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TOMOYO Linux Cross Reference
Linux/arch/x86/boot/compressed/kaslr.c

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  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 }
911 

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