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 #include <linux/mm.h> /* find_and_lock_vma() */ 23 24 #include <asm/cpufeature.h> /* boot_cpu_has, ... */ 25 #include <asm/traps.h> /* dotraplinkage, ... */ 26 #include <asm/fixmap.h> /* VSYSCALL_ADDR */ 27 #include <asm/vsyscall.h> /* emulate_vsyscall */ 28 #include <asm/vm86.h> /* struct vm86 */ 29 #include <asm/mmu_context.h> /* vma_pkey() */ 30 #include <asm/efi.h> /* efi_crash_gracefully_on_page_fault()*/ 31 #include <asm/desc.h> /* store_idt(), ... */ 32 #include <asm/cpu_entry_area.h> /* exception stack */ 33 #include <asm/pgtable_areas.h> /* VMALLOC_START, ... */ 34 #include <asm/kvm_para.h> /* kvm_handle_async_pf */ 35 #include <asm/vdso.h> /* fixup_vdso_exception() */ 36 #include <asm/irq_stack.h> 37 38 #define CREATE_TRACE_POINTS 39 #include <asm/trace/exceptions.h> 40 41 /* 42 * Returns 0 if mmiotrace is disabled, or if the fault is not 43 * handled by mmiotrace: 44 */ 45 static nokprobe_inline int 46 kmmio_fault(struct pt_regs *regs, unsigned long addr) 47 { 48 if (unlikely(is_kmmio_active())) 49 if (kmmio_handler(regs, addr) == 1) 50 return -1; 51 return 0; 52 } 53 54 /* 55 * Prefetch quirks: 56 * 57 * 32-bit mode: 58 * 59 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch. 60 * Check that here and ignore it. This is AMD erratum #91. 61 * 62 * 64-bit mode: 63 * 64 * Sometimes the CPU reports invalid exceptions on prefetch. 65 * Check that here and ignore it. 66 * 67 * Opcode checker based on code by Richard Brunner. 68 */ 69 static inline int 70 check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr, 71 unsigned char opcode, int *prefetch) 72 { 73 unsigned char instr_hi = opcode & 0xf0; 74 unsigned char instr_lo = opcode & 0x0f; 75 76 switch (instr_hi) { 77 case 0x20: 78 case 0x30: 79 /* 80 * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes. 81 * In X86_64 long mode, the CPU will signal invalid 82 * opcode if some of these prefixes are present so 83 * X86_64 will never get here anyway 84 */ 85 return ((instr_lo & 7) == 0x6); 86 #ifdef CONFIG_X86_64 87 case 0x40: 88 /* 89 * In 64-bit mode 0x40..0x4F are valid REX prefixes 90 */ 91 return (!user_mode(regs) || user_64bit_mode(regs)); 92 #endif 93 case 0x60: 94 /* 0x64 thru 0x67 are valid prefixes in all modes. */ 95 return (instr_lo & 0xC) == 0x4; 96 case 0xF0: 97 /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */ 98 return !instr_lo || (instr_lo>>1) == 1; 99 case 0x00: 100 /* Prefetch instruction is 0x0F0D or 0x0F18 */ 101 if (get_kernel_nofault(opcode, instr)) 102 return 0; 103 104 *prefetch = (instr_lo == 0xF) && 105 (opcode == 0x0D || opcode == 0x18); 106 return 0; 107 default: 108 return 0; 109 } 110 } 111 112 static bool is_amd_k8_pre_npt(void) 113 { 114 struct cpuinfo_x86 *c = &boot_cpu_data; 115 116 return unlikely(IS_ENABLED(CONFIG_CPU_SUP_AMD) && 117 c->x86_vendor == X86_VENDOR_AMD && 118 c->x86 == 0xf && c->x86_model < 0x40); 119 } 120 121 static int 122 is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr) 123 { 124 unsigned char *max_instr; 125 unsigned char *instr; 126 int prefetch = 0; 127 128 /* Erratum #91 affects AMD K8, pre-NPT CPUs */ 129 if (!is_amd_k8_pre_npt()) 130 return 0; 131 132 /* 133 * If it was a exec (instruction fetch) fault on NX page, then 134 * do not ignore the fault: 135 */ 136 if (error_code & X86_PF_INSTR) 137 return 0; 138 139 instr = (void *)convert_ip_to_linear(current, regs); 140 max_instr = instr + 15; 141 142 /* 143 * This code has historically always bailed out if IP points to a 144 * not-present page (e.g. due to a race). No one has ever 145 * complained about this. 146 */ 147 pagefault_disable(); 148 149 while (instr < max_instr) { 150 unsigned char opcode; 151 152 if (user_mode(regs)) { 153 if (get_user(opcode, (unsigned char __user *) instr)) 154 break; 155 } else { 156 if (get_kernel_nofault(opcode, instr)) 157 break; 158 } 159 160 instr++; 161 162 if (!check_prefetch_opcode(regs, instr, opcode, &prefetch)) 163 break; 164 } 165 166 pagefault_enable(); 167 return prefetch; 168 } 169 170 DEFINE_SPINLOCK(pgd_lock); 171 LIST_HEAD(pgd_list); 172 173 #ifdef CONFIG_X86_32 174 static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address) 175 { 176 unsigned index = pgd_index(address); 177 pgd_t *pgd_k; 178 p4d_t *p4d, *p4d_k; 179 pud_t *pud, *pud_k; 180 pmd_t *pmd, *pmd_k; 181 182 pgd += index; 183 pgd_k = init_mm.pgd + index; 184 185 if (!pgd_present(*pgd_k)) 186 return NULL; 187 188 /* 189 * set_pgd(pgd, *pgd_k); here would be useless on PAE 190 * and redundant with the set_pmd() on non-PAE. As would 191 * set_p4d/set_pud. 192 */ 193 p4d = p4d_offset(pgd, address); 194 p4d_k = p4d_offset(pgd_k, address); 195 if (!p4d_present(*p4d_k)) 196 return NULL; 197 198 pud = pud_offset(p4d, address); 199 pud_k = pud_offset(p4d_k, address); 200 if (!pud_present(*pud_k)) 201 return NULL; 202 203 pmd = pmd_offset(pud, address); 204 pmd_k = pmd_offset(pud_k, address); 205 206 if (pmd_present(*pmd) != pmd_present(*pmd_k)) 207 set_pmd(pmd, *pmd_k); 208 209 if (!pmd_present(*pmd_k)) 210 return NULL; 211 else 212 BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k)); 213 214 return pmd_k; 215 } 216 217 /* 218 * Handle a fault on the vmalloc or module mapping area 219 * 220 * This is needed because there is a race condition between the time 221 * when the vmalloc mapping code updates the PMD to the point in time 222 * where it synchronizes this update with the other page-tables in the 223 * system. 224 * 225 * In this race window another thread/CPU can map an area on the same 226 * PMD, finds it already present and does not synchronize it with the 227 * rest of the system yet. As a result v[mz]alloc might return areas 228 * which are not mapped in every page-table in the system, causing an 229 * unhandled page-fault when they are accessed. 230 */ 231 static noinline int vmalloc_fault(unsigned long address) 232 { 233 unsigned long pgd_paddr; 234 pmd_t *pmd_k; 235 pte_t *pte_k; 236 237 /* Make sure we are in vmalloc area: */ 238 if (!(address >= VMALLOC_START && address < VMALLOC_END)) 239 return -1; 240 241 /* 242 * Synchronize this task's top level page-table 243 * with the 'reference' page table. 244 * 245 * Do _not_ use "current" here. We might be inside 246 * an interrupt in the middle of a task switch.. 247 */ 248 pgd_paddr = read_cr3_pa(); 249 pmd_k = vmalloc_sync_one(__va(pgd_paddr), address); 250 if (!pmd_k) 251 return -1; 252 253 if (pmd_large(*pmd_k)) 254 return 0; 255 256 pte_k = pte_offset_kernel(pmd_k, address); 257 if (!pte_present(*pte_k)) 258 return -1; 259 260 return 0; 261 } 262 NOKPROBE_SYMBOL(vmalloc_fault); 263 264 void arch_sync_kernel_mappings(unsigned long start, unsigned long end) 265 { 266 unsigned long addr; 267 268 for (addr = start & PMD_MASK; 269 addr >= TASK_SIZE_MAX && addr < VMALLOC_END; 270 addr += PMD_SIZE) { 271 struct page *page; 272 273 spin_lock(&pgd_lock); 274 list_for_each_entry(page, &pgd_list, lru) { 275 spinlock_t *pgt_lock; 276 277 /* the pgt_lock only for Xen */ 278 pgt_lock = &pgd_page_get_mm(page)->page_table_lock; 279 280 spin_lock(pgt_lock); 281 vmalloc_sync_one(page_address(page), addr); 282 spin_unlock(pgt_lock); 283 } 284 spin_unlock(&pgd_lock); 285 } 286 } 287 288 static bool low_pfn(unsigned long pfn) 289 { 290 return pfn < max_low_pfn; 291 } 292 293 static void dump_pagetable(unsigned long address) 294 { 295 pgd_t *base = __va(read_cr3_pa()); 296 pgd_t *pgd = &base[pgd_index(address)]; 297 p4d_t *p4d; 298 pud_t *pud; 299 pmd_t *pmd; 300 pte_t *pte; 301 302 #ifdef CONFIG_X86_PAE 303 pr_info("*pdpt = %016Lx ", pgd_val(*pgd)); 304 if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd)) 305 goto out; 306 #define pr_pde pr_cont 307 #else 308 #define pr_pde pr_info 309 #endif 310 p4d = p4d_offset(pgd, address); 311 pud = pud_offset(p4d, address); 312 pmd = pmd_offset(pud, address); 313 pr_pde("*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd)); 314 #undef pr_pde 315 316 /* 317 * We must not directly access the pte in the highpte 318 * case if the page table is located in highmem. 319 * And let's rather not kmap-atomic the pte, just in case 320 * it's allocated already: 321 */ 322 if (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_large(*pmd)) 323 goto out; 324 325 pte = pte_offset_kernel(pmd, address); 326 pr_cont("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte)); 327 out: 328 pr_cont("\n"); 329 } 330 331 #else /* CONFIG_X86_64: */ 332 333 #ifdef CONFIG_CPU_SUP_AMD 334 static const char errata93_warning[] = 335 KERN_ERR 336 "******* Your BIOS seems to not contain a fix for K8 errata #93\n" 337 "******* Working around it, but it may cause SEGVs or burn power.\n" 338 "******* Please consider a BIOS update.\n" 339 "******* Disabling USB legacy in the BIOS may also help.\n"; 340 #endif 341 342 static int bad_address(void *p) 343 { 344 unsigned long dummy; 345 346 return get_kernel_nofault(dummy, (unsigned long *)p); 347 } 348 349 static void dump_pagetable(unsigned long address) 350 { 351 pgd_t *base = __va(read_cr3_pa()); 352 pgd_t *pgd = base + pgd_index(address); 353 p4d_t *p4d; 354 pud_t *pud; 355 pmd_t *pmd; 356 pte_t *pte; 357 358 if (bad_address(pgd)) 359 goto bad; 360 361 pr_info("PGD %lx ", pgd_val(*pgd)); 362 363 if (!pgd_present(*pgd)) 364 goto out; 365 366 p4d = p4d_offset(pgd, address); 367 if (bad_address(p4d)) 368 goto bad; 369 370 pr_cont("P4D %lx ", p4d_val(*p4d)); 371 if (!p4d_present(*p4d) || p4d_large(*p4d)) 372 goto out; 373 374 pud = pud_offset(p4d, address); 375 if (bad_address(pud)) 376 goto bad; 377 378 pr_cont("PUD %lx ", pud_val(*pud)); 379 if (!pud_present(*pud) || pud_large(*pud)) 380 goto out; 381 382 pmd = pmd_offset(pud, address); 383 if (bad_address(pmd)) 384 goto bad; 385 386 pr_cont("PMD %lx ", pmd_val(*pmd)); 387 if (!pmd_present(*pmd) || pmd_large(*pmd)) 388 goto out; 389 390 pte = pte_offset_kernel(pmd, address); 391 if (bad_address(pte)) 392 goto bad; 393 394 pr_cont("PTE %lx", pte_val(*pte)); 395 out: 396 pr_cont("\n"); 397 return; 398 bad: 399 pr_info("BAD\n"); 400 } 401 402 #endif /* CONFIG_X86_64 */ 403 404 /* 405 * Workaround for K8 erratum #93 & buggy BIOS. 406 * 407 * BIOS SMM functions are required to use a specific workaround 408 * to avoid corruption of the 64bit RIP register on C stepping K8. 409 * 410 * A lot of BIOS that didn't get tested properly miss this. 411 * 412 * The OS sees this as a page fault with the upper 32bits of RIP cleared. 413 * Try to work around it here. 414 * 415 * Note we only handle faults in kernel here. 416 * Does nothing on 32-bit. 417 */ 418 static int is_errata93(struct pt_regs *regs, unsigned long address) 419 { 420 #if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD) 421 if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD 422 || boot_cpu_data.x86 != 0xf) 423 return 0; 424 425 if (user_mode(regs)) 426 return 0; 427 428 if (address != regs->ip) 429 return 0; 430 431 if ((address >> 32) != 0) 432 return 0; 433 434 address |= 0xffffffffUL << 32; 435 if ((address >= (u64)_stext && address <= (u64)_etext) || 436 (address >= MODULES_VADDR && address <= MODULES_END)) { 437 printk_once(errata93_warning); 438 regs->ip = address; 439 return 1; 440 } 441 #endif 442 return 0; 443 } 444 445 /* 446 * Work around K8 erratum #100 K8 in compat mode occasionally jumps 447 * to illegal addresses >4GB. 448 * 449 * We catch this in the page fault handler because these addresses 450 * are not reachable. Just detect this case and return. Any code 451 * segment in LDT is compatibility mode. 452 */ 453 static int is_errata100(struct pt_regs *regs, unsigned long address) 454 { 455 #ifdef CONFIG_X86_64 456 if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32)) 457 return 1; 458 #endif 459 return 0; 460 } 461 462 /* Pentium F0 0F C7 C8 bug workaround: */ 463 static int is_f00f_bug(struct pt_regs *regs, unsigned long error_code, 464 unsigned long address) 465 { 466 #ifdef CONFIG_X86_F00F_BUG 467 if (boot_cpu_has_bug(X86_BUG_F00F) && !(error_code & X86_PF_USER) && 468 idt_is_f00f_address(address)) { 469 handle_invalid_op(regs); 470 return 1; 471 } 472 #endif 473 return 0; 474 } 475 476 static void show_ldttss(const struct desc_ptr *gdt, const char *name, u16 index) 477 { 478 u32 offset = (index >> 3) * sizeof(struct desc_struct); 479 unsigned long addr; 480 struct ldttss_desc desc; 481 482 if (index == 0) { 483 pr_alert("%s: NULL\n", name); 484 return; 485 } 486 487 if (offset + sizeof(struct ldttss_desc) >= gdt->size) { 488 pr_alert("%s: 0x%hx -- out of bounds\n", name, index); 489 return; 490 } 491 492 if (copy_from_kernel_nofault(&desc, (void *)(gdt->address + offset), 493 sizeof(struct ldttss_desc))) { 494 pr_alert("%s: 0x%hx -- GDT entry is not readable\n", 495 name, index); 496 return; 497 } 498 499 addr = desc.base0 | (desc.base1 << 16) | ((unsigned long)desc.base2 << 24); 500 #ifdef CONFIG_X86_64 501 addr |= ((u64)desc.base3 << 32); 502 #endif 503 pr_alert("%s: 0x%hx -- base=0x%lx limit=0x%x\n", 504 name, index, addr, (desc.limit0 | (desc.limit1 << 16))); 505 } 506 507 static void 508 show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long address) 509 { 510 if (!oops_may_print()) 511 return; 512 513 if (error_code & X86_PF_INSTR) { 514 unsigned int level; 515 pgd_t *pgd; 516 pte_t *pte; 517 518 pgd = __va(read_cr3_pa()); 519 pgd += pgd_index(address); 520 521 pte = lookup_address_in_pgd(pgd, address, &level); 522 523 if (pte && pte_present(*pte) && !pte_exec(*pte)) 524 pr_crit("kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n", 525 from_kuid(&init_user_ns, current_uid())); 526 if (pte && pte_present(*pte) && pte_exec(*pte) && 527 (pgd_flags(*pgd) & _PAGE_USER) && 528 (__read_cr4() & X86_CR4_SMEP)) 529 pr_crit("unable to execute userspace code (SMEP?) (uid: %d)\n", 530 from_kuid(&init_user_ns, current_uid())); 531 } 532 533 if (address < PAGE_SIZE && !user_mode(regs)) 534 pr_alert("BUG: kernel NULL pointer dereference, address: %px\n", 535 (void *)address); 536 else 537 pr_alert("BUG: unable to handle page fault for address: %px\n", 538 (void *)address); 539 540 pr_alert("#PF: %s %s in %s mode\n", 541 (error_code & X86_PF_USER) ? "user" : "supervisor", 542 (error_code & X86_PF_INSTR) ? "instruction fetch" : 543 (error_code & X86_PF_WRITE) ? "write access" : 544 "read access", 545 user_mode(regs) ? "user" : "kernel"); 546 pr_alert("#PF: error_code(0x%04lx) - %s\n", error_code, 547 !(error_code & X86_PF_PROT) ? "not-present page" : 548 (error_code & X86_PF_RSVD) ? "reserved bit violation" : 549 (error_code & X86_PF_PK) ? "protection keys violation" : 550 "permissions violation"); 551 552 if (!(error_code & X86_PF_USER) && user_mode(regs)) { 553 struct desc_ptr idt, gdt; 554 u16 ldtr, tr; 555 556 /* 557 * This can happen for quite a few reasons. The more obvious 558 * ones are faults accessing the GDT, or LDT. Perhaps 559 * surprisingly, if the CPU tries to deliver a benign or 560 * contributory exception from user code and gets a page fault 561 * during delivery, the page fault can be delivered as though 562 * it originated directly from user code. This could happen 563 * due to wrong permissions on the IDT, GDT, LDT, TSS, or 564 * kernel or IST stack. 565 */ 566 store_idt(&idt); 567 568 /* Usable even on Xen PV -- it's just slow. */ 569 native_store_gdt(&gdt); 570 571 pr_alert("IDT: 0x%lx (limit=0x%hx) GDT: 0x%lx (limit=0x%hx)\n", 572 idt.address, idt.size, gdt.address, gdt.size); 573 574 store_ldt(ldtr); 575 show_ldttss(&gdt, "LDTR", ldtr); 576 577 store_tr(tr); 578 show_ldttss(&gdt, "TR", tr); 579 } 580 581 dump_pagetable(address); 582 } 583 584 static noinline void 585 pgtable_bad(struct pt_regs *regs, unsigned long error_code, 586 unsigned long address) 587 { 588 struct task_struct *tsk; 589 unsigned long flags; 590 int sig; 591 592 flags = oops_begin(); 593 tsk = current; 594 sig = SIGKILL; 595 596 printk(KERN_ALERT "%s: Corrupted page table at address %lx\n", 597 tsk->comm, address); 598 dump_pagetable(address); 599 600 if (__die("Bad pagetable", regs, error_code)) 601 sig = 0; 602 603 oops_end(flags, regs, sig); 604 } 605 606 static void sanitize_error_code(unsigned long address, 607 unsigned long *error_code) 608 { 609 /* 610 * To avoid leaking information about the kernel page 611 * table layout, pretend that user-mode accesses to 612 * kernel addresses are always protection faults. 613 * 614 * NB: This means that failed vsyscalls with vsyscall=none 615 * will have the PROT bit. This doesn't leak any 616 * information and does not appear to cause any problems. 617 */ 618 if (address >= TASK_SIZE_MAX) 619 *error_code |= X86_PF_PROT; 620 } 621 622 static void set_signal_archinfo(unsigned long address, 623 unsigned long error_code) 624 { 625 struct task_struct *tsk = current; 626 627 tsk->thread.trap_nr = X86_TRAP_PF; 628 tsk->thread.error_code = error_code | X86_PF_USER; 629 tsk->thread.cr2 = address; 630 } 631 632 static noinline void 633 page_fault_oops(struct pt_regs *regs, unsigned long error_code, 634 unsigned long address) 635 { 636 #ifdef CONFIG_VMAP_STACK 637 struct stack_info info; 638 #endif 639 unsigned long flags; 640 int sig; 641 642 if (user_mode(regs)) { 643 /* 644 * Implicit kernel access from user mode? Skip the stack 645 * overflow and EFI special cases. 646 */ 647 goto oops; 648 } 649 650 #ifdef CONFIG_VMAP_STACK 651 /* 652 * Stack overflow? During boot, we can fault near the initial 653 * stack in the direct map, but that's not an overflow -- check 654 * that we're in vmalloc space to avoid this. 655 */ 656 if (is_vmalloc_addr((void *)address) && 657 get_stack_guard_info((void *)address, &info)) { 658 /* 659 * We're likely to be running with very little stack space 660 * left. It's plausible that we'd hit this condition but 661 * double-fault even before we get this far, in which case 662 * we're fine: the double-fault handler will deal with it. 663 * 664 * We don't want to make it all the way into the oops code 665 * and then double-fault, though, because we're likely to 666 * break the console driver and lose most of the stack dump. 667 */ 668 call_on_stack(__this_cpu_ist_top_va(DF) - sizeof(void*), 669 handle_stack_overflow, 670 ASM_CALL_ARG3, 671 , [arg1] "r" (regs), [arg2] "r" (address), [arg3] "r" (&info)); 672 673 unreachable(); 674 } 675 #endif 676 677 /* 678 * Buggy firmware could access regions which might page fault. If 679 * this happens, EFI has a special OOPS path that will try to 680 * avoid hanging the system. 681 */ 682 if (IS_ENABLED(CONFIG_EFI)) 683 efi_crash_gracefully_on_page_fault(address); 684 685 /* Only not-present faults should be handled by KFENCE. */ 686 if (!(error_code & X86_PF_PROT) && 687 kfence_handle_page_fault(address, error_code & X86_PF_WRITE, regs)) 688 return; 689 690 oops: 691 /* 692 * Oops. The kernel tried to access some bad page. We'll have to 693 * terminate things with extreme prejudice: 694 */ 695 flags = oops_begin(); 696 697 show_fault_oops(regs, error_code, address); 698 699 if (task_stack_end_corrupted(current)) 700 printk(KERN_EMERG "Thread overran stack, or stack corrupted\n"); 701 702 sig = SIGKILL; 703 if (__die("Oops", regs, error_code)) 704 sig = 0; 705 706 /* Executive summary in case the body of the oops scrolled away */ 707 printk(KERN_DEFAULT "CR2: %016lx\n", address); 708 709 oops_end(flags, regs, sig); 710 } 711 712 static noinline void 713 kernelmode_fixup_or_oops(struct pt_regs *regs, unsigned long error_code, 714 unsigned long address, int signal, int si_code, 715 u32 pkey) 716 { 717 WARN_ON_ONCE(user_mode(regs)); 718 719 /* Are we prepared to handle this kernel fault? */ 720 if (fixup_exception(regs, X86_TRAP_PF, error_code, address)) { 721 /* 722 * Any interrupt that takes a fault gets the fixup. This makes 723 * the below recursive fault logic only apply to a faults from 724 * task context. 725 */ 726 if (in_interrupt()) 727 return; 728 729 /* 730 * Per the above we're !in_interrupt(), aka. task context. 731 * 732 * In this case we need to make sure we're not recursively 733 * faulting through the emulate_vsyscall() logic. 734 */ 735 if (current->thread.sig_on_uaccess_err && signal) { 736 sanitize_error_code(address, &error_code); 737 738 set_signal_archinfo(address, error_code); 739 740 if (si_code == SEGV_PKUERR) { 741 force_sig_pkuerr((void __user *)address, pkey); 742 } else { 743 /* XXX: hwpoison faults will set the wrong code. */ 744 force_sig_fault(signal, si_code, (void __user *)address); 745 } 746 } 747 748 /* 749 * Barring that, we can do the fixup and be happy. 750 */ 751 return; 752 } 753 754 /* 755 * AMD erratum #91 manifests as a spurious page fault on a PREFETCH 756 * instruction. 757 */ 758 if (is_prefetch(regs, error_code, address)) 759 return; 760 761 page_fault_oops(regs, error_code, address); 762 } 763 764 /* 765 * Print out info about fatal segfaults, if the show_unhandled_signals 766 * sysctl is set: 767 */ 768 static inline void 769 show_signal_msg(struct pt_regs *regs, unsigned long error_code, 770 unsigned long address, struct task_struct *tsk) 771 { 772 const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG; 773 /* This is a racy snapshot, but it's better than nothing. */ 774 int cpu = raw_smp_processor_id(); 775 776 if (!unhandled_signal(tsk, SIGSEGV)) 777 return; 778 779 if (!printk_ratelimit()) 780 return; 781 782 printk("%s%s[%d]: segfault at %lx ip %px sp %px error %lx", 783 loglvl, tsk->comm, task_pid_nr(tsk), address, 784 (void *)regs->ip, (void *)regs->sp, error_code); 785 786 print_vma_addr(KERN_CONT " in ", regs->ip); 787 788 /* 789 * Dump the likely CPU where the fatal segfault happened. 790 * This can help identify faulty hardware. 791 */ 792 printk(KERN_CONT " likely on CPU %d (core %d, socket %d)", cpu, 793 topology_core_id(cpu), topology_physical_package_id(cpu)); 794 795 796 printk(KERN_CONT "\n"); 797 798 show_opcodes(regs, loglvl); 799 } 800 801 /* 802 * The (legacy) vsyscall page is the long page in the kernel portion 803 * of the address space that has user-accessible permissions. 804 */ 805 static bool is_vsyscall_vaddr(unsigned long vaddr) 806 { 807 return unlikely((vaddr & PAGE_MASK) == VSYSCALL_ADDR); 808 } 809 810 static void 811 __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, 812 unsigned long address, u32 pkey, int si_code) 813 { 814 struct task_struct *tsk = current; 815 816 if (!user_mode(regs)) { 817 kernelmode_fixup_or_oops(regs, error_code, address, 818 SIGSEGV, si_code, pkey); 819 return; 820 } 821 822 if (!(error_code & X86_PF_USER)) { 823 /* Implicit user access to kernel memory -- just oops */ 824 page_fault_oops(regs, error_code, address); 825 return; 826 } 827 828 /* 829 * User mode accesses just cause a SIGSEGV. 830 * It's possible to have interrupts off here: 831 */ 832 local_irq_enable(); 833 834 /* 835 * Valid to do another page fault here because this one came 836 * from user space: 837 */ 838 if (is_prefetch(regs, error_code, address)) 839 return; 840 841 if (is_errata100(regs, address)) 842 return; 843 844 sanitize_error_code(address, &error_code); 845 846 if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address)) 847 return; 848 849 if (likely(show_unhandled_signals)) 850 show_signal_msg(regs, error_code, address, tsk); 851 852 set_signal_archinfo(address, error_code); 853 854 if (si_code == SEGV_PKUERR) 855 force_sig_pkuerr((void __user *)address, pkey); 856 else 857 force_sig_fault(SIGSEGV, si_code, (void __user *)address); 858 859 local_irq_disable(); 860 } 861 862 static noinline void 863 bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, 864 unsigned long address) 865 { 866 __bad_area_nosemaphore(regs, error_code, address, 0, SEGV_MAPERR); 867 } 868 869 static void 870 __bad_area(struct pt_regs *regs, unsigned long error_code, 871 unsigned long address, u32 pkey, int si_code) 872 { 873 struct mm_struct *mm = current->mm; 874 /* 875 * Something tried to access memory that isn't in our memory map.. 876 * Fix it, but check if it's kernel or user first.. 877 */ 878 mmap_read_unlock(mm); 879 880 __bad_area_nosemaphore(regs, error_code, address, pkey, si_code); 881 } 882 883 static inline bool bad_area_access_from_pkeys(unsigned long error_code, 884 struct vm_area_struct *vma) 885 { 886 /* This code is always called on the current mm */ 887 bool foreign = false; 888 889 if (!cpu_feature_enabled(X86_FEATURE_OSPKE)) 890 return false; 891 if (error_code & X86_PF_PK) 892 return true; 893 /* this checks permission keys on the VMA: */ 894 if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE), 895 (error_code & X86_PF_INSTR), foreign)) 896 return true; 897 return false; 898 } 899 900 static noinline void 901 bad_area_access_error(struct pt_regs *regs, unsigned long error_code, 902 unsigned long address, struct vm_area_struct *vma) 903 { 904 /* 905 * This OSPKE check is not strictly necessary at runtime. 906 * But, doing it this way allows compiler optimizations 907 * if pkeys are compiled out. 908 */ 909 if (bad_area_access_from_pkeys(error_code, vma)) { 910 /* 911 * A protection key fault means that the PKRU value did not allow 912 * access to some PTE. Userspace can figure out what PKRU was 913 * from the XSAVE state. This function captures the pkey from 914 * the vma and passes it to userspace so userspace can discover 915 * which protection key was set on the PTE. 916 * 917 * If we get here, we know that the hardware signaled a X86_PF_PK 918 * fault and that there was a VMA once we got in the fault 919 * handler. It does *not* guarantee that the VMA we find here 920 * was the one that we faulted on. 921 * 922 * 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4); 923 * 2. T1 : set PKRU to deny access to pkey=4, touches page 924 * 3. T1 : faults... 925 * 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5); 926 * 5. T1 : enters fault handler, takes mmap_lock, etc... 927 * 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really 928 * faulted on a pte with its pkey=4. 929 */ 930 u32 pkey = vma_pkey(vma); 931 932 __bad_area(regs, error_code, address, pkey, SEGV_PKUERR); 933 } else { 934 __bad_area(regs, error_code, address, 0, SEGV_ACCERR); 935 } 936 } 937 938 static void 939 do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address, 940 vm_fault_t fault) 941 { 942 /* Kernel mode? Handle exceptions or die: */ 943 if (!user_mode(regs)) { 944 kernelmode_fixup_or_oops(regs, error_code, address, 945 SIGBUS, BUS_ADRERR, ARCH_DEFAULT_PKEY); 946 return; 947 } 948 949 /* User-space => ok to do another page fault: */ 950 if (is_prefetch(regs, error_code, address)) 951 return; 952 953 sanitize_error_code(address, &error_code); 954 955 if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address)) 956 return; 957 958 set_signal_archinfo(address, error_code); 959 960 #ifdef CONFIG_MEMORY_FAILURE 961 if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) { 962 struct task_struct *tsk = current; 963 unsigned lsb = 0; 964 965 pr_err( 966 "MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n", 967 tsk->comm, tsk->pid, address); 968 if (fault & VM_FAULT_HWPOISON_LARGE) 969 lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault)); 970 if (fault & VM_FAULT_HWPOISON) 971 lsb = PAGE_SHIFT; 972 force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb); 973 return; 974 } 975 #endif 976 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address); 977 } 978 979 static int spurious_kernel_fault_check(unsigned long error_code, pte_t *pte) 980 { 981 if ((error_code & X86_PF_WRITE) && !pte_write(*pte)) 982 return 0; 983 984 if ((error_code & X86_PF_INSTR) && !pte_exec(*pte)) 985 return 0; 986 987 return 1; 988 } 989 990 /* 991 * Handle a spurious fault caused by a stale TLB entry. 992 * 993 * This allows us to lazily refresh the TLB when increasing the 994 * permissions of a kernel page (RO -> RW or NX -> X). Doing it 995 * eagerly is very expensive since that implies doing a full 996 * cross-processor TLB flush, even if no stale TLB entries exist 997 * on other processors. 998 * 999 * Spurious faults may only occur if the TLB contains an entry with 1000 * fewer permission than the page table entry. Non-present (P = 0) 1001 * and reserved bit (R = 1) faults are never spurious. 1002 * 1003 * There are no security implications to leaving a stale TLB when 1004 * increasing the permissions on a page. 1005 * 1006 * Returns non-zero if a spurious fault was handled, zero otherwise. 1007 * 1008 * See Intel Developer's Manual Vol 3 Section 4.10.4.3, bullet 3 1009 * (Optional Invalidation). 1010 */ 1011 static noinline int 1012 spurious_kernel_fault(unsigned long error_code, unsigned long address) 1013 { 1014 pgd_t *pgd; 1015 p4d_t *p4d; 1016 pud_t *pud; 1017 pmd_t *pmd; 1018 pte_t *pte; 1019 int ret; 1020 1021 /* 1022 * Only writes to RO or instruction fetches from NX may cause 1023 * spurious faults. 1024 * 1025 * These could be from user or supervisor accesses but the TLB 1026 * is only lazily flushed after a kernel mapping protection 1027 * change, so user accesses are not expected to cause spurious 1028 * faults. 1029 */ 1030 if (error_code != (X86_PF_WRITE | X86_PF_PROT) && 1031 error_code != (X86_PF_INSTR | X86_PF_PROT)) 1032 return 0; 1033 1034 pgd = init_mm.pgd + pgd_index(address); 1035 if (!pgd_present(*pgd)) 1036 return 0; 1037 1038 p4d = p4d_offset(pgd, address); 1039 if (!p4d_present(*p4d)) 1040 return 0; 1041 1042 if (p4d_large(*p4d)) 1043 return spurious_kernel_fault_check(error_code, (pte_t *) p4d); 1044 1045 pud = pud_offset(p4d, address); 1046 if (!pud_present(*pud)) 1047 return 0; 1048 1049 if (pud_large(*pud)) 1050 return spurious_kernel_fault_check(error_code, (pte_t *) pud); 1051 1052 pmd = pmd_offset(pud, address); 1053 if (!pmd_present(*pmd)) 1054 return 0; 1055 1056 if (pmd_large(*pmd)) 1057 return spurious_kernel_fault_check(error_code, (pte_t *) pmd); 1058 1059 pte = pte_offset_kernel(pmd, address); 1060 if (!pte_present(*pte)) 1061 return 0; 1062 1063 ret = spurious_kernel_fault_check(error_code, pte); 1064 if (!ret) 1065 return 0; 1066 1067 /* 1068 * Make sure we have permissions in PMD. 1069 * If not, then there's a bug in the page tables: 1070 */ 1071 ret = spurious_kernel_fault_check(error_code, (pte_t *) pmd); 1072 WARN_ONCE(!ret, "PMD has incorrect permission bits\n"); 1073 1074 return ret; 1075 } 1076 NOKPROBE_SYMBOL(spurious_kernel_fault); 1077 1078 int show_unhandled_signals = 1; 1079 1080 static inline int 1081 access_error(unsigned long error_code, struct vm_area_struct *vma) 1082 { 1083 /* This is only called for the current mm, so: */ 1084 bool foreign = false; 1085 1086 /* 1087 * Read or write was blocked by protection keys. This is 1088 * always an unconditional error and can never result in 1089 * a follow-up action to resolve the fault, like a COW. 1090 */ 1091 if (error_code & X86_PF_PK) 1092 return 1; 1093 1094 /* 1095 * SGX hardware blocked the access. This usually happens 1096 * when the enclave memory contents have been destroyed, like 1097 * after a suspend/resume cycle. In any case, the kernel can't 1098 * fix the cause of the fault. Handle the fault as an access 1099 * error even in cases where no actual access violation 1100 * occurred. This allows userspace to rebuild the enclave in 1101 * response to the signal. 1102 */ 1103 if (unlikely(error_code & X86_PF_SGX)) 1104 return 1; 1105 1106 /* 1107 * Make sure to check the VMA so that we do not perform 1108 * faults just to hit a X86_PF_PK as soon as we fill in a 1109 * page. 1110 */ 1111 if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE), 1112 (error_code & X86_PF_INSTR), foreign)) 1113 return 1; 1114 1115 if (error_code & X86_PF_WRITE) { 1116 /* write, present and write, not present: */ 1117 if (unlikely(!(vma->vm_flags & VM_WRITE))) 1118 return 1; 1119 return 0; 1120 } 1121 1122 /* read, present: */ 1123 if (unlikely(error_code & X86_PF_PROT)) 1124 return 1; 1125 1126 /* read, not present: */ 1127 if (unlikely(!vma_is_accessible(vma))) 1128 return 1; 1129 1130 return 0; 1131 } 1132 1133 bool fault_in_kernel_space(unsigned long address) 1134 { 1135 /* 1136 * On 64-bit systems, the vsyscall page is at an address above 1137 * TASK_SIZE_MAX, but is not considered part of the kernel 1138 * address space. 1139 */ 1140 if (IS_ENABLED(CONFIG_X86_64) && is_vsyscall_vaddr(address)) 1141 return false; 1142 1143 return address >= TASK_SIZE_MAX; 1144 } 1145 1146 /* 1147 * Called for all faults where 'address' is part of the kernel address 1148 * space. Might get called for faults that originate from *code* that 1149 * ran in userspace or the kernel. 1150 */ 1151 static void 1152 do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code, 1153 unsigned long address) 1154 { 1155 /* 1156 * Protection keys exceptions only happen on user pages. We 1157 * have no user pages in the kernel portion of the address 1158 * space, so do not expect them here. 1159 */ 1160 WARN_ON_ONCE(hw_error_code & X86_PF_PK); 1161 1162 #ifdef CONFIG_X86_32 1163 /* 1164 * We can fault-in kernel-space virtual memory on-demand. The 1165 * 'reference' page table is init_mm.pgd. 1166 * 1167 * NOTE! We MUST NOT take any locks for this case. We may 1168 * be in an interrupt or a critical region, and should 1169 * only copy the information from the master page table, 1170 * nothing more. 1171 * 1172 * Before doing this on-demand faulting, ensure that the 1173 * fault is not any of the following: 1174 * 1. A fault on a PTE with a reserved bit set. 1175 * 2. A fault caused by a user-mode access. (Do not demand- 1176 * fault kernel memory due to user-mode accesses). 1177 * 3. A fault caused by a page-level protection violation. 1178 * (A demand fault would be on a non-present page which 1179 * would have X86_PF_PROT==0). 1180 * 1181 * This is only needed to close a race condition on x86-32 in 1182 * the vmalloc mapping/unmapping code. See the comment above 1183 * vmalloc_fault() for details. On x86-64 the race does not 1184 * exist as the vmalloc mappings don't need to be synchronized 1185 * there. 1186 */ 1187 if (!(hw_error_code & (X86_PF_RSVD | X86_PF_USER | X86_PF_PROT))) { 1188 if (vmalloc_fault(address) >= 0) 1189 return; 1190 } 1191 #endif 1192 1193 if (is_f00f_bug(regs, hw_error_code, address)) 1194 return; 1195 1196 /* Was the fault spurious, caused by lazy TLB invalidation? */ 1197 if (spurious_kernel_fault(hw_error_code, address)) 1198 return; 1199 1200 /* kprobes don't want to hook the spurious faults: */ 1201 if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF))) 1202 return; 1203 1204 /* 1205 * Note, despite being a "bad area", there are quite a few 1206 * acceptable reasons to get here, such as erratum fixups 1207 * and handling kernel code that can fault, like get_user(). 1208 * 1209 * Don't take the mm semaphore here. If we fixup a prefetch 1210 * fault we could otherwise deadlock: 1211 */ 1212 bad_area_nosemaphore(regs, hw_error_code, address); 1213 } 1214 NOKPROBE_SYMBOL(do_kern_addr_fault); 1215 1216 /* 1217 * Handle faults in the user portion of the address space. Nothing in here 1218 * should check X86_PF_USER without a specific justification: for almost 1219 * all purposes, we should treat a normal kernel access to user memory 1220 * (e.g. get_user(), put_user(), etc.) the same as the WRUSS instruction. 1221 * The one exception is AC flag handling, which is, per the x86 1222 * architecture, special for WRUSS. 1223 */ 1224 static inline 1225 void do_user_addr_fault(struct pt_regs *regs, 1226 unsigned long error_code, 1227 unsigned long address) 1228 { 1229 struct vm_area_struct *vma; 1230 struct task_struct *tsk; 1231 struct mm_struct *mm; 1232 vm_fault_t fault; 1233 unsigned int flags = FAULT_FLAG_DEFAULT; 1234 1235 tsk = current; 1236 mm = tsk->mm; 1237 1238 if (unlikely((error_code & (X86_PF_USER | X86_PF_INSTR)) == X86_PF_INSTR)) { 1239 /* 1240 * Whoops, this is kernel mode code trying to execute from 1241 * user memory. Unless this is AMD erratum #93, which 1242 * corrupts RIP such that it looks like a user address, 1243 * this is unrecoverable. Don't even try to look up the 1244 * VMA or look for extable entries. 1245 */ 1246 if (is_errata93(regs, address)) 1247 return; 1248 1249 page_fault_oops(regs, error_code, address); 1250 return; 1251 } 1252 1253 /* kprobes don't want to hook the spurious faults: */ 1254 if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF))) 1255 return; 1256 1257 /* 1258 * Reserved bits are never expected to be set on 1259 * entries in the user portion of the page tables. 1260 */ 1261 if (unlikely(error_code & X86_PF_RSVD)) 1262 pgtable_bad(regs, error_code, address); 1263 1264 /* 1265 * If SMAP is on, check for invalid kernel (supervisor) access to user 1266 * pages in the user address space. The odd case here is WRUSS, 1267 * which, according to the preliminary documentation, does not respect 1268 * SMAP and will have the USER bit set so, in all cases, SMAP 1269 * enforcement appears to be consistent with the USER bit. 1270 */ 1271 if (unlikely(cpu_feature_enabled(X86_FEATURE_SMAP) && 1272 !(error_code & X86_PF_USER) && 1273 !(regs->flags & X86_EFLAGS_AC))) { 1274 /* 1275 * No extable entry here. This was a kernel access to an 1276 * invalid pointer. get_kernel_nofault() will not get here. 1277 */ 1278 page_fault_oops(regs, error_code, address); 1279 return; 1280 } 1281 1282 /* 1283 * If we're in an interrupt, have no user context or are running 1284 * in a region with pagefaults disabled then we must not take the fault 1285 */ 1286 if (unlikely(faulthandler_disabled() || !mm)) { 1287 bad_area_nosemaphore(regs, error_code, address); 1288 return; 1289 } 1290 1291 /* 1292 * It's safe to allow irq's after cr2 has been saved and the 1293 * vmalloc fault has been handled. 1294 * 1295 * User-mode registers count as a user access even for any 1296 * potential system fault or CPU buglet: 1297 */ 1298 if (user_mode(regs)) { 1299 local_irq_enable(); 1300 flags |= FAULT_FLAG_USER; 1301 } else { 1302 if (regs->flags & X86_EFLAGS_IF) 1303 local_irq_enable(); 1304 } 1305 1306 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address); 1307 1308 if (error_code & X86_PF_WRITE) 1309 flags |= FAULT_FLAG_WRITE; 1310 if (error_code & X86_PF_INSTR) 1311 flags |= FAULT_FLAG_INSTRUCTION; 1312 1313 #ifdef CONFIG_X86_64 1314 /* 1315 * Faults in the vsyscall page might need emulation. The 1316 * vsyscall page is at a high address (>PAGE_OFFSET), but is 1317 * considered to be part of the user address space. 1318 * 1319 * The vsyscall page does not have a "real" VMA, so do this 1320 * emulation before we go searching for VMAs. 1321 * 1322 * PKRU never rejects instruction fetches, so we don't need 1323 * to consider the PF_PK bit. 1324 */ 1325 if (is_vsyscall_vaddr(address)) { 1326 if (emulate_vsyscall(error_code, regs, address)) 1327 return; 1328 } 1329 #endif 1330 1331 #ifdef CONFIG_PER_VMA_LOCK 1332 if (!(flags & FAULT_FLAG_USER)) 1333 goto lock_mmap; 1334 1335 vma = lock_vma_under_rcu(mm, address); 1336 if (!vma) 1337 goto lock_mmap; 1338 1339 if (unlikely(access_error(error_code, vma))) { 1340 vma_end_read(vma); 1341 goto lock_mmap; 1342 } 1343 fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs); 1344 vma_end_read(vma); 1345 1346 if (!(fault & VM_FAULT_RETRY)) { 1347 count_vm_vma_lock_event(VMA_LOCK_SUCCESS); 1348 goto done; 1349 } 1350 count_vm_vma_lock_event(VMA_LOCK_RETRY); 1351 1352 /* Quick path to respond to signals */ 1353 if (fault_signal_pending(fault, regs)) { 1354 if (!user_mode(regs)) 1355 kernelmode_fixup_or_oops(regs, error_code, address, 1356 SIGBUS, BUS_ADRERR, 1357 ARCH_DEFAULT_PKEY); 1358 return; 1359 } 1360 lock_mmap: 1361 #endif /* CONFIG_PER_VMA_LOCK */ 1362 1363 retry: 1364 vma = lock_mm_and_find_vma(mm, address, regs); 1365 if (unlikely(!vma)) { 1366 bad_area_nosemaphore(regs, error_code, address); 1367 return; 1368 } 1369 1370 /* 1371 * Ok, we have a good vm_area for this memory access, so 1372 * we can handle it.. 1373 */ 1374 if (unlikely(access_error(error_code, vma))) { 1375 bad_area_access_error(regs, error_code, address, vma); 1376 return; 1377 } 1378 1379 /* 1380 * If for any reason at all we couldn't handle the fault, 1381 * make sure we exit gracefully rather than endlessly redo 1382 * the fault. Since we never set FAULT_FLAG_RETRY_NOWAIT, if 1383 * we get VM_FAULT_RETRY back, the mmap_lock has been unlocked. 1384 * 1385 * Note that handle_userfault() may also release and reacquire mmap_lock 1386 * (and not return with VM_FAULT_RETRY), when returning to userland to 1387 * repeat the page fault later with a VM_FAULT_NOPAGE retval 1388 * (potentially after handling any pending signal during the return to 1389 * userland). The return to userland is identified whenever 1390 * FAULT_FLAG_USER|FAULT_FLAG_KILLABLE are both set in flags. 1391 */ 1392 fault = handle_mm_fault(vma, address, flags, regs); 1393 1394 if (fault_signal_pending(fault, regs)) { 1395 /* 1396 * Quick path to respond to signals. The core mm code 1397 * has unlocked the mm for us if we get here. 1398 */ 1399 if (!user_mode(regs)) 1400 kernelmode_fixup_or_oops(regs, error_code, address, 1401 SIGBUS, BUS_ADRERR, 1402 ARCH_DEFAULT_PKEY); 1403 return; 1404 } 1405 1406 /* The fault is fully completed (including releasing mmap lock) */ 1407 if (fault & VM_FAULT_COMPLETED) 1408 return; 1409 1410 /* 1411 * If we need to retry the mmap_lock has already been released, 1412 * and if there is a fatal signal pending there is no guarantee 1413 * that we made any progress. Handle this case first. 1414 */ 1415 if (unlikely(fault & VM_FAULT_RETRY)) { 1416 flags |= FAULT_FLAG_TRIED; 1417 goto retry; 1418 } 1419 1420 mmap_read_unlock(mm); 1421 #ifdef CONFIG_PER_VMA_LOCK 1422 done: 1423 #endif 1424 if (likely(!(fault & VM_FAULT_ERROR))) 1425 return; 1426 1427 if (fatal_signal_pending(current) && !user_mode(regs)) { 1428 kernelmode_fixup_or_oops(regs, error_code, address, 1429 0, 0, ARCH_DEFAULT_PKEY); 1430 return; 1431 } 1432 1433 if (fault & VM_FAULT_OOM) { 1434 /* Kernel mode? Handle exceptions or die: */ 1435 if (!user_mode(regs)) { 1436 kernelmode_fixup_or_oops(regs, error_code, address, 1437 SIGSEGV, SEGV_MAPERR, 1438 ARCH_DEFAULT_PKEY); 1439 return; 1440 } 1441 1442 /* 1443 * We ran out of memory, call the OOM killer, and return the 1444 * userspace (which will retry the fault, or kill us if we got 1445 * oom-killed): 1446 */ 1447 pagefault_out_of_memory(); 1448 } else { 1449 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON| 1450 VM_FAULT_HWPOISON_LARGE)) 1451 do_sigbus(regs, error_code, address, fault); 1452 else if (fault & VM_FAULT_SIGSEGV) 1453 bad_area_nosemaphore(regs, error_code, address); 1454 else 1455 BUG(); 1456 } 1457 } 1458 NOKPROBE_SYMBOL(do_user_addr_fault); 1459 1460 static __always_inline void 1461 trace_page_fault_entries(struct pt_regs *regs, unsigned long error_code, 1462 unsigned long address) 1463 { 1464 if (!trace_pagefault_enabled()) 1465 return; 1466 1467 if (user_mode(regs)) 1468 trace_page_fault_user(address, regs, error_code); 1469 else 1470 trace_page_fault_kernel(address, regs, error_code); 1471 } 1472 1473 static __always_inline void 1474 handle_page_fault(struct pt_regs *regs, unsigned long error_code, 1475 unsigned long address) 1476 { 1477 trace_page_fault_entries(regs, error_code, address); 1478 1479 if (unlikely(kmmio_fault(regs, address))) 1480 return; 1481 1482 /* Was the fault on kernel-controlled part of the address space? */ 1483 if (unlikely(fault_in_kernel_space(address))) { 1484 do_kern_addr_fault(regs, error_code, address); 1485 } else { 1486 do_user_addr_fault(regs, error_code, address); 1487 /* 1488 * User address page fault handling might have reenabled 1489 * interrupts. Fixing up all potential exit points of 1490 * do_user_addr_fault() and its leaf functions is just not 1491 * doable w/o creating an unholy mess or turning the code 1492 * upside down. 1493 */ 1494 local_irq_disable(); 1495 } 1496 } 1497 1498 DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault) 1499 { 1500 unsigned long address = read_cr2(); 1501 irqentry_state_t state; 1502 1503 prefetchw(¤t->mm->mmap_lock); 1504 1505 /* 1506 * KVM uses #PF vector to deliver 'page not present' events to guests 1507 * (asynchronous page fault mechanism). The event happens when a 1508 * userspace task is trying to access some valid (from guest's point of 1509 * view) memory which is not currently mapped by the host (e.g. the 1510 * memory is swapped out). Note, the corresponding "page ready" event 1511 * which is injected when the memory becomes available, is delivered via 1512 * an interrupt mechanism and not a #PF exception 1513 * (see arch/x86/kernel/kvm.c: sysvec_kvm_asyncpf_interrupt()). 1514 * 1515 * We are relying on the interrupted context being sane (valid RSP, 1516 * relevant locks not held, etc.), which is fine as long as the 1517 * interrupted context had IF=1. We are also relying on the KVM 1518 * async pf type field and CR2 being read consistently instead of 1519 * getting values from real and async page faults mixed up. 1520 * 1521 * Fingers crossed. 1522 * 1523 * The async #PF handling code takes care of idtentry handling 1524 * itself. 1525 */ 1526 if (kvm_handle_async_pf(regs, (u32)address)) 1527 return; 1528 1529 /* 1530 * Entry handling for valid #PF from kernel mode is slightly 1531 * different: RCU is already watching and ct_irq_enter() must not 1532 * be invoked because a kernel fault on a user space address might 1533 * sleep. 1534 * 1535 * In case the fault hit a RCU idle region the conditional entry 1536 * code reenabled RCU to avoid subsequent wreckage which helps 1537 * debuggability. 1538 */ 1539 state = irqentry_enter(regs); 1540 1541 instrumentation_begin(); 1542 handle_page_fault(regs, error_code, address); 1543 instrumentation_end(); 1544 1545 irqentry_exit(regs, state); 1546 } 1547