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/memblock.h> /* max_low_pfn */ 11 #include <linux/kfence.h> /* kfence_handle_page_fault */ 12 #include <linux/kprobes.h> /* NOKPROBE_SYMBOL, ... */ 13 #include <linux/mmiotrace.h> /* kmmio_handler, ... */ 14 #include <linux/perf_event.h> /* perf_sw_event */ 15 #include <linux/hugetlb.h> /* hstate_index_to_shift */ 16 #include <linux/context_tracking.h> /* exception_enter(), ... */ 17 #include <linux/uaccess.h> /* faulthandler_disabled() */ 18 #include <linux/efi.h> /* efi_crash_gracefully_on_page_fault()*/ 19 #include <linux/mm_types.h> 20 #include <linux/mm.h> /* find_and_lock_vma() */ 21 #include <linux/vmalloc.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 #include <asm/fred.h> 37 #include <asm/sev.h> /* snp_dump_hva_rmpentry() */ 38 39 #define CREATE_TRACE_POINTS 40 #include <trace/events/exceptions.h> 41 42 /* 43 * Returns 0 if mmiotrace is disabled, or if the fault is not 44 * handled by mmiotrace: 45 */ 46 static nokprobe_inline int 47 kmmio_fault(struct pt_regs *regs, unsigned long addr) 48 { 49 if (unlikely(is_kmmio_active())) 50 if (kmmio_handler(regs, addr) == 1) 51 return -1; 52 return 0; 53 } 54 55 /* 56 * Prefetch quirks: 57 * 58 * 32-bit mode: 59 * 60 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch. 61 * Check that here and ignore it. This is AMD erratum #91. 62 * 63 * 64-bit mode: 64 * 65 * Sometimes the CPU reports invalid exceptions on prefetch. 66 * Check that here and ignore it. 67 * 68 * Opcode checker based on code by Richard Brunner. 69 */ 70 static inline int 71 check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr, 72 unsigned char opcode, int *prefetch) 73 { 74 unsigned char instr_hi = opcode & 0xf0; 75 unsigned char instr_lo = opcode & 0x0f; 76 77 switch (instr_hi) { 78 case 0x20: 79 case 0x30: 80 /* 81 * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes. 82 * In X86_64 long mode, the CPU will signal invalid 83 * opcode if some of these prefixes are present so 84 * X86_64 will never get here anyway 85 */ 86 return ((instr_lo & 7) == 0x6); 87 #ifdef CONFIG_X86_64 88 case 0x40: 89 /* 90 * In 64-bit mode 0x40..0x4F are valid REX prefixes 91 */ 92 return (!user_mode(regs) || user_64bit_mode(regs)); 93 #endif 94 case 0x60: 95 /* 0x64 thru 0x67 are valid prefixes in all modes. */ 96 return (instr_lo & 0xC) == 0x4; 97 case 0xF0: 98 /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */ 99 return !instr_lo || (instr_lo>>1) == 1; 100 case 0x00: 101 /* Prefetch instruction is 0x0F0D or 0x0F18 */ 102 if (get_kernel_nofault(opcode, instr)) 103 return 0; 104 105 *prefetch = (instr_lo == 0xF) && 106 (opcode == 0x0D || opcode == 0x18); 107 return 0; 108 default: 109 return 0; 110 } 111 } 112 113 static bool is_amd_k8_pre_npt(void) 114 { 115 struct cpuinfo_x86 *c = &boot_cpu_data; 116 117 return unlikely(IS_ENABLED(CONFIG_CPU_SUP_AMD) && 118 c->x86_vendor == X86_VENDOR_AMD && 119 c->x86 == 0xf && c->x86_model < 0x40); 120 } 121 122 static int 123 is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr) 124 { 125 unsigned char *max_instr; 126 unsigned char *instr; 127 int prefetch = 0; 128 129 /* Erratum #91 affects AMD K8, pre-NPT CPUs */ 130 if (!is_amd_k8_pre_npt()) 131 return 0; 132 133 /* 134 * If it was a exec (instruction fetch) fault on NX page, then 135 * do not ignore the fault: 136 */ 137 if (error_code & X86_PF_INSTR) 138 return 0; 139 140 instr = (void *)convert_ip_to_linear(current, regs); 141 max_instr = instr + 15; 142 143 /* 144 * This code has historically always bailed out if IP points to a 145 * not-present page (e.g. due to a race). No one has ever 146 * complained about this. 147 */ 148 pagefault_disable(); 149 150 while (instr < max_instr) { 151 unsigned char opcode; 152 153 if (user_mode(regs)) { 154 if (get_user(opcode, (unsigned char __user *) instr)) 155 break; 156 } else { 157 if (get_kernel_nofault(opcode, instr)) 158 break; 159 } 160 161 instr++; 162 163 if (!check_prefetch_opcode(regs, instr, opcode, &prefetch)) 164 break; 165 } 166 167 pagefault_enable(); 168 return prefetch; 169 } 170 171 DEFINE_SPINLOCK(pgd_lock); 172 LIST_HEAD(pgd_list); 173 174 #ifdef CONFIG_X86_32 175 static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address) 176 { 177 unsigned index = pgd_index(address); 178 pgd_t *pgd_k; 179 p4d_t *p4d, *p4d_k; 180 pud_t *pud, *pud_k; 181 pmd_t *pmd, *pmd_k; 182 183 pgd += index; 184 pgd_k = init_mm.pgd + index; 185 186 if (!pgd_present(*pgd_k)) 187 return NULL; 188 189 /* 190 * set_pgd(pgd, *pgd_k); here would be useless on PAE 191 * and redundant with the set_pmd() on non-PAE. As would 192 * set_p4d/set_pud. 193 */ 194 p4d = p4d_offset(pgd, address); 195 p4d_k = p4d_offset(pgd_k, address); 196 if (!p4d_present(*p4d_k)) 197 return NULL; 198 199 pud = pud_offset(p4d, address); 200 pud_k = pud_offset(p4d_k, address); 201 if (!pud_present(*pud_k)) 202 return NULL; 203 204 pmd = pmd_offset(pud, address); 205 pmd_k = pmd_offset(pud_k, address); 206 207 if (pmd_present(*pmd) != pmd_present(*pmd_k)) 208 set_pmd(pmd, *pmd_k); 209 210 if (!pmd_present(*pmd_k)) 211 return NULL; 212 else 213 BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k)); 214 215 return pmd_k; 216 } 217 218 /* 219 * Handle a fault on the vmalloc or module mapping area 220 * 221 * This is needed because there is a race condition between the time 222 * when the vmalloc mapping code updates the PMD to the point in time 223 * where it synchronizes this update with the other page-tables in the 224 * system. 225 * 226 * In this race window another thread/CPU can map an area on the same 227 * PMD, finds it already present and does not synchronize it with the 228 * rest of the system yet. As a result v[mz]alloc might return areas 229 * which are not mapped in every page-table in the system, causing an 230 * unhandled page-fault when they are accessed. 231 */ 232 static noinline int vmalloc_fault(unsigned long address) 233 { 234 unsigned long pgd_paddr; 235 pmd_t *pmd_k; 236 pte_t *pte_k; 237 238 /* Make sure we are in vmalloc area: */ 239 if (!(address >= VMALLOC_START && address < VMALLOC_END)) 240 return -1; 241 242 /* 243 * Synchronize this task's top level page-table 244 * with the 'reference' page table. 245 * 246 * Do _not_ use "current" here. We might be inside 247 * an interrupt in the middle of a task switch.. 248 */ 249 pgd_paddr = read_cr3_pa(); 250 pmd_k = vmalloc_sync_one(__va(pgd_paddr), address); 251 if (!pmd_k) 252 return -1; 253 254 if (pmd_leaf(*pmd_k)) 255 return 0; 256 257 pte_k = pte_offset_kernel(pmd_k, address); 258 if (!pte_present(*pte_k)) 259 return -1; 260 261 return 0; 262 } 263 NOKPROBE_SYMBOL(vmalloc_fault); 264 265 void arch_sync_kernel_mappings(unsigned long start, unsigned long end) 266 { 267 unsigned long addr; 268 269 for (addr = start & PMD_MASK; 270 addr >= TASK_SIZE_MAX && addr < VMALLOC_END; 271 addr += PMD_SIZE) { 272 struct page *page; 273 274 spin_lock(&pgd_lock); 275 list_for_each_entry(page, &pgd_list, lru) { 276 spinlock_t *pgt_lock; 277 278 /* the pgt_lock only for Xen */ 279 pgt_lock = &pgd_page_get_mm(page)->page_table_lock; 280 281 spin_lock(pgt_lock); 282 vmalloc_sync_one(page_address(page), addr); 283 spin_unlock(pgt_lock); 284 } 285 spin_unlock(&pgd_lock); 286 } 287 } 288 289 static bool low_pfn(unsigned long pfn) 290 { 291 return pfn < max_low_pfn; 292 } 293 294 static void dump_pagetable(unsigned long address) 295 { 296 pgd_t *base = __va(read_cr3_pa()); 297 pgd_t *pgd = &base[pgd_index(address)]; 298 p4d_t *p4d; 299 pud_t *pud; 300 pmd_t *pmd; 301 pte_t *pte; 302 303 #ifdef CONFIG_X86_PAE 304 pr_info("*pdpt = %016Lx ", pgd_val(*pgd)); 305 if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd)) 306 goto out; 307 #define pr_pde pr_cont 308 #else 309 #define pr_pde pr_info 310 #endif 311 p4d = p4d_offset(pgd, address); 312 pud = pud_offset(p4d, address); 313 pmd = pmd_offset(pud, address); 314 pr_pde("*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd)); 315 #undef pr_pde 316 317 /* 318 * We must not directly access the pte in the highpte 319 * case if the page table is located in highmem. 320 * And let's rather not kmap-atomic the pte, just in case 321 * it's allocated already: 322 */ 323 if (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_leaf(*pmd)) 324 goto out; 325 326 pte = pte_offset_kernel(pmd, address); 327 pr_cont("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte)); 328 out: 329 pr_cont("\n"); 330 } 331 332 #else /* CONFIG_X86_64: */ 333 334 #ifdef CONFIG_CPU_SUP_AMD 335 static const char errata93_warning[] = 336 KERN_ERR 337 "******* Your BIOS seems to not contain a fix for K8 errata #93\n" 338 "******* Working around it, but it may cause SEGVs or burn power.\n" 339 "******* Please consider a BIOS update.\n" 340 "******* Disabling USB legacy in the BIOS may also help.\n"; 341 #endif 342 343 static int bad_address(void *p) 344 { 345 unsigned long dummy; 346 347 return get_kernel_nofault(dummy, (unsigned long *)p); 348 } 349 350 static void dump_pagetable(unsigned long address) 351 { 352 pgd_t *base = __va(read_cr3_pa()); 353 pgd_t *pgd = base + pgd_index(address); 354 p4d_t *p4d; 355 pud_t *pud; 356 pmd_t *pmd; 357 pte_t *pte; 358 359 if (bad_address(pgd)) 360 goto bad; 361 362 pr_info("PGD %lx ", pgd_val(*pgd)); 363 364 if (!pgd_present(*pgd)) 365 goto out; 366 367 p4d = p4d_offset(pgd, address); 368 if (bad_address(p4d)) 369 goto bad; 370 371 pr_cont("P4D %lx ", p4d_val(*p4d)); 372 if (!p4d_present(*p4d) || p4d_leaf(*p4d)) 373 goto out; 374 375 pud = pud_offset(p4d, address); 376 if (bad_address(pud)) 377 goto bad; 378 379 pr_cont("PUD %lx ", pud_val(*pud)); 380 if (!pud_present(*pud) || pud_leaf(*pud)) 381 goto out; 382 383 pmd = pmd_offset(pud, address); 384 if (bad_address(pmd)) 385 goto bad; 386 387 pr_cont("PMD %lx ", pmd_val(*pmd)); 388 if (!pmd_present(*pmd) || pmd_leaf(*pmd)) 389 goto out; 390 391 pte = pte_offset_kernel(pmd, address); 392 if (bad_address(pte)) 393 goto bad; 394 395 pr_cont("PTE %lx", pte_val(*pte)); 396 out: 397 pr_cont("\n"); 398 return; 399 bad: 400 pr_info("BAD\n"); 401 } 402 403 #endif /* CONFIG_X86_64 */ 404 405 /* 406 * Workaround for K8 erratum #93 & buggy BIOS. 407 * 408 * BIOS SMM functions are required to use a specific workaround 409 * to avoid corruption of the 64bit RIP register on C stepping K8. 410 * 411 * A lot of BIOS that didn't get tested properly miss this. 412 * 413 * The OS sees this as a page fault with the upper 32bits of RIP cleared. 414 * Try to work around it here. 415 * 416 * Note we only handle faults in kernel here. 417 * Does nothing on 32-bit. 418 */ 419 static int is_errata93(struct pt_regs *regs, unsigned long address) 420 { 421 #if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD) 422 if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD 423 || boot_cpu_data.x86 != 0xf) 424 return 0; 425 426 if (user_mode(regs)) 427 return 0; 428 429 if (address != regs->ip) 430 return 0; 431 432 if ((address >> 32) != 0) 433 return 0; 434 435 address |= 0xffffffffUL << 32; 436 if ((address >= (u64)_stext && address <= (u64)_etext) || 437 (address >= MODULES_VADDR && address <= MODULES_END)) { 438 printk_once(errata93_warning); 439 regs->ip = address; 440 return 1; 441 } 442 #endif 443 return 0; 444 } 445 446 /* 447 * Work around K8 erratum #100 K8 in compat mode occasionally jumps 448 * to illegal addresses >4GB. 449 * 450 * We catch this in the page fault handler because these addresses 451 * are not reachable. Just detect this case and return. Any code 452 * segment in LDT is compatibility mode. 453 */ 454 static int is_errata100(struct pt_regs *regs, unsigned long address) 455 { 456 #ifdef CONFIG_X86_64 457 if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32)) 458 return 1; 459 #endif 460 return 0; 461 } 462 463 /* Pentium F0 0F C7 C8 bug workaround: */ 464 static int is_f00f_bug(struct pt_regs *regs, unsigned long error_code, 465 unsigned long address) 466 { 467 #ifdef CONFIG_X86_F00F_BUG 468 if (boot_cpu_has_bug(X86_BUG_F00F) && !(error_code & X86_PF_USER) && 469 idt_is_f00f_address(address)) { 470 handle_invalid_op(regs); 471 return 1; 472 } 473 #endif 474 return 0; 475 } 476 477 static void show_ldttss(const struct desc_ptr *gdt, const char *name, u16 index) 478 { 479 u32 offset = (index >> 3) * sizeof(struct desc_struct); 480 unsigned long addr; 481 struct ldttss_desc desc; 482 483 if (index == 0) { 484 pr_alert("%s: NULL\n", name); 485 return; 486 } 487 488 if (offset + sizeof(struct ldttss_desc) >= gdt->size) { 489 pr_alert("%s: 0x%hx -- out of bounds\n", name, index); 490 return; 491 } 492 493 if (copy_from_kernel_nofault(&desc, (void *)(gdt->address + offset), 494 sizeof(struct ldttss_desc))) { 495 pr_alert("%s: 0x%hx -- GDT entry is not readable\n", 496 name, index); 497 return; 498 } 499 500 addr = desc.base0 | (desc.base1 << 16) | ((unsigned long)desc.base2 << 24); 501 #ifdef CONFIG_X86_64 502 addr |= ((u64)desc.base3 << 32); 503 #endif 504 pr_alert("%s: 0x%hx -- base=0x%lx limit=0x%x\n", 505 name, index, addr, (desc.limit0 | (desc.limit1 << 16))); 506 } 507 508 static void 509 show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long address) 510 { 511 if (!oops_may_print()) 512 return; 513 514 if (error_code & X86_PF_INSTR) { 515 unsigned int level; 516 bool nx, rw; 517 pgd_t *pgd; 518 pte_t *pte; 519 520 pgd = __va(read_cr3_pa()); 521 pgd += pgd_index(address); 522 523 pte = lookup_address_in_pgd_attr(pgd, address, &level, &nx, &rw); 524 525 if (pte && pte_present(*pte) && (!pte_exec(*pte) || nx)) 526 pr_crit("kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n", 527 from_kuid(&init_user_ns, current_uid())); 528 if (pte && pte_present(*pte) && pte_exec(*pte) && !nx && 529 (pgd_flags(*pgd) & _PAGE_USER) && 530 (__read_cr4() & X86_CR4_SMEP)) 531 pr_crit("unable to execute userspace code (SMEP?) (uid: %d)\n", 532 from_kuid(&init_user_ns, current_uid())); 533 } 534 535 if (address < PAGE_SIZE && !user_mode(regs)) 536 pr_alert("BUG: kernel NULL pointer dereference, address: %px\n", 537 (void *)address); 538 else 539 pr_alert("BUG: unable to handle page fault for address: %px\n", 540 (void *)address); 541 542 pr_alert("#PF: %s %s in %s mode\n", 543 (error_code & X86_PF_USER) ? "user" : "supervisor", 544 (error_code & X86_PF_INSTR) ? "instruction fetch" : 545 (error_code & X86_PF_WRITE) ? "write access" : 546 "read access", 547 user_mode(regs) ? "user" : "kernel"); 548 pr_alert("#PF: error_code(0x%04lx) - %s\n", error_code, 549 !(error_code & X86_PF_PROT) ? "not-present page" : 550 (error_code & X86_PF_RSVD) ? "reserved bit violation" : 551 (error_code & X86_PF_PK) ? "protection keys violation" : 552 (error_code & X86_PF_RMP) ? "RMP violation" : 553 "permissions violation"); 554 555 if (!(error_code & X86_PF_USER) && user_mode(regs)) { 556 struct desc_ptr idt, gdt; 557 u16 ldtr, tr; 558 559 /* 560 * This can happen for quite a few reasons. The more obvious 561 * ones are faults accessing the GDT, or LDT. Perhaps 562 * surprisingly, if the CPU tries to deliver a benign or 563 * contributory exception from user code and gets a page fault 564 * during delivery, the page fault can be delivered as though 565 * it originated directly from user code. This could happen 566 * due to wrong permissions on the IDT, GDT, LDT, TSS, or 567 * kernel or IST stack. 568 */ 569 store_idt(&idt); 570 571 /* Usable even on Xen PV -- it's just slow. */ 572 native_store_gdt(&gdt); 573 574 pr_alert("IDT: 0x%lx (limit=0x%hx) GDT: 0x%lx (limit=0x%hx)\n", 575 idt.address, idt.size, gdt.address, gdt.size); 576 577 store_ldt(ldtr); 578 show_ldttss(&gdt, "LDTR", ldtr); 579 580 store_tr(tr); 581 show_ldttss(&gdt, "TR", tr); 582 } 583 584 dump_pagetable(address); 585 586 if (error_code & X86_PF_RMP) 587 snp_dump_hva_rmpentry(address); 588 } 589 590 static noinline void 591 pgtable_bad(struct pt_regs *regs, unsigned long error_code, 592 unsigned long address) 593 { 594 struct task_struct *tsk; 595 unsigned long flags; 596 int sig; 597 598 flags = oops_begin(); 599 tsk = current; 600 sig = SIGKILL; 601 602 printk(KERN_ALERT "%s: Corrupted page table at address %lx\n", 603 tsk->comm, address); 604 dump_pagetable(address); 605 606 if (__die("Bad pagetable", regs, error_code)) 607 sig = 0; 608 609 oops_end(flags, regs, sig); 610 } 611 612 static void sanitize_error_code(unsigned long address, 613 unsigned long *error_code) 614 { 615 /* 616 * To avoid leaking information about the kernel page 617 * table layout, pretend that user-mode accesses to 618 * kernel addresses are always protection faults. 619 * 620 * NB: This means that failed vsyscalls with vsyscall=none 621 * will have the PROT bit. This doesn't leak any 622 * information and does not appear to cause any problems. 623 */ 624 if (address >= TASK_SIZE_MAX) 625 *error_code |= X86_PF_PROT; 626 } 627 628 static void set_signal_archinfo(unsigned long address, 629 unsigned long error_code) 630 { 631 struct task_struct *tsk = current; 632 633 tsk->thread.trap_nr = X86_TRAP_PF; 634 tsk->thread.error_code = error_code | X86_PF_USER; 635 tsk->thread.cr2 = address; 636 } 637 638 static noinline void 639 page_fault_oops(struct pt_regs *regs, unsigned long error_code, 640 unsigned long address) 641 { 642 #ifdef CONFIG_VMAP_STACK 643 struct stack_info info; 644 #endif 645 unsigned long flags; 646 int sig; 647 648 if (user_mode(regs)) { 649 /* 650 * Implicit kernel access from user mode? Skip the stack 651 * overflow and EFI special cases. 652 */ 653 goto oops; 654 } 655 656 #ifdef CONFIG_VMAP_STACK 657 /* 658 * Stack overflow? During boot, we can fault near the initial 659 * stack in the direct map, but that's not an overflow -- check 660 * that we're in vmalloc space to avoid this. 661 */ 662 if (is_vmalloc_addr((void *)address) && 663 get_stack_guard_info((void *)address, &info)) { 664 /* 665 * We're likely to be running with very little stack space 666 * left. It's plausible that we'd hit this condition but 667 * double-fault even before we get this far, in which case 668 * we're fine: the double-fault handler will deal with it. 669 * 670 * We don't want to make it all the way into the oops code 671 * and then double-fault, though, because we're likely to 672 * break the console driver and lose most of the stack dump. 673 */ 674 call_on_stack(__this_cpu_ist_top_va(DF) - sizeof(void*), 675 handle_stack_overflow, 676 ASM_CALL_ARG3, 677 , [arg1] "r" (regs), [arg2] "r" (address), [arg3] "r" (&info)); 678 679 BUG(); 680 } 681 #endif 682 683 /* 684 * Buggy firmware could access regions which might page fault. If 685 * this happens, EFI has a special OOPS path that will try to 686 * avoid hanging the system. 687 */ 688 if (IS_ENABLED(CONFIG_EFI)) 689 efi_crash_gracefully_on_page_fault(address); 690 691 /* Only not-present faults should be handled by KFENCE. */ 692 if (!(error_code & X86_PF_PROT) && 693 kfence_handle_page_fault(address, error_code & X86_PF_WRITE, regs)) 694 return; 695 696 oops: 697 /* 698 * Oops. The kernel tried to access some bad page. We'll have to 699 * terminate things with extreme prejudice: 700 */ 701 flags = oops_begin(); 702 703 show_fault_oops(regs, error_code, address); 704 705 if (task_stack_end_corrupted(current)) 706 printk(KERN_EMERG "Thread overran stack, or stack corrupted\n"); 707 708 sig = SIGKILL; 709 if (__die("Oops", regs, error_code)) 710 sig = 0; 711 712 /* Executive summary in case the body of the oops scrolled away */ 713 printk(KERN_DEFAULT "CR2: %016lx\n", address); 714 715 oops_end(flags, regs, sig); 716 } 717 718 static noinline void 719 kernelmode_fixup_or_oops(struct pt_regs *regs, unsigned long error_code, 720 unsigned long address, int signal, int si_code, 721 u32 pkey) 722 { 723 WARN_ON_ONCE(user_mode(regs)); 724 725 /* Are we prepared to handle this kernel fault? */ 726 if (fixup_exception(regs, X86_TRAP_PF, error_code, address)) 727 return; 728 729 /* 730 * AMD erratum #91 manifests as a spurious page fault on a PREFETCH 731 * instruction. 732 */ 733 if (is_prefetch(regs, error_code, address)) 734 return; 735 736 page_fault_oops(regs, error_code, address); 737 } 738 739 /* 740 * Print out info about fatal segfaults, if the show_unhandled_signals 741 * sysctl is set: 742 */ 743 static inline void 744 show_signal_msg(struct pt_regs *regs, unsigned long error_code, 745 unsigned long address, struct task_struct *tsk) 746 { 747 const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG; 748 /* This is a racy snapshot, but it's better than nothing. */ 749 int cpu = raw_smp_processor_id(); 750 751 if (!unhandled_signal(tsk, SIGSEGV)) 752 return; 753 754 if (!printk_ratelimit()) 755 return; 756 757 printk("%s%s[%d]: segfault at %lx ip %px sp %px error %lx", 758 loglvl, tsk->comm, task_pid_nr(tsk), address, 759 (void *)regs->ip, (void *)regs->sp, error_code); 760 761 print_vma_addr(KERN_CONT " in ", regs->ip); 762 763 /* 764 * Dump the likely CPU where the fatal segfault happened. 765 * This can help identify faulty hardware. 766 */ 767 printk(KERN_CONT " likely on CPU %d (core %d, socket %d)", cpu, 768 topology_core_id(cpu), topology_physical_package_id(cpu)); 769 770 771 printk(KERN_CONT "\n"); 772 773 show_opcodes(regs, loglvl); 774 } 775 776 static void 777 __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, 778 unsigned long address, u32 pkey, int si_code) 779 { 780 struct task_struct *tsk = current; 781 782 if (!user_mode(regs)) { 783 kernelmode_fixup_or_oops(regs, error_code, address, 784 SIGSEGV, si_code, pkey); 785 return; 786 } 787 788 if (!(error_code & X86_PF_USER)) { 789 /* Implicit user access to kernel memory -- just oops */ 790 page_fault_oops(regs, error_code, address); 791 return; 792 } 793 794 /* 795 * User mode accesses just cause a SIGSEGV. 796 * It's possible to have interrupts off here: 797 */ 798 local_irq_enable(); 799 800 /* 801 * Valid to do another page fault here because this one came 802 * from user space: 803 */ 804 if (is_prefetch(regs, error_code, address)) 805 return; 806 807 if (is_errata100(regs, address)) 808 return; 809 810 sanitize_error_code(address, &error_code); 811 812 if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address)) 813 return; 814 815 if (likely(show_unhandled_signals)) 816 show_signal_msg(regs, error_code, address, tsk); 817 818 set_signal_archinfo(address, error_code); 819 820 if (si_code == SEGV_PKUERR) 821 force_sig_pkuerr((void __user *)address, pkey); 822 else 823 force_sig_fault(SIGSEGV, si_code, (void __user *)address); 824 825 local_irq_disable(); 826 } 827 828 static noinline void 829 bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code, 830 unsigned long address) 831 { 832 __bad_area_nosemaphore(regs, error_code, address, 0, SEGV_MAPERR); 833 } 834 835 static void 836 __bad_area(struct pt_regs *regs, unsigned long error_code, 837 unsigned long address, struct mm_struct *mm, 838 struct vm_area_struct *vma, u32 pkey, int si_code) 839 { 840 /* 841 * Something tried to access memory that isn't in our memory map.. 842 * Fix it, but check if it's kernel or user first.. 843 */ 844 if (mm) 845 mmap_read_unlock(mm); 846 else 847 vma_end_read(vma); 848 849 __bad_area_nosemaphore(regs, error_code, address, pkey, si_code); 850 } 851 852 static inline bool bad_area_access_from_pkeys(unsigned long error_code, 853 struct vm_area_struct *vma) 854 { 855 /* This code is always called on the current mm */ 856 bool foreign = false; 857 858 if (!cpu_feature_enabled(X86_FEATURE_OSPKE)) 859 return false; 860 if (error_code & X86_PF_PK) 861 return true; 862 /* this checks permission keys on the VMA: */ 863 if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE), 864 (error_code & X86_PF_INSTR), foreign)) 865 return true; 866 return false; 867 } 868 869 static noinline void 870 bad_area_access_error(struct pt_regs *regs, unsigned long error_code, 871 unsigned long address, struct mm_struct *mm, 872 struct vm_area_struct *vma) 873 { 874 /* 875 * This OSPKE check is not strictly necessary at runtime. 876 * But, doing it this way allows compiler optimizations 877 * if pkeys are compiled out. 878 */ 879 if (bad_area_access_from_pkeys(error_code, vma)) { 880 /* 881 * A protection key fault means that the PKRU value did not allow 882 * access to some PTE. Userspace can figure out what PKRU was 883 * from the XSAVE state. This function captures the pkey from 884 * the vma and passes it to userspace so userspace can discover 885 * which protection key was set on the PTE. 886 * 887 * If we get here, we know that the hardware signaled a X86_PF_PK 888 * fault and that there was a VMA once we got in the fault 889 * handler. It does *not* guarantee that the VMA we find here 890 * was the one that we faulted on. 891 * 892 * 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4); 893 * 2. T1 : set PKRU to deny access to pkey=4, touches page 894 * 3. T1 : faults... 895 * 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5); 896 * 5. T1 : enters fault handler, takes mmap_lock, etc... 897 * 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really 898 * faulted on a pte with its pkey=4. 899 */ 900 u32 pkey = vma_pkey(vma); 901 902 __bad_area(regs, error_code, address, mm, vma, pkey, SEGV_PKUERR); 903 } else { 904 __bad_area(regs, error_code, address, mm, vma, 0, SEGV_ACCERR); 905 } 906 } 907 908 static void 909 do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address, 910 vm_fault_t fault) 911 { 912 /* Kernel mode? Handle exceptions or die: */ 913 if (!user_mode(regs)) { 914 kernelmode_fixup_or_oops(regs, error_code, address, 915 SIGBUS, BUS_ADRERR, ARCH_DEFAULT_PKEY); 916 return; 917 } 918 919 /* User-space => ok to do another page fault: */ 920 if (is_prefetch(regs, error_code, address)) 921 return; 922 923 sanitize_error_code(address, &error_code); 924 925 if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address)) 926 return; 927 928 set_signal_archinfo(address, error_code); 929 930 #ifdef CONFIG_MEMORY_FAILURE 931 if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) { 932 struct task_struct *tsk = current; 933 unsigned lsb = 0; 934 935 pr_err( 936 "MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n", 937 tsk->comm, tsk->pid, address); 938 if (fault & VM_FAULT_HWPOISON_LARGE) 939 lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault)); 940 if (fault & VM_FAULT_HWPOISON) 941 lsb = PAGE_SHIFT; 942 force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb); 943 return; 944 } 945 #endif 946 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address); 947 } 948 949 static int spurious_kernel_fault_check(unsigned long error_code, pte_t *pte) 950 { 951 if ((error_code & X86_PF_WRITE) && !pte_write(*pte)) 952 return 0; 953 954 if ((error_code & X86_PF_INSTR) && !pte_exec(*pte)) 955 return 0; 956 957 return 1; 958 } 959 960 /* 961 * Handle a spurious fault caused by a stale TLB entry. 962 * 963 * This allows us to lazily refresh the TLB when increasing the 964 * permissions of a kernel page (RO -> RW or NX -> X). Doing it 965 * eagerly is very expensive since that implies doing a full 966 * cross-processor TLB flush, even if no stale TLB entries exist 967 * on other processors. 968 * 969 * Spurious faults may only occur if the TLB contains an entry with 970 * fewer permission than the page table entry. Non-present (P = 0) 971 * and reserved bit (R = 1) faults are never spurious. 972 * 973 * There are no security implications to leaving a stale TLB when 974 * increasing the permissions on a page. 975 * 976 * Returns non-zero if a spurious fault was handled, zero otherwise. 977 * 978 * See Intel Developer's Manual Vol 3 Section 4.10.4.3, bullet 3 979 * (Optional Invalidation). 980 */ 981 static noinline int 982 spurious_kernel_fault(unsigned long error_code, unsigned long address) 983 { 984 pgd_t *pgd; 985 p4d_t *p4d; 986 pud_t *pud; 987 pmd_t *pmd; 988 pte_t *pte; 989 int ret; 990 991 /* 992 * Only writes to RO or instruction fetches from NX may cause 993 * spurious faults. 994 * 995 * These could be from user or supervisor accesses but the TLB 996 * is only lazily flushed after a kernel mapping protection 997 * change, so user accesses are not expected to cause spurious 998 * faults. 999 */ 1000 if (error_code != (X86_PF_WRITE | X86_PF_PROT) && 1001 error_code != (X86_PF_INSTR | X86_PF_PROT)) 1002 return 0; 1003 1004 pgd = init_mm.pgd + pgd_index(address); 1005 if (!pgd_present(*pgd)) 1006 return 0; 1007 1008 p4d = p4d_offset(pgd, address); 1009 if (!p4d_present(*p4d)) 1010 return 0; 1011 1012 if (p4d_leaf(*p4d)) 1013 return spurious_kernel_fault_check(error_code, (pte_t *) p4d); 1014 1015 pud = pud_offset(p4d, address); 1016 if (!pud_present(*pud)) 1017 return 0; 1018 1019 if (pud_leaf(*pud)) 1020 return spurious_kernel_fault_check(error_code, (pte_t *) pud); 1021 1022 pmd = pmd_offset(pud, address); 1023 if (!pmd_present(*pmd)) 1024 return 0; 1025 1026 if (pmd_leaf(*pmd)) 1027 return spurious_kernel_fault_check(error_code, (pte_t *) pmd); 1028 1029 pte = pte_offset_kernel(pmd, address); 1030 if (!pte_present(*pte)) 1031 return 0; 1032 1033 ret = spurious_kernel_fault_check(error_code, pte); 1034 if (!ret) 1035 return 0; 1036 1037 /* 1038 * Make sure we have permissions in PMD. 1039 * If not, then there's a bug in the page tables: 1040 */ 1041 ret = spurious_kernel_fault_check(error_code, (pte_t *) pmd); 1042 WARN_ONCE(!ret, "PMD has incorrect permission bits\n"); 1043 1044 return ret; 1045 } 1046 NOKPROBE_SYMBOL(spurious_kernel_fault); 1047 1048 int show_unhandled_signals = 1; 1049 1050 static inline int 1051 access_error(unsigned long error_code, struct vm_area_struct *vma) 1052 { 1053 /* This is only called for the current mm, so: */ 1054 bool foreign = false; 1055 1056 /* 1057 * Read or write was blocked by protection keys. This is 1058 * always an unconditional error and can never result in 1059 * a follow-up action to resolve the fault, like a COW. 1060 */ 1061 if (error_code & X86_PF_PK) 1062 return 1; 1063 1064 /* 1065 * SGX hardware blocked the access. This usually happens 1066 * when the enclave memory contents have been destroyed, like 1067 * after a suspend/resume cycle. In any case, the kernel can't 1068 * fix the cause of the fault. Handle the fault as an access 1069 * error even in cases where no actual access violation 1070 * occurred. This allows userspace to rebuild the enclave in 1071 * response to the signal. 1072 */ 1073 if (unlikely(error_code & X86_PF_SGX)) 1074 return 1; 1075 1076 /* 1077 * Make sure to check the VMA so that we do not perform 1078 * faults just to hit a X86_PF_PK as soon as we fill in a 1079 * page. 1080 */ 1081 if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE), 1082 (error_code & X86_PF_INSTR), foreign)) 1083 return 1; 1084 1085 /* 1086 * Shadow stack accesses (PF_SHSTK=1) are only permitted to 1087 * shadow stack VMAs. All other accesses result in an error. 1088 */ 1089 if (error_code & X86_PF_SHSTK) { 1090 if (unlikely(!(vma->vm_flags & VM_SHADOW_STACK))) 1091 return 1; 1092 if (unlikely(!(vma->vm_flags & VM_WRITE))) 1093 return 1; 1094 return 0; 1095 } 1096 1097 if (error_code & X86_PF_WRITE) { 1098 /* write, present and write, not present: */ 1099 if (unlikely(vma->vm_flags & VM_SHADOW_STACK)) 1100 return 1; 1101 if (unlikely(!(vma->vm_flags & VM_WRITE))) 1102 return 1; 1103 return 0; 1104 } 1105 1106 /* read, present: */ 1107 if (unlikely(error_code & X86_PF_PROT)) 1108 return 1; 1109 1110 /* read, not present: */ 1111 if (unlikely(!vma_is_accessible(vma))) 1112 return 1; 1113 1114 return 0; 1115 } 1116 1117 bool fault_in_kernel_space(unsigned long address) 1118 { 1119 /* 1120 * On 64-bit systems, the vsyscall page is at an address above 1121 * TASK_SIZE_MAX, but is not considered part of the kernel 1122 * address space. 1123 */ 1124 if (IS_ENABLED(CONFIG_X86_64) && is_vsyscall_vaddr(address)) 1125 return false; 1126 1127 return address >= TASK_SIZE_MAX; 1128 } 1129 1130 /* 1131 * Called for all faults where 'address' is part of the kernel address 1132 * space. Might get called for faults that originate from *code* that 1133 * ran in userspace or the kernel. 1134 */ 1135 static void 1136 do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code, 1137 unsigned long address) 1138 { 1139 /* 1140 * Protection keys exceptions only happen on user pages. We 1141 * have no user pages in the kernel portion of the address 1142 * space, so do not expect them here. 1143 */ 1144 WARN_ON_ONCE(hw_error_code & X86_PF_PK); 1145 1146 #ifdef CONFIG_X86_32 1147 /* 1148 * We can fault-in kernel-space virtual memory on-demand. The 1149 * 'reference' page table is init_mm.pgd. 1150 * 1151 * NOTE! We MUST NOT take any locks for this case. We may 1152 * be in an interrupt or a critical region, and should 1153 * only copy the information from the master page table, 1154 * nothing more. 1155 * 1156 * Before doing this on-demand faulting, ensure that the 1157 * fault is not any of the following: 1158 * 1. A fault on a PTE with a reserved bit set. 1159 * 2. A fault caused by a user-mode access. (Do not demand- 1160 * fault kernel memory due to user-mode accesses). 1161 * 3. A fault caused by a page-level protection violation. 1162 * (A demand fault would be on a non-present page which 1163 * would have X86_PF_PROT==0). 1164 * 1165 * This is only needed to close a race condition on x86-32 in 1166 * the vmalloc mapping/unmapping code. See the comment above 1167 * vmalloc_fault() for details. On x86-64 the race does not 1168 * exist as the vmalloc mappings don't need to be synchronized 1169 * there. 1170 */ 1171 if (!(hw_error_code & (X86_PF_RSVD | X86_PF_USER | X86_PF_PROT))) { 1172 if (vmalloc_fault(address) >= 0) 1173 return; 1174 } 1175 #endif 1176 1177 if (is_f00f_bug(regs, hw_error_code, address)) 1178 return; 1179 1180 /* Was the fault spurious, caused by lazy TLB invalidation? */ 1181 if (spurious_kernel_fault(hw_error_code, address)) 1182 return; 1183 1184 /* kprobes don't want to hook the spurious faults: */ 1185 if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF))) 1186 return; 1187 1188 /* 1189 * Note, despite being a "bad area", there are quite a few 1190 * acceptable reasons to get here, such as erratum fixups 1191 * and handling kernel code that can fault, like get_user(). 1192 * 1193 * Don't take the mm semaphore here. If we fixup a prefetch 1194 * fault we could otherwise deadlock: 1195 */ 1196 bad_area_nosemaphore(regs, hw_error_code, address); 1197 } 1198 NOKPROBE_SYMBOL(do_kern_addr_fault); 1199 1200 /* 1201 * Handle faults in the user portion of the address space. Nothing in here 1202 * should check X86_PF_USER without a specific justification: for almost 1203 * all purposes, we should treat a normal kernel access to user memory 1204 * (e.g. get_user(), put_user(), etc.) the same as the WRUSS instruction. 1205 * The one exception is AC flag handling, which is, per the x86 1206 * architecture, special for WRUSS. 1207 */ 1208 static inline 1209 void do_user_addr_fault(struct pt_regs *regs, 1210 unsigned long error_code, 1211 unsigned long address) 1212 { 1213 struct vm_area_struct *vma; 1214 struct task_struct *tsk; 1215 struct mm_struct *mm; 1216 vm_fault_t fault; 1217 unsigned int flags = FAULT_FLAG_DEFAULT; 1218 1219 tsk = current; 1220 mm = tsk->mm; 1221 1222 if (unlikely((error_code & (X86_PF_USER | X86_PF_INSTR)) == X86_PF_INSTR)) { 1223 /* 1224 * Whoops, this is kernel mode code trying to execute from 1225 * user memory. Unless this is AMD erratum #93, which 1226 * corrupts RIP such that it looks like a user address, 1227 * this is unrecoverable. Don't even try to look up the 1228 * VMA or look for extable entries. 1229 */ 1230 if (is_errata93(regs, address)) 1231 return; 1232 1233 page_fault_oops(regs, error_code, address); 1234 return; 1235 } 1236 1237 /* kprobes don't want to hook the spurious faults: */ 1238 if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF))) 1239 return; 1240 1241 /* 1242 * Reserved bits are never expected to be set on 1243 * entries in the user portion of the page tables. 1244 */ 1245 if (unlikely(error_code & X86_PF_RSVD)) 1246 pgtable_bad(regs, error_code, address); 1247 1248 /* 1249 * If SMAP is on, check for invalid kernel (supervisor) access to user 1250 * pages in the user address space. The odd case here is WRUSS, 1251 * which, according to the preliminary documentation, does not respect 1252 * SMAP and will have the USER bit set so, in all cases, SMAP 1253 * enforcement appears to be consistent with the USER bit. 1254 */ 1255 if (unlikely(cpu_feature_enabled(X86_FEATURE_SMAP) && 1256 !(error_code & X86_PF_USER) && 1257 !(regs->flags & X86_EFLAGS_AC))) { 1258 /* 1259 * No extable entry here. This was a kernel access to an 1260 * invalid pointer. get_kernel_nofault() will not get here. 1261 */ 1262 page_fault_oops(regs, error_code, address); 1263 return; 1264 } 1265 1266 /* 1267 * If we're in an interrupt, have no user context or are running 1268 * in a region with pagefaults disabled then we must not take the fault 1269 */ 1270 if (unlikely(faulthandler_disabled() || !mm)) { 1271 bad_area_nosemaphore(regs, error_code, address); 1272 return; 1273 } 1274 1275 /* Legacy check - remove this after verifying that it doesn't trigger */ 1276 if (WARN_ON_ONCE(!(regs->flags & X86_EFLAGS_IF))) { 1277 bad_area_nosemaphore(regs, error_code, address); 1278 return; 1279 } 1280 1281 local_irq_enable(); 1282 1283 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address); 1284 1285 /* 1286 * Read-only permissions can not be expressed in shadow stack PTEs. 1287 * Treat all shadow stack accesses as WRITE faults. This ensures 1288 * that the MM will prepare everything (e.g., break COW) such that 1289 * maybe_mkwrite() can create a proper shadow stack PTE. 1290 */ 1291 if (error_code & X86_PF_SHSTK) 1292 flags |= FAULT_FLAG_WRITE; 1293 if (error_code & X86_PF_WRITE) 1294 flags |= FAULT_FLAG_WRITE; 1295 if (error_code & X86_PF_INSTR) 1296 flags |= FAULT_FLAG_INSTRUCTION; 1297 1298 /* 1299 * We set FAULT_FLAG_USER based on the register state, not 1300 * based on X86_PF_USER. User space accesses that cause 1301 * system page faults are still user accesses. 1302 */ 1303 if (user_mode(regs)) 1304 flags |= FAULT_FLAG_USER; 1305 1306 #ifdef CONFIG_X86_64 1307 /* 1308 * Faults in the vsyscall page might need emulation. The 1309 * vsyscall page is at a high address (>PAGE_OFFSET), but is 1310 * considered to be part of the user address space. 1311 * 1312 * The vsyscall page does not have a "real" VMA, so do this 1313 * emulation before we go searching for VMAs. 1314 * 1315 * PKRU never rejects instruction fetches, so we don't need 1316 * to consider the PF_PK bit. 1317 */ 1318 if (is_vsyscall_vaddr(address)) { 1319 if (emulate_vsyscall(error_code, regs, address)) 1320 return; 1321 } 1322 #endif 1323 1324 if (!(flags & FAULT_FLAG_USER)) 1325 goto lock_mmap; 1326 1327 vma = lock_vma_under_rcu(mm, address); 1328 if (!vma) 1329 goto lock_mmap; 1330 1331 if (unlikely(access_error(error_code, vma))) { 1332 bad_area_access_error(regs, error_code, address, NULL, vma); 1333 count_vm_vma_lock_event(VMA_LOCK_SUCCESS); 1334 return; 1335 } 1336 fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs); 1337 if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED))) 1338 vma_end_read(vma); 1339 1340 if (!(fault & VM_FAULT_RETRY)) { 1341 count_vm_vma_lock_event(VMA_LOCK_SUCCESS); 1342 goto done; 1343 } 1344 count_vm_vma_lock_event(VMA_LOCK_RETRY); 1345 if (fault & VM_FAULT_MAJOR) 1346 flags |= FAULT_FLAG_TRIED; 1347 1348 /* Quick path to respond to signals */ 1349 if (fault_signal_pending(fault, regs)) { 1350 if (!user_mode(regs)) 1351 kernelmode_fixup_or_oops(regs, error_code, address, 1352 SIGBUS, BUS_ADRERR, 1353 ARCH_DEFAULT_PKEY); 1354 return; 1355 } 1356 lock_mmap: 1357 1358 retry: 1359 vma = lock_mm_and_find_vma(mm, address, regs); 1360 if (unlikely(!vma)) { 1361 bad_area_nosemaphore(regs, error_code, address); 1362 return; 1363 } 1364 1365 /* 1366 * Ok, we have a good vm_area for this memory access, so 1367 * we can handle it.. 1368 */ 1369 if (unlikely(access_error(error_code, vma))) { 1370 bad_area_access_error(regs, error_code, address, mm, vma); 1371 return; 1372 } 1373 1374 /* 1375 * If for any reason at all we couldn't handle the fault, 1376 * make sure we exit gracefully rather than endlessly redo 1377 * the fault. Since we never set FAULT_FLAG_RETRY_NOWAIT, if 1378 * we get VM_FAULT_RETRY back, the mmap_lock has been unlocked. 1379 * 1380 * Note that handle_userfault() may also release and reacquire mmap_lock 1381 * (and not return with VM_FAULT_RETRY), when returning to userland to 1382 * repeat the page fault later with a VM_FAULT_NOPAGE retval 1383 * (potentially after handling any pending signal during the return to 1384 * userland). The return to userland is identified whenever 1385 * FAULT_FLAG_USER|FAULT_FLAG_KILLABLE are both set in flags. 1386 */ 1387 fault = handle_mm_fault(vma, address, flags, regs); 1388 1389 if (fault_signal_pending(fault, regs)) { 1390 /* 1391 * Quick path to respond to signals. The core mm code 1392 * has unlocked the mm for us if we get here. 1393 */ 1394 if (!user_mode(regs)) 1395 kernelmode_fixup_or_oops(regs, error_code, address, 1396 SIGBUS, BUS_ADRERR, 1397 ARCH_DEFAULT_PKEY); 1398 return; 1399 } 1400 1401 /* The fault is fully completed (including releasing mmap lock) */ 1402 if (fault & VM_FAULT_COMPLETED) 1403 return; 1404 1405 /* 1406 * If we need to retry the mmap_lock has already been released, 1407 * and if there is a fatal signal pending there is no guarantee 1408 * that we made any progress. Handle this case first. 1409 */ 1410 if (unlikely(fault & VM_FAULT_RETRY)) { 1411 flags |= FAULT_FLAG_TRIED; 1412 goto retry; 1413 } 1414 1415 mmap_read_unlock(mm); 1416 done: 1417 if (likely(!(fault & VM_FAULT_ERROR))) 1418 return; 1419 1420 if (fatal_signal_pending(current) && !user_mode(regs)) { 1421 kernelmode_fixup_or_oops(regs, error_code, address, 1422 0, 0, ARCH_DEFAULT_PKEY); 1423 return; 1424 } 1425 1426 if (fault & VM_FAULT_OOM) { 1427 /* Kernel mode? Handle exceptions or die: */ 1428 if (!user_mode(regs)) { 1429 kernelmode_fixup_or_oops(regs, error_code, address, 1430 SIGSEGV, SEGV_MAPERR, 1431 ARCH_DEFAULT_PKEY); 1432 return; 1433 } 1434 1435 /* 1436 * We ran out of memory, call the OOM killer, and return the 1437 * userspace (which will retry the fault, or kill us if we got 1438 * oom-killed): 1439 */ 1440 pagefault_out_of_memory(); 1441 } else { 1442 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON| 1443 VM_FAULT_HWPOISON_LARGE)) 1444 do_sigbus(regs, error_code, address, fault); 1445 else if (fault & VM_FAULT_SIGSEGV) 1446 bad_area_nosemaphore(regs, error_code, address); 1447 else 1448 BUG(); 1449 } 1450 } 1451 NOKPROBE_SYMBOL(do_user_addr_fault); 1452 1453 static __always_inline void 1454 trace_page_fault_entries(struct pt_regs *regs, unsigned long error_code, 1455 unsigned long address) 1456 { 1457 if (user_mode(regs)) 1458 trace_page_fault_user(address, regs, error_code); 1459 else 1460 trace_page_fault_kernel(address, regs, error_code); 1461 } 1462 1463 static __always_inline void 1464 handle_page_fault(struct pt_regs *regs, unsigned long error_code, 1465 unsigned long address) 1466 { 1467 trace_page_fault_entries(regs, error_code, address); 1468 1469 if (unlikely(kmmio_fault(regs, address))) 1470 return; 1471 1472 /* Was the fault on kernel-controlled part of the address space? */ 1473 if (unlikely(fault_in_kernel_space(address))) { 1474 do_kern_addr_fault(regs, error_code, address); 1475 } else { 1476 do_user_addr_fault(regs, error_code, address); 1477 /* 1478 * User address page fault handling might have reenabled 1479 * interrupts. Fixing up all potential exit points of 1480 * do_user_addr_fault() and its leaf functions is just not 1481 * doable w/o creating an unholy mess or turning the code 1482 * upside down. 1483 */ 1484 local_irq_disable(); 1485 } 1486 } 1487 1488 DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault) 1489 { 1490 irqentry_state_t state; 1491 unsigned long address; 1492 1493 address = cpu_feature_enabled(X86_FEATURE_FRED) ? fred_event_data(regs) : read_cr2(); 1494 1495 /* 1496 * KVM uses #PF vector to deliver 'page not present' events to guests 1497 * (asynchronous page fault mechanism). The event happens when a 1498 * userspace task is trying to access some valid (from guest's point of 1499 * view) memory which is not currently mapped by the host (e.g. the 1500 * memory is swapped out). Note, the corresponding "page ready" event 1501 * which is injected when the memory becomes available, is delivered via 1502 * an interrupt mechanism and not a #PF exception 1503 * (see arch/x86/kernel/kvm.c: sysvec_kvm_asyncpf_interrupt()). 1504 * 1505 * We are relying on the interrupted context being sane (valid RSP, 1506 * relevant locks not held, etc.), which is fine as long as the 1507 * interrupted context had IF=1. We are also relying on the KVM 1508 * async pf type field and CR2 being read consistently instead of 1509 * getting values from real and async page faults mixed up. 1510 * 1511 * Fingers crossed. 1512 * 1513 * The async #PF handling code takes care of idtentry handling 1514 * itself. 1515 */ 1516 if (kvm_handle_async_pf(regs, (u32)address)) 1517 return; 1518 1519 /* 1520 * Entry handling for valid #PF from kernel mode is slightly 1521 * different: RCU is already watching and ct_irq_enter() must not 1522 * be invoked because a kernel fault on a user space address might 1523 * sleep. 1524 * 1525 * In case the fault hit a RCU idle region the conditional entry 1526 * code reenabled RCU to avoid subsequent wreckage which helps 1527 * debuggability. 1528 */ 1529 state = irqentry_enter(regs); 1530 1531 instrumentation_begin(); 1532 handle_page_fault(regs, error_code, address); 1533 instrumentation_end(); 1534 1535 irqentry_exit(regs, state); 1536 } 1537