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