fault.c

   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 */
  46static nokprobe_inline int
  47kmmio_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 */
  70static inline int
  71check_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
 113static 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
 122static int
 123is_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
 171DEFINE_SPINLOCK(pgd_lock);
 172LIST_HEAD(pgd_list);
 173
 174#ifdef CONFIG_X86_32
 175static 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 */
 232static 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}
 263NOKPROBE_SYMBOL(vmalloc_fault);
 264
 265void 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
 289static bool low_pfn(unsigned long pfn)
 290{
 291	return pfn < max_low_pfn;
 292}
 293
 294static 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));
 328out:
 329	pr_cont("\n");
 330}
 331
 332#else /* CONFIG_X86_64: */
 333
 334#ifdef CONFIG_CPU_SUP_AMD
 335static const char errata93_warning[] =
 336KERN_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
 343static int bad_address(void *p)
 344{
 345	unsigned long dummy;
 346
 347	return get_kernel_nofault(dummy, (unsigned long *)p);
 348}
 349
 350static 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));
 396out:
 397	pr_cont("\n");
 398	return;
 399bad:
 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 */
 419static 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 */
 454static 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: */
 464static 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
 477static 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
 508static void
 509show_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
 590static noinline void
 591pgtable_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
 612static 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
 628static 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
 638static noinline void
 639page_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
 696oops:
 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
 718static noinline void
 719kernelmode_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 */
 743static inline void
 744show_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
 776static 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
 826static noinline void
 827bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
 828		     unsigned long address)
 829{
 830	__bad_area_nosemaphore(regs, error_code, address, 0, SEGV_MAPERR);
 831}
 832
 833static void
 834__bad_area(struct pt_regs *regs, unsigned long error_code,
 835	   unsigned long address, struct mm_struct *mm,
 836	   struct vm_area_struct *vma, u32 pkey, int si_code)
 837{
 838	/*
 839	 * Something tried to access memory that isn't in our memory map..
 840	 * Fix it, but check if it's kernel or user first..
 841	 */
 842	if (mm)
 843		mmap_read_unlock(mm);
 844	else
 845		vma_end_read(vma);
 846
 847	__bad_area_nosemaphore(regs, error_code, address, pkey, si_code);
 848}
 849
 850static inline bool bad_area_access_from_pkeys(unsigned long error_code,
 851		struct vm_area_struct *vma)
 852{
 853	/* This code is always called on the current mm */
 854	bool foreign = false;
 855
 856	if (!cpu_feature_enabled(X86_FEATURE_OSPKE))
 857		return false;
 858	if (error_code & X86_PF_PK)
 859		return true;
 860	/* this checks permission keys on the VMA: */
 861	if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE),
 862				       (error_code & X86_PF_INSTR), foreign))
 863		return true;
 864	return false;
 865}
 866
 867static noinline void
 868bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
 869		      unsigned long address, struct mm_struct *mm,
 870		      struct vm_area_struct *vma)
 871{
 872	/*
 873	 * This OSPKE check is not strictly necessary at runtime.
 874	 * But, doing it this way allows compiler optimizations
 875	 * if pkeys are compiled out.
 876	 */
 877	if (bad_area_access_from_pkeys(error_code, vma)) {
 878		/*
 879		 * A protection key fault means that the PKRU value did not allow
 880		 * access to some PTE.  Userspace can figure out what PKRU was
 881		 * from the XSAVE state.  This function captures the pkey from
 882		 * the vma and passes it to userspace so userspace can discover
 883		 * which protection key was set on the PTE.
 884		 *
 885		 * If we get here, we know that the hardware signaled a X86_PF_PK
 886		 * fault and that there was a VMA once we got in the fault
 887		 * handler.  It does *not* guarantee that the VMA we find here
 888		 * was the one that we faulted on.
 889		 *
 890		 * 1. T1   : mprotect_key(foo, PAGE_SIZE, pkey=4);
 891		 * 2. T1   : set PKRU to deny access to pkey=4, touches page
 892		 * 3. T1   : faults...
 893		 * 4.    T2: mprotect_key(foo, PAGE_SIZE, pkey=5);
 894		 * 5. T1   : enters fault handler, takes mmap_lock, etc...
 895		 * 6. T1   : reaches here, sees vma_pkey(vma)=5, when we really
 896		 *	     faulted on a pte with its pkey=4.
 897		 */
 898		u32 pkey = vma_pkey(vma);
 899
 900		__bad_area(regs, error_code, address, mm, vma, pkey, SEGV_PKUERR);
 901	} else {
 902		__bad_area(regs, error_code, address, mm, vma, 0, SEGV_ACCERR);
 903	}
 904}
 905
 906static void
 907do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
 908	  vm_fault_t fault)
 909{
 910	/* Kernel mode? Handle exceptions or die: */
 911	if (!user_mode(regs)) {
 912		kernelmode_fixup_or_oops(regs, error_code, address,
 913					 SIGBUS, BUS_ADRERR, ARCH_DEFAULT_PKEY);
 914		return;
 915	}
 916
 917	/* User-space => ok to do another page fault: */
 918	if (is_prefetch(regs, error_code, address))
 919		return;
 920
 921	sanitize_error_code(address, &error_code);
 922
 923	if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address))
 924		return;
 925
 926	set_signal_archinfo(address, error_code);
 927
 928#ifdef CONFIG_MEMORY_FAILURE
 929	if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
 930		struct task_struct *tsk = current;
 931		unsigned lsb = 0;
 932
 933		pr_err(
 934	"MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
 935			tsk->comm, tsk->pid, address);
 936		if (fault & VM_FAULT_HWPOISON_LARGE)
 937			lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
 938		if (fault & VM_FAULT_HWPOISON)
 939			lsb = PAGE_SHIFT;
 940		force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb);
 941		return;
 942	}
 943#endif
 944	force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
 945}
 946
 947static int spurious_kernel_fault_check(unsigned long error_code, pte_t *pte)
 948{
 949	if ((error_code & X86_PF_WRITE) && !pte_write(*pte))
 950		return 0;
 951
 952	if ((error_code & X86_PF_INSTR) && !pte_exec(*pte))
 953		return 0;
 954
 955	return 1;
 956}
 957
 958/*
 959 * Handle a spurious fault caused by a stale TLB entry.
 960 *
 961 * This allows us to lazily refresh the TLB when increasing the
 962 * permissions of a kernel page (RO -> RW or NX -> X).  Doing it
 963 * eagerly is very expensive since that implies doing a full
 964 * cross-processor TLB flush, even if no stale TLB entries exist
 965 * on other processors.
 966 *
 967 * Spurious faults may only occur if the TLB contains an entry with
 968 * fewer permission than the page table entry.  Non-present (P = 0)
 969 * and reserved bit (R = 1) faults are never spurious.
 970 *
 971 * There are no security implications to leaving a stale TLB when
 972 * increasing the permissions on a page.
 973 *
 974 * Returns non-zero if a spurious fault was handled, zero otherwise.
 975 *
 976 * See Intel Developer's Manual Vol 3 Section 4.10.4.3, bullet 3
 977 * (Optional Invalidation).
 978 */
 979static noinline int
 980spurious_kernel_fault(unsigned long error_code, unsigned long address)
 981{
 982	pgd_t *pgd;
 983	p4d_t *p4d;
 984	pud_t *pud;
 985	pmd_t *pmd;
 986	pte_t *pte;
 987	int ret;
 988
 989	/*
 990	 * Only writes to RO or instruction fetches from NX may cause
 991	 * spurious faults.
 992	 *
 993	 * These could be from user or supervisor accesses but the TLB
 994	 * is only lazily flushed after a kernel mapping protection
 995	 * change, so user accesses are not expected to cause spurious
 996	 * faults.
 997	 */
 998	if (error_code != (X86_PF_WRITE | X86_PF_PROT) &&
 999	    error_code != (X86_PF_INSTR | X86_PF_PROT))
1000		return 0;
1001
1002	pgd = init_mm.pgd + pgd_index(address);
1003	if (!pgd_present(*pgd))
1004		return 0;
1005
1006	p4d = p4d_offset(pgd, address);
1007	if (!p4d_present(*p4d))
1008		return 0;
1009
1010	if (p4d_leaf(*p4d))
1011		return spurious_kernel_fault_check(error_code, (pte_t *) p4d);
1012
1013	pud = pud_offset(p4d, address);
1014	if (!pud_present(*pud))
1015		return 0;
1016
1017	if (pud_leaf(*pud))
1018		return spurious_kernel_fault_check(error_code, (pte_t *) pud);
1019
1020	pmd = pmd_offset(pud, address);
1021	if (!pmd_present(*pmd))
1022		return 0;
1023
1024	if (pmd_leaf(*pmd))
1025		return spurious_kernel_fault_check(error_code, (pte_t *) pmd);
1026
1027	pte = pte_offset_kernel(pmd, address);
1028	if (!pte_present(*pte))
1029		return 0;
1030
1031	ret = spurious_kernel_fault_check(error_code, pte);
1032	if (!ret)
1033		return 0;
1034
1035	/*
1036	 * Make sure we have permissions in PMD.
1037	 * If not, then there's a bug in the page tables:
1038	 */
1039	ret = spurious_kernel_fault_check(error_code, (pte_t *) pmd);
1040	WARN_ONCE(!ret, "PMD has incorrect permission bits\n");
1041
1042	return ret;
1043}
1044NOKPROBE_SYMBOL(spurious_kernel_fault);
1045
1046int show_unhandled_signals = 1;
1047
1048static inline int
1049access_error(unsigned long error_code, struct vm_area_struct *vma)
1050{
1051	/* This is only called for the current mm, so: */
1052	bool foreign = false;
1053
1054	/*
1055	 * Read or write was blocked by protection keys.  This is
1056	 * always an unconditional error and can never result in
1057	 * a follow-up action to resolve the fault, like a COW.
1058	 */
1059	if (error_code & X86_PF_PK)
1060		return 1;
1061
1062	/*
1063	 * SGX hardware blocked the access.  This usually happens
1064	 * when the enclave memory contents have been destroyed, like
1065	 * after a suspend/resume cycle. In any case, the kernel can't
1066	 * fix the cause of the fault.  Handle the fault as an access
1067	 * error even in cases where no actual access violation
1068	 * occurred.  This allows userspace to rebuild the enclave in
1069	 * response to the signal.
1070	 */
1071	if (unlikely(error_code & X86_PF_SGX))
1072		return 1;
1073
1074	/*
1075	 * Make sure to check the VMA so that we do not perform
1076	 * faults just to hit a X86_PF_PK as soon as we fill in a
1077	 * page.
1078	 */
1079	if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE),
1080				       (error_code & X86_PF_INSTR), foreign))
1081		return 1;
1082
1083	/*
1084	 * Shadow stack accesses (PF_SHSTK=1) are only permitted to
1085	 * shadow stack VMAs. All other accesses result in an error.
1086	 */
1087	if (error_code & X86_PF_SHSTK) {
1088		if (unlikely(!(vma->vm_flags & VM_SHADOW_STACK)))
1089			return 1;
1090		if (unlikely(!(vma->vm_flags & VM_WRITE)))
1091			return 1;
1092		return 0;
1093	}
1094
1095	if (error_code & X86_PF_WRITE) {
1096		/* write, present and write, not present: */
1097		if (unlikely(vma->vm_flags & VM_SHADOW_STACK))
1098			return 1;
1099		if (unlikely(!(vma->vm_flags & VM_WRITE)))
1100			return 1;
1101		return 0;
1102	}
1103
1104	/* read, present: */
1105	if (unlikely(error_code & X86_PF_PROT))
1106		return 1;
1107
1108	/* read, not present: */
1109	if (unlikely(!vma_is_accessible(vma)))
1110		return 1;
1111
1112	return 0;
1113}
1114
1115bool fault_in_kernel_space(unsigned long address)
1116{
1117	/*
1118	 * On 64-bit systems, the vsyscall page is at an address above
1119	 * TASK_SIZE_MAX, but is not considered part of the kernel
1120	 * address space.
1121	 */
1122	if (IS_ENABLED(CONFIG_X86_64) && is_vsyscall_vaddr(address))
1123		return false;
1124
1125	return address >= TASK_SIZE_MAX;
1126}
1127
1128/*
1129 * Called for all faults where 'address' is part of the kernel address
1130 * space.  Might get called for faults that originate from *code* that
1131 * ran in userspace or the kernel.
1132 */
1133static void
1134do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code,
1135		   unsigned long address)
1136{
1137	/*
1138	 * Protection keys exceptions only happen on user pages.  We
1139	 * have no user pages in the kernel portion of the address
1140	 * space, so do not expect them here.
1141	 */
1142	WARN_ON_ONCE(hw_error_code & X86_PF_PK);
1143
1144#ifdef CONFIG_X86_32
1145	/*
1146	 * We can fault-in kernel-space virtual memory on-demand. The
1147	 * 'reference' page table is init_mm.pgd.
1148	 *
1149	 * NOTE! We MUST NOT take any locks for this case. We may
1150	 * be in an interrupt or a critical region, and should
1151	 * only copy the information from the master page table,
1152	 * nothing more.
1153	 *
1154	 * Before doing this on-demand faulting, ensure that the
1155	 * fault is not any of the following:
1156	 * 1. A fault on a PTE with a reserved bit set.
1157	 * 2. A fault caused by a user-mode access.  (Do not demand-
1158	 *    fault kernel memory due to user-mode accesses).
1159	 * 3. A fault caused by a page-level protection violation.
1160	 *    (A demand fault would be on a non-present page which
1161	 *     would have X86_PF_PROT==0).
1162	 *
1163	 * This is only needed to close a race condition on x86-32 in
1164	 * the vmalloc mapping/unmapping code. See the comment above
1165	 * vmalloc_fault() for details. On x86-64 the race does not
1166	 * exist as the vmalloc mappings don't need to be synchronized
1167	 * there.
1168	 */
1169	if (!(hw_error_code & (X86_PF_RSVD | X86_PF_USER | X86_PF_PROT))) {
1170		if (vmalloc_fault(address) >= 0)
1171			return;
1172	}
1173#endif
1174
1175	if (is_f00f_bug(regs, hw_error_code, address))
1176		return;
1177
1178	/* Was the fault spurious, caused by lazy TLB invalidation? */
1179	if (spurious_kernel_fault(hw_error_code, address))
1180		return;
1181
1182	/* kprobes don't want to hook the spurious faults: */
1183	if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF)))
1184		return;
1185
1186	/*
1187	 * Note, despite being a "bad area", there are quite a few
1188	 * acceptable reasons to get here, such as erratum fixups
1189	 * and handling kernel code that can fault, like get_user().
1190	 *
1191	 * Don't take the mm semaphore here. If we fixup a prefetch
1192	 * fault we could otherwise deadlock:
1193	 */
1194	bad_area_nosemaphore(regs, hw_error_code, address);
1195}
1196NOKPROBE_SYMBOL(do_kern_addr_fault);
1197
1198/*
1199 * Handle faults in the user portion of the address space.  Nothing in here
1200 * should check X86_PF_USER without a specific justification: for almost
1201 * all purposes, we should treat a normal kernel access to user memory
1202 * (e.g. get_user(), put_user(), etc.) the same as the WRUSS instruction.
1203 * The one exception is AC flag handling, which is, per the x86
1204 * architecture, special for WRUSS.
1205 */
1206static inline
1207void do_user_addr_fault(struct pt_regs *regs,
1208			unsigned long error_code,
1209			unsigned long address)
1210{
1211	struct vm_area_struct *vma;
1212	struct task_struct *tsk;
1213	struct mm_struct *mm;
1214	vm_fault_t fault;
1215	unsigned int flags = FAULT_FLAG_DEFAULT;
1216
1217	tsk = current;
1218	mm = tsk->mm;
1219
1220	if (unlikely((error_code & (X86_PF_USER | X86_PF_INSTR)) == X86_PF_INSTR)) {
1221		/*
1222		 * Whoops, this is kernel mode code trying to execute from
1223		 * user memory.  Unless this is AMD erratum #93, which
1224		 * corrupts RIP such that it looks like a user address,
1225		 * this is unrecoverable.  Don't even try to look up the
1226		 * VMA or look for extable entries.
1227		 */
1228		if (is_errata93(regs, address))
1229			return;
1230
1231		page_fault_oops(regs, error_code, address);
1232		return;
1233	}
1234
1235	/* kprobes don't want to hook the spurious faults: */
1236	if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF)))
1237		return;
1238
1239	/*
1240	 * Reserved bits are never expected to be set on
1241	 * entries in the user portion of the page tables.
1242	 */
1243	if (unlikely(error_code & X86_PF_RSVD))
1244		pgtable_bad(regs, error_code, address);
1245
1246	/*
1247	 * If SMAP is on, check for invalid kernel (supervisor) access to user
1248	 * pages in the user address space.  The odd case here is WRUSS,
1249	 * which, according to the preliminary documentation, does not respect
1250	 * SMAP and will have the USER bit set so, in all cases, SMAP
1251	 * enforcement appears to be consistent with the USER bit.
1252	 */
1253	if (unlikely(cpu_feature_enabled(X86_FEATURE_SMAP) &&
1254		     !(error_code & X86_PF_USER) &&
1255		     !(regs->flags & X86_EFLAGS_AC))) {
1256		/*
1257		 * No extable entry here.  This was a kernel access to an
1258		 * invalid pointer.  get_kernel_nofault() will not get here.
1259		 */
1260		page_fault_oops(regs, error_code, address);
1261		return;
1262	}
1263
1264	/*
1265	 * If we're in an interrupt, have no user context or are running
1266	 * in a region with pagefaults disabled then we must not take the fault
1267	 */
1268	if (unlikely(faulthandler_disabled() || !mm)) {
1269		bad_area_nosemaphore(regs, error_code, address);
1270		return;
1271	}
1272
1273	/* Legacy check - remove this after verifying that it doesn't trigger */
1274	if (WARN_ON_ONCE(!(regs->flags & X86_EFLAGS_IF))) {
1275		bad_area_nosemaphore(regs, error_code, address);
1276		return;
1277	}
1278
1279	local_irq_enable();
1280
1281	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
1282
1283	/*
1284	 * Read-only permissions can not be expressed in shadow stack PTEs.
1285	 * Treat all shadow stack accesses as WRITE faults. This ensures
1286	 * that the MM will prepare everything (e.g., break COW) such that
1287	 * maybe_mkwrite() can create a proper shadow stack PTE.
1288	 */
1289	if (error_code & X86_PF_SHSTK)
1290		flags |= FAULT_FLAG_WRITE;
1291	if (error_code & X86_PF_WRITE)
1292		flags |= FAULT_FLAG_WRITE;
1293	if (error_code & X86_PF_INSTR)
1294		flags |= FAULT_FLAG_INSTRUCTION;
1295
1296	/*
1297	 * We set FAULT_FLAG_USER based on the register state, not
1298	 * based on X86_PF_USER. User space accesses that cause
1299	 * system page faults are still user accesses.
1300	 */
1301	if (user_mode(regs))
1302		flags |= FAULT_FLAG_USER;
1303
1304#ifdef CONFIG_X86_64
1305	/*
1306	 * Faults in the vsyscall page might need emulation.  The
1307	 * vsyscall page is at a high address (>PAGE_OFFSET), but is
1308	 * considered to be part of the user address space.
1309	 *
1310	 * The vsyscall page does not have a "real" VMA, so do this
1311	 * emulation before we go searching for VMAs.
1312	 *
1313	 * PKRU never rejects instruction fetches, so we don't need
1314	 * to consider the PF_PK bit.
1315	 */
1316	if (is_vsyscall_vaddr(address)) {
1317		if (emulate_vsyscall(error_code, regs, address))
1318			return;
1319	}
1320#endif
1321
1322	if (!(flags & FAULT_FLAG_USER))
1323		goto lock_mmap;
1324
1325	vma = lock_vma_under_rcu(mm, address);
1326	if (!vma)
1327		goto lock_mmap;
1328
1329	if (unlikely(access_error(error_code, vma))) {
1330		bad_area_access_error(regs, error_code, address, NULL, vma);
1331		count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
1332		return;
1333	}
1334	fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
1335	if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
1336		vma_end_read(vma);
1337
1338	if (!(fault & VM_FAULT_RETRY)) {
1339		count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
1340		goto done;
1341	}
1342	count_vm_vma_lock_event(VMA_LOCK_RETRY);
1343	if (fault & VM_FAULT_MAJOR)
1344		flags |= FAULT_FLAG_TRIED;
1345
1346	/* Quick path to respond to signals */
1347	if (fault_signal_pending(fault, regs)) {
1348		if (!user_mode(regs))
1349			kernelmode_fixup_or_oops(regs, error_code, address,
1350						 SIGBUS, BUS_ADRERR,
1351						 ARCH_DEFAULT_PKEY);
1352		return;
1353	}
1354lock_mmap:
1355
1356retry:
1357	vma = lock_mm_and_find_vma(mm, address, regs);
1358	if (unlikely(!vma)) {
1359		bad_area_nosemaphore(regs, error_code, address);
1360		return;
1361	}
1362
1363	/*
1364	 * Ok, we have a good vm_area for this memory access, so
1365	 * we can handle it..
1366	 */
1367	if (unlikely(access_error(error_code, vma))) {
1368		bad_area_access_error(regs, error_code, address, mm, vma);
1369		return;
1370	}
1371
1372	/*
1373	 * If for any reason at all we couldn't handle the fault,
1374	 * make sure we exit gracefully rather than endlessly redo
1375	 * the fault.  Since we never set FAULT_FLAG_RETRY_NOWAIT, if
1376	 * we get VM_FAULT_RETRY back, the mmap_lock has been unlocked.
1377	 *
1378	 * Note that handle_userfault() may also release and reacquire mmap_lock
1379	 * (and not return with VM_FAULT_RETRY), when returning to userland to
1380	 * repeat the page fault later with a VM_FAULT_NOPAGE retval
1381	 * (potentially after handling any pending signal during the return to
1382	 * userland). The return to userland is identified whenever
1383	 * FAULT_FLAG_USER|FAULT_FLAG_KILLABLE are both set in flags.
1384	 */
1385	fault = handle_mm_fault(vma, address, flags, regs);
1386
1387	if (fault_signal_pending(fault, regs)) {
1388		/*
1389		 * Quick path to respond to signals.  The core mm code
1390		 * has unlocked the mm for us if we get here.
1391		 */
1392		if (!user_mode(regs))
1393			kernelmode_fixup_or_oops(regs, error_code, address,
1394						 SIGBUS, BUS_ADRERR,
1395						 ARCH_DEFAULT_PKEY);
1396		return;
1397	}
1398
1399	/* The fault is fully completed (including releasing mmap lock) */
1400	if (fault & VM_FAULT_COMPLETED)
1401		return;
1402
1403	/*
1404	 * If we need to retry the mmap_lock has already been released,
1405	 * and if there is a fatal signal pending there is no guarantee
1406	 * that we made any progress. Handle this case first.
1407	 */
1408	if (unlikely(fault & VM_FAULT_RETRY)) {
1409		flags |= FAULT_FLAG_TRIED;
1410		goto retry;
1411	}
1412
1413	mmap_read_unlock(mm);
1414done:
1415	if (likely(!(fault & VM_FAULT_ERROR)))
1416		return;
1417
1418	if (fatal_signal_pending(current) && !user_mode(regs)) {
1419		kernelmode_fixup_or_oops(regs, error_code, address,
1420					 0, 0, ARCH_DEFAULT_PKEY);
1421		return;
1422	}
1423
1424	if (fault & VM_FAULT_OOM) {
1425		/* Kernel mode? Handle exceptions or die: */
1426		if (!user_mode(regs)) {
1427			kernelmode_fixup_or_oops(regs, error_code, address,
1428						 SIGSEGV, SEGV_MAPERR,
1429						 ARCH_DEFAULT_PKEY);
1430			return;
1431		}
1432
1433		/*
1434		 * We ran out of memory, call the OOM killer, and return the
1435		 * userspace (which will retry the fault, or kill us if we got
1436		 * oom-killed):
1437		 */
1438		pagefault_out_of_memory();
1439	} else {
1440		if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
1441			     VM_FAULT_HWPOISON_LARGE))
1442			do_sigbus(regs, error_code, address, fault);
1443		else if (fault & VM_FAULT_SIGSEGV)
1444			bad_area_nosemaphore(regs, error_code, address);
1445		else
1446			BUG();
1447	}
1448}
1449NOKPROBE_SYMBOL(do_user_addr_fault);
1450
1451static __always_inline void
1452trace_page_fault_entries(struct pt_regs *regs, unsigned long error_code,
1453			 unsigned long address)
1454{
1455	if (user_mode(regs))
1456		trace_page_fault_user(address, regs, error_code);
1457	else
1458		trace_page_fault_kernel(address, regs, error_code);
1459}
1460
1461static __always_inline void
1462handle_page_fault(struct pt_regs *regs, unsigned long error_code,
1463			      unsigned long address)
1464{
1465	trace_page_fault_entries(regs, error_code, address);
1466
1467	if (unlikely(kmmio_fault(regs, address)))
1468		return;
1469
1470	/* Was the fault on kernel-controlled part of the address space? */
1471	if (unlikely(fault_in_kernel_space(address))) {
1472		do_kern_addr_fault(regs, error_code, address);
1473	} else {
1474		do_user_addr_fault(regs, error_code, address);
1475	}
1476	/*
1477	 * page fault handling might have reenabled interrupts,
1478	 * make sure to disable them again.
1479	 */
1480	local_irq_disable();
1481}
1482
1483DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault)
1484{
1485	irqentry_state_t state;
1486	unsigned long address;
1487
1488	address = cpu_feature_enabled(X86_FEATURE_FRED) ? fred_event_data(regs) : read_cr2();
1489
1490	/*
1491	 * KVM uses #PF vector to deliver 'page not present' events to guests
1492	 * (asynchronous page fault mechanism). The event happens when a
1493	 * userspace task is trying to access some valid (from guest's point of
1494	 * view) memory which is not currently mapped by the host (e.g. the
1495	 * memory is swapped out). Note, the corresponding "page ready" event
1496	 * which is injected when the memory becomes available, is delivered via
1497	 * an interrupt mechanism and not a #PF exception
1498	 * (see arch/x86/kernel/kvm.c: sysvec_kvm_asyncpf_interrupt()).
1499	 *
1500	 * We are relying on the interrupted context being sane (valid RSP,
1501	 * relevant locks not held, etc.), which is fine as long as the
1502	 * interrupted context had IF=1.  We are also relying on the KVM
1503	 * async pf type field and CR2 being read consistently instead of
1504	 * getting values from real and async page faults mixed up.
1505	 *
1506	 * Fingers crossed.
1507	 *
1508	 * The async #PF handling code takes care of idtentry handling
1509	 * itself.
1510	 */
1511	if (kvm_handle_async_pf(regs, (u32)address))
1512		return;
1513
1514	/*
1515	 * Entry handling for valid #PF from kernel mode is slightly
1516	 * different: RCU is already watching and ct_irq_enter() must not
1517	 * be invoked because a kernel fault on a user space address might
1518	 * sleep.
1519	 *
1520	 * In case the fault hit a RCU idle region the conditional entry
1521	 * code reenabled RCU to avoid subsequent wreckage which helps
1522	 * debuggability.
1523	 */
1524	state = irqentry_enter(regs);
1525
1526	instrumentation_begin();
1527	handle_page_fault(regs, error_code, address);
1528	instrumentation_end();
1529
1530	irqentry_exit(regs, state);
1531}