1 // SPDX-License-Identifier: GPL-2.0
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.
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
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.
27 #define __DISABLE_EXPORTS
31 #include "../string.h"
33 #include <generated/compile.h>
34 #include <linux/module.h>
35 #include <linux/uts.h>
36 #include <linux/utsname.h>
37 #include <linux/ctype.h>
38 #include <linux/efi.h>
39 #include <generated/utsrelease.h>
42 /* Macros used by the included decompressor code below. */
44 #include <linux/decompress/mm.h>
46 #ifdef CONFIG_X86_5LEVEL
47 unsigned int __pgtable_l5_enabled;
48 unsigned int pgdir_shift __ro_after_init = 39;
49 unsigned int ptrs_per_p4d __ro_after_init = 1;
52 extern unsigned long get_cmd_line_ptr(void);
54 /* Used by PAGE_KERN* macros: */
55 pteval_t __default_kernel_pte_mask __read_mostly = ~0;
57 /* Simplified build-specific string for starting entropy. */
58 static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
59 LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
61 static unsigned long rotate_xor(unsigned long hash, const void *area,
65 unsigned long *ptr = (unsigned long *)area;
67 for (i = 0; i < size / sizeof(hash); i++) {
68 /* Rotate by odd number of bits and XOR. */
69 hash = (hash << ((sizeof(hash) * 8) - 7)) | (hash >> 7);
76 /* Attempt to create a simple but unpredictable starting entropy. */
77 static unsigned long get_boot_seed(void)
79 unsigned long hash = 0;
81 hash = rotate_xor(hash, build_str, sizeof(build_str));
82 hash = rotate_xor(hash, boot_params, sizeof(*boot_params));
87 #define KASLR_COMPRESSED_BOOT
88 #include "../../lib/kaslr.c"
91 /* Only supporting at most 4 unusable memmap regions with kaslr */
92 #define MAX_MEMMAP_REGIONS 4
94 static bool memmap_too_large;
97 /* Store memory limit specified by "mem=nn[KMG]" or "memmap=nn[KMG]" */
98 static unsigned long long mem_limit = ULLONG_MAX;
100 /* Number of immovable memory regions */
101 static int num_immovable_mem;
103 enum mem_avoid_index {
104 MEM_AVOID_ZO_RANGE = 0,
107 MEM_AVOID_BOOTPARAMS,
108 MEM_AVOID_MEMMAP_BEGIN,
109 MEM_AVOID_MEMMAP_END = MEM_AVOID_MEMMAP_BEGIN + MAX_MEMMAP_REGIONS - 1,
113 static struct mem_vector mem_avoid[MEM_AVOID_MAX];
115 static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
117 /* Item one is entirely before item two. */
118 if (one->start + one->size <= two->start)
120 /* Item one is entirely after item two. */
121 if (one->start >= two->start + two->size)
126 char *skip_spaces(const char *str)
128 while (isspace(*str))
132 #include "../../../../lib/ctype.c"
133 #include "../../../../lib/cmdline.c"
136 parse_memmap(char *p, unsigned long long *start, unsigned long long *size)
143 /* We don't care about this option here */
144 if (!strncmp(p, "exactmap", 8))
148 *size = memparse(p, &p);
156 *start = memparse(p + 1, &p);
159 /* memmap=nn@ss specifies usable region, should be skipped */
164 * If w/o offset, only size specified, memmap=nn[KMG] has the
165 * same behaviour as mem=nn[KMG]. It limits the max address
166 * system can use. Region above the limit should be avoided.
175 static void mem_avoid_memmap(char *str)
179 if (i >= MAX_MEMMAP_REGIONS)
182 while (str && (i < MAX_MEMMAP_REGIONS)) {
184 unsigned long long start, size;
185 char *k = strchr(str, ',');
190 rc = parse_memmap(str, &start, &size);
196 /* Store the specified memory limit if size > 0 */
203 mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].start = start;
204 mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].size = size;
208 /* More than 4 memmaps, fail kaslr */
209 if ((i >= MAX_MEMMAP_REGIONS) && str)
210 memmap_too_large = true;
213 /* Store the number of 1GB huge pages which users specified: */
214 static unsigned long max_gb_huge_pages;
216 static void parse_gb_huge_pages(char *param, char *val)
218 static bool gbpage_sz;
221 if (!strcmp(param, "hugepagesz")) {
223 if (memparse(p, &p) != PUD_SIZE) {
229 warn("Repeatedly set hugeTLB page size of 1G!\n");
234 if (!strcmp(param, "hugepages") && gbpage_sz) {
236 max_gb_huge_pages = simple_strtoull(p, &p, 0);
242 static void handle_mem_options(void)
244 char *args = (char *)get_cmd_line_ptr();
245 size_t len = strlen((char *)args);
250 if (!strstr(args, "memmap=") && !strstr(args, "mem=") &&
251 !strstr(args, "hugepages"))
254 tmp_cmdline = malloc(len + 1);
256 error("Failed to allocate space for tmp_cmdline");
258 memcpy(tmp_cmdline, args, len);
259 tmp_cmdline[len] = 0;
262 /* Chew leading spaces */
263 args = skip_spaces(args);
266 args = next_arg(args, ¶m, &val);
268 if (!val && strcmp(param, "--") == 0) {
269 warn("Only '--' specified in cmdline");
273 if (!strcmp(param, "memmap")) {
274 mem_avoid_memmap(val);
275 } else if (strstr(param, "hugepages")) {
276 parse_gb_huge_pages(param, val);
277 } else if (!strcmp(param, "mem")) {
280 if (!strcmp(p, "nopentium"))
282 mem_size = memparse(p, &p);
286 mem_limit = mem_size;
296 * In theory, KASLR can put the kernel anywhere in the range of [16M, 64T).
297 * The mem_avoid array is used to store the ranges that need to be avoided
298 * when KASLR searches for an appropriate random address. We must avoid any
299 * regions that are unsafe to overlap with during decompression, and other
300 * things like the initrd, cmdline and boot_params. This comment seeks to
301 * explain mem_avoid as clearly as possible since incorrect mem_avoid
302 * memory ranges lead to really hard to debug boot failures.
304 * The initrd, cmdline, and boot_params are trivial to identify for
305 * avoiding. They are MEM_AVOID_INITRD, MEM_AVOID_CMDLINE, and
306 * MEM_AVOID_BOOTPARAMS respectively below.
308 * What is not obvious how to avoid is the range of memory that is used
309 * during decompression (MEM_AVOID_ZO_RANGE below). This range must cover
310 * the compressed kernel (ZO) and its run space, which is used to extract
311 * the uncompressed kernel (VO) and relocs.
313 * ZO's full run size sits against the end of the decompression buffer, so
314 * we can calculate where text, data, bss, etc of ZO are positioned more
317 * For additional background, the decompression calculations can be found
318 * in header.S, and the memory diagram is based on the one found in misc.c.
320 * The following conditions are already enforced by the image layouts and
322 * - input + input_size >= output + output_size
323 * - kernel_total_size <= init_size
324 * - kernel_total_size <= output_size (see Note below)
325 * - output + init_size >= output + output_size
327 * (Note that kernel_total_size and output_size have no fundamental
328 * relationship, but output_size is passed to choose_random_location
329 * as a maximum of the two. The diagram is showing a case where
330 * kernel_total_size is larger than output_size, but this case is
331 * handled by bumping output_size.)
333 * The above conditions can be illustrated by a diagram:
335 * 0 output input input+input_size output+init_size
338 * |-----|--------|--------|--------------|-----------|--|-------------|
341 * output+init_size-ZO_INIT_SIZE output+output_size output+kernel_total_size
343 * [output, output+init_size) is the entire memory range used for
344 * extracting the compressed image.
346 * [output, output+kernel_total_size) is the range needed for the
347 * uncompressed kernel (VO) and its run size (bss, brk, etc).
349 * [output, output+output_size) is VO plus relocs (i.e. the entire
350 * uncompressed payload contained by ZO). This is the area of the buffer
351 * written to during decompression.
353 * [output+init_size-ZO_INIT_SIZE, output+init_size) is the worst-case
354 * range of the copied ZO and decompression code. (i.e. the range
355 * covered backwards of size ZO_INIT_SIZE, starting from output+init_size.)
357 * [input, input+input_size) is the original copied compressed image (ZO)
358 * (i.e. it does not include its run size). This range must be avoided
359 * because it contains the data used for decompression.
361 * [input+input_size, output+init_size) is [_text, _end) for ZO. This
362 * range includes ZO's heap and stack, and must be avoided since it
363 * performs the decompression.
365 * Since the above two ranges need to be avoided and they are adjacent,
366 * they can be merged, resulting in: [input, output+init_size) which
367 * becomes the MEM_AVOID_ZO_RANGE below.
369 static void mem_avoid_init(unsigned long input, unsigned long input_size,
370 unsigned long output)
372 unsigned long init_size = boot_params->hdr.init_size;
373 u64 initrd_start, initrd_size;
374 u64 cmd_line, cmd_line_size;
378 * Avoid the region that is unsafe to overlap during
381 mem_avoid[MEM_AVOID_ZO_RANGE].start = input;
382 mem_avoid[MEM_AVOID_ZO_RANGE].size = (output + init_size) - input;
383 add_identity_map(mem_avoid[MEM_AVOID_ZO_RANGE].start,
384 mem_avoid[MEM_AVOID_ZO_RANGE].size);
387 initrd_start = (u64)boot_params->ext_ramdisk_image << 32;
388 initrd_start |= boot_params->hdr.ramdisk_image;
389 initrd_size = (u64)boot_params->ext_ramdisk_size << 32;
390 initrd_size |= boot_params->hdr.ramdisk_size;
391 mem_avoid[MEM_AVOID_INITRD].start = initrd_start;
392 mem_avoid[MEM_AVOID_INITRD].size = initrd_size;
393 /* No need to set mapping for initrd, it will be handled in VO. */
395 /* Avoid kernel command line. */
396 cmd_line = (u64)boot_params->ext_cmd_line_ptr << 32;
397 cmd_line |= boot_params->hdr.cmd_line_ptr;
398 /* Calculate size of cmd_line. */
399 ptr = (char *)(unsigned long)cmd_line;
400 for (cmd_line_size = 0; ptr[cmd_line_size++];)
402 mem_avoid[MEM_AVOID_CMDLINE].start = cmd_line;
403 mem_avoid[MEM_AVOID_CMDLINE].size = cmd_line_size;
404 add_identity_map(mem_avoid[MEM_AVOID_CMDLINE].start,
405 mem_avoid[MEM_AVOID_CMDLINE].size);
407 /* Avoid boot parameters. */
408 mem_avoid[MEM_AVOID_BOOTPARAMS].start = (unsigned long)boot_params;
409 mem_avoid[MEM_AVOID_BOOTPARAMS].size = sizeof(*boot_params);
410 add_identity_map(mem_avoid[MEM_AVOID_BOOTPARAMS].start,
411 mem_avoid[MEM_AVOID_BOOTPARAMS].size);
413 /* We don't need to set a mapping for setup_data. */
415 /* Mark the memmap regions we need to avoid */
416 handle_mem_options();
418 /* Enumerate the immovable memory regions */
419 num_immovable_mem = count_immovable_mem_regions();
421 #ifdef CONFIG_X86_VERBOSE_BOOTUP
422 /* Make sure video RAM can be used. */
423 add_identity_map(0, PMD_SIZE);
428 * Does this memory vector overlap a known avoided area? If so, record the
429 * overlap region with the lowest address.
431 static bool mem_avoid_overlap(struct mem_vector *img,
432 struct mem_vector *overlap)
435 struct setup_data *ptr;
436 unsigned long earliest = img->start + img->size;
437 bool is_overlapping = false;
439 for (i = 0; i < MEM_AVOID_MAX; i++) {
440 if (mem_overlaps(img, &mem_avoid[i]) &&
441 mem_avoid[i].start < earliest) {
442 *overlap = mem_avoid[i];
443 earliest = overlap->start;
444 is_overlapping = true;
448 /* Avoid all entries in the setup_data linked list. */
449 ptr = (struct setup_data *)(unsigned long)boot_params->hdr.setup_data;
451 struct mem_vector avoid;
453 avoid.start = (unsigned long)ptr;
454 avoid.size = sizeof(*ptr) + ptr->len;
456 if (mem_overlaps(img, &avoid) && (avoid.start < earliest)) {
458 earliest = overlap->start;
459 is_overlapping = true;
462 ptr = (struct setup_data *)(unsigned long)ptr->next;
465 return is_overlapping;
473 #define MAX_SLOT_AREA 100
475 static struct slot_area slot_areas[MAX_SLOT_AREA];
477 static unsigned long slot_max;
479 static unsigned long slot_area_index;
481 static void store_slot_info(struct mem_vector *region, unsigned long image_size)
483 struct slot_area slot_area;
485 if (slot_area_index == MAX_SLOT_AREA)
488 slot_area.addr = region->start;
489 slot_area.num = (region->size - image_size) /
490 CONFIG_PHYSICAL_ALIGN + 1;
492 if (slot_area.num > 0) {
493 slot_areas[slot_area_index++] = slot_area;
494 slot_max += slot_area.num;
499 * Skip as many 1GB huge pages as possible in the passed region
500 * according to the number which users specified:
503 process_gb_huge_pages(struct mem_vector *region, unsigned long image_size)
505 unsigned long addr, size = 0;
506 struct mem_vector tmp;
509 if (!max_gb_huge_pages) {
510 store_slot_info(region, image_size);
514 addr = ALIGN(region->start, PUD_SIZE);
515 /* Did we raise the address above the passed in memory entry? */
516 if (addr < region->start + region->size)
517 size = region->size - (addr - region->start);
519 /* Check how many 1GB huge pages can be filtered out: */
520 while (size > PUD_SIZE && max_gb_huge_pages) {
526 /* No good 1GB huge pages found: */
528 store_slot_info(region, image_size);
533 * Skip those 'i'*1GB good huge pages, and continue checking and
534 * processing the remaining head or tail part of the passed region
538 if (addr >= region->start + image_size) {
539 tmp.start = region->start;
540 tmp.size = addr - region->start;
541 store_slot_info(&tmp, image_size);
544 size = region->size - (addr - region->start) - i * PUD_SIZE;
545 if (size >= image_size) {
546 tmp.start = addr + i * PUD_SIZE;
548 store_slot_info(&tmp, image_size);
552 static unsigned long slots_fetch_random(void)
557 /* Handle case of no slots stored. */
561 slot = kaslr_get_random_long("Physical") % slot_max;
563 for (i = 0; i < slot_area_index; i++) {
564 if (slot >= slot_areas[i].num) {
565 slot -= slot_areas[i].num;
568 return slot_areas[i].addr + slot * CONFIG_PHYSICAL_ALIGN;
571 if (i == slot_area_index)
572 debug_putstr("slots_fetch_random() failed!?\n");
576 static void __process_mem_region(struct mem_vector *entry,
577 unsigned long minimum,
578 unsigned long image_size)
580 struct mem_vector region, overlap;
581 unsigned long start_orig, end;
582 struct mem_vector cur_entry;
584 /* On 32-bit, ignore entries entirely above our maximum. */
585 if (IS_ENABLED(CONFIG_X86_32) && entry->start >= KERNEL_IMAGE_SIZE)
588 /* Ignore entries entirely below our minimum. */
589 if (entry->start + entry->size < minimum)
592 /* Ignore entries above memory limit */
593 end = min(entry->size + entry->start, mem_limit);
594 if (entry->start >= end)
596 cur_entry.start = entry->start;
597 cur_entry.size = end - entry->start;
599 region.start = cur_entry.start;
600 region.size = cur_entry.size;
602 /* Give up if slot area array is full. */
603 while (slot_area_index < MAX_SLOT_AREA) {
604 start_orig = region.start;
606 /* Potentially raise address to minimum location. */
607 if (region.start < minimum)
608 region.start = minimum;
610 /* Potentially raise address to meet alignment needs. */
611 region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);
613 /* Did we raise the address above the passed in memory entry? */
614 if (region.start > cur_entry.start + cur_entry.size)
617 /* Reduce size by any delta from the original address. */
618 region.size -= region.start - start_orig;
620 /* On 32-bit, reduce region size to fit within max size. */
621 if (IS_ENABLED(CONFIG_X86_32) &&
622 region.start + region.size > KERNEL_IMAGE_SIZE)
623 region.size = KERNEL_IMAGE_SIZE - region.start;
625 /* Return if region can't contain decompressed kernel */
626 if (region.size < image_size)
629 /* If nothing overlaps, store the region and return. */
630 if (!mem_avoid_overlap(®ion, &overlap)) {
631 process_gb_huge_pages(®ion, image_size);
635 /* Store beginning of region if holds at least image_size. */
636 if (overlap.start > region.start + image_size) {
637 struct mem_vector beginning;
639 beginning.start = region.start;
640 beginning.size = overlap.start - region.start;
641 process_gb_huge_pages(&beginning, image_size);
644 /* Return if overlap extends to or past end of region. */
645 if (overlap.start + overlap.size >= region.start + region.size)
648 /* Clip off the overlapping region and start over. */
649 region.size -= overlap.start - region.start + overlap.size;
650 region.start = overlap.start + overlap.size;
654 static bool process_mem_region(struct mem_vector *region,
655 unsigned long long minimum,
656 unsigned long long image_size)
660 * If no immovable memory found, or MEMORY_HOTREMOVE disabled,
661 * use @region directly.
663 if (!num_immovable_mem) {
664 __process_mem_region(region, minimum, image_size);
666 if (slot_area_index == MAX_SLOT_AREA) {
667 debug_putstr("Aborted e820/efi memmap scan (slot_areas full)!\n");
673 #if defined(CONFIG_MEMORY_HOTREMOVE) && defined(CONFIG_ACPI)
675 * If immovable memory found, filter the intersection between
676 * immovable memory and @region.
678 for (i = 0; i < num_immovable_mem; i++) {
679 unsigned long long start, end, entry_end, region_end;
680 struct mem_vector entry;
682 if (!mem_overlaps(region, &immovable_mem[i]))
685 start = immovable_mem[i].start;
686 end = start + immovable_mem[i].size;
687 region_end = region->start + region->size;
689 entry.start = clamp(region->start, start, end);
690 entry_end = clamp(region_end, start, end);
691 entry.size = entry_end - entry.start;
693 __process_mem_region(&entry, minimum, image_size);
695 if (slot_area_index == MAX_SLOT_AREA) {
696 debug_putstr("Aborted e820/efi memmap scan when walking immovable regions(slot_areas full)!\n");
706 * Returns true if mirror region found (and must have been processed
710 process_efi_entries(unsigned long minimum, unsigned long image_size)
712 struct efi_info *e = &boot_params->efi_info;
713 bool efi_mirror_found = false;
714 struct mem_vector region;
715 efi_memory_desc_t *md;
721 signature = (char *)&e->efi_loader_signature;
722 if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
723 strncmp(signature, EFI64_LOADER_SIGNATURE, 4))
727 /* Can't handle data above 4GB at this time */
728 if (e->efi_memmap_hi) {
729 warn("EFI memmap is above 4GB, can't be handled now on x86_32. EFI should be disabled.\n");
732 pmap = e->efi_memmap;
734 pmap = (e->efi_memmap | ((__u64)e->efi_memmap_hi << 32));
737 nr_desc = e->efi_memmap_size / e->efi_memdesc_size;
738 for (i = 0; i < nr_desc; i++) {
739 md = efi_early_memdesc_ptr(pmap, e->efi_memdesc_size, i);
740 if (md->attribute & EFI_MEMORY_MORE_RELIABLE) {
741 efi_mirror_found = true;
746 for (i = 0; i < nr_desc; i++) {
747 md = efi_early_memdesc_ptr(pmap, e->efi_memdesc_size, i);
750 * Here we are more conservative in picking free memory than
751 * the EFI spec allows:
753 * According to the spec, EFI_BOOT_SERVICES_{CODE|DATA} are also
754 * free memory and thus available to place the kernel image into,
755 * but in practice there's firmware where using that memory leads
758 * Only EFI_CONVENTIONAL_MEMORY is guaranteed to be free.
760 if (md->type != EFI_CONVENTIONAL_MEMORY)
763 if (efi_mirror_found &&
764 !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
767 region.start = md->phys_addr;
768 region.size = md->num_pages << EFI_PAGE_SHIFT;
769 if (process_mem_region(®ion, minimum, image_size))
776 process_efi_entries(unsigned long minimum, unsigned long image_size)
782 static void process_e820_entries(unsigned long minimum,
783 unsigned long image_size)
786 struct mem_vector region;
787 struct boot_e820_entry *entry;
789 /* Verify potential e820 positions, appending to slots list. */
790 for (i = 0; i < boot_params->e820_entries; i++) {
791 entry = &boot_params->e820_table[i];
792 /* Skip non-RAM entries. */
793 if (entry->type != E820_TYPE_RAM)
795 region.start = entry->addr;
796 region.size = entry->size;
797 if (process_mem_region(®ion, minimum, image_size))
802 static unsigned long find_random_phys_addr(unsigned long minimum,
803 unsigned long image_size)
805 /* Check if we had too many memmaps. */
806 if (memmap_too_large) {
807 debug_putstr("Aborted memory entries scan (more than 4 memmap= args)!\n");
811 /* Make sure minimum is aligned. */
812 minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
814 if (process_efi_entries(minimum, image_size))
815 return slots_fetch_random();
817 process_e820_entries(minimum, image_size);
818 return slots_fetch_random();
821 static unsigned long find_random_virt_addr(unsigned long minimum,
822 unsigned long image_size)
824 unsigned long slots, random_addr;
826 /* Make sure minimum is aligned. */
827 minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
828 /* Align image_size for easy slot calculations. */
829 image_size = ALIGN(image_size, CONFIG_PHYSICAL_ALIGN);
832 * There are how many CONFIG_PHYSICAL_ALIGN-sized slots
833 * that can hold image_size within the range of minimum to
836 slots = (KERNEL_IMAGE_SIZE - minimum - image_size) /
837 CONFIG_PHYSICAL_ALIGN + 1;
839 random_addr = kaslr_get_random_long("Virtual") % slots;
841 return random_addr * CONFIG_PHYSICAL_ALIGN + minimum;
845 * Since this function examines addresses much more numerically,
846 * it takes the input and output pointers as 'unsigned long'.
848 void choose_random_location(unsigned long input,
849 unsigned long input_size,
850 unsigned long *output,
851 unsigned long output_size,
852 unsigned long *virt_addr)
854 unsigned long random_addr, min_addr;
856 if (cmdline_find_option_bool("nokaslr")) {
857 warn("KASLR disabled: 'nokaslr' on cmdline.");
861 #ifdef CONFIG_X86_5LEVEL
862 if (__read_cr4() & X86_CR4_LA57) {
863 __pgtable_l5_enabled = 1;
869 boot_params->hdr.loadflags |= KASLR_FLAG;
871 /* Prepare to add new identity pagetables on demand. */
872 initialize_identity_maps();
874 /* Record the various known unsafe memory ranges. */
875 mem_avoid_init(input, input_size, *output);
878 * Low end of the randomization range should be the
879 * smaller of 512M or the initial kernel image
882 min_addr = min(*output, 512UL << 20);
884 /* Walk available memory entries to find a random address. */
885 random_addr = find_random_phys_addr(min_addr, output_size);
887 warn("Physical KASLR disabled: no suitable memory region!");
889 /* Update the new physical address location. */
890 if (*output != random_addr) {
891 add_identity_map(random_addr, output_size);
892 *output = random_addr;
896 * This loads the identity mapping page table.
897 * This should only be done if a new physical address
898 * is found for the kernel, otherwise we should keep
899 * the old page table to make it be like the "nokaslr"
902 finalize_identity_maps();
906 /* Pick random virtual address starting from LOAD_PHYSICAL_ADDR. */
907 if (IS_ENABLED(CONFIG_X86_64))
908 random_addr = find_random_virt_addr(LOAD_PHYSICAL_ADDR, output_size);
909 *virt_addr = random_addr;