[mirror_ubuntu-focal-kernel.git] / arch / x86 / boot / compressed / kaslr.c

/*
 * kaslr.c
 *
 * This contains the routines needed to generate a reasonable level of
 * entropy to choose a randomized kernel base address offset in support
 * of Kernel Address Space Layout Randomization (KASLR). Additionally
 * handles walking the physical memory maps (and tracking memory regions
 * to avoid) in order to select a physical memory location that can
 * contain the entire properly aligned running kernel image.
 *
 */
#include "misc.h"
#include "error.h"

#include <asm/msr.h>
#include <asm/archrandom.h>
#include <asm/e820.h>

#include <generated/compile.h>
#include <linux/module.h>
#include <linux/uts.h>
#include <linux/utsname.h>
#include <generated/utsrelease.h>

/* Simplified build-specific string for starting entropy. */
static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
		LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;

#define I8254_PORT_CONTROL	0x43
#define I8254_PORT_COUNTER0	0x40
#define I8254_CMD_READBACK	0xC0
#define I8254_SELECT_COUNTER0	0x02
#define I8254_STATUS_NOTREADY	0x40
static inline u16 i8254(void)
{
	u16 status, timer;

	do {
		outb(I8254_PORT_CONTROL,
		     I8254_CMD_READBACK | I8254_SELECT_COUNTER0);
		status = inb(I8254_PORT_COUNTER0);
		timer  = inb(I8254_PORT_COUNTER0);
		timer |= inb(I8254_PORT_COUNTER0) << 8;
	} while (status & I8254_STATUS_NOTREADY);

	return timer;
}

static unsigned long rotate_xor(unsigned long hash, const void *area,
				size_t size)
{
	size_t i;
	unsigned long *ptr = (unsigned long *)area;

	for (i = 0; i < size / sizeof(hash); i++) {
		/* Rotate by odd number of bits and XOR. */
		hash = (hash << ((sizeof(hash) * 8) - 7)) | (hash >> 7);
		hash ^= ptr[i];
	}

	return hash;
}

/* Attempt to create a simple but unpredictable starting entropy. */
static unsigned long get_random_boot(void)
{
	unsigned long hash = 0;

	hash = rotate_xor(hash, build_str, sizeof(build_str));
	hash = rotate_xor(hash, boot_params, sizeof(*boot_params));

	return hash;
}

static unsigned long get_random_long(void)
{
#ifdef CONFIG_X86_64
	const unsigned long mix_const = 0x5d6008cbf3848dd3UL;
#else
	const unsigned long mix_const = 0x3f39e593UL;
#endif
	unsigned long raw, random = get_random_boot();
	bool use_i8254 = true;

	debug_putstr("KASLR using");

	if (has_cpuflag(X86_FEATURE_RDRAND)) {
		debug_putstr(" RDRAND");
		if (rdrand_long(&raw)) {
			random ^= raw;
			use_i8254 = false;
		}
	}

	if (has_cpuflag(X86_FEATURE_TSC)) {
		debug_putstr(" RDTSC");
		raw = rdtsc();

		random ^= raw;
		use_i8254 = false;
	}

	if (use_i8254) {
		debug_putstr(" i8254");
		random ^= i8254();
	}

	/* Circular multiply for better bit diffusion */
	asm("mul %3"
	    : "=a" (random), "=d" (raw)
	    : "a" (random), "rm" (mix_const));
	random += raw;

	debug_putstr("...\n");

	return random;
}

struct mem_vector {
	unsigned long start;
	unsigned long size;
};

enum mem_avoid_index {
	MEM_AVOID_ZO_RANGE = 0,
	MEM_AVOID_INITRD,
	MEM_AVOID_CMDLINE,
	MEM_AVOID_BOOTPARAMS,
	MEM_AVOID_MAX,
};

static struct mem_vector mem_avoid[MEM_AVOID_MAX];

static bool mem_contains(struct mem_vector *region, struct mem_vector *item)
{
	/* Item at least partially before region. */
	if (item->start < region->start)
		return false;
	/* Item at least partially after region. */
	if (item->start + item->size > region->start + region->size)
		return false;
	return true;
}

static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
{
	/* Item one is entirely before item two. */
	if (one->start + one->size <= two->start)
		return false;
	/* Item one is entirely after item two. */
	if (one->start >= two->start + two->size)
		return false;
	return true;
}

/*
 * In theory, KASLR can put the kernel anywhere in the range of [16M, 64T).
 * The mem_avoid array is used to store the ranges that need to be avoided
 * when KASLR searches for an appropriate random address. We must avoid any
 * regions that are unsafe to overlap with during decompression, and other
 * things like the initrd, cmdline and boot_params. This comment seeks to
 * explain mem_avoid as clearly as possible since incorrect mem_avoid
 * memory ranges lead to really hard to debug boot failures.
 *
 * The initrd, cmdline, and boot_params are trivial to identify for
 * avoiding. They are MEM_AVOID_INITRD, MEM_AVOID_CMDLINE, and
 * MEM_AVOID_BOOTPARAMS respectively below.
 *
 * What is not obvious how to avoid is the range of memory that is used
 * during decompression (MEM_AVOID_ZO_RANGE below). This range must cover
 * the compressed kernel (ZO) and its run space, which is used to extract
 * the uncompressed kernel (VO) and relocs.
 *
 * ZO's full run size sits against the end of the decompression buffer, so
 * we can calculate where text, data, bss, etc of ZO are positioned more
 * easily.
 *
 * For additional background, the decompression calculations can be found
 * in header.S, and the memory diagram is based on the one found in misc.c.
 *
 * The following conditions are already enforced by the image layouts and
 * associated code:
 *  - input + input_size >= output + output_size
 *  - kernel_total_size <= init_size
 *  - kernel_total_size <= output_size (see Note below)
 *  - output + init_size >= output + output_size
 *
 * (Note that kernel_total_size and output_size have no fundamental
 * relationship, but output_size is passed to choose_random_location
 * as a maximum of the two. The diagram is showing a case where
 * kernel_total_size is larger than output_size, but this case is
 * handled by bumping output_size.)
 *
 * The above conditions can be illustrated by a diagram:
 *
 * 0   output            input            input+input_size    output+init_size
 * |     |                 |                             |             |
 * |     |                 |                             |             |
 * |-----|--------|--------|--------------|-----------|--|-------------|
 *                |                       |           |
 *                |                       |           |
 * output+init_size-ZO_INIT_SIZE  output+output_size  output+kernel_total_size
 *
 * [output, output+init_size) is the entire memory range used for
 * extracting the compressed image.
 *
 * [output, output+kernel_total_size) is the range needed for the
 * uncompressed kernel (VO) and its run size (bss, brk, etc).
 *
 * [output, output+output_size) is VO plus relocs (i.e. the entire
 * uncompressed payload contained by ZO). This is the area of the buffer
 * written to during decompression.
 *
 * [output+init_size-ZO_INIT_SIZE, output+init_size) is the worst-case
 * range of the copied ZO and decompression code. (i.e. the range
 * covered backwards of size ZO_INIT_SIZE, starting from output+init_size.)
 *
 * [input, input+input_size) is the original copied compressed image (ZO)
 * (i.e. it does not include its run size). This range must be avoided
 * because it contains the data used for decompression.
 *
 * [input+input_size, output+init_size) is [_text, _end) for ZO. This
 * range includes ZO's heap and stack, and must be avoided since it
 * performs the decompression.
 *
 * Since the above two ranges need to be avoided and they are adjacent,
 * they can be merged, resulting in: [input, output+init_size) which
 * becomes the MEM_AVOID_ZO_RANGE below.
 */
static void mem_avoid_init(unsigned long input, unsigned long input_size,
			   unsigned long output)
{
	unsigned long init_size = boot_params->hdr.init_size;
	u64 initrd_start, initrd_size;
	u64 cmd_line, cmd_line_size;
	char *ptr;

	/*
	 * Avoid the region that is unsafe to overlap during
	 * decompression.
	 */
	mem_avoid[MEM_AVOID_ZO_RANGE].start = input;
	mem_avoid[MEM_AVOID_ZO_RANGE].size = (output + init_size) - input;
	add_identity_map(mem_avoid[MEM_AVOID_ZO_RANGE].start,
			 mem_avoid[MEM_AVOID_ZO_RANGE].size);

	/* Avoid initrd. */
	initrd_start  = (u64)boot_params->ext_ramdisk_image << 32;
	initrd_start |= boot_params->hdr.ramdisk_image;
	initrd_size  = (u64)boot_params->ext_ramdisk_size << 32;
	initrd_size |= boot_params->hdr.ramdisk_size;
	mem_avoid[MEM_AVOID_INITRD].start = initrd_start;
	mem_avoid[MEM_AVOID_INITRD].size = initrd_size;
	/* No need to set mapping for initrd, it will be handled in VO. */

	/* Avoid kernel command line. */
	cmd_line  = (u64)boot_params->ext_cmd_line_ptr << 32;
	cmd_line |= boot_params->hdr.cmd_line_ptr;
	/* Calculate size of cmd_line. */
	ptr = (char *)(unsigned long)cmd_line;
	for (cmd_line_size = 0; ptr[cmd_line_size++]; )
		;
	mem_avoid[MEM_AVOID_CMDLINE].start = cmd_line;
	mem_avoid[MEM_AVOID_CMDLINE].size = cmd_line_size;
	add_identity_map(mem_avoid[MEM_AVOID_CMDLINE].start,
			 mem_avoid[MEM_AVOID_CMDLINE].size);

	/* Avoid boot parameters. */
	mem_avoid[MEM_AVOID_BOOTPARAMS].start = (unsigned long)boot_params;
	mem_avoid[MEM_AVOID_BOOTPARAMS].size = sizeof(*boot_params);
	add_identity_map(mem_avoid[MEM_AVOID_BOOTPARAMS].start,
			 mem_avoid[MEM_AVOID_BOOTPARAMS].size);

	/* We don't need to set a mapping for setup_data. */

#ifdef CONFIG_X86_VERBOSE_BOOTUP
	/* Make sure video RAM can be used. */
	add_identity_map(0, PMD_SIZE);
#endif
}

/* Does this memory vector overlap a known avoided area? */
static bool mem_avoid_overlap(struct mem_vector *img)
{
	int i;
	struct setup_data *ptr;

	for (i = 0; i < MEM_AVOID_MAX; i++) {
		if (mem_overlaps(img, &mem_avoid[i]))
			return true;
	}

	/* Avoid all entries in the setup_data linked list. */
	ptr = (struct setup_data *)(unsigned long)boot_params->hdr.setup_data;
	while (ptr) {
		struct mem_vector avoid;

		avoid.start = (unsigned long)ptr;
		avoid.size = sizeof(*ptr) + ptr->len;

		if (mem_overlaps(img, &avoid))
			return true;

		ptr = (struct setup_data *)(unsigned long)ptr->next;
	}

	return false;
}

static unsigned long slots[KERNEL_IMAGE_SIZE / CONFIG_PHYSICAL_ALIGN];
static unsigned long slot_max;

static void slots_append(unsigned long addr)
{
	/* Overflowing the slots list should be impossible. */
	if (slot_max >= KERNEL_IMAGE_SIZE / CONFIG_PHYSICAL_ALIGN)
		return;

	slots[slot_max++] = addr;
}

static unsigned long slots_fetch_random(void)
{
	/* Handle case of no slots stored. */
	if (slot_max == 0)
		return 0;

	return slots[get_random_long() % slot_max];
}

static void process_e820_entry(struct e820entry *entry,
			       unsigned long minimum,
			       unsigned long image_size)
{
	struct mem_vector region, img;

	/* Skip non-RAM entries. */
	if (entry->type != E820_RAM)
		return;

	/* Ignore entries entirely above our maximum. */
	if (entry->addr >= KERNEL_IMAGE_SIZE)
		return;

	/* Ignore entries entirely below our minimum. */
	if (entry->addr + entry->size < minimum)
		return;

	region.start = entry->addr;
	region.size = entry->size;

	/* Potentially raise address to minimum location. */
	if (region.start < minimum)
		region.start = minimum;

	/* Potentially raise address to meet alignment requirements. */
	region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);

	/* Did we raise the address above the bounds of this e820 region? */
	if (region.start > entry->addr + entry->size)
		return;

	/* Reduce size by any delta from the original address. */
	region.size -= region.start - entry->addr;

	/* Reduce maximum size to fit end of image within maximum limit. */
	if (region.start + region.size > KERNEL_IMAGE_SIZE)
		region.size = KERNEL_IMAGE_SIZE - region.start;

	/* Walk each aligned slot and check for avoided areas. */
	for (img.start = region.start, img.size = image_size ;
	     mem_contains(&region, &img) ;
	     img.start += CONFIG_PHYSICAL_ALIGN) {
		if (mem_avoid_overlap(&img))
			continue;
		slots_append(img.start);
	}
}

static unsigned long find_random_addr(unsigned long minimum,
				      unsigned long size)
{
	int i;
	unsigned long addr;

	/* Make sure minimum is aligned. */
	minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);

	/* Verify potential e820 positions, appending to slots list. */
	for (i = 0; i < boot_params->e820_entries; i++) {
		process_e820_entry(&boot_params->e820_map[i], minimum, size);
	}

	return slots_fetch_random();
}

/*
 * Since this function examines addresses much more numerically,
 * it takes the input and output pointers as 'unsigned long'.
 */
unsigned char *choose_random_location(unsigned long input,
				      unsigned long input_size,
				      unsigned long output,
				      unsigned long output_size)
{
	unsigned long choice = output;
	unsigned long random_addr;

#ifdef CONFIG_HIBERNATION
	if (!cmdline_find_option_bool("kaslr")) {
		warn("KASLR disabled: 'kaslr' not on cmdline (hibernation selected).");
		goto out;
	}
#else
	if (cmdline_find_option_bool("nokaslr")) {
		warn("KASLR disabled: 'nokaslr' on cmdline.");
		goto out;
	}
#endif

	boot_params->hdr.loadflags |= KASLR_FLAG;

	/* Record the various known unsafe memory ranges. */
	mem_avoid_init(input, input_size, output);

	/* Walk e820 and find a random address. */
	random_addr = find_random_addr(output, output_size);
	if (!random_addr) {
		warn("KASLR disabled: could not find suitable E820 region!");
		goto out;
	}

	/* Always enforce the minimum. */
	if (random_addr < choice)
		goto out;

	choice = random_addr;

	add_identity_map(choice, output_size);

	/* This actually loads the identity pagetable on x86_64. */
	finalize_identity_maps();
out:
	return (unsigned char *)choice;
}
Commit	Line	Data
7de828df KC	1	/*
	2	* kaslr.c
	3	*
	4	* This contains the routines needed to generate a reasonable level of
	5	* entropy to choose a randomized kernel base address offset in support
	6	* of Kernel Address Space Layout Randomization (KASLR). Additionally
	7	* handles walking the physical memory maps (and tracking memory regions
	8	* to avoid) in order to select a physical memory location that can
	9	* contain the entire properly aligned running kernel image.
	10	*
	11	*/
8ab3820f	12	#include "misc.h"
dc425a6e	13	#include "error.h"
8ab3820f	14
5bfce5ef KC	15	#include <asm/msr.h>
5bfce5ef KC	16	#include <asm/archrandom.h>
82fa9637	17	#include <asm/e820.h>
5bfce5ef	18
a653f356 KC	19	#include <generated/compile.h>
	20	#include <linux/module.h>
	21	#include <linux/uts.h>
	22	#include <linux/utsname.h>
	23	#include <generated/utsrelease.h>
a653f356 KC	24
a653f356 KC	25	/* Simplified build-specific string for starting entropy. */
327f7d72	26	static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
a653f356 KC	27	LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
a653f356 KC	28
5bfce5ef KC	29	#define I8254_PORT_CONTROL 0x43
	30	#define I8254_PORT_COUNTER0 0x40
	31	#define I8254_CMD_READBACK 0xC0
	32	#define I8254_SELECT_COUNTER0 0x02
	33	#define I8254_STATUS_NOTREADY 0x40
	34	static inline u16 i8254(void)
	35	{
	36	u16 status, timer;
	37
	38	do {
	39	outb(I8254_PORT_CONTROL,
	40	I8254_CMD_READBACK \| I8254_SELECT_COUNTER0);
	41	status = inb(I8254_PORT_COUNTER0);
	42	timer = inb(I8254_PORT_COUNTER0);
	43	timer \|= inb(I8254_PORT_COUNTER0) << 8;
	44	} while (status & I8254_STATUS_NOTREADY);
	45
	46	return timer;
	47	}
	48
a653f356 KC	49	static unsigned long rotate_xor(unsigned long hash, const void *area,
	50	size_t size)
	51	{
	52	size_t i;
	53	unsigned long ptr = (unsigned long )area;
	54
	55	for (i = 0; i < size / sizeof(hash); i++) {
	56	/* Rotate by odd number of bits and XOR. */
	57	hash = (hash << ((sizeof(hash) * 8) - 7)) \| (hash >> 7);
	58	hash ^= ptr[i];
	59	}
	60
	61	return hash;
	62	}
	63
	64	/* Attempt to create a simple but unpredictable starting entropy. */
	65	static unsigned long get_random_boot(void)
	66	{
	67	unsigned long hash = 0;
	68
	69	hash = rotate_xor(hash, build_str, sizeof(build_str));
6655e0aa	70	hash = rotate_xor(hash, boot_params, sizeof(*boot_params));
a653f356 KC	71
	72	return hash;
	73	}
	74
5bfce5ef KC	75	static unsigned long get_random_long(void)
5bfce5ef KC	76	{
e8236c4d PA	77	#ifdef CONFIG_X86_64
	78	const unsigned long mix_const = 0x5d6008cbf3848dd3UL;
	79	#else
	80	const unsigned long mix_const = 0x3f39e593UL;
	81	#endif
a653f356 KC	82	unsigned long raw, random = get_random_boot();
	83	bool use_i8254 = true;
	84
	85	debug_putstr("KASLR using");
5bfce5ef KC	86
5bfce5ef KC	87	if (has_cpuflag(X86_FEATURE_RDRAND)) {
a653f356 KC	88	debug_putstr(" RDRAND");
	89	if (rdrand_long(&raw)) {
	90	random ^= raw;
	91	use_i8254 = false;
	92	}
5bfce5ef KC	93	}
	94
	95	if (has_cpuflag(X86_FEATURE_TSC)) {
a653f356	96	debug_putstr(" RDTSC");
4ea1636b	97	raw = rdtsc();
5bfce5ef	98
a653f356 KC	99	random ^= raw;
	100	use_i8254 = false;
	101	}
5bfce5ef	102
a653f356 KC	103	if (use_i8254) {
	104	debug_putstr(" i8254");
	105	random ^= i8254();
5bfce5ef KC	106	}
5bfce5ef KC	107
e8236c4d PA	108	/* Circular multiply for better bit diffusion */
	109	asm("mul %3"
	110	: "=a" (random), "=d" (raw)
	111	: "a" (random), "rm" (mix_const));
	112	random += raw;
	113
a653f356 KC	114	debug_putstr("...\n");
a653f356 KC	115
5bfce5ef KC	116	return random;
5bfce5ef KC	117	}
8ab3820f	118
82fa9637 KC	119	struct mem_vector {
	120	unsigned long start;
	121	unsigned long size;
	122	};
	123
ed09acde KC	124	enum mem_avoid_index {
	125	MEM_AVOID_ZO_RANGE = 0,
	126	MEM_AVOID_INITRD,
	127	MEM_AVOID_CMDLINE,
	128	MEM_AVOID_BOOTPARAMS,
	129	MEM_AVOID_MAX,
	130	};
	131
e290e8c5	132	static struct mem_vector mem_avoid[MEM_AVOID_MAX];
82fa9637 KC	133
	134	static bool mem_contains(struct mem_vector region, struct mem_vector item)
	135	{
	136	/* Item at least partially before region. */
	137	if (item->start < region->start)
	138	return false;
	139	/* Item at least partially after region. */
	140	if (item->start + item->size > region->start + region->size)
	141	return false;
	142	return true;
	143	}
	144
	145	static bool mem_overlaps(struct mem_vector one, struct mem_vector two)
	146	{
	147	/* Item one is entirely before item two. */
	148	if (one->start + one->size <= two->start)
	149	return false;
	150	/* Item one is entirely after item two. */
	151	if (one->start >= two->start + two->size)
	152	return false;
	153	return true;
	154	}
	155
9dc1969c	156	/*
ed09acde KC	157	* In theory, KASLR can put the kernel anywhere in the range of [16M, 64T).
	158	* The mem_avoid array is used to store the ranges that need to be avoided
	159	* when KASLR searches for an appropriate random address. We must avoid any
9dc1969c	160	* regions that are unsafe to overlap with during decompression, and other
ed09acde KC	161	* things like the initrd, cmdline and boot_params. This comment seeks to
	162	* explain mem_avoid as clearly as possible since incorrect mem_avoid
	163	* memory ranges lead to really hard to debug boot failures.
	164	*
	165	* The initrd, cmdline, and boot_params are trivial to identify for
cb18ef0d	166	* avoiding. They are MEM_AVOID_INITRD, MEM_AVOID_CMDLINE, and
ed09acde KC	167	* MEM_AVOID_BOOTPARAMS respectively below.
	168	*
	169	* What is not obvious how to avoid is the range of memory that is used
	170	* during decompression (MEM_AVOID_ZO_RANGE below). This range must cover
	171	* the compressed kernel (ZO) and its run space, which is used to extract
	172	* the uncompressed kernel (VO) and relocs.
	173	*
	174	* ZO's full run size sits against the end of the decompression buffer, so
	175	* we can calculate where text, data, bss, etc of ZO are positioned more
	176	* easily.
	177	*
	178	* For additional background, the decompression calculations can be found
	179	* in header.S, and the memory diagram is based on the one found in misc.c.
	180	*
	181	* The following conditions are already enforced by the image layouts and
	182	* associated code:
	183	* - input + input_size >= output + output_size
	184	* - kernel_total_size <= init_size
	185	* - kernel_total_size <= output_size (see Note below)
	186	* - output + init_size >= output + output_size
9dc1969c	187	*
ed09acde KC	188	* (Note that kernel_total_size and output_size have no fundamental
	189	* relationship, but output_size is passed to choose_random_location
	190	* as a maximum of the two. The diagram is showing a case where
	191	* kernel_total_size is larger than output_size, but this case is
	192	* handled by bumping output_size.)
9dc1969c	193	*
ed09acde	194	* The above conditions can be illustrated by a diagram:
9dc1969c	195	*
ed09acde KC	196	* 0 output input input+input_size output+init_size
	197	* \| \| \| \| \|
	198	* \| \| \| \| \|
	199	* \|-----\|--------\|--------\|--------------\|-----------\|--\|-------------\|
	200	* \| \| \|
	201	* \| \| \|
	202	* output+init_size-ZO_INIT_SIZE output+output_size output+kernel_total_size
9dc1969c	203	*
ed09acde KC	204	* [output, output+init_size) is the entire memory range used for
ed09acde KC	205	* extracting the compressed image.
9dc1969c	206	*
ed09acde KC	207	* [output, output+kernel_total_size) is the range needed for the
ed09acde KC	208	* uncompressed kernel (VO) and its run size (bss, brk, etc).
9dc1969c	209	*
ed09acde KC	210	* [output, output+output_size) is VO plus relocs (i.e. the entire
	211	* uncompressed payload contained by ZO). This is the area of the buffer
	212	* written to during decompression.
9dc1969c	213	*
ed09acde KC	214	* [output+init_size-ZO_INIT_SIZE, output+init_size) is the worst-case
	215	* range of the copied ZO and decompression code. (i.e. the range
	216	* covered backwards of size ZO_INIT_SIZE, starting from output+init_size.)
9dc1969c	217	*
ed09acde KC	218	* [input, input+input_size) is the original copied compressed image (ZO)
	219	* (i.e. it does not include its run size). This range must be avoided
	220	* because it contains the data used for decompression.
9dc1969c	221	*
ed09acde KC	222	* [input+input_size, output+init_size) is [_text, _end) for ZO. This
	223	* range includes ZO's heap and stack, and must be avoided since it
	224	* performs the decompression.
9dc1969c	225	*
ed09acde KC	226	* Since the above two ranges need to be avoided and they are adjacent,
	227	* they can be merged, resulting in: [input, output+init_size) which
	228	* becomes the MEM_AVOID_ZO_RANGE below.
9dc1969c	229	*/
82fa9637	230	static void mem_avoid_init(unsigned long input, unsigned long input_size,
9dc1969c	231	unsigned long output)
82fa9637	232	{
9dc1969c	233	unsigned long init_size = boot_params->hdr.init_size;
82fa9637 KC	234	u64 initrd_start, initrd_size;
82fa9637 KC	235	u64 cmd_line, cmd_line_size;
82fa9637 KC	236	char *ptr;
	237
	238	/*
	239	* Avoid the region that is unsafe to overlap during
9dc1969c	240	* decompression.
82fa9637	241	*/
ed09acde KC	242	mem_avoid[MEM_AVOID_ZO_RANGE].start = input;
ed09acde KC	243	mem_avoid[MEM_AVOID_ZO_RANGE].size = (output + init_size) - input;
3a94707d KC	244	add_identity_map(mem_avoid[MEM_AVOID_ZO_RANGE].start,
3a94707d KC	245	mem_avoid[MEM_AVOID_ZO_RANGE].size);
82fa9637 KC	246
82fa9637 KC	247	/* Avoid initrd. */
6655e0aa KC	248	initrd_start = (u64)boot_params->ext_ramdisk_image << 32;
	249	initrd_start \|= boot_params->hdr.ramdisk_image;
	250	initrd_size = (u64)boot_params->ext_ramdisk_size << 32;
	251	initrd_size \|= boot_params->hdr.ramdisk_size;
ed09acde KC	252	mem_avoid[MEM_AVOID_INITRD].start = initrd_start;
ed09acde KC	253	mem_avoid[MEM_AVOID_INITRD].size = initrd_size;
3a94707d	254	/* No need to set mapping for initrd, it will be handled in VO. */
82fa9637 KC	255
82fa9637 KC	256	/* Avoid kernel command line. */
6655e0aa KC	257	cmd_line = (u64)boot_params->ext_cmd_line_ptr << 32;
6655e0aa KC	258	cmd_line \|= boot_params->hdr.cmd_line_ptr;
82fa9637 KC	259	/* Calculate size of cmd_line. */
	260	ptr = (char *)(unsigned long)cmd_line;
	261	for (cmd_line_size = 0; ptr[cmd_line_size++]; )
	262	;
ed09acde KC	263	mem_avoid[MEM_AVOID_CMDLINE].start = cmd_line;
ed09acde KC	264	mem_avoid[MEM_AVOID_CMDLINE].size = cmd_line_size;
3a94707d KC	265	add_identity_map(mem_avoid[MEM_AVOID_CMDLINE].start,
3a94707d KC	266	mem_avoid[MEM_AVOID_CMDLINE].size);
82fa9637	267
ed09acde KC	268	/* Avoid boot parameters. */
	269	mem_avoid[MEM_AVOID_BOOTPARAMS].start = (unsigned long)boot_params;
	270	mem_avoid[MEM_AVOID_BOOTPARAMS].size = sizeof(*boot_params);
3a94707d KC	271	add_identity_map(mem_avoid[MEM_AVOID_BOOTPARAMS].start,
	272	mem_avoid[MEM_AVOID_BOOTPARAMS].size);
	273
	274	/* We don't need to set a mapping for setup_data. */
	275
	276	#ifdef CONFIG_X86_VERBOSE_BOOTUP
	277	/* Make sure video RAM can be used. */
	278	add_identity_map(0, PMD_SIZE);
	279	#endif
82fa9637 KC	280	}
	281
	282	/* Does this memory vector overlap a known avoided area? */
e290e8c5	283	static bool mem_avoid_overlap(struct mem_vector *img)
82fa9637 KC	284	{
82fa9637 KC	285	int i;
0cacbfbe	286	struct setup_data *ptr;
82fa9637 KC	287
	288	for (i = 0; i < MEM_AVOID_MAX; i++) {
	289	if (mem_overlaps(img, &mem_avoid[i]))
	290	return true;
	291	}
	292
0cacbfbe	293	/* Avoid all entries in the setup_data linked list. */
6655e0aa	294	ptr = (struct setup_data *)(unsigned long)boot_params->hdr.setup_data;
0cacbfbe KC	295	while (ptr) {
	296	struct mem_vector avoid;
	297
20cc2888	298	avoid.start = (unsigned long)ptr;
0cacbfbe KC	299	avoid.size = sizeof(*ptr) + ptr->len;
	300
	301	if (mem_overlaps(img, &avoid))
	302	return true;
	303
	304	ptr = (struct setup_data *)(unsigned long)ptr->next;
	305	}
	306
82fa9637 KC	307	return false;
	308	}
	309
e8581e3d	310	static unsigned long slots[KERNEL_IMAGE_SIZE / CONFIG_PHYSICAL_ALIGN];
e290e8c5	311	static unsigned long slot_max;
82fa9637 KC	312
	313	static void slots_append(unsigned long addr)
	314	{
	315	/* Overflowing the slots list should be impossible. */
e8581e3d	316	if (slot_max >= KERNEL_IMAGE_SIZE / CONFIG_PHYSICAL_ALIGN)
82fa9637 KC	317	return;
	318
	319	slots[slot_max++] = addr;
	320	}
	321
	322	static unsigned long slots_fetch_random(void)
	323	{
	324	/* Handle case of no slots stored. */
	325	if (slot_max == 0)
	326	return 0;
	327
	328	return slots[get_random_long() % slot_max];
	329	}
	330
	331	static void process_e820_entry(struct e820entry *entry,
	332	unsigned long minimum,
	333	unsigned long image_size)
	334	{
	335	struct mem_vector region, img;
	336
	337	/* Skip non-RAM entries. */
	338	if (entry->type != E820_RAM)
	339	return;
	340
	341	/* Ignore entries entirely above our maximum. */
e8581e3d	342	if (entry->addr >= KERNEL_IMAGE_SIZE)
82fa9637 KC	343	return;
	344
	345	/* Ignore entries entirely below our minimum. */
	346	if (entry->addr + entry->size < minimum)
	347	return;
	348
	349	region.start = entry->addr;
	350	region.size = entry->size;
	351
	352	/* Potentially raise address to minimum location. */
	353	if (region.start < minimum)
	354	region.start = minimum;
	355
	356	/* Potentially raise address to meet alignment requirements. */
	357	region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);
	358
	359	/* Did we raise the address above the bounds of this e820 region? */
	360	if (region.start > entry->addr + entry->size)
	361	return;
	362
	363	/* Reduce size by any delta from the original address. */
	364	region.size -= region.start - entry->addr;
	365
	366	/* Reduce maximum size to fit end of image within maximum limit. */
e8581e3d BH	367	if (region.start + region.size > KERNEL_IMAGE_SIZE)
e8581e3d BH	368	region.size = KERNEL_IMAGE_SIZE - region.start;
82fa9637 KC	369
	370	/* Walk each aligned slot and check for avoided areas. */
	371	for (img.start = region.start, img.size = image_size ;
	372	mem_contains(&region, &img) ;
	373	img.start += CONFIG_PHYSICAL_ALIGN) {
	374	if (mem_avoid_overlap(&img))
	375	continue;
	376	slots_append(img.start);
	377	}
	378	}
	379
	380	static unsigned long find_random_addr(unsigned long minimum,
	381	unsigned long size)
	382	{
	383	int i;
	384	unsigned long addr;
	385
	386	/* Make sure minimum is aligned. */
	387	minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
	388
	389	/* Verify potential e820 positions, appending to slots list. */
6655e0aa KC	390	for (i = 0; i < boot_params->e820_entries; i++) {
6655e0aa KC	391	process_e820_entry(&boot_params->e820_map[i], minimum, size);
82fa9637 KC	392	}
	393
	394	return slots_fetch_random();
	395	}
	396
549f90db BP	397	/*
	398	* Since this function examines addresses much more numerically,
	399	* it takes the input and output pointers as 'unsigned long'.
	400	*/
	401	unsigned char *choose_random_location(unsigned long input,
8ab3820f	402	unsigned long input_size,
549f90db	403	unsigned long output,
8ab3820f KC	404	unsigned long output_size)
8ab3820f KC	405	{
2bc1cd39	406	unsigned long choice = output;
9016875d	407	unsigned long random_addr;
8ab3820f	408
24f2e027 KC	409	#ifdef CONFIG_HIBERNATION
24f2e027 KC	410	if (!cmdline_find_option_bool("kaslr")) {
0f8ede1b	411	warn("KASLR disabled: 'kaslr' not on cmdline (hibernation selected).");
24f2e027 KC	412	goto out;
	413	}
	414	#else
8ab3820f	415	if (cmdline_find_option_bool("nokaslr")) {
0f8ede1b	416	warn("KASLR disabled: 'nokaslr' on cmdline.");
8ab3820f KC	417	goto out;
8ab3820f KC	418	}
24f2e027	419	#endif
8ab3820f	420
6655e0aa	421	boot_params->hdr.loadflags \|= KASLR_FLAG;
78cac48c	422
82fa9637	423	/* Record the various known unsafe memory ranges. */
9dc1969c	424	mem_avoid_init(input, input_size, output);
82fa9637 KC	425
82fa9637 KC	426	/* Walk e820 and find a random address. */
2bc1cd39	427	random_addr = find_random_addr(output, output_size);
9016875d	428	if (!random_addr) {
0f8ede1b	429	warn("KASLR disabled: could not find suitable E820 region!");
82fa9637 KC	430	goto out;
	431	}
	432
	433	/* Always enforce the minimum. */
9016875d	434	if (random_addr < choice)
82fa9637	435	goto out;
8ab3820f	436
9016875d	437	choice = random_addr;
3a94707d KC	438
3a94707d KC	439	add_identity_map(choice, output_size);
36a39ac9 BP	440
36a39ac9 BP	441	/* This actually loads the identity pagetable on x86_64. */
3a94707d	442	finalize_identity_maps();
8ab3820f KC	443	out:
	444	return (unsigned char *)choice;
	445	}