root/arch/x86/boot/compressed/kaslr.c

DEFINITIONS

1. rotate_xor
2. get_boot_seed
3. mem_overlaps
4. skip_spaces
5. parse_memmap
6. mem_avoid_memmap
7. parse_gb_huge_pages
8. handle_mem_options
9. mem_avoid_init
10. mem_avoid_overlap
11. store_slot_info
12. process_gb_huge_pages
13. slots_fetch_random
14. __process_mem_region
15. process_mem_region
16. process_efi_entries
17. process_efi_entries
18. process_e820_entries
19. find_random_phys_addr
20. find_random_virt_addr
21. choose_random_location

   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  */
  27 #define __DISABLE_EXPORTS
  28 
  29 #include "misc.h"
  30 #include "error.h"
  31 #include "../string.h"
  32 
  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>
  40 #include <asm/efi.h>
  41 
  42 /* Macros used by the included decompressor code below. */
  43 #define STATIC
  44 #include <linux/decompress/mm.h>
  45 
  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;
  50 #endif
  51 
  52 extern unsigned long get_cmd_line_ptr(void);
  53 
  54 /* Used by PAGE_KERN* macros: */
  55 pteval_t __default_kernel_pte_mask __read_mostly = ~0;
  56 
  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;
  60 
  61 static unsigned long rotate_xor(unsigned long hash, const void *area,
  62                                 size_t size)
  63 {
  64         size_t i;
  65         unsigned long *ptr = (unsigned long *)area;
  66 
  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);
  70                 hash ^= ptr[i];
  71         }
  72 
  73         return hash;
  74 }
  75 
  76 /* Attempt to create a simple but unpredictable starting entropy. */
  77 static unsigned long get_boot_seed(void)
  78 {
  79         unsigned long hash = 0;
  80 
  81         hash = rotate_xor(hash, build_str, sizeof(build_str));
  82         hash = rotate_xor(hash, boot_params, sizeof(*boot_params));
  83 
  84         return hash;
  85 }
  86 
  87 #define KASLR_COMPRESSED_BOOT
  88 #include "../../lib/kaslr.c"
  89 
  90 
  91 /* Only supporting at most 4 unusable memmap regions with kaslr */
  92 #define MAX_MEMMAP_REGIONS      4
  93 
  94 static bool memmap_too_large;
  95 
  96 
  97 /* Store memory limit specified by "mem=nn[KMG]" or "memmap=nn[KMG]" */
  98 static unsigned long long mem_limit = ULLONG_MAX;
  99 
 100 /* Number of immovable memory regions */
 101 static int num_immovable_mem;
 102 
 103 enum mem_avoid_index {
 104         MEM_AVOID_ZO_RANGE = 0,
 105         MEM_AVOID_INITRD,
 106         MEM_AVOID_CMDLINE,
 107         MEM_AVOID_BOOTPARAMS,
 108         MEM_AVOID_MEMMAP_BEGIN,
 109         MEM_AVOID_MEMMAP_END = MEM_AVOID_MEMMAP_BEGIN + MAX_MEMMAP_REGIONS - 1,
 110         MEM_AVOID_MAX,
 111 };
 112 
 113 static struct mem_vector mem_avoid[MEM_AVOID_MAX];
 114 
 115 static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
 116 {
 117         /* Item one is entirely before item two. */
 118         if (one->start + one->size <= two->start)
 119                 return false;
 120         /* Item one is entirely after item two. */
 121         if (one->start >= two->start + two->size)
 122                 return false;
 123         return true;
 124 }
 125 
 126 char *skip_spaces(const char *str)
 127 {
 128         while (isspace(*str))
 129                 ++str;
 130         return (char *)str;
 131 }
 132 #include "../../../../lib/ctype.c"
 133 #include "../../../../lib/cmdline.c"
 134 
 135 static int
 136 parse_memmap(char *p, unsigned long long *start, unsigned long long *size)
 137 {
 138         char *oldp;
 139 
 140         if (!p)
 141                 return -EINVAL;
 142 
 143         /* We don't care about this option here */
 144         if (!strncmp(p, "exactmap", 8))
 145                 return -EINVAL;
 146 
 147         oldp = p;
 148         *size = memparse(p, &p);
 149         if (p == oldp)
 150                 return -EINVAL;
 151 
 152         switch (*p) {
 153         case '#':
 154         case '$':
 155         case '!':
 156                 *start = memparse(p + 1, &p);
 157                 return 0;
 158         case '@':
 159                 /* memmap=nn@ss specifies usable region, should be skipped */
 160                 *size = 0;
 161                 /* Fall through */
 162         default:
 163                 /*
 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.
 167                  */
 168                 *start = 0;
 169                 return 0;
 170         }
 171 
 172         return -EINVAL;
 173 }
 174 
 175 static void mem_avoid_memmap(char *str)
 176 {
 177         static int i;
 178 
 179         if (i >= MAX_MEMMAP_REGIONS)
 180                 return;
 181 
 182         while (str && (i < MAX_MEMMAP_REGIONS)) {
 183                 int rc;
 184                 unsigned long long start, size;
 185                 char *k = strchr(str, ',');
 186 
 187                 if (k)
 188                         *k++ = 0;
 189 
 190                 rc = parse_memmap(str, &start, &size);
 191                 if (rc < 0)
 192                         break;
 193                 str = k;
 194 
 195                 if (start == 0) {
 196                         /* Store the specified memory limit if size > 0 */
 197                         if (size > 0)
 198                                 mem_limit = size;
 199 
 200                         continue;
 201                 }
 202 
 203                 mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].start = start;
 204                 mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].size = size;
 205                 i++;
 206         }
 207 
 208         /* More than 4 memmaps, fail kaslr */
 209         if ((i >= MAX_MEMMAP_REGIONS) && str)
 210                 memmap_too_large = true;
 211 }
 212 
 213 /* Store the number of 1GB huge pages which users specified: */
 214 static unsigned long max_gb_huge_pages;
 215 
 216 static void parse_gb_huge_pages(char *param, char *val)
 217 {
 218         static bool gbpage_sz;
 219         char *p;
 220 
 221         if (!strcmp(param, "hugepagesz")) {
 222                 p = val;
 223                 if (memparse(p, &p) != PUD_SIZE) {
 224                         gbpage_sz = false;
 225                         return;
 226                 }
 227 
 228                 if (gbpage_sz)
 229                         warn("Repeatedly set hugeTLB page size of 1G!\n");
 230                 gbpage_sz = true;
 231                 return;
 232         }
 233 
 234         if (!strcmp(param, "hugepages") && gbpage_sz) {
 235                 p = val;
 236                 max_gb_huge_pages = simple_strtoull(p, &p, 0);
 237                 return;
 238         }
 239 }
 240 
 241 
 242 static void handle_mem_options(void)
 243 {
 244         char *args = (char *)get_cmd_line_ptr();
 245         size_t len = strlen((char *)args);
 246         char *tmp_cmdline;
 247         char *param, *val;
 248         u64 mem_size;
 249 
 250         if (!strstr(args, "memmap=") && !strstr(args, "mem=") &&
 251                 !strstr(args, "hugepages"))
 252                 return;
 253 
 254         tmp_cmdline = malloc(len + 1);
 255         if (!tmp_cmdline)
 256                 error("Failed to allocate space for tmp_cmdline");
 257 
 258         memcpy(tmp_cmdline, args, len);
 259         tmp_cmdline[len] = 0;
 260         args = tmp_cmdline;
 261 
 262         /* Chew leading spaces */
 263         args = skip_spaces(args);
 264 
 265         while (*args) {
 266                 args = next_arg(args, &param, &val);
 267                 /* Stop at -- */
 268                 if (!val && strcmp(param, "--") == 0) {
 269                         warn("Only '--' specified in cmdline");
 270                         goto out;
 271                 }
 272 
 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")) {
 278                         char *p = val;
 279 
 280                         if (!strcmp(p, "nopentium"))
 281                                 continue;
 282                         mem_size = memparse(p, &p);
 283                         if (mem_size == 0)
 284                                 goto out;
 285 
 286                         mem_limit = mem_size;
 287                 }
 288         }
 289 
 290 out:
 291         free(tmp_cmdline);
 292         return;
 293 }
 294 
 295 /*
 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.
 303  *
 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.
 307  *
 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.
 312  *
 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
 315  * easily.
 316  *
 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.
 319  *
 320  * The following conditions are already enforced by the image layouts and
 321  * associated code:
 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
 326  *
 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.)
 332  *
 333  * The above conditions can be illustrated by a diagram:
 334  *
 335  * 0   output            input            input+input_size    output+init_size
 336  * |     |                 |                             |             |
 337  * |     |                 |                             |             |
 338  * |-----|--------|--------|--------------|-----------|--|-------------|
 339  *                |                       |           |
 340  *                |                       |           |
 341  * output+init_size-ZO_INIT_SIZE  output+output_size  output+kernel_total_size
 342  *
 343  * [output, output+init_size) is the entire memory range used for
 344  * extracting the compressed image.
 345  *
 346  * [output, output+kernel_total_size) is the range needed for the
 347  * uncompressed kernel (VO) and its run size (bss, brk, etc).
 348  *
 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.
 352  *
 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.)
 356  *
 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.
 360  *
 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.
 364  *
 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.
 368  */
 369 static void mem_avoid_init(unsigned long input, unsigned long input_size,
 370                            unsigned long output)
 371 {
 372         unsigned long init_size = boot_params->hdr.init_size;
 373         u64 initrd_start, initrd_size;
 374         u64 cmd_line, cmd_line_size;
 375         char *ptr;
 376 
 377         /*
 378          * Avoid the region that is unsafe to overlap during
 379          * decompression.
 380          */
 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);
 385 
 386         /* Avoid initrd. */
 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. */
 394 
 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++];)
 401                 ;
 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);
 406 
 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);
 412 
 413         /* We don't need to set a mapping for setup_data. */
 414 
 415         /* Mark the memmap regions we need to avoid */
 416         handle_mem_options();
 417 
 418         /* Enumerate the immovable memory regions */
 419         num_immovable_mem = count_immovable_mem_regions();
 420 
 421 #ifdef CONFIG_X86_VERBOSE_BOOTUP
 422         /* Make sure video RAM can be used. */
 423         add_identity_map(0, PMD_SIZE);
 424 #endif
 425 }
 426 
 427 /*
 428  * Does this memory vector overlap a known avoided area? If so, record the
 429  * overlap region with the lowest address.
 430  */
 431 static bool mem_avoid_overlap(struct mem_vector *img,
 432                               struct mem_vector *overlap)
 433 {
 434         int i;
 435         struct setup_data *ptr;
 436         unsigned long earliest = img->start + img->size;
 437         bool is_overlapping = false;
 438 
 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;
 445                 }
 446         }
 447 
 448         /* Avoid all entries in the setup_data linked list. */
 449         ptr = (struct setup_data *)(unsigned long)boot_params->hdr.setup_data;
 450         while (ptr) {
 451                 struct mem_vector avoid;
 452 
 453                 avoid.start = (unsigned long)ptr;
 454                 avoid.size = sizeof(*ptr) + ptr->len;
 455 
 456                 if (mem_overlaps(img, &avoid) && (avoid.start < earliest)) {
 457                         *overlap = avoid;
 458                         earliest = overlap->start;
 459                         is_overlapping = true;
 460                 }
 461 
 462                 ptr = (struct setup_data *)(unsigned long)ptr->next;
 463         }
 464 
 465         return is_overlapping;
 466 }
 467 
 468 struct slot_area {
 469         unsigned long addr;
 470         int num;
 471 };
 472 
 473 #define MAX_SLOT_AREA 100
 474 
 475 static struct slot_area slot_areas[MAX_SLOT_AREA];
 476 
 477 static unsigned long slot_max;
 478 
 479 static unsigned long slot_area_index;
 480 
 481 static void store_slot_info(struct mem_vector *region, unsigned long image_size)
 482 {
 483         struct slot_area slot_area;
 484 
 485         if (slot_area_index == MAX_SLOT_AREA)
 486                 return;
 487 
 488         slot_area.addr = region->start;
 489         slot_area.num = (region->size - image_size) /
 490                         CONFIG_PHYSICAL_ALIGN + 1;
 491 
 492         if (slot_area.num > 0) {
 493                 slot_areas[slot_area_index++] = slot_area;
 494                 slot_max += slot_area.num;
 495         }
 496 }
 497 
 498 /*
 499  * Skip as many 1GB huge pages as possible in the passed region
 500  * according to the number which users specified:
 501  */
 502 static void
 503 process_gb_huge_pages(struct mem_vector *region, unsigned long image_size)
 504 {
 505         unsigned long addr, size = 0;
 506         struct mem_vector tmp;
 507         int i = 0;
 508 
 509         if (!max_gb_huge_pages) {
 510                 store_slot_info(region, image_size);
 511                 return;
 512         }
 513 
 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);
 518 
 519         /* Check how many 1GB huge pages can be filtered out: */
 520         while (size > PUD_SIZE && max_gb_huge_pages) {
 521                 size -= PUD_SIZE;
 522                 max_gb_huge_pages--;
 523                 i++;
 524         }
 525 
 526         /* No good 1GB huge pages found: */
 527         if (!i) {
 528                 store_slot_info(region, image_size);
 529                 return;
 530         }
 531 
 532         /*
 533          * Skip those 'i'*1GB good huge pages, and continue checking and
 534          * processing the remaining head or tail part of the passed region
 535          * if available.
 536          */
 537 
 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);
 542         }
 543 
 544         size  = region->size - (addr - region->start) - i * PUD_SIZE;
 545         if (size >= image_size) {
 546                 tmp.start = addr + i * PUD_SIZE;
 547                 tmp.size = size;
 548                 store_slot_info(&tmp, image_size);
 549         }
 550 }
 551 
 552 static unsigned long slots_fetch_random(void)
 553 {
 554         unsigned long slot;
 555         int i;
 556 
 557         /* Handle case of no slots stored. */
 558         if (slot_max == 0)
 559                 return 0;
 560 
 561         slot = kaslr_get_random_long("Physical") % slot_max;
 562 
 563         for (i = 0; i < slot_area_index; i++) {
 564                 if (slot >= slot_areas[i].num) {
 565                         slot -= slot_areas[i].num;
 566                         continue;
 567                 }
 568                 return slot_areas[i].addr + slot * CONFIG_PHYSICAL_ALIGN;
 569         }
 570 
 571         if (i == slot_area_index)
 572                 debug_putstr("slots_fetch_random() failed!?\n");
 573         return 0;
 574 }
 575 
 576 static void __process_mem_region(struct mem_vector *entry,
 577                                  unsigned long minimum,
 578                                  unsigned long image_size)
 579 {
 580         struct mem_vector region, overlap;
 581         unsigned long start_orig, end;
 582         struct mem_vector cur_entry;
 583 
 584         /* On 32-bit, ignore entries entirely above our maximum. */
 585         if (IS_ENABLED(CONFIG_X86_32) && entry->start >= KERNEL_IMAGE_SIZE)
 586                 return;
 587 
 588         /* Ignore entries entirely below our minimum. */
 589         if (entry->start + entry->size < minimum)
 590                 return;
 591 
 592         /* Ignore entries above memory limit */
 593         end = min(entry->size + entry->start, mem_limit);
 594         if (entry->start >= end)
 595                 return;
 596         cur_entry.start = entry->start;
 597         cur_entry.size = end - entry->start;
 598 
 599         region.start = cur_entry.start;
 600         region.size = cur_entry.size;
 601 
 602         /* Give up if slot area array is full. */
 603         while (slot_area_index < MAX_SLOT_AREA) {
 604                 start_orig = region.start;
 605 
 606                 /* Potentially raise address to minimum location. */
 607                 if (region.start < minimum)
 608                         region.start = minimum;
 609 
 610                 /* Potentially raise address to meet alignment needs. */
 611                 region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);
 612 
 613                 /* Did we raise the address above the passed in memory entry? */
 614                 if (region.start > cur_entry.start + cur_entry.size)
 615                         return;
 616 
 617                 /* Reduce size by any delta from the original address. */
 618                 region.size -= region.start - start_orig;
 619 
 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;
 624 
 625                 /* Return if region can't contain decompressed kernel */
 626                 if (region.size < image_size)
 627                         return;
 628 
 629                 /* If nothing overlaps, store the region and return. */
 630                 if (!mem_avoid_overlap(&region, &overlap)) {
 631                         process_gb_huge_pages(&region, image_size);
 632                         return;
 633                 }
 634 
 635                 /* Store beginning of region if holds at least image_size. */
 636                 if (overlap.start > region.start + image_size) {
 637                         struct mem_vector beginning;
 638 
 639                         beginning.start = region.start;
 640                         beginning.size = overlap.start - region.start;
 641                         process_gb_huge_pages(&beginning, image_size);
 642                 }
 643 
 644                 /* Return if overlap extends to or past end of region. */
 645                 if (overlap.start + overlap.size >= region.start + region.size)
 646                         return;
 647 
 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;
 651         }
 652 }
 653 
 654 static bool process_mem_region(struct mem_vector *region,
 655                                unsigned long long minimum,
 656                                unsigned long long image_size)
 657 {
 658         int i;
 659         /*
 660          * If no immovable memory found, or MEMORY_HOTREMOVE disabled,
 661          * use @region directly.
 662          */
 663         if (!num_immovable_mem) {
 664                 __process_mem_region(region, minimum, image_size);
 665 
 666                 if (slot_area_index == MAX_SLOT_AREA) {
 667                         debug_putstr("Aborted e820/efi memmap scan (slot_areas full)!\n");
 668                         return 1;
 669                 }
 670                 return 0;
 671         }
 672 
 673 #if defined(CONFIG_MEMORY_HOTREMOVE) && defined(CONFIG_ACPI)
 674         /*
 675          * If immovable memory found, filter the intersection between
 676          * immovable memory and @region.
 677          */
 678         for (i = 0; i < num_immovable_mem; i++) {
 679                 unsigned long long start, end, entry_end, region_end;
 680                 struct mem_vector entry;
 681 
 682                 if (!mem_overlaps(region, &immovable_mem[i]))
 683                         continue;
 684 
 685                 start = immovable_mem[i].start;
 686                 end = start + immovable_mem[i].size;
 687                 region_end = region->start + region->size;
 688 
 689                 entry.start = clamp(region->start, start, end);
 690                 entry_end = clamp(region_end, start, end);
 691                 entry.size = entry_end - entry.start;
 692 
 693                 __process_mem_region(&entry, minimum, image_size);
 694 
 695                 if (slot_area_index == MAX_SLOT_AREA) {
 696                         debug_putstr("Aborted e820/efi memmap scan when walking immovable regions(slot_areas full)!\n");
 697                         return 1;
 698                 }
 699         }
 700 #endif
 701         return 0;
 702 }
 703 
 704 #ifdef CONFIG_EFI
 705 /*
 706  * Returns true if mirror region found (and must have been processed
 707  * for slots adding)
 708  */
 709 static bool
 710 process_efi_entries(unsigned long minimum, unsigned long image_size)
 711 {
 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;
 716         unsigned long pmap;
 717         char *signature;
 718         u32 nr_desc;
 719         int i;
 720 
 721         signature = (char *)&e->efi_loader_signature;
 722         if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
 723             strncmp(signature, EFI64_LOADER_SIGNATURE, 4))
 724                 return false;
 725 
 726 #ifdef CONFIG_X86_32
 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");
 730                 return false;
 731         }
 732         pmap =  e->efi_memmap;
 733 #else
 734         pmap = (e->efi_memmap | ((__u64)e->efi_memmap_hi << 32));
 735 #endif
 736 
 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;
 742                         break;
 743                 }
 744         }
 745 
 746         for (i = 0; i < nr_desc; i++) {
 747                 md = efi_early_memdesc_ptr(pmap, e->efi_memdesc_size, i);
 748 
 749                 /*
 750                  * Here we are more conservative in picking free memory than
 751                  * the EFI spec allows:
 752                  *
 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
 756                  * to crashes.
 757                  *
 758                  * Only EFI_CONVENTIONAL_MEMORY is guaranteed to be free.
 759                  */
 760                 if (md->type != EFI_CONVENTIONAL_MEMORY)
 761                         continue;
 762 
 763                 if (efi_mirror_found &&
 764                     !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
 765                         continue;
 766 
 767                 region.start = md->phys_addr;
 768                 region.size = md->num_pages << EFI_PAGE_SHIFT;
 769                 if (process_mem_region(&region, minimum, image_size))
 770                         break;
 771         }
 772         return true;
 773 }
 774 #else
 775 static inline bool
 776 process_efi_entries(unsigned long minimum, unsigned long image_size)
 777 {
 778         return false;
 779 }
 780 #endif
 781 
 782 static void process_e820_entries(unsigned long minimum,
 783                                  unsigned long image_size)
 784 {
 785         int i;
 786         struct mem_vector region;
 787         struct boot_e820_entry *entry;
 788 
 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)
 794                         continue;
 795                 region.start = entry->addr;
 796                 region.size = entry->size;
 797                 if (process_mem_region(&region, minimum, image_size))
 798                         break;
 799         }
 800 }
 801 
 802 static unsigned long find_random_phys_addr(unsigned long minimum,
 803                                            unsigned long image_size)
 804 {
 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");
 808                 return 0;
 809         }
 810 
 811         /* Make sure minimum is aligned. */
 812         minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
 813 
 814         if (process_efi_entries(minimum, image_size))
 815                 return slots_fetch_random();
 816 
 817         process_e820_entries(minimum, image_size);
 818         return slots_fetch_random();
 819 }
 820 
 821 static unsigned long find_random_virt_addr(unsigned long minimum,
 822                                            unsigned long image_size)
 823 {
 824         unsigned long slots, random_addr;
 825 
 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);
 830 
 831         /*
 832          * There are how many CONFIG_PHYSICAL_ALIGN-sized slots
 833          * that can hold image_size within the range of minimum to
 834          * KERNEL_IMAGE_SIZE?
 835          */
 836         slots = (KERNEL_IMAGE_SIZE - minimum - image_size) /
 837                  CONFIG_PHYSICAL_ALIGN + 1;
 838 
 839         random_addr = kaslr_get_random_long("Virtual") % slots;
 840 
 841         return random_addr * CONFIG_PHYSICAL_ALIGN + minimum;
 842 }
 843 
 844 /*
 845  * Since this function examines addresses much more numerically,
 846  * it takes the input and output pointers as 'unsigned long'.
 847  */
 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)
 853 {
 854         unsigned long random_addr, min_addr;
 855 
 856         if (cmdline_find_option_bool("nokaslr")) {
 857                 warn("KASLR disabled: 'nokaslr' on cmdline.");
 858                 return;
 859         }
 860 
 861 #ifdef CONFIG_X86_5LEVEL
 862         if (__read_cr4() & X86_CR4_LA57) {
 863                 __pgtable_l5_enabled = 1;
 864                 pgdir_shift = 48;
 865                 ptrs_per_p4d = 512;
 866         }
 867 #endif
 868 
 869         boot_params->hdr.loadflags |= KASLR_FLAG;
 870 
 871         /* Prepare to add new identity pagetables on demand. */
 872         initialize_identity_maps();
 873 
 874         /* Record the various known unsafe memory ranges. */
 875         mem_avoid_init(input, input_size, *output);
 876 
 877         /*
 878          * Low end of the randomization range should be the
 879          * smaller of 512M or the initial kernel image
 880          * location:
 881          */
 882         min_addr = min(*output, 512UL << 20);
 883 
 884         /* Walk available memory entries to find a random address. */
 885         random_addr = find_random_phys_addr(min_addr, output_size);
 886         if (!random_addr) {
 887                 warn("Physical KASLR disabled: no suitable memory region!");
 888         } else {
 889                 /* Update the new physical address location. */
 890                 if (*output != random_addr) {
 891                         add_identity_map(random_addr, output_size);
 892                         *output = random_addr;
 893                 }
 894 
 895                 /*
 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"
 900                  * case.
 901                  */
 902                 finalize_identity_maps();
 903         }
 904 
 905 
 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;
 910 }