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 #include <asm/irq_stack.h> 36 37 #define CREATE_TRACE_POINTS 38 #include <asm/trace/exceptions.h> 39 40 /* 41 * Returns 0 if mmiotrace is disabled, or if the fault is not 42 * handled by mmiotrace: 43 */ 44 static nokprobe_inline int 45 kmmio_fault(struct pt_regs *regs, unsigned long addr) 46 { 47 if (unlikely(is_kmmio_active())) 48 if (kmmio_handler(regs, addr) == 1) 49 return -1; 50 return 0; 51 } 52 53 /* 54 * Prefetch quirks: 55 * 56 * 32-bit mode: 57 * 58 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch. 59 * Check that here and ignore it. This is AMD erratum #91. 60 * 61 * 64-bit mode: 62 * 63 * Sometimes the CPU reports invalid exceptions on prefetch. 64 * Check that here and ignore it. 65 * 66 * Opcode checker based on code by Richard Brunner. 67 */ 68 static inline int 69 check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr, 70 unsigned char opcode, int *prefetch) 71 { 72 unsigned char instr_hi = opcode & 0xf0; 73 unsigned char instr_lo = opcode & 0x0f; 74 75 switch (instr_hi) { 76 case 0x20: 77 case 0x30: 78 /* 79 * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes. 80 * In X86_64 long mode, the CPU will signal invalid 81 * opcode if some of these prefixes are present so 82 * X86_64 will never get here anyway 83 */ 84 return ((instr_lo & 7) == 0x6); 85 #ifdef CONFIG_X86_64 86 case 0x40: 87 /* 88 * In 64-bit mode 0x40..0x4F are valid REX prefixes 89 */ 90 return (!user_mode(regs) || user_64bit_mode(regs)); 91 #endif 92 case 0x60: 93 /* 0x64 thru 0x67 are valid prefixes in all modes. */ 94 return (instr_lo & 0xC) == 0x4; 95 case 0xF0: 96 /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */ 97 return !instr_lo || (instr_lo>>1) == 1; 98 case 0x00: 99 /* Prefetch instruction is 0x0F0D or 0x0F18 */ 100 if (get_kernel_nofault(opcode, instr)) 101 return 0; 102 103 *prefetch = (instr_lo == 0xF) && 104 (opcode == 0x0D || opcode == 0x18); 105 return 0; 106 default: 107 return 0; 108 } 109 } 110 111 static bool is_amd_k8_pre_npt(void) 112 { 113 struct cpuinfo_x86 *c = &boot_cpu_data; 114 115 return unlikely(IS_ENABLED(CONFIG_CPU_SUP_AMD) && 116 c->x86_vendor == X86_VENDOR_AMD && 117 c->x86 == 0xf && c->x86_model < 0x40); 118 } 119 120 static int 121 is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr) 122 { 123 unsigned char *max_instr; 124 unsigned char *instr; 125 int prefetch = 0; 126 127 /* Erratum #91 affects AMD K8, pre-NPT CPUs */ 128 if (!is_amd_k8_pre_npt()) 129 return 0; 130 131 /* 132 * If it was a exec (instruction fetch) fault on NX page, then 133 * do not ignore the fault: 134 */ 135 if (error_code & X86_PF_INSTR) 136 return 0; 137 138 instr = (void *)convert_ip_to_linear(current, regs); 139 max_instr = instr + 15; 140 141 /* 142 * This code has historically always bailed out if IP points to a 143 * not-present page (e.g. due to a race). No one has ever 144 * complained about this. 145 */ 146 pagefault_disable(); 147 148 while (instr < max_instr) { 149 unsigned char opcode; 150 151 if (user_mode(regs)) { 152 if (get_user(opcode, (unsigned char __user *) instr)) 153 break; 154 } else { 155 if (get_kernel_nofault(opcode, instr)) 156 break; 157 } 158 159 instr++; 160 161 if (!check_prefetch_opcode(regs, instr, opcode, &prefetch)) 162 break; 163 } 164 165 pagefault_enable(); 166 return prefetch; 167 } 168 169 DEFINE_SPINLOCK(pgd_lock); 170 LIST_HEAD(pgd_list); 171 172 #ifdef CONFIG_X86_32 173 static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address) 174 { 175 unsigned index = pgd_index(address); 176 pgd_t *pgd_k; 177 p4d_t *p4d, *p4d_k; 178 pud_t *pud, *pud_k; 179 pmd_t *pmd, *pmd_k; 180 181 pgd += index; 182 pgd_k = init_mm.pgd + index; 183 184 if (!pgd_present(*pgd_k)) 185 return NULL; 186 187 /* 188 * set_pgd(pgd, *pgd_k); here would be useless on PAE 189 * and redundant with the set_pmd() on non-PAE. As would 190 * set_p4d/set_pud. 191 */ 192 p4d = p4d_offset(pgd, address); 193 p4d_k = p4d_offset(pgd_k, address); 194 if (!p4d_present(*p4d_k)) 195 return NULL; 196 197 pud = pud_offset(p4d, address); 198 pud_k = pud_offset(p4d_k, address); 199 if (!pud_present(*pud_k)) 200 return NULL; 201 202 pmd = pmd_offset(pud, address); 203 pmd_k = pmd_offset(pud_k, address); 204 205 if (pmd_present(*pmd) != pmd_present(*pmd_k)) 206 set_pmd(pmd, *pmd_k); 207 208 if (!pmd_present(*pmd_k)) 209 return NULL; 210 else 211 BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k)); 212 213 return pmd_k; 214 } 215 216 /* 217 * Handle a fault on the vmalloc or module mapping area 218 * 219 * This is needed because there is a race condition between the time 220 * when the vmalloc mapping code updates the PMD to the point in time 221 * where it synchronizes this update with the other page-tables in the 222 * system. 223 * 224 * In this race window another thread/CPU can map an area on the same 225 * PMD, finds it already present and does not synchronize it with the 226 * rest of the system yet. As a result v[mz]alloc might return areas 227 * which are not mapped in every page-table in the system, causing an 228 * unhandled page-fault when they are accessed. 229 */ 230 static noinline int vmalloc_fault(unsigned long address) 231 { 232 unsigned long pgd_paddr; 233 pmd_t *pmd_k; 234 pte_t *pte_k; 235 236 /* Make sure we are in vmalloc area: */ 237 if (!(address >= VMALLOC_START && address < VMALLOC_END)) 238 return -1; 239 240 /* 241 * Synchronize this task's top level page-table 242 * with the 'reference' page table. 243 * 244 * Do _not_ use "current" here. We might be inside 245 * an interrupt in the middle of a task switch.. 246 */ 247 pgd_paddr = read_cr3_pa(); 248 pmd_k = vmalloc_sync_one(__va(pgd_paddr), address); 249 if (!pmd_k) 250 return -1; 251 252 if (pmd_large(*pmd_k)) 253 return 0; 254 255 pte_k = pte_offset_kernel(pmd_k, address); 256 if (!pte_present(*pte_k)) 257 return -1; 258 259 return 0; 260 } 261 NOKPROBE_SYMBOL(vmalloc_fault); 262 263 void arch_sync_kernel_mappings(unsigned long start, unsigned long end) 264 { 265 unsigned long addr; 266 267 for (addr = start & PMD_MASK; 268 addr >= TASK_SIZE_MAX && addr < VMALLOC_END; 269 addr += PMD_SIZE) { 270 struct page *page; 271 272 spin_lock(&pgd_lock); 273 list_for_each_entry(page, &pgd_list, lru) { 274 spinlock_t *pgt_lock; 275 276 /* the pgt_lock only for Xen */ 277 pgt_lock = &pgd_page_get_mm(page)->page_table_lock; 278 279 spin_lock(pgt_lock); 280 vmalloc_sync_one(page_address(page), addr); 281 spin_unlock(pgt_lock); 282 } 283 spin_unlock(&pgd_lock); 284 } 285 } 286 287 static bool low_pfn(unsigned long pfn) 288 { 289 return pfn < max_low_pfn; 290 } 291 292 static void dump_pagetable(unsigned long address) 293 { 294 pgd_t *base = __va(read_cr3_pa()); 295 pgd_t *pgd = &base[pgd_index(address)]; 296 p4d_t *p4d; 297 pud_t *pud; 298 pmd_t *pmd; 299 pte_t *pte; 300 301 #ifdef CONFIG_X86_PAE 302 pr_info("*pdpt = %016Lx ", pgd_val(*pgd)); 303 if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd)) 304 goto out; 305 #define pr_pde pr_cont 306 #else 307 #define pr_pde pr_info 308 #endif 309 p4d = p4d_offset(pgd, address); 310 pud = pud_offset(p4d, address); 311 pmd = pmd_offset(pud, address); 312 pr_pde("*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd)); 313 #undef pr_pde 314 315 /* 316 * We must not directly access the pte in the highpte 317 * case if the page table is located in highmem. 318 * And let's rather not kmap-atomic the pte, just in case 319 * it's allocated already: 320 */ 321 if (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_large(*pmd)) 322 goto out; 323 324 pte = pte_offset_kernel(pmd, address); 325 pr_cont("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte)); 326 out: 327 pr_cont("\n"); 328 } 329 330 #else /* CONFIG_X86_64: */ 331 332 #ifdef CONFIG_CPU_SUP_AMD 333 static const char errata93_warning[] = 334 KERN_ERR 335 "******* Your BIOS seems to not contain a fix for K8 errata #93\n" 336 "******* Working around it, but it may cause SEGVs or burn power.\n" 337 "******* Please consider a BIOS update.\n" 338 "******* Disabling USB legacy in the BIOS may also help.\n"; 339 #endif 340 341 static int bad_address(void *p) 342 { 343 unsigned long dummy; 344 345 return get_kernel_nofault(dummy, (unsigned long *)p); 346 } 347 348 static void dump_pagetable(unsigned long address) 349 { 350 pgd_t *base = __va(read_cr3_pa()); 351 pgd_t *pgd = base + pgd_index(address); 352 p4d_t *p4d; 353 pud_t *pud; 354 pmd_t *pmd; 355 pte_t *pte; 356 357 if (bad_address(pgd)) 358 goto bad; 359 360 pr_info("PGD %lx ", pgd_val(*pgd)); 361 362 if (!pgd_present(*pgd)) 363 goto out; 364 365 p4d = p4d_offset(pgd, address); 366 if (bad_address(p4d)) 367 goto bad; 368 369 pr_cont("P4D %lx ", p4d_val(*p4d)); 370 if (!p4d_present(*p4d) || p4d_large(*p4d)) 371 goto out; 372 373 pud = pud_offset(p4d, address); 374 if (bad_address(pud)) 375 goto bad; 376 377 pr_cont("PUD %lx ", pud_val(*pud)); 378 if (!pud_present(*pud) || pud_large(*pud)) 379 goto out; 380 381 pmd = pmd_offset(pud, address); 382 if (bad_address(pmd)) 383 goto bad; 384 385 pr_cont("PMD %lx ", pmd_val(*pmd)); 386 if (!pmd_present(*pmd) || pmd_large(*pmd)) 387 goto out; 388 389 pte = pte_offset_kernel(pmd, address); 390 if (bad_address(pte)) 391 goto bad; 392 393 pr_cont("PTE %lx", pte_val(*pte)); 394 out: 395 pr_cont("\n"); 396 return; 397 bad: 398 pr_info("BAD\n"); 399 } 400 401 #endif /* CONFIG_X86_64 */ 402 403 /* 404 * Workaround for K8 erratum #93 & buggy BIOS. 405 * 406 * BIOS SMM functions are required to use a specific workaround 407 * to avoid corruption of the 64bit RIP register on C stepping K8. 408 * 409 * A lot of BIOS that didn't get tested properly miss this. 410 * 411 * The OS sees this as a page fault with the upper 32bits of RIP cleared. 412 * Try to work around it here. 413 * 414 * Note we only handle faults in kernel here. 415 * Does nothing on 32-bit. 416 */ 417 static int is_errata93(struct pt_regs *regs, unsigned long address) 418 { 419 #if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD) 420 if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD 421 || boot_cpu_data.x86 != 0xf) 422 return 0; 423 424 if (user_mode(regs)) 425 return 0; 426 427 if (address != regs->ip) 428 return 0; 429 430 if ((address >> 32) != 0) 431 return 0; 432 433 address |= 0xffffffffUL << 32; 434 if ((address >= (u64)_stext && address <= (u64)_etext) || 435 (address >= MODULES_VADDR && address <= MODULES_END)) { 436 printk_once(errata93_warning); 437 regs->ip = address; 438 return 1; 439 } 440 #endif 441 return 0; 442 } 443 444 /* 445 * Work around K8 erratum #100 K8 in compat mode occasionally jumps 446 * to illegal addresses >4GB. 447 * 448 * We catch this in the page fault handler because these addresses 449 * are not reachable. Just detect this case and return. Any code 450 * segment in LDT is compatibility mode. 451 */ 452 static int is_errata100(struct pt_regs *regs, unsigned long address) 453 { 454 #ifdef CONFIG_X86_64 455 if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32)) 456 return 1; 457 #endif 458 return 0; 459 } 460 461 /* Pentium F0 0F C7 C8 bug workaround: */ 462 static int is_f00f_bug(struct pt_regs *regs, unsigned long error_code, 463 unsigned long address) 464 { 465 #ifdef CONFIG_X86_F00F_BUG 466 if (boot_cpu_has_bug(X86_BUG_F00F) && !(error_code & X86_PF_USER) && 467 idt_is_f00f_address(address)) { 468 handle_invalid_op(regs); 469 return 1; 470 } 471 #endif 472 return 0; 473 } 474 475 static void show_ldttss(const struct desc_ptr *gdt, const char *name, u16 index) 476 { 477 u32 offset = (index >> 3) * sizeof(struct desc_struct); 478 unsigned long addr; 479 struct ldttss_desc desc; 480 481 if (index == 0) { 482 pr_alert("%s: NULL\n", name); 483 return; 484 } 485 486 if (offset + sizeof(struct ldttss_desc) >= gdt->size) { 487 pr_alert("%s: 0x%hx -- out of bounds\n", name, index); 488 return; 489 } 490 491 if (copy_from_kernel_nofault(&desc, (void *)(gdt->address + offset), 492 sizeof(struct ldttss_desc))) { 493 pr_alert("%s: 0x%hx -- GDT entry is not readable\n", 494 name, index); 495 return; 496 } 497 498 addr = desc.base0 | (desc.base1 << 16) | ((unsigned long)desc.base2 << 24); 499 #ifdef CONFIG_X86_64 500 addr |= ((u64)desc.base3 << 32); 501 #endif 502 pr_alert("%s: 0x%hx -- base=0x%lx limit=0x%x\n", 503 name, index, addr, (desc.limit0 | (desc.limit1 << 16))); 504 } 505 506 static void 507 show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long address) 508 { 509 if (!oops_may_print()) 510 return; 511 512 if (error_code & X86_PF_INSTR) { 513 unsigned int level; 514 pgd_t *pgd; 515 pte_t *pte; 516 517 pgd = __va(read_cr3_pa()); 518 pgd += pgd_index(address); 519 520 pte = lookup_address_in_pgd(pgd, address, &level); 521 522 if (pte && pte_present(*pte) && !pte_exec(*pte)) 523 pr_crit("kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n", 524 from_kuid(&init_user_ns, current_uid())); 525 if (pte && pte_present(*pte) && pte_exec(*pte) && 526 (pgd_flags(*pgd) & _PAGE_USER) && 527 (__read_cr4() & X86_CR4_SMEP)) 528 pr_crit("unable to execute userspace code (SMEP?) (uid: %d)\n", 529 from_kuid(&init_user_ns, current_uid())); 530 } 531 532 if (address < PAGE_SIZE && !user_mode(regs)) 533 pr_alert("BUG: kernel NULL pointer dereference, address: %px\n", 534 (void *)address); 535 else 536 pr_alert("BUG: unable to handle page fault for address: %px\n", 537 (void *)address); 538 539 pr_alert("#PF: %s %s in %s mode\n", 540 (error_code & X86_PF_USER) ? "user" : "supervisor", 541 (error_code & X86_PF_INSTR) ? "instruction fetch" : 542 (error_code & X86_PF_WRITE) ? "write access" : 543 "read access", 544 user_mode(regs) ? "user" : "kernel"); 545 pr_alert("#PF: error_code(0x%04lx) - %s\n", error_code, 546 !(error_code & X86_PF_PROT) ? "not-present page" : 547 (error_code & X86_PF_RSVD) ? "reserved bit violation" : 548 (error_code & X86_PF_PK) ? "protection keys violation" : 549 "permissions violation"); 550 551 if (!(error_code & X86_PF_USER) && user_mode(regs)) { 552 struct desc_ptr idt, gdt; 553 u16 ldtr, tr; 554 555 /* 556 * This can happen for quite a few reasons. The more obvious 557 * ones are faults accessing the GDT, or LDT. Perhaps 558 * surprisingly, if the CPU tries to deliver a benign or 559 * contributory exception from user code and gets a page fault 560 * during delivery, the page fault can be delivered as though 561 * it originated directly from user code. This could happen 562 * due to wrong permissions on the IDT, GDT, LDT, TSS, or 563 * kernel or IST stack. 564 */ 565 store_idt(&idt); 566 567 /* Usable even on Xen PV -- it's just slow. */ 568 native_store_gdt(&gdt); 569 570 pr_alert("IDT: 0x%lx (limit=0x%hx) GDT: 0x%lx (limit=0x%hx)\n", 571 idt.address, idt.size, gdt.address, gdt.size); 572 573 store_ldt(ldtr); 574 show_ldttss(&gdt, "LDTR", ldtr); 575 576 store_tr(tr); 577 show_ldttss(&gdt, "TR", tr); 578 } 579 580 dump_pagetable(address); 581 } 582 583 static noinline void 584 pgtable_bad(struct pt_regs *regs, unsigned long error_code, 585 unsigned long address) 586 { 587 struct task_struct *tsk; 588 unsigned long flags; 589 int sig; 590 591 flags = oops_begin(); 592 tsk = current; 593 sig = SIGKILL; 594 595 printk(KERN_ALERT "%s: Corrupted page table at address %lx\n", 596 tsk->comm, address); 597 dump_pagetable(address); 598 599 if (__die("Bad pagetable", regs, error_code)) 600 sig = 0; 601 602 oops_end(flags, regs, sig); 603 } 604 605 static void sanitize_error_code(unsigned long address, 606 unsigned long *error_code) 607 { 608 /* 609 * To avoid leaking information about the kernel page 610 * table layout, pretend that user-mode accesses to 611 * kernel addresses are always protection faults. 612 * 613 * NB: This means that failed vsyscalls with vsyscall=none 614 * will have the PROT bit. This doesn't leak any 615 * information and does not appear to cause any problems. 616 */ 617 if (address >= TASK_SIZE_MAX) 618 *error_code |= X86_PF_PROT; 619 } 620 621 static void set_signal_archinfo(unsigned long address, 622 unsigned long error_code) 623 { 624 struct task_struct *tsk = current; 625 626 tsk->thread.trap_nr = X86_TRAP_PF; 627 tsk->thread.error_code = error_code | X86_PF_USER; 628 tsk->thread.cr2 = address; 629 } 630 631 static noinline void 632 page_fault_oops(struct pt_regs *regs, unsigned long error_code, 633 unsigned long address) 634 { 635 #ifdef CONFIG_VMAP_STACK 636 struct stack_info info; 637 #endif 638 unsigned long flags; 639 int sig; 640 641 if (user_mode(regs)) { 642 /* 643 * Implicit kernel access from user mode? Skip the stack 644 * overflow and EFI special cases. 645 */ 646 goto oops; 647 } 648 649 #ifdef CONFIG_VMAP_STACK 650 /* 651 * Stack overflow? During boot, we can fault near the initial 652 * stack in the direct map, but that's not an overflow -- check 653 * that we're in vmalloc space to avoid this. 654 */ 655 if (is_vmalloc_addr((void *)address) && 656 get_stack_guard_info((void *)address, &info)) { 657 /* 658 * We're likely to be running with very little stack space 659 * left. It's plausible that we'd hit this condition but 660 * double-fault even before we get this far, in which case 661 * we're fine: the double-fault handler will deal with it. 662 * 663 * We don't want to make it all the way into the oops code 664 * and then double-fault, though, because we're likely to 665 * break the console driver and lose most of the stack dump. 666 */ 667 call_on_stack(__this_cpu_ist_top_va(DF) - sizeof(void*), 668 handle_stack_overflow, 669 ASM_CALL_ARG3, 670 , [arg1] "r" (regs), [arg2] "r" (address), [arg3] "r" (&info)); 671 672 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 u32 pkey) 715 { 716 WARN_ON_ONCE(user_mode(regs)); 717 718 /* Are we prepared to handle this kernel fault? */ 719 if (fixup_exception(regs, X86_TRAP_PF, error_code, address)) { 720 /* 721 * Any interrupt that takes a fault gets the fixup. This makes 722 * the below recursive fault logic only apply to a faults from 723 * task context. 724 */ 725 if (in_interrupt()) 726 return; 727 728 /* 729 * Per the above we're !in_interrupt(), aka. task context. 730 * 731 * In this case we need to make sure we're not recursively 732 * faulting through the emulate_vsyscall() logic. 733 */ 734 if (current->thread.sig_on_uaccess_err && signal) { 735 sanitize_error_code(address, &error_code); 736 737 set_signal_archinfo(address, error_code); 738 739 if (si_code == SEGV_PKUERR) { 740 force_sig_pkuerr((void __user *)address, pkey); 741 } else { 742 /* XXX: hwpoison faults will set the wrong code. */ 743 force_sig_fault(signal, si_code, (void __user *)address); 744 } 745 } 746 747 /* 748 * Barring that, we can do the fixup and be happy. 749 */ 750 return; 751 } 752 753 /* 754 * AMD erratum #91 manifests as a spurious page fault on a PREFETCH 755 * instruction. 756 */ 757 if (is_prefetch(regs, error_code, address)) 758 return; 759 760 page_fault_oops(regs, error_code, address); 761 } 762 763 /* 764 * Print out info about fatal segfaults, if the show_unhandled_signals 765 * sysctl is set: 766 */ 767 static inline void 768 show_signal_msg(struct pt_regs *regs, unsigned long error_code, 769 unsigned long address, struct task_struct *tsk) 770 { 771 const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG; 772 773 if (!unhandled_signal(tsk, SIGSEGV)) 774 return; 775 776 if (!printk_ratelimit()) 777 return; 778 779 printk("%s%s[%d]: segfault at %lx ip %px sp %px error %lx", 780 loglvl, tsk->comm, task_pid_nr(tsk), address, 781 (void *)regs->ip, (void *)regs->sp, error_code); 782 783 print_vma_addr(KERN_CONT " in ", regs->ip); 784 785 printk(KERN_CONT "\n"); 786 787 show_opcodes(regs, loglvl); 788 } 789 790 /* 791 * The (legacy) vsyscall page is the long page in the kernel portion 792 * of the address space that has user-accessible permissions. 793 */ 794 static bool is_vsyscall_vaddr(unsigned long vaddr) 795 { 796 return unlikely((vaddr & PAGE_MASK) == VSYSCALL_ADDR); 797 } 798 799 static void 800 __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, 801 unsigned long address, u32 pkey, int si_code) 802 { 803 struct task_struct *tsk = current; 804 805 if (!user_mode(regs)) { 806 kernelmode_fixup_or_oops(regs, error_code, address, 807 SIGSEGV, si_code, pkey); 808 return; 809 } 810 811 if (!(error_code & X86_PF_USER)) { 812 /* Implicit user access to kernel memory -- just oops */ 813 page_fault_oops(regs, error_code, address); 814 return; 815 } 816 817 /* 818 * User mode accesses just cause a SIGSEGV. 819 * It's possible to have interrupts off here: 820 */ 821 local_irq_enable(); 822 823 /* 824 * Valid to do another page fault here because this one came 825 * from user space: 826 */ 827 if (is_prefetch(regs, error_code, address)) 828 return; 829 830 if (is_errata100(regs, address)) 831 return; 832 833 sanitize_error_code(address, &error_code); 834 835 if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address)) 836 return; 837 838 if (likely(show_unhandled_signals)) 839 show_signal_msg(regs, error_code, address, tsk); 840 841 set_signal_archinfo(address, error_code); 842 843 if (si_code == SEGV_PKUERR) 844 force_sig_pkuerr((void __user *)address, pkey); 845 else 846 force_sig_fault(SIGSEGV, si_code, (void __user *)address); 847 848 local_irq_disable(); 849 } 850 851 static noinline void 852 bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, 853 unsigned long address) 854 { 855 __bad_area_nosemaphore(regs, error_code, address, 0, SEGV_MAPERR); 856 } 857 858 static void 859 __bad_area(struct pt_regs *regs, unsigned long error_code, 860 unsigned long address, u32 pkey, int si_code) 861 { 862 struct mm_struct *mm = current->mm; 863 /* 864 * Something tried to access memory that isn't in our memory map.. 865 * Fix it, but check if it's kernel or user first.. 866 */ 867 mmap_read_unlock(mm); 868 869 __bad_area_nosemaphore(regs, error_code, address, pkey, si_code); 870 } 871 872 static noinline void 873 bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address) 874 { 875 __bad_area(regs, error_code, address, 0, SEGV_MAPERR); 876 } 877 878 static inline bool bad_area_access_from_pkeys(unsigned long error_code, 879 struct vm_area_struct *vma) 880 { 881 /* This code is always called on the current mm */ 882 bool foreign = false; 883 884 if (!cpu_feature_enabled(X86_FEATURE_OSPKE)) 885 return false; 886 if (error_code & X86_PF_PK) 887 return true; 888 /* this checks permission keys on the VMA: */ 889 if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE), 890 (error_code & X86_PF_INSTR), foreign)) 891 return true; 892 return false; 893 } 894 895 static noinline void 896 bad_area_access_error(struct pt_regs *regs, unsigned long error_code, 897 unsigned long address, struct vm_area_struct *vma) 898 { 899 /* 900 * This OSPKE check is not strictly necessary at runtime. 901 * But, doing it this way allows compiler optimizations 902 * if pkeys are compiled out. 903 */ 904 if (bad_area_access_from_pkeys(error_code, vma)) { 905 /* 906 * A protection key fault means that the PKRU value did not allow 907 * access to some PTE. Userspace can figure out what PKRU was 908 * from the XSAVE state. This function captures the pkey from 909 * the vma and passes it to userspace so userspace can discover 910 * which protection key was set on the PTE. 911 * 912 * If we get here, we know that the hardware signaled a X86_PF_PK 913 * fault and that there was a VMA once we got in the fault 914 * handler. It does *not* guarantee that the VMA we find here 915 * was the one that we faulted on. 916 * 917 * 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4); 918 * 2. T1 : set PKRU to deny access to pkey=4, touches page 919 * 3. T1 : faults... 920 * 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5); 921 * 5. T1 : enters fault handler, takes mmap_lock, etc... 922 * 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really 923 * faulted on a pte with its pkey=4. 924 */ 925 u32 pkey = vma_pkey(vma); 926 927 __bad_area(regs, error_code, address, pkey, SEGV_PKUERR); 928 } else { 929 __bad_area(regs, error_code, address, 0, SEGV_ACCERR); 930 } 931 } 932 933 static void 934 do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address, 935 vm_fault_t fault) 936 { 937 /* Kernel mode? Handle exceptions or die: */ 938 if (!user_mode(regs)) { 939 kernelmode_fixup_or_oops(regs, error_code, address, 940 SIGBUS, BUS_ADRERR, ARCH_DEFAULT_PKEY); 941 return; 942 } 943 944 /* User-space => ok to do another page fault: */ 945 if (is_prefetch(regs, error_code, address)) 946 return; 947 948 sanitize_error_code(address, &error_code); 949 950 if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address)) 951 return; 952 953 set_signal_archinfo(address, error_code); 954 955 #ifdef CONFIG_MEMORY_FAILURE 956 if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) { 957 struct task_struct *tsk = current; 958 unsigned lsb = 0; 959 960 pr_err( 961 "MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n", 962 tsk->comm, tsk->pid, address); 963 if (fault & VM_FAULT_HWPOISON_LARGE) 964 lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault)); 965 if (fault & VM_FAULT_HWPOISON) 966 lsb = PAGE_SHIFT; 967 force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb); 968 return; 969 } 970 #endif 971 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address); 972 } 973 974 static int spurious_kernel_fault_check(unsigned long error_code, pte_t *pte) 975 { 976 if ((error_code & X86_PF_WRITE) && !pte_write(*pte)) 977 return 0; 978 979 if ((error_code & X86_PF_INSTR) && !pte_exec(*pte)) 980 return 0; 981 982 return 1; 983 } 984 985 /* 986 * Handle a spurious fault caused by a stale TLB entry. 987 * 988 * This allows us to lazily refresh the TLB when increasing the 989 * permissions of a kernel page (RO -> RW or NX -> X). Doing it 990 * eagerly is very expensive since that implies doing a full 991 * cross-processor TLB flush, even if no stale TLB entries exist 992 * on other processors. 993 * 994 * Spurious faults may only occur if the TLB contains an entry with 995 * fewer permission than the page table entry. Non-present (P = 0) 996 * and reserved bit (R = 1) faults are never spurious. 997 * 998 * There are no security implications to leaving a stale TLB when 999 * increasing the permissions on a page. 1000 * 1001 * Returns non-zero if a spurious fault was handled, zero otherwise. 1002 * 1003 * See Intel Developer's Manual Vol 3 Section 4.10.4.3, bullet 3 1004 * (Optional Invalidation). 1005 */ 1006 static noinline int 1007 spurious_kernel_fault(unsigned long error_code, unsigned long address) 1008 { 1009 pgd_t *pgd; 1010 p4d_t *p4d; 1011 pud_t *pud; 1012 pmd_t *pmd; 1013 pte_t *pte; 1014 int ret; 1015 1016 /* 1017 * Only writes to RO or instruction fetches from NX may cause 1018 * spurious faults. 1019 * 1020 * These could be from user or supervisor accesses but the TLB 1021 * is only lazily flushed after a kernel mapping protection 1022 * change, so user accesses are not expected to cause spurious 1023 * faults. 1024 */ 1025 if (error_code != (X86_PF_WRITE | X86_PF_PROT) && 1026 error_code != (X86_PF_INSTR | X86_PF_PROT)) 1027 return 0; 1028 1029 pgd = init_mm.pgd + pgd_index(address); 1030 if (!pgd_present(*pgd)) 1031 return 0; 1032 1033 p4d = p4d_offset(pgd, address); 1034 if (!p4d_present(*p4d)) 1035 return 0; 1036 1037 if (p4d_large(*p4d)) 1038 return spurious_kernel_fault_check(error_code, (pte_t *) p4d); 1039 1040 pud = pud_offset(p4d, address); 1041 if (!pud_present(*pud)) 1042 return 0; 1043 1044 if (pud_large(*pud)) 1045 return spurious_kernel_fault_check(error_code, (pte_t *) pud); 1046 1047 pmd = pmd_offset(pud, address); 1048 if (!pmd_present(*pmd)) 1049 return 0; 1050 1051 if (pmd_large(*pmd)) 1052 return spurious_kernel_fault_check(error_code, (pte_t *) pmd); 1053 1054 pte = pte_offset_kernel(pmd, address); 1055 if (!pte_present(*pte)) 1056 return 0; 1057 1058 ret = spurious_kernel_fault_check(error_code, pte); 1059 if (!ret) 1060 return 0; 1061 1062 /* 1063 * Make sure we have permissions in PMD. 1064 * If not, then there's a bug in the page tables: 1065 */ 1066 ret = spurious_kernel_fault_check(error_code, (pte_t *) pmd); 1067 WARN_ONCE(!ret, "PMD has incorrect permission bits\n"); 1068 1069 return ret; 1070 } 1071 NOKPROBE_SYMBOL(spurious_kernel_fault); 1072 1073 int show_unhandled_signals = 1; 1074 1075 static inline int 1076 access_error(unsigned long error_code, struct vm_area_struct *vma) 1077 { 1078 /* This is only called for the current mm, so: */ 1079 bool foreign = false; 1080 1081 /* 1082 * Read or write was blocked by protection keys. This is 1083 * always an unconditional error and can never result in 1084 * a follow-up action to resolve the fault, like a COW. 1085 */ 1086 if (error_code & X86_PF_PK) 1087 return 1; 1088 1089 /* 1090 * SGX hardware blocked the access. This usually happens 1091 * when the enclave memory contents have been destroyed, like 1092 * after a suspend/resume cycle. In any case, the kernel can't 1093 * fix the cause of the fault. Handle the fault as an access 1094 * error even in cases where no actual access violation 1095 * occurred. This allows userspace to rebuild the enclave in 1096 * response to the signal. 1097 */ 1098 if (unlikely(error_code & X86_PF_SGX)) 1099 return 1; 1100 1101 /* 1102 * Make sure to check the VMA so that we do not perform 1103 * faults just to hit a X86_PF_PK as soon as we fill in a 1104 * page. 1105 */ 1106 if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE), 1107 (error_code & X86_PF_INSTR), foreign)) 1108 return 1; 1109 1110 if (error_code & X86_PF_WRITE) { 1111 /* write, present and write, not present: */ 1112 if (unlikely(!(vma->vm_flags & VM_WRITE))) 1113 return 1; 1114 return 0; 1115 } 1116 1117 /* read, present: */ 1118 if (unlikely(error_code & X86_PF_PROT)) 1119 return 1; 1120 1121 /* read, not present: */ 1122 if (unlikely(!vma_is_accessible(vma))) 1123 return 1; 1124 1125 return 0; 1126 } 1127 1128 bool fault_in_kernel_space(unsigned long address) 1129 { 1130 /* 1131 * On 64-bit systems, the vsyscall page is at an address above 1132 * TASK_SIZE_MAX, but is not considered part of the kernel 1133 * address space. 1134 */ 1135 if (IS_ENABLED(CONFIG_X86_64) && is_vsyscall_vaddr(address)) 1136 return false; 1137 1138 return address >= TASK_SIZE_MAX; 1139 } 1140 1141 /* 1142 * Called for all faults where 'address' is part of the kernel address 1143 * space. Might get called for faults that originate from *code* that 1144 * ran in userspace or the kernel. 1145 */ 1146 static void 1147 do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code, 1148 unsigned long address) 1149 { 1150 /* 1151 * Protection keys exceptions only happen on user pages. We 1152 * have no user pages in the kernel portion of the address 1153 * space, so do not expect them here. 1154 */ 1155 WARN_ON_ONCE(hw_error_code & X86_PF_PK); 1156 1157 #ifdef CONFIG_X86_32 1158 /* 1159 * We can fault-in kernel-space virtual memory on-demand. The 1160 * 'reference' page table is init_mm.pgd. 1161 * 1162 * NOTE! We MUST NOT take any locks for this case. We may 1163 * be in an interrupt or a critical region, and should 1164 * only copy the information from the master page table, 1165 * nothing more. 1166 * 1167 * Before doing this on-demand faulting, ensure that the 1168 * fault is not any of the following: 1169 * 1. A fault on a PTE with a reserved bit set. 1170 * 2. A fault caused by a user-mode access. (Do not demand- 1171 * fault kernel memory due to user-mode accesses). 1172 * 3. A fault caused by a page-level protection violation. 1173 * (A demand fault would be on a non-present page which 1174 * would have X86_PF_PROT==0). 1175 * 1176 * This is only needed to close a race condition on x86-32 in 1177 * the vmalloc mapping/unmapping code. See the comment above 1178 * vmalloc_fault() for details. On x86-64 the race does not 1179 * exist as the vmalloc mappings don't need to be synchronized 1180 * there. 1181 */ 1182 if (!(hw_error_code & (X86_PF_RSVD | X86_PF_USER | X86_PF_PROT))) { 1183 if (vmalloc_fault(address) >= 0) 1184 return; 1185 } 1186 #endif 1187 1188 if (is_f00f_bug(regs, hw_error_code, address)) 1189 return; 1190 1191 /* Was the fault spurious, caused by lazy TLB invalidation? */ 1192 if (spurious_kernel_fault(hw_error_code, address)) 1193 return; 1194 1195 /* kprobes don't want to hook the spurious faults: */ 1196 if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF))) 1197 return; 1198 1199 /* 1200 * Note, despite being a "bad area", there are quite a few 1201 * acceptable reasons to get here, such as erratum fixups 1202 * and handling kernel code that can fault, like get_user(). 1203 * 1204 * Don't take the mm semaphore here. If we fixup a prefetch 1205 * fault we could otherwise deadlock: 1206 */ 1207 bad_area_nosemaphore(regs, hw_error_code, address); 1208 } 1209 NOKPROBE_SYMBOL(do_kern_addr_fault); 1210 1211 /* 1212 * Handle faults in the user portion of the address space. Nothing in here 1213 * should check X86_PF_USER without a specific justification: for almost 1214 * all purposes, we should treat a normal kernel access to user memory 1215 * (e.g. get_user(), put_user(), etc.) the same as the WRUSS instruction. 1216 * The one exception is AC flag handling, which is, per the x86 1217 * architecture, special for WRUSS. 1218 */ 1219 static inline 1220 void do_user_addr_fault(struct pt_regs *regs, 1221 unsigned long error_code, 1222 unsigned long address) 1223 { 1224 struct vm_area_struct *vma; 1225 struct task_struct *tsk; 1226 struct mm_struct *mm; 1227 vm_fault_t fault; 1228 unsigned int flags = FAULT_FLAG_DEFAULT; 1229 1230 tsk = current; 1231 mm = tsk->mm; 1232 1233 if (unlikely((error_code & (X86_PF_USER | X86_PF_INSTR)) == X86_PF_INSTR)) { 1234 /* 1235 * Whoops, this is kernel mode code trying to execute from 1236 * user memory. Unless this is AMD erratum #93, which 1237 * corrupts RIP such that it looks like a user address, 1238 * this is unrecoverable. Don't even try to look up the 1239 * VMA or look for extable entries. 1240 */ 1241 if (is_errata93(regs, address)) 1242 return; 1243 1244 page_fault_oops(regs, error_code, address); 1245 return; 1246 } 1247 1248 /* kprobes don't want to hook the spurious faults: */ 1249 if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF))) 1250 return; 1251 1252 /* 1253 * Reserved bits are never expected to be set on 1254 * entries in the user portion of the page tables. 1255 */ 1256 if (unlikely(error_code & X86_PF_RSVD)) 1257 pgtable_bad(regs, error_code, address); 1258 1259 /* 1260 * If SMAP is on, check for invalid kernel (supervisor) access to user 1261 * pages in the user address space. The odd case here is WRUSS, 1262 * which, according to the preliminary documentation, does not respect 1263 * SMAP and will have the USER bit set so, in all cases, SMAP 1264 * enforcement appears to be consistent with the USER bit. 1265 */ 1266 if (unlikely(cpu_feature_enabled(X86_FEATURE_SMAP) && 1267 !(error_code & X86_PF_USER) && 1268 !(regs->flags & X86_EFLAGS_AC))) { 1269 /* 1270 * No extable entry here. This was a kernel access to an 1271 * invalid pointer. get_kernel_nofault() will not get here. 1272 */ 1273 page_fault_oops(regs, error_code, address); 1274 return; 1275 } 1276 1277 /* 1278 * If we're in an interrupt, have no user context or are running 1279 * in a region with pagefaults disabled then we must not take the fault 1280 */ 1281 if (unlikely(faulthandler_disabled() || !mm)) { 1282 bad_area_nosemaphore(regs, error_code, address); 1283 return; 1284 } 1285 1286 /* 1287 * It's safe to allow irq's after cr2 has been saved and the 1288 * vmalloc fault has been handled. 1289 * 1290 * User-mode registers count as a user access even for any 1291 * potential system fault or CPU buglet: 1292 */ 1293 if (user_mode(regs)) { 1294 local_irq_enable(); 1295 flags |= FAULT_FLAG_USER; 1296 } else { 1297 if (regs->flags & X86_EFLAGS_IF) 1298 local_irq_enable(); 1299 } 1300 1301 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address); 1302 1303 if (error_code & X86_PF_WRITE) 1304 flags |= FAULT_FLAG_WRITE; 1305 if (error_code & X86_PF_INSTR) 1306 flags |= FAULT_FLAG_INSTRUCTION; 1307 1308 #ifdef CONFIG_X86_64 1309 /* 1310 * Faults in the vsyscall page might need emulation. The 1311 * vsyscall page is at a high address (>PAGE_OFFSET), but is 1312 * considered to be part of the user address space. 1313 * 1314 * The vsyscall page does not have a "real" VMA, so do this 1315 * emulation before we go searching for VMAs. 1316 * 1317 * PKRU never rejects instruction fetches, so we don't need 1318 * to consider the PF_PK bit. 1319 */ 1320 if (is_vsyscall_vaddr(address)) { 1321 if (emulate_vsyscall(error_code, regs, address)) 1322 return; 1323 } 1324 #endif 1325 1326 /* 1327 * Kernel-mode access to the user address space should only occur 1328 * on well-defined single instructions listed in the exception 1329 * tables. But, an erroneous kernel fault occurring outside one of 1330 * those areas which also holds mmap_lock might deadlock attempting 1331 * to validate the fault against the address space. 1332 * 1333 * Only do the expensive exception table search when we might be at 1334 * risk of a deadlock. This happens if we 1335 * 1. Failed to acquire mmap_lock, and 1336 * 2. The access did not originate in userspace. 1337 */ 1338 if (unlikely(!mmap_read_trylock(mm))) { 1339 if (!user_mode(regs) && !search_exception_tables(regs->ip)) { 1340 /* 1341 * Fault from code in kernel from 1342 * which we do not expect faults. 1343 */ 1344 bad_area_nosemaphore(regs, error_code, address); 1345 return; 1346 } 1347 retry: 1348 mmap_read_lock(mm); 1349 } else { 1350 /* 1351 * The above down_read_trylock() might have succeeded in 1352 * which case we'll have missed the might_sleep() from 1353 * down_read(): 1354 */ 1355 might_sleep(); 1356 } 1357 1358 vma = find_vma(mm, address); 1359 if (unlikely(!vma)) { 1360 bad_area(regs, error_code, address); 1361 return; 1362 } 1363 if (likely(vma->vm_start <= address)) 1364 goto good_area; 1365 if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) { 1366 bad_area(regs, error_code, address); 1367 return; 1368 } 1369 if (unlikely(expand_stack(vma, address))) { 1370 bad_area(regs, error_code, address); 1371 return; 1372 } 1373 1374 /* 1375 * Ok, we have a good vm_area for this memory access, so 1376 * we can handle it.. 1377 */ 1378 good_area: 1379 if (unlikely(access_error(error_code, vma))) { 1380 bad_area_access_error(regs, error_code, address, vma); 1381 return; 1382 } 1383 1384 /* 1385 * If for any reason at all we couldn't handle the fault, 1386 * make sure we exit gracefully rather than endlessly redo 1387 * the fault. Since we never set FAULT_FLAG_RETRY_NOWAIT, if 1388 * we get VM_FAULT_RETRY back, the mmap_lock has been unlocked. 1389 * 1390 * Note that handle_userfault() may also release and reacquire mmap_lock 1391 * (and not return with VM_FAULT_RETRY), when returning to userland to 1392 * repeat the page fault later with a VM_FAULT_NOPAGE retval 1393 * (potentially after handling any pending signal during the return to 1394 * userland). The return to userland is identified whenever 1395 * FAULT_FLAG_USER|FAULT_FLAG_KILLABLE are both set in flags. 1396 */ 1397 fault = handle_mm_fault(vma, address, flags, regs); 1398 1399 if (fault_signal_pending(fault, regs)) { 1400 /* 1401 * Quick path to respond to signals. The core mm code 1402 * has unlocked the mm for us if we get here. 1403 */ 1404 if (!user_mode(regs)) 1405 kernelmode_fixup_or_oops(regs, error_code, address, 1406 SIGBUS, BUS_ADRERR, 1407 ARCH_DEFAULT_PKEY); 1408 return; 1409 } 1410 1411 /* 1412 * If we need to retry the mmap_lock has already been released, 1413 * and if there is a fatal signal pending there is no guarantee 1414 * that we made any progress. Handle this case first. 1415 */ 1416 if (unlikely(fault & VM_FAULT_RETRY)) { 1417 flags |= FAULT_FLAG_TRIED; 1418 goto retry; 1419 } 1420 1421 mmap_read_unlock(mm); 1422 if (likely(!(fault & VM_FAULT_ERROR))) 1423 return; 1424 1425 if (fatal_signal_pending(current) && !user_mode(regs)) { 1426 kernelmode_fixup_or_oops(regs, error_code, address, 1427 0, 0, ARCH_DEFAULT_PKEY); 1428 return; 1429 } 1430 1431 if (fault & VM_FAULT_OOM) { 1432 /* Kernel mode? Handle exceptions or die: */ 1433 if (!user_mode(regs)) { 1434 kernelmode_fixup_or_oops(regs, error_code, address, 1435 SIGSEGV, SEGV_MAPERR, 1436 ARCH_DEFAULT_PKEY); 1437 return; 1438 } 1439 1440 /* 1441 * We ran out of memory, call the OOM killer, and return the 1442 * userspace (which will retry the fault, or kill us if we got 1443 * oom-killed): 1444 */ 1445 pagefault_out_of_memory(); 1446 } else { 1447 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON| 1448 VM_FAULT_HWPOISON_LARGE)) 1449 do_sigbus(regs, error_code, address, fault); 1450 else if (fault & VM_FAULT_SIGSEGV) 1451 bad_area_nosemaphore(regs, error_code, address); 1452 else 1453 BUG(); 1454 } 1455 } 1456 NOKPROBE_SYMBOL(do_user_addr_fault); 1457 1458 static __always_inline void 1459 trace_page_fault_entries(struct pt_regs *regs, unsigned long error_code, 1460 unsigned long address) 1461 { 1462 if (!trace_pagefault_enabled()) 1463 return; 1464 1465 if (user_mode(regs)) 1466 trace_page_fault_user(address, regs, error_code); 1467 else 1468 trace_page_fault_kernel(address, regs, error_code); 1469 } 1470 1471 static __always_inline void 1472 handle_page_fault(struct pt_regs *regs, unsigned long error_code, 1473 unsigned long address) 1474 { 1475 trace_page_fault_entries(regs, error_code, address); 1476 1477 if (unlikely(kmmio_fault(regs, address))) 1478 return; 1479 1480 /* Was the fault on kernel-controlled part of the address space? */ 1481 if (unlikely(fault_in_kernel_space(address))) { 1482 do_kern_addr_fault(regs, error_code, address); 1483 } else { 1484 do_user_addr_fault(regs, error_code, address); 1485 /* 1486 * User address page fault handling might have reenabled 1487 * interrupts. Fixing up all potential exit points of 1488 * do_user_addr_fault() and its leaf functions is just not 1489 * doable w/o creating an unholy mess or turning the code 1490 * upside down. 1491 */ 1492 local_irq_disable(); 1493 } 1494 } 1495 1496 DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault) 1497 { 1498 unsigned long address = read_cr2(); 1499 irqentry_state_t state; 1500 1501 prefetchw(¤t->mm->mmap_lock); 1502 1503 /* 1504 * KVM uses #PF vector to deliver 'page not present' events to guests 1505 * (asynchronous page fault mechanism). The event happens when a 1506 * userspace task is trying to access some valid (from guest's point of 1507 * view) memory which is not currently mapped by the host (e.g. the 1508 * memory is swapped out). Note, the corresponding "page ready" event 1509 * which is injected when the memory becomes available, is delivered via 1510 * an interrupt mechanism and not a #PF exception 1511 * (see arch/x86/kernel/kvm.c: sysvec_kvm_asyncpf_interrupt()). 1512 * 1513 * We are relying on the interrupted context being sane (valid RSP, 1514 * relevant locks not held, etc.), which is fine as long as the 1515 * interrupted context had IF=1. We are also relying on the KVM 1516 * async pf type field and CR2 being read consistently instead of 1517 * getting values from real and async page faults mixed up. 1518 * 1519 * Fingers crossed. 1520 * 1521 * The async #PF handling code takes care of idtentry handling 1522 * itself. 1523 */ 1524 if (kvm_handle_async_pf(regs, (u32)address)) 1525 return; 1526 1527 /* 1528 * Entry handling for valid #PF from kernel mode is slightly 1529 * different: RCU is already watching and rcu_irq_enter() must not 1530 * be invoked because a kernel fault on a user space address might 1531 * sleep. 1532 * 1533 * In case the fault hit a RCU idle region the conditional entry 1534 * code reenabled RCU to avoid subsequent wreckage which helps 1535 * debuggability. 1536 */ 1537 state = irqentry_enter(regs); 1538 1539 instrumentation_begin(); 1540 handle_page_fault(regs, error_code, address); 1541 instrumentation_end(); 1542 1543 irqentry_exit(regs, state); 1544 } 1545