summaryrefslogtreecommitdiff
path: root/arch/x86/mm/pti.c
blob: a3c6757a65c75fd79fe77649ae41998fc6d3219c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright(c) 2017 Intel Corporation. All rights reserved.
 *
 * This code is based in part on work published here:
 *
 *	https://github.com/IAIK/KAISER
 *
 * The original work was written by and and signed off by for the Linux
 * kernel by:
 *
 *   Signed-off-by: Richard Fellner <richard.fellner@student.tugraz.at>
 *   Signed-off-by: Moritz Lipp <moritz.lipp@iaik.tugraz.at>
 *   Signed-off-by: Daniel Gruss <daniel.gruss@iaik.tugraz.at>
 *   Signed-off-by: Michael Schwarz <michael.schwarz@iaik.tugraz.at>
 *
 * Major changes to the original code by: Dave Hansen <dave.hansen@intel.com>
 * Mostly rewritten by Thomas Gleixner <tglx@linutronix.de> and
 *		       Andy Lutomirsky <luto@amacapital.net>
 */
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/bug.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/mm.h>
#include <linux/uaccess.h>
#include <linux/cpu.h>

#include <asm/cpufeature.h>
#include <asm/hypervisor.h>
#include <asm/vsyscall.h>
#include <asm/cmdline.h>
#include <asm/pti.h>
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include <asm/desc.h>
#include <asm/sections.h>
#include <asm/set_memory.h>

#undef pr_fmt
#define pr_fmt(fmt)     "Kernel/User page tables isolation: " fmt

/* Backporting helper */
#ifndef __GFP_NOTRACK
#define __GFP_NOTRACK	0
#endif

/*
 * Define the page-table levels we clone for user-space on 32
 * and 64 bit.
 */
#ifdef CONFIG_X86_64
#define	PTI_LEVEL_KERNEL_IMAGE	PTI_CLONE_PMD
#else
#define	PTI_LEVEL_KERNEL_IMAGE	PTI_CLONE_PTE
#endif

static void __init pti_print_if_insecure(const char *reason)
{
	if (boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN))
		pr_info("%s\n", reason);
}

static void __init pti_print_if_secure(const char *reason)
{
	if (!boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN))
		pr_info("%s\n", reason);
}

static enum pti_mode {
	PTI_AUTO = 0,
	PTI_FORCE_OFF,
	PTI_FORCE_ON
} pti_mode;

void __init pti_check_boottime_disable(void)
{
	char arg[5];
	int ret;

	/* Assume mode is auto unless overridden. */
	pti_mode = PTI_AUTO;

	if (hypervisor_is_type(X86_HYPER_XEN_PV)) {
		pti_mode = PTI_FORCE_OFF;
		pti_print_if_insecure("disabled on XEN PV.");
		return;
	}

	ret = cmdline_find_option(boot_command_line, "pti", arg, sizeof(arg));
	if (ret > 0)  {
		if (ret == 3 && !strncmp(arg, "off", 3)) {
			pti_mode = PTI_FORCE_OFF;
			pti_print_if_insecure("disabled on command line.");
			return;
		}
		if (ret == 2 && !strncmp(arg, "on", 2)) {
			pti_mode = PTI_FORCE_ON;
			pti_print_if_secure("force enabled on command line.");
			goto enable;
		}
		if (ret == 4 && !strncmp(arg, "auto", 4)) {
			pti_mode = PTI_AUTO;
			goto autosel;
		}
	}

	if (cmdline_find_option_bool(boot_command_line, "nopti") ||
	    cpu_mitigations_off()) {
		pti_mode = PTI_FORCE_OFF;
		pti_print_if_insecure("disabled on command line.");
		return;
	}

autosel:
	if (!boot_cpu_has_bug(X86_BUG_CPU_MELTDOWN))
		return;
enable:
	setup_force_cpu_cap(X86_FEATURE_PTI);
}

pgd_t __pti_set_user_pgtbl(pgd_t *pgdp, pgd_t pgd)
{
	/*
	 * Changes to the high (kernel) portion of the kernelmode page
	 * tables are not automatically propagated to the usermode tables.
	 *
	 * Users should keep in mind that, unlike the kernelmode tables,
	 * there is no vmalloc_fault equivalent for the usermode tables.
	 * Top-level entries added to init_mm's usermode pgd after boot
	 * will not be automatically propagated to other mms.
	 */
	if (!pgdp_maps_userspace(pgdp))
		return pgd;

	/*
	 * The user page tables get the full PGD, accessible from
	 * userspace:
	 */
	kernel_to_user_pgdp(pgdp)->pgd = pgd.pgd;

	/*
	 * If this is normal user memory, make it NX in the kernel
	 * pagetables so that, if we somehow screw up and return to
	 * usermode with the kernel CR3 loaded, we'll get a page fault
	 * instead of allowing user code to execute with the wrong CR3.
	 *
	 * As exceptions, we don't set NX if:
	 *  - _PAGE_USER is not set.  This could be an executable
	 *     EFI runtime mapping or something similar, and the kernel
	 *     may execute from it
	 *  - we don't have NX support
	 *  - we're clearing the PGD (i.e. the new pgd is not present).
	 */
	if ((pgd.pgd & (_PAGE_USER|_PAGE_PRESENT)) == (_PAGE_USER|_PAGE_PRESENT) &&
	    (__supported_pte_mask & _PAGE_NX))
		pgd.pgd |= _PAGE_NX;

	/* return the copy of the PGD we want the kernel to use: */
	return pgd;
}

/*
 * Walk the user copy of the page tables (optionally) trying to allocate
 * page table pages on the way down.
 *
 * Returns a pointer to a P4D on success, or NULL on failure.
 */
static p4d_t *pti_user_pagetable_walk_p4d(unsigned long address)
{
	pgd_t *pgd = kernel_to_user_pgdp(pgd_offset_k(address));
	gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);

	if (address < PAGE_OFFSET) {
		WARN_ONCE(1, "attempt to walk user address\n");
		return NULL;
	}

	if (pgd_none(*pgd)) {
		unsigned long new_p4d_page = __get_free_page(gfp);
		if (WARN_ON_ONCE(!new_p4d_page))
			return NULL;

		set_pgd(pgd, __pgd(_KERNPG_TABLE | __pa(new_p4d_page)));
	}
	BUILD_BUG_ON(pgd_large(*pgd) != 0);

	return p4d_offset(pgd, address);
}

/*
 * Walk the user copy of the page tables (optionally) trying to allocate
 * page table pages on the way down.
 *
 * Returns a pointer to a PMD on success, or NULL on failure.
 */
static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)
{
	gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);
	p4d_t *p4d;
	pud_t *pud;

	p4d = pti_user_pagetable_walk_p4d(address);
	if (!p4d)
		return NULL;

	BUILD_BUG_ON(p4d_large(*p4d) != 0);
	if (p4d_none(*p4d)) {
		unsigned long new_pud_page = __get_free_page(gfp);
		if (WARN_ON_ONCE(!new_pud_page))
			return NULL;

		set_p4d(p4d, __p4d(_KERNPG_TABLE | __pa(new_pud_page)));
	}

	pud = pud_offset(p4d, address);
	/* The user page tables do not use large mappings: */
	if (pud_large(*pud)) {
		WARN_ON(1);
		return NULL;
	}
	if (pud_none(*pud)) {
		unsigned long new_pmd_page = __get_free_page(gfp);
		if (WARN_ON_ONCE(!new_pmd_page))
			return NULL;

		set_pud(pud, __pud(_KERNPG_TABLE | __pa(new_pmd_page)));
	}

	return pmd_offset(pud, address);
}

/*
 * Walk the shadow copy of the page tables (optionally) trying to allocate
 * page table pages on the way down.  Does not support large pages.
 *
 * Note: this is only used when mapping *new* kernel data into the
 * user/shadow page tables.  It is never used for userspace data.
 *
 * Returns a pointer to a PTE on success, or NULL on failure.
 */
static pte_t *pti_user_pagetable_walk_pte(unsigned long address)
{
	gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);
	pmd_t *pmd;
	pte_t *pte;

	pmd = pti_user_pagetable_walk_pmd(address);
	if (!pmd)
		return NULL;

	/* We can't do anything sensible if we hit a large mapping. */
	if (pmd_large(*pmd)) {
		WARN_ON(1);
		return NULL;
	}

	if (pmd_none(*pmd)) {
		unsigned long new_pte_page = __get_free_page(gfp);
		if (!new_pte_page)
			return NULL;

		set_pmd(pmd, __pmd(_KERNPG_TABLE | __pa(new_pte_page)));
	}

	pte = pte_offset_kernel(pmd, address);
	if (pte_flags(*pte) & _PAGE_USER) {
		WARN_ONCE(1, "attempt to walk to user pte\n");
		return NULL;
	}
	return pte;
}

#ifdef CONFIG_X86_VSYSCALL_EMULATION
static void __init pti_setup_vsyscall(void)
{
	pte_t *pte, *target_pte;
	unsigned int level;

	pte = lookup_address(VSYSCALL_ADDR, &level);
	if (!pte || WARN_ON(level != PG_LEVEL_4K) || pte_none(*pte))
		return;

	target_pte = pti_user_pagetable_walk_pte(VSYSCALL_ADDR);
	if (WARN_ON(!target_pte))
		return;

	*target_pte = *pte;
	set_vsyscall_pgtable_user_bits(kernel_to_user_pgdp(swapper_pg_dir));
}
#else
static void __init pti_setup_vsyscall(void) { }
#endif

enum pti_clone_level {
	PTI_CLONE_PMD,
	PTI_CLONE_PTE,
};

static void
pti_clone_pgtable(unsigned long start, unsigned long end,
		  enum pti_clone_level level)
{
	unsigned long addr;

	/*
	 * Clone the populated PMDs which cover start to end. These PMD areas
	 * can have holes.
	 */
	for (addr = start; addr < end;) {
		pte_t *pte, *target_pte;
		pmd_t *pmd, *target_pmd;
		pgd_t *pgd;
		p4d_t *p4d;
		pud_t *pud;

		/* Overflow check */
		if (addr < start)
			break;

		pgd = pgd_offset_k(addr);
		if (WARN_ON(pgd_none(*pgd)))
			return;
		p4d = p4d_offset(pgd, addr);
		if (WARN_ON(p4d_none(*p4d)))
			return;

		pud = pud_offset(p4d, addr);
		if (pud_none(*pud)) {
			WARN_ON_ONCE(addr & ~PUD_MASK);
			addr = round_up(addr + 1, PUD_SIZE);
			continue;
		}

		pmd = pmd_offset(pud, addr);
		if (pmd_none(*pmd)) {
			WARN_ON_ONCE(addr & ~PMD_MASK);
			addr = round_up(addr + 1, PMD_SIZE);
			continue;
		}

		if (pmd_large(*pmd) || level == PTI_CLONE_PMD) {
			target_pmd = pti_user_pagetable_walk_pmd(addr);
			if (WARN_ON(!target_pmd))
				return;

			/*
			 * Only clone present PMDs.  This ensures only setting
			 * _PAGE_GLOBAL on present PMDs.  This should only be
			 * called on well-known addresses anyway, so a non-
			 * present PMD would be a surprise.
			 */
			if (WARN_ON(!(pmd_flags(*pmd) & _PAGE_PRESENT)))
				return;

			/*
			 * Setting 'target_pmd' below creates a mapping in both
			 * the user and kernel page tables.  It is effectively
			 * global, so set it as global in both copies.  Note:
			 * the X86_FEATURE_PGE check is not _required_ because
			 * the CPU ignores _PAGE_GLOBAL when PGE is not
			 * supported.  The check keeps consistentency with
			 * code that only set this bit when supported.
			 */
			if (boot_cpu_has(X86_FEATURE_PGE))
				*pmd = pmd_set_flags(*pmd, _PAGE_GLOBAL);

			/*
			 * Copy the PMD.  That is, the kernelmode and usermode
			 * tables will share the last-level page tables of this
			 * address range
			 */
			*target_pmd = *pmd;

			addr += PMD_SIZE;

		} else if (level == PTI_CLONE_PTE) {

			/* Walk the page-table down to the pte level */
			pte = pte_offset_kernel(pmd, addr);
			if (pte_none(*pte)) {
				addr += PAGE_SIZE;
				continue;
			}

			/* Only clone present PTEs */
			if (WARN_ON(!(pte_flags(*pte) & _PAGE_PRESENT)))
				return;

			/* Allocate PTE in the user page-table */
			target_pte = pti_user_pagetable_walk_pte(addr);
			if (WARN_ON(!target_pte))
				return;

			/* Set GLOBAL bit in both PTEs */
			if (boot_cpu_has(X86_FEATURE_PGE))
				*pte = pte_set_flags(*pte, _PAGE_GLOBAL);

			/* Clone the PTE */
			*target_pte = *pte;

			addr += PAGE_SIZE;

		} else {
			BUG();
		}
	}
}

#ifdef CONFIG_X86_64
/*
 * Clone a single p4d (i.e. a top-level entry on 4-level systems and a
 * next-level entry on 5-level systems.
 */
static void __init pti_clone_p4d(unsigned long addr)
{
	p4d_t *kernel_p4d, *user_p4d;
	pgd_t *kernel_pgd;

	user_p4d = pti_user_pagetable_walk_p4d(addr);
	if (!user_p4d)
		return;

	kernel_pgd = pgd_offset_k(addr);
	kernel_p4d = p4d_offset(kernel_pgd, addr);
	*user_p4d = *kernel_p4d;
}

/*
 * Clone the CPU_ENTRY_AREA and associated data into the user space visible
 * page table.
 */
static void __init pti_clone_user_shared(void)
{
	unsigned int cpu;

	pti_clone_p4d(CPU_ENTRY_AREA_BASE);

	for_each_possible_cpu(cpu) {
		/*
		 * The SYSCALL64 entry code needs to be able to find the
		 * thread stack and needs one word of scratch space in which
		 * to spill a register.  All of this lives in the TSS, in
		 * the sp1 and sp2 slots.
		 *
		 * This is done for all possible CPUs during boot to ensure
		 * that it's propagated to all mms.
		 */

		unsigned long va = (unsigned long)&per_cpu(cpu_tss_rw, cpu);
		phys_addr_t pa = per_cpu_ptr_to_phys((void *)va);
		pte_t *target_pte;

		target_pte = pti_user_pagetable_walk_pte(va);
		if (WARN_ON(!target_pte))
			return;

		*target_pte = pfn_pte(pa >> PAGE_SHIFT, PAGE_KERNEL);
	}
}

#else /* CONFIG_X86_64 */

/*
 * On 32 bit PAE systems with 1GB of Kernel address space there is only
 * one pgd/p4d for the whole kernel. Cloning that would map the whole
 * address space into the user page-tables, making PTI useless. So clone
 * the page-table on the PMD level to prevent that.
 */
static void __init pti_clone_user_shared(void)
{
	unsigned long start, end;

	start = CPU_ENTRY_AREA_BASE;
	end   = start + (PAGE_SIZE * CPU_ENTRY_AREA_PAGES);

	pti_clone_pgtable(start, end, PTI_CLONE_PMD);
}
#endif /* CONFIG_X86_64 */

/*
 * Clone the ESPFIX P4D into the user space visible page table
 */
static void __init pti_setup_espfix64(void)
{
#ifdef CONFIG_X86_ESPFIX64
	pti_clone_p4d(ESPFIX_BASE_ADDR);
#endif
}

/*
 * Clone the populated PMDs of the entry and irqentry text and force it RO.
 */
static void pti_clone_entry_text(void)
{
	pti_clone_pgtable((unsigned long) __entry_text_start,
			  (unsigned long) __irqentry_text_end,
			  PTI_CLONE_PMD);
}

/*
 * Global pages and PCIDs are both ways to make kernel TLB entries
 * live longer, reduce TLB misses and improve kernel performance.
 * But, leaving all kernel text Global makes it potentially accessible
 * to Meltdown-style attacks which make it trivial to find gadgets or
 * defeat KASLR.
 *
 * Only use global pages when it is really worth it.
 */
static inline bool pti_kernel_image_global_ok(void)
{
	/*
	 * Systems with PCIDs get litlle benefit from global
	 * kernel text and are not worth the downsides.
	 */
	if (cpu_feature_enabled(X86_FEATURE_PCID))
		return false;

	/*
	 * Only do global kernel image for pti=auto.  Do the most
	 * secure thing (not global) if pti=on specified.
	 */
	if (pti_mode != PTI_AUTO)
		return false;

	/*
	 * K8 may not tolerate the cleared _PAGE_RW on the userspace
	 * global kernel image pages.  Do the safe thing (disable
	 * global kernel image).  This is unlikely to ever be
	 * noticed because PTI is disabled by default on AMD CPUs.
	 */
	if (boot_cpu_has(X86_FEATURE_K8))
		return false;

	/*
	 * RANDSTRUCT derives its hardening benefits from the
	 * attacker's lack of knowledge about the layout of kernel
	 * data structures.  Keep the kernel image non-global in
	 * cases where RANDSTRUCT is in use to help keep the layout a
	 * secret.
	 */
	if (IS_ENABLED(CONFIG_GCC_PLUGIN_RANDSTRUCT))
		return false;

	return true;
}

/*
 * For some configurations, map all of kernel text into the user page
 * tables.  This reduces TLB misses, especially on non-PCID systems.
 */
static void pti_clone_kernel_text(void)
{
	/*
	 * rodata is part of the kernel image and is normally
	 * readable on the filesystem or on the web.  But, do not
	 * clone the areas past rodata, they might contain secrets.
	 */
	unsigned long start = PFN_ALIGN(_text);
	unsigned long end_clone  = (unsigned long)__end_rodata_aligned;
	unsigned long end_global = PFN_ALIGN((unsigned long)_etext);

	if (!pti_kernel_image_global_ok())
		return;

	pr_debug("mapping partial kernel image into user address space\n");

	/*
	 * Note that this will undo _some_ of the work that
	 * pti_set_kernel_image_nonglobal() did to clear the
	 * global bit.
	 */
	pti_clone_pgtable(start, end_clone, PTI_LEVEL_KERNEL_IMAGE);

	/*
	 * pti_clone_pgtable() will set the global bit in any PMDs
	 * that it clones, but we also need to get any PTEs in
	 * the last level for areas that are not huge-page-aligned.
	 */

	/* Set the global bit for normal non-__init kernel text: */
	set_memory_global(start, (end_global - start) >> PAGE_SHIFT);
}

static void pti_set_kernel_image_nonglobal(void)
{
	/*
	 * The identity map is created with PMDs, regardless of the
	 * actual length of the kernel.  We need to clear
	 * _PAGE_GLOBAL up to a PMD boundary, not just to the end
	 * of the image.
	 */
	unsigned long start = PFN_ALIGN(_text);
	unsigned long end = ALIGN((unsigned long)_end, PMD_PAGE_SIZE);

	/*
	 * This clears _PAGE_GLOBAL from the entire kernel image.
	 * pti_clone_kernel_text() map put _PAGE_GLOBAL back for
	 * areas that are mapped to userspace.
	 */
	set_memory_nonglobal(start, (end - start) >> PAGE_SHIFT);
}

/*
 * Initialize kernel page table isolation
 */
void __init pti_init(void)
{
	if (!boot_cpu_has(X86_FEATURE_PTI))
		return;

	pr_info("enabled\n");

#ifdef CONFIG_X86_32
	/*
	 * We check for X86_FEATURE_PCID here. But the init-code will
	 * clear the feature flag on 32 bit because the feature is not
	 * supported on 32 bit anyway. To print the warning we need to
	 * check with cpuid directly again.
	 */
	if (cpuid_ecx(0x1) & BIT(17)) {
		/* Use printk to work around pr_fmt() */
		printk(KERN_WARNING "\n");
		printk(KERN_WARNING "************************************************************\n");
		printk(KERN_WARNING "** WARNING! WARNING! WARNING! WARNING! WARNING! WARNING!  **\n");
		printk(KERN_WARNING "**                                                        **\n");
		printk(KERN_WARNING "** You are using 32-bit PTI on a 64-bit PCID-capable CPU. **\n");
		printk(KERN_WARNING "** Your performance will increase dramatically if you     **\n");
		printk(KERN_WARNING "** switch to a 64-bit kernel!                             **\n");
		printk(KERN_WARNING "**                                                        **\n");
		printk(KERN_WARNING "** WARNING! WARNING! WARNING! WARNING! WARNING! WARNING!  **\n");
		printk(KERN_WARNING "************************************************************\n");
	}
#endif

	pti_clone_user_shared();

	/* Undo all global bits from the init pagetables in head_64.S: */
	pti_set_kernel_image_nonglobal();
	/* Replace some of the global bits just for shared entry text: */
	pti_clone_entry_text();
	pti_setup_espfix64();
	pti_setup_vsyscall();
}

/*
 * Finalize the kernel mappings in the userspace page-table. Some of the
 * mappings for the kernel image might have changed since pti_init()
 * cloned them. This is because parts of the kernel image have been
 * mapped RO and/or NX.  These changes need to be cloned again to the
 * userspace page-table.
 */
void pti_finalize(void)
{
	if (!boot_cpu_has(X86_FEATURE_PTI))
		return;
	/*
	 * We need to clone everything (again) that maps parts of the
	 * kernel image.
	 */
	pti_clone_entry_text();
	pti_clone_kernel_text();

	debug_checkwx_user();
}