xref: /linux/arch/x86/boot/compressed/kaslr.c (revision c6ed444fd6fffaaf2e3857d926ed18bf3df81e8e)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * kaslr.c
4  *
5  * This contains the routines needed to generate a reasonable level of
6  * entropy to choose a randomized kernel base address offset in support
7  * of Kernel Address Space Layout Randomization (KASLR). Additionally
8  * handles walking the physical memory maps (and tracking memory regions
9  * to avoid) in order to select a physical memory location that can
10  * contain the entire properly aligned running kernel image.
11  *
12  */
13 
14 /*
15  * isspace() in linux/ctype.h is expected by next_args() to filter
16  * out "space/lf/tab". While boot/ctype.h conflicts with linux/ctype.h,
17  * since isdigit() is implemented in both of them. Hence disable it
18  * here.
19  */
20 #define BOOT_CTYPE_H
21 
22 /*
23  * _ctype[] in lib/ctype.c is needed by isspace() of linux/ctype.h.
24  * While both lib/ctype.c and lib/cmdline.c will bring EXPORT_SYMBOL
25  * which is meaningless and will cause compiling error in some cases.
26  * So do not include linux/export.h and define EXPORT_SYMBOL(sym)
27  * as empty.
28  */
29 #define _LINUX_EXPORT_H
30 #define EXPORT_SYMBOL(sym)
31 
32 #include "misc.h"
33 #include "error.h"
34 #include "../string.h"
35 
36 #include <generated/compile.h>
37 #include <linux/module.h>
38 #include <linux/uts.h>
39 #include <linux/utsname.h>
40 #include <linux/ctype.h>
41 #include <linux/efi.h>
42 #include <generated/utsrelease.h>
43 #include <asm/efi.h>
44 
45 /* Macros used by the included decompressor code below. */
46 #define STATIC
47 #include <linux/decompress/mm.h>
48 
49 #ifdef CONFIG_X86_5LEVEL
50 unsigned int __pgtable_l5_enabled;
51 unsigned int pgdir_shift __ro_after_init = 39;
52 unsigned int ptrs_per_p4d __ro_after_init = 1;
53 #endif
54 
55 extern unsigned long get_cmd_line_ptr(void);
56 
57 /* Used by PAGE_KERN* macros: */
58 pteval_t __default_kernel_pte_mask __read_mostly = ~0;
59 
60 /* Simplified build-specific string for starting entropy. */
61 static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
62 		LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
63 
64 static unsigned long rotate_xor(unsigned long hash, const void *area,
65 				size_t size)
66 {
67 	size_t i;
68 	unsigned long *ptr = (unsigned long *)area;
69 
70 	for (i = 0; i < size / sizeof(hash); i++) {
71 		/* Rotate by odd number of bits and XOR. */
72 		hash = (hash << ((sizeof(hash) * 8) - 7)) | (hash >> 7);
73 		hash ^= ptr[i];
74 	}
75 
76 	return hash;
77 }
78 
79 /* Attempt to create a simple but unpredictable starting entropy. */
80 static unsigned long get_boot_seed(void)
81 {
82 	unsigned long hash = 0;
83 
84 	hash = rotate_xor(hash, build_str, sizeof(build_str));
85 	hash = rotate_xor(hash, boot_params, sizeof(*boot_params));
86 
87 	return hash;
88 }
89 
90 #define KASLR_COMPRESSED_BOOT
91 #include "../../lib/kaslr.c"
92 
93 struct mem_vector {
94 	unsigned long long start;
95 	unsigned long long size;
96 };
97 
98 /* Only supporting at most 4 unusable memmap regions with kaslr */
99 #define MAX_MEMMAP_REGIONS	4
100 
101 static bool memmap_too_large;
102 
103 
104 /* Store memory limit specified by "mem=nn[KMG]" or "memmap=nn[KMG]" */
105 static unsigned long long mem_limit = ULLONG_MAX;
106 
107 
108 enum mem_avoid_index {
109 	MEM_AVOID_ZO_RANGE = 0,
110 	MEM_AVOID_INITRD,
111 	MEM_AVOID_CMDLINE,
112 	MEM_AVOID_BOOTPARAMS,
113 	MEM_AVOID_MEMMAP_BEGIN,
114 	MEM_AVOID_MEMMAP_END = MEM_AVOID_MEMMAP_BEGIN + MAX_MEMMAP_REGIONS - 1,
115 	MEM_AVOID_MAX,
116 };
117 
118 static struct mem_vector mem_avoid[MEM_AVOID_MAX];
119 
120 static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
121 {
122 	/* Item one is entirely before item two. */
123 	if (one->start + one->size <= two->start)
124 		return false;
125 	/* Item one is entirely after item two. */
126 	if (one->start >= two->start + two->size)
127 		return false;
128 	return true;
129 }
130 
131 char *skip_spaces(const char *str)
132 {
133 	while (isspace(*str))
134 		++str;
135 	return (char *)str;
136 }
137 #include "../../../../lib/ctype.c"
138 #include "../../../../lib/cmdline.c"
139 
140 static int
141 parse_memmap(char *p, unsigned long long *start, unsigned long long *size)
142 {
143 	char *oldp;
144 
145 	if (!p)
146 		return -EINVAL;
147 
148 	/* We don't care about this option here */
149 	if (!strncmp(p, "exactmap", 8))
150 		return -EINVAL;
151 
152 	oldp = p;
153 	*size = memparse(p, &p);
154 	if (p == oldp)
155 		return -EINVAL;
156 
157 	switch (*p) {
158 	case '#':
159 	case '$':
160 	case '!':
161 		*start = memparse(p + 1, &p);
162 		return 0;
163 	case '@':
164 		/* memmap=nn@ss specifies usable region, should be skipped */
165 		*size = 0;
166 		/* Fall through */
167 	default:
168 		/*
169 		 * If w/o offset, only size specified, memmap=nn[KMG] has the
170 		 * same behaviour as mem=nn[KMG]. It limits the max address
171 		 * system can use. Region above the limit should be avoided.
172 		 */
173 		*start = 0;
174 		return 0;
175 	}
176 
177 	return -EINVAL;
178 }
179 
180 static void mem_avoid_memmap(char *str)
181 {
182 	static int i;
183 
184 	if (i >= MAX_MEMMAP_REGIONS)
185 		return;
186 
187 	while (str && (i < MAX_MEMMAP_REGIONS)) {
188 		int rc;
189 		unsigned long long start, size;
190 		char *k = strchr(str, ',');
191 
192 		if (k)
193 			*k++ = 0;
194 
195 		rc = parse_memmap(str, &start, &size);
196 		if (rc < 0)
197 			break;
198 		str = k;
199 
200 		if (start == 0) {
201 			/* Store the specified memory limit if size > 0 */
202 			if (size > 0)
203 				mem_limit = size;
204 
205 			continue;
206 		}
207 
208 		mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].start = start;
209 		mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].size = size;
210 		i++;
211 	}
212 
213 	/* More than 4 memmaps, fail kaslr */
214 	if ((i >= MAX_MEMMAP_REGIONS) && str)
215 		memmap_too_large = true;
216 }
217 
218 /* Store the number of 1GB huge pages which users specified: */
219 static unsigned long max_gb_huge_pages;
220 
221 static void parse_gb_huge_pages(char *param, char *val)
222 {
223 	static bool gbpage_sz;
224 	char *p;
225 
226 	if (!strcmp(param, "hugepagesz")) {
227 		p = val;
228 		if (memparse(p, &p) != PUD_SIZE) {
229 			gbpage_sz = false;
230 			return;
231 		}
232 
233 		if (gbpage_sz)
234 			warn("Repeatedly set hugeTLB page size of 1G!\n");
235 		gbpage_sz = true;
236 		return;
237 	}
238 
239 	if (!strcmp(param, "hugepages") && gbpage_sz) {
240 		p = val;
241 		max_gb_huge_pages = simple_strtoull(p, &p, 0);
242 		return;
243 	}
244 }
245 
246 
247 static int handle_mem_options(void)
248 {
249 	char *args = (char *)get_cmd_line_ptr();
250 	size_t len = strlen((char *)args);
251 	char *tmp_cmdline;
252 	char *param, *val;
253 	u64 mem_size;
254 
255 	if (!strstr(args, "memmap=") && !strstr(args, "mem=") &&
256 		!strstr(args, "hugepages"))
257 		return 0;
258 
259 	tmp_cmdline = malloc(len + 1);
260 	if (!tmp_cmdline)
261 		error("Failed to allocate space for tmp_cmdline");
262 
263 	memcpy(tmp_cmdline, args, len);
264 	tmp_cmdline[len] = 0;
265 	args = tmp_cmdline;
266 
267 	/* Chew leading spaces */
268 	args = skip_spaces(args);
269 
270 	while (*args) {
271 		args = next_arg(args, &param, &val);
272 		/* Stop at -- */
273 		if (!val && strcmp(param, "--") == 0) {
274 			warn("Only '--' specified in cmdline");
275 			free(tmp_cmdline);
276 			return -1;
277 		}
278 
279 		if (!strcmp(param, "memmap")) {
280 			mem_avoid_memmap(val);
281 		} else if (strstr(param, "hugepages")) {
282 			parse_gb_huge_pages(param, val);
283 		} else if (!strcmp(param, "mem")) {
284 			char *p = val;
285 
286 			if (!strcmp(p, "nopentium"))
287 				continue;
288 			mem_size = memparse(p, &p);
289 			if (mem_size == 0) {
290 				free(tmp_cmdline);
291 				return -EINVAL;
292 			}
293 			mem_limit = mem_size;
294 		}
295 	}
296 
297 	free(tmp_cmdline);
298 	return 0;
299 }
300 
301 /*
302  * In theory, KASLR can put the kernel anywhere in the range of [16M, 64T).
303  * The mem_avoid array is used to store the ranges that need to be avoided
304  * when KASLR searches for an appropriate random address. We must avoid any
305  * regions that are unsafe to overlap with during decompression, and other
306  * things like the initrd, cmdline and boot_params. This comment seeks to
307  * explain mem_avoid as clearly as possible since incorrect mem_avoid
308  * memory ranges lead to really hard to debug boot failures.
309  *
310  * The initrd, cmdline, and boot_params are trivial to identify for
311  * avoiding. They are MEM_AVOID_INITRD, MEM_AVOID_CMDLINE, and
312  * MEM_AVOID_BOOTPARAMS respectively below.
313  *
314  * What is not obvious how to avoid is the range of memory that is used
315  * during decompression (MEM_AVOID_ZO_RANGE below). This range must cover
316  * the compressed kernel (ZO) and its run space, which is used to extract
317  * the uncompressed kernel (VO) and relocs.
318  *
319  * ZO's full run size sits against the end of the decompression buffer, so
320  * we can calculate where text, data, bss, etc of ZO are positioned more
321  * easily.
322  *
323  * For additional background, the decompression calculations can be found
324  * in header.S, and the memory diagram is based on the one found in misc.c.
325  *
326  * The following conditions are already enforced by the image layouts and
327  * associated code:
328  *  - input + input_size >= output + output_size
329  *  - kernel_total_size <= init_size
330  *  - kernel_total_size <= output_size (see Note below)
331  *  - output + init_size >= output + output_size
332  *
333  * (Note that kernel_total_size and output_size have no fundamental
334  * relationship, but output_size is passed to choose_random_location
335  * as a maximum of the two. The diagram is showing a case where
336  * kernel_total_size is larger than output_size, but this case is
337  * handled by bumping output_size.)
338  *
339  * The above conditions can be illustrated by a diagram:
340  *
341  * 0   output            input            input+input_size    output+init_size
342  * |     |                 |                             |             |
343  * |     |                 |                             |             |
344  * |-----|--------|--------|--------------|-----------|--|-------------|
345  *                |                       |           |
346  *                |                       |           |
347  * output+init_size-ZO_INIT_SIZE  output+output_size  output+kernel_total_size
348  *
349  * [output, output+init_size) is the entire memory range used for
350  * extracting the compressed image.
351  *
352  * [output, output+kernel_total_size) is the range needed for the
353  * uncompressed kernel (VO) and its run size (bss, brk, etc).
354  *
355  * [output, output+output_size) is VO plus relocs (i.e. the entire
356  * uncompressed payload contained by ZO). This is the area of the buffer
357  * written to during decompression.
358  *
359  * [output+init_size-ZO_INIT_SIZE, output+init_size) is the worst-case
360  * range of the copied ZO and decompression code. (i.e. the range
361  * covered backwards of size ZO_INIT_SIZE, starting from output+init_size.)
362  *
363  * [input, input+input_size) is the original copied compressed image (ZO)
364  * (i.e. it does not include its run size). This range must be avoided
365  * because it contains the data used for decompression.
366  *
367  * [input+input_size, output+init_size) is [_text, _end) for ZO. This
368  * range includes ZO's heap and stack, and must be avoided since it
369  * performs the decompression.
370  *
371  * Since the above two ranges need to be avoided and they are adjacent,
372  * they can be merged, resulting in: [input, output+init_size) which
373  * becomes the MEM_AVOID_ZO_RANGE below.
374  */
375 static void mem_avoid_init(unsigned long input, unsigned long input_size,
376 			   unsigned long output)
377 {
378 	unsigned long init_size = boot_params->hdr.init_size;
379 	u64 initrd_start, initrd_size;
380 	u64 cmd_line, cmd_line_size;
381 	char *ptr;
382 
383 	/*
384 	 * Avoid the region that is unsafe to overlap during
385 	 * decompression.
386 	 */
387 	mem_avoid[MEM_AVOID_ZO_RANGE].start = input;
388 	mem_avoid[MEM_AVOID_ZO_RANGE].size = (output + init_size) - input;
389 	add_identity_map(mem_avoid[MEM_AVOID_ZO_RANGE].start,
390 			 mem_avoid[MEM_AVOID_ZO_RANGE].size);
391 
392 	/* Avoid initrd. */
393 	initrd_start  = (u64)boot_params->ext_ramdisk_image << 32;
394 	initrd_start |= boot_params->hdr.ramdisk_image;
395 	initrd_size  = (u64)boot_params->ext_ramdisk_size << 32;
396 	initrd_size |= boot_params->hdr.ramdisk_size;
397 	mem_avoid[MEM_AVOID_INITRD].start = initrd_start;
398 	mem_avoid[MEM_AVOID_INITRD].size = initrd_size;
399 	/* No need to set mapping for initrd, it will be handled in VO. */
400 
401 	/* Avoid kernel command line. */
402 	cmd_line  = (u64)boot_params->ext_cmd_line_ptr << 32;
403 	cmd_line |= boot_params->hdr.cmd_line_ptr;
404 	/* Calculate size of cmd_line. */
405 	ptr = (char *)(unsigned long)cmd_line;
406 	for (cmd_line_size = 0; ptr[cmd_line_size++];)
407 		;
408 	mem_avoid[MEM_AVOID_CMDLINE].start = cmd_line;
409 	mem_avoid[MEM_AVOID_CMDLINE].size = cmd_line_size;
410 	add_identity_map(mem_avoid[MEM_AVOID_CMDLINE].start,
411 			 mem_avoid[MEM_AVOID_CMDLINE].size);
412 
413 	/* Avoid boot parameters. */
414 	mem_avoid[MEM_AVOID_BOOTPARAMS].start = (unsigned long)boot_params;
415 	mem_avoid[MEM_AVOID_BOOTPARAMS].size = sizeof(*boot_params);
416 	add_identity_map(mem_avoid[MEM_AVOID_BOOTPARAMS].start,
417 			 mem_avoid[MEM_AVOID_BOOTPARAMS].size);
418 
419 	/* We don't need to set a mapping for setup_data. */
420 
421 	/* Mark the memmap regions we need to avoid */
422 	handle_mem_options();
423 
424 #ifdef CONFIG_X86_VERBOSE_BOOTUP
425 	/* Make sure video RAM can be used. */
426 	add_identity_map(0, PMD_SIZE);
427 #endif
428 }
429 
430 /*
431  * Does this memory vector overlap a known avoided area? If so, record the
432  * overlap region with the lowest address.
433  */
434 static bool mem_avoid_overlap(struct mem_vector *img,
435 			      struct mem_vector *overlap)
436 {
437 	int i;
438 	struct setup_data *ptr;
439 	unsigned long earliest = img->start + img->size;
440 	bool is_overlapping = false;
441 
442 	for (i = 0; i < MEM_AVOID_MAX; i++) {
443 		if (mem_overlaps(img, &mem_avoid[i]) &&
444 		    mem_avoid[i].start < earliest) {
445 			*overlap = mem_avoid[i];
446 			earliest = overlap->start;
447 			is_overlapping = true;
448 		}
449 	}
450 
451 	/* Avoid all entries in the setup_data linked list. */
452 	ptr = (struct setup_data *)(unsigned long)boot_params->hdr.setup_data;
453 	while (ptr) {
454 		struct mem_vector avoid;
455 
456 		avoid.start = (unsigned long)ptr;
457 		avoid.size = sizeof(*ptr) + ptr->len;
458 
459 		if (mem_overlaps(img, &avoid) && (avoid.start < earliest)) {
460 			*overlap = avoid;
461 			earliest = overlap->start;
462 			is_overlapping = true;
463 		}
464 
465 		ptr = (struct setup_data *)(unsigned long)ptr->next;
466 	}
467 
468 	return is_overlapping;
469 }
470 
471 struct slot_area {
472 	unsigned long addr;
473 	int num;
474 };
475 
476 #define MAX_SLOT_AREA 100
477 
478 static struct slot_area slot_areas[MAX_SLOT_AREA];
479 
480 static unsigned long slot_max;
481 
482 static unsigned long slot_area_index;
483 
484 static void store_slot_info(struct mem_vector *region, unsigned long image_size)
485 {
486 	struct slot_area slot_area;
487 
488 	if (slot_area_index == MAX_SLOT_AREA)
489 		return;
490 
491 	slot_area.addr = region->start;
492 	slot_area.num = (region->size - image_size) /
493 			CONFIG_PHYSICAL_ALIGN + 1;
494 
495 	if (slot_area.num > 0) {
496 		slot_areas[slot_area_index++] = slot_area;
497 		slot_max += slot_area.num;
498 	}
499 }
500 
501 /*
502  * Skip as many 1GB huge pages as possible in the passed region
503  * according to the number which users specified:
504  */
505 static void
506 process_gb_huge_pages(struct mem_vector *region, unsigned long image_size)
507 {
508 	unsigned long addr, size = 0;
509 	struct mem_vector tmp;
510 	int i = 0;
511 
512 	if (!max_gb_huge_pages) {
513 		store_slot_info(region, image_size);
514 		return;
515 	}
516 
517 	addr = ALIGN(region->start, PUD_SIZE);
518 	/* Did we raise the address above the passed in memory entry? */
519 	if (addr < region->start + region->size)
520 		size = region->size - (addr - region->start);
521 
522 	/* Check how many 1GB huge pages can be filtered out: */
523 	while (size > PUD_SIZE && max_gb_huge_pages) {
524 		size -= PUD_SIZE;
525 		max_gb_huge_pages--;
526 		i++;
527 	}
528 
529 	/* No good 1GB huge pages found: */
530 	if (!i) {
531 		store_slot_info(region, image_size);
532 		return;
533 	}
534 
535 	/*
536 	 * Skip those 'i'*1GB good huge pages, and continue checking and
537 	 * processing the remaining head or tail part of the passed region
538 	 * if available.
539 	 */
540 
541 	if (addr >= region->start + image_size) {
542 		tmp.start = region->start;
543 		tmp.size = addr - region->start;
544 		store_slot_info(&tmp, image_size);
545 	}
546 
547 	size  = region->size - (addr - region->start) - i * PUD_SIZE;
548 	if (size >= image_size) {
549 		tmp.start = addr + i * PUD_SIZE;
550 		tmp.size = size;
551 		store_slot_info(&tmp, image_size);
552 	}
553 }
554 
555 static unsigned long slots_fetch_random(void)
556 {
557 	unsigned long slot;
558 	int i;
559 
560 	/* Handle case of no slots stored. */
561 	if (slot_max == 0)
562 		return 0;
563 
564 	slot = kaslr_get_random_long("Physical") % slot_max;
565 
566 	for (i = 0; i < slot_area_index; i++) {
567 		if (slot >= slot_areas[i].num) {
568 			slot -= slot_areas[i].num;
569 			continue;
570 		}
571 		return slot_areas[i].addr + slot * CONFIG_PHYSICAL_ALIGN;
572 	}
573 
574 	if (i == slot_area_index)
575 		debug_putstr("slots_fetch_random() failed!?\n");
576 	return 0;
577 }
578 
579 static void process_mem_region(struct mem_vector *entry,
580 			       unsigned long minimum,
581 			       unsigned long image_size)
582 {
583 	struct mem_vector region, overlap;
584 	struct slot_area slot_area;
585 	unsigned long start_orig, end;
586 	struct mem_vector cur_entry;
587 
588 	/* On 32-bit, ignore entries entirely above our maximum. */
589 	if (IS_ENABLED(CONFIG_X86_32) && entry->start >= KERNEL_IMAGE_SIZE)
590 		return;
591 
592 	/* Ignore entries entirely below our minimum. */
593 	if (entry->start + entry->size < minimum)
594 		return;
595 
596 	/* Ignore entries above memory limit */
597 	end = min(entry->size + entry->start, mem_limit);
598 	if (entry->start >= end)
599 		return;
600 	cur_entry.start = entry->start;
601 	cur_entry.size = end - entry->start;
602 
603 	region.start = cur_entry.start;
604 	region.size = cur_entry.size;
605 
606 	/* Give up if slot area array is full. */
607 	while (slot_area_index < MAX_SLOT_AREA) {
608 		start_orig = region.start;
609 
610 		/* Potentially raise address to minimum location. */
611 		if (region.start < minimum)
612 			region.start = minimum;
613 
614 		/* Potentially raise address to meet alignment needs. */
615 		region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);
616 
617 		/* Did we raise the address above the passed in memory entry? */
618 		if (region.start > cur_entry.start + cur_entry.size)
619 			return;
620 
621 		/* Reduce size by any delta from the original address. */
622 		region.size -= region.start - start_orig;
623 
624 		/* On 32-bit, reduce region size to fit within max size. */
625 		if (IS_ENABLED(CONFIG_X86_32) &&
626 		    region.start + region.size > KERNEL_IMAGE_SIZE)
627 			region.size = KERNEL_IMAGE_SIZE - region.start;
628 
629 		/* Return if region can't contain decompressed kernel */
630 		if (region.size < image_size)
631 			return;
632 
633 		/* If nothing overlaps, store the region and return. */
634 		if (!mem_avoid_overlap(&region, &overlap)) {
635 			process_gb_huge_pages(&region, image_size);
636 			return;
637 		}
638 
639 		/* Store beginning of region if holds at least image_size. */
640 		if (overlap.start > region.start + image_size) {
641 			struct mem_vector beginning;
642 
643 			beginning.start = region.start;
644 			beginning.size = overlap.start - region.start;
645 			process_gb_huge_pages(&beginning, image_size);
646 		}
647 
648 		/* Return if overlap extends to or past end of region. */
649 		if (overlap.start + overlap.size >= region.start + region.size)
650 			return;
651 
652 		/* Clip off the overlapping region and start over. */
653 		region.size -= overlap.start - region.start + overlap.size;
654 		region.start = overlap.start + overlap.size;
655 	}
656 }
657 
658 #ifdef CONFIG_EFI
659 /*
660  * Returns true if mirror region found (and must have been processed
661  * for slots adding)
662  */
663 static bool
664 process_efi_entries(unsigned long minimum, unsigned long image_size)
665 {
666 	struct efi_info *e = &boot_params->efi_info;
667 	bool efi_mirror_found = false;
668 	struct mem_vector region;
669 	efi_memory_desc_t *md;
670 	unsigned long pmap;
671 	char *signature;
672 	u32 nr_desc;
673 	int i;
674 
675 	signature = (char *)&e->efi_loader_signature;
676 	if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
677 	    strncmp(signature, EFI64_LOADER_SIGNATURE, 4))
678 		return false;
679 
680 #ifdef CONFIG_X86_32
681 	/* Can't handle data above 4GB at this time */
682 	if (e->efi_memmap_hi) {
683 		warn("EFI memmap is above 4GB, can't be handled now on x86_32. EFI should be disabled.\n");
684 		return false;
685 	}
686 	pmap =  e->efi_memmap;
687 #else
688 	pmap = (e->efi_memmap | ((__u64)e->efi_memmap_hi << 32));
689 #endif
690 
691 	nr_desc = e->efi_memmap_size / e->efi_memdesc_size;
692 	for (i = 0; i < nr_desc; i++) {
693 		md = efi_early_memdesc_ptr(pmap, e->efi_memdesc_size, i);
694 		if (md->attribute & EFI_MEMORY_MORE_RELIABLE) {
695 			efi_mirror_found = true;
696 			break;
697 		}
698 	}
699 
700 	for (i = 0; i < nr_desc; i++) {
701 		md = efi_early_memdesc_ptr(pmap, e->efi_memdesc_size, i);
702 
703 		/*
704 		 * Here we are more conservative in picking free memory than
705 		 * the EFI spec allows:
706 		 *
707 		 * According to the spec, EFI_BOOT_SERVICES_{CODE|DATA} are also
708 		 * free memory and thus available to place the kernel image into,
709 		 * but in practice there's firmware where using that memory leads
710 		 * to crashes.
711 		 *
712 		 * Only EFI_CONVENTIONAL_MEMORY is guaranteed to be free.
713 		 */
714 		if (md->type != EFI_CONVENTIONAL_MEMORY)
715 			continue;
716 
717 		if (efi_mirror_found &&
718 		    !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
719 			continue;
720 
721 		region.start = md->phys_addr;
722 		region.size = md->num_pages << EFI_PAGE_SHIFT;
723 		process_mem_region(&region, minimum, image_size);
724 		if (slot_area_index == MAX_SLOT_AREA) {
725 			debug_putstr("Aborted EFI scan (slot_areas full)!\n");
726 			break;
727 		}
728 	}
729 	return true;
730 }
731 #else
732 static inline bool
733 process_efi_entries(unsigned long minimum, unsigned long image_size)
734 {
735 	return false;
736 }
737 #endif
738 
739 static void process_e820_entries(unsigned long minimum,
740 				 unsigned long image_size)
741 {
742 	int i;
743 	struct mem_vector region;
744 	struct boot_e820_entry *entry;
745 
746 	/* Verify potential e820 positions, appending to slots list. */
747 	for (i = 0; i < boot_params->e820_entries; i++) {
748 		entry = &boot_params->e820_table[i];
749 		/* Skip non-RAM entries. */
750 		if (entry->type != E820_TYPE_RAM)
751 			continue;
752 		region.start = entry->addr;
753 		region.size = entry->size;
754 		process_mem_region(&region, minimum, image_size);
755 		if (slot_area_index == MAX_SLOT_AREA) {
756 			debug_putstr("Aborted e820 scan (slot_areas full)!\n");
757 			break;
758 		}
759 	}
760 }
761 
762 static unsigned long find_random_phys_addr(unsigned long minimum,
763 					   unsigned long image_size)
764 {
765 	/* Check if we had too many memmaps. */
766 	if (memmap_too_large) {
767 		debug_putstr("Aborted memory entries scan (more than 4 memmap= args)!\n");
768 		return 0;
769 	}
770 
771 	/* Make sure minimum is aligned. */
772 	minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
773 
774 	if (process_efi_entries(minimum, image_size))
775 		return slots_fetch_random();
776 
777 	process_e820_entries(minimum, image_size);
778 	return slots_fetch_random();
779 }
780 
781 static unsigned long find_random_virt_addr(unsigned long minimum,
782 					   unsigned long image_size)
783 {
784 	unsigned long slots, random_addr;
785 
786 	/* Make sure minimum is aligned. */
787 	minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
788 	/* Align image_size for easy slot calculations. */
789 	image_size = ALIGN(image_size, CONFIG_PHYSICAL_ALIGN);
790 
791 	/*
792 	 * There are how many CONFIG_PHYSICAL_ALIGN-sized slots
793 	 * that can hold image_size within the range of minimum to
794 	 * KERNEL_IMAGE_SIZE?
795 	 */
796 	slots = (KERNEL_IMAGE_SIZE - minimum - image_size) /
797 		 CONFIG_PHYSICAL_ALIGN + 1;
798 
799 	random_addr = kaslr_get_random_long("Virtual") % slots;
800 
801 	return random_addr * CONFIG_PHYSICAL_ALIGN + minimum;
802 }
803 
804 /*
805  * Since this function examines addresses much more numerically,
806  * it takes the input and output pointers as 'unsigned long'.
807  */
808 void choose_random_location(unsigned long input,
809 			    unsigned long input_size,
810 			    unsigned long *output,
811 			    unsigned long output_size,
812 			    unsigned long *virt_addr)
813 {
814 	unsigned long random_addr, min_addr;
815 
816 	if (cmdline_find_option_bool("nokaslr")) {
817 		warn("KASLR disabled: 'nokaslr' on cmdline.");
818 		return;
819 	}
820 
821 #ifdef CONFIG_X86_5LEVEL
822 	if (__read_cr4() & X86_CR4_LA57) {
823 		__pgtable_l5_enabled = 1;
824 		pgdir_shift = 48;
825 		ptrs_per_p4d = 512;
826 	}
827 #endif
828 
829 	boot_params->hdr.loadflags |= KASLR_FLAG;
830 
831 	/* Prepare to add new identity pagetables on demand. */
832 	initialize_identity_maps();
833 
834 	/* Record the various known unsafe memory ranges. */
835 	mem_avoid_init(input, input_size, *output);
836 
837 	/*
838 	 * Low end of the randomization range should be the
839 	 * smaller of 512M or the initial kernel image
840 	 * location:
841 	 */
842 	min_addr = min(*output, 512UL << 20);
843 
844 	/* Walk available memory entries to find a random address. */
845 	random_addr = find_random_phys_addr(min_addr, output_size);
846 	if (!random_addr) {
847 		warn("Physical KASLR disabled: no suitable memory region!");
848 	} else {
849 		/* Update the new physical address location. */
850 		if (*output != random_addr) {
851 			add_identity_map(random_addr, output_size);
852 			*output = random_addr;
853 		}
854 
855 		/*
856 		 * This loads the identity mapping page table.
857 		 * This should only be done if a new physical address
858 		 * is found for the kernel, otherwise we should keep
859 		 * the old page table to make it be like the "nokaslr"
860 		 * case.
861 		 */
862 		finalize_identity_maps();
863 	}
864 
865 
866 	/* Pick random virtual address starting from LOAD_PHYSICAL_ADDR. */
867 	if (IS_ENABLED(CONFIG_X86_64))
868 		random_addr = find_random_virt_addr(LOAD_PHYSICAL_ADDR, output_size);
869 	*virt_addr = random_addr;
870 }
871