summaryrefslogtreecommitdiffstats
path: root/arch/x86/boot/compressed/kaslr.c
blob: 0048269180d58ab1ca597df5ada2a7fcd66c8c9e (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
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
// SPDX-License-Identifier: GPL-2.0
/*
 * kaslr.c
 *
 * This contains the routines needed to generate a reasonable level of
 * entropy to choose a randomized kernel base address offset in support
 * of Kernel Address Space Layout Randomization (KASLR). Additionally
 * handles walking the physical memory maps (and tracking memory regions
 * to avoid) in order to select a physical memory location that can
 * contain the entire properly aligned running kernel image.
 *
 */

/*
 * isspace() in linux/ctype.h is expected by next_args() to filter
 * out "space/lf/tab". While boot/ctype.h conflicts with linux/ctype.h,
 * since isdigit() is implemented in both of them. Hence disable it
 * here.
 */
#define BOOT_CTYPE_H

#include "misc.h"
#include "error.h"
#include "../string.h"

#include <generated/compile.h>
#include <linux/module.h>
#include <linux/uts.h>
#include <linux/utsname.h>
#include <linux/ctype.h>
#include <linux/efi.h>
#include <generated/utsrelease.h>
#include <asm/efi.h>

/* Macros used by the included decompressor code below. */
#define STATIC
#include <linux/decompress/mm.h>

#ifdef CONFIG_X86_5LEVEL
unsigned int __pgtable_l5_enabled;
unsigned int pgdir_shift __ro_after_init = 39;
unsigned int ptrs_per_p4d __ro_after_init = 1;
#endif

extern unsigned long get_cmd_line_ptr(void);

/* Used by PAGE_KERN* macros: */
pteval_t __default_kernel_pte_mask __read_mostly = ~0;

/* Simplified build-specific string for starting entropy. */
static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
		LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;

static unsigned long rotate_xor(unsigned long hash, const void *area,
				size_t size)
{
	size_t i;
	unsigned long *ptr = (unsigned long *)area;

	for (i = 0; i < size / sizeof(hash); i++) {
		/* Rotate by odd number of bits and XOR. */
		hash = (hash << ((sizeof(hash) * 8) - 7)) | (hash >> 7);
		hash ^= ptr[i];
	}

	return hash;
}

/* Attempt to create a simple but unpredictable starting entropy. */
static unsigned long get_boot_seed(void)
{
	unsigned long hash = 0;

	hash = rotate_xor(hash, build_str, sizeof(build_str));
	hash = rotate_xor(hash, boot_params, sizeof(*boot_params));

	return hash;
}

#define KASLR_COMPRESSED_BOOT
#include "../../lib/kaslr.c"


/* Only supporting at most 4 unusable memmap regions with kaslr */
#define MAX_MEMMAP_REGIONS	4

static bool memmap_too_large;


/* Store memory limit specified by "mem=nn[KMG]" or "memmap=nn[KMG]" */
static unsigned long long mem_limit = ULLONG_MAX;

/* Number of immovable memory regions */
static int num_immovable_mem;

enum mem_avoid_index {
	MEM_AVOID_ZO_RANGE = 0,
	MEM_AVOID_INITRD,
	MEM_AVOID_CMDLINE,
	MEM_AVOID_BOOTPARAMS,
	MEM_AVOID_MEMMAP_BEGIN,
	MEM_AVOID_MEMMAP_END = MEM_AVOID_MEMMAP_BEGIN + MAX_MEMMAP_REGIONS - 1,
	MEM_AVOID_MAX,
};

static struct mem_vector mem_avoid[MEM_AVOID_MAX];

static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
{
	/* Item one is entirely before item two. */
	if (one->start + one->size <= two->start)
		return false;
	/* Item one is entirely after item two. */
	if (one->start >= two->start + two->size)
		return false;
	return true;
}

char *skip_spaces(const char *str)
{
	while (isspace(*str))
		++str;
	return (char *)str;
}
#include "../../../../lib/ctype.c"
#include "../../../../lib/cmdline.c"

enum parse_mode {
	PARSE_MEMMAP,
	PARSE_EFI,
};

static int
parse_memmap(char *p, unsigned long long *start, unsigned long long *size,
		enum parse_mode mode)
{
	char *oldp;

	if (!p)
		return -EINVAL;

	/* We don't care about this option here */
	if (!strncmp(p, "exactmap", 8))
		return -EINVAL;

	oldp = p;
	*size = memparse(p, &p);
	if (p == oldp)
		return -EINVAL;

	switch (*p) {
	case '#':
	case '$':
	case '!':
		*start = memparse(p + 1, &p);
		return 0;
	case '@':
		if (mode == PARSE_MEMMAP) {
			/*
			 * memmap=nn@ss specifies usable region, should
			 * be skipped
			 */
			*size = 0;
		} else {
			unsigned long long flags;

			/*
			 * efi_fake_mem=nn@ss:attr the attr specifies
			 * flags that might imply a soft-reservation.
			 */
			*start = memparse(p + 1, &p);
			if (p && *p == ':') {
				p++;
				if (kstrtoull(p, 0, &flags) < 0)
					*size = 0;
				else if (flags & EFI_MEMORY_SP)
					return 0;
			}
			*size = 0;
		}
		/* Fall through */
	default:
		/*
		 * If w/o offset, only size specified, memmap=nn[KMG] has the
		 * same behaviour as mem=nn[KMG]. It limits the max address
		 * system can use. Region above the limit should be avoided.
		 */
		*start = 0;
		return 0;
	}

	return -EINVAL;
}

static void mem_avoid_memmap(enum parse_mode mode, char *str)
{
	static int i;

	if (i >= MAX_MEMMAP_REGIONS)
		return;

	while (str && (i < MAX_MEMMAP_REGIONS)) {
		int rc;
		unsigned long long start, size;
		char *k = strchr(str, ',');

		if (k)
			*k++ = 0;

		rc = parse_memmap(str, &start, &size, mode);
		if (rc < 0)
			break;
		str = k;

		if (start == 0) {
			/* Store the specified memory limit if size > 0 */
			if (size > 0)
				mem_limit = size;

			continue;
		}

		mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].start = start;
		mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].size = size;
		i++;
	}

	/* More than 4 memmaps, fail kaslr */
	if ((i >= MAX_MEMMAP_REGIONS) && str)
		memmap_too_large = true;
}

/* Store the number of 1GB huge pages which users specified: */
static unsigned long max_gb_huge_pages;

static void parse_gb_huge_pages(char *param, char *val)
{
	static bool gbpage_sz;
	char *p;

	if (!strcmp(param, "hugepagesz")) {
		p = val;
		if (memparse(p, &p) != PUD_SIZE) {
			gbpage_sz = false;
			return;
		}

		if (gbpage_sz)
			warn("Repeatedly set hugeTLB page size of 1G!\n");
		gbpage_sz = true;
		return;
	}

	if (!strcmp(param, "hugepages") && gbpage_sz) {
		p = val;
		max_gb_huge_pages = simple_strtoull(p, &p, 0);
		return;
	}
}

static void handle_mem_options(void)
{
	char *args = (char *)get_cmd_line_ptr();
	size_t len = strlen((char *)args);
	char *tmp_cmdline;
	char *param, *val;
	u64 mem_size;

	if (!strstr(args, "memmap=") && !strstr(args, "mem=") &&
		!strstr(args, "hugepages"))
		return;

	tmp_cmdline = malloc(len + 1);
	if (!tmp_cmdline)
		error("Failed to allocate space for tmp_cmdline");

	memcpy(tmp_cmdline, args, len);
	tmp_cmdline[len] = 0;
	args = tmp_cmdline;

	/* Chew leading spaces */
	args = skip_spaces(args);

	while (*args) {
		args = next_arg(args, &param, &val);
		/* Stop at -- */
		if (!val && strcmp(param, "--") == 0) {
			warn("Only '--' specified in cmdline");
			goto out;
		}

		if (!strcmp(param, "memmap")) {
			mem_avoid_memmap(PARSE_MEMMAP, val);
		} else if (strstr(param, "hugepages")) {
			parse_gb_huge_pages(param, val);
		} else if (!strcmp(param, "mem")) {
			char *p = val;

			if (!strcmp(p, "nopentium"))
				continue;
			mem_size = memparse(p, &p);
			if (mem_size == 0)
				goto out;

			mem_limit = mem_size;
		} else if (!strcmp(param, "efi_fake_mem")) {
			mem_avoid_memmap(PARSE_EFI, val);
		}
	}

out:
	free(tmp_cmdline);
	return;
}

/*
 * In theory, KASLR can put the kernel anywhere in the range of [16M, 64T).
 * The mem_avoid array is used to store the ranges that need to be avoided
 * when KASLR searches for an appropriate random address. We must avoid any
 * regions that are unsafe to overlap with during decompression, and other
 * things like the initrd, cmdline and boot_params. This comment seeks to
 * explain mem_avoid as clearly as possible since incorrect mem_avoid
 * memory ranges lead to really hard to debug boot failures.
 *
 * The initrd, cmdline, and boot_params are trivial to identify for
 * avoiding. They are MEM_AVOID_INITRD, MEM_AVOID_CMDLINE, and
 * MEM_AVOID_BOOTPARAMS respectively below.
 *
 * What is not obvious how to avoid is the range of memory that is used
 * during decompression (MEM_AVOID_ZO_RANGE below). This range must cover
 * the compressed kernel (ZO) and its run space, which is used to extract
 * the uncompressed kernel (VO) and relocs.
 *
 * ZO's full run size sits against the end of the decompression buffer, so
 * we can calculate where text, data, bss, etc of ZO are positioned more
 * easily.
 *
 * For additional background, the decompression calculations can be found
 * in header.S, and the memory diagram is based on the one found in misc.c.
 *
 * The following conditions are already enforced by the image layouts and
 * associated code:
 *  - input + input_size >= output + output_size
 *  - kernel_total_size <= init_size
 *  - kernel_total_size <= output_size (see Note below)
 *  - output + init_size >= output + output_size
 *
 * (Note that kernel_total_size and output_size have no fundamental
 * relationship, but output_size is passed to choose_random_location
 * as a maximum of the two. The diagram is showing a case where
 * kernel_total_size is larger than output_size, but this case is
 * handled by bumping output_size.)
 *
 * The above conditions can be illustrated by a diagram:
 *
 * 0   output            input            input+input_size    output+init_size
 * |     |                 |                             |             |
 * |     |                 |                             |             |
 * |-----|--------|--------|--------------|-----------|--|-------------|
 *                |                       |           |
 *                |                       |           |
 * output+init_size-ZO_INIT_SIZE  output+output_size  output+kernel_total_size
 *
 * [output, output+init_size) is the entire memory range used for
 * extracting the compressed image.
 *
 * [output, output+kernel_total_size) is the range needed for the
 * uncompressed kernel (VO) and its run size (bss, brk, etc).
 *
 * [output, output+output_size) is VO plus relocs (i.e. the entire
 * uncompressed payload contained by ZO). This is the area of the buffer
 * written to during decompression.
 *
 * [output+init_size-ZO_INIT_SIZE, output+init_size) is the worst-case
 * range of the copied ZO and decompression code. (i.e. the range
 * covered backwards of size ZO_INIT_SIZE, starting from output+init_size.)
 *
 * [input, input+input_size) is the original copied compressed image (ZO)
 * (i.e. it does not include its run size). This range must be avoided
 * because it contains the data used for decompression.
 *
 * [input+input_size, output+init_size) is [_text, _end) for ZO. This
 * range includes ZO's heap and stack, and must be avoided since it
 * performs the decompression.
 *
 * Since the above two ranges need to be avoided and they are adjacent,
 * they can be merged, resulting in: [input, output+init_size) which
 * becomes the MEM_AVOID_ZO_RANGE below.
 */
static void mem_avoid_init(unsigned long input, unsigned long input_size,
			   unsigned long output)
{
	unsigned long init_size = boot_params->hdr.init_size;
	u64 initrd_start, initrd_size;
	u64 cmd_line, cmd_line_size;
	char *ptr;

	/*
	 * Avoid the region that is unsafe to overlap during
	 * decompression.
	 */
	mem_avoid[MEM_AVOID_ZO_RANGE].start = input;
	mem_avoid[MEM_AVOID_ZO_RANGE].size = (output + init_size) - input;
	add_identity_map(mem_avoid[MEM_AVOID_ZO_RANGE].start,
			 mem_avoid[MEM_AVOID_ZO_RANGE].size);

	/* Avoid initrd. */
	initrd_start  = (u64)boot_params->ext_ramdisk_image << 32;
	initrd_start |= boot_params->hdr.ramdisk_image;
	initrd_size  = (u64)boot_params->ext_ramdisk_size << 32;
	initrd_size |= boot_params->hdr.ramdisk_size;
	mem_avoid[MEM_AVOID_INITRD].start = initrd_start;
	mem_avoid[MEM_AVOID_INITRD].size = initrd_size;
	/* No need to set mapping for initrd, it will be handled in VO. */

	/* Avoid kernel command line. */
	cmd_line  = (u64)boot_params->ext_cmd_line_ptr << 32;
	cmd_line |= boot_params->hdr.cmd_line_ptr;
	/* Calculate size of cmd_line. */
	ptr = (char *)(unsigned long)cmd_line;
	for (cmd_line_size = 0; ptr[cmd_line_size++];)
		;
	mem_avoid[MEM_AVOID_CMDLINE].start = cmd_line;
	mem_avoid[MEM_AVOID_CMDLINE].size = cmd_line_size;
	add_identity_map(mem_avoid[MEM_AVOID_CMDLINE].start,
			 mem_avoid[MEM_AVOID_CMDLINE].size);

	/* Avoid boot parameters. */
	mem_avoid[MEM_AVOID_BOOTPARAMS].start = (unsigned long)boot_params;
	mem_avoid[MEM_AVOID_BOOTPARAMS].size = sizeof(*boot_params);
	add_identity_map(mem_avoid[MEM_AVOID_BOOTPARAMS].start,
			 mem_avoid[MEM_AVOID_BOOTPARAMS].size);

	/* We don't need to set a mapping for setup_data. */

	/* Mark the memmap regions we need to avoid */
	handle_mem_options();

	/* Enumerate the immovable memory regions */
	num_immovable_mem = count_immovable_mem_regions();

#ifdef CONFIG_X86_VERBOSE_BOOTUP
	/* Make sure video RAM can be used. */
	add_identity_map(0, PMD_SIZE);
#endif
}

/*
 * Does this memory vector overlap a known avoided area? If so, record the
 * overlap region with the lowest address.
 */
static bool mem_avoid_overlap(struct mem_vector *img,
			      struct mem_vector *overlap)
{
	int i;
	struct setup_data *ptr;
	unsigned long earliest = img->start + img->size;
	bool is_overlapping = false;

	for (i = 0; i < MEM_AVOID_MAX; i++) {
		if (mem_overlaps(img, &mem_avoid[i]) &&
		    mem_avoid[i].start < earliest) {
			*overlap = mem_avoid[i];
			earliest = overlap->start;
			is_overlapping = true;
		}
	}

	/* Avoid all entries in the setup_data linked list. */
	ptr = (struct setup_data *)(unsigned long)boot_params->hdr.setup_data;
	while (ptr) {
		struct mem_vector avoid;

		avoid.start = (unsigned long)ptr;
		avoid.size = sizeof(*ptr) + ptr->len;

		if (mem_overlaps(img, &avoid) && (avoid.start < earliest)) {
			*overlap = avoid;
			earliest = overlap->start;
			is_overlapping = true;
		}

		if (ptr->type == SETUP_INDIRECT &&
		    ((struct setup_indirect *)ptr->data)->type != SETUP_INDIRECT) {
			avoid.start = ((struct setup_indirect *)ptr->data)->addr;
			avoid.size = ((struct setup_indirect *)ptr->data)->len;

			if (mem_overlaps(img, &avoid) && (avoid.start < earliest)) {
				*overlap = avoid;
				earliest = overlap->start;
				is_overlapping = true;
			}
		}

		ptr = (struct setup_data *)(unsigned long)ptr->next;
	}

	return is_overlapping;
}

struct slot_area {
	unsigned long addr;
	int num;
};

#define MAX_SLOT_AREA 100

static struct slot_area slot_areas[MAX_SLOT_AREA];

static unsigned long slot_max;

static unsigned long slot_area_index;

static void store_slot_info(struct mem_vector *region, unsigned long image_size)
{
	struct slot_area slot_area;

	if (slot_area_index == MAX_SLOT_AREA)
		return;

	slot_area.addr = region->start;
	slot_area.num = (region->size - image_size) /
			CONFIG_PHYSICAL_ALIGN + 1;

	if (slot_area.num > 0) {
		slot_areas[slot_area_index++] = slot_area;
		slot_max += slot_area.num;
	}
}

/*
 * Skip as many 1GB huge pages as possible in the passed region
 * according to the number which users specified:
 */
static void
process_gb_huge_pages(struct mem_vector *region, unsigned long image_size)
{
	unsigned long addr, size = 0;
	struct mem_vector tmp;
	int i = 0;

	if (!max_gb_huge_pages) {
		store_slot_info(region, image_size);
		return;
	}

	addr = ALIGN(region->start, PUD_SIZE);
	/* Did we raise the address above the passed in memory entry? */
	if (addr < region->start + region->size)
		size = region->size - (addr - region->start);

	/* Check how many 1GB huge pages can be filtered out: */
	while (size > PUD_SIZE && max_gb_huge_pages) {
		size -= PUD_SIZE;
		max_gb_huge_pages--;
		i++;
	}

	/* No good 1GB huge pages found: */
	if (!i) {
		store_slot_info(region, image_size);
		return;
	}

	/*
	 * Skip those 'i'*1GB good huge pages, and continue checking and
	 * processing the remaining head or tail part of the passed region
	 * if available.
	 */

	if (addr >= region->start + image_size) {
		tmp.start = region->start;
		tmp.size = addr - region->start;
		store_slot_info(&tmp, image_size);
	}

	size  = region->size - (addr - region->start) - i * PUD_SIZE;
	if (size >= image_size) {
		tmp.start = addr + i * PUD_SIZE;
		tmp.size = size;
		store_slot_info(&tmp, image_size);
	}
}

static unsigned long slots_fetch_random(void)
{
	unsigned long slot;
	int i;

	/* Handle case of no slots stored. */
	if (slot_max == 0)
		return 0;

	slot = kaslr_get_random_long("Physical") % slot_max;

	for (i = 0; i < slot_area_index; i++) {
		if (slot >= slot_areas[i].num) {
			slot -= slot_areas[i].num;
			continue;
		}
		return slot_areas[i].addr + slot * CONFIG_PHYSICAL_ALIGN;
	}

	if (i == slot_area_index)
		debug_putstr("slots_fetch_random() failed!?\n");
	return 0;
}

static void __process_mem_region(struct mem_vector *entry,
				 unsigned long minimum,
				 unsigned long image_size)
{
	struct mem_vector region, overlap;
	unsigned long start_orig, end;
	struct mem_vector cur_entry;

	/* On 32-bit, ignore entries entirely above our maximum. */
	if (IS_ENABLED(CONFIG_X86_32) && entry->start >= KERNEL_IMAGE_SIZE)
		return;

	/* Ignore entries entirely below our minimum. */
	if (entry->start + entry->size < minimum)
		return;

	/* Ignore entries above memory limit */
	end = min(entry->size + entry->start, mem_limit);
	if (entry->start >= end)
		return;
	cur_entry.start = entry->start;
	cur_entry.size = end - entry->start;

	region.start = cur_entry.start;
	region.size = cur_entry.size;

	/* Give up if slot area array is full. */
	while (slot_area_index < MAX_SLOT_AREA) {
		start_orig = region.start;

		/* Potentially raise address to minimum location. */
		if (region.start < minimum)
			region.start = minimum;

		/* Potentially raise address to meet alignment needs. */
		region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);

		/* Did we raise the address above the passed in memory entry? */
		if (region.start > cur_entry.start + cur_entry.size)
			return;

		/* Reduce size by any delta from the original address. */
		region.size -= region.start - start_orig;

		/* On 32-bit, reduce region size to fit within max size. */
		if (IS_ENABLED(CONFIG_X86_32) &&
		    region.start + region.size > KERNEL_IMAGE_SIZE)
			region.size = KERNEL_IMAGE_SIZE - region.start;

		/* Return if region can't contain decompressed kernel */
		if (region.size < image_size)
			return;

		/* If nothing overlaps, store the region and return. */
		if (!mem_avoid_overlap(&region, &overlap)) {
			process_gb_huge_pages(&region, image_size);
			return;
		}

		/* Store beginning of region if holds at least image_size. */
		if (overlap.start > region.start + image_size) {
			struct mem_vector beginning;

			beginning.start = region.start;
			beginning.size = overlap.start - region.start;
			process_gb_huge_pages(&beginning, image_size);
		}

		/* Return if overlap extends to or past end of region. */
		if (overlap.start + overlap.size >= region.start + region.size)
			return;

		/* Clip off the overlapping region and start over. */
		region.size -= overlap.start - region.start + overlap.size;
		region.start = overlap.start + overlap.size;
	}
}

static bool process_mem_region(struct mem_vector *region,
			       unsigned long long minimum,
			       unsigned long long image_size)
{
	int i;
	/*
	 * If no immovable memory found, or MEMORY_HOTREMOVE disabled,
	 * use @region directly.
	 */
	if (!num_immovable_mem) {
		__process_mem_region(region, minimum, image_size);

		if (slot_area_index == MAX_SLOT_AREA) {
			debug_putstr("Aborted e820/efi memmap scan (slot_areas full)!\n");
			return 1;
		}
		return 0;
	}

#if defined(CONFIG_MEMORY_HOTREMOVE) && defined(CONFIG_ACPI)
	/*
	 * If immovable memory found, filter the intersection between
	 * immovable memory and @region.
	 */
	for (i = 0; i < num_immovable_mem; i++) {
		unsigned long long start, end, entry_end, region_end;
		struct mem_vector entry;

		if (!mem_overlaps(region, &immovable_mem[i]))
			continue;

		start = immovable_mem[i].start;
		end = start + immovable_mem[i].size;
		region_end = region->start + region->size;

		entry.start = clamp(region->start, start, end);
		entry_end = clamp(region_end, start, end);
		entry.size = entry_end - entry.start;

		__process_mem_region(&entry, minimum, image_size);

		if (slot_area_index == MAX_SLOT_AREA) {
			debug_putstr("Aborted e820/efi memmap scan when walking immovable regions(slot_areas full)!\n");
			return 1;
		}
	}
#endif
	return 0;
}

#ifdef CONFIG_EFI
/*
 * Returns true if mirror region found (and must have been processed
 * for slots adding)
 */
static bool
process_efi_entries(unsigned long minimum, unsigned long image_size)
{
	struct efi_info *e = &boot_params->efi_info;
	bool efi_mirror_found = false;
	struct mem_vector region;
	efi_memory_desc_t *md;
	unsigned long pmap;
	char *signature;
	u32 nr_desc;
	int i;

	signature = (char *)&e->efi_loader_signature;
	if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
	    strncmp(signature, EFI64_LOADER_SIGNATURE, 4))
		return false;

#ifdef CONFIG_X86_32
	/* Can't handle data above 4GB at this time */
	if (e->efi_memmap_hi) {
		warn("EFI memmap is above 4GB, can't be handled now on x86_32. EFI should be disabled.\n");
		return false;
	}
	pmap =  e->efi_memmap;
#else
	pmap = (e->efi_memmap | ((__u64)e->efi_memmap_hi << 32));
#endif

	nr_desc = e->efi_memmap_size / e->efi_memdesc_size;
	for (i = 0; i < nr_desc; i++) {
		md = efi_early_memdesc_ptr(pmap, e->efi_memdesc_size, i);
		if (md->attribute & EFI_MEMORY_MORE_RELIABLE) {
			efi_mirror_found = true;
			break;
		}
	}

	for (i = 0; i < nr_desc; i++) {
		md = efi_early_memdesc_ptr(pmap, e->efi_memdesc_size, i);

		/*
		 * Here we are more conservative in picking free memory than
		 * the EFI spec allows:
		 *
		 * According to the spec, EFI_BOOT_SERVICES_{CODE|DATA} are also
		 * free memory and thus available to place the kernel image into,
		 * but in practice there's firmware where using that memory leads
		 * to crashes.
		 *
		 * Only EFI_CONVENTIONAL_MEMORY is guaranteed to be free.
		 */
		if (md->type != EFI_CONVENTIONAL_MEMORY)
			continue;

		if (efi_soft_reserve_enabled() &&
		    (md->attribute & EFI_MEMORY_SP))
			continue;

		if (efi_mirror_found &&
		    !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
			continue;

		region.start = md->phys_addr;
		region.size = md->num_pages << EFI_PAGE_SHIFT;
		if (process_mem_region(&region, minimum, image_size))
			break;
	}
	return true;
}
#else
static inline bool
process_efi_entries(unsigned long minimum, unsigned long image_size)
{
	return false;
}
#endif

static void process_e820_entries(unsigned long minimum,
				 unsigned long image_size)
{
	int i;
	struct mem_vector region;
	struct boot_e820_entry *entry;

	/* Verify potential e820 positions, appending to slots list. */
	for (i = 0; i < boot_params->e820_entries; i++) {
		entry = &boot_params->e820_table[i];
		/* Skip non-RAM entries. */
		if (entry->type != E820_TYPE_RAM)
			continue;
		region.start = entry->addr;
		region.size = entry->size;
		if (process_mem_region(&region, minimum, image_size))
			break;
	}
}

static unsigned long find_random_phys_addr(unsigned long minimum,
					   unsigned long image_size)
{
	/* Check if we had too many memmaps. */
	if (memmap_too_large) {
		debug_putstr("Aborted memory entries scan (more than 4 memmap= args)!\n");
		return 0;
	}

	/* Make sure minimum is aligned. */
	minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);

	if (process_efi_entries(minimum, image_size))
		return slots_fetch_random();

	process_e820_entries(minimum, image_size);
	return slots_fetch_random();
}

static unsigned long find_random_virt_addr(unsigned long minimum,
					   unsigned long image_size)
{
	unsigned long slots, random_addr;

	/* Make sure minimum is aligned. */
	minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
	/* Align image_size for easy slot calculations. */
	image_size = ALIGN(image_size, CONFIG_PHYSICAL_ALIGN);

	/*
	 * There are how many CONFIG_PHYSICAL_ALIGN-sized slots
	 * that can hold image_size within the range of minimum to
	 * KERNEL_IMAGE_SIZE?
	 */
	slots = (KERNEL_IMAGE_SIZE - minimum - image_size) /
		 CONFIG_PHYSICAL_ALIGN + 1;

	random_addr = kaslr_get_random_long("Virtual") % slots;

	return random_addr * CONFIG_PHYSICAL_ALIGN + minimum;
}

/*
 * Since this function examines addresses much more numerically,
 * it takes the input and output pointers as 'unsigned long'.
 */
void choose_random_location(unsigned long input,
			    unsigned long input_size,
			    unsigned long *output,
			    unsigned long output_size,
			    unsigned long *virt_addr)
{
	unsigned long random_addr, min_addr;

	if (cmdline_find_option_bool("nokaslr")) {
		warn("KASLR disabled: 'nokaslr' on cmdline.");
		return;
	}

#ifdef CONFIG_X86_5LEVEL
	if (__read_cr4() & X86_CR4_LA57) {
		__pgtable_l5_enabled = 1;
		pgdir_shift = 48;
		ptrs_per_p4d = 512;
	}
#endif

	boot_params->hdr.loadflags |= KASLR_FLAG;

	/* Prepare to add new identity pagetables on demand. */
	initialize_identity_maps();

	/* Record the various known unsafe memory ranges. */
	mem_avoid_init(input, input_size, *output);

	/*
	 * Low end of the randomization range should be the
	 * smaller of 512M or the initial kernel image
	 * location:
	 */
	min_addr = min(*output, 512UL << 20);

	/* Walk available memory entries to find a random address. */
	random_addr = find_random_phys_addr(min_addr, output_size);
	if (!random_addr) {
		warn("Physical KASLR disabled: no suitable memory region!");
	} else {
		/* Update the new physical address location. */
		if (*output != random_addr) {
			add_identity_map(random_addr, output_size);
			*output = random_addr;
		}

		/*
		 * This loads the identity mapping page table.
		 * This should only be done if a new physical address
		 * is found for the kernel, otherwise we should keep
		 * the old page table to make it be like the "nokaslr"
		 * case.
		 */
		finalize_identity_maps();
	}


	/* Pick random virtual address starting from LOAD_PHYSICAL_ADDR. */
	if (IS_ENABLED(CONFIG_X86_64))
		random_addr = find_random_virt_addr(LOAD_PHYSICAL_ADDR, output_size);
	*virt_addr = random_addr;
}