1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright (C) 1995 Linus Torvalds
4 * Copyright (C) 2001, 2002 Andi Kleen, SuSE Labs.
5 * Copyright (C) 2008-2009, Red Hat Inc., Ingo Molnar
6 */
7#include <linux/sched.h> /* test_thread_flag(), ... */
8#include <linux/sched/task_stack.h> /* task_stack_*(), ... */
9#include <linux/kdebug.h> /* oops_begin/end, ... */
10#include <linux/extable.h> /* search_exception_tables */
11#include <linux/memblock.h> /* max_low_pfn */
12#include <linux/kfence.h> /* kfence_handle_page_fault */
13#include <linux/kprobes.h> /* NOKPROBE_SYMBOL, ... */
14#include <linux/mmiotrace.h> /* kmmio_handler, ... */
15#include <linux/perf_event.h> /* perf_sw_event */
16#include <linux/hugetlb.h> /* hstate_index_to_shift */
17#include <linux/prefetch.h> /* prefetchw */
18#include <linux/context_tracking.h> /* exception_enter(), ... */
19#include <linux/uaccess.h> /* faulthandler_disabled() */
20#include <linux/efi.h> /* efi_crash_gracefully_on_page_fault()*/
21#include <linux/mm_types.h>
22#include <linux/mm.h> /* find_and_lock_vma() */
23
24#include <asm/cpufeature.h> /* boot_cpu_has, ... */
25#include <asm/traps.h> /* dotraplinkage, ... */
26#include <asm/fixmap.h> /* VSYSCALL_ADDR */
27#include <asm/vsyscall.h> /* emulate_vsyscall */
28#include <asm/vm86.h> /* struct vm86 */
29#include <asm/mmu_context.h> /* vma_pkey() */
30#include <asm/efi.h> /* efi_crash_gracefully_on_page_fault()*/
31#include <asm/desc.h> /* store_idt(), ... */
32#include <asm/cpu_entry_area.h> /* exception stack */
33#include <asm/pgtable_areas.h> /* VMALLOC_START, ... */
34#include <asm/kvm_para.h> /* kvm_handle_async_pf */
35#include <asm/vdso.h> /* fixup_vdso_exception() */
36#include <asm/irq_stack.h>
37
38#define CREATE_TRACE_POINTS
39#include <asm/trace/exceptions.h>
40
41/*
42 * Returns 0 if mmiotrace is disabled, or if the fault is not
43 * handled by mmiotrace:
44 */
45static nokprobe_inline int
46kmmio_fault(struct pt_regs *regs, unsigned long addr)
47{
48 if (unlikely(is_kmmio_active()))
49 if (kmmio_handler(regs, addr) == 1)
50 return -1;
51 return 0;
52}
53
54/*
55 * Prefetch quirks:
56 *
57 * 32-bit mode:
58 *
59 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
60 * Check that here and ignore it. This is AMD erratum #91.
61 *
62 * 64-bit mode:
63 *
64 * Sometimes the CPU reports invalid exceptions on prefetch.
65 * Check that here and ignore it.
66 *
67 * Opcode checker based on code by Richard Brunner.
68 */
69static inline int
70check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr,
71 unsigned char opcode, int *prefetch)
72{
73 unsigned char instr_hi = opcode & 0xf0;
74 unsigned char instr_lo = opcode & 0x0f;
75
76 switch (instr_hi) {
77 case 0x20:
78 case 0x30:
79 /*
80 * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes.
81 * In X86_64 long mode, the CPU will signal invalid
82 * opcode if some of these prefixes are present so
83 * X86_64 will never get here anyway
84 */
85 return ((instr_lo & 7) == 0x6);
86#ifdef CONFIG_X86_64
87 case 0x40:
88 /*
89 * In 64-bit mode 0x40..0x4F are valid REX prefixes
90 */
91 return (!user_mode(regs) || user_64bit_mode(regs));
92#endif
93 case 0x60:
94 /* 0x64 thru 0x67 are valid prefixes in all modes. */
95 return (instr_lo & 0xC) == 0x4;
96 case 0xF0:
97 /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */
98 return !instr_lo || (instr_lo>>1) == 1;
99 case 0x00:
100 /* Prefetch instruction is 0x0F0D or 0x0F18 */
101 if (get_kernel_nofault(opcode, instr))
102 return 0;
103
104 *prefetch = (instr_lo == 0xF) &&
105 (opcode == 0x0D || opcode == 0x18);
106 return 0;
107 default:
108 return 0;
109 }
110}
111
112static bool is_amd_k8_pre_npt(void)
113{
114 struct cpuinfo_x86 *c = &boot_cpu_data;
115
116 return unlikely(IS_ENABLED(CONFIG_CPU_SUP_AMD) &&
117 c->x86_vendor == X86_VENDOR_AMD &&
118 c->x86 == 0xf && c->x86_model < 0x40);
119}
120
121static int
122is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr)
123{
124 unsigned char *max_instr;
125 unsigned char *instr;
126 int prefetch = 0;
127
128 /* Erratum #91 affects AMD K8, pre-NPT CPUs */
129 if (!is_amd_k8_pre_npt())
130 return 0;
131
132 /*
133 * If it was a exec (instruction fetch) fault on NX page, then
134 * do not ignore the fault:
135 */
136 if (error_code & X86_PF_INSTR)
137 return 0;
138
139 instr = (void *)convert_ip_to_linear(current, regs);
140 max_instr = instr + 15;
141
142 /*
143 * This code has historically always bailed out if IP points to a
144 * not-present page (e.g. due to a race). No one has ever
145 * complained about this.
146 */
147 pagefault_disable();
148
149 while (instr < max_instr) {
150 unsigned char opcode;
151
152 if (user_mode(regs)) {
153 if (get_user(opcode, (unsigned char __user *) instr))
154 break;
155 } else {
156 if (get_kernel_nofault(opcode, instr))
157 break;
158 }
159
160 instr++;
161
162 if (!check_prefetch_opcode(regs, instr, opcode, prefetch: &prefetch))
163 break;
164 }
165
166 pagefault_enable();
167 return prefetch;
168}
169
170DEFINE_SPINLOCK(pgd_lock);
171LIST_HEAD(pgd_list);
172
173#ifdef CONFIG_X86_32
174static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
175{
176 unsigned index = pgd_index(address);
177 pgd_t *pgd_k;
178 p4d_t *p4d, *p4d_k;
179 pud_t *pud, *pud_k;
180 pmd_t *pmd, *pmd_k;
181
182 pgd += index;
183 pgd_k = init_mm.pgd + index;
184
185 if (!pgd_present(*pgd_k))
186 return NULL;
187
188 /*
189 * set_pgd(pgd, *pgd_k); here would be useless on PAE
190 * and redundant with the set_pmd() on non-PAE. As would
191 * set_p4d/set_pud.
192 */
193 p4d = p4d_offset(pgd, address);
194 p4d_k = p4d_offset(pgd_k, address);
195 if (!p4d_present(*p4d_k))
196 return NULL;
197
198 pud = pud_offset(p4d, address);
199 pud_k = pud_offset(p4d_k, address);
200 if (!pud_present(*pud_k))
201 return NULL;
202
203 pmd = pmd_offset(pud, address);
204 pmd_k = pmd_offset(pud_k, address);
205
206 if (pmd_present(*pmd) != pmd_present(*pmd_k))
207 set_pmd(pmd, *pmd_k);
208
209 if (!pmd_present(*pmd_k))
210 return NULL;
211 else
212 BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k));
213
214 return pmd_k;
215}
216
217/*
218 * Handle a fault on the vmalloc or module mapping area
219 *
220 * This is needed because there is a race condition between the time
221 * when the vmalloc mapping code updates the PMD to the point in time
222 * where it synchronizes this update with the other page-tables in the
223 * system.
224 *
225 * In this race window another thread/CPU can map an area on the same
226 * PMD, finds it already present and does not synchronize it with the
227 * rest of the system yet. As a result v[mz]alloc might return areas
228 * which are not mapped in every page-table in the system, causing an
229 * unhandled page-fault when they are accessed.
230 */
231static noinline int vmalloc_fault(unsigned long address)
232{
233 unsigned long pgd_paddr;
234 pmd_t *pmd_k;
235 pte_t *pte_k;
236
237 /* Make sure we are in vmalloc area: */
238 if (!(address >= VMALLOC_START && address < VMALLOC_END))
239 return -1;
240
241 /*
242 * Synchronize this task's top level page-table
243 * with the 'reference' page table.
244 *
245 * Do _not_ use "current" here. We might be inside
246 * an interrupt in the middle of a task switch..
247 */
248 pgd_paddr = read_cr3_pa();
249 pmd_k = vmalloc_sync_one(__va(pgd_paddr), address);
250 if (!pmd_k)
251 return -1;
252
253 if (pmd_large(*pmd_k))
254 return 0;
255
256 pte_k = pte_offset_kernel(pmd_k, address);
257 if (!pte_present(*pte_k))
258 return -1;
259
260 return 0;
261}
262NOKPROBE_SYMBOL(vmalloc_fault);
263
264void arch_sync_kernel_mappings(unsigned long start, unsigned long end)
265{
266 unsigned long addr;
267
268 for (addr = start & PMD_MASK;
269 addr >= TASK_SIZE_MAX && addr < VMALLOC_END;
270 addr += PMD_SIZE) {
271 struct page *page;
272
273 spin_lock(&pgd_lock);
274 list_for_each_entry(page, &pgd_list, lru) {
275 spinlock_t *pgt_lock;
276
277 /* the pgt_lock only for Xen */
278 pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
279
280 spin_lock(pgt_lock);
281 vmalloc_sync_one(page_address(page), addr);
282 spin_unlock(pgt_lock);
283 }
284 spin_unlock(&pgd_lock);
285 }
286}
287
288static bool low_pfn(unsigned long pfn)
289{
290 return pfn < max_low_pfn;
291}
292
293static void dump_pagetable(unsigned long address)
294{
295 pgd_t *base = __va(read_cr3_pa());
296 pgd_t *pgd = &base[pgd_index(address)];
297 p4d_t *p4d;
298 pud_t *pud;
299 pmd_t *pmd;
300 pte_t *pte;
301
302#ifdef CONFIG_X86_PAE
303 pr_info("*pdpt = %016Lx ", pgd_val(*pgd));
304 if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd))
305 goto out;
306#define pr_pde pr_cont
307#else
308#define pr_pde pr_info
309#endif
310 p4d = p4d_offset(pgd, address);
311 pud = pud_offset(p4d, address);
312 pmd = pmd_offset(pud, address);
313 pr_pde("*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd));
314#undef pr_pde
315
316 /*
317 * We must not directly access the pte in the highpte
318 * case if the page table is located in highmem.
319 * And let's rather not kmap-atomic the pte, just in case
320 * it's allocated already:
321 */
322 if (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_large(*pmd))
323 goto out;
324
325 pte = pte_offset_kernel(pmd, address);
326 pr_cont("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte));
327out:
328 pr_cont("\n");
329}
330
331#else /* CONFIG_X86_64: */
332
333#ifdef CONFIG_CPU_SUP_AMD
334static const char errata93_warning[] =
335KERN_ERR
336"******* Your BIOS seems to not contain a fix for K8 errata #93\n"
337"******* Working around it, but it may cause SEGVs or burn power.\n"
338"******* Please consider a BIOS update.\n"
339"******* Disabling USB legacy in the BIOS may also help.\n";
340#endif
341
342static int bad_address(void *p)
343{
344 unsigned long dummy;
345
346 return get_kernel_nofault(dummy, (unsigned long *)p);
347}
348
349static void dump_pagetable(unsigned long address)
350{
351 pgd_t *base = __va(read_cr3_pa());
352 pgd_t *pgd = base + pgd_index(address);
353 p4d_t *p4d;
354 pud_t *pud;
355 pmd_t *pmd;
356 pte_t *pte;
357
358 if (bad_address(p: pgd))
359 goto bad;
360
361 pr_info("PGD %lx ", pgd_val(*pgd));
362
363 if (!pgd_present(pgd: *pgd))
364 goto out;
365
366 p4d = p4d_offset(pgd, address);
367 if (bad_address(p: p4d))
368 goto bad;
369
370 pr_cont("P4D %lx ", p4d_val(*p4d));
371 if (!p4d_present(p4d: *p4d) || p4d_large(p4d: *p4d))
372 goto out;
373
374 pud = pud_offset(p4d, address);
375 if (bad_address(p: pud))
376 goto bad;
377
378 pr_cont("PUD %lx ", pud_val(*pud));
379 if (!pud_present(pud: *pud) || pud_large(pud: *pud))
380 goto out;
381
382 pmd = pmd_offset(pud, address);
383 if (bad_address(p: pmd))
384 goto bad;
385
386 pr_cont("PMD %lx ", pmd_val(*pmd));
387 if (!pmd_present(pmd: *pmd) || pmd_large(pte: *pmd))
388 goto out;
389
390 pte = pte_offset_kernel(pmd, address);
391 if (bad_address(p: pte))
392 goto bad;
393
394 pr_cont("PTE %lx", pte_val(*pte));
395out:
396 pr_cont("\n");
397 return;
398bad:
399 pr_info("BAD\n");
400}
401
402#endif /* CONFIG_X86_64 */
403
404/*
405 * Workaround for K8 erratum #93 & buggy BIOS.
406 *
407 * BIOS SMM functions are required to use a specific workaround
408 * to avoid corruption of the 64bit RIP register on C stepping K8.
409 *
410 * A lot of BIOS that didn't get tested properly miss this.
411 *
412 * The OS sees this as a page fault with the upper 32bits of RIP cleared.
413 * Try to work around it here.
414 *
415 * Note we only handle faults in kernel here.
416 * Does nothing on 32-bit.
417 */
418static int is_errata93(struct pt_regs *regs, unsigned long address)
419{
420#if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD)
421 if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD
422 || boot_cpu_data.x86 != 0xf)
423 return 0;
424
425 if (user_mode(regs))
426 return 0;
427
428 if (address != regs->ip)
429 return 0;
430
431 if ((address >> 32) != 0)
432 return 0;
433
434 address |= 0xffffffffUL << 32;
435 if ((address >= (u64)_stext && address <= (u64)_etext) ||
436 (address >= MODULES_VADDR && address <= MODULES_END)) {
437 printk_once(errata93_warning);
438 regs->ip = address;
439 return 1;
440 }
441#endif
442 return 0;
443}
444
445/*
446 * Work around K8 erratum #100 K8 in compat mode occasionally jumps
447 * to illegal addresses >4GB.
448 *
449 * We catch this in the page fault handler because these addresses
450 * are not reachable. Just detect this case and return. Any code
451 * segment in LDT is compatibility mode.
452 */
453static int is_errata100(struct pt_regs *regs, unsigned long address)
454{
455#ifdef CONFIG_X86_64
456 if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32))
457 return 1;
458#endif
459 return 0;
460}
461
462/* Pentium F0 0F C7 C8 bug workaround: */
463static int is_f00f_bug(struct pt_regs *regs, unsigned long error_code,
464 unsigned long address)
465{
466#ifdef CONFIG_X86_F00F_BUG
467 if (boot_cpu_has_bug(X86_BUG_F00F) && !(error_code & X86_PF_USER) &&
468 idt_is_f00f_address(address)) {
469 handle_invalid_op(regs);
470 return 1;
471 }
472#endif
473 return 0;
474}
475
476static void show_ldttss(const struct desc_ptr *gdt, const char *name, u16 index)
477{
478 u32 offset = (index >> 3) * sizeof(struct desc_struct);
479 unsigned long addr;
480 struct ldttss_desc desc;
481
482 if (index == 0) {
483 pr_alert("%s: NULL\n", name);
484 return;
485 }
486
487 if (offset + sizeof(struct ldttss_desc) >= gdt->size) {
488 pr_alert("%s: 0x%hx -- out of bounds\n", name, index);
489 return;
490 }
491
492 if (copy_from_kernel_nofault(dst: &desc, src: (void *)(gdt->address + offset),
493 size: sizeof(struct ldttss_desc))) {
494 pr_alert("%s: 0x%hx -- GDT entry is not readable\n",
495 name, index);
496 return;
497 }
498
499 addr = desc.base0 | (desc.base1 << 16) | ((unsigned long)desc.base2 << 24);
500#ifdef CONFIG_X86_64
501 addr |= ((u64)desc.base3 << 32);
502#endif
503 pr_alert("%s: 0x%hx -- base=0x%lx limit=0x%x\n",
504 name, index, addr, (desc.limit0 | (desc.limit1 << 16)));
505}
506
507static void
508show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long address)
509{
510 if (!oops_may_print())
511 return;
512
513 if (error_code & X86_PF_INSTR) {
514 unsigned int level;
515 pgd_t *pgd;
516 pte_t *pte;
517
518 pgd = __va(read_cr3_pa());
519 pgd += pgd_index(address);
520
521 pte = lookup_address_in_pgd(pgd, address, level: &level);
522
523 if (pte && pte_present(a: *pte) && !pte_exec(pte: *pte))
524 pr_crit("kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n",
525 from_kuid(&init_user_ns, current_uid()));
526 if (pte && pte_present(a: *pte) && pte_exec(pte: *pte) &&
527 (pgd_flags(pgd: *pgd) & _PAGE_USER) &&
528 (__read_cr4() & X86_CR4_SMEP))
529 pr_crit("unable to execute userspace code (SMEP?) (uid: %d)\n",
530 from_kuid(&init_user_ns, current_uid()));
531 }
532
533 if (address < PAGE_SIZE && !user_mode(regs))
534 pr_alert("BUG: kernel NULL pointer dereference, address: %px\n",
535 (void *)address);
536 else
537 pr_alert("BUG: unable to handle page fault for address: %px\n",
538 (void *)address);
539
540 pr_alert("#PF: %s %s in %s mode\n",
541 (error_code & X86_PF_USER) ? "user" : "supervisor",
542 (error_code & X86_PF_INSTR) ? "instruction fetch" :
543 (error_code & X86_PF_WRITE) ? "write access" :
544 "read access",
545 user_mode(regs) ? "user" : "kernel");
546 pr_alert("#PF: error_code(0x%04lx) - %s\n", error_code,
547 !(error_code & X86_PF_PROT) ? "not-present page" :
548 (error_code & X86_PF_RSVD) ? "reserved bit violation" :
549 (error_code & X86_PF_PK) ? "protection keys violation" :
550 "permissions violation");
551
552 if (!(error_code & X86_PF_USER) && user_mode(regs)) {
553 struct desc_ptr idt, gdt;
554 u16 ldtr, tr;
555
556 /*
557 * This can happen for quite a few reasons. The more obvious
558 * ones are faults accessing the GDT, or LDT. Perhaps
559 * surprisingly, if the CPU tries to deliver a benign or
560 * contributory exception from user code and gets a page fault
561 * during delivery, the page fault can be delivered as though
562 * it originated directly from user code. This could happen
563 * due to wrong permissions on the IDT, GDT, LDT, TSS, or
564 * kernel or IST stack.
565 */
566 store_idt(dtr: &idt);
567
568 /* Usable even on Xen PV -- it's just slow. */
569 native_store_gdt(dtr: &gdt);
570
571 pr_alert("IDT: 0x%lx (limit=0x%hx) GDT: 0x%lx (limit=0x%hx)\n",
572 idt.address, idt.size, gdt.address, gdt.size);
573
574 store_ldt(ldtr);
575 show_ldttss(gdt: &gdt, name: "LDTR", index: ldtr);
576
577 store_tr(tr);
578 show_ldttss(gdt: &gdt, name: "TR", index: tr);
579 }
580
581 dump_pagetable(address);
582}
583
584static noinline void
585pgtable_bad(struct pt_regs *regs, unsigned long error_code,
586 unsigned long address)
587{
588 struct task_struct *tsk;
589 unsigned long flags;
590 int sig;
591
592 flags = oops_begin();
593 tsk = current;
594 sig = SIGKILL;
595
596 printk(KERN_ALERT "%s: Corrupted page table at address %lx\n",
597 tsk->comm, address);
598 dump_pagetable(address);
599
600 if (__die("Bad pagetable", regs, error_code))
601 sig = 0;
602
603 oops_end(flags, regs, signr: sig);
604}
605
606static void sanitize_error_code(unsigned long address,
607 unsigned long *error_code)
608{
609 /*
610 * To avoid leaking information about the kernel page
611 * table layout, pretend that user-mode accesses to
612 * kernel addresses are always protection faults.
613 *
614 * NB: This means that failed vsyscalls with vsyscall=none
615 * will have the PROT bit. This doesn't leak any
616 * information and does not appear to cause any problems.
617 */
618 if (address >= TASK_SIZE_MAX)
619 *error_code |= X86_PF_PROT;
620}
621
622static void set_signal_archinfo(unsigned long address,
623 unsigned long error_code)
624{
625 struct task_struct *tsk = current;
626
627 tsk->thread.trap_nr = X86_TRAP_PF;
628 tsk->thread.error_code = error_code | X86_PF_USER;
629 tsk->thread.cr2 = address;
630}
631
632static noinline void
633page_fault_oops(struct pt_regs *regs, unsigned long error_code,
634 unsigned long address)
635{
636#ifdef CONFIG_VMAP_STACK
637 struct stack_info info;
638#endif
639 unsigned long flags;
640 int sig;
641
642 if (user_mode(regs)) {
643 /*
644 * Implicit kernel access from user mode? Skip the stack
645 * overflow and EFI special cases.
646 */
647 goto oops;
648 }
649
650#ifdef CONFIG_VMAP_STACK
651 /*
652 * Stack overflow? During boot, we can fault near the initial
653 * stack in the direct map, but that's not an overflow -- check
654 * that we're in vmalloc space to avoid this.
655 */
656 if (is_vmalloc_addr(x: (void *)address) &&
657 get_stack_guard_info(stack: (void *)address, info: &info)) {
658 /*
659 * We're likely to be running with very little stack space
660 * left. It's plausible that we'd hit this condition but
661 * double-fault even before we get this far, in which case
662 * we're fine: the double-fault handler will deal with it.
663 *
664 * We don't want to make it all the way into the oops code
665 * and then double-fault, though, because we're likely to
666 * break the console driver and lose most of the stack dump.
667 */
668 call_on_stack(__this_cpu_ist_top_va(DF) - sizeof(void*),
669 handle_stack_overflow,
670 ASM_CALL_ARG3,
671 , [arg1] "r" (regs), [arg2] "r" (address), [arg3] "r" (&info));
672
673 unreachable();
674 }
675#endif
676
677 /*
678 * Buggy firmware could access regions which might page fault. If
679 * this happens, EFI has a special OOPS path that will try to
680 * avoid hanging the system.
681 */
682 if (IS_ENABLED(CONFIG_EFI))
683 efi_crash_gracefully_on_page_fault(phys_addr: address);
684
685 /* Only not-present faults should be handled by KFENCE. */
686 if (!(error_code & X86_PF_PROT) &&
687 kfence_handle_page_fault(addr: address, is_write: error_code & X86_PF_WRITE, regs))
688 return;
689
690oops:
691 /*
692 * Oops. The kernel tried to access some bad page. We'll have to
693 * terminate things with extreme prejudice:
694 */
695 flags = oops_begin();
696
697 show_fault_oops(regs, error_code, address);
698
699 if (task_stack_end_corrupted(current))
700 printk(KERN_EMERG "Thread overran stack, or stack corrupted\n");
701
702 sig = SIGKILL;
703 if (__die("Oops", regs, error_code))
704 sig = 0;
705
706 /* Executive summary in case the body of the oops scrolled away */
707 printk(KERN_DEFAULT "CR2: %016lx\n", address);
708
709 oops_end(flags, regs, signr: sig);
710}
711
712static noinline void
713kernelmode_fixup_or_oops(struct pt_regs *regs, unsigned long error_code,
714 unsigned long address, int signal, int si_code,
715 u32 pkey)
716{
717 WARN_ON_ONCE(user_mode(regs));
718
719 /* Are we prepared to handle this kernel fault? */
720 if (fixup_exception(regs, X86_TRAP_PF, error_code, fault_addr: address)) {
721 /*
722 * Any interrupt that takes a fault gets the fixup. This makes
723 * the below recursive fault logic only apply to a faults from
724 * task context.
725 */
726 if (in_interrupt())
727 return;
728
729 /*
730 * Per the above we're !in_interrupt(), aka. task context.
731 *
732 * In this case we need to make sure we're not recursively
733 * faulting through the emulate_vsyscall() logic.
734 */
735 if (current->thread.sig_on_uaccess_err && signal) {
736 sanitize_error_code(address, error_code: &error_code);
737
738 set_signal_archinfo(address, error_code);
739
740 if (si_code == SEGV_PKUERR) {
741 force_sig_pkuerr(addr: (void __user *)address, pkey);
742 } else {
743 /* XXX: hwpoison faults will set the wrong code. */
744 force_sig_fault(sig: signal, code: si_code, addr: (void __user *)address);
745 }
746 }
747
748 /*
749 * Barring that, we can do the fixup and be happy.
750 */
751 return;
752 }
753
754 /*
755 * AMD erratum #91 manifests as a spurious page fault on a PREFETCH
756 * instruction.
757 */
758 if (is_prefetch(regs, error_code, addr: address))
759 return;
760
761 page_fault_oops(regs, error_code, address);
762}
763
764/*
765 * Print out info about fatal segfaults, if the show_unhandled_signals
766 * sysctl is set:
767 */
768static inline void
769show_signal_msg(struct pt_regs *regs, unsigned long error_code,
770 unsigned long address, struct task_struct *tsk)
771{
772 const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG;
773 /* This is a racy snapshot, but it's better than nothing. */
774 int cpu = raw_smp_processor_id();
775
776 if (!unhandled_signal(tsk, SIGSEGV))
777 return;
778
779 if (!printk_ratelimit())
780 return;
781
782 printk("%s%s[%d]: segfault at %lx ip %px sp %px error %lx",
783 loglvl, tsk->comm, task_pid_nr(tsk), address,
784 (void *)regs->ip, (void *)regs->sp, error_code);
785
786 print_vma_addr(KERN_CONT " in ", rip: regs->ip);
787
788 /*
789 * Dump the likely CPU where the fatal segfault happened.
790 * This can help identify faulty hardware.
791 */
792 printk(KERN_CONT " likely on CPU %d (core %d, socket %d)", cpu,
793 topology_core_id(cpu), topology_physical_package_id(cpu));
794
795
796 printk(KERN_CONT "\n");
797
798 show_opcodes(regs, loglvl);
799}
800
801/*
802 * The (legacy) vsyscall page is the long page in the kernel portion
803 * of the address space that has user-accessible permissions.
804 */
805static bool is_vsyscall_vaddr(unsigned long vaddr)
806{
807 return unlikely((vaddr & PAGE_MASK) == VSYSCALL_ADDR);
808}
809
810static void
811__bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
812 unsigned long address, u32 pkey, int si_code)
813{
814 struct task_struct *tsk = current;
815
816 if (!user_mode(regs)) {
817 kernelmode_fixup_or_oops(regs, error_code, address,
818 SIGSEGV, si_code, pkey);
819 return;
820 }
821
822 if (!(error_code & X86_PF_USER)) {
823 /* Implicit user access to kernel memory -- just oops */
824 page_fault_oops(regs, error_code, address);
825 return;
826 }
827
828 /*
829 * User mode accesses just cause a SIGSEGV.
830 * It's possible to have interrupts off here:
831 */
832 local_irq_enable();
833
834 /*
835 * Valid to do another page fault here because this one came
836 * from user space:
837 */
838 if (is_prefetch(regs, error_code, addr: address))
839 return;
840
841 if (is_errata100(regs, address))
842 return;
843
844 sanitize_error_code(address, error_code: &error_code);
845
846 if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, fault_addr: address))
847 return;
848
849 if (likely(show_unhandled_signals))
850 show_signal_msg(regs, error_code, address, tsk);
851
852 set_signal_archinfo(address, error_code);
853
854 if (si_code == SEGV_PKUERR)
855 force_sig_pkuerr(addr: (void __user *)address, pkey);
856 else
857 force_sig_fault(SIGSEGV, code: si_code, addr: (void __user *)address);
858
859 local_irq_disable();
860}
861
862static noinline void
863bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
864 unsigned long address)
865{
866 __bad_area_nosemaphore(regs, error_code, address, pkey: 0, SEGV_MAPERR);
867}
868
869static void
870__bad_area(struct pt_regs *regs, unsigned long error_code,
871 unsigned long address, u32 pkey, int si_code)
872{
873 struct mm_struct *mm = current->mm;
874 /*
875 * Something tried to access memory that isn't in our memory map..
876 * Fix it, but check if it's kernel or user first..
877 */
878 mmap_read_unlock(mm);
879
880 __bad_area_nosemaphore(regs, error_code, address, pkey, si_code);
881}
882
883static inline bool bad_area_access_from_pkeys(unsigned long error_code,
884 struct vm_area_struct *vma)
885{
886 /* This code is always called on the current mm */
887 bool foreign = false;
888
889 if (!cpu_feature_enabled(X86_FEATURE_OSPKE))
890 return false;
891 if (error_code & X86_PF_PK)
892 return true;
893 /* this checks permission keys on the VMA: */
894 if (!arch_vma_access_permitted(vma, write: (error_code & X86_PF_WRITE),
895 execute: (error_code & X86_PF_INSTR), foreign))
896 return true;
897 return false;
898}
899
900static noinline void
901bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
902 unsigned long address, struct vm_area_struct *vma)
903{
904 /*
905 * This OSPKE check is not strictly necessary at runtime.
906 * But, doing it this way allows compiler optimizations
907 * if pkeys are compiled out.
908 */
909 if (bad_area_access_from_pkeys(error_code, vma)) {
910 /*
911 * A protection key fault means that the PKRU value did not allow
912 * access to some PTE. Userspace can figure out what PKRU was
913 * from the XSAVE state. This function captures the pkey from
914 * the vma and passes it to userspace so userspace can discover
915 * which protection key was set on the PTE.
916 *
917 * If we get here, we know that the hardware signaled a X86_PF_PK
918 * fault and that there was a VMA once we got in the fault
919 * handler. It does *not* guarantee that the VMA we find here
920 * was the one that we faulted on.
921 *
922 * 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4);
923 * 2. T1 : set PKRU to deny access to pkey=4, touches page
924 * 3. T1 : faults...
925 * 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5);
926 * 5. T1 : enters fault handler, takes mmap_lock, etc...
927 * 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really
928 * faulted on a pte with its pkey=4.
929 */
930 u32 pkey = vma_pkey(vma);
931
932 __bad_area(regs, error_code, address, pkey, SEGV_PKUERR);
933 } else {
934 __bad_area(regs, error_code, address, pkey: 0, SEGV_ACCERR);
935 }
936}
937
938static void
939do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
940 vm_fault_t fault)
941{
942 /* Kernel mode? Handle exceptions or die: */
943 if (!user_mode(regs)) {
944 kernelmode_fixup_or_oops(regs, error_code, address,
945 SIGBUS, BUS_ADRERR, ARCH_DEFAULT_PKEY);
946 return;
947 }
948
949 /* User-space => ok to do another page fault: */
950 if (is_prefetch(regs, error_code, addr: address))
951 return;
952
953 sanitize_error_code(address, error_code: &error_code);
954
955 if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, fault_addr: address))
956 return;
957
958 set_signal_archinfo(address, error_code);
959
960#ifdef CONFIG_MEMORY_FAILURE
961 if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
962 struct task_struct *tsk = current;
963 unsigned lsb = 0;
964
965 pr_err(
966 "MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
967 tsk->comm, tsk->pid, address);
968 if (fault & VM_FAULT_HWPOISON_LARGE)
969 lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
970 if (fault & VM_FAULT_HWPOISON)
971 lsb = PAGE_SHIFT;
972 force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb);
973 return;
974 }
975#endif
976 force_sig_fault(SIGBUS, BUS_ADRERR, addr: (void __user *)address);
977}
978
979static int spurious_kernel_fault_check(unsigned long error_code, pte_t *pte)
980{
981 if ((error_code & X86_PF_WRITE) && !pte_write(pte: *pte))
982 return 0;
983
984 if ((error_code & X86_PF_INSTR) && !pte_exec(pte: *pte))
985 return 0;
986
987 return 1;
988}
989
990/*
991 * Handle a spurious fault caused by a stale TLB entry.
992 *
993 * This allows us to lazily refresh the TLB when increasing the
994 * permissions of a kernel page (RO -> RW or NX -> X). Doing it
995 * eagerly is very expensive since that implies doing a full
996 * cross-processor TLB flush, even if no stale TLB entries exist
997 * on other processors.
998 *
999 * Spurious faults may only occur if the TLB contains an entry with
1000 * fewer permission than the page table entry. Non-present (P = 0)
1001 * and reserved bit (R = 1) faults are never spurious.
1002 *
1003 * There are no security implications to leaving a stale TLB when
1004 * increasing the permissions on a page.
1005 *
1006 * Returns non-zero if a spurious fault was handled, zero otherwise.
1007 *
1008 * See Intel Developer's Manual Vol 3 Section 4.10.4.3, bullet 3
1009 * (Optional Invalidation).
1010 */
1011static noinline int
1012spurious_kernel_fault(unsigned long error_code, unsigned long address)
1013{
1014 pgd_t *pgd;
1015 p4d_t *p4d;
1016 pud_t *pud;
1017 pmd_t *pmd;
1018 pte_t *pte;
1019 int ret;
1020
1021 /*
1022 * Only writes to RO or instruction fetches from NX may cause
1023 * spurious faults.
1024 *
1025 * These could be from user or supervisor accesses but the TLB
1026 * is only lazily flushed after a kernel mapping protection
1027 * change, so user accesses are not expected to cause spurious
1028 * faults.
1029 */
1030 if (error_code != (X86_PF_WRITE | X86_PF_PROT) &&
1031 error_code != (X86_PF_INSTR | X86_PF_PROT))
1032 return 0;
1033
1034 pgd = init_mm.pgd + pgd_index(address);
1035 if (!pgd_present(pgd: *pgd))
1036 return 0;
1037
1038 p4d = p4d_offset(pgd, address);
1039 if (!p4d_present(p4d: *p4d))
1040 return 0;
1041
1042 if (p4d_large(p4d: *p4d))
1043 return spurious_kernel_fault_check(error_code, pte: (pte_t *) p4d);
1044
1045 pud = pud_offset(p4d, address);
1046 if (!pud_present(pud: *pud))
1047 return 0;
1048
1049 if (pud_large(pud: *pud))
1050 return spurious_kernel_fault_check(error_code, pte: (pte_t *) pud);
1051
1052 pmd = pmd_offset(pud, address);
1053 if (!pmd_present(pmd: *pmd))
1054 return 0;
1055
1056 if (pmd_large(pte: *pmd))
1057 return spurious_kernel_fault_check(error_code, pte: (pte_t *) pmd);
1058
1059 pte = pte_offset_kernel(pmd, address);
1060 if (!pte_present(a: *pte))
1061 return 0;
1062
1063 ret = spurious_kernel_fault_check(error_code, pte);
1064 if (!ret)
1065 return 0;
1066
1067 /*
1068 * Make sure we have permissions in PMD.
1069 * If not, then there's a bug in the page tables:
1070 */
1071 ret = spurious_kernel_fault_check(error_code, pte: (pte_t *) pmd);
1072 WARN_ONCE(!ret, "PMD has incorrect permission bits\n");
1073
1074 return ret;
1075}
1076NOKPROBE_SYMBOL(spurious_kernel_fault);
1077
1078int show_unhandled_signals = 1;
1079
1080static inline int
1081access_error(unsigned long error_code, struct vm_area_struct *vma)
1082{
1083 /* This is only called for the current mm, so: */
1084 bool foreign = false;
1085
1086 /*
1087 * Read or write was blocked by protection keys. This is
1088 * always an unconditional error and can never result in
1089 * a follow-up action to resolve the fault, like a COW.
1090 */
1091 if (error_code & X86_PF_PK)
1092 return 1;
1093
1094 /*
1095 * SGX hardware blocked the access. This usually happens
1096 * when the enclave memory contents have been destroyed, like
1097 * after a suspend/resume cycle. In any case, the kernel can't
1098 * fix the cause of the fault. Handle the fault as an access
1099 * error even in cases where no actual access violation
1100 * occurred. This allows userspace to rebuild the enclave in
1101 * response to the signal.
1102 */
1103 if (unlikely(error_code & X86_PF_SGX))
1104 return 1;
1105
1106 /*
1107 * Make sure to check the VMA so that we do not perform
1108 * faults just to hit a X86_PF_PK as soon as we fill in a
1109 * page.
1110 */
1111 if (!arch_vma_access_permitted(vma, write: (error_code & X86_PF_WRITE),
1112 execute: (error_code & X86_PF_INSTR), foreign))
1113 return 1;
1114
1115 /*
1116 * Shadow stack accesses (PF_SHSTK=1) are only permitted to
1117 * shadow stack VMAs. All other accesses result in an error.
1118 */
1119 if (error_code & X86_PF_SHSTK) {
1120 if (unlikely(!(vma->vm_flags & VM_SHADOW_STACK)))
1121 return 1;
1122 if (unlikely(!(vma->vm_flags & VM_WRITE)))
1123 return 1;
1124 return 0;
1125 }
1126
1127 if (error_code & X86_PF_WRITE) {
1128 /* write, present and write, not present: */
1129 if (unlikely(vma->vm_flags & VM_SHADOW_STACK))
1130 return 1;
1131 if (unlikely(!(vma->vm_flags & VM_WRITE)))
1132 return 1;
1133 return 0;
1134 }
1135
1136 /* read, present: */
1137 if (unlikely(error_code & X86_PF_PROT))
1138 return 1;
1139
1140 /* read, not present: */
1141 if (unlikely(!vma_is_accessible(vma)))
1142 return 1;
1143
1144 return 0;
1145}
1146
1147bool fault_in_kernel_space(unsigned long address)
1148{
1149 /*
1150 * On 64-bit systems, the vsyscall page is at an address above
1151 * TASK_SIZE_MAX, but is not considered part of the kernel
1152 * address space.
1153 */
1154 if (IS_ENABLED(CONFIG_X86_64) && is_vsyscall_vaddr(vaddr: address))
1155 return false;
1156
1157 return address >= TASK_SIZE_MAX;
1158}
1159
1160/*
1161 * Called for all faults where 'address' is part of the kernel address
1162 * space. Might get called for faults that originate from *code* that
1163 * ran in userspace or the kernel.
1164 */
1165static void
1166do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code,
1167 unsigned long address)
1168{
1169 /*
1170 * Protection keys exceptions only happen on user pages. We
1171 * have no user pages in the kernel portion of the address
1172 * space, so do not expect them here.
1173 */
1174 WARN_ON_ONCE(hw_error_code & X86_PF_PK);
1175
1176#ifdef CONFIG_X86_32
1177 /*
1178 * We can fault-in kernel-space virtual memory on-demand. The
1179 * 'reference' page table is init_mm.pgd.
1180 *
1181 * NOTE! We MUST NOT take any locks for this case. We may
1182 * be in an interrupt or a critical region, and should
1183 * only copy the information from the master page table,
1184 * nothing more.
1185 *
1186 * Before doing this on-demand faulting, ensure that the
1187 * fault is not any of the following:
1188 * 1. A fault on a PTE with a reserved bit set.
1189 * 2. A fault caused by a user-mode access. (Do not demand-
1190 * fault kernel memory due to user-mode accesses).
1191 * 3. A fault caused by a page-level protection violation.
1192 * (A demand fault would be on a non-present page which
1193 * would have X86_PF_PROT==0).
1194 *
1195 * This is only needed to close a race condition on x86-32 in
1196 * the vmalloc mapping/unmapping code. See the comment above
1197 * vmalloc_fault() for details. On x86-64 the race does not
1198 * exist as the vmalloc mappings don't need to be synchronized
1199 * there.
1200 */
1201 if (!(hw_error_code & (X86_PF_RSVD | X86_PF_USER | X86_PF_PROT))) {
1202 if (vmalloc_fault(address) >= 0)
1203 return;
1204 }
1205#endif
1206
1207 if (is_f00f_bug(regs, error_code: hw_error_code, address))
1208 return;
1209
1210 /* Was the fault spurious, caused by lazy TLB invalidation? */
1211 if (spurious_kernel_fault(error_code: hw_error_code, address))
1212 return;
1213
1214 /* kprobes don't want to hook the spurious faults: */
1215 if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF)))
1216 return;
1217
1218 /*
1219 * Note, despite being a "bad area", there are quite a few
1220 * acceptable reasons to get here, such as erratum fixups
1221 * and handling kernel code that can fault, like get_user().
1222 *
1223 * Don't take the mm semaphore here. If we fixup a prefetch
1224 * fault we could otherwise deadlock:
1225 */
1226 bad_area_nosemaphore(regs, error_code: hw_error_code, address);
1227}
1228NOKPROBE_SYMBOL(do_kern_addr_fault);
1229
1230/*
1231 * Handle faults in the user portion of the address space. Nothing in here
1232 * should check X86_PF_USER without a specific justification: for almost
1233 * all purposes, we should treat a normal kernel access to user memory
1234 * (e.g. get_user(), put_user(), etc.) the same as the WRUSS instruction.
1235 * The one exception is AC flag handling, which is, per the x86
1236 * architecture, special for WRUSS.
1237 */
1238static inline
1239void do_user_addr_fault(struct pt_regs *regs,
1240 unsigned long error_code,
1241 unsigned long address)
1242{
1243 struct vm_area_struct *vma;
1244 struct task_struct *tsk;
1245 struct mm_struct *mm;
1246 vm_fault_t fault;
1247 unsigned int flags = FAULT_FLAG_DEFAULT;
1248
1249 tsk = current;
1250 mm = tsk->mm;
1251
1252 if (unlikely((error_code & (X86_PF_USER | X86_PF_INSTR)) == X86_PF_INSTR)) {
1253 /*
1254 * Whoops, this is kernel mode code trying to execute from
1255 * user memory. Unless this is AMD erratum #93, which
1256 * corrupts RIP such that it looks like a user address,
1257 * this is unrecoverable. Don't even try to look up the
1258 * VMA or look for extable entries.
1259 */
1260 if (is_errata93(regs, address))
1261 return;
1262
1263 page_fault_oops(regs, error_code, address);
1264 return;
1265 }
1266
1267 /* kprobes don't want to hook the spurious faults: */
1268 if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF)))
1269 return;
1270
1271 /*
1272 * Reserved bits are never expected to be set on
1273 * entries in the user portion of the page tables.
1274 */
1275 if (unlikely(error_code & X86_PF_RSVD))
1276 pgtable_bad(regs, error_code, address);
1277
1278 /*
1279 * If SMAP is on, check for invalid kernel (supervisor) access to user
1280 * pages in the user address space. The odd case here is WRUSS,
1281 * which, according to the preliminary documentation, does not respect
1282 * SMAP and will have the USER bit set so, in all cases, SMAP
1283 * enforcement appears to be consistent with the USER bit.
1284 */
1285 if (unlikely(cpu_feature_enabled(X86_FEATURE_SMAP) &&
1286 !(error_code & X86_PF_USER) &&
1287 !(regs->flags & X86_EFLAGS_AC))) {
1288 /*
1289 * No extable entry here. This was a kernel access to an
1290 * invalid pointer. get_kernel_nofault() will not get here.
1291 */
1292 page_fault_oops(regs, error_code, address);
1293 return;
1294 }
1295
1296 /*
1297 * If we're in an interrupt, have no user context or are running
1298 * in a region with pagefaults disabled then we must not take the fault
1299 */
1300 if (unlikely(faulthandler_disabled() || !mm)) {
1301 bad_area_nosemaphore(regs, error_code, address);
1302 return;
1303 }
1304
1305 /*
1306 * It's safe to allow irq's after cr2 has been saved and the
1307 * vmalloc fault has been handled.
1308 *
1309 * User-mode registers count as a user access even for any
1310 * potential system fault or CPU buglet:
1311 */
1312 if (user_mode(regs)) {
1313 local_irq_enable();
1314 flags |= FAULT_FLAG_USER;
1315 } else {
1316 if (regs->flags & X86_EFLAGS_IF)
1317 local_irq_enable();
1318 }
1319
1320 perf_sw_event(event_id: PERF_COUNT_SW_PAGE_FAULTS, nr: 1, regs, addr: address);
1321
1322 /*
1323 * Read-only permissions can not be expressed in shadow stack PTEs.
1324 * Treat all shadow stack accesses as WRITE faults. This ensures
1325 * that the MM will prepare everything (e.g., break COW) such that
1326 * maybe_mkwrite() can create a proper shadow stack PTE.
1327 */
1328 if (error_code & X86_PF_SHSTK)
1329 flags |= FAULT_FLAG_WRITE;
1330 if (error_code & X86_PF_WRITE)
1331 flags |= FAULT_FLAG_WRITE;
1332 if (error_code & X86_PF_INSTR)
1333 flags |= FAULT_FLAG_INSTRUCTION;
1334
1335#ifdef CONFIG_X86_64
1336 /*
1337 * Faults in the vsyscall page might need emulation. The
1338 * vsyscall page is at a high address (>PAGE_OFFSET), but is
1339 * considered to be part of the user address space.
1340 *
1341 * The vsyscall page does not have a "real" VMA, so do this
1342 * emulation before we go searching for VMAs.
1343 *
1344 * PKRU never rejects instruction fetches, so we don't need
1345 * to consider the PF_PK bit.
1346 */
1347 if (is_vsyscall_vaddr(vaddr: address)) {
1348 if (emulate_vsyscall(error_code, regs, address))
1349 return;
1350 }
1351#endif
1352
1353 if (!(flags & FAULT_FLAG_USER))
1354 goto lock_mmap;
1355
1356 vma = lock_vma_under_rcu(mm, address);
1357 if (!vma)
1358 goto lock_mmap;
1359
1360 if (unlikely(access_error(error_code, vma))) {
1361 vma_end_read(vma);
1362 goto lock_mmap;
1363 }
1364 fault = handle_mm_fault(vma, address, flags: flags | FAULT_FLAG_VMA_LOCK, regs);
1365 if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
1366 vma_end_read(vma);
1367
1368 if (!(fault & VM_FAULT_RETRY)) {
1369 count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
1370 goto done;
1371 }
1372 count_vm_vma_lock_event(VMA_LOCK_RETRY);
1373
1374 /* Quick path to respond to signals */
1375 if (fault_signal_pending(fault_flags: fault, regs)) {
1376 if (!user_mode(regs))
1377 kernelmode_fixup_or_oops(regs, error_code, address,
1378 SIGBUS, BUS_ADRERR,
1379 ARCH_DEFAULT_PKEY);
1380 return;
1381 }
1382lock_mmap:
1383
1384retry:
1385 vma = lock_mm_and_find_vma(mm, address, regs);
1386 if (unlikely(!vma)) {
1387 bad_area_nosemaphore(regs, error_code, address);
1388 return;
1389 }
1390
1391 /*
1392 * Ok, we have a good vm_area for this memory access, so
1393 * we can handle it..
1394 */
1395 if (unlikely(access_error(error_code, vma))) {
1396 bad_area_access_error(regs, error_code, address, vma);
1397 return;
1398 }
1399
1400 /*
1401 * If for any reason at all we couldn't handle the fault,
1402 * make sure we exit gracefully rather than endlessly redo
1403 * the fault. Since we never set FAULT_FLAG_RETRY_NOWAIT, if
1404 * we get VM_FAULT_RETRY back, the mmap_lock has been unlocked.
1405 *
1406 * Note that handle_userfault() may also release and reacquire mmap_lock
1407 * (and not return with VM_FAULT_RETRY), when returning to userland to
1408 * repeat the page fault later with a VM_FAULT_NOPAGE retval
1409 * (potentially after handling any pending signal during the return to
1410 * userland). The return to userland is identified whenever
1411 * FAULT_FLAG_USER|FAULT_FLAG_KILLABLE are both set in flags.
1412 */
1413 fault = handle_mm_fault(vma, address, flags, regs);
1414
1415 if (fault_signal_pending(fault_flags: fault, regs)) {
1416 /*
1417 * Quick path to respond to signals. The core mm code
1418 * has unlocked the mm for us if we get here.
1419 */
1420 if (!user_mode(regs))
1421 kernelmode_fixup_or_oops(regs, error_code, address,
1422 SIGBUS, BUS_ADRERR,
1423 ARCH_DEFAULT_PKEY);
1424 return;
1425 }
1426
1427 /* The fault is fully completed (including releasing mmap lock) */
1428 if (fault & VM_FAULT_COMPLETED)
1429 return;
1430
1431 /*
1432 * If we need to retry the mmap_lock has already been released,
1433 * and if there is a fatal signal pending there is no guarantee
1434 * that we made any progress. Handle this case first.
1435 */
1436 if (unlikely(fault & VM_FAULT_RETRY)) {
1437 flags |= FAULT_FLAG_TRIED;
1438 goto retry;
1439 }
1440
1441 mmap_read_unlock(mm);
1442done:
1443 if (likely(!(fault & VM_FAULT_ERROR)))
1444 return;
1445
1446 if (fatal_signal_pending(current) && !user_mode(regs)) {
1447 kernelmode_fixup_or_oops(regs, error_code, address,
1448 signal: 0, si_code: 0, ARCH_DEFAULT_PKEY);
1449 return;
1450 }
1451
1452 if (fault & VM_FAULT_OOM) {
1453 /* Kernel mode? Handle exceptions or die: */
1454 if (!user_mode(regs)) {
1455 kernelmode_fixup_or_oops(regs, error_code, address,
1456 SIGSEGV, SEGV_MAPERR,
1457 ARCH_DEFAULT_PKEY);
1458 return;
1459 }
1460
1461 /*
1462 * We ran out of memory, call the OOM killer, and return the
1463 * userspace (which will retry the fault, or kill us if we got
1464 * oom-killed):
1465 */
1466 pagefault_out_of_memory();
1467 } else {
1468 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
1469 VM_FAULT_HWPOISON_LARGE))
1470 do_sigbus(regs, error_code, address, fault);
1471 else if (fault & VM_FAULT_SIGSEGV)
1472 bad_area_nosemaphore(regs, error_code, address);
1473 else
1474 BUG();
1475 }
1476}
1477NOKPROBE_SYMBOL(do_user_addr_fault);
1478
1479static __always_inline void
1480trace_page_fault_entries(struct pt_regs *regs, unsigned long error_code,
1481 unsigned long address)
1482{
1483 if (!trace_pagefault_enabled())
1484 return;
1485
1486 if (user_mode(regs))
1487 trace_page_fault_user(address, regs, error_code);
1488 else
1489 trace_page_fault_kernel(address, regs, error_code);
1490}
1491
1492static __always_inline void
1493handle_page_fault(struct pt_regs *regs, unsigned long error_code,
1494 unsigned long address)
1495{
1496 trace_page_fault_entries(regs, error_code, address);
1497
1498 if (unlikely(kmmio_fault(regs, address)))
1499 return;
1500
1501 /* Was the fault on kernel-controlled part of the address space? */
1502 if (unlikely(fault_in_kernel_space(address))) {
1503 do_kern_addr_fault(regs, hw_error_code: error_code, address);
1504 } else {
1505 do_user_addr_fault(regs, error_code, address);
1506 /*
1507 * User address page fault handling might have reenabled
1508 * interrupts. Fixing up all potential exit points of
1509 * do_user_addr_fault() and its leaf functions is just not
1510 * doable w/o creating an unholy mess or turning the code
1511 * upside down.
1512 */
1513 local_irq_disable();
1514 }
1515}
1516
1517DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault)
1518{
1519 unsigned long address = read_cr2();
1520 irqentry_state_t state;
1521
1522 prefetchw(x: &current->mm->mmap_lock);
1523
1524 /*
1525 * KVM uses #PF vector to deliver 'page not present' events to guests
1526 * (asynchronous page fault mechanism). The event happens when a
1527 * userspace task is trying to access some valid (from guest's point of
1528 * view) memory which is not currently mapped by the host (e.g. the
1529 * memory is swapped out). Note, the corresponding "page ready" event
1530 * which is injected when the memory becomes available, is delivered via
1531 * an interrupt mechanism and not a #PF exception
1532 * (see arch/x86/kernel/kvm.c: sysvec_kvm_asyncpf_interrupt()).
1533 *
1534 * We are relying on the interrupted context being sane (valid RSP,
1535 * relevant locks not held, etc.), which is fine as long as the
1536 * interrupted context had IF=1. We are also relying on the KVM
1537 * async pf type field and CR2 being read consistently instead of
1538 * getting values from real and async page faults mixed up.
1539 *
1540 * Fingers crossed.
1541 *
1542 * The async #PF handling code takes care of idtentry handling
1543 * itself.
1544 */
1545 if (kvm_handle_async_pf(regs, token: (u32)address))
1546 return;
1547
1548 /*
1549 * Entry handling for valid #PF from kernel mode is slightly
1550 * different: RCU is already watching and ct_irq_enter() must not
1551 * be invoked because a kernel fault on a user space address might
1552 * sleep.
1553 *
1554 * In case the fault hit a RCU idle region the conditional entry
1555 * code reenabled RCU to avoid subsequent wreckage which helps
1556 * debuggability.
1557 */
1558 state = irqentry_enter(regs);
1559
1560 instrumentation_begin();
1561 handle_page_fault(regs, error_code, address);
1562 instrumentation_end();
1563
1564 irqentry_exit(regs, state);
1565}
1566

source code of linux/arch/x86/mm/fault.c