093 1094 /* 1095 * Make sure to check the VMA so that we do not perform 1096 * faults just to hit a X86_PF_PK as soon as we fill in a 1097 * page. 1098 */ 1099 if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE), 1100 (error_code & X86_PF_INSTR), foreign)) 1101 return 1; 1102 1103 if (error_code & X86_PF_WRITE) { 1104 /* write, present and write, not present: */ 1105 if (unlikely(!(vma->vm_flags & VM_WRITE))) 1106 return 1; 1107 return 0; 1108 } 1109 1110 /* read, present: */ 1111 if (unlikely(error_code & X86_PF_PROT)) 1112 return 1; 1113 1114 /* read, not present: */ 1115 if (unlikely(!vma_is_accessible(vma))) 1116 return 1; 1117 1118 return 0; 1119 } 1120 1121 bool fault_in_kernel_space(unsigned long address) 1122 { 1123 /* 1124 * On 64-bit systems, the vsyscall page is at an address above 1125 * TASK_SIZE_MAX, but is not considered part of the kernel 1126 * address space. 1127 */ 1128 if (IS_ENABLED(CONFIG_X86_64) && is_vsyscall_vaddr(address)) 1129 return false; 1130 1131 return address >= TASK_SIZE_MAX; 1132 } 1133 1134 /* 1135 * Called for all faults where 'address' is part of the kernel address 1136 * space. Might get called for faults that originate from *code* that 1137 * ran in userspace or the kernel. 1138 */ 1139 static void 1140 do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code, 1141 unsigned long address) 1142 { 1143 /* 1144 * Protection keys exceptions only happen on user pages. We 1145 * have no user pages in the kernel portion of the address 1146 * space, so do not expect them here. 1147 */ 1148 WARN_ON_ONCE(hw_error_code & X86_PF_PK); 1149 1150 #ifdef CONFIG_X86_32 1151 /* 1152 * We can fault-in kernel-space virtual memory on-demand. The 1153 * 'reference' page table is init_mm.pgd. 1154 * 1155 * NOTE! We MUST NOT take any locks for this case. We may 1156 * be in an interrupt or a critical region, and should 1157 * only copy the information from the master page table, 1158 * nothing more. 1159 * 1160 * Before doing this on-demand faulting, ensure that the 1161 * fault is not any of the following: 1162 * 1. A fault on a PTE with a reserved bit set. 1163 * 2. A fault caused by a user-mode access. (Do not demand- 1164 * fault kernel memory due to user-mode accesses). 1165 * 3. A fault caused by a page-level protection violation. 1166 * (A demand fault would be on a non-present page which 1167 * would have X86_PF_PROT==0). 1168 * 1169 * This is only needed to close a race condition on x86-32 in 1170 * the vmalloc mapping/unmapping code. See the comment above 1171 * vmalloc_fault() for details. On x86-64 the race does not 1172 * exist as the vmalloc mappings don't need to be synchronized 1173 * there. 1174 */ 1175 if (!(hw_error_code & (X86_PF_RSVD | X86_PF_USER | X86_PF_PROT))) { 1176 if (vmalloc_fault(address) >= 0) 1177 return; 1178 } 1179 #endif 1180 1181 if (is_f00f_bug(regs, hw_error_code, address)) 1182 return; 1183 1184 /* Was the fault spurious, caused by lazy TLB invalidation? */ 1185 if (spurious_kernel_fault(hw_error_code, address)) 1186 return; 1187 1188 /* kprobes don't want to hook the spurious faults: */ 1189 if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF))) 1190 return; 1191 1192 /* 1193 * Note, despite being a "bad area", there are quite a few 1194 * acceptable reasons to get here, such as erratum fixups 1195 * and handling kernel code that can fault, like get_user(). 1196 * 1197 * Don't take the mm semaphore here. If we fixup a prefetch 1198 * fault we could otherwise deadlock: 1199 */ 1200 bad_area_nosemaphore(regs, hw_error_code, address); 1201 } 1202 NOKPROBE_SYMBOL(do_kern_addr_fault); 1203 1204 /* 1205 * Handle faults in the user portion of the address space. Nothing in here 1206 * should check X86_PF_USER without a specific justification: for almost 1207 * all purposes, we should treat a normal kernel access to user memory 1208 * (e.g. get_user(), put_user(), etc.) the same as the WRUSS instruction. 1209 * The one exception is AC flag handling, which is, per the x86 1210 * architecture, special for WRUSS. 1211 */ 1212 static inline 1213 void do_user_addr_fault(struct pt_regs *regs, 1214 unsigned long error_code, 1215 unsigned long address) 1216 { 1217 struct vm_area_struct *vma; 1218 struct task_struct *tsk; 1219 struct mm_struct *mm; 1220 vm_fault_t fault; 1221 unsigned int flags = FAULT_FLAG_DEFAULT; 1222 1223 tsk = current; 1224 mm = tsk->mm; 1225 1226 if (unlikely((error_code & (X86_PF_USER | X86_PF_INSTR)) == X86_PF_INSTR)) { 1227 /* 1228 * Whoops, this is kernel mode code trying to execute from 1229 * user memory. Unless this is AMD erratum #93, which 1230 * corrupts RIP such that it looks like a user address, 1231 * this is unrecoverable. Don't even try to look up the 1232 * VMA or look for extable entries. 1233 */ 1234 if (is_errata93(regs, address)) 1235 return; 1236 1237 page_fault_oops(regs, error_code, address); 1238 return; 1239 } 1240 1241 /* kprobes don't want to hook the spurious faults: */ 1242 if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF))) 1243 return; 1244 1245 /* 1246 * Reserved bits are never expected to be set on 1247 * entries in the user portion of the page tables. 1248 */ 1249 if (unlikely(error_code & X86_PF_RSVD)) 1250 pgtable_bad(regs, error_code, address); 1251 1252 /* 1253 * If SMAP is on, check for invalid kernel (supervisor) access to user 1254 * pages in the user address space. The odd case here is WRUSS, 1255 * which, according to the preliminary documentation, does not respect 1256 * SMAP and will have the USER bit set so, in all cases, SMAP 1257 * enforcement appears to be consistent with the USER bit. 1258 */ 1259 if (unlikely(cpu_feature_enabled(X86_FEATURE_SMAP) && 1260 !(error_code & X86_PF_USER) && 1261 !(regs->flags & X86_EFLAGS_AC))) { 1262 /* 1263 * No extable entry here. This was a kernel access to an 1264 * invalid pointer. get_kernel_nofault() will not get here. 1265 */ 1266 page_fault_oops(regs, error_code, address); 1267 return; 1268 } 1269 1270 /* 1271 * If we're in an interrupt, have no user context or are running 1272 * in a region with pagefaults disabled then we must not take the fault 1273 */ 1274 if (unlikely(faulthandler_disabled() || !mm)) { 1275 bad_area_nosemaphore(regs, error_code, address); 1276 return; 1277 } 1278 1279 /* 1280 * It's safe to allow irq's after cr2 has been saved and the 1281 * vmalloc fault has been handled. 1282 * 1283 * User-mode registers count as a user access even for any 1284 * potential system fault or CPU buglet: 1285 */ 1286 if (user_mode(regs)) { 1287 local_irq_enable(); 1288 flags |= FAULT_FLAG_USER; 1289 } else { 1290 if (regs->flags & X86_EFLAGS_IF) 1291 local_irq_enable(); 1292 } 1293 1294 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address); 1295 1296 if (error_code & X86_PF_WRITE) 1297 flags |= FAULT_FLAG_WRITE; 1298 if (error_code & X86_PF_INSTR) 1299 flags |= FAULT_FLAG_INSTRUCTION; 1300 1301 #ifdef CONFIG_X86_64 1302 /* 1303 * Faults in the vsyscall page might need emulation. The 1304 * vsyscall page is at a high address (>PAGE_OFFSET), but is 1305 * considered to be part of the user address space. 1306 * 1307 * The vsyscall page does not have a "real" VMA, so do this 1308 * emulation before we go searching for VMAs. 1309 * 1310 * PKRU never rejects instruction fetches, so we don't need 1311 * to consider the PF_PK bit. 1312 */ 1313 if (is_vsyscall_vaddr(address)) { 1314 if (emulate_vsyscall(error_code, regs, address)) 1315 return; 1316 } 1317 #endif 1318 1319 /* 1320 * Kernel-mode access to the user address space should only occur 1321 * on well-defined single instructions listed in the exception 1322 * tables. But, an erroneous kernel fault occurring outside one of 1323 * those areas which also holds mmap_lock might deadlock attempting 1324 * to validate the fault against the address space. 1325 * 1326 * Only do the expensive exception table search when we might be at 1327 * risk of a deadlock. This happens if we 1328 * 1. Failed to acquire mmap_lock, and 1329 * 2. The access did not originate in userspace. 1330 */ 1331 if (unlikely(!mmap_read_trylock(mm))) { 1332 if (!user_mode(regs) && !search_exception_tables(regs->ip)) { 1333 /* 1334 * Fault from code in kernel from 1335 * which we do not expect faults. 1336 */ 1337 bad_area_nosemaphore(regs, error_code, address); 1338 return; 1339 } 1340 retry: 1341 mmap_read_lock(mm); 1342 } else { 1343 /* 1344 * The above down_read_trylock() might have succeeded in 1345 * which case we'll have missed the might_sleep() from 1346 * down_read(): 1347 */ 1348 might_sleep(); 1349 } 1350 1351 vma = find_vma(mm, address); 1352 if (unlikely(!vma)) { 1353 bad_area(regs, error_code, address); 1354 return; 1355 } 1356 if (likely(vma->vm_start <= address)) 1357 goto good_area; 1358 if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) { 1359 bad_area(regs, error_code, address); 1360 return; 1361 } 1362 if (unlikely(expand_stack(vma, address))) { 1363 bad_area(regs, error_code, address); 1364 return; 1365 } 1366 1367 /* 1368 * Ok, we have a good vm_area for this memory access, so 1369 * we can handle it.. 1370 */ 1371 good_area: 1372 if (unlikely(access_error(error_code, vma))) { 1373 bad_area_access_error(regs, error_code, address, vma); 1374 return; 1375 } 1376 1377 /* 1378 * If for any reason at all we couldn't handle the fault, 1379 * make sure we exit gracefully rather than endlessly redo 1380 * the fault. Since we never set FAULT_FLAG_RETRY_NOWAIT, if 1381 * we get VM_FAULT_RETRY back, the mmap_lock has been unlocked. 1382 * 1383 * Note that handle_userfault() may also release and reacquire mmap_lock 1384 * (and not return with VM_FAULT_RETRY), when returning to userland to 1385 * repeat the page fault later with a VM_FAULT_NOPAGE retval 1386 * (potentially after handling any pending signal during the return to 1387 * userland). The return to userland is identified whenever 1388 * FAULT_FLAG_USER|FAULT_FLAG_KILLABLE are both set in flags. 1389 */ 1390 fault = handle_mm_fault(vma, address, flags, regs); 1391 1392 if (fault_signal_pending(fault, regs)) { 1393 /* 1394 * Quick path to respond to signals. The core mm code 1395 * has unlocked the mm for us if we get here. 1396 */ 1397 if (!user_mode(regs)) 1398 kernelmode_fixup_or_oops(regs, error_code, address, 1399 SIGBUS, BUS_ADRERR); 1400 return; 1401 } 1402 1403 /* 1404 * If we need to retry the mmap_lock has already been released, 1405 * and if there is a fatal signal pending there is no guarantee 1406 * that we made any progress. Handle this case first. 1407 */ 1408 if (unlikely((fault & VM_FAULT_RETRY) && 1409 (flags & FAULT_FLAG_ALLOW_RETRY))) { 1410 flags |= FAULT_FLAG_TRIED; 1411 goto retry; 1412 } 1413 1414 mmap_read_unlock(mm); 1415 if (likely(!(fault & VM_FAULT_ERROR))) 1416 return; 1417 1418 if (fatal_signal_pending(current) && !user_mode(regs)) { 1419 kernelmode_fixup_or_oops(regs, error_code, address, 0, 0); 1420 return; 1421 } 1422 1423 if (fault & VM_FAULT_OOM) { 1424 /* Kernel mode? Handle exceptions or die: */ 1425 if (!user_mode(regs)) { 1426 kernelmode_fixup_or_oops(regs, error_code, address, 1427 SIGSEGV, SEGV_MAPERR); 1428 return; 1429 } 1430 1431 /* 1432 * We ran out of memory, call the OOM killer, and return the 1433 * userspace (which will retry the fault, or kill us if we got 1434 * oom-killed): 1435 */ 1436 pagefault_out_of_memory(); 1437 } else { 1438 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON| 1439 VM_FAULT_HWPOISON_LARGE)) 1440 do_sigbus(regs, error_code, address, fault); 1441 else if (fault & VM_FAULT_SIGSEGV) 1442 bad_area_nosemaphore(regs, error_code, address); 1443 else 1444 BUG(); 1445 } 1446 } 1447 NOKPROBE_SYMBOL(do_user_addr_fault); 1448 1449 static __always_inline void 1450 trace_page_fault_entries(struct pt_regs *regs, unsigned long error_code, 1451 unsigned long address) 1452 { 1453 if (!trace_pagefault_enabled()) 1454 return; 1455 1456 if (user_mode(regs)) 1457 trace_page_fault_user(address, regs, error_code); 1458 else 1459 trace_page_fault_kernel(address, regs, error_code); 1460 } 1461 1462 static __always_inline void 1463 handle_page_fault(struct pt_regs *regs, unsigned long error_code, 1464 unsigned long address) 1465 { 1466 trace_page_fault_entries(regs, error_code, address); 1467 1468 if (unlikely(kmmio_fault(regs, address))) 1469 return; 1470 1471 /* Was the fault on kernel-controlled part of the address space? */ 1472 if (unlikely(fault_in_kernel_space(address))) { 1473 do_kern_addr_fault(regs, error_code, address); 1474 } else { 1475 do_user_addr_fault(regs, error_code, address); 1476 /* 1477 * User address page fault handling might have reenabled 1478 * interrupts. Fixing up all potential exit points of 1479 * do_user_addr_fault() and its leaf functions is just not 1480 * doable w/o creating an unholy mess or turning the code 1481 * upside down. 1482 */ 1483 local_irq_disable(); 1484 } 1485 } 1486 1487 DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault) 1488 { 1489 unsigned long address = read_cr2(); 1490 irqentry_state_t state; 1491 1492 prefetchw(¤t->mm->mmap_lock); 1493 1494 /* 1495 * KVM uses #PF vector to deliver 'page not present' events to guests 1496 * (asynchronous page fault mechanism). The event happens when a 1497 * userspace task is trying to access some valid (from guest's point of 1498 * view) memory which is not currently mapped by the host (e.g. the 1499 * memory is swapped out). Note, the corresponding "page ready" event 1500 * which is injected when the memory becomes available, is delivered via 1501 * an interrupt mechanism and not a #PF exception 1502 * (see arch/x86/kernel/kvm.c: sysvec_kvm_asyncpf_interrupt()). 1503 * 1504 * We are relying on the interrupted context being sane (valid RSP, 1505 * relevant locks not held, etc.), which is fine as long as the 1506 * interrupted context had IF=1. We are also relying on the KVM 1507 * async pf type field and CR2 being read consistently instead of 1508 * getting values from real and async page faults mixed up. 1509 * 1510 * Fingers crossed. 1511 * 1512 * The async #PF handling code takes care of idtentry handling 1513 * itself. 1514 */ 1515 if (kvm_handle_async_pf(regs, (u32)address)) 1516 return; 1517 1518 /* 1519 * Entry handling for valid #PF from kernel mode is slightly 1520 * different: RCU is already watching and rcu_irq_enter() must not 1521 * be invoked because a kernel fault on a user space address might 1522 * sleep. 1523 * 1524 * In case the fault hit a RCU idle region the conditional entry 1525 * code reenabled RCU to avoid subsequent wreckage which helps 1526 * debuggability. 1527 */ 1528 state = irqentry_enter(regs); 1529 1530 instrumentation_begin(); 1531 handle_page_fault(regs, error_code, address); 1532 instrumentation_end(); 1533 1534 irqentry_exit(regs, state); 1535 } 1536