]>
git.proxmox.com Git - mirror_ubuntu-kernels.git/blob - arch/x86/boot/compressed/kaslr.c
1 // SPDX-License-Identifier: GPL-2.0
5 * This contains the routines needed to generate a reasonable level of
6 * entropy to choose a randomized kernel base address offset in support
7 * of Kernel Address Space Layout Randomization (KASLR). Additionally
8 * handles walking the physical memory maps (and tracking memory regions
9 * to avoid) in order to select a physical memory location that can
10 * contain the entire properly aligned running kernel image.
15 * isspace() in linux/ctype.h is expected by next_args() to filter
16 * out "space/lf/tab". While boot/ctype.h conflicts with linux/ctype.h,
17 * since isdigit() is implemented in both of them. Hence disable it
23 * _ctype[] in lib/ctype.c is needed by isspace() of linux/ctype.h.
24 * While both lib/ctype.c and lib/cmdline.c will bring EXPORT_SYMBOL
25 * which is meaningless and will cause compiling error in some cases.
26 * So do not include linux/export.h and define EXPORT_SYMBOL(sym)
29 #define _LINUX_EXPORT_H
30 #define EXPORT_SYMBOL(sym)
34 #include "../string.h"
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>
45 /* Macros used by the included decompressor code below. */
47 #include <linux/decompress/mm.h>
49 extern unsigned long get_cmd_line_ptr(void);
51 /* Simplified build-specific string for starting entropy. */
52 static const char build_str
[] = UTS_RELEASE
" (" LINUX_COMPILE_BY
"@"
53 LINUX_COMPILE_HOST
") (" LINUX_COMPILER
") " UTS_VERSION
;
55 static unsigned long rotate_xor(unsigned long hash
, const void *area
,
59 unsigned long *ptr
= (unsigned long *)area
;
61 for (i
= 0; i
< size
/ sizeof(hash
); i
++) {
62 /* Rotate by odd number of bits and XOR. */
63 hash
= (hash
<< ((sizeof(hash
) * 8) - 7)) | (hash
>> 7);
70 /* Attempt to create a simple but unpredictable starting entropy. */
71 static unsigned long get_boot_seed(void)
73 unsigned long hash
= 0;
75 hash
= rotate_xor(hash
, build_str
, sizeof(build_str
));
76 hash
= rotate_xor(hash
, boot_params
, sizeof(*boot_params
));
81 #define KASLR_COMPRESSED_BOOT
82 #include "../../lib/kaslr.c"
85 unsigned long long start
;
86 unsigned long long size
;
89 /* Only supporting at most 4 unusable memmap regions with kaslr */
90 #define MAX_MEMMAP_REGIONS 4
92 static bool memmap_too_large
;
95 /* Store memory limit specified by "mem=nn[KMG]" or "memmap=nn[KMG]" */
96 unsigned long long mem_limit
= ULLONG_MAX
;
99 enum mem_avoid_index
{
100 MEM_AVOID_ZO_RANGE
= 0,
103 MEM_AVOID_BOOTPARAMS
,
104 MEM_AVOID_MEMMAP_BEGIN
,
105 MEM_AVOID_MEMMAP_END
= MEM_AVOID_MEMMAP_BEGIN
+ MAX_MEMMAP_REGIONS
- 1,
109 static struct mem_vector mem_avoid
[MEM_AVOID_MAX
];
111 static bool mem_overlaps(struct mem_vector
*one
, struct mem_vector
*two
)
113 /* Item one is entirely before item two. */
114 if (one
->start
+ one
->size
<= two
->start
)
116 /* Item one is entirely after item two. */
117 if (one
->start
>= two
->start
+ two
->size
)
122 char *skip_spaces(const char *str
)
124 while (isspace(*str
))
128 #include "../../../../lib/ctype.c"
129 #include "../../../../lib/cmdline.c"
132 parse_memmap(char *p
, unsigned long long *start
, unsigned long long *size
)
139 /* We don't care about this option here */
140 if (!strncmp(p
, "exactmap", 8))
144 *size
= memparse(p
, &p
);
152 *start
= memparse(p
+ 1, &p
);
155 /* memmap=nn@ss specifies usable region, should be skipped */
160 * If w/o offset, only size specified, memmap=nn[KMG] has the
161 * same behaviour as mem=nn[KMG]. It limits the max address
162 * system can use. Region above the limit should be avoided.
171 static void mem_avoid_memmap(char *str
)
176 if (i
>= MAX_MEMMAP_REGIONS
)
179 while (str
&& (i
< MAX_MEMMAP_REGIONS
)) {
181 unsigned long long start
, size
;
182 char *k
= strchr(str
, ',');
187 rc
= parse_memmap(str
, &start
, &size
);
193 /* Store the specified memory limit if size > 0 */
200 mem_avoid
[MEM_AVOID_MEMMAP_BEGIN
+ i
].start
= start
;
201 mem_avoid
[MEM_AVOID_MEMMAP_BEGIN
+ i
].size
= size
;
205 /* More than 4 memmaps, fail kaslr */
206 if ((i
>= MAX_MEMMAP_REGIONS
) && str
)
207 memmap_too_large
= true;
210 static int handle_mem_memmap(void)
212 char *args
= (char *)get_cmd_line_ptr();
213 size_t len
= strlen((char *)args
);
218 if (!strstr(args
, "memmap=") && !strstr(args
, "mem="))
221 tmp_cmdline
= malloc(len
+ 1);
223 error("Failed to allocate space for tmp_cmdline");
225 memcpy(tmp_cmdline
, args
, len
);
226 tmp_cmdline
[len
] = 0;
229 /* Chew leading spaces */
230 args
= skip_spaces(args
);
233 args
= next_arg(args
, ¶m
, &val
);
235 if (!val
&& strcmp(param
, "--") == 0) {
236 warn("Only '--' specified in cmdline");
241 if (!strcmp(param
, "memmap")) {
242 mem_avoid_memmap(val
);
243 } else if (!strcmp(param
, "mem")) {
246 if (!strcmp(p
, "nopentium"))
248 mem_size
= memparse(p
, &p
);
253 mem_limit
= mem_size
;
262 * In theory, KASLR can put the kernel anywhere in the range of [16M, 64T).
263 * The mem_avoid array is used to store the ranges that need to be avoided
264 * when KASLR searches for an appropriate random address. We must avoid any
265 * regions that are unsafe to overlap with during decompression, and other
266 * things like the initrd, cmdline and boot_params. This comment seeks to
267 * explain mem_avoid as clearly as possible since incorrect mem_avoid
268 * memory ranges lead to really hard to debug boot failures.
270 * The initrd, cmdline, and boot_params are trivial to identify for
271 * avoiding. They are MEM_AVOID_INITRD, MEM_AVOID_CMDLINE, and
272 * MEM_AVOID_BOOTPARAMS respectively below.
274 * What is not obvious how to avoid is the range of memory that is used
275 * during decompression (MEM_AVOID_ZO_RANGE below). This range must cover
276 * the compressed kernel (ZO) and its run space, which is used to extract
277 * the uncompressed kernel (VO) and relocs.
279 * ZO's full run size sits against the end of the decompression buffer, so
280 * we can calculate where text, data, bss, etc of ZO are positioned more
283 * For additional background, the decompression calculations can be found
284 * in header.S, and the memory diagram is based on the one found in misc.c.
286 * The following conditions are already enforced by the image layouts and
288 * - input + input_size >= output + output_size
289 * - kernel_total_size <= init_size
290 * - kernel_total_size <= output_size (see Note below)
291 * - output + init_size >= output + output_size
293 * (Note that kernel_total_size and output_size have no fundamental
294 * relationship, but output_size is passed to choose_random_location
295 * as a maximum of the two. The diagram is showing a case where
296 * kernel_total_size is larger than output_size, but this case is
297 * handled by bumping output_size.)
299 * The above conditions can be illustrated by a diagram:
301 * 0 output input input+input_size output+init_size
304 * |-----|--------|--------|--------------|-----------|--|-------------|
307 * output+init_size-ZO_INIT_SIZE output+output_size output+kernel_total_size
309 * [output, output+init_size) is the entire memory range used for
310 * extracting the compressed image.
312 * [output, output+kernel_total_size) is the range needed for the
313 * uncompressed kernel (VO) and its run size (bss, brk, etc).
315 * [output, output+output_size) is VO plus relocs (i.e. the entire
316 * uncompressed payload contained by ZO). This is the area of the buffer
317 * written to during decompression.
319 * [output+init_size-ZO_INIT_SIZE, output+init_size) is the worst-case
320 * range of the copied ZO and decompression code. (i.e. the range
321 * covered backwards of size ZO_INIT_SIZE, starting from output+init_size.)
323 * [input, input+input_size) is the original copied compressed image (ZO)
324 * (i.e. it does not include its run size). This range must be avoided
325 * because it contains the data used for decompression.
327 * [input+input_size, output+init_size) is [_text, _end) for ZO. This
328 * range includes ZO's heap and stack, and must be avoided since it
329 * performs the decompression.
331 * Since the above two ranges need to be avoided and they are adjacent,
332 * they can be merged, resulting in: [input, output+init_size) which
333 * becomes the MEM_AVOID_ZO_RANGE below.
335 static void mem_avoid_init(unsigned long input
, unsigned long input_size
,
336 unsigned long output
)
338 unsigned long init_size
= boot_params
->hdr
.init_size
;
339 u64 initrd_start
, initrd_size
;
340 u64 cmd_line
, cmd_line_size
;
344 * Avoid the region that is unsafe to overlap during
347 mem_avoid
[MEM_AVOID_ZO_RANGE
].start
= input
;
348 mem_avoid
[MEM_AVOID_ZO_RANGE
].size
= (output
+ init_size
) - input
;
349 add_identity_map(mem_avoid
[MEM_AVOID_ZO_RANGE
].start
,
350 mem_avoid
[MEM_AVOID_ZO_RANGE
].size
);
353 initrd_start
= (u64
)boot_params
->ext_ramdisk_image
<< 32;
354 initrd_start
|= boot_params
->hdr
.ramdisk_image
;
355 initrd_size
= (u64
)boot_params
->ext_ramdisk_size
<< 32;
356 initrd_size
|= boot_params
->hdr
.ramdisk_size
;
357 mem_avoid
[MEM_AVOID_INITRD
].start
= initrd_start
;
358 mem_avoid
[MEM_AVOID_INITRD
].size
= initrd_size
;
359 /* No need to set mapping for initrd, it will be handled in VO. */
361 /* Avoid kernel command line. */
362 cmd_line
= (u64
)boot_params
->ext_cmd_line_ptr
<< 32;
363 cmd_line
|= boot_params
->hdr
.cmd_line_ptr
;
364 /* Calculate size of cmd_line. */
365 ptr
= (char *)(unsigned long)cmd_line
;
366 for (cmd_line_size
= 0; ptr
[cmd_line_size
++]; )
368 mem_avoid
[MEM_AVOID_CMDLINE
].start
= cmd_line
;
369 mem_avoid
[MEM_AVOID_CMDLINE
].size
= cmd_line_size
;
370 add_identity_map(mem_avoid
[MEM_AVOID_CMDLINE
].start
,
371 mem_avoid
[MEM_AVOID_CMDLINE
].size
);
373 /* Avoid boot parameters. */
374 mem_avoid
[MEM_AVOID_BOOTPARAMS
].start
= (unsigned long)boot_params
;
375 mem_avoid
[MEM_AVOID_BOOTPARAMS
].size
= sizeof(*boot_params
);
376 add_identity_map(mem_avoid
[MEM_AVOID_BOOTPARAMS
].start
,
377 mem_avoid
[MEM_AVOID_BOOTPARAMS
].size
);
379 /* We don't need to set a mapping for setup_data. */
381 /* Mark the memmap regions we need to avoid */
384 #ifdef CONFIG_X86_VERBOSE_BOOTUP
385 /* Make sure video RAM can be used. */
386 add_identity_map(0, PMD_SIZE
);
391 * Does this memory vector overlap a known avoided area? If so, record the
392 * overlap region with the lowest address.
394 static bool mem_avoid_overlap(struct mem_vector
*img
,
395 struct mem_vector
*overlap
)
398 struct setup_data
*ptr
;
399 unsigned long earliest
= img
->start
+ img
->size
;
400 bool is_overlapping
= false;
402 for (i
= 0; i
< MEM_AVOID_MAX
; i
++) {
403 if (mem_overlaps(img
, &mem_avoid
[i
]) &&
404 mem_avoid
[i
].start
< earliest
) {
405 *overlap
= mem_avoid
[i
];
406 earliest
= overlap
->start
;
407 is_overlapping
= true;
411 /* Avoid all entries in the setup_data linked list. */
412 ptr
= (struct setup_data
*)(unsigned long)boot_params
->hdr
.setup_data
;
414 struct mem_vector avoid
;
416 avoid
.start
= (unsigned long)ptr
;
417 avoid
.size
= sizeof(*ptr
) + ptr
->len
;
419 if (mem_overlaps(img
, &avoid
) && (avoid
.start
< earliest
)) {
421 earliest
= overlap
->start
;
422 is_overlapping
= true;
425 ptr
= (struct setup_data
*)(unsigned long)ptr
->next
;
428 return is_overlapping
;
436 #define MAX_SLOT_AREA 100
438 static struct slot_area slot_areas
[MAX_SLOT_AREA
];
440 static unsigned long slot_max
;
442 static unsigned long slot_area_index
;
444 static void store_slot_info(struct mem_vector
*region
, unsigned long image_size
)
446 struct slot_area slot_area
;
448 if (slot_area_index
== MAX_SLOT_AREA
)
451 slot_area
.addr
= region
->start
;
452 slot_area
.num
= (region
->size
- image_size
) /
453 CONFIG_PHYSICAL_ALIGN
+ 1;
455 if (slot_area
.num
> 0) {
456 slot_areas
[slot_area_index
++] = slot_area
;
457 slot_max
+= slot_area
.num
;
461 static unsigned long slots_fetch_random(void)
466 /* Handle case of no slots stored. */
470 slot
= kaslr_get_random_long("Physical") % slot_max
;
472 for (i
= 0; i
< slot_area_index
; i
++) {
473 if (slot
>= slot_areas
[i
].num
) {
474 slot
-= slot_areas
[i
].num
;
477 return slot_areas
[i
].addr
+ slot
* CONFIG_PHYSICAL_ALIGN
;
480 if (i
== slot_area_index
)
481 debug_putstr("slots_fetch_random() failed!?\n");
485 static void process_mem_region(struct mem_vector
*entry
,
486 unsigned long minimum
,
487 unsigned long image_size
)
489 struct mem_vector region
, overlap
;
490 struct slot_area slot_area
;
491 unsigned long start_orig
, end
;
492 struct mem_vector cur_entry
;
494 /* On 32-bit, ignore entries entirely above our maximum. */
495 if (IS_ENABLED(CONFIG_X86_32
) && entry
->start
>= KERNEL_IMAGE_SIZE
)
498 /* Ignore entries entirely below our minimum. */
499 if (entry
->start
+ entry
->size
< minimum
)
502 /* Ignore entries above memory limit */
503 end
= min(entry
->size
+ entry
->start
, mem_limit
);
504 if (entry
->start
>= end
)
506 cur_entry
.start
= entry
->start
;
507 cur_entry
.size
= end
- entry
->start
;
509 region
.start
= cur_entry
.start
;
510 region
.size
= cur_entry
.size
;
512 /* Give up if slot area array is full. */
513 while (slot_area_index
< MAX_SLOT_AREA
) {
514 start_orig
= region
.start
;
516 /* Potentially raise address to minimum location. */
517 if (region
.start
< minimum
)
518 region
.start
= minimum
;
520 /* Potentially raise address to meet alignment needs. */
521 region
.start
= ALIGN(region
.start
, CONFIG_PHYSICAL_ALIGN
);
523 /* Did we raise the address above the passed in memory entry? */
524 if (region
.start
> cur_entry
.start
+ cur_entry
.size
)
527 /* Reduce size by any delta from the original address. */
528 region
.size
-= region
.start
- start_orig
;
530 /* On 32-bit, reduce region size to fit within max size. */
531 if (IS_ENABLED(CONFIG_X86_32
) &&
532 region
.start
+ region
.size
> KERNEL_IMAGE_SIZE
)
533 region
.size
= KERNEL_IMAGE_SIZE
- region
.start
;
535 /* Return if region can't contain decompressed kernel */
536 if (region
.size
< image_size
)
539 /* If nothing overlaps, store the region and return. */
540 if (!mem_avoid_overlap(®ion
, &overlap
)) {
541 store_slot_info(®ion
, image_size
);
545 /* Store beginning of region if holds at least image_size. */
546 if (overlap
.start
> region
.start
+ image_size
) {
547 struct mem_vector beginning
;
549 beginning
.start
= region
.start
;
550 beginning
.size
= overlap
.start
- region
.start
;
551 store_slot_info(&beginning
, image_size
);
554 /* Return if overlap extends to or past end of region. */
555 if (overlap
.start
+ overlap
.size
>= region
.start
+ region
.size
)
558 /* Clip off the overlapping region and start over. */
559 region
.size
-= overlap
.start
- region
.start
+ overlap
.size
;
560 region
.start
= overlap
.start
+ overlap
.size
;
566 * Returns true if mirror region found (and must have been processed
570 process_efi_entries(unsigned long minimum
, unsigned long image_size
)
572 struct efi_info
*e
= &boot_params
->efi_info
;
573 bool efi_mirror_found
= false;
574 struct mem_vector region
;
575 efi_memory_desc_t
*md
;
581 signature
= (char *)&e
->efi_loader_signature
;
582 if (strncmp(signature
, EFI32_LOADER_SIGNATURE
, 4) &&
583 strncmp(signature
, EFI64_LOADER_SIGNATURE
, 4))
587 /* Can't handle data above 4GB at this time */
588 if (e
->efi_memmap_hi
) {
589 warn("EFI memmap is above 4GB, can't be handled now on x86_32. EFI should be disabled.\n");
592 pmap
= e
->efi_memmap
;
594 pmap
= (e
->efi_memmap
| ((__u64
)e
->efi_memmap_hi
<< 32));
597 nr_desc
= e
->efi_memmap_size
/ e
->efi_memdesc_size
;
598 for (i
= 0; i
< nr_desc
; i
++) {
599 md
= efi_early_memdesc_ptr(pmap
, e
->efi_memdesc_size
, i
);
600 if (md
->attribute
& EFI_MEMORY_MORE_RELIABLE
) {
601 efi_mirror_found
= true;
606 for (i
= 0; i
< nr_desc
; i
++) {
607 md
= efi_early_memdesc_ptr(pmap
, e
->efi_memdesc_size
, i
);
610 * Here we are more conservative in picking free memory than
611 * the EFI spec allows:
613 * According to the spec, EFI_BOOT_SERVICES_{CODE|DATA} are also
614 * free memory and thus available to place the kernel image into,
615 * but in practice there's firmware where using that memory leads
618 * Only EFI_CONVENTIONAL_MEMORY is guaranteed to be free.
620 if (md
->type
!= EFI_CONVENTIONAL_MEMORY
)
623 if (efi_mirror_found
&&
624 !(md
->attribute
& EFI_MEMORY_MORE_RELIABLE
))
627 region
.start
= md
->phys_addr
;
628 region
.size
= md
->num_pages
<< EFI_PAGE_SHIFT
;
629 process_mem_region(®ion
, minimum
, image_size
);
630 if (slot_area_index
== MAX_SLOT_AREA
) {
631 debug_putstr("Aborted EFI scan (slot_areas full)!\n");
639 process_efi_entries(unsigned long minimum
, unsigned long image_size
)
645 static void process_e820_entries(unsigned long minimum
,
646 unsigned long image_size
)
649 struct mem_vector region
;
650 struct boot_e820_entry
*entry
;
652 /* Verify potential e820 positions, appending to slots list. */
653 for (i
= 0; i
< boot_params
->e820_entries
; i
++) {
654 entry
= &boot_params
->e820_table
[i
];
655 /* Skip non-RAM entries. */
656 if (entry
->type
!= E820_TYPE_RAM
)
658 region
.start
= entry
->addr
;
659 region
.size
= entry
->size
;
660 process_mem_region(®ion
, minimum
, image_size
);
661 if (slot_area_index
== MAX_SLOT_AREA
) {
662 debug_putstr("Aborted e820 scan (slot_areas full)!\n");
668 static unsigned long find_random_phys_addr(unsigned long minimum
,
669 unsigned long image_size
)
671 /* Check if we had too many memmaps. */
672 if (memmap_too_large
) {
673 debug_putstr("Aborted memory entries scan (more than 4 memmap= args)!\n");
677 /* Make sure minimum is aligned. */
678 minimum
= ALIGN(minimum
, CONFIG_PHYSICAL_ALIGN
);
680 if (process_efi_entries(minimum
, image_size
))
681 return slots_fetch_random();
683 process_e820_entries(minimum
, image_size
);
684 return slots_fetch_random();
687 static unsigned long find_random_virt_addr(unsigned long minimum
,
688 unsigned long image_size
)
690 unsigned long slots
, random_addr
;
692 /* Make sure minimum is aligned. */
693 minimum
= ALIGN(minimum
, CONFIG_PHYSICAL_ALIGN
);
694 /* Align image_size for easy slot calculations. */
695 image_size
= ALIGN(image_size
, CONFIG_PHYSICAL_ALIGN
);
698 * There are how many CONFIG_PHYSICAL_ALIGN-sized slots
699 * that can hold image_size within the range of minimum to
702 slots
= (KERNEL_IMAGE_SIZE
- minimum
- image_size
) /
703 CONFIG_PHYSICAL_ALIGN
+ 1;
705 random_addr
= kaslr_get_random_long("Virtual") % slots
;
707 return random_addr
* CONFIG_PHYSICAL_ALIGN
+ minimum
;
711 * Since this function examines addresses much more numerically,
712 * it takes the input and output pointers as 'unsigned long'.
714 void choose_random_location(unsigned long input
,
715 unsigned long input_size
,
716 unsigned long *output
,
717 unsigned long output_size
,
718 unsigned long *virt_addr
)
720 unsigned long random_addr
, min_addr
;
722 if (cmdline_find_option_bool("nokaslr")) {
723 warn("KASLR disabled: 'nokaslr' on cmdline.");
727 boot_params
->hdr
.loadflags
|= KASLR_FLAG
;
729 /* Prepare to add new identity pagetables on demand. */
730 initialize_identity_maps();
732 /* Record the various known unsafe memory ranges. */
733 mem_avoid_init(input
, input_size
, *output
);
736 * Low end of the randomization range should be the
737 * smaller of 512M or the initial kernel image
740 min_addr
= min(*output
, 512UL << 20);
742 /* Walk available memory entries to find a random address. */
743 random_addr
= find_random_phys_addr(min_addr
, output_size
);
745 warn("Physical KASLR disabled: no suitable memory region!");
747 /* Update the new physical address location. */
748 if (*output
!= random_addr
) {
749 add_identity_map(random_addr
, output_size
);
750 *output
= random_addr
;
754 * This loads the identity mapping page table.
755 * This should only be done if a new physical address
756 * is found for the kernel, otherwise we should keep
757 * the old page table to make it be like the "nokaslr"
760 finalize_identity_maps();
764 /* Pick random virtual address starting from LOAD_PHYSICAL_ADDR. */
765 if (IS_ENABLED(CONFIG_X86_64
))
766 random_addr
= find_random_virt_addr(LOAD_PHYSICAL_ADDR
, output_size
);
767 *virt_addr
= random_addr
;