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, ¶m, &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(®ion, &overlap)) { 635 process_gb_huge_pages(®ion, 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(®ion, 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(®ion, 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