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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/kfence.h> /* kfence_handle_page_fault */
13#include <linux/kprobes.h> /* NOKPROBE_SYMBOL, ... */
14#include <linux/mmiotrace.h> /* kmmio_handler, ... */
15#include <linux/perf_event.h> /* perf_sw_event */
16#include <linux/hugetlb.h> /* hstate_index_to_shift */
17#include <linux/prefetch.h> /* prefetchw */
18#include <linux/context_tracking.h> /* exception_enter(), ... */
19#include <linux/uaccess.h> /* faulthandler_disabled() */
20#include <linux/efi.h> /* efi_crash_gracefully_on_page_fault()*/
21#include <linux/mm_types.h>
22#include <linux/mm.h> /* find_and_lock_vma() */
23#include <linux/vmalloc.h>
24
25#include <asm/cpufeature.h> /* boot_cpu_has, ... */
26#include <asm/traps.h> /* dotraplinkage, ... */
27#include <asm/fixmap.h> /* VSYSCALL_ADDR */
28#include <asm/vsyscall.h> /* emulate_vsyscall */
29#include <asm/vm86.h> /* struct vm86 */
30#include <asm/mmu_context.h> /* vma_pkey() */
31#include <asm/efi.h> /* efi_crash_gracefully_on_page_fault()*/
32#include <asm/desc.h> /* store_idt(), ... */
33#include <asm/cpu_entry_area.h> /* exception stack */
34#include <asm/pgtable_areas.h> /* VMALLOC_START, ... */
35#include <asm/kvm_para.h> /* kvm_handle_async_pf */
36#include <asm/vdso.h> /* fixup_vdso_exception() */
37#include <asm/irq_stack.h>
38#include <asm/fred.h>
39#include <asm/sev.h> /* snp_dump_hva_rmpentry() */
40
41#define CREATE_TRACE_POINTS
42#include <asm/trace/exceptions.h>
43
44/*
45 * Returns 0 if mmiotrace is disabled, or if the fault is not
46 * handled by mmiotrace:
47 */
48static nokprobe_inline int
49kmmio_fault(struct pt_regs *regs, unsigned long addr)
50{
51 if (unlikely(is_kmmio_active()))
52 if (kmmio_handler(regs, addr) == 1)
53 return -1;
54 return 0;
55}
56
57/*
58 * Prefetch quirks:
59 *
60 * 32-bit mode:
61 *
62 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
63 * Check that here and ignore it. This is AMD erratum #91.
64 *
65 * 64-bit mode:
66 *
67 * Sometimes the CPU reports invalid exceptions on prefetch.
68 * Check that here and ignore it.
69 *
70 * Opcode checker based on code by Richard Brunner.
71 */
72static inline int
73check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr,
74 unsigned char opcode, int *prefetch)
75{
76 unsigned char instr_hi = opcode & 0xf0;
77 unsigned char instr_lo = opcode & 0x0f;
78
79 switch (instr_hi) {
80 case 0x20:
81 case 0x30:
82 /*
83 * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes.
84 * In X86_64 long mode, the CPU will signal invalid
85 * opcode if some of these prefixes are present so
86 * X86_64 will never get here anyway
87 */
88 return ((instr_lo & 7) == 0x6);
89#ifdef CONFIG_X86_64
90 case 0x40:
91 /*
92 * In 64-bit mode 0x40..0x4F are valid REX prefixes
93 */
94 return (!user_mode(regs) || user_64bit_mode(regs));
95#endif
96 case 0x60:
97 /* 0x64 thru 0x67 are valid prefixes in all modes. */
98 return (instr_lo & 0xC) == 0x4;
99 case 0xF0:
100 /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */
101 return !instr_lo || (instr_lo>>1) == 1;
102 case 0x00:
103 /* Prefetch instruction is 0x0F0D or 0x0F18 */
104 if (get_kernel_nofault(opcode, instr))
105 return 0;
106
107 *prefetch = (instr_lo == 0xF) &&
108 (opcode == 0x0D || opcode == 0x18);
109 return 0;
110 default:
111 return 0;
112 }
113}
114
115static bool is_amd_k8_pre_npt(void)
116{
117 struct cpuinfo_x86 *c = &boot_cpu_data;
118
119 return unlikely(IS_ENABLED(CONFIG_CPU_SUP_AMD) &&
120 c->x86_vendor == X86_VENDOR_AMD &&
121 c->x86 == 0xf && c->x86_model < 0x40);
122}
123
124static int
125is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr)
126{
127 unsigned char *max_instr;
128 unsigned char *instr;
129 int prefetch = 0;
130
131 /* Erratum #91 affects AMD K8, pre-NPT CPUs */
132 if (!is_amd_k8_pre_npt())
133 return 0;
134
135 /*
136 * If it was a exec (instruction fetch) fault on NX page, then
137 * do not ignore the fault:
138 */
139 if (error_code & X86_PF_INSTR)
140 return 0;
141
142 instr = (void *)convert_ip_to_linear(current, regs);
143 max_instr = instr + 15;
144
145 /*
146 * This code has historically always bailed out if IP points to a
147 * not-present page (e.g. due to a race). No one has ever
148 * complained about this.
149 */
150 pagefault_disable();
151
152 while (instr < max_instr) {
153 unsigned char opcode;
154
155 if (user_mode(regs)) {
156 if (get_user(opcode, (unsigned char __user *) instr))
157 break;
158 } else {
159 if (get_kernel_nofault(opcode, instr))
160 break;
161 }
162
163 instr++;
164
165 if (!check_prefetch_opcode(regs, instr, opcode, &prefetch))
166 break;
167 }
168
169 pagefault_enable();
170 return prefetch;
171}
172
173DEFINE_SPINLOCK(pgd_lock);
174LIST_HEAD(pgd_list);
175
176#ifdef CONFIG_X86_32
177static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
178{
179 unsigned index = pgd_index(address);
180 pgd_t *pgd_k;
181 p4d_t *p4d, *p4d_k;
182 pud_t *pud, *pud_k;
183 pmd_t *pmd, *pmd_k;
184
185 pgd += index;
186 pgd_k = init_mm.pgd + index;
187
188 if (!pgd_present(*pgd_k))
189 return NULL;
190
191 /*
192 * set_pgd(pgd, *pgd_k); here would be useless on PAE
193 * and redundant with the set_pmd() on non-PAE. As would
194 * set_p4d/set_pud.
195 */
196 p4d = p4d_offset(pgd, address);
197 p4d_k = p4d_offset(pgd_k, address);
198 if (!p4d_present(*p4d_k))
199 return NULL;
200
201 pud = pud_offset(p4d, address);
202 pud_k = pud_offset(p4d_k, address);
203 if (!pud_present(*pud_k))
204 return NULL;
205
206 pmd = pmd_offset(pud, address);
207 pmd_k = pmd_offset(pud_k, address);
208
209 if (pmd_present(*pmd) != pmd_present(*pmd_k))
210 set_pmd(pmd, *pmd_k);
211
212 if (!pmd_present(*pmd_k))
213 return NULL;
214 else
215 BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k));
216
217 return pmd_k;
218}
219
220/*
221 * Handle a fault on the vmalloc or module mapping area
222 *
223 * This is needed because there is a race condition between the time
224 * when the vmalloc mapping code updates the PMD to the point in time
225 * where it synchronizes this update with the other page-tables in the
226 * system.
227 *
228 * In this race window another thread/CPU can map an area on the same
229 * PMD, finds it already present and does not synchronize it with the
230 * rest of the system yet. As a result v[mz]alloc might return areas
231 * which are not mapped in every page-table in the system, causing an
232 * unhandled page-fault when they are accessed.
233 */
234static noinline int vmalloc_fault(unsigned long address)
235{
236 unsigned long pgd_paddr;
237 pmd_t *pmd_k;
238 pte_t *pte_k;
239
240 /* Make sure we are in vmalloc area: */
241 if (!(address >= VMALLOC_START && address < VMALLOC_END))
242 return -1;
243
244 /*
245 * Synchronize this task's top level page-table
246 * with the 'reference' page table.
247 *
248 * Do _not_ use "current" here. We might be inside
249 * an interrupt in the middle of a task switch..
250 */
251 pgd_paddr = read_cr3_pa();
252 pmd_k = vmalloc_sync_one(__va(pgd_paddr), address);
253 if (!pmd_k)
254 return -1;
255
256 if (pmd_leaf(*pmd_k))
257 return 0;
258
259 pte_k = pte_offset_kernel(pmd_k, address);
260 if (!pte_present(*pte_k))
261 return -1;
262
263 return 0;
264}
265NOKPROBE_SYMBOL(vmalloc_fault);
266
267void arch_sync_kernel_mappings(unsigned long start, unsigned long end)
268{
269 unsigned long addr;
270
271 for (addr = start & PMD_MASK;
272 addr >= TASK_SIZE_MAX && addr < VMALLOC_END;
273 addr += PMD_SIZE) {
274 struct page *page;
275
276 spin_lock(&pgd_lock);
277 list_for_each_entry(page, &pgd_list, lru) {
278 spinlock_t *pgt_lock;
279
280 /* the pgt_lock only for Xen */
281 pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
282
283 spin_lock(pgt_lock);
284 vmalloc_sync_one(page_address(page), addr);
285 spin_unlock(pgt_lock);
286 }
287 spin_unlock(&pgd_lock);
288 }
289}
290
291static bool low_pfn(unsigned long pfn)
292{
293 return pfn < max_low_pfn;
294}
295
296static void dump_pagetable(unsigned long address)
297{
298 pgd_t *base = __va(read_cr3_pa());
299 pgd_t *pgd = &base[pgd_index(address)];
300 p4d_t *p4d;
301 pud_t *pud;
302 pmd_t *pmd;
303 pte_t *pte;
304
305#ifdef CONFIG_X86_PAE
306 pr_info("*pdpt = %016Lx ", pgd_val(*pgd));
307 if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd))
308 goto out;
309#define pr_pde pr_cont
310#else
311#define pr_pde pr_info
312#endif
313 p4d = p4d_offset(pgd, address);
314 pud = pud_offset(p4d, address);
315 pmd = pmd_offset(pud, address);
316 pr_pde("*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd));
317#undef pr_pde
318
319 /*
320 * We must not directly access the pte in the highpte
321 * case if the page table is located in highmem.
322 * And let's rather not kmap-atomic the pte, just in case
323 * it's allocated already:
324 */
325 if (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_leaf(*pmd))
326 goto out;
327
328 pte = pte_offset_kernel(pmd, address);
329 pr_cont("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte));
330out:
331 pr_cont("\n");
332}
333
334#else /* CONFIG_X86_64: */
335
336#ifdef CONFIG_CPU_SUP_AMD
337static const char errata93_warning[] =
338KERN_ERR
339"******* Your BIOS seems to not contain a fix for K8 errata #93\n"
340"******* Working around it, but it may cause SEGVs or burn power.\n"
341"******* Please consider a BIOS update.\n"
342"******* Disabling USB legacy in the BIOS may also help.\n";
343#endif
344
345static int bad_address(void *p)
346{
347 unsigned long dummy;
348
349 return get_kernel_nofault(dummy, (unsigned long *)p);
350}
351
352static void dump_pagetable(unsigned long address)
353{
354 pgd_t *base = __va(read_cr3_pa());
355 pgd_t *pgd = base + pgd_index(address);
356 p4d_t *p4d;
357 pud_t *pud;
358 pmd_t *pmd;
359 pte_t *pte;
360
361 if (bad_address(pgd))
362 goto bad;
363
364 pr_info("PGD %lx ", pgd_val(*pgd));
365
366 if (!pgd_present(*pgd))
367 goto out;
368
369 p4d = p4d_offset(pgd, address);
370 if (bad_address(p4d))
371 goto bad;
372
373 pr_cont("P4D %lx ", p4d_val(*p4d));
374 if (!p4d_present(*p4d) || p4d_leaf(*p4d))
375 goto out;
376
377 pud = pud_offset(p4d, address);
378 if (bad_address(pud))
379 goto bad;
380
381 pr_cont("PUD %lx ", pud_val(*pud));
382 if (!pud_present(*pud) || pud_leaf(*pud))
383 goto out;
384
385 pmd = pmd_offset(pud, address);
386 if (bad_address(pmd))
387 goto bad;
388
389 pr_cont("PMD %lx ", pmd_val(*pmd));
390 if (!pmd_present(*pmd) || pmd_leaf(*pmd))
391 goto out;
392
393 pte = pte_offset_kernel(pmd, address);
394 if (bad_address(pte))
395 goto bad;
396
397 pr_cont("PTE %lx", pte_val(*pte));
398out:
399 pr_cont("\n");
400 return;
401bad:
402 pr_info("BAD\n");
403}
404
405#endif /* CONFIG_X86_64 */
406
407/*
408 * Workaround for K8 erratum #93 & buggy BIOS.
409 *
410 * BIOS SMM functions are required to use a specific workaround
411 * to avoid corruption of the 64bit RIP register on C stepping K8.
412 *
413 * A lot of BIOS that didn't get tested properly miss this.
414 *
415 * The OS sees this as a page fault with the upper 32bits of RIP cleared.
416 * Try to work around it here.
417 *
418 * Note we only handle faults in kernel here.
419 * Does nothing on 32-bit.
420 */
421static int is_errata93(struct pt_regs *regs, unsigned long address)
422{
423#if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD)
424 if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD
425 || boot_cpu_data.x86 != 0xf)
426 return 0;
427
428 if (user_mode(regs))
429 return 0;
430
431 if (address != regs->ip)
432 return 0;
433
434 if ((address >> 32) != 0)
435 return 0;
436
437 address |= 0xffffffffUL << 32;
438 if ((address >= (u64)_stext && address <= (u64)_etext) ||
439 (address >= MODULES_VADDR && address <= MODULES_END)) {
440 printk_once(errata93_warning);
441 regs->ip = address;
442 return 1;
443 }
444#endif
445 return 0;
446}
447
448/*
449 * Work around K8 erratum #100 K8 in compat mode occasionally jumps
450 * to illegal addresses >4GB.
451 *
452 * We catch this in the page fault handler because these addresses
453 * are not reachable. Just detect this case and return. Any code
454 * segment in LDT is compatibility mode.
455 */
456static int is_errata100(struct pt_regs *regs, unsigned long address)
457{
458#ifdef CONFIG_X86_64
459 if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32))
460 return 1;
461#endif
462 return 0;
463}
464
465/* Pentium F0 0F C7 C8 bug workaround: */
466static int is_f00f_bug(struct pt_regs *regs, unsigned long error_code,
467 unsigned long address)
468{
469#ifdef CONFIG_X86_F00F_BUG
470 if (boot_cpu_has_bug(X86_BUG_F00F) && !(error_code & X86_PF_USER) &&
471 idt_is_f00f_address(address)) {
472 handle_invalid_op(regs);
473 return 1;
474 }
475#endif
476 return 0;
477}
478
479static void show_ldttss(const struct desc_ptr *gdt, const char *name, u16 index)
480{
481 u32 offset = (index >> 3) * sizeof(struct desc_struct);
482 unsigned long addr;
483 struct ldttss_desc desc;
484
485 if (index == 0) {
486 pr_alert("%s: NULL\n", name);
487 return;
488 }
489
490 if (offset + sizeof(struct ldttss_desc) >= gdt->size) {
491 pr_alert("%s: 0x%hx -- out of bounds\n", name, index);
492 return;
493 }
494
495 if (copy_from_kernel_nofault(&desc, (void *)(gdt->address + offset),
496 sizeof(struct ldttss_desc))) {
497 pr_alert("%s: 0x%hx -- GDT entry is not readable\n",
498 name, index);
499 return;
500 }
501
502 addr = desc.base0 | (desc.base1 << 16) | ((unsigned long)desc.base2 << 24);
503#ifdef CONFIG_X86_64
504 addr |= ((u64)desc.base3 << 32);
505#endif
506 pr_alert("%s: 0x%hx -- base=0x%lx limit=0x%x\n",
507 name, index, addr, (desc.limit0 | (desc.limit1 << 16)));
508}
509
510static void
511show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long address)
512{
513 if (!oops_may_print())
514 return;
515
516 if (error_code & X86_PF_INSTR) {
517 unsigned int level;
518 bool nx, rw;
519 pgd_t *pgd;
520 pte_t *pte;
521
522 pgd = __va(read_cr3_pa());
523 pgd += pgd_index(address);
524
525 pte = lookup_address_in_pgd_attr(pgd, address, &level, &nx, &rw);
526
527 if (pte && pte_present(*pte) && (!pte_exec(*pte) || nx))
528 pr_crit("kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n",
529 from_kuid(&init_user_ns, current_uid()));
530 if (pte && pte_present(*pte) && pte_exec(*pte) && !nx &&
531 (pgd_flags(*pgd) & _PAGE_USER) &&
532 (__read_cr4() & X86_CR4_SMEP))
533 pr_crit("unable to execute userspace code (SMEP?) (uid: %d)\n",
534 from_kuid(&init_user_ns, current_uid()));
535 }
536
537 if (address < PAGE_SIZE && !user_mode(regs))
538 pr_alert("BUG: kernel NULL pointer dereference, address: %px\n",
539 (void *)address);
540 else
541 pr_alert("BUG: unable to handle page fault for address: %px\n",
542 (void *)address);
543
544 pr_alert("#PF: %s %s in %s mode\n",
545 (error_code & X86_PF_USER) ? "user" : "supervisor",
546 (error_code & X86_PF_INSTR) ? "instruction fetch" :
547 (error_code & X86_PF_WRITE) ? "write access" :
548 "read access",
549 user_mode(regs) ? "user" : "kernel");
550 pr_alert("#PF: error_code(0x%04lx) - %s\n", error_code,
551 !(error_code & X86_PF_PROT) ? "not-present page" :
552 (error_code & X86_PF_RSVD) ? "reserved bit violation" :
553 (error_code & X86_PF_PK) ? "protection keys violation" :
554 (error_code & X86_PF_RMP) ? "RMP violation" :
555 "permissions violation");
556
557 if (!(error_code & X86_PF_USER) && user_mode(regs)) {
558 struct desc_ptr idt, gdt;
559 u16 ldtr, tr;
560
561 /*
562 * This can happen for quite a few reasons. The more obvious
563 * ones are faults accessing the GDT, or LDT. Perhaps
564 * surprisingly, if the CPU tries to deliver a benign or
565 * contributory exception from user code and gets a page fault
566 * during delivery, the page fault can be delivered as though
567 * it originated directly from user code. This could happen
568 * due to wrong permissions on the IDT, GDT, LDT, TSS, or
569 * kernel or IST stack.
570 */
571 store_idt(&idt);
572
573 /* Usable even on Xen PV -- it's just slow. */
574 native_store_gdt(&gdt);
575
576 pr_alert("IDT: 0x%lx (limit=0x%hx) GDT: 0x%lx (limit=0x%hx)\n",
577 idt.address, idt.size, gdt.address, gdt.size);
578
579 store_ldt(ldtr);
580 show_ldttss(&gdt, "LDTR", ldtr);
581
582 store_tr(tr);
583 show_ldttss(&gdt, "TR", tr);
584 }
585
586 dump_pagetable(address);
587
588 if (error_code & X86_PF_RMP)
589 snp_dump_hva_rmpentry(address);
590}
591
592static noinline void
593pgtable_bad(struct pt_regs *regs, unsigned long error_code,
594 unsigned long address)
595{
596 struct task_struct *tsk;
597 unsigned long flags;
598 int sig;
599
600 flags = oops_begin();
601 tsk = current;
602 sig = SIGKILL;
603
604 printk(KERN_ALERT "%s: Corrupted page table at address %lx\n",
605 tsk->comm, address);
606 dump_pagetable(address);
607
608 if (__die("Bad pagetable", regs, error_code))
609 sig = 0;
610
611 oops_end(flags, regs, sig);
612}
613
614static void sanitize_error_code(unsigned long address,
615 unsigned long *error_code)
616{
617 /*
618 * To avoid leaking information about the kernel page
619 * table layout, pretend that user-mode accesses to
620 * kernel addresses are always protection faults.
621 *
622 * NB: This means that failed vsyscalls with vsyscall=none
623 * will have the PROT bit. This doesn't leak any
624 * information and does not appear to cause any problems.
625 */
626 if (address >= TASK_SIZE_MAX)
627 *error_code |= X86_PF_PROT;
628}
629
630static void set_signal_archinfo(unsigned long address,
631 unsigned long error_code)
632{
633 struct task_struct *tsk = current;
634
635 tsk->thread.trap_nr = X86_TRAP_PF;
636 tsk->thread.error_code = error_code | X86_PF_USER;
637 tsk->thread.cr2 = address;
638}
639
640static noinline void
641page_fault_oops(struct pt_regs *regs, unsigned long error_code,
642 unsigned long address)
643{
644#ifdef CONFIG_VMAP_STACK
645 struct stack_info info;
646#endif
647 unsigned long flags;
648 int sig;
649
650 if (user_mode(regs)) {
651 /*
652 * Implicit kernel access from user mode? Skip the stack
653 * overflow and EFI special cases.
654 */
655 goto oops;
656 }
657
658#ifdef CONFIG_VMAP_STACK
659 /*
660 * Stack overflow? During boot, we can fault near the initial
661 * stack in the direct map, but that's not an overflow -- check
662 * that we're in vmalloc space to avoid this.
663 */
664 if (is_vmalloc_addr((void *)address) &&
665 get_stack_guard_info((void *)address, &info)) {
666 /*
667 * We're likely to be running with very little stack space
668 * left. It's plausible that we'd hit this condition but
669 * double-fault even before we get this far, in which case
670 * we're fine: the double-fault handler will deal with it.
671 *
672 * We don't want to make it all the way into the oops code
673 * and then double-fault, though, because we're likely to
674 * break the console driver and lose most of the stack dump.
675 */
676 call_on_stack(__this_cpu_ist_top_va(DF) - sizeof(void*),
677 handle_stack_overflow,
678 ASM_CALL_ARG3,
679 , [arg1] "r" (regs), [arg2] "r" (address), [arg3] "r" (&info));
680
681 BUG();
682 }
683#endif
684
685 /*
686 * Buggy firmware could access regions which might page fault. If
687 * this happens, EFI has a special OOPS path that will try to
688 * avoid hanging the system.
689 */
690 if (IS_ENABLED(CONFIG_EFI))
691 efi_crash_gracefully_on_page_fault(address);
692
693 /* Only not-present faults should be handled by KFENCE. */
694 if (!(error_code & X86_PF_PROT) &&
695 kfence_handle_page_fault(address, error_code & X86_PF_WRITE, regs))
696 return;
697
698oops:
699 /*
700 * Oops. The kernel tried to access some bad page. We'll have to
701 * terminate things with extreme prejudice:
702 */
703 flags = oops_begin();
704
705 show_fault_oops(regs, error_code, address);
706
707 if (task_stack_end_corrupted(current))
708 printk(KERN_EMERG "Thread overran stack, or stack corrupted\n");
709
710 sig = SIGKILL;
711 if (__die("Oops", regs, error_code))
712 sig = 0;
713
714 /* Executive summary in case the body of the oops scrolled away */
715 printk(KERN_DEFAULT "CR2: %016lx\n", address);
716
717 oops_end(flags, regs, sig);
718}
719
720static noinline void
721kernelmode_fixup_or_oops(struct pt_regs *regs, unsigned long error_code,
722 unsigned long address, int signal, int si_code,
723 u32 pkey)
724{
725 WARN_ON_ONCE(user_mode(regs));
726
727 /* Are we prepared to handle this kernel fault? */
728 if (fixup_exception(regs, X86_TRAP_PF, error_code, address))
729 return;
730
731 /*
732 * AMD erratum #91 manifests as a spurious page fault on a PREFETCH
733 * instruction.
734 */
735 if (is_prefetch(regs, error_code, address))
736 return;
737
738 page_fault_oops(regs, error_code, address);
739}
740
741/*
742 * Print out info about fatal segfaults, if the show_unhandled_signals
743 * sysctl is set:
744 */
745static inline void
746show_signal_msg(struct pt_regs *regs, unsigned long error_code,
747 unsigned long address, struct task_struct *tsk)
748{
749 const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG;
750 /* This is a racy snapshot, but it's better than nothing. */
751 int cpu = raw_smp_processor_id();
752
753 if (!unhandled_signal(tsk, SIGSEGV))
754 return;
755
756 if (!printk_ratelimit())
757 return;
758
759 printk("%s%s[%d]: segfault at %lx ip %px sp %px error %lx",
760 loglvl, tsk->comm, task_pid_nr(tsk), address,
761 (void *)regs->ip, (void *)regs->sp, error_code);
762
763 print_vma_addr(KERN_CONT " in ", regs->ip);
764
765 /*
766 * Dump the likely CPU where the fatal segfault happened.
767 * This can help identify faulty hardware.
768 */
769 printk(KERN_CONT " likely on CPU %d (core %d, socket %d)", cpu,
770 topology_core_id(cpu), topology_physical_package_id(cpu));
771
772
773 printk(KERN_CONT "\n");
774
775 show_opcodes(regs, loglvl);
776}
777
778static void
779__bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
780 unsigned long address, u32 pkey, int si_code)
781{
782 struct task_struct *tsk = current;
783
784 if (!user_mode(regs)) {
785 kernelmode_fixup_or_oops(regs, error_code, address,
786 SIGSEGV, si_code, pkey);
787 return;
788 }
789
790 if (!(error_code & X86_PF_USER)) {
791 /* Implicit user access to kernel memory -- just oops */
792 page_fault_oops(regs, error_code, address);
793 return;
794 }
795
796 /*
797 * User mode accesses just cause a SIGSEGV.
798 * It's possible to have interrupts off here:
799 */
800 local_irq_enable();
801
802 /*
803 * Valid to do another page fault here because this one came
804 * from user space:
805 */
806 if (is_prefetch(regs, error_code, address))
807 return;
808
809 if (is_errata100(regs, address))
810 return;
811
812 sanitize_error_code(address, &error_code);
813
814 if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address))
815 return;
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 else
825 force_sig_fault(SIGSEGV, si_code, (void __user *)address);
826
827 local_irq_disable();
828}
829
830static noinline void
831bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
832 unsigned long address)
833{
834 __bad_area_nosemaphore(regs, error_code, address, 0, SEGV_MAPERR);
835}
836
837static void
838__bad_area(struct pt_regs *regs, unsigned long error_code,
839 unsigned long address, struct mm_struct *mm,
840 struct vm_area_struct *vma, u32 pkey, int si_code)
841{
842 /*
843 * Something tried to access memory that isn't in our memory map..
844 * Fix it, but check if it's kernel or user first..
845 */
846 if (mm)
847 mmap_read_unlock(mm);
848 else
849 vma_end_read(vma);
850
851 __bad_area_nosemaphore(regs, error_code, address, pkey, si_code);
852}
853
854static inline bool bad_area_access_from_pkeys(unsigned long error_code,
855 struct vm_area_struct *vma)
856{
857 /* This code is always called on the current mm */
858 bool foreign = false;
859
860 if (!cpu_feature_enabled(X86_FEATURE_OSPKE))
861 return false;
862 if (error_code & X86_PF_PK)
863 return true;
864 /* this checks permission keys on the VMA: */
865 if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE),
866 (error_code & X86_PF_INSTR), foreign))
867 return true;
868 return false;
869}
870
871static noinline void
872bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
873 unsigned long address, struct mm_struct *mm,
874 struct vm_area_struct *vma)
875{
876 /*
877 * This OSPKE check is not strictly necessary at runtime.
878 * But, doing it this way allows compiler optimizations
879 * if pkeys are compiled out.
880 */
881 if (bad_area_access_from_pkeys(error_code, vma)) {
882 /*
883 * A protection key fault means that the PKRU value did not allow
884 * access to some PTE. Userspace can figure out what PKRU was
885 * from the XSAVE state. This function captures the pkey from
886 * the vma and passes it to userspace so userspace can discover
887 * which protection key was set on the PTE.
888 *
889 * If we get here, we know that the hardware signaled a X86_PF_PK
890 * fault and that there was a VMA once we got in the fault
891 * handler. It does *not* guarantee that the VMA we find here
892 * was the one that we faulted on.
893 *
894 * 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4);
895 * 2. T1 : set PKRU to deny access to pkey=4, touches page
896 * 3. T1 : faults...
897 * 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5);
898 * 5. T1 : enters fault handler, takes mmap_lock, etc...
899 * 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really
900 * faulted on a pte with its pkey=4.
901 */
902 u32 pkey = vma_pkey(vma);
903
904 __bad_area(regs, error_code, address, mm, vma, pkey, SEGV_PKUERR);
905 } else {
906 __bad_area(regs, error_code, address, mm, vma, 0, SEGV_ACCERR);
907 }
908}
909
910static void
911do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
912 vm_fault_t fault)
913{
914 /* Kernel mode? Handle exceptions or die: */
915 if (!user_mode(regs)) {
916 kernelmode_fixup_or_oops(regs, error_code, address,
917 SIGBUS, BUS_ADRERR, ARCH_DEFAULT_PKEY);
918 return;
919 }
920
921 /* User-space => ok to do another page fault: */
922 if (is_prefetch(regs, error_code, address))
923 return;
924
925 sanitize_error_code(address, &error_code);
926
927 if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address))
928 return;
929
930 set_signal_archinfo(address, error_code);
931
932#ifdef CONFIG_MEMORY_FAILURE
933 if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
934 struct task_struct *tsk = current;
935 unsigned lsb = 0;
936
937 pr_err(
938 "MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
939 tsk->comm, tsk->pid, address);
940 if (fault & VM_FAULT_HWPOISON_LARGE)
941 lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
942 if (fault & VM_FAULT_HWPOISON)
943 lsb = PAGE_SHIFT;
944 force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb);
945 return;
946 }
947#endif
948 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
949}
950
951static int spurious_kernel_fault_check(unsigned long error_code, pte_t *pte)
952{
953 if ((error_code & X86_PF_WRITE) && !pte_write(*pte))
954 return 0;
955
956 if ((error_code & X86_PF_INSTR) && !pte_exec(*pte))
957 return 0;
958
959 return 1;
960}
961
962/*
963 * Handle a spurious fault caused by a stale TLB entry.
964 *
965 * This allows us to lazily refresh the TLB when increasing the
966 * permissions of a kernel page (RO -> RW or NX -> X). Doing it
967 * eagerly is very expensive since that implies doing a full
968 * cross-processor TLB flush, even if no stale TLB entries exist
969 * on other processors.
970 *
971 * Spurious faults may only occur if the TLB contains an entry with
972 * fewer permission than the page table entry. Non-present (P = 0)
973 * and reserved bit (R = 1) faults are never spurious.
974 *
975 * There are no security implications to leaving a stale TLB when
976 * increasing the permissions on a page.
977 *
978 * Returns non-zero if a spurious fault was handled, zero otherwise.
979 *
980 * See Intel Developer's Manual Vol 3 Section 4.10.4.3, bullet 3
981 * (Optional Invalidation).
982 */
983static noinline int
984spurious_kernel_fault(unsigned long error_code, unsigned long address)
985{
986 pgd_t *pgd;
987 p4d_t *p4d;
988 pud_t *pud;
989 pmd_t *pmd;
990 pte_t *pte;
991 int ret;
992
993 /*
994 * Only writes to RO or instruction fetches from NX may cause
995 * spurious faults.
996 *
997 * These could be from user or supervisor accesses but the TLB
998 * is only lazily flushed after a kernel mapping protection
999 * change, so user accesses are not expected to cause spurious
1000 * faults.
1001 */
1002 if (error_code != (X86_PF_WRITE | X86_PF_PROT) &&
1003 error_code != (X86_PF_INSTR | X86_PF_PROT))
1004 return 0;
1005
1006 pgd = init_mm.pgd + pgd_index(address);
1007 if (!pgd_present(*pgd))
1008 return 0;
1009
1010 p4d = p4d_offset(pgd, address);
1011 if (!p4d_present(*p4d))
1012 return 0;
1013
1014 if (p4d_leaf(*p4d))
1015 return spurious_kernel_fault_check(error_code, (pte_t *) p4d);
1016
1017 pud = pud_offset(p4d, address);
1018 if (!pud_present(*pud))
1019 return 0;
1020
1021 if (pud_leaf(*pud))
1022 return spurious_kernel_fault_check(error_code, (pte_t *) pud);
1023
1024 pmd = pmd_offset(pud, address);
1025 if (!pmd_present(*pmd))
1026 return 0;
1027
1028 if (pmd_leaf(*pmd))
1029 return spurious_kernel_fault_check(error_code, (pte_t *) pmd);
1030
1031 pte = pte_offset_kernel(pmd, address);
1032 if (!pte_present(*pte))
1033 return 0;
1034
1035 ret = spurious_kernel_fault_check(error_code, pte);
1036 if (!ret)
1037 return 0;
1038
1039 /*
1040 * Make sure we have permissions in PMD.
1041 * If not, then there's a bug in the page tables:
1042 */
1043 ret = spurious_kernel_fault_check(error_code, (pte_t *) pmd);
1044 WARN_ONCE(!ret, "PMD has incorrect permission bits\n");
1045
1046 return ret;
1047}
1048NOKPROBE_SYMBOL(spurious_kernel_fault);
1049
1050int show_unhandled_signals = 1;
1051
1052static inline int
1053access_error(unsigned long error_code, struct vm_area_struct *vma)
1054{
1055 /* This is only called for the current mm, so: */
1056 bool foreign = false;
1057
1058 /*
1059 * Read or write was blocked by protection keys. This is
1060 * always an unconditional error and can never result in
1061 * a follow-up action to resolve the fault, like a COW.
1062 */
1063 if (error_code & X86_PF_PK)
1064 return 1;
1065
1066 /*
1067 * SGX hardware blocked the access. This usually happens
1068 * when the enclave memory contents have been destroyed, like
1069 * after a suspend/resume cycle. In any case, the kernel can't
1070 * fix the cause of the fault. Handle the fault as an access
1071 * error even in cases where no actual access violation
1072 * occurred. This allows userspace to rebuild the enclave in
1073 * response to the signal.
1074 */
1075 if (unlikely(error_code & X86_PF_SGX))
1076 return 1;
1077
1078 /*
1079 * Make sure to check the VMA so that we do not perform
1080 * faults just to hit a X86_PF_PK as soon as we fill in a
1081 * page.
1082 */
1083 if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE),
1084 (error_code & X86_PF_INSTR), foreign))
1085 return 1;
1086
1087 /*
1088 * Shadow stack accesses (PF_SHSTK=1) are only permitted to
1089 * shadow stack VMAs. All other accesses result in an error.
1090 */
1091 if (error_code & X86_PF_SHSTK) {
1092 if (unlikely(!(vma->vm_flags & VM_SHADOW_STACK)))
1093 return 1;
1094 if (unlikely(!(vma->vm_flags & VM_WRITE)))
1095 return 1;
1096 return 0;
1097 }
1098
1099 if (error_code & X86_PF_WRITE) {
1100 /* write, present and write, not present: */
1101 if (unlikely(vma->vm_flags & VM_SHADOW_STACK))
1102 return 1;
1103 if (unlikely(!(vma->vm_flags & VM_WRITE)))
1104 return 1;
1105 return 0;
1106 }
1107
1108 /* read, present: */
1109 if (unlikely(error_code & X86_PF_PROT))
1110 return 1;
1111
1112 /* read, not present: */
1113 if (unlikely(!vma_is_accessible(vma)))
1114 return 1;
1115
1116 return 0;
1117}
1118
1119bool fault_in_kernel_space(unsigned long address)
1120{
1121 /*
1122 * On 64-bit systems, the vsyscall page is at an address above
1123 * TASK_SIZE_MAX, but is not considered part of the kernel
1124 * address space.
1125 */
1126 if (IS_ENABLED(CONFIG_X86_64) && is_vsyscall_vaddr(address))
1127 return false;
1128
1129 return address >= TASK_SIZE_MAX;
1130}
1131
1132/*
1133 * Called for all faults where 'address' is part of the kernel address
1134 * space. Might get called for faults that originate from *code* that
1135 * ran in userspace or the kernel.
1136 */
1137static void
1138do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code,
1139 unsigned long address)
1140{
1141 /*
1142 * Protection keys exceptions only happen on user pages. We
1143 * have no user pages in the kernel portion of the address
1144 * space, so do not expect them here.
1145 */
1146 WARN_ON_ONCE(hw_error_code & X86_PF_PK);
1147
1148#ifdef CONFIG_X86_32
1149 /*
1150 * We can fault-in kernel-space virtual memory on-demand. The
1151 * 'reference' page table is init_mm.pgd.
1152 *
1153 * NOTE! We MUST NOT take any locks for this case. We may
1154 * be in an interrupt or a critical region, and should
1155 * only copy the information from the master page table,
1156 * nothing more.
1157 *
1158 * Before doing this on-demand faulting, ensure that the
1159 * fault is not any of the following:
1160 * 1. A fault on a PTE with a reserved bit set.
1161 * 2. A fault caused by a user-mode access. (Do not demand-
1162 * fault kernel memory due to user-mode accesses).
1163 * 3. A fault caused by a page-level protection violation.
1164 * (A demand fault would be on a non-present page which
1165 * would have X86_PF_PROT==0).
1166 *
1167 * This is only needed to close a race condition on x86-32 in
1168 * the vmalloc mapping/unmapping code. See the comment above
1169 * vmalloc_fault() for details. On x86-64 the race does not
1170 * exist as the vmalloc mappings don't need to be synchronized
1171 * there.
1172 */
1173 if (!(hw_error_code & (X86_PF_RSVD | X86_PF_USER | X86_PF_PROT))) {
1174 if (vmalloc_fault(address) >= 0)
1175 return;
1176 }
1177#endif
1178
1179 if (is_f00f_bug(regs, hw_error_code, address))
1180 return;
1181
1182 /* Was the fault spurious, caused by lazy TLB invalidation? */
1183 if (spurious_kernel_fault(hw_error_code, address))
1184 return;
1185
1186 /* kprobes don't want to hook the spurious faults: */
1187 if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF)))
1188 return;
1189
1190 /*
1191 * Note, despite being a "bad area", there are quite a few
1192 * acceptable reasons to get here, such as erratum fixups
1193 * and handling kernel code that can fault, like get_user().
1194 *
1195 * Don't take the mm semaphore here. If we fixup a prefetch
1196 * fault we could otherwise deadlock:
1197 */
1198 bad_area_nosemaphore(regs, hw_error_code, address);
1199}
1200NOKPROBE_SYMBOL(do_kern_addr_fault);
1201
1202/*
1203 * Handle faults in the user portion of the address space. Nothing in here
1204 * should check X86_PF_USER without a specific justification: for almost
1205 * all purposes, we should treat a normal kernel access to user memory
1206 * (e.g. get_user(), put_user(), etc.) the same as the WRUSS instruction.
1207 * The one exception is AC flag handling, which is, per the x86
1208 * architecture, special for WRUSS.
1209 */
1210static inline
1211void do_user_addr_fault(struct pt_regs *regs,
1212 unsigned long error_code,
1213 unsigned long address)
1214{
1215 struct vm_area_struct *vma;
1216 struct task_struct *tsk;
1217 struct mm_struct *mm;
1218 vm_fault_t fault;
1219 unsigned int flags = FAULT_FLAG_DEFAULT;
1220
1221 tsk = current;
1222 mm = tsk->mm;
1223
1224 if (unlikely((error_code & (X86_PF_USER | X86_PF_INSTR)) == X86_PF_INSTR)) {
1225 /*
1226 * Whoops, this is kernel mode code trying to execute from
1227 * user memory. Unless this is AMD erratum #93, which
1228 * corrupts RIP such that it looks like a user address,
1229 * this is unrecoverable. Don't even try to look up the
1230 * VMA or look for extable entries.
1231 */
1232 if (is_errata93(regs, address))
1233 return;
1234
1235 page_fault_oops(regs, error_code, address);
1236 return;
1237 }
1238
1239 /* kprobes don't want to hook the spurious faults: */
1240 if (WARN_ON_ONCE(kprobe_page_fault(regs, X86_TRAP_PF)))
1241 return;
1242
1243 /*
1244 * Reserved bits are never expected to be set on
1245 * entries in the user portion of the page tables.
1246 */
1247 if (unlikely(error_code & X86_PF_RSVD))
1248 pgtable_bad(regs, error_code, address);
1249
1250 /*
1251 * If SMAP is on, check for invalid kernel (supervisor) access to user
1252 * pages in the user address space. The odd case here is WRUSS,
1253 * which, according to the preliminary documentation, does not respect
1254 * SMAP and will have the USER bit set so, in all cases, SMAP
1255 * enforcement appears to be consistent with the USER bit.
1256 */
1257 if (unlikely(cpu_feature_enabled(X86_FEATURE_SMAP) &&
1258 !(error_code & X86_PF_USER) &&
1259 !(regs->flags & X86_EFLAGS_AC))) {
1260 /*
1261 * No extable entry here. This was a kernel access to an
1262 * invalid pointer. get_kernel_nofault() will not get here.
1263 */
1264 page_fault_oops(regs, error_code, address);
1265 return;
1266 }
1267
1268 /*
1269 * If we're in an interrupt, have no user context or are running
1270 * in a region with pagefaults disabled then we must not take the fault
1271 */
1272 if (unlikely(faulthandler_disabled() || !mm)) {
1273 bad_area_nosemaphore(regs, error_code, address);
1274 return;
1275 }
1276
1277 /* Legacy check - remove this after verifying that it doesn't trigger */
1278 if (WARN_ON_ONCE(!(regs->flags & X86_EFLAGS_IF))) {
1279 bad_area_nosemaphore(regs, error_code, address);
1280 return;
1281 }
1282
1283 local_irq_enable();
1284
1285 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
1286
1287 /*
1288 * Read-only permissions can not be expressed in shadow stack PTEs.
1289 * Treat all shadow stack accesses as WRITE faults. This ensures
1290 * that the MM will prepare everything (e.g., break COW) such that
1291 * maybe_mkwrite() can create a proper shadow stack PTE.
1292 */
1293 if (error_code & X86_PF_SHSTK)
1294 flags |= FAULT_FLAG_WRITE;
1295 if (error_code & X86_PF_WRITE)
1296 flags |= FAULT_FLAG_WRITE;
1297 if (error_code & X86_PF_INSTR)
1298 flags |= FAULT_FLAG_INSTRUCTION;
1299
1300 /*
1301 * We set FAULT_FLAG_USER based on the register state, not
1302 * based on X86_PF_USER. User space accesses that cause
1303 * system page faults are still user accesses.
1304 */
1305 if (user_mode(regs))
1306 flags |= FAULT_FLAG_USER;
1307
1308#ifdef CONFIG_X86_64
1309 /*
1310 * Faults in the vsyscall page might need emulation. The
1311 * vsyscall page is at a high address (>PAGE_OFFSET), but is
1312 * considered to be part of the user address space.
1313 *
1314 * The vsyscall page does not have a "real" VMA, so do this
1315 * emulation before we go searching for VMAs.
1316 *
1317 * PKRU never rejects instruction fetches, so we don't need
1318 * to consider the PF_PK bit.
1319 */
1320 if (is_vsyscall_vaddr(address)) {
1321 if (emulate_vsyscall(error_code, regs, address))
1322 return;
1323 }
1324#endif
1325
1326 if (!(flags & FAULT_FLAG_USER))
1327 goto lock_mmap;
1328
1329 vma = lock_vma_under_rcu(mm, address);
1330 if (!vma)
1331 goto lock_mmap;
1332
1333 if (unlikely(access_error(error_code, vma))) {
1334 bad_area_access_error(regs, error_code, address, NULL, vma);
1335 count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
1336 return;
1337 }
1338 fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
1339 if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
1340 vma_end_read(vma);
1341
1342 if (!(fault & VM_FAULT_RETRY)) {
1343 count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
1344 goto done;
1345 }
1346 count_vm_vma_lock_event(VMA_LOCK_RETRY);
1347 if (fault & VM_FAULT_MAJOR)
1348 flags |= FAULT_FLAG_TRIED;
1349
1350 /* Quick path to respond to signals */
1351 if (fault_signal_pending(fault, regs)) {
1352 if (!user_mode(regs))
1353 kernelmode_fixup_or_oops(regs, error_code, address,
1354 SIGBUS, BUS_ADRERR,
1355 ARCH_DEFAULT_PKEY);
1356 return;
1357 }
1358lock_mmap:
1359
1360retry:
1361 vma = lock_mm_and_find_vma(mm, address, regs);
1362 if (unlikely(!vma)) {
1363 bad_area_nosemaphore(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 if (unlikely(access_error(error_code, vma))) {
1372 bad_area_access_error(regs, error_code, address, mm, vma);
1373 return;
1374 }
1375
1376 /*
1377 * If for any reason at all we couldn't handle the fault,
1378 * make sure we exit gracefully rather than endlessly redo
1379 * the fault. Since we never set FAULT_FLAG_RETRY_NOWAIT, if
1380 * we get VM_FAULT_RETRY back, the mmap_lock has been unlocked.
1381 *
1382 * Note that handle_userfault() may also release and reacquire mmap_lock
1383 * (and not return with VM_FAULT_RETRY), when returning to userland to
1384 * repeat the page fault later with a VM_FAULT_NOPAGE retval
1385 * (potentially after handling any pending signal during the return to
1386 * userland). The return to userland is identified whenever
1387 * FAULT_FLAG_USER|FAULT_FLAG_KILLABLE are both set in flags.
1388 */
1389 fault = handle_mm_fault(vma, address, flags, regs);
1390
1391 if (fault_signal_pending(fault, regs)) {
1392 /*
1393 * Quick path to respond to signals. The core mm code
1394 * has unlocked the mm for us if we get here.
1395 */
1396 if (!user_mode(regs))
1397 kernelmode_fixup_or_oops(regs, error_code, address,
1398 SIGBUS, BUS_ADRERR,
1399 ARCH_DEFAULT_PKEY);
1400 return;
1401 }
1402
1403 /* The fault is fully completed (including releasing mmap lock) */
1404 if (fault & VM_FAULT_COMPLETED)
1405 return;
1406
1407 /*
1408 * If we need to retry the mmap_lock has already been released,
1409 * and if there is a fatal signal pending there is no guarantee
1410 * that we made any progress. Handle this case first.
1411 */
1412 if (unlikely(fault & VM_FAULT_RETRY)) {
1413 flags |= FAULT_FLAG_TRIED;
1414 goto retry;
1415 }
1416
1417 mmap_read_unlock(mm);
1418done:
1419 if (likely(!(fault & VM_FAULT_ERROR)))
1420 return;
1421
1422 if (fatal_signal_pending(current) && !user_mode(regs)) {
1423 kernelmode_fixup_or_oops(regs, error_code, address,
1424 0, 0, ARCH_DEFAULT_PKEY);
1425 return;
1426 }
1427
1428 if (fault & VM_FAULT_OOM) {
1429 /* Kernel mode? Handle exceptions or die: */
1430 if (!user_mode(regs)) {
1431 kernelmode_fixup_or_oops(regs, error_code, address,
1432 SIGSEGV, SEGV_MAPERR,
1433 ARCH_DEFAULT_PKEY);
1434 return;
1435 }
1436
1437 /*
1438 * We ran out of memory, call the OOM killer, and return the
1439 * userspace (which will retry the fault, or kill us if we got
1440 * oom-killed):
1441 */
1442 pagefault_out_of_memory();
1443 } else {
1444 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
1445 VM_FAULT_HWPOISON_LARGE))
1446 do_sigbus(regs, error_code, address, fault);
1447 else if (fault & VM_FAULT_SIGSEGV)
1448 bad_area_nosemaphore(regs, error_code, address);
1449 else
1450 BUG();
1451 }
1452}
1453NOKPROBE_SYMBOL(do_user_addr_fault);
1454
1455static __always_inline void
1456trace_page_fault_entries(struct pt_regs *regs, unsigned long error_code,
1457 unsigned long address)
1458{
1459 if (!trace_pagefault_enabled())
1460 return;
1461
1462 if (user_mode(regs))
1463 trace_page_fault_user(address, regs, error_code);
1464 else
1465 trace_page_fault_kernel(address, regs, error_code);
1466}
1467
1468static __always_inline void
1469handle_page_fault(struct pt_regs *regs, unsigned long error_code,
1470 unsigned long address)
1471{
1472 trace_page_fault_entries(regs, error_code, address);
1473
1474 if (unlikely(kmmio_fault(regs, address)))
1475 return;
1476
1477 /* Was the fault on kernel-controlled part of the address space? */
1478 if (unlikely(fault_in_kernel_space(address))) {
1479 do_kern_addr_fault(regs, error_code, address);
1480 } else {
1481 do_user_addr_fault(regs, error_code, address);
1482 /*
1483 * User address page fault handling might have reenabled
1484 * interrupts. Fixing up all potential exit points of
1485 * do_user_addr_fault() and its leaf functions is just not
1486 * doable w/o creating an unholy mess or turning the code
1487 * upside down.
1488 */
1489 local_irq_disable();
1490 }
1491}
1492
1493DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault)
1494{
1495 irqentry_state_t state;
1496 unsigned long address;
1497
1498 address = cpu_feature_enabled(X86_FEATURE_FRED) ? fred_event_data(regs) : read_cr2();
1499
1500 prefetchw(¤t->mm->mmap_lock);
1501
1502 /*
1503 * KVM uses #PF vector to deliver 'page not present' events to guests
1504 * (asynchronous page fault mechanism). The event happens when a
1505 * userspace task is trying to access some valid (from guest's point of
1506 * view) memory which is not currently mapped by the host (e.g. the
1507 * memory is swapped out). Note, the corresponding "page ready" event
1508 * which is injected when the memory becomes available, is delivered via
1509 * an interrupt mechanism and not a #PF exception
1510 * (see arch/x86/kernel/kvm.c: sysvec_kvm_asyncpf_interrupt()).
1511 *
1512 * We are relying on the interrupted context being sane (valid RSP,
1513 * relevant locks not held, etc.), which is fine as long as the
1514 * interrupted context had IF=1. We are also relying on the KVM
1515 * async pf type field and CR2 being read consistently instead of
1516 * getting values from real and async page faults mixed up.
1517 *
1518 * Fingers crossed.
1519 *
1520 * The async #PF handling code takes care of idtentry handling
1521 * itself.
1522 */
1523 if (kvm_handle_async_pf(regs, (u32)address))
1524 return;
1525
1526 /*
1527 * Entry handling for valid #PF from kernel mode is slightly
1528 * different: RCU is already watching and ct_irq_enter() must not
1529 * be invoked because a kernel fault on a user space address might
1530 * sleep.
1531 *
1532 * In case the fault hit a RCU idle region the conditional entry
1533 * code reenabled RCU to avoid subsequent wreckage which helps
1534 * debuggability.
1535 */
1536 state = irqentry_enter(regs);
1537
1538 instrumentation_begin();
1539 handle_page_fault(regs, error_code, address);
1540 instrumentation_end();
1541
1542 irqentry_exit(regs, state);
1543}
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/bootmem.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
20#include <asm/cpufeature.h> /* boot_cpu_has, ... */
21#include <asm/traps.h> /* dotraplinkage, ... */
22#include <asm/pgalloc.h> /* pgd_*(), ... */
23#include <asm/fixmap.h> /* VSYSCALL_ADDR */
24#include <asm/vsyscall.h> /* emulate_vsyscall */
25#include <asm/vm86.h> /* struct vm86 */
26#include <asm/mmu_context.h> /* vma_pkey() */
27
28#define CREATE_TRACE_POINTS
29#include <asm/trace/exceptions.h>
30
31/*
32 * Returns 0 if mmiotrace is disabled, or if the fault is not
33 * handled by mmiotrace:
34 */
35static nokprobe_inline int
36kmmio_fault(struct pt_regs *regs, unsigned long addr)
37{
38 if (unlikely(is_kmmio_active()))
39 if (kmmio_handler(regs, addr) == 1)
40 return -1;
41 return 0;
42}
43
44static nokprobe_inline int kprobes_fault(struct pt_regs *regs)
45{
46 int ret = 0;
47
48 /* kprobe_running() needs smp_processor_id() */
49 if (kprobes_built_in() && !user_mode(regs)) {
50 preempt_disable();
51 if (kprobe_running() && kprobe_fault_handler(regs, 14))
52 ret = 1;
53 preempt_enable();
54 }
55
56 return ret;
57}
58
59/*
60 * Prefetch quirks:
61 *
62 * 32-bit mode:
63 *
64 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
65 * Check that here and ignore it.
66 *
67 * 64-bit mode:
68 *
69 * Sometimes the CPU reports invalid exceptions on prefetch.
70 * Check that here and ignore it.
71 *
72 * Opcode checker based on code by Richard Brunner.
73 */
74static inline int
75check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr,
76 unsigned char opcode, int *prefetch)
77{
78 unsigned char instr_hi = opcode & 0xf0;
79 unsigned char instr_lo = opcode & 0x0f;
80
81 switch (instr_hi) {
82 case 0x20:
83 case 0x30:
84 /*
85 * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes.
86 * In X86_64 long mode, the CPU will signal invalid
87 * opcode if some of these prefixes are present so
88 * X86_64 will never get here anyway
89 */
90 return ((instr_lo & 7) == 0x6);
91#ifdef CONFIG_X86_64
92 case 0x40:
93 /*
94 * In AMD64 long mode 0x40..0x4F are valid REX prefixes
95 * Need to figure out under what instruction mode the
96 * instruction was issued. Could check the LDT for lm,
97 * but for now it's good enough to assume that long
98 * mode only uses well known segments or kernel.
99 */
100 return (!user_mode(regs) || user_64bit_mode(regs));
101#endif
102 case 0x60:
103 /* 0x64 thru 0x67 are valid prefixes in all modes. */
104 return (instr_lo & 0xC) == 0x4;
105 case 0xF0:
106 /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */
107 return !instr_lo || (instr_lo>>1) == 1;
108 case 0x00:
109 /* Prefetch instruction is 0x0F0D or 0x0F18 */
110 if (probe_kernel_address(instr, opcode))
111 return 0;
112
113 *prefetch = (instr_lo == 0xF) &&
114 (opcode == 0x0D || opcode == 0x18);
115 return 0;
116 default:
117 return 0;
118 }
119}
120
121static int
122is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr)
123{
124 unsigned char *max_instr;
125 unsigned char *instr;
126 int prefetch = 0;
127
128 /*
129 * If it was a exec (instruction fetch) fault on NX page, then
130 * do not ignore the fault:
131 */
132 if (error_code & X86_PF_INSTR)
133 return 0;
134
135 instr = (void *)convert_ip_to_linear(current, regs);
136 max_instr = instr + 15;
137
138 if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE_MAX)
139 return 0;
140
141 while (instr < max_instr) {
142 unsigned char opcode;
143
144 if (probe_kernel_address(instr, opcode))
145 break;
146
147 instr++;
148
149 if (!check_prefetch_opcode(regs, instr, opcode, &prefetch))
150 break;
151 }
152 return prefetch;
153}
154
155/*
156 * A protection key fault means that the PKRU value did not allow
157 * access to some PTE. Userspace can figure out what PKRU was
158 * from the XSAVE state, and this function fills out a field in
159 * siginfo so userspace can discover which protection key was set
160 * on the PTE.
161 *
162 * If we get here, we know that the hardware signaled a X86_PF_PK
163 * fault and that there was a VMA once we got in the fault
164 * handler. It does *not* guarantee that the VMA we find here
165 * was the one that we faulted on.
166 *
167 * 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4);
168 * 2. T1 : set PKRU to deny access to pkey=4, touches page
169 * 3. T1 : faults...
170 * 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5);
171 * 5. T1 : enters fault handler, takes mmap_sem, etc...
172 * 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really
173 * faulted on a pte with its pkey=4.
174 */
175static void fill_sig_info_pkey(int si_signo, int si_code, siginfo_t *info,
176 u32 *pkey)
177{
178 /* This is effectively an #ifdef */
179 if (!boot_cpu_has(X86_FEATURE_OSPKE))
180 return;
181
182 /* Fault not from Protection Keys: nothing to do */
183 if ((si_code != SEGV_PKUERR) || (si_signo != SIGSEGV))
184 return;
185 /*
186 * force_sig_info_fault() is called from a number of
187 * contexts, some of which have a VMA and some of which
188 * do not. The X86_PF_PK handing happens after we have a
189 * valid VMA, so we should never reach this without a
190 * valid VMA.
191 */
192 if (!pkey) {
193 WARN_ONCE(1, "PKU fault with no VMA passed in");
194 info->si_pkey = 0;
195 return;
196 }
197 /*
198 * si_pkey should be thought of as a strong hint, but not
199 * absolutely guranteed to be 100% accurate because of
200 * the race explained above.
201 */
202 info->si_pkey = *pkey;
203}
204
205static void
206force_sig_info_fault(int si_signo, int si_code, unsigned long address,
207 struct task_struct *tsk, u32 *pkey, int fault)
208{
209 unsigned lsb = 0;
210 siginfo_t info;
211
212 info.si_signo = si_signo;
213 info.si_errno = 0;
214 info.si_code = si_code;
215 info.si_addr = (void __user *)address;
216 if (fault & VM_FAULT_HWPOISON_LARGE)
217 lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
218 if (fault & VM_FAULT_HWPOISON)
219 lsb = PAGE_SHIFT;
220 info.si_addr_lsb = lsb;
221
222 fill_sig_info_pkey(si_signo, si_code, &info, pkey);
223
224 force_sig_info(si_signo, &info, tsk);
225}
226
227DEFINE_SPINLOCK(pgd_lock);
228LIST_HEAD(pgd_list);
229
230#ifdef CONFIG_X86_32
231static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
232{
233 unsigned index = pgd_index(address);
234 pgd_t *pgd_k;
235 p4d_t *p4d, *p4d_k;
236 pud_t *pud, *pud_k;
237 pmd_t *pmd, *pmd_k;
238
239 pgd += index;
240 pgd_k = init_mm.pgd + index;
241
242 if (!pgd_present(*pgd_k))
243 return NULL;
244
245 /*
246 * set_pgd(pgd, *pgd_k); here would be useless on PAE
247 * and redundant with the set_pmd() on non-PAE. As would
248 * set_p4d/set_pud.
249 */
250 p4d = p4d_offset(pgd, address);
251 p4d_k = p4d_offset(pgd_k, address);
252 if (!p4d_present(*p4d_k))
253 return NULL;
254
255 pud = pud_offset(p4d, address);
256 pud_k = pud_offset(p4d_k, address);
257 if (!pud_present(*pud_k))
258 return NULL;
259
260 pmd = pmd_offset(pud, address);
261 pmd_k = pmd_offset(pud_k, address);
262 if (!pmd_present(*pmd_k))
263 return NULL;
264
265 if (!pmd_present(*pmd))
266 set_pmd(pmd, *pmd_k);
267 else
268 BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k));
269
270 return pmd_k;
271}
272
273void vmalloc_sync_all(void)
274{
275 unsigned long address;
276
277 if (SHARED_KERNEL_PMD)
278 return;
279
280 for (address = VMALLOC_START & PMD_MASK;
281 address >= TASK_SIZE_MAX && address < FIXADDR_TOP;
282 address += PMD_SIZE) {
283 struct page *page;
284
285 spin_lock(&pgd_lock);
286 list_for_each_entry(page, &pgd_list, lru) {
287 spinlock_t *pgt_lock;
288 pmd_t *ret;
289
290 /* the pgt_lock only for Xen */
291 pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
292
293 spin_lock(pgt_lock);
294 ret = vmalloc_sync_one(page_address(page), address);
295 spin_unlock(pgt_lock);
296
297 if (!ret)
298 break;
299 }
300 spin_unlock(&pgd_lock);
301 }
302}
303
304/*
305 * 32-bit:
306 *
307 * Handle a fault on the vmalloc or module mapping area
308 */
309static noinline int vmalloc_fault(unsigned long address)
310{
311 unsigned long pgd_paddr;
312 pmd_t *pmd_k;
313 pte_t *pte_k;
314
315 /* Make sure we are in vmalloc area: */
316 if (!(address >= VMALLOC_START && address < VMALLOC_END))
317 return -1;
318
319 WARN_ON_ONCE(in_nmi());
320
321 /*
322 * Synchronize this task's top level page-table
323 * with the 'reference' page table.
324 *
325 * Do _not_ use "current" here. We might be inside
326 * an interrupt in the middle of a task switch..
327 */
328 pgd_paddr = read_cr3_pa();
329 pmd_k = vmalloc_sync_one(__va(pgd_paddr), address);
330 if (!pmd_k)
331 return -1;
332
333 if (pmd_large(*pmd_k))
334 return 0;
335
336 pte_k = pte_offset_kernel(pmd_k, address);
337 if (!pte_present(*pte_k))
338 return -1;
339
340 return 0;
341}
342NOKPROBE_SYMBOL(vmalloc_fault);
343
344/*
345 * Did it hit the DOS screen memory VA from vm86 mode?
346 */
347static inline void
348check_v8086_mode(struct pt_regs *regs, unsigned long address,
349 struct task_struct *tsk)
350{
351#ifdef CONFIG_VM86
352 unsigned long bit;
353
354 if (!v8086_mode(regs) || !tsk->thread.vm86)
355 return;
356
357 bit = (address - 0xA0000) >> PAGE_SHIFT;
358 if (bit < 32)
359 tsk->thread.vm86->screen_bitmap |= 1 << bit;
360#endif
361}
362
363static bool low_pfn(unsigned long pfn)
364{
365 return pfn < max_low_pfn;
366}
367
368static void dump_pagetable(unsigned long address)
369{
370 pgd_t *base = __va(read_cr3_pa());
371 pgd_t *pgd = &base[pgd_index(address)];
372 p4d_t *p4d;
373 pud_t *pud;
374 pmd_t *pmd;
375 pte_t *pte;
376
377#ifdef CONFIG_X86_PAE
378 pr_info("*pdpt = %016Lx ", pgd_val(*pgd));
379 if (!low_pfn(pgd_val(*pgd) >> PAGE_SHIFT) || !pgd_present(*pgd))
380 goto out;
381#define pr_pde pr_cont
382#else
383#define pr_pde pr_info
384#endif
385 p4d = p4d_offset(pgd, address);
386 pud = pud_offset(p4d, address);
387 pmd = pmd_offset(pud, address);
388 pr_pde("*pde = %0*Lx ", sizeof(*pmd) * 2, (u64)pmd_val(*pmd));
389#undef pr_pde
390
391 /*
392 * We must not directly access the pte in the highpte
393 * case if the page table is located in highmem.
394 * And let's rather not kmap-atomic the pte, just in case
395 * it's allocated already:
396 */
397 if (!low_pfn(pmd_pfn(*pmd)) || !pmd_present(*pmd) || pmd_large(*pmd))
398 goto out;
399
400 pte = pte_offset_kernel(pmd, address);
401 pr_cont("*pte = %0*Lx ", sizeof(*pte) * 2, (u64)pte_val(*pte));
402out:
403 pr_cont("\n");
404}
405
406#else /* CONFIG_X86_64: */
407
408void vmalloc_sync_all(void)
409{
410 sync_global_pgds(VMALLOC_START & PGDIR_MASK, VMALLOC_END);
411}
412
413/*
414 * 64-bit:
415 *
416 * Handle a fault on the vmalloc area
417 */
418static noinline int vmalloc_fault(unsigned long address)
419{
420 pgd_t *pgd, *pgd_k;
421 p4d_t *p4d, *p4d_k;
422 pud_t *pud;
423 pmd_t *pmd;
424 pte_t *pte;
425
426 /* Make sure we are in vmalloc area: */
427 if (!(address >= VMALLOC_START && address < VMALLOC_END))
428 return -1;
429
430 WARN_ON_ONCE(in_nmi());
431
432 /*
433 * Copy kernel mappings over when needed. This can also
434 * happen within a race in page table update. In the later
435 * case just flush:
436 */
437 pgd = (pgd_t *)__va(read_cr3_pa()) + pgd_index(address);
438 pgd_k = pgd_offset_k(address);
439 if (pgd_none(*pgd_k))
440 return -1;
441
442 if (pgtable_l5_enabled) {
443 if (pgd_none(*pgd)) {
444 set_pgd(pgd, *pgd_k);
445 arch_flush_lazy_mmu_mode();
446 } else {
447 BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_k));
448 }
449 }
450
451 /* With 4-level paging, copying happens on the p4d level. */
452 p4d = p4d_offset(pgd, address);
453 p4d_k = p4d_offset(pgd_k, address);
454 if (p4d_none(*p4d_k))
455 return -1;
456
457 if (p4d_none(*p4d) && !pgtable_l5_enabled) {
458 set_p4d(p4d, *p4d_k);
459 arch_flush_lazy_mmu_mode();
460 } else {
461 BUG_ON(p4d_pfn(*p4d) != p4d_pfn(*p4d_k));
462 }
463
464 BUILD_BUG_ON(CONFIG_PGTABLE_LEVELS < 4);
465
466 pud = pud_offset(p4d, address);
467 if (pud_none(*pud))
468 return -1;
469
470 if (pud_large(*pud))
471 return 0;
472
473 pmd = pmd_offset(pud, address);
474 if (pmd_none(*pmd))
475 return -1;
476
477 if (pmd_large(*pmd))
478 return 0;
479
480 pte = pte_offset_kernel(pmd, address);
481 if (!pte_present(*pte))
482 return -1;
483
484 return 0;
485}
486NOKPROBE_SYMBOL(vmalloc_fault);
487
488#ifdef CONFIG_CPU_SUP_AMD
489static const char errata93_warning[] =
490KERN_ERR
491"******* Your BIOS seems to not contain a fix for K8 errata #93\n"
492"******* Working around it, but it may cause SEGVs or burn power.\n"
493"******* Please consider a BIOS update.\n"
494"******* Disabling USB legacy in the BIOS may also help.\n";
495#endif
496
497/*
498 * No vm86 mode in 64-bit mode:
499 */
500static inline void
501check_v8086_mode(struct pt_regs *regs, unsigned long address,
502 struct task_struct *tsk)
503{
504}
505
506static int bad_address(void *p)
507{
508 unsigned long dummy;
509
510 return probe_kernel_address((unsigned long *)p, dummy);
511}
512
513static void dump_pagetable(unsigned long address)
514{
515 pgd_t *base = __va(read_cr3_pa());
516 pgd_t *pgd = base + pgd_index(address);
517 p4d_t *p4d;
518 pud_t *pud;
519 pmd_t *pmd;
520 pte_t *pte;
521
522 if (bad_address(pgd))
523 goto bad;
524
525 pr_info("PGD %lx ", pgd_val(*pgd));
526
527 if (!pgd_present(*pgd))
528 goto out;
529
530 p4d = p4d_offset(pgd, address);
531 if (bad_address(p4d))
532 goto bad;
533
534 pr_cont("P4D %lx ", p4d_val(*p4d));
535 if (!p4d_present(*p4d) || p4d_large(*p4d))
536 goto out;
537
538 pud = pud_offset(p4d, address);
539 if (bad_address(pud))
540 goto bad;
541
542 pr_cont("PUD %lx ", pud_val(*pud));
543 if (!pud_present(*pud) || pud_large(*pud))
544 goto out;
545
546 pmd = pmd_offset(pud, address);
547 if (bad_address(pmd))
548 goto bad;
549
550 pr_cont("PMD %lx ", pmd_val(*pmd));
551 if (!pmd_present(*pmd) || pmd_large(*pmd))
552 goto out;
553
554 pte = pte_offset_kernel(pmd, address);
555 if (bad_address(pte))
556 goto bad;
557
558 pr_cont("PTE %lx", pte_val(*pte));
559out:
560 pr_cont("\n");
561 return;
562bad:
563 pr_info("BAD\n");
564}
565
566#endif /* CONFIG_X86_64 */
567
568/*
569 * Workaround for K8 erratum #93 & buggy BIOS.
570 *
571 * BIOS SMM functions are required to use a specific workaround
572 * to avoid corruption of the 64bit RIP register on C stepping K8.
573 *
574 * A lot of BIOS that didn't get tested properly miss this.
575 *
576 * The OS sees this as a page fault with the upper 32bits of RIP cleared.
577 * Try to work around it here.
578 *
579 * Note we only handle faults in kernel here.
580 * Does nothing on 32-bit.
581 */
582static int is_errata93(struct pt_regs *regs, unsigned long address)
583{
584#if defined(CONFIG_X86_64) && defined(CONFIG_CPU_SUP_AMD)
585 if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD
586 || boot_cpu_data.x86 != 0xf)
587 return 0;
588
589 if (address != regs->ip)
590 return 0;
591
592 if ((address >> 32) != 0)
593 return 0;
594
595 address |= 0xffffffffUL << 32;
596 if ((address >= (u64)_stext && address <= (u64)_etext) ||
597 (address >= MODULES_VADDR && address <= MODULES_END)) {
598 printk_once(errata93_warning);
599 regs->ip = address;
600 return 1;
601 }
602#endif
603 return 0;
604}
605
606/*
607 * Work around K8 erratum #100 K8 in compat mode occasionally jumps
608 * to illegal addresses >4GB.
609 *
610 * We catch this in the page fault handler because these addresses
611 * are not reachable. Just detect this case and return. Any code
612 * segment in LDT is compatibility mode.
613 */
614static int is_errata100(struct pt_regs *regs, unsigned long address)
615{
616#ifdef CONFIG_X86_64
617 if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32))
618 return 1;
619#endif
620 return 0;
621}
622
623static int is_f00f_bug(struct pt_regs *regs, unsigned long address)
624{
625#ifdef CONFIG_X86_F00F_BUG
626 unsigned long nr;
627
628 /*
629 * Pentium F0 0F C7 C8 bug workaround:
630 */
631 if (boot_cpu_has_bug(X86_BUG_F00F)) {
632 nr = (address - idt_descr.address) >> 3;
633
634 if (nr == 6) {
635 do_invalid_op(regs, 0);
636 return 1;
637 }
638 }
639#endif
640 return 0;
641}
642
643static const char nx_warning[] = KERN_CRIT
644"kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n";
645static const char smep_warning[] = KERN_CRIT
646"unable to execute userspace code (SMEP?) (uid: %d)\n";
647
648static void
649show_fault_oops(struct pt_regs *regs, unsigned long error_code,
650 unsigned long address)
651{
652 if (!oops_may_print())
653 return;
654
655 if (error_code & X86_PF_INSTR) {
656 unsigned int level;
657 pgd_t *pgd;
658 pte_t *pte;
659
660 pgd = __va(read_cr3_pa());
661 pgd += pgd_index(address);
662
663 pte = lookup_address_in_pgd(pgd, address, &level);
664
665 if (pte && pte_present(*pte) && !pte_exec(*pte))
666 printk(nx_warning, from_kuid(&init_user_ns, current_uid()));
667 if (pte && pte_present(*pte) && pte_exec(*pte) &&
668 (pgd_flags(*pgd) & _PAGE_USER) &&
669 (__read_cr4() & X86_CR4_SMEP))
670 printk(smep_warning, from_kuid(&init_user_ns, current_uid()));
671 }
672
673 printk(KERN_ALERT "BUG: unable to handle kernel ");
674 if (address < PAGE_SIZE)
675 printk(KERN_CONT "NULL pointer dereference");
676 else
677 printk(KERN_CONT "paging request");
678
679 printk(KERN_CONT " at %px\n", (void *) address);
680
681 dump_pagetable(address);
682}
683
684static noinline void
685pgtable_bad(struct pt_regs *regs, unsigned long error_code,
686 unsigned long address)
687{
688 struct task_struct *tsk;
689 unsigned long flags;
690 int sig;
691
692 flags = oops_begin();
693 tsk = current;
694 sig = SIGKILL;
695
696 printk(KERN_ALERT "%s: Corrupted page table at address %lx\n",
697 tsk->comm, address);
698 dump_pagetable(address);
699
700 tsk->thread.cr2 = address;
701 tsk->thread.trap_nr = X86_TRAP_PF;
702 tsk->thread.error_code = error_code;
703
704 if (__die("Bad pagetable", regs, error_code))
705 sig = 0;
706
707 oops_end(flags, regs, sig);
708}
709
710static noinline void
711no_context(struct pt_regs *regs, unsigned long error_code,
712 unsigned long address, int signal, int si_code)
713{
714 struct task_struct *tsk = current;
715 unsigned long flags;
716 int sig;
717
718 /* Are we prepared to handle this kernel fault? */
719 if (fixup_exception(regs, X86_TRAP_PF)) {
720 /*
721 * Any interrupt that takes a fault gets the fixup. This makes
722 * the below recursive fault logic only apply to a faults from
723 * task context.
724 */
725 if (in_interrupt())
726 return;
727
728 /*
729 * Per the above we're !in_interrupt(), aka. task context.
730 *
731 * In this case we need to make sure we're not recursively
732 * faulting through the emulate_vsyscall() logic.
733 */
734 if (current->thread.sig_on_uaccess_err && signal) {
735 tsk->thread.trap_nr = X86_TRAP_PF;
736 tsk->thread.error_code = error_code | X86_PF_USER;
737 tsk->thread.cr2 = address;
738
739 /* XXX: hwpoison faults will set the wrong code. */
740 force_sig_info_fault(signal, si_code, address,
741 tsk, NULL, 0);
742 }
743
744 /*
745 * Barring that, we can do the fixup and be happy.
746 */
747 return;
748 }
749
750#ifdef CONFIG_VMAP_STACK
751 /*
752 * Stack overflow? During boot, we can fault near the initial
753 * stack in the direct map, but that's not an overflow -- check
754 * that we're in vmalloc space to avoid this.
755 */
756 if (is_vmalloc_addr((void *)address) &&
757 (((unsigned long)tsk->stack - 1 - address < PAGE_SIZE) ||
758 address - ((unsigned long)tsk->stack + THREAD_SIZE) < PAGE_SIZE)) {
759 unsigned long stack = this_cpu_read(orig_ist.ist[DOUBLEFAULT_STACK]) - sizeof(void *);
760 /*
761 * We're likely to be running with very little stack space
762 * left. It's plausible that we'd hit this condition but
763 * double-fault even before we get this far, in which case
764 * we're fine: the double-fault handler will deal with it.
765 *
766 * We don't want to make it all the way into the oops code
767 * and then double-fault, though, because we're likely to
768 * break the console driver and lose most of the stack dump.
769 */
770 asm volatile ("movq %[stack], %%rsp\n\t"
771 "call handle_stack_overflow\n\t"
772 "1: jmp 1b"
773 : ASM_CALL_CONSTRAINT
774 : "D" ("kernel stack overflow (page fault)"),
775 "S" (regs), "d" (address),
776 [stack] "rm" (stack));
777 unreachable();
778 }
779#endif
780
781 /*
782 * 32-bit:
783 *
784 * Valid to do another page fault here, because if this fault
785 * had been triggered by is_prefetch fixup_exception would have
786 * handled it.
787 *
788 * 64-bit:
789 *
790 * Hall of shame of CPU/BIOS bugs.
791 */
792 if (is_prefetch(regs, error_code, address))
793 return;
794
795 if (is_errata93(regs, address))
796 return;
797
798 /*
799 * Oops. The kernel tried to access some bad page. We'll have to
800 * terminate things with extreme prejudice:
801 */
802 flags = oops_begin();
803
804 show_fault_oops(regs, error_code, address);
805
806 if (task_stack_end_corrupted(tsk))
807 printk(KERN_EMERG "Thread overran stack, or stack corrupted\n");
808
809 tsk->thread.cr2 = address;
810 tsk->thread.trap_nr = X86_TRAP_PF;
811 tsk->thread.error_code = error_code;
812
813 sig = SIGKILL;
814 if (__die("Oops", regs, error_code))
815 sig = 0;
816
817 /* Executive summary in case the body of the oops scrolled away */
818 printk(KERN_DEFAULT "CR2: %016lx\n", address);
819
820 oops_end(flags, regs, sig);
821}
822
823/*
824 * Print out info about fatal segfaults, if the show_unhandled_signals
825 * sysctl is set:
826 */
827static inline void
828show_signal_msg(struct pt_regs *regs, unsigned long error_code,
829 unsigned long address, struct task_struct *tsk)
830{
831 if (!unhandled_signal(tsk, SIGSEGV))
832 return;
833
834 if (!printk_ratelimit())
835 return;
836
837 printk("%s%s[%d]: segfault at %lx ip %px sp %px error %lx",
838 task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
839 tsk->comm, task_pid_nr(tsk), address,
840 (void *)regs->ip, (void *)regs->sp, error_code);
841
842 print_vma_addr(KERN_CONT " in ", regs->ip);
843
844 printk(KERN_CONT "\n");
845}
846
847static void
848__bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
849 unsigned long address, u32 *pkey, int si_code)
850{
851 struct task_struct *tsk = current;
852
853 /* User mode accesses just cause a SIGSEGV */
854 if (error_code & X86_PF_USER) {
855 /*
856 * It's possible to have interrupts off here:
857 */
858 local_irq_enable();
859
860 /*
861 * Valid to do another page fault here because this one came
862 * from user space:
863 */
864 if (is_prefetch(regs, error_code, address))
865 return;
866
867 if (is_errata100(regs, address))
868 return;
869
870#ifdef CONFIG_X86_64
871 /*
872 * Instruction fetch faults in the vsyscall page might need
873 * emulation.
874 */
875 if (unlikely((error_code & X86_PF_INSTR) &&
876 ((address & ~0xfff) == VSYSCALL_ADDR))) {
877 if (emulate_vsyscall(regs, address))
878 return;
879 }
880#endif
881
882 /*
883 * To avoid leaking information about the kernel page table
884 * layout, pretend that user-mode accesses to kernel addresses
885 * are always protection faults.
886 */
887 if (address >= TASK_SIZE_MAX)
888 error_code |= X86_PF_PROT;
889
890 if (likely(show_unhandled_signals))
891 show_signal_msg(regs, error_code, address, tsk);
892
893 tsk->thread.cr2 = address;
894 tsk->thread.error_code = error_code;
895 tsk->thread.trap_nr = X86_TRAP_PF;
896
897 force_sig_info_fault(SIGSEGV, si_code, address, tsk, pkey, 0);
898
899 return;
900 }
901
902 if (is_f00f_bug(regs, address))
903 return;
904
905 no_context(regs, error_code, address, SIGSEGV, si_code);
906}
907
908static noinline void
909bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
910 unsigned long address, u32 *pkey)
911{
912 __bad_area_nosemaphore(regs, error_code, address, pkey, SEGV_MAPERR);
913}
914
915static void
916__bad_area(struct pt_regs *regs, unsigned long error_code,
917 unsigned long address, struct vm_area_struct *vma, int si_code)
918{
919 struct mm_struct *mm = current->mm;
920 u32 pkey;
921
922 if (vma)
923 pkey = vma_pkey(vma);
924
925 /*
926 * Something tried to access memory that isn't in our memory map..
927 * Fix it, but check if it's kernel or user first..
928 */
929 up_read(&mm->mmap_sem);
930
931 __bad_area_nosemaphore(regs, error_code, address,
932 (vma) ? &pkey : NULL, si_code);
933}
934
935static noinline void
936bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address)
937{
938 __bad_area(regs, error_code, address, NULL, SEGV_MAPERR);
939}
940
941static inline bool bad_area_access_from_pkeys(unsigned long error_code,
942 struct vm_area_struct *vma)
943{
944 /* This code is always called on the current mm */
945 bool foreign = false;
946
947 if (!boot_cpu_has(X86_FEATURE_OSPKE))
948 return false;
949 if (error_code & X86_PF_PK)
950 return true;
951 /* this checks permission keys on the VMA: */
952 if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE),
953 (error_code & X86_PF_INSTR), foreign))
954 return true;
955 return false;
956}
957
958static noinline void
959bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
960 unsigned long address, struct vm_area_struct *vma)
961{
962 /*
963 * This OSPKE check is not strictly necessary at runtime.
964 * But, doing it this way allows compiler optimizations
965 * if pkeys are compiled out.
966 */
967 if (bad_area_access_from_pkeys(error_code, vma))
968 __bad_area(regs, error_code, address, vma, SEGV_PKUERR);
969 else
970 __bad_area(regs, error_code, address, vma, SEGV_ACCERR);
971}
972
973static void
974do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
975 u32 *pkey, unsigned int fault)
976{
977 struct task_struct *tsk = current;
978 int code = BUS_ADRERR;
979
980 /* Kernel mode? Handle exceptions or die: */
981 if (!(error_code & X86_PF_USER)) {
982 no_context(regs, error_code, address, SIGBUS, BUS_ADRERR);
983 return;
984 }
985
986 /* User-space => ok to do another page fault: */
987 if (is_prefetch(regs, error_code, address))
988 return;
989
990 tsk->thread.cr2 = address;
991 tsk->thread.error_code = error_code;
992 tsk->thread.trap_nr = X86_TRAP_PF;
993
994#ifdef CONFIG_MEMORY_FAILURE
995 if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
996 printk(KERN_ERR
997 "MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
998 tsk->comm, tsk->pid, address);
999 code = BUS_MCEERR_AR;
1000 }
1001#endif
1002 force_sig_info_fault(SIGBUS, code, address, tsk, pkey, fault);
1003}
1004
1005static noinline void
1006mm_fault_error(struct pt_regs *regs, unsigned long error_code,
1007 unsigned long address, u32 *pkey, unsigned int fault)
1008{
1009 if (fatal_signal_pending(current) && !(error_code & X86_PF_USER)) {
1010 no_context(regs, error_code, address, 0, 0);
1011 return;
1012 }
1013
1014 if (fault & VM_FAULT_OOM) {
1015 /* Kernel mode? Handle exceptions or die: */
1016 if (!(error_code & X86_PF_USER)) {
1017 no_context(regs, error_code, address,
1018 SIGSEGV, SEGV_MAPERR);
1019 return;
1020 }
1021
1022 /*
1023 * We ran out of memory, call the OOM killer, and return the
1024 * userspace (which will retry the fault, or kill us if we got
1025 * oom-killed):
1026 */
1027 pagefault_out_of_memory();
1028 } else {
1029 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
1030 VM_FAULT_HWPOISON_LARGE))
1031 do_sigbus(regs, error_code, address, pkey, fault);
1032 else if (fault & VM_FAULT_SIGSEGV)
1033 bad_area_nosemaphore(regs, error_code, address, pkey);
1034 else
1035 BUG();
1036 }
1037}
1038
1039static int spurious_fault_check(unsigned long error_code, pte_t *pte)
1040{
1041 if ((error_code & X86_PF_WRITE) && !pte_write(*pte))
1042 return 0;
1043
1044 if ((error_code & X86_PF_INSTR) && !pte_exec(*pte))
1045 return 0;
1046 /*
1047 * Note: We do not do lazy flushing on protection key
1048 * changes, so no spurious fault will ever set X86_PF_PK.
1049 */
1050 if ((error_code & X86_PF_PK))
1051 return 1;
1052
1053 return 1;
1054}
1055
1056/*
1057 * Handle a spurious fault caused by a stale TLB entry.
1058 *
1059 * This allows us to lazily refresh the TLB when increasing the
1060 * permissions of a kernel page (RO -> RW or NX -> X). Doing it
1061 * eagerly is very expensive since that implies doing a full
1062 * cross-processor TLB flush, even if no stale TLB entries exist
1063 * on other processors.
1064 *
1065 * Spurious faults may only occur if the TLB contains an entry with
1066 * fewer permission than the page table entry. Non-present (P = 0)
1067 * and reserved bit (R = 1) faults are never spurious.
1068 *
1069 * There are no security implications to leaving a stale TLB when
1070 * increasing the permissions on a page.
1071 *
1072 * Returns non-zero if a spurious fault was handled, zero otherwise.
1073 *
1074 * See Intel Developer's Manual Vol 3 Section 4.10.4.3, bullet 3
1075 * (Optional Invalidation).
1076 */
1077static noinline int
1078spurious_fault(unsigned long error_code, unsigned long address)
1079{
1080 pgd_t *pgd;
1081 p4d_t *p4d;
1082 pud_t *pud;
1083 pmd_t *pmd;
1084 pte_t *pte;
1085 int ret;
1086
1087 /*
1088 * Only writes to RO or instruction fetches from NX may cause
1089 * spurious faults.
1090 *
1091 * These could be from user or supervisor accesses but the TLB
1092 * is only lazily flushed after a kernel mapping protection
1093 * change, so user accesses are not expected to cause spurious
1094 * faults.
1095 */
1096 if (error_code != (X86_PF_WRITE | X86_PF_PROT) &&
1097 error_code != (X86_PF_INSTR | X86_PF_PROT))
1098 return 0;
1099
1100 pgd = init_mm.pgd + pgd_index(address);
1101 if (!pgd_present(*pgd))
1102 return 0;
1103
1104 p4d = p4d_offset(pgd, address);
1105 if (!p4d_present(*p4d))
1106 return 0;
1107
1108 if (p4d_large(*p4d))
1109 return spurious_fault_check(error_code, (pte_t *) p4d);
1110
1111 pud = pud_offset(p4d, address);
1112 if (!pud_present(*pud))
1113 return 0;
1114
1115 if (pud_large(*pud))
1116 return spurious_fault_check(error_code, (pte_t *) pud);
1117
1118 pmd = pmd_offset(pud, address);
1119 if (!pmd_present(*pmd))
1120 return 0;
1121
1122 if (pmd_large(*pmd))
1123 return spurious_fault_check(error_code, (pte_t *) pmd);
1124
1125 pte = pte_offset_kernel(pmd, address);
1126 if (!pte_present(*pte))
1127 return 0;
1128
1129 ret = spurious_fault_check(error_code, pte);
1130 if (!ret)
1131 return 0;
1132
1133 /*
1134 * Make sure we have permissions in PMD.
1135 * If not, then there's a bug in the page tables:
1136 */
1137 ret = spurious_fault_check(error_code, (pte_t *) pmd);
1138 WARN_ONCE(!ret, "PMD has incorrect permission bits\n");
1139
1140 return ret;
1141}
1142NOKPROBE_SYMBOL(spurious_fault);
1143
1144int show_unhandled_signals = 1;
1145
1146static inline int
1147access_error(unsigned long error_code, struct vm_area_struct *vma)
1148{
1149 /* This is only called for the current mm, so: */
1150 bool foreign = false;
1151
1152 /*
1153 * Read or write was blocked by protection keys. This is
1154 * always an unconditional error and can never result in
1155 * a follow-up action to resolve the fault, like a COW.
1156 */
1157 if (error_code & X86_PF_PK)
1158 return 1;
1159
1160 /*
1161 * Make sure to check the VMA so that we do not perform
1162 * faults just to hit a X86_PF_PK as soon as we fill in a
1163 * page.
1164 */
1165 if (!arch_vma_access_permitted(vma, (error_code & X86_PF_WRITE),
1166 (error_code & X86_PF_INSTR), foreign))
1167 return 1;
1168
1169 if (error_code & X86_PF_WRITE) {
1170 /* write, present and write, not present: */
1171 if (unlikely(!(vma->vm_flags & VM_WRITE)))
1172 return 1;
1173 return 0;
1174 }
1175
1176 /* read, present: */
1177 if (unlikely(error_code & X86_PF_PROT))
1178 return 1;
1179
1180 /* read, not present: */
1181 if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))))
1182 return 1;
1183
1184 return 0;
1185}
1186
1187static int fault_in_kernel_space(unsigned long address)
1188{
1189 return address >= TASK_SIZE_MAX;
1190}
1191
1192static inline bool smap_violation(int error_code, struct pt_regs *regs)
1193{
1194 if (!IS_ENABLED(CONFIG_X86_SMAP))
1195 return false;
1196
1197 if (!static_cpu_has(X86_FEATURE_SMAP))
1198 return false;
1199
1200 if (error_code & X86_PF_USER)
1201 return false;
1202
1203 if (!user_mode(regs) && (regs->flags & X86_EFLAGS_AC))
1204 return false;
1205
1206 return true;
1207}
1208
1209/*
1210 * This routine handles page faults. It determines the address,
1211 * and the problem, and then passes it off to one of the appropriate
1212 * routines.
1213 */
1214static noinline void
1215__do_page_fault(struct pt_regs *regs, unsigned long error_code,
1216 unsigned long address)
1217{
1218 struct vm_area_struct *vma;
1219 struct task_struct *tsk;
1220 struct mm_struct *mm;
1221 int fault, major = 0;
1222 unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
1223 u32 pkey;
1224
1225 tsk = current;
1226 mm = tsk->mm;
1227
1228 prefetchw(&mm->mmap_sem);
1229
1230 if (unlikely(kmmio_fault(regs, address)))
1231 return;
1232
1233 /*
1234 * We fault-in kernel-space virtual memory on-demand. The
1235 * 'reference' page table is init_mm.pgd.
1236 *
1237 * NOTE! We MUST NOT take any locks for this case. We may
1238 * be in an interrupt or a critical region, and should
1239 * only copy the information from the master page table,
1240 * nothing more.
1241 *
1242 * This verifies that the fault happens in kernel space
1243 * (error_code & 4) == 0, and that the fault was not a
1244 * protection error (error_code & 9) == 0.
1245 */
1246 if (unlikely(fault_in_kernel_space(address))) {
1247 if (!(error_code & (X86_PF_RSVD | X86_PF_USER | X86_PF_PROT))) {
1248 if (vmalloc_fault(address) >= 0)
1249 return;
1250 }
1251
1252 /* Can handle a stale RO->RW TLB: */
1253 if (spurious_fault(error_code, address))
1254 return;
1255
1256 /* kprobes don't want to hook the spurious faults: */
1257 if (kprobes_fault(regs))
1258 return;
1259 /*
1260 * Don't take the mm semaphore here. If we fixup a prefetch
1261 * fault we could otherwise deadlock:
1262 */
1263 bad_area_nosemaphore(regs, error_code, address, NULL);
1264
1265 return;
1266 }
1267
1268 /* kprobes don't want to hook the spurious faults: */
1269 if (unlikely(kprobes_fault(regs)))
1270 return;
1271
1272 if (unlikely(error_code & X86_PF_RSVD))
1273 pgtable_bad(regs, error_code, address);
1274
1275 if (unlikely(smap_violation(error_code, regs))) {
1276 bad_area_nosemaphore(regs, error_code, address, NULL);
1277 return;
1278 }
1279
1280 /*
1281 * If we're in an interrupt, have no user context or are running
1282 * in a region with pagefaults disabled then we must not take the fault
1283 */
1284 if (unlikely(faulthandler_disabled() || !mm)) {
1285 bad_area_nosemaphore(regs, error_code, address, NULL);
1286 return;
1287 }
1288
1289 /*
1290 * It's safe to allow irq's after cr2 has been saved and the
1291 * vmalloc fault has been handled.
1292 *
1293 * User-mode registers count as a user access even for any
1294 * potential system fault or CPU buglet:
1295 */
1296 if (user_mode(regs)) {
1297 local_irq_enable();
1298 error_code |= X86_PF_USER;
1299 flags |= FAULT_FLAG_USER;
1300 } else {
1301 if (regs->flags & X86_EFLAGS_IF)
1302 local_irq_enable();
1303 }
1304
1305 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
1306
1307 if (error_code & X86_PF_WRITE)
1308 flags |= FAULT_FLAG_WRITE;
1309 if (error_code & X86_PF_INSTR)
1310 flags |= FAULT_FLAG_INSTRUCTION;
1311
1312 /*
1313 * When running in the kernel we expect faults to occur only to
1314 * addresses in user space. All other faults represent errors in
1315 * the kernel and should generate an OOPS. Unfortunately, in the
1316 * case of an erroneous fault occurring in a code path which already
1317 * holds mmap_sem we will deadlock attempting to validate the fault
1318 * against the address space. Luckily the kernel only validly
1319 * references user space from well defined areas of code, which are
1320 * listed in the exceptions table.
1321 *
1322 * As the vast majority of faults will be valid we will only perform
1323 * the source reference check when there is a possibility of a
1324 * deadlock. Attempt to lock the address space, if we cannot we then
1325 * validate the source. If this is invalid we can skip the address
1326 * space check, thus avoiding the deadlock:
1327 */
1328 if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
1329 if (!(error_code & X86_PF_USER) &&
1330 !search_exception_tables(regs->ip)) {
1331 bad_area_nosemaphore(regs, error_code, address, NULL);
1332 return;
1333 }
1334retry:
1335 down_read(&mm->mmap_sem);
1336 } else {
1337 /*
1338 * The above down_read_trylock() might have succeeded in
1339 * which case we'll have missed the might_sleep() from
1340 * down_read():
1341 */
1342 might_sleep();
1343 }
1344
1345 vma = find_vma(mm, address);
1346 if (unlikely(!vma)) {
1347 bad_area(regs, error_code, address);
1348 return;
1349 }
1350 if (likely(vma->vm_start <= address))
1351 goto good_area;
1352 if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
1353 bad_area(regs, error_code, address);
1354 return;
1355 }
1356 if (error_code & X86_PF_USER) {
1357 /*
1358 * Accessing the stack below %sp is always a bug.
1359 * The large cushion allows instructions like enter
1360 * and pusha to work. ("enter $65535, $31" pushes
1361 * 32 pointers and then decrements %sp by 65535.)
1362 */
1363 if (unlikely(address + 65536 + 32 * sizeof(unsigned long) < regs->sp)) {
1364 bad_area(regs, error_code, address);
1365 return;
1366 }
1367 }
1368 if (unlikely(expand_stack(vma, address))) {
1369 bad_area(regs, error_code, address);
1370 return;
1371 }
1372
1373 /*
1374 * Ok, we have a good vm_area for this memory access, so
1375 * we can handle it..
1376 */
1377good_area:
1378 if (unlikely(access_error(error_code, vma))) {
1379 bad_area_access_error(regs, error_code, address, vma);
1380 return;
1381 }
1382
1383 /*
1384 * If for any reason at all we couldn't handle the fault,
1385 * make sure we exit gracefully rather than endlessly redo
1386 * the fault. Since we never set FAULT_FLAG_RETRY_NOWAIT, if
1387 * we get VM_FAULT_RETRY back, the mmap_sem has been unlocked.
1388 *
1389 * Note that handle_userfault() may also release and reacquire mmap_sem
1390 * (and not return with VM_FAULT_RETRY), when returning to userland to
1391 * repeat the page fault later with a VM_FAULT_NOPAGE retval
1392 * (potentially after handling any pending signal during the return to
1393 * userland). The return to userland is identified whenever
1394 * FAULT_FLAG_USER|FAULT_FLAG_KILLABLE are both set in flags.
1395 * Thus we have to be careful about not touching vma after handling the
1396 * fault, so we read the pkey beforehand.
1397 */
1398 pkey = vma_pkey(vma);
1399 fault = handle_mm_fault(vma, address, flags);
1400 major |= fault & VM_FAULT_MAJOR;
1401
1402 /*
1403 * If we need to retry the mmap_sem has already been released,
1404 * and if there is a fatal signal pending there is no guarantee
1405 * that we made any progress. Handle this case first.
1406 */
1407 if (unlikely(fault & VM_FAULT_RETRY)) {
1408 /* Retry at most once */
1409 if (flags & FAULT_FLAG_ALLOW_RETRY) {
1410 flags &= ~FAULT_FLAG_ALLOW_RETRY;
1411 flags |= FAULT_FLAG_TRIED;
1412 if (!fatal_signal_pending(tsk))
1413 goto retry;
1414 }
1415
1416 /* User mode? Just return to handle the fatal exception */
1417 if (flags & FAULT_FLAG_USER)
1418 return;
1419
1420 /* Not returning to user mode? Handle exceptions or die: */
1421 no_context(regs, error_code, address, SIGBUS, BUS_ADRERR);
1422 return;
1423 }
1424
1425 up_read(&mm->mmap_sem);
1426 if (unlikely(fault & VM_FAULT_ERROR)) {
1427 mm_fault_error(regs, error_code, address, &pkey, fault);
1428 return;
1429 }
1430
1431 /*
1432 * Major/minor page fault accounting. If any of the events
1433 * returned VM_FAULT_MAJOR, we account it as a major fault.
1434 */
1435 if (major) {
1436 tsk->maj_flt++;
1437 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, address);
1438 } else {
1439 tsk->min_flt++;
1440 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, address);
1441 }
1442
1443 check_v8086_mode(regs, address, tsk);
1444}
1445NOKPROBE_SYMBOL(__do_page_fault);
1446
1447static nokprobe_inline void
1448trace_page_fault_entries(unsigned long address, struct pt_regs *regs,
1449 unsigned long error_code)
1450{
1451 if (user_mode(regs))
1452 trace_page_fault_user(address, regs, error_code);
1453 else
1454 trace_page_fault_kernel(address, regs, error_code);
1455}
1456
1457/*
1458 * We must have this function blacklisted from kprobes, tagged with notrace
1459 * and call read_cr2() before calling anything else. To avoid calling any
1460 * kind of tracing machinery before we've observed the CR2 value.
1461 *
1462 * exception_{enter,exit}() contains all sorts of tracepoints.
1463 */
1464dotraplinkage void notrace
1465do_page_fault(struct pt_regs *regs, unsigned long error_code)
1466{
1467 unsigned long address = read_cr2(); /* Get the faulting address */
1468 enum ctx_state prev_state;
1469
1470 prev_state = exception_enter();
1471 if (trace_pagefault_enabled())
1472 trace_page_fault_entries(address, regs, error_code);
1473
1474 __do_page_fault(regs, error_code, address);
1475 exception_exit(prev_state);
1476}
1477NOKPROBE_SYMBOL(do_page_fault);