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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/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/prefetch.h> /* prefetchw */
17#include <linux/context_tracking.h> /* exception_enter(), ... */
18#include <linux/uaccess.h> /* faulthandler_disabled() */
19#include <linux/efi.h> /* efi_recover_from_page_fault()*/
20#include <linux/mm_types.h>
21
22#include <asm/cpufeature.h> /* boot_cpu_has, ... */
23#include <asm/traps.h> /* dotraplinkage, ... */
24#include <asm/fixmap.h> /* VSYSCALL_ADDR */
25#include <asm/vsyscall.h> /* emulate_vsyscall */
26#include <asm/vm86.h> /* struct vm86 */
27#include <asm/mmu_context.h> /* vma_pkey() */
28#include <asm/efi.h> /* efi_recover_from_page_fault()*/
29#include <asm/desc.h> /* store_idt(), ... */
30#include <asm/cpu_entry_area.h> /* exception stack */
31#include <asm/pgtable_areas.h> /* VMALLOC_START, ... */
32#include <asm/kvm_para.h> /* kvm_handle_async_pf */
33
34#define CREATE_TRACE_POINTS
35#include <asm/trace/exceptions.h>
36
37/*
38 * Returns 0 if mmiotrace is disabled, or if the fault is not
39 * handled by mmiotrace:
40 */
41static nokprobe_inline int
42kmmio_fault(struct pt_regs *regs, unsigned long addr)
43{
44 if (unlikely(is_kmmio_active()))
45 if (kmmio_handler(regs, addr) == 1)
46 return -1;
47 return 0;
48}
49
50/*
51 * Prefetch quirks:
52 *
53 * 32-bit mode:
54 *
55 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
56 * Check that here and ignore it.
57 *
58 * 64-bit mode:
59 *
60 * Sometimes the CPU reports invalid exceptions on prefetch.
61 * Check that here and ignore it.
62 *
63 * Opcode checker based on code by Richard Brunner.
64 */
65static inline int
66check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr,
67 unsigned char opcode, int *prefetch)
68{
69 unsigned char instr_hi = opcode & 0xf0;
70 unsigned char instr_lo = opcode & 0x0f;
71
72 switch (instr_hi) {
73 case 0x20:
74 case 0x30:
75 /*
76 * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes.
77 * In X86_64 long mode, the CPU will signal invalid
78 * opcode if some of these prefixes are present so
79 * X86_64 will never get here anyway
80 */
81 return ((instr_lo & 7) == 0x6);
82#ifdef CONFIG_X86_64
83 case 0x40:
84 /*
85 * In AMD64 long mode 0x40..0x4F are valid REX prefixes
86 * Need to figure out under what instruction mode the
87 * instruction was issued. Could check the LDT for lm,
88 * but for now it's good enough to assume that long
89 * mode only uses well known segments or kernel.
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 int
113is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr)
114{
115 unsigned char *max_instr;
116 unsigned char *instr;
117 int prefetch = 0;
118
119 /*
120 * If it was a exec (instruction fetch) fault on NX page, then
121 * do not ignore the fault:
122 */
123 if (error_code & X86_PF_INSTR)
124 return 0;
125
126 instr = (void *)convert_ip_to_linear(current, regs);
127 max_instr = instr + 15;
128
129 if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE_MAX)
130 return 0;
131
132 while (instr < max_instr) {
133 unsigned char opcode;
134
135 if (get_kernel_nofault(opcode, instr))
136 break;
137
138 instr++;
139
140 if (!check_prefetch_opcode(regs, instr, opcode, &prefetch))
141 break;
142 }
143 return prefetch;
144}
145
146DEFINE_SPINLOCK(pgd_lock);
147LIST_HEAD(pgd_list);
148
149#ifdef CONFIG_X86_32
150static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
151{
152 unsigned index = pgd_index(address);
153 pgd_t *pgd_k;
154 p4d_t *p4d, *p4d_k;
155 pud_t *pud, *pud_k;
156 pmd_t *pmd, *pmd_k;
157
158 pgd += index;
159 pgd_k = init_mm.pgd + index;
160
161 if (!pgd_present(*pgd_k))
162 return NULL;
163
164 /*
165 * set_pgd(pgd, *pgd_k); here would be useless on PAE
166 * and redundant with the set_pmd() on non-PAE. As would
167 * set_p4d/set_pud.
168 */
169 p4d = p4d_offset(pgd, address);
170 p4d_k = p4d_offset(pgd_k, address);
171 if (!p4d_present(*p4d_k))
172 return NULL;
173
174 pud = pud_offset(p4d, address);
175 pud_k = pud_offset(p4d_k, address);
176 if (!pud_present(*pud_k))
177 return NULL;
178
179 pmd = pmd_offset(pud, address);
180 pmd_k = pmd_offset(pud_k, address);
181
182 if (pmd_present(*pmd) != pmd_present(*pmd_k))
183 set_pmd(pmd, *pmd_k);
184
185 if (!pmd_present(*pmd_k))
186 return NULL;
187 else
188 BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k));
189
190 return pmd_k;
191}
192
193/*
194 * Handle a fault on the vmalloc or module mapping area
195 *
196 * This is needed because there is a race condition between the time
197 * when the vmalloc mapping code updates the PMD to the point in time
198 * where it synchronizes this update with the other page-tables in the
199 * system.
200 *
201 * In this race window another thread/CPU can map an area on the same
202 * PMD, finds it already present and does not synchronize it with the
203 * rest of the system yet. As a result v[mz]alloc might return areas
204 * which are not mapped in every page-table in the system, causing an
205 * unhandled page-fault when they are accessed.
206 */
207static noinline int vmalloc_fault(unsigned long address)
208{
209 unsigned long pgd_paddr;
210 pmd_t *pmd_k;
211 pte_t *pte_k;
212
213 /* Make sure we are in vmalloc area: */
214 if (!(address >= VMALLOC_START && address < VMALLOC_END))
215 return -1;
216
217 /*
218 * Synchronize this task's top level page-table
219 * with the 'reference' page table.
220 *
221 * Do _not_ use "current" here. We might be inside
222 * an interrupt in the middle of a task switch..
223 */
224 pgd_paddr = read_cr3_pa();
225 pmd_k = vmalloc_sync_one(__va(pgd_paddr), address);
226 if (!pmd_k)
227 return -1;
228
229 if (pmd_large(*pmd_k))
230 return 0;
231
232 pte_k = pte_offset_kernel(pmd_k, address);
233 if (!pte_present(*pte_k))
234 return -1;
235
236 return 0;
237}
238NOKPROBE_SYMBOL(vmalloc_fault);
239
240void arch_sync_kernel_mappings(unsigned long start, unsigned long end)
241{
242 unsigned long addr;
243
244 for (addr = start & PMD_MASK;
245 addr >= TASK_SIZE_MAX && addr < VMALLOC_END;
246 addr += PMD_SIZE) {
247 struct page *page;
248
249 spin_lock(&pgd_lock);
250 list_for_each_entry(page, &pgd_list, lru) {
251 spinlock_t *pgt_lock;
252
253 /* the pgt_lock only for Xen */
254 pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
255
256 spin_lock(pgt_lock);
257 vmalloc_sync_one(page_address(page), addr);
258 spin_unlock(pgt_lock);
259 }
260 spin_unlock(&pgd_lock);
261 }
262}
263
264/*
265 * Did it hit the DOS screen memory VA from vm86 mode?
266 */
267static inline void
268check_v8086_mode(struct pt_regs *regs, unsigned long address,
269 struct task_struct *tsk)
270{
271#ifdef CONFIG_VM86
272 unsigned long bit;
273
274 if (!v8086_mode(regs) || !tsk->thread.vm86)
275 return;
276
277 bit = (address - 0xA0000) >> PAGE_SHIFT;
278 if (bit < 32)
279 tsk->thread.vm86->screen_bitmap |= 1 << bit;
280#endif
281}
282
283static bool low_pfn(unsigned long pfn)
284{
285 return pfn < max_low_pfn;
286}
287
288static void dump_pagetable(unsigned long address)
289{
290 pgd_t *base = __va(read_cr3_pa());
291 pgd_t *pgd = &base[pgd_index(address)];
292 p4d_t *p4d;
293 pud_t *pud;
294 pmd_t *pmd;
295 pte_t *pte;
296
297#ifdef CONFIG_X86_PAE
298 pr_info("*pdpt = %016Lx ", pgd_val(*pgd));
299 if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd))
300 goto out;
301#define pr_pde pr_cont
302#else
303#define pr_pde pr_info
304#endif
305 p4d = p4d_offset(pgd, address);
306 pud = pud_offset(p4d, address);
307 pmd = pmd_offset(pud, address);
308 pr_pde("*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd));
309#undef pr_pde
310
311 /*
312 * We must not directly access the pte in the highpte
313 * case if the page table is located in highmem.
314 * And let's rather not kmap-atomic the pte, just in case
315 * it's allocated already:
316 */
317 if (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_large(*pmd))
318 goto out;
319
320 pte = pte_offset_kernel(pmd, address);
321 pr_cont("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte));
322out:
323 pr_cont("\n");
324}
325
326#else /* CONFIG_X86_64: */
327
328#ifdef CONFIG_CPU_SUP_AMD
329static const char errata93_warning[] =
330KERN_ERR
331"******* Your BIOS seems to not contain a fix for K8 errata #93\n"
332"******* Working around it, but it may cause SEGVs or burn power.\n"
333"******* Please consider a BIOS update.\n"
334"******* Disabling USB legacy in the BIOS may also help.\n";
335#endif
336
337/*
338 * No vm86 mode in 64-bit mode:
339 */
340static inline void
341check_v8086_mode(struct pt_regs *regs, unsigned long address,
342 struct task_struct *tsk)
343{
344}
345
346static int bad_address(void *p)
347{
348 unsigned long dummy;
349
350 return get_kernel_nofault(dummy, (unsigned long *)p);
351}
352
353static void dump_pagetable(unsigned long address)
354{
355 pgd_t *base = __va(read_cr3_pa());
356 pgd_t *pgd = base + pgd_index(address);
357 p4d_t *p4d;
358 pud_t *pud;
359 pmd_t *pmd;
360 pte_t *pte;
361
362 if (bad_address(pgd))
363 goto bad;
364
365 pr_info("PGD %lx ", pgd_val(*pgd));
366
367 if (!pgd_present(*pgd))
368 goto out;
369
370 p4d = p4d_offset(pgd, address);
371 if (bad_address(p4d))
372 goto bad;
373
374 pr_cont("P4D %lx ", p4d_val(*p4d));
375 if (!p4d_present(*p4d) || p4d_large(*p4d))
376 goto out;
377
378 pud = pud_offset(p4d, address);
379 if (bad_address(pud))
380 goto bad;
381
382 pr_cont("PUD %lx ", pud_val(*pud));
383 if (!pud_present(*pud) || pud_large(*pud))
384 goto out;
385
386 pmd = pmd_offset(pud, address);
387 if (bad_address(pmd))
388 goto bad;
389
390 pr_cont("PMD %lx ", pmd_val(*pmd));
391 if (!pmd_present(*pmd) || pmd_large(*pmd))
392 goto out;
393
394 pte = pte_offset_kernel(pmd, address);
395 if (bad_address(pte))
396 goto bad;
397
398 pr_cont("PTE %lx", pte_val(*pte));
399out:
400 pr_cont("\n");
401 return;
402bad:
403 pr_info("BAD\n");
404}
405
406#endif /* CONFIG_X86_64 */
407
408/*
409 * Workaround for K8 erratum #93 & buggy BIOS.
410 *
411 * BIOS SMM functions are required to use a specific workaround
412 * to avoid corruption of the 64bit RIP register on C stepping K8.
413 *
414 * A lot of BIOS that didn't get tested properly miss this.
415 *
416 * The OS sees this as a page fault with the upper 32bits of RIP cleared.
417 * Try to work around it here.
418 *
419 * Note we only handle faults in kernel here.
420 * Does nothing on 32-bit.
421 */
422static int is_errata93(struct pt_regs *regs, unsigned long address)
423{
424#if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD)
425 if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD
426 || boot_cpu_data.x86 != 0xf)
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 address)
465{
466#ifdef CONFIG_X86_F00F_BUG
467 if (boot_cpu_has_bug(X86_BUG_F00F) && idt_is_f00f_address(address)) {
468 handle_invalid_op(regs);
469 return 1;
470 }
471#endif
472 return 0;
473}
474
475static void show_ldttss(const struct desc_ptr *gdt, const char *name, u16 index)
476{
477 u32 offset = (index >> 3) * sizeof(struct desc_struct);
478 unsigned long addr;
479 struct ldttss_desc desc;
480
481 if (index == 0) {
482 pr_alert("%s: NULL\n", name);
483 return;
484 }
485
486 if (offset + sizeof(struct ldttss_desc) >= gdt->size) {
487 pr_alert("%s: 0x%hx -- out of bounds\n", name, index);
488 return;
489 }
490
491 if (copy_from_kernel_nofault(&desc, (void *)(gdt->address + offset),
492 sizeof(struct ldttss_desc))) {
493 pr_alert("%s: 0x%hx -- GDT entry is not readable\n",
494 name, index);
495 return;
496 }
497
498 addr = desc.base0 | (desc.base1 << 16) | ((unsigned long)desc.base2 << 24);
499#ifdef CONFIG_X86_64
500 addr |= ((u64)desc.base3 << 32);
501#endif
502 pr_alert("%s: 0x%hx -- base=0x%lx limit=0x%x\n",
503 name, index, addr, (desc.limit0 | (desc.limit1 << 16)));
504}
505
506static void
507show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long address)
508{
509 if (!oops_may_print())
510 return;
511
512 if (error_code & X86_PF_INSTR) {
513 unsigned int level;
514 pgd_t *pgd;
515 pte_t *pte;
516
517 pgd = __va(read_cr3_pa());
518 pgd += pgd_index(address);
519
520 pte = lookup_address_in_pgd(pgd, address, &level);
521
522 if (pte && pte_present(*pte) && !pte_exec(*pte))
523 pr_crit("kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n",
524 from_kuid(&init_user_ns, current_uid()));
525 if (pte && pte_present(*pte) && pte_exec(*pte) &&
526 (pgd_flags(*pgd) & _PAGE_USER) &&
527 (__read_cr4() & X86_CR4_SMEP))
528 pr_crit("unable to execute userspace code (SMEP?) (uid: %d)\n",
529 from_kuid(&init_user_ns, current_uid()));
530 }
531
532 if (address < PAGE_SIZE && !user_mode(regs))
533 pr_alert("BUG: kernel NULL pointer dereference, address: %px\n",
534 (void *)address);
535 else
536 pr_alert("BUG: unable to handle page fault for address: %px\n",
537 (void *)address);
538
539 pr_alert("#PF: %s %s in %s mode\n",
540 (error_code & X86_PF_USER) ? "user" : "supervisor",
541 (error_code & X86_PF_INSTR) ? "instruction fetch" :
542 (error_code & X86_PF_WRITE) ? "write access" :
543 "read access",
544 user_mode(regs) ? "user" : "kernel");
545 pr_alert("#PF: error_code(0x%04lx) - %s\n", error_code,
546 !(error_code & X86_PF_PROT) ? "not-present page" :
547 (error_code & X86_PF_RSVD) ? "reserved bit violation" :
548 (error_code & X86_PF_PK) ? "protection keys violation" :
549 "permissions violation");
550
551 if (!(error_code & X86_PF_USER) && user_mode(regs)) {
552 struct desc_ptr idt, gdt;
553 u16 ldtr, tr;
554
555 /*
556 * This can happen for quite a few reasons. The more obvious
557 * ones are faults accessing the GDT, or LDT. Perhaps
558 * surprisingly, if the CPU tries to deliver a benign or
559 * contributory exception from user code and gets a page fault
560 * during delivery, the page fault can be delivered as though
561 * it originated directly from user code. This could happen
562 * due to wrong permissions on the IDT, GDT, LDT, TSS, or
563 * kernel or IST stack.
564 */
565 store_idt(&idt);
566
567 /* Usable even on Xen PV -- it's just slow. */
568 native_store_gdt(&gdt);
569
570 pr_alert("IDT: 0x%lx (limit=0x%hx) GDT: 0x%lx (limit=0x%hx)\n",
571 idt.address, idt.size, gdt.address, gdt.size);
572
573 store_ldt(ldtr);
574 show_ldttss(&gdt, "LDTR", ldtr);
575
576 store_tr(tr);
577 show_ldttss(&gdt, "TR", tr);
578 }
579
580 dump_pagetable(address);
581}
582
583static noinline void
584pgtable_bad(struct pt_regs *regs, unsigned long error_code,
585 unsigned long address)
586{
587 struct task_struct *tsk;
588 unsigned long flags;
589 int sig;
590
591 flags = oops_begin();
592 tsk = current;
593 sig = SIGKILL;
594
595 printk(KERN_ALERT "%s: Corrupted page table at address %lx\n",
596 tsk->comm, address);
597 dump_pagetable(address);
598
599 if (__die("Bad pagetable", regs, error_code))
600 sig = 0;
601
602 oops_end(flags, regs, sig);
603}
604
605static void set_signal_archinfo(unsigned long address,
606 unsigned long error_code)
607{
608 struct task_struct *tsk = current;
609
610 /*
611 * To avoid leaking information about the kernel page
612 * table layout, pretend that user-mode accesses to
613 * kernel addresses are always protection faults.
614 *
615 * NB: This means that failed vsyscalls with vsyscall=none
616 * will have the PROT bit. This doesn't leak any
617 * information and does not appear to cause any problems.
618 */
619 if (address >= TASK_SIZE_MAX)
620 error_code |= X86_PF_PROT;
621
622 tsk->thread.trap_nr = X86_TRAP_PF;
623 tsk->thread.error_code = error_code | X86_PF_USER;
624 tsk->thread.cr2 = address;
625}
626
627static noinline void
628no_context(struct pt_regs *regs, unsigned long error_code,
629 unsigned long address, int signal, int si_code)
630{
631 struct task_struct *tsk = current;
632 unsigned long flags;
633 int sig;
634
635 if (user_mode(regs)) {
636 /*
637 * This is an implicit supervisor-mode access from user
638 * mode. Bypass all the kernel-mode recovery code and just
639 * OOPS.
640 */
641 goto oops;
642 }
643
644 /* Are we prepared to handle this kernel fault? */
645 if (fixup_exception(regs, X86_TRAP_PF, error_code, address)) {
646 /*
647 * Any interrupt that takes a fault gets the fixup. This makes
648 * the below recursive fault logic only apply to a faults from
649 * task context.
650 */
651 if (in_interrupt())
652 return;
653
654 /*
655 * Per the above we're !in_interrupt(), aka. task context.
656 *
657 * In this case we need to make sure we're not recursively
658 * faulting through the emulate_vsyscall() logic.
659 */
660 if (current->thread.sig_on_uaccess_err && signal) {
661 set_signal_archinfo(address, error_code);
662
663 /* XXX: hwpoison faults will set the wrong code. */
664 force_sig_fault(signal, si_code, (void __user *)address);
665 }
666
667 /*
668 * Barring that, we can do the fixup and be happy.
669 */
670 return;
671 }
672
673#ifdef CONFIG_VMAP_STACK
674 /*
675 * Stack overflow? During boot, we can fault near the initial
676 * stack in the direct map, but that's not an overflow -- check
677 * that we're in vmalloc space to avoid this.
678 */
679 if (is_vmalloc_addr((void *)address) &&
680 (((unsigned long)tsk->stack - 1 - address < PAGE_SIZE) ||
681 address - ((unsigned long)tsk->stack + THREAD_SIZE) < PAGE_SIZE)) {
682 unsigned long stack = __this_cpu_ist_top_va(DF) - sizeof(void *);
683 /*
684 * We're likely to be running with very little stack space
685 * left. It's plausible that we'd hit this condition but
686 * double-fault even before we get this far, in which case
687 * we're fine: the double-fault handler will deal with it.
688 *
689 * We don't want to make it all the way into the oops code
690 * and then double-fault, though, because we're likely to
691 * break the console driver and lose most of the stack dump.
692 */
693 asm volatile ("movq %[stack], %%rsp\n\t"
694 "call handle_stack_overflow\n\t"
695 "1: jmp 1b"
696 : ASM_CALL_CONSTRAINT
697 : "D" ("kernel stack overflow (page fault)"),
698 "S" (regs), "d" (address),
699 [stack] "rm" (stack));
700 unreachable();
701 }
702#endif
703
704 /*
705 * 32-bit:
706 *
707 * Valid to do another page fault here, because if this fault
708 * had been triggered by is_prefetch fixup_exception would have
709 * handled it.
710 *
711 * 64-bit:
712 *
713 * Hall of shame of CPU/BIOS bugs.
714 */
715 if (is_prefetch(regs, error_code, address))
716 return;
717
718 if (is_errata93(regs, address))
719 return;
720
721 /*
722 * Buggy firmware could access regions which might page fault, try to
723 * recover from such faults.
724 */
725 if (IS_ENABLED(CONFIG_EFI))
726 efi_recover_from_page_fault(address);
727
728oops:
729 /*
730 * Oops. The kernel tried to access some bad page. We'll have to
731 * terminate things with extreme prejudice:
732 */
733 flags = oops_begin();
734
735 show_fault_oops(regs, error_code, address);
736
737 if (task_stack_end_corrupted(tsk))
738 printk(KERN_EMERG "Thread overran stack, or stack corrupted\n");
739
740 sig = SIGKILL;
741 if (__die("Oops", regs, error_code))
742 sig = 0;
743
744 /* Executive summary in case the body of the oops scrolled away */
745 printk(KERN_DEFAULT "CR2: %016lx\n", address);
746
747 oops_end(flags, regs, sig);
748}
749
750/*
751 * Print out info about fatal segfaults, if the show_unhandled_signals
752 * sysctl is set:
753 */
754static inline void
755show_signal_msg(struct pt_regs *regs, unsigned long error_code,
756 unsigned long address, struct task_struct *tsk)
757{
758 const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG;
759
760 if (!unhandled_signal(tsk, SIGSEGV))
761 return;
762
763 if (!printk_ratelimit())
764 return;
765
766 printk("%s%s[%d]: segfault at %lx ip %px sp %px error %lx",
767 loglvl, tsk->comm, task_pid_nr(tsk), address,
768 (void *)regs->ip, (void *)regs->sp, error_code);
769
770 print_vma_addr(KERN_CONT " in ", regs->ip);
771
772 printk(KERN_CONT "\n");
773
774 show_opcodes(regs, loglvl);
775}
776
777/*
778 * The (legacy) vsyscall page is the long page in the kernel portion
779 * of the address space that has user-accessible permissions.
780 */
781static bool is_vsyscall_vaddr(unsigned long vaddr)
782{
783 return unlikely((vaddr & PAGE_MASK) == VSYSCALL_ADDR);
784}
785
786static void
787__bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
788 unsigned long address, u32 pkey, int si_code)
789{
790 struct task_struct *tsk = current;
791
792 /* User mode accesses just cause a SIGSEGV */
793 if (user_mode(regs) && (error_code & X86_PF_USER)) {
794 /*
795 * It's possible to have interrupts off here:
796 */
797 local_irq_enable();
798
799 /*
800 * Valid to do another page fault here because this one came
801 * from user space:
802 */
803 if (is_prefetch(regs, error_code, address))
804 return;
805
806 if (is_errata100(regs, address))
807 return;
808
809 /*
810 * To avoid leaking information about the kernel page table
811 * layout, pretend that user-mode accesses to kernel addresses
812 * are always protection faults.
813 */
814 if (address >= TASK_SIZE_MAX)
815 error_code |= X86_PF_PROT;
816
817 if (likely(show_unhandled_signals))
818 show_signal_msg(regs, error_code, address, tsk);
819
820 set_signal_archinfo(address, error_code);
821
822 if (si_code == SEGV_PKUERR)
823 force_sig_pkuerr((void __user *)address, pkey);
824
825 force_sig_fault(SIGSEGV, si_code, (void __user *)address);
826
827 local_irq_disable();
828
829 return;
830 }
831
832 if (is_f00f_bug(regs, address))
833 return;
834
835 no_context(regs, error_code, address, SIGSEGV, si_code);
836}
837
838static noinline void
839bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
840 unsigned long address)
841{
842 __bad_area_nosemaphore(regs, error_code, address, 0, SEGV_MAPERR);
843}
844
845static void
846__bad_area(struct pt_regs *regs, unsigned long error_code,
847 unsigned long address, u32 pkey, int si_code)
848{
849 struct mm_struct *mm = current->mm;
850 /*
851 * Something tried to access memory that isn't in our memory map..
852 * Fix it, but check if it's kernel or user first..
853 */
854 mmap_read_unlock(mm);
855
856 __bad_area_nosemaphore(regs, error_code, address, pkey, si_code);
857}
858
859static noinline void
860bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address)
861{
862 __bad_area(regs, error_code, address, 0, SEGV_MAPERR);
863}
864
865static inline bool bad_area_access_from_pkeys(unsigned long error_code,
866 struct vm_area_struct *vma)
867{
868 /* This code is always called on the current mm */
869 bool foreign = false;
870
871 if (!boot_cpu_has(X86_FEATURE_OSPKE))
872 return false;
873 if (error_code & X86_PF_PK)
874 return true;
875 /* this checks permission keys on the VMA: */
876 if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE),
877 (error_code & X86_PF_INSTR), foreign))
878 return true;
879 return false;
880}
881
882static noinline void
883bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
884 unsigned long address, struct vm_area_struct *vma)
885{
886 /*
887 * This OSPKE check is not strictly necessary at runtime.
888 * But, doing it this way allows compiler optimizations
889 * if pkeys are compiled out.
890 */
891 if (bad_area_access_from_pkeys(error_code, vma)) {
892 /*
893 * A protection key fault means that the PKRU value did not allow
894 * access to some PTE. Userspace can figure out what PKRU was
895 * from the XSAVE state. This function captures the pkey from
896 * the vma and passes it to userspace so userspace can discover
897 * which protection key was set on the PTE.
898 *
899 * If we get here, we know that the hardware signaled a X86_PF_PK
900 * fault and that there was a VMA once we got in the fault
901 * handler. It does *not* guarantee that the VMA we find here
902 * was the one that we faulted on.
903 *
904 * 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4);
905 * 2. T1 : set PKRU to deny access to pkey=4, touches page
906 * 3. T1 : faults...
907 * 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5);
908 * 5. T1 : enters fault handler, takes mmap_lock, etc...
909 * 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really
910 * faulted on a pte with its pkey=4.
911 */
912 u32 pkey = vma_pkey(vma);
913
914 __bad_area(regs, error_code, address, pkey, SEGV_PKUERR);
915 } else {
916 __bad_area(regs, error_code, address, 0, SEGV_ACCERR);
917 }
918}
919
920static void
921do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
922 vm_fault_t fault)
923{
924 /* Kernel mode? Handle exceptions or die: */
925 if (!(error_code & X86_PF_USER)) {
926 no_context(regs, error_code, address, SIGBUS, BUS_ADRERR);
927 return;
928 }
929
930 /* User-space => ok to do another page fault: */
931 if (is_prefetch(regs, error_code, address))
932 return;
933
934 set_signal_archinfo(address, error_code);
935
936#ifdef CONFIG_MEMORY_FAILURE
937 if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
938 struct task_struct *tsk = current;
939 unsigned lsb = 0;
940
941 pr_err(
942 "MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
943 tsk->comm, tsk->pid, address);
944 if (fault & VM_FAULT_HWPOISON_LARGE)
945 lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
946 if (fault & VM_FAULT_HWPOISON)
947 lsb = PAGE_SHIFT;
948 force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb);
949 return;
950 }
951#endif
952 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
953}
954
955static noinline void
956mm_fault_error(struct pt_regs *regs, unsigned long error_code,
957 unsigned long address, vm_fault_t fault)
958{
959 if (fatal_signal_pending(current) && !(error_code & X86_PF_USER)) {
960 no_context(regs, error_code, address, 0, 0);
961 return;
962 }
963
964 if (fault & VM_FAULT_OOM) {
965 /* Kernel mode? Handle exceptions or die: */
966 if (!(error_code & X86_PF_USER)) {
967 no_context(regs, error_code, address,
968 SIGSEGV, SEGV_MAPERR);
969 return;
970 }
971
972 /*
973 * We ran out of memory, call the OOM killer, and return the
974 * userspace (which will retry the fault, or kill us if we got
975 * oom-killed):
976 */
977 pagefault_out_of_memory();
978 } else {
979 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
980 VM_FAULT_HWPOISON_LARGE))
981 do_sigbus(regs, error_code, address, fault);
982 else if (fault & VM_FAULT_SIGSEGV)
983 bad_area_nosemaphore(regs, error_code, address);
984 else
985 BUG();
986 }
987}
988
989static int spurious_kernel_fault_check(unsigned long error_code, pte_t *pte)
990{
991 if ((error_code & X86_PF_WRITE) && !pte_write(*pte))
992 return 0;
993
994 if ((error_code & X86_PF_INSTR) && !pte_exec(*pte))
995 return 0;
996
997 return 1;
998}
999
1000/*
1001 * Handle a spurious fault caused by a stale TLB entry.
1002 *
1003 * This allows us to lazily refresh the TLB when increasing the
1004 * permissions of a kernel page (RO -> RW or NX -> X). Doing it
1005 * eagerly is very expensive since that implies doing a full
1006 * cross-processor TLB flush, even if no stale TLB entries exist
1007 * on other processors.
1008 *
1009 * Spurious faults may only occur if the TLB contains an entry with
1010 * fewer permission than the page table entry. Non-present (P = 0)
1011 * and reserved bit (R = 1) faults are never spurious.
1012 *
1013 * There are no security implications to leaving a stale TLB when
1014 * increasing the permissions on a page.
1015 *
1016 * Returns non-zero if a spurious fault was handled, zero otherwise.
1017 *
1018 * See Intel Developer's Manual Vol 3 Section 4.10.4.3, bullet 3
1019 * (Optional Invalidation).
1020 */
1021static noinline int
1022spurious_kernel_fault(unsigned long error_code, unsigned long address)
1023{
1024 pgd_t *pgd;
1025 p4d_t *p4d;
1026 pud_t *pud;
1027 pmd_t *pmd;
1028 pte_t *pte;
1029 int ret;
1030
1031 /*
1032 * Only writes to RO or instruction fetches from NX may cause
1033 * spurious faults.
1034 *
1035 * These could be from user or supervisor accesses but the TLB
1036 * is only lazily flushed after a kernel mapping protection
1037 * change, so user accesses are not expected to cause spurious
1038 * faults.
1039 */
1040 if (error_code != (X86_PF_WRITE | X86_PF_PROT) &&
1041 error_code != (X86_PF_INSTR | X86_PF_PROT))
1042 return 0;
1043
1044 pgd = init_mm.pgd + pgd_index(address);
1045 if (!pgd_present(*pgd))
1046 return 0;
1047
1048 p4d = p4d_offset(pgd, address);
1049 if (!p4d_present(*p4d))
1050 return 0;
1051
1052 if (p4d_large(*p4d))
1053 return spurious_kernel_fault_check(error_code, (pte_t *) p4d);
1054
1055 pud = pud_offset(p4d, address);
1056 if (!pud_present(*pud))
1057 return 0;
1058
1059 if (pud_large(*pud))
1060 return spurious_kernel_fault_check(error_code, (pte_t *) pud);
1061
1062 pmd = pmd_offset(pud, address);
1063 if (!pmd_present(*pmd))
1064 return 0;
1065
1066 if (pmd_large(*pmd))
1067 return spurious_kernel_fault_check(error_code, (pte_t *) pmd);
1068
1069 pte = pte_offset_kernel(pmd, address);
1070 if (!pte_present(*pte))
1071 return 0;
1072
1073 ret = spurious_kernel_fault_check(error_code, pte);
1074 if (!ret)
1075 return 0;
1076
1077 /*
1078 * Make sure we have permissions in PMD.
1079 * If not, then there's a bug in the page tables:
1080 */
1081 ret = spurious_kernel_fault_check(error_code, (pte_t *) pmd);
1082 WARN_ONCE(!ret, "PMD has incorrect permission bits\n");
1083
1084 return ret;
1085}
1086NOKPROBE_SYMBOL(spurious_kernel_fault);
1087
1088int show_unhandled_signals = 1;
1089
1090static inline int
1091access_error(unsigned long error_code, struct vm_area_struct *vma)
1092{
1093 /* This is only called for the current mm, so: */
1094 bool foreign = false;
1095
1096 /*
1097 * Read or write was blocked by protection keys. This is
1098 * always an unconditional error and can never result in
1099 * a follow-up action to resolve the fault, like a COW.
1100 */
1101 if (error_code & X86_PF_PK)
1102 return 1;
1103
1104 /*
1105 * Make sure to check the VMA so that we do not perform
1106 * faults just to hit a X86_PF_PK as soon as we fill in a
1107 * page.
1108 */
1109 if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE),
1110 (error_code & X86_PF_INSTR), foreign))
1111 return 1;
1112
1113 if (error_code & X86_PF_WRITE) {
1114 /* write, present and write, not present: */
1115 if (unlikely(!(vma->vm_flags & VM_WRITE)))
1116 return 1;
1117 return 0;
1118 }
1119
1120 /* read, present: */
1121 if (unlikely(error_code & X86_PF_PROT))
1122 return 1;
1123
1124 /* read, not present: */
1125 if (unlikely(!vma_is_accessible(vma)))
1126 return 1;
1127
1128 return 0;
1129}
1130
1131static int fault_in_kernel_space(unsigned long address)
1132{
1133 /*
1134 * On 64-bit systems, the vsyscall page is at an address above
1135 * TASK_SIZE_MAX, but is not considered part of the kernel
1136 * address space.
1137 */
1138 if (IS_ENABLED(CONFIG_X86_64) && is_vsyscall_vaddr(address))
1139 return false;
1140
1141 return address >= TASK_SIZE_MAX;
1142}
1143
1144/*
1145 * Called for all faults where 'address' is part of the kernel address
1146 * space. Might get called for faults that originate from *code* that
1147 * ran in userspace or the kernel.
1148 */
1149static void
1150do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code,
1151 unsigned long address)
1152{
1153 /*
1154 * Protection keys exceptions only happen on user pages. We
1155 * have no user pages in the kernel portion of the address
1156 * space, so do not expect them here.
1157 */
1158 WARN_ON_ONCE(hw_error_code & X86_PF_PK);
1159
1160#ifdef CONFIG_X86_32
1161 /*
1162 * We can fault-in kernel-space virtual memory on-demand. The
1163 * 'reference' page table is init_mm.pgd.
1164 *
1165 * NOTE! We MUST NOT take any locks for this case. We may
1166 * be in an interrupt or a critical region, and should
1167 * only copy the information from the master page table,
1168 * nothing more.
1169 *
1170 * Before doing this on-demand faulting, ensure that the
1171 * fault is not any of the following:
1172 * 1. A fault on a PTE with a reserved bit set.
1173 * 2. A fault caused by a user-mode access. (Do not demand-
1174 * fault kernel memory due to user-mode accesses).
1175 * 3. A fault caused by a page-level protection violation.
1176 * (A demand fault would be on a non-present page which
1177 * would have X86_PF_PROT==0).
1178 *
1179 * This is only needed to close a race condition on x86-32 in
1180 * the vmalloc mapping/unmapping code. See the comment above
1181 * vmalloc_fault() for details. On x86-64 the race does not
1182 * exist as the vmalloc mappings don't need to be synchronized
1183 * there.
1184 */
1185 if (!(hw_error_code & (X86_PF_RSVD | X86_PF_USER | X86_PF_PROT))) {
1186 if (vmalloc_fault(address) >= 0)
1187 return;
1188 }
1189#endif
1190
1191 /* Was the fault spurious, caused by lazy TLB invalidation? */
1192 if (spurious_kernel_fault(hw_error_code, address))
1193 return;
1194
1195 /* kprobes don't want to hook the spurious faults: */
1196 if (kprobe_page_fault(regs, X86_TRAP_PF))
1197 return;
1198
1199 /*
1200 * Note, despite being a "bad area", there are quite a few
1201 * acceptable reasons to get here, such as erratum fixups
1202 * and handling kernel code that can fault, like get_user().
1203 *
1204 * Don't take the mm semaphore here. If we fixup a prefetch
1205 * fault we could otherwise deadlock:
1206 */
1207 bad_area_nosemaphore(regs, hw_error_code, address);
1208}
1209NOKPROBE_SYMBOL(do_kern_addr_fault);
1210
1211/* Handle faults in the user portion of the address space */
1212static inline
1213void do_user_addr_fault(struct pt_regs *regs,
1214 unsigned long hw_error_code,
1215 unsigned long address)
1216{
1217 struct vm_area_struct *vma;
1218 struct task_struct *tsk;
1219 struct mm_struct *mm;
1220 vm_fault_t fault;
1221 unsigned int flags = FAULT_FLAG_DEFAULT;
1222
1223 tsk = current;
1224 mm = tsk->mm;
1225
1226 /* kprobes don't want to hook the spurious faults: */
1227 if (unlikely(kprobe_page_fault(regs, X86_TRAP_PF)))
1228 return;
1229
1230 /*
1231 * Reserved bits are never expected to be set on
1232 * entries in the user portion of the page tables.
1233 */
1234 if (unlikely(hw_error_code & X86_PF_RSVD))
1235 pgtable_bad(regs, hw_error_code, address);
1236
1237 /*
1238 * If SMAP is on, check for invalid kernel (supervisor) access to user
1239 * pages in the user address space. The odd case here is WRUSS,
1240 * which, according to the preliminary documentation, does not respect
1241 * SMAP and will have the USER bit set so, in all cases, SMAP
1242 * enforcement appears to be consistent with the USER bit.
1243 */
1244 if (unlikely(cpu_feature_enabled(X86_FEATURE_SMAP) &&
1245 !(hw_error_code & X86_PF_USER) &&
1246 !(regs->flags & X86_EFLAGS_AC)))
1247 {
1248 bad_area_nosemaphore(regs, hw_error_code, address);
1249 return;
1250 }
1251
1252 /*
1253 * If we're in an interrupt, have no user context or are running
1254 * in a region with pagefaults disabled then we must not take the fault
1255 */
1256 if (unlikely(faulthandler_disabled() || !mm)) {
1257 bad_area_nosemaphore(regs, hw_error_code, address);
1258 return;
1259 }
1260
1261 /*
1262 * It's safe to allow irq's after cr2 has been saved and the
1263 * vmalloc fault has been handled.
1264 *
1265 * User-mode registers count as a user access even for any
1266 * potential system fault or CPU buglet:
1267 */
1268 if (user_mode(regs)) {
1269 local_irq_enable();
1270 flags |= FAULT_FLAG_USER;
1271 } else {
1272 if (regs->flags & X86_EFLAGS_IF)
1273 local_irq_enable();
1274 }
1275
1276 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
1277
1278 if (hw_error_code & X86_PF_WRITE)
1279 flags |= FAULT_FLAG_WRITE;
1280 if (hw_error_code & X86_PF_INSTR)
1281 flags |= FAULT_FLAG_INSTRUCTION;
1282
1283#ifdef CONFIG_X86_64
1284 /*
1285 * Faults in the vsyscall page might need emulation. The
1286 * vsyscall page is at a high address (>PAGE_OFFSET), but is
1287 * considered to be part of the user address space.
1288 *
1289 * The vsyscall page does not have a "real" VMA, so do this
1290 * emulation before we go searching for VMAs.
1291 *
1292 * PKRU never rejects instruction fetches, so we don't need
1293 * to consider the PF_PK bit.
1294 */
1295 if (is_vsyscall_vaddr(address)) {
1296 if (emulate_vsyscall(hw_error_code, regs, address))
1297 return;
1298 }
1299#endif
1300
1301 /*
1302 * Kernel-mode access to the user address space should only occur
1303 * on well-defined single instructions listed in the exception
1304 * tables. But, an erroneous kernel fault occurring outside one of
1305 * those areas which also holds mmap_lock might deadlock attempting
1306 * to validate the fault against the address space.
1307 *
1308 * Only do the expensive exception table search when we might be at
1309 * risk of a deadlock. This happens if we
1310 * 1. Failed to acquire mmap_lock, and
1311 * 2. The access did not originate in userspace.
1312 */
1313 if (unlikely(!mmap_read_trylock(mm))) {
1314 if (!user_mode(regs) && !search_exception_tables(regs->ip)) {
1315 /*
1316 * Fault from code in kernel from
1317 * which we do not expect faults.
1318 */
1319 bad_area_nosemaphore(regs, hw_error_code, address);
1320 return;
1321 }
1322retry:
1323 mmap_read_lock(mm);
1324 } else {
1325 /*
1326 * The above down_read_trylock() might have succeeded in
1327 * which case we'll have missed the might_sleep() from
1328 * down_read():
1329 */
1330 might_sleep();
1331 }
1332
1333 vma = find_vma(mm, address);
1334 if (unlikely(!vma)) {
1335 bad_area(regs, hw_error_code, address);
1336 return;
1337 }
1338 if (likely(vma->vm_start <= address))
1339 goto good_area;
1340 if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
1341 bad_area(regs, hw_error_code, address);
1342 return;
1343 }
1344 if (unlikely(expand_stack(vma, address))) {
1345 bad_area(regs, hw_error_code, address);
1346 return;
1347 }
1348
1349 /*
1350 * Ok, we have a good vm_area for this memory access, so
1351 * we can handle it..
1352 */
1353good_area:
1354 if (unlikely(access_error(hw_error_code, vma))) {
1355 bad_area_access_error(regs, hw_error_code, address, vma);
1356 return;
1357 }
1358
1359 /*
1360 * If for any reason at all we couldn't handle the fault,
1361 * make sure we exit gracefully rather than endlessly redo
1362 * the fault. Since we never set FAULT_FLAG_RETRY_NOWAIT, if
1363 * we get VM_FAULT_RETRY back, the mmap_lock has been unlocked.
1364 *
1365 * Note that handle_userfault() may also release and reacquire mmap_lock
1366 * (and not return with VM_FAULT_RETRY), when returning to userland to
1367 * repeat the page fault later with a VM_FAULT_NOPAGE retval
1368 * (potentially after handling any pending signal during the return to
1369 * userland). The return to userland is identified whenever
1370 * FAULT_FLAG_USER|FAULT_FLAG_KILLABLE are both set in flags.
1371 */
1372 fault = handle_mm_fault(vma, address, flags, regs);
1373
1374 /* Quick path to respond to signals */
1375 if (fault_signal_pending(fault, regs)) {
1376 if (!user_mode(regs))
1377 no_context(regs, hw_error_code, address, SIGBUS,
1378 BUS_ADRERR);
1379 return;
1380 }
1381
1382 /*
1383 * If we need to retry the mmap_lock has already been released,
1384 * and if there is a fatal signal pending there is no guarantee
1385 * that we made any progress. Handle this case first.
1386 */
1387 if (unlikely((fault & VM_FAULT_RETRY) &&
1388 (flags & FAULT_FLAG_ALLOW_RETRY))) {
1389 flags |= FAULT_FLAG_TRIED;
1390 goto retry;
1391 }
1392
1393 mmap_read_unlock(mm);
1394 if (unlikely(fault & VM_FAULT_ERROR)) {
1395 mm_fault_error(regs, hw_error_code, address, fault);
1396 return;
1397 }
1398
1399 check_v8086_mode(regs, address, tsk);
1400}
1401NOKPROBE_SYMBOL(do_user_addr_fault);
1402
1403static __always_inline void
1404trace_page_fault_entries(struct pt_regs *regs, unsigned long error_code,
1405 unsigned long address)
1406{
1407 if (!trace_pagefault_enabled())
1408 return;
1409
1410 if (user_mode(regs))
1411 trace_page_fault_user(address, regs, error_code);
1412 else
1413 trace_page_fault_kernel(address, regs, error_code);
1414}
1415
1416static __always_inline void
1417handle_page_fault(struct pt_regs *regs, unsigned long error_code,
1418 unsigned long address)
1419{
1420 trace_page_fault_entries(regs, error_code, address);
1421
1422 if (unlikely(kmmio_fault(regs, address)))
1423 return;
1424
1425 /* Was the fault on kernel-controlled part of the address space? */
1426 if (unlikely(fault_in_kernel_space(address))) {
1427 do_kern_addr_fault(regs, error_code, address);
1428 } else {
1429 do_user_addr_fault(regs, error_code, address);
1430 /*
1431 * User address page fault handling might have reenabled
1432 * interrupts. Fixing up all potential exit points of
1433 * do_user_addr_fault() and its leaf functions is just not
1434 * doable w/o creating an unholy mess or turning the code
1435 * upside down.
1436 */
1437 local_irq_disable();
1438 }
1439}
1440
1441DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault)
1442{
1443 unsigned long address = read_cr2();
1444 irqentry_state_t state;
1445
1446 prefetchw(¤t->mm->mmap_lock);
1447
1448 /*
1449 * KVM has two types of events that are, logically, interrupts, but
1450 * are unfortunately delivered using the #PF vector. These events are
1451 * "you just accessed valid memory, but the host doesn't have it right
1452 * now, so I'll put you to sleep if you continue" and "that memory
1453 * you tried to access earlier is available now."
1454 *
1455 * We are relying on the interrupted context being sane (valid RSP,
1456 * relevant locks not held, etc.), which is fine as long as the
1457 * interrupted context had IF=1. We are also relying on the KVM
1458 * async pf type field and CR2 being read consistently instead of
1459 * getting values from real and async page faults mixed up.
1460 *
1461 * Fingers crossed.
1462 *
1463 * The async #PF handling code takes care of idtentry handling
1464 * itself.
1465 */
1466 if (kvm_handle_async_pf(regs, (u32)address))
1467 return;
1468
1469 /*
1470 * Entry handling for valid #PF from kernel mode is slightly
1471 * different: RCU is already watching and rcu_irq_enter() must not
1472 * be invoked because a kernel fault on a user space address might
1473 * sleep.
1474 *
1475 * In case the fault hit a RCU idle region the conditional entry
1476 * code reenabled RCU to avoid subsequent wreckage which helps
1477 * debugability.
1478 */
1479 state = irqentry_enter(regs);
1480
1481 instrumentation_begin();
1482 handle_page_fault(regs, error_code, address);
1483 instrumentation_end();
1484
1485 irqentry_exit(regs, state);
1486}
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/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/prefetch.h> /* prefetchw */
17#include <linux/context_tracking.h> /* exception_enter(), ... */
18#include <linux/uaccess.h> /* faulthandler_disabled() */
19#include <linux/efi.h> /* efi_recover_from_page_fault()*/
20#include <linux/mm_types.h>
21
22#include <asm/cpufeature.h> /* boot_cpu_has, ... */
23#include <asm/traps.h> /* dotraplinkage, ... */
24#include <asm/pgalloc.h> /* pgd_*(), ... */
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_recover_from_page_fault()*/
30#include <asm/desc.h> /* store_idt(), ... */
31#include <asm/cpu_entry_area.h> /* exception stack */
32
33#define CREATE_TRACE_POINTS
34#include <asm/trace/exceptions.h>
35
36/*
37 * Returns 0 if mmiotrace is disabled, or if the fault is not
38 * handled by mmiotrace:
39 */
40static nokprobe_inline int
41kmmio_fault(struct pt_regs *regs, unsigned long addr)
42{
43 if (unlikely(is_kmmio_active()))
44 if (kmmio_handler(regs, addr) == 1)
45 return -1;
46 return 0;
47}
48
49/*
50 * Prefetch quirks:
51 *
52 * 32-bit mode:
53 *
54 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
55 * Check that here and ignore it.
56 *
57 * 64-bit mode:
58 *
59 * Sometimes the CPU reports invalid exceptions on prefetch.
60 * Check that here and ignore it.
61 *
62 * Opcode checker based on code by Richard Brunner.
63 */
64static inline int
65check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr,
66 unsigned char opcode, int *prefetch)
67{
68 unsigned char instr_hi = opcode & 0xf0;
69 unsigned char instr_lo = opcode & 0x0f;
70
71 switch (instr_hi) {
72 case 0x20:
73 case 0x30:
74 /*
75 * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes.
76 * In X86_64 long mode, the CPU will signal invalid
77 * opcode if some of these prefixes are present so
78 * X86_64 will never get here anyway
79 */
80 return ((instr_lo & 7) == 0x6);
81#ifdef CONFIG_X86_64
82 case 0x40:
83 /*
84 * In AMD64 long mode 0x40..0x4F are valid REX prefixes
85 * Need to figure out under what instruction mode the
86 * instruction was issued. Could check the LDT for lm,
87 * but for now it's good enough to assume that long
88 * mode only uses well known segments or kernel.
89 */
90 return (!user_mode(regs) || user_64bit_mode(regs));
91#endif
92 case 0x60:
93 /* 0x64 thru 0x67 are valid prefixes in all modes. */
94 return (instr_lo & 0xC) == 0x4;
95 case 0xF0:
96 /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */
97 return !instr_lo || (instr_lo>>1) == 1;
98 case 0x00:
99 /* Prefetch instruction is 0x0F0D or 0x0F18 */
100 if (probe_kernel_address(instr, opcode))
101 return 0;
102
103 *prefetch = (instr_lo == 0xF) &&
104 (opcode == 0x0D || opcode == 0x18);
105 return 0;
106 default:
107 return 0;
108 }
109}
110
111static int
112is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr)
113{
114 unsigned char *max_instr;
115 unsigned char *instr;
116 int prefetch = 0;
117
118 /*
119 * If it was a exec (instruction fetch) fault on NX page, then
120 * do not ignore the fault:
121 */
122 if (error_code & X86_PF_INSTR)
123 return 0;
124
125 instr = (void *)convert_ip_to_linear(current, regs);
126 max_instr = instr + 15;
127
128 if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE_MAX)
129 return 0;
130
131 while (instr < max_instr) {
132 unsigned char opcode;
133
134 if (probe_kernel_address(instr, opcode))
135 break;
136
137 instr++;
138
139 if (!check_prefetch_opcode(regs, instr, opcode, &prefetch))
140 break;
141 }
142 return prefetch;
143}
144
145DEFINE_SPINLOCK(pgd_lock);
146LIST_HEAD(pgd_list);
147
148#ifdef CONFIG_X86_32
149static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
150{
151 unsigned index = pgd_index(address);
152 pgd_t *pgd_k;
153 p4d_t *p4d, *p4d_k;
154 pud_t *pud, *pud_k;
155 pmd_t *pmd, *pmd_k;
156
157 pgd += index;
158 pgd_k = init_mm.pgd + index;
159
160 if (!pgd_present(*pgd_k))
161 return NULL;
162
163 /*
164 * set_pgd(pgd, *pgd_k); here would be useless on PAE
165 * and redundant with the set_pmd() on non-PAE. As would
166 * set_p4d/set_pud.
167 */
168 p4d = p4d_offset(pgd, address);
169 p4d_k = p4d_offset(pgd_k, address);
170 if (!p4d_present(*p4d_k))
171 return NULL;
172
173 pud = pud_offset(p4d, address);
174 pud_k = pud_offset(p4d_k, address);
175 if (!pud_present(*pud_k))
176 return NULL;
177
178 pmd = pmd_offset(pud, address);
179 pmd_k = pmd_offset(pud_k, address);
180
181 if (pmd_present(*pmd) != pmd_present(*pmd_k))
182 set_pmd(pmd, *pmd_k);
183
184 if (!pmd_present(*pmd_k))
185 return NULL;
186 else
187 BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k));
188
189 return pmd_k;
190}
191
192void vmalloc_sync_all(void)
193{
194 unsigned long address;
195
196 if (SHARED_KERNEL_PMD)
197 return;
198
199 for (address = VMALLOC_START & PMD_MASK;
200 address >= TASK_SIZE_MAX && address < FIXADDR_TOP;
201 address += PMD_SIZE) {
202 struct page *page;
203
204 spin_lock(&pgd_lock);
205 list_for_each_entry(page, &pgd_list, lru) {
206 spinlock_t *pgt_lock;
207
208 /* the pgt_lock only for Xen */
209 pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
210
211 spin_lock(pgt_lock);
212 vmalloc_sync_one(page_address(page), address);
213 spin_unlock(pgt_lock);
214 }
215 spin_unlock(&pgd_lock);
216 }
217}
218
219/*
220 * 32-bit:
221 *
222 * Handle a fault on the vmalloc or module mapping area
223 */
224static noinline int vmalloc_fault(unsigned long address)
225{
226 unsigned long pgd_paddr;
227 pmd_t *pmd_k;
228 pte_t *pte_k;
229
230 /* Make sure we are in vmalloc area: */
231 if (!(address >= VMALLOC_START && address < VMALLOC_END))
232 return -1;
233
234 /*
235 * Synchronize this task's top level page-table
236 * with the 'reference' page table.
237 *
238 * Do _not_ use "current" here. We might be inside
239 * an interrupt in the middle of a task switch..
240 */
241 pgd_paddr = read_cr3_pa();
242 pmd_k = vmalloc_sync_one(__va(pgd_paddr), address);
243 if (!pmd_k)
244 return -1;
245
246 if (pmd_large(*pmd_k))
247 return 0;
248
249 pte_k = pte_offset_kernel(pmd_k, address);
250 if (!pte_present(*pte_k))
251 return -1;
252
253 return 0;
254}
255NOKPROBE_SYMBOL(vmalloc_fault);
256
257/*
258 * Did it hit the DOS screen memory VA from vm86 mode?
259 */
260static inline void
261check_v8086_mode(struct pt_regs *regs, unsigned long address,
262 struct task_struct *tsk)
263{
264#ifdef CONFIG_VM86
265 unsigned long bit;
266
267 if (!v8086_mode(regs) || !tsk->thread.vm86)
268 return;
269
270 bit = (address - 0xA0000) >> PAGE_SHIFT;
271 if (bit < 32)
272 tsk->thread.vm86->screen_bitmap |= 1 << bit;
273#endif
274}
275
276static bool low_pfn(unsigned long pfn)
277{
278 return pfn < max_low_pfn;
279}
280
281static void dump_pagetable(unsigned long address)
282{
283 pgd_t *base = __va(read_cr3_pa());
284 pgd_t *pgd = &base[pgd_index(address)];
285 p4d_t *p4d;
286 pud_t *pud;
287 pmd_t *pmd;
288 pte_t *pte;
289
290#ifdef CONFIG_X86_PAE
291 pr_info("*pdpt = %016Lx ", pgd_val(*pgd));
292 if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd))
293 goto out;
294#define pr_pde pr_cont
295#else
296#define pr_pde pr_info
297#endif
298 p4d = p4d_offset(pgd, address);
299 pud = pud_offset(p4d, address);
300 pmd = pmd_offset(pud, address);
301 pr_pde("*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd));
302#undef pr_pde
303
304 /*
305 * We must not directly access the pte in the highpte
306 * case if the page table is located in highmem.
307 * And let's rather not kmap-atomic the pte, just in case
308 * it's allocated already:
309 */
310 if (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_large(*pmd))
311 goto out;
312
313 pte = pte_offset_kernel(pmd, address);
314 pr_cont("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte));
315out:
316 pr_cont("\n");
317}
318
319#else /* CONFIG_X86_64: */
320
321void vmalloc_sync_all(void)
322{
323 sync_global_pgds(VMALLOC_START & PGDIR_MASK, VMALLOC_END);
324}
325
326/*
327 * 64-bit:
328 *
329 * Handle a fault on the vmalloc area
330 */
331static noinline int vmalloc_fault(unsigned long address)
332{
333 pgd_t *pgd, *pgd_k;
334 p4d_t *p4d, *p4d_k;
335 pud_t *pud;
336 pmd_t *pmd;
337 pte_t *pte;
338
339 /* Make sure we are in vmalloc area: */
340 if (!(address >= VMALLOC_START && address < VMALLOC_END))
341 return -1;
342
343 /*
344 * Copy kernel mappings over when needed. This can also
345 * happen within a race in page table update. In the later
346 * case just flush:
347 */
348 pgd = (pgd_t *)__va(read_cr3_pa()) + pgd_index(address);
349 pgd_k = pgd_offset_k(address);
350 if (pgd_none(*pgd_k))
351 return -1;
352
353 if (pgtable_l5_enabled()) {
354 if (pgd_none(*pgd)) {
355 set_pgd(pgd, *pgd_k);
356 arch_flush_lazy_mmu_mode();
357 } else {
358 BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_k));
359 }
360 }
361
362 /* With 4-level paging, copying happens on the p4d level. */
363 p4d = p4d_offset(pgd, address);
364 p4d_k = p4d_offset(pgd_k, address);
365 if (p4d_none(*p4d_k))
366 return -1;
367
368 if (p4d_none(*p4d) && !pgtable_l5_enabled()) {
369 set_p4d(p4d, *p4d_k);
370 arch_flush_lazy_mmu_mode();
371 } else {
372 BUG_ON(p4d_pfn(*p4d) != p4d_pfn(*p4d_k));
373 }
374
375 BUILD_BUG_ON(CONFIG_PGTABLE_LEVELS < 4);
376
377 pud = pud_offset(p4d, address);
378 if (pud_none(*pud))
379 return -1;
380
381 if (pud_large(*pud))
382 return 0;
383
384 pmd = pmd_offset(pud, address);
385 if (pmd_none(*pmd))
386 return -1;
387
388 if (pmd_large(*pmd))
389 return 0;
390
391 pte = pte_offset_kernel(pmd, address);
392 if (!pte_present(*pte))
393 return -1;
394
395 return 0;
396}
397NOKPROBE_SYMBOL(vmalloc_fault);
398
399#ifdef CONFIG_CPU_SUP_AMD
400static const char errata93_warning[] =
401KERN_ERR
402"******* Your BIOS seems to not contain a fix for K8 errata #93\n"
403"******* Working around it, but it may cause SEGVs or burn power.\n"
404"******* Please consider a BIOS update.\n"
405"******* Disabling USB legacy in the BIOS may also help.\n";
406#endif
407
408/*
409 * No vm86 mode in 64-bit mode:
410 */
411static inline void
412check_v8086_mode(struct pt_regs *regs, unsigned long address,
413 struct task_struct *tsk)
414{
415}
416
417static int bad_address(void *p)
418{
419 unsigned long dummy;
420
421 return probe_kernel_address((unsigned long *)p, dummy);
422}
423
424static void dump_pagetable(unsigned long address)
425{
426 pgd_t *base = __va(read_cr3_pa());
427 pgd_t *pgd = base + pgd_index(address);
428 p4d_t *p4d;
429 pud_t *pud;
430 pmd_t *pmd;
431 pte_t *pte;
432
433 if (bad_address(pgd))
434 goto bad;
435
436 pr_info("PGD %lx ", pgd_val(*pgd));
437
438 if (!pgd_present(*pgd))
439 goto out;
440
441 p4d = p4d_offset(pgd, address);
442 if (bad_address(p4d))
443 goto bad;
444
445 pr_cont("P4D %lx ", p4d_val(*p4d));
446 if (!p4d_present(*p4d) || p4d_large(*p4d))
447 goto out;
448
449 pud = pud_offset(p4d, address);
450 if (bad_address(pud))
451 goto bad;
452
453 pr_cont("PUD %lx ", pud_val(*pud));
454 if (!pud_present(*pud) || pud_large(*pud))
455 goto out;
456
457 pmd = pmd_offset(pud, address);
458 if (bad_address(pmd))
459 goto bad;
460
461 pr_cont("PMD %lx ", pmd_val(*pmd));
462 if (!pmd_present(*pmd) || pmd_large(*pmd))
463 goto out;
464
465 pte = pte_offset_kernel(pmd, address);
466 if (bad_address(pte))
467 goto bad;
468
469 pr_cont("PTE %lx", pte_val(*pte));
470out:
471 pr_cont("\n");
472 return;
473bad:
474 pr_info("BAD\n");
475}
476
477#endif /* CONFIG_X86_64 */
478
479/*
480 * Workaround for K8 erratum #93 & buggy BIOS.
481 *
482 * BIOS SMM functions are required to use a specific workaround
483 * to avoid corruption of the 64bit RIP register on C stepping K8.
484 *
485 * A lot of BIOS that didn't get tested properly miss this.
486 *
487 * The OS sees this as a page fault with the upper 32bits of RIP cleared.
488 * Try to work around it here.
489 *
490 * Note we only handle faults in kernel here.
491 * Does nothing on 32-bit.
492 */
493static int is_errata93(struct pt_regs *regs, unsigned long address)
494{
495#if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD)
496 if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD
497 || boot_cpu_data.x86 != 0xf)
498 return 0;
499
500 if (address != regs->ip)
501 return 0;
502
503 if ((address >> 32) != 0)
504 return 0;
505
506 address |= 0xffffffffUL << 32;
507 if ((address >= (u64)_stext && address <= (u64)_etext) ||
508 (address >= MODULES_VADDR && address <= MODULES_END)) {
509 printk_once(errata93_warning);
510 regs->ip = address;
511 return 1;
512 }
513#endif
514 return 0;
515}
516
517/*
518 * Work around K8 erratum #100 K8 in compat mode occasionally jumps
519 * to illegal addresses >4GB.
520 *
521 * We catch this in the page fault handler because these addresses
522 * are not reachable. Just detect this case and return. Any code
523 * segment in LDT is compatibility mode.
524 */
525static int is_errata100(struct pt_regs *regs, unsigned long address)
526{
527#ifdef CONFIG_X86_64
528 if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32))
529 return 1;
530#endif
531 return 0;
532}
533
534static int is_f00f_bug(struct pt_regs *regs, unsigned long address)
535{
536#ifdef CONFIG_X86_F00F_BUG
537 unsigned long nr;
538
539 /*
540 * Pentium F0 0F C7 C8 bug workaround:
541 */
542 if (boot_cpu_has_bug(X86_BUG_F00F)) {
543 nr = (address - idt_descr.address) >> 3;
544
545 if (nr == 6) {
546 do_invalid_op(regs, 0);
547 return 1;
548 }
549 }
550#endif
551 return 0;
552}
553
554static void show_ldttss(const struct desc_ptr *gdt, const char *name, u16 index)
555{
556 u32 offset = (index >> 3) * sizeof(struct desc_struct);
557 unsigned long addr;
558 struct ldttss_desc desc;
559
560 if (index == 0) {
561 pr_alert("%s: NULL\n", name);
562 return;
563 }
564
565 if (offset + sizeof(struct ldttss_desc) >= gdt->size) {
566 pr_alert("%s: 0x%hx -- out of bounds\n", name, index);
567 return;
568 }
569
570 if (probe_kernel_read(&desc, (void *)(gdt->address + offset),
571 sizeof(struct ldttss_desc))) {
572 pr_alert("%s: 0x%hx -- GDT entry is not readable\n",
573 name, index);
574 return;
575 }
576
577 addr = desc.base0 | (desc.base1 << 16) | ((unsigned long)desc.base2 << 24);
578#ifdef CONFIG_X86_64
579 addr |= ((u64)desc.base3 << 32);
580#endif
581 pr_alert("%s: 0x%hx -- base=0x%lx limit=0x%x\n",
582 name, index, addr, (desc.limit0 | (desc.limit1 << 16)));
583}
584
585static void
586show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long address)
587{
588 if (!oops_may_print())
589 return;
590
591 if (error_code & X86_PF_INSTR) {
592 unsigned int level;
593 pgd_t *pgd;
594 pte_t *pte;
595
596 pgd = __va(read_cr3_pa());
597 pgd += pgd_index(address);
598
599 pte = lookup_address_in_pgd(pgd, address, &level);
600
601 if (pte && pte_present(*pte) && !pte_exec(*pte))
602 pr_crit("kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n",
603 from_kuid(&init_user_ns, current_uid()));
604 if (pte && pte_present(*pte) && pte_exec(*pte) &&
605 (pgd_flags(*pgd) & _PAGE_USER) &&
606 (__read_cr4() & X86_CR4_SMEP))
607 pr_crit("unable to execute userspace code (SMEP?) (uid: %d)\n",
608 from_kuid(&init_user_ns, current_uid()));
609 }
610
611 if (address < PAGE_SIZE && !user_mode(regs))
612 pr_alert("BUG: kernel NULL pointer dereference, address: %px\n",
613 (void *)address);
614 else
615 pr_alert("BUG: unable to handle page fault for address: %px\n",
616 (void *)address);
617
618 pr_alert("#PF: %s %s in %s mode\n",
619 (error_code & X86_PF_USER) ? "user" : "supervisor",
620 (error_code & X86_PF_INSTR) ? "instruction fetch" :
621 (error_code & X86_PF_WRITE) ? "write access" :
622 "read access",
623 user_mode(regs) ? "user" : "kernel");
624 pr_alert("#PF: error_code(0x%04lx) - %s\n", error_code,
625 !(error_code & X86_PF_PROT) ? "not-present page" :
626 (error_code & X86_PF_RSVD) ? "reserved bit violation" :
627 (error_code & X86_PF_PK) ? "protection keys violation" :
628 "permissions violation");
629
630 if (!(error_code & X86_PF_USER) && user_mode(regs)) {
631 struct desc_ptr idt, gdt;
632 u16 ldtr, tr;
633
634 /*
635 * This can happen for quite a few reasons. The more obvious
636 * ones are faults accessing the GDT, or LDT. Perhaps
637 * surprisingly, if the CPU tries to deliver a benign or
638 * contributory exception from user code and gets a page fault
639 * during delivery, the page fault can be delivered as though
640 * it originated directly from user code. This could happen
641 * due to wrong permissions on the IDT, GDT, LDT, TSS, or
642 * kernel or IST stack.
643 */
644 store_idt(&idt);
645
646 /* Usable even on Xen PV -- it's just slow. */
647 native_store_gdt(&gdt);
648
649 pr_alert("IDT: 0x%lx (limit=0x%hx) GDT: 0x%lx (limit=0x%hx)\n",
650 idt.address, idt.size, gdt.address, gdt.size);
651
652 store_ldt(ldtr);
653 show_ldttss(&gdt, "LDTR", ldtr);
654
655 store_tr(tr);
656 show_ldttss(&gdt, "TR", tr);
657 }
658
659 dump_pagetable(address);
660}
661
662static noinline void
663pgtable_bad(struct pt_regs *regs, unsigned long error_code,
664 unsigned long address)
665{
666 struct task_struct *tsk;
667 unsigned long flags;
668 int sig;
669
670 flags = oops_begin();
671 tsk = current;
672 sig = SIGKILL;
673
674 printk(KERN_ALERT "%s: Corrupted page table at address %lx\n",
675 tsk->comm, address);
676 dump_pagetable(address);
677
678 if (__die("Bad pagetable", regs, error_code))
679 sig = 0;
680
681 oops_end(flags, regs, sig);
682}
683
684static void set_signal_archinfo(unsigned long address,
685 unsigned long error_code)
686{
687 struct task_struct *tsk = current;
688
689 /*
690 * To avoid leaking information about the kernel page
691 * table layout, pretend that user-mode accesses to
692 * kernel addresses are always protection faults.
693 *
694 * NB: This means that failed vsyscalls with vsyscall=none
695 * will have the PROT bit. This doesn't leak any
696 * information and does not appear to cause any problems.
697 */
698 if (address >= TASK_SIZE_MAX)
699 error_code |= X86_PF_PROT;
700
701 tsk->thread.trap_nr = X86_TRAP_PF;
702 tsk->thread.error_code = error_code | X86_PF_USER;
703 tsk->thread.cr2 = address;
704}
705
706static noinline void
707no_context(struct pt_regs *regs, unsigned long error_code,
708 unsigned long address, int signal, int si_code)
709{
710 struct task_struct *tsk = current;
711 unsigned long flags;
712 int sig;
713
714 if (user_mode(regs)) {
715 /*
716 * This is an implicit supervisor-mode access from user
717 * mode. Bypass all the kernel-mode recovery code and just
718 * OOPS.
719 */
720 goto oops;
721 }
722
723 /* Are we prepared to handle this kernel fault? */
724 if (fixup_exception(regs, X86_TRAP_PF, error_code, address)) {
725 /*
726 * Any interrupt that takes a fault gets the fixup. This makes
727 * the below recursive fault logic only apply to a faults from
728 * task context.
729 */
730 if (in_interrupt())
731 return;
732
733 /*
734 * Per the above we're !in_interrupt(), aka. task context.
735 *
736 * In this case we need to make sure we're not recursively
737 * faulting through the emulate_vsyscall() logic.
738 */
739 if (current->thread.sig_on_uaccess_err && signal) {
740 set_signal_archinfo(address, error_code);
741
742 /* XXX: hwpoison faults will set the wrong code. */
743 force_sig_fault(signal, si_code, (void __user *)address);
744 }
745
746 /*
747 * Barring that, we can do the fixup and be happy.
748 */
749 return;
750 }
751
752#ifdef CONFIG_VMAP_STACK
753 /*
754 * Stack overflow? During boot, we can fault near the initial
755 * stack in the direct map, but that's not an overflow -- check
756 * that we're in vmalloc space to avoid this.
757 */
758 if (is_vmalloc_addr((void *)address) &&
759 (((unsigned long)tsk->stack - 1 - address < PAGE_SIZE) ||
760 address - ((unsigned long)tsk->stack + THREAD_SIZE) < PAGE_SIZE)) {
761 unsigned long stack = __this_cpu_ist_top_va(DF) - sizeof(void *);
762 /*
763 * We're likely to be running with very little stack space
764 * left. It's plausible that we'd hit this condition but
765 * double-fault even before we get this far, in which case
766 * we're fine: the double-fault handler will deal with it.
767 *
768 * We don't want to make it all the way into the oops code
769 * and then double-fault, though, because we're likely to
770 * break the console driver and lose most of the stack dump.
771 */
772 asm volatile ("movq %[stack], %%rsp\n\t"
773 "call handle_stack_overflow\n\t"
774 "1: jmp 1b"
775 : ASM_CALL_CONSTRAINT
776 : "D" ("kernel stack overflow (page fault)"),
777 "S" (regs), "d" (address),
778 [stack] "rm" (stack));
779 unreachable();
780 }
781#endif
782
783 /*
784 * 32-bit:
785 *
786 * Valid to do another page fault here, because if this fault
787 * had been triggered by is_prefetch fixup_exception would have
788 * handled it.
789 *
790 * 64-bit:
791 *
792 * Hall of shame of CPU/BIOS bugs.
793 */
794 if (is_prefetch(regs, error_code, address))
795 return;
796
797 if (is_errata93(regs, address))
798 return;
799
800 /*
801 * Buggy firmware could access regions which might page fault, try to
802 * recover from such faults.
803 */
804 if (IS_ENABLED(CONFIG_EFI))
805 efi_recover_from_page_fault(address);
806
807oops:
808 /*
809 * Oops. The kernel tried to access some bad page. We'll have to
810 * terminate things with extreme prejudice:
811 */
812 flags = oops_begin();
813
814 show_fault_oops(regs, error_code, address);
815
816 if (task_stack_end_corrupted(tsk))
817 printk(KERN_EMERG "Thread overran stack, or stack corrupted\n");
818
819 sig = SIGKILL;
820 if (__die("Oops", regs, error_code))
821 sig = 0;
822
823 /* Executive summary in case the body of the oops scrolled away */
824 printk(KERN_DEFAULT "CR2: %016lx\n", address);
825
826 oops_end(flags, regs, sig);
827}
828
829/*
830 * Print out info about fatal segfaults, if the show_unhandled_signals
831 * sysctl is set:
832 */
833static inline void
834show_signal_msg(struct pt_regs *regs, unsigned long error_code,
835 unsigned long address, struct task_struct *tsk)
836{
837 const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG;
838
839 if (!unhandled_signal(tsk, SIGSEGV))
840 return;
841
842 if (!printk_ratelimit())
843 return;
844
845 printk("%s%s[%d]: segfault at %lx ip %px sp %px error %lx",
846 loglvl, tsk->comm, task_pid_nr(tsk), address,
847 (void *)regs->ip, (void *)regs->sp, error_code);
848
849 print_vma_addr(KERN_CONT " in ", regs->ip);
850
851 printk(KERN_CONT "\n");
852
853 show_opcodes(regs, loglvl);
854}
855
856/*
857 * The (legacy) vsyscall page is the long page in the kernel portion
858 * of the address space that has user-accessible permissions.
859 */
860static bool is_vsyscall_vaddr(unsigned long vaddr)
861{
862 return unlikely((vaddr & PAGE_MASK) == VSYSCALL_ADDR);
863}
864
865static void
866__bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
867 unsigned long address, u32 pkey, int si_code)
868{
869 struct task_struct *tsk = current;
870
871 /* User mode accesses just cause a SIGSEGV */
872 if (user_mode(regs) && (error_code & X86_PF_USER)) {
873 /*
874 * It's possible to have interrupts off here:
875 */
876 local_irq_enable();
877
878 /*
879 * Valid to do another page fault here because this one came
880 * from user space:
881 */
882 if (is_prefetch(regs, error_code, address))
883 return;
884
885 if (is_errata100(regs, address))
886 return;
887
888 /*
889 * To avoid leaking information about the kernel page table
890 * layout, pretend that user-mode accesses to kernel addresses
891 * are always protection faults.
892 */
893 if (address >= TASK_SIZE_MAX)
894 error_code |= X86_PF_PROT;
895
896 if (likely(show_unhandled_signals))
897 show_signal_msg(regs, error_code, address, tsk);
898
899 set_signal_archinfo(address, error_code);
900
901 if (si_code == SEGV_PKUERR)
902 force_sig_pkuerr((void __user *)address, pkey);
903
904 force_sig_fault(SIGSEGV, si_code, (void __user *)address);
905
906 return;
907 }
908
909 if (is_f00f_bug(regs, address))
910 return;
911
912 no_context(regs, error_code, address, SIGSEGV, si_code);
913}
914
915static noinline void
916bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
917 unsigned long address)
918{
919 __bad_area_nosemaphore(regs, error_code, address, 0, SEGV_MAPERR);
920}
921
922static void
923__bad_area(struct pt_regs *regs, unsigned long error_code,
924 unsigned long address, u32 pkey, int si_code)
925{
926 struct mm_struct *mm = current->mm;
927 /*
928 * Something tried to access memory that isn't in our memory map..
929 * Fix it, but check if it's kernel or user first..
930 */
931 up_read(&mm->mmap_sem);
932
933 __bad_area_nosemaphore(regs, error_code, address, pkey, si_code);
934}
935
936static noinline void
937bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address)
938{
939 __bad_area(regs, error_code, address, 0, SEGV_MAPERR);
940}
941
942static inline bool bad_area_access_from_pkeys(unsigned long error_code,
943 struct vm_area_struct *vma)
944{
945 /* This code is always called on the current mm */
946 bool foreign = false;
947
948 if (!boot_cpu_has(X86_FEATURE_OSPKE))
949 return false;
950 if (error_code & X86_PF_PK)
951 return true;
952 /* this checks permission keys on the VMA: */
953 if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE),
954 (error_code & X86_PF_INSTR), foreign))
955 return true;
956 return false;
957}
958
959static noinline void
960bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
961 unsigned long address, struct vm_area_struct *vma)
962{
963 /*
964 * This OSPKE check is not strictly necessary at runtime.
965 * But, doing it this way allows compiler optimizations
966 * if pkeys are compiled out.
967 */
968 if (bad_area_access_from_pkeys(error_code, vma)) {
969 /*
970 * A protection key fault means that the PKRU value did not allow
971 * access to some PTE. Userspace can figure out what PKRU was
972 * from the XSAVE state. This function captures the pkey from
973 * the vma and passes it to userspace so userspace can discover
974 * which protection key was set on the PTE.
975 *
976 * If we get here, we know that the hardware signaled a X86_PF_PK
977 * fault and that there was a VMA once we got in the fault
978 * handler. It does *not* guarantee that the VMA we find here
979 * was the one that we faulted on.
980 *
981 * 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4);
982 * 2. T1 : set PKRU to deny access to pkey=4, touches page
983 * 3. T1 : faults...
984 * 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5);
985 * 5. T1 : enters fault handler, takes mmap_sem, etc...
986 * 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really
987 * faulted on a pte with its pkey=4.
988 */
989 u32 pkey = vma_pkey(vma);
990
991 __bad_area(regs, error_code, address, pkey, SEGV_PKUERR);
992 } else {
993 __bad_area(regs, error_code, address, 0, SEGV_ACCERR);
994 }
995}
996
997static void
998do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
999 vm_fault_t fault)
1000{
1001 /* Kernel mode? Handle exceptions or die: */
1002 if (!(error_code & X86_PF_USER)) {
1003 no_context(regs, error_code, address, SIGBUS, BUS_ADRERR);
1004 return;
1005 }
1006
1007 /* User-space => ok to do another page fault: */
1008 if (is_prefetch(regs, error_code, address))
1009 return;
1010
1011 set_signal_archinfo(address, error_code);
1012
1013#ifdef CONFIG_MEMORY_FAILURE
1014 if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
1015 struct task_struct *tsk = current;
1016 unsigned lsb = 0;
1017
1018 pr_err(
1019 "MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
1020 tsk->comm, tsk->pid, address);
1021 if (fault & VM_FAULT_HWPOISON_LARGE)
1022 lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
1023 if (fault & VM_FAULT_HWPOISON)
1024 lsb = PAGE_SHIFT;
1025 force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb);
1026 return;
1027 }
1028#endif
1029 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
1030}
1031
1032static noinline void
1033mm_fault_error(struct pt_regs *regs, unsigned long error_code,
1034 unsigned long address, vm_fault_t fault)
1035{
1036 if (fatal_signal_pending(current) && !(error_code & X86_PF_USER)) {
1037 no_context(regs, error_code, address, 0, 0);
1038 return;
1039 }
1040
1041 if (fault & VM_FAULT_OOM) {
1042 /* Kernel mode? Handle exceptions or die: */
1043 if (!(error_code & X86_PF_USER)) {
1044 no_context(regs, error_code, address,
1045 SIGSEGV, SEGV_MAPERR);
1046 return;
1047 }
1048
1049 /*
1050 * We ran out of memory, call the OOM killer, and return the
1051 * userspace (which will retry the fault, or kill us if we got
1052 * oom-killed):
1053 */
1054 pagefault_out_of_memory();
1055 } else {
1056 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
1057 VM_FAULT_HWPOISON_LARGE))
1058 do_sigbus(regs, error_code, address, fault);
1059 else if (fault & VM_FAULT_SIGSEGV)
1060 bad_area_nosemaphore(regs, error_code, address);
1061 else
1062 BUG();
1063 }
1064}
1065
1066static int spurious_kernel_fault_check(unsigned long error_code, pte_t *pte)
1067{
1068 if ((error_code & X86_PF_WRITE) && !pte_write(*pte))
1069 return 0;
1070
1071 if ((error_code & X86_PF_INSTR) && !pte_exec(*pte))
1072 return 0;
1073
1074 return 1;
1075}
1076
1077/*
1078 * Handle a spurious fault caused by a stale TLB entry.
1079 *
1080 * This allows us to lazily refresh the TLB when increasing the
1081 * permissions of a kernel page (RO -> RW or NX -> X). Doing it
1082 * eagerly is very expensive since that implies doing a full
1083 * cross-processor TLB flush, even if no stale TLB entries exist
1084 * on other processors.
1085 *
1086 * Spurious faults may only occur if the TLB contains an entry with
1087 * fewer permission than the page table entry. Non-present (P = 0)
1088 * and reserved bit (R = 1) faults are never spurious.
1089 *
1090 * There are no security implications to leaving a stale TLB when
1091 * increasing the permissions on a page.
1092 *
1093 * Returns non-zero if a spurious fault was handled, zero otherwise.
1094 *
1095 * See Intel Developer's Manual Vol 3 Section 4.10.4.3, bullet 3
1096 * (Optional Invalidation).
1097 */
1098static noinline int
1099spurious_kernel_fault(unsigned long error_code, unsigned long address)
1100{
1101 pgd_t *pgd;
1102 p4d_t *p4d;
1103 pud_t *pud;
1104 pmd_t *pmd;
1105 pte_t *pte;
1106 int ret;
1107
1108 /*
1109 * Only writes to RO or instruction fetches from NX may cause
1110 * spurious faults.
1111 *
1112 * These could be from user or supervisor accesses but the TLB
1113 * is only lazily flushed after a kernel mapping protection
1114 * change, so user accesses are not expected to cause spurious
1115 * faults.
1116 */
1117 if (error_code != (X86_PF_WRITE | X86_PF_PROT) &&
1118 error_code != (X86_PF_INSTR | X86_PF_PROT))
1119 return 0;
1120
1121 pgd = init_mm.pgd + pgd_index(address);
1122 if (!pgd_present(*pgd))
1123 return 0;
1124
1125 p4d = p4d_offset(pgd, address);
1126 if (!p4d_present(*p4d))
1127 return 0;
1128
1129 if (p4d_large(*p4d))
1130 return spurious_kernel_fault_check(error_code, (pte_t *) p4d);
1131
1132 pud = pud_offset(p4d, address);
1133 if (!pud_present(*pud))
1134 return 0;
1135
1136 if (pud_large(*pud))
1137 return spurious_kernel_fault_check(error_code, (pte_t *) pud);
1138
1139 pmd = pmd_offset(pud, address);
1140 if (!pmd_present(*pmd))
1141 return 0;
1142
1143 if (pmd_large(*pmd))
1144 return spurious_kernel_fault_check(error_code, (pte_t *) pmd);
1145
1146 pte = pte_offset_kernel(pmd, address);
1147 if (!pte_present(*pte))
1148 return 0;
1149
1150 ret = spurious_kernel_fault_check(error_code, pte);
1151 if (!ret)
1152 return 0;
1153
1154 /*
1155 * Make sure we have permissions in PMD.
1156 * If not, then there's a bug in the page tables:
1157 */
1158 ret = spurious_kernel_fault_check(error_code, (pte_t *) pmd);
1159 WARN_ONCE(!ret, "PMD has incorrect permission bits\n");
1160
1161 return ret;
1162}
1163NOKPROBE_SYMBOL(spurious_kernel_fault);
1164
1165int show_unhandled_signals = 1;
1166
1167static inline int
1168access_error(unsigned long error_code, struct vm_area_struct *vma)
1169{
1170 /* This is only called for the current mm, so: */
1171 bool foreign = false;
1172
1173 /*
1174 * Read or write was blocked by protection keys. This is
1175 * always an unconditional error and can never result in
1176 * a follow-up action to resolve the fault, like a COW.
1177 */
1178 if (error_code & X86_PF_PK)
1179 return 1;
1180
1181 /*
1182 * Make sure to check the VMA so that we do not perform
1183 * faults just to hit a X86_PF_PK as soon as we fill in a
1184 * page.
1185 */
1186 if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE),
1187 (error_code & X86_PF_INSTR), foreign))
1188 return 1;
1189
1190 if (error_code & X86_PF_WRITE) {
1191 /* write, present and write, not present: */
1192 if (unlikely(!(vma->vm_flags & VM_WRITE)))
1193 return 1;
1194 return 0;
1195 }
1196
1197 /* read, present: */
1198 if (unlikely(error_code & X86_PF_PROT))
1199 return 1;
1200
1201 /* read, not present: */
1202 if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))))
1203 return 1;
1204
1205 return 0;
1206}
1207
1208static int fault_in_kernel_space(unsigned long address)
1209{
1210 /*
1211 * On 64-bit systems, the vsyscall page is at an address above
1212 * TASK_SIZE_MAX, but is not considered part of the kernel
1213 * address space.
1214 */
1215 if (IS_ENABLED(CONFIG_X86_64) && is_vsyscall_vaddr(address))
1216 return false;
1217
1218 return address >= TASK_SIZE_MAX;
1219}
1220
1221/*
1222 * Called for all faults where 'address' is part of the kernel address
1223 * space. Might get called for faults that originate from *code* that
1224 * ran in userspace or the kernel.
1225 */
1226static void
1227do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code,
1228 unsigned long address)
1229{
1230 /*
1231 * Protection keys exceptions only happen on user pages. We
1232 * have no user pages in the kernel portion of the address
1233 * space, so do not expect them here.
1234 */
1235 WARN_ON_ONCE(hw_error_code & X86_PF_PK);
1236
1237 /*
1238 * We can fault-in kernel-space virtual memory on-demand. The
1239 * 'reference' page table is init_mm.pgd.
1240 *
1241 * NOTE! We MUST NOT take any locks for this case. We may
1242 * be in an interrupt or a critical region, and should
1243 * only copy the information from the master page table,
1244 * nothing more.
1245 *
1246 * Before doing this on-demand faulting, ensure that the
1247 * fault is not any of the following:
1248 * 1. A fault on a PTE with a reserved bit set.
1249 * 2. A fault caused by a user-mode access. (Do not demand-
1250 * fault kernel memory due to user-mode accesses).
1251 * 3. A fault caused by a page-level protection violation.
1252 * (A demand fault would be on a non-present page which
1253 * would have X86_PF_PROT==0).
1254 */
1255 if (!(hw_error_code & (X86_PF_RSVD | X86_PF_USER | X86_PF_PROT))) {
1256 if (vmalloc_fault(address) >= 0)
1257 return;
1258 }
1259
1260 /* Was the fault spurious, caused by lazy TLB invalidation? */
1261 if (spurious_kernel_fault(hw_error_code, address))
1262 return;
1263
1264 /* kprobes don't want to hook the spurious faults: */
1265 if (kprobe_page_fault(regs, X86_TRAP_PF))
1266 return;
1267
1268 /*
1269 * Note, despite being a "bad area", there are quite a few
1270 * acceptable reasons to get here, such as erratum fixups
1271 * and handling kernel code that can fault, like get_user().
1272 *
1273 * Don't take the mm semaphore here. If we fixup a prefetch
1274 * fault we could otherwise deadlock:
1275 */
1276 bad_area_nosemaphore(regs, hw_error_code, address);
1277}
1278NOKPROBE_SYMBOL(do_kern_addr_fault);
1279
1280/* Handle faults in the user portion of the address space */
1281static inline
1282void do_user_addr_fault(struct pt_regs *regs,
1283 unsigned long hw_error_code,
1284 unsigned long address)
1285{
1286 struct vm_area_struct *vma;
1287 struct task_struct *tsk;
1288 struct mm_struct *mm;
1289 vm_fault_t fault, major = 0;
1290 unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
1291
1292 tsk = current;
1293 mm = tsk->mm;
1294
1295 /* kprobes don't want to hook the spurious faults: */
1296 if (unlikely(kprobe_page_fault(regs, X86_TRAP_PF)))
1297 return;
1298
1299 /*
1300 * Reserved bits are never expected to be set on
1301 * entries in the user portion of the page tables.
1302 */
1303 if (unlikely(hw_error_code & X86_PF_RSVD))
1304 pgtable_bad(regs, hw_error_code, address);
1305
1306 /*
1307 * If SMAP is on, check for invalid kernel (supervisor) access to user
1308 * pages in the user address space. The odd case here is WRUSS,
1309 * which, according to the preliminary documentation, does not respect
1310 * SMAP and will have the USER bit set so, in all cases, SMAP
1311 * enforcement appears to be consistent with the USER bit.
1312 */
1313 if (unlikely(cpu_feature_enabled(X86_FEATURE_SMAP) &&
1314 !(hw_error_code & X86_PF_USER) &&
1315 !(regs->flags & X86_EFLAGS_AC)))
1316 {
1317 bad_area_nosemaphore(regs, hw_error_code, address);
1318 return;
1319 }
1320
1321 /*
1322 * If we're in an interrupt, have no user context or are running
1323 * in a region with pagefaults disabled then we must not take the fault
1324 */
1325 if (unlikely(faulthandler_disabled() || !mm)) {
1326 bad_area_nosemaphore(regs, hw_error_code, address);
1327 return;
1328 }
1329
1330 /*
1331 * It's safe to allow irq's after cr2 has been saved and the
1332 * vmalloc fault has been handled.
1333 *
1334 * User-mode registers count as a user access even for any
1335 * potential system fault or CPU buglet:
1336 */
1337 if (user_mode(regs)) {
1338 local_irq_enable();
1339 flags |= FAULT_FLAG_USER;
1340 } else {
1341 if (regs->flags & X86_EFLAGS_IF)
1342 local_irq_enable();
1343 }
1344
1345 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
1346
1347 if (hw_error_code & X86_PF_WRITE)
1348 flags |= FAULT_FLAG_WRITE;
1349 if (hw_error_code & X86_PF_INSTR)
1350 flags |= FAULT_FLAG_INSTRUCTION;
1351
1352#ifdef CONFIG_X86_64
1353 /*
1354 * Faults in the vsyscall page might need emulation. The
1355 * vsyscall page is at a high address (>PAGE_OFFSET), but is
1356 * considered to be part of the user address space.
1357 *
1358 * The vsyscall page does not have a "real" VMA, so do this
1359 * emulation before we go searching for VMAs.
1360 *
1361 * PKRU never rejects instruction fetches, so we don't need
1362 * to consider the PF_PK bit.
1363 */
1364 if (is_vsyscall_vaddr(address)) {
1365 if (emulate_vsyscall(hw_error_code, regs, address))
1366 return;
1367 }
1368#endif
1369
1370 /*
1371 * Kernel-mode access to the user address space should only occur
1372 * on well-defined single instructions listed in the exception
1373 * tables. But, an erroneous kernel fault occurring outside one of
1374 * those areas which also holds mmap_sem might deadlock attempting
1375 * to validate the fault against the address space.
1376 *
1377 * Only do the expensive exception table search when we might be at
1378 * risk of a deadlock. This happens if we
1379 * 1. Failed to acquire mmap_sem, and
1380 * 2. The access did not originate in userspace.
1381 */
1382 if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
1383 if (!user_mode(regs) && !search_exception_tables(regs->ip)) {
1384 /*
1385 * Fault from code in kernel from
1386 * which we do not expect faults.
1387 */
1388 bad_area_nosemaphore(regs, hw_error_code, address);
1389 return;
1390 }
1391retry:
1392 down_read(&mm->mmap_sem);
1393 } else {
1394 /*
1395 * The above down_read_trylock() might have succeeded in
1396 * which case we'll have missed the might_sleep() from
1397 * down_read():
1398 */
1399 might_sleep();
1400 }
1401
1402 vma = find_vma(mm, address);
1403 if (unlikely(!vma)) {
1404 bad_area(regs, hw_error_code, address);
1405 return;
1406 }
1407 if (likely(vma->vm_start <= address))
1408 goto good_area;
1409 if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
1410 bad_area(regs, hw_error_code, address);
1411 return;
1412 }
1413 if (unlikely(expand_stack(vma, address))) {
1414 bad_area(regs, hw_error_code, address);
1415 return;
1416 }
1417
1418 /*
1419 * Ok, we have a good vm_area for this memory access, so
1420 * we can handle it..
1421 */
1422good_area:
1423 if (unlikely(access_error(hw_error_code, vma))) {
1424 bad_area_access_error(regs, hw_error_code, address, vma);
1425 return;
1426 }
1427
1428 /*
1429 * If for any reason at all we couldn't handle the fault,
1430 * make sure we exit gracefully rather than endlessly redo
1431 * the fault. Since we never set FAULT_FLAG_RETRY_NOWAIT, if
1432 * we get VM_FAULT_RETRY back, the mmap_sem has been unlocked.
1433 *
1434 * Note that handle_userfault() may also release and reacquire mmap_sem
1435 * (and not return with VM_FAULT_RETRY), when returning to userland to
1436 * repeat the page fault later with a VM_FAULT_NOPAGE retval
1437 * (potentially after handling any pending signal during the return to
1438 * userland). The return to userland is identified whenever
1439 * FAULT_FLAG_USER|FAULT_FLAG_KILLABLE are both set in flags.
1440 */
1441 fault = handle_mm_fault(vma, address, flags);
1442 major |= fault & VM_FAULT_MAJOR;
1443
1444 /*
1445 * If we need to retry the mmap_sem has already been released,
1446 * and if there is a fatal signal pending there is no guarantee
1447 * that we made any progress. Handle this case first.
1448 */
1449 if (unlikely(fault & VM_FAULT_RETRY)) {
1450 /* Retry at most once */
1451 if (flags & FAULT_FLAG_ALLOW_RETRY) {
1452 flags &= ~FAULT_FLAG_ALLOW_RETRY;
1453 flags |= FAULT_FLAG_TRIED;
1454 if (!fatal_signal_pending(tsk))
1455 goto retry;
1456 }
1457
1458 /* User mode? Just return to handle the fatal exception */
1459 if (flags & FAULT_FLAG_USER)
1460 return;
1461
1462 /* Not returning to user mode? Handle exceptions or die: */
1463 no_context(regs, hw_error_code, address, SIGBUS, BUS_ADRERR);
1464 return;
1465 }
1466
1467 up_read(&mm->mmap_sem);
1468 if (unlikely(fault & VM_FAULT_ERROR)) {
1469 mm_fault_error(regs, hw_error_code, address, fault);
1470 return;
1471 }
1472
1473 /*
1474 * Major/minor page fault accounting. If any of the events
1475 * returned VM_FAULT_MAJOR, we account it as a major fault.
1476 */
1477 if (major) {
1478 tsk->maj_flt++;
1479 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, address);
1480 } else {
1481 tsk->min_flt++;
1482 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, address);
1483 }
1484
1485 check_v8086_mode(regs, address, tsk);
1486}
1487NOKPROBE_SYMBOL(do_user_addr_fault);
1488
1489/*
1490 * Explicitly marked noinline such that the function tracer sees this as the
1491 * page_fault entry point.
1492 */
1493static noinline void
1494__do_page_fault(struct pt_regs *regs, unsigned long hw_error_code,
1495 unsigned long address)
1496{
1497 prefetchw(¤t->mm->mmap_sem);
1498
1499 if (unlikely(kmmio_fault(regs, address)))
1500 return;
1501
1502 /* Was the fault on kernel-controlled part of the address space? */
1503 if (unlikely(fault_in_kernel_space(address)))
1504 do_kern_addr_fault(regs, hw_error_code, address);
1505 else
1506 do_user_addr_fault(regs, hw_error_code, address);
1507}
1508NOKPROBE_SYMBOL(__do_page_fault);
1509
1510static __always_inline void
1511trace_page_fault_entries(struct pt_regs *regs, unsigned long error_code,
1512 unsigned long address)
1513{
1514 if (!trace_pagefault_enabled())
1515 return;
1516
1517 if (user_mode(regs))
1518 trace_page_fault_user(address, regs, error_code);
1519 else
1520 trace_page_fault_kernel(address, regs, error_code);
1521}
1522
1523dotraplinkage void
1524do_page_fault(struct pt_regs *regs, unsigned long error_code, unsigned long address)
1525{
1526 enum ctx_state prev_state;
1527
1528 prev_state = exception_enter();
1529 trace_page_fault_entries(regs, error_code, address);
1530 __do_page_fault(regs, error_code, address);
1531 exception_exit(prev_state);
1532}
1533NOKPROBE_SYMBOL(do_page_fault);