[linux-2.6-block.git] / arch / x86 / boot / compressed / aslr.c

#include "misc.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;

struct kaslr_setup_data {
	__u64 next;
	__u32 type;
	__u32 len;
	__u8 data[1];
} kaslr_setup_data;

#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, real_mode, sizeof(*real_mode));

	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");
		rdtscll(raw);

		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;
};

#define MEM_AVOID_MAX 5
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;
}

static void mem_avoid_init(unsigned long input, unsigned long input_size,
			   unsigned long output, unsigned long output_size)
{
	u64 initrd_start, initrd_size;
	u64 cmd_line, cmd_line_size;
	unsigned long unsafe, unsafe_len;
	char *ptr;

	/*
	 * Avoid the region that is unsafe to overlap during
	 * decompression (see calculations at top of misc.c).
	 */
	unsafe_len = (output_size >> 12) + 32768 + 18;
	unsafe = (unsigned long)input + input_size - unsafe_len;
	mem_avoid[0].start = unsafe;
	mem_avoid[0].size = unsafe_len;

	/* Avoid initrd. */
	initrd_start  = (u64)real_mode->ext_ramdisk_image << 32;
	initrd_start |= real_mode->hdr.ramdisk_image;
	initrd_size  = (u64)real_mode->ext_ramdisk_size << 32;
	initrd_size |= real_mode->hdr.ramdisk_size;
	mem_avoid[1].start = initrd_start;
	mem_avoid[1].size = initrd_size;

	/* Avoid kernel command line. */
	cmd_line  = (u64)real_mode->ext_cmd_line_ptr << 32;
	cmd_line |= real_mode->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[2].start = cmd_line;
	mem_avoid[2].size = cmd_line_size;

	/* Avoid heap memory. */
	mem_avoid[3].start = (unsigned long)free_mem_ptr;
	mem_avoid[3].size = BOOT_HEAP_SIZE;

	/* Avoid stack memory. */
	mem_avoid[4].start = (unsigned long)free_mem_end_ptr;
	mem_avoid[4].size = BOOT_STACK_SIZE;
}

/* 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)real_mode->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[CONFIG_RANDOMIZE_BASE_MAX_OFFSET /
			   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 >= CONFIG_RANDOMIZE_BASE_MAX_OFFSET /
			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 >= CONFIG_RANDOMIZE_BASE_MAX_OFFSET)
		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 > CONFIG_RANDOMIZE_BASE_MAX_OFFSET)
		region.size = CONFIG_RANDOMIZE_BASE_MAX_OFFSET - 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 < real_mode->e820_entries; i++) {
		process_e820_entry(&real_mode->e820_map[i], minimum, size);
	}

	return slots_fetch_random();
}

static void add_kaslr_setup_data(struct boot_params *params, __u8 enabled)
{
	struct setup_data *data;

	kaslr_setup_data.type = SETUP_KASLR;
	kaslr_setup_data.len = 1;
	kaslr_setup_data.next = 0;
	kaslr_setup_data.data[0] = enabled;

	data = (struct setup_data *)(unsigned long)params->hdr.setup_data;

	while (data && data->next)
		data = (struct setup_data *)(unsigned long)data->next;

	if (data)
		data->next = (unsigned long)&kaslr_setup_data;
	else
		params->hdr.setup_data = (unsigned long)&kaslr_setup_data;

}

unsigned char *choose_kernel_location(struct boot_params *params,
				      unsigned char *input,
				      unsigned long input_size,
				      unsigned char *output,
				      unsigned long output_size)
{
	unsigned long choice = (unsigned long)output;
	unsigned long random;

#ifdef CONFIG_HIBERNATION
	if (!cmdline_find_option_bool("kaslr")) {
		debug_putstr("KASLR disabled by default...\n");
		add_kaslr_setup_data(params, 0);
		goto out;
	}
#else
	if (cmdline_find_option_bool("nokaslr")) {
		debug_putstr("KASLR disabled by cmdline...\n");
		add_kaslr_setup_data(params, 0);
		goto out;
	}
#endif
	add_kaslr_setup_data(params, 1);

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

	/* Walk e820 and find a random address. */
	random = find_random_addr(choice, output_size);
	if (!random) {
		debug_putstr("KASLR could not find suitable E820 region...\n");
		goto out;
	}

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

	choice = random;
out:
	return (unsigned char *)choice;
}
Commit	Line	Data
8ab3820f KC	1	#include "misc.h"
8ab3820f KC	2
5bfce5ef KC	3	#include <asm/msr.h>
5bfce5ef KC	4	#include <asm/archrandom.h>
82fa9637	5	#include <asm/e820.h>
5bfce5ef	6
a653f356 KC	7	#include <generated/compile.h>
	8	#include <linux/module.h>
	9	#include <linux/uts.h>
	10	#include <linux/utsname.h>
	11	#include <generated/utsrelease.h>
a653f356 KC	12
a653f356 KC	13	/* Simplified build-specific string for starting entropy. */
327f7d72	14	static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
a653f356 KC	15	LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
a653f356 KC	16
f47233c2 JK	17	struct kaslr_setup_data {
	18	__u64 next;
	19	__u32 type;
	20	__u32 len;
	21	__u8 data[1];
	22	} kaslr_setup_data;
	23
5bfce5ef KC	24	#define I8254_PORT_CONTROL 0x43
	25	#define I8254_PORT_COUNTER0 0x40
	26	#define I8254_CMD_READBACK 0xC0
	27	#define I8254_SELECT_COUNTER0 0x02
	28	#define I8254_STATUS_NOTREADY 0x40
	29	static inline u16 i8254(void)
	30	{
	31	u16 status, timer;
	32
	33	do {
	34	outb(I8254_PORT_CONTROL,
	35	I8254_CMD_READBACK \| I8254_SELECT_COUNTER0);
	36	status = inb(I8254_PORT_COUNTER0);
	37	timer = inb(I8254_PORT_COUNTER0);
	38	timer \|= inb(I8254_PORT_COUNTER0) << 8;
	39	} while (status & I8254_STATUS_NOTREADY);
	40
	41	return timer;
	42	}
	43
a653f356 KC	44	static unsigned long rotate_xor(unsigned long hash, const void *area,
	45	size_t size)
	46	{
	47	size_t i;
	48	unsigned long ptr = (unsigned long )area;
	49
	50	for (i = 0; i < size / sizeof(hash); i++) {
	51	/* Rotate by odd number of bits and XOR. */
	52	hash = (hash << ((sizeof(hash) * 8) - 7)) \| (hash >> 7);
	53	hash ^= ptr[i];
	54	}
	55
	56	return hash;
	57	}
	58
	59	/* Attempt to create a simple but unpredictable starting entropy. */
	60	static unsigned long get_random_boot(void)
	61	{
	62	unsigned long hash = 0;
	63
	64	hash = rotate_xor(hash, build_str, sizeof(build_str));
	65	hash = rotate_xor(hash, real_mode, sizeof(*real_mode));
	66
	67	return hash;
	68	}
	69
5bfce5ef KC	70	static unsigned long get_random_long(void)
5bfce5ef KC	71	{
e8236c4d PA	72	#ifdef CONFIG_X86_64
	73	const unsigned long mix_const = 0x5d6008cbf3848dd3UL;
	74	#else
	75	const unsigned long mix_const = 0x3f39e593UL;
	76	#endif
a653f356 KC	77	unsigned long raw, random = get_random_boot();
	78	bool use_i8254 = true;
	79
	80	debug_putstr("KASLR using");
5bfce5ef KC	81
5bfce5ef KC	82	if (has_cpuflag(X86_FEATURE_RDRAND)) {
a653f356 KC	83	debug_putstr(" RDRAND");
	84	if (rdrand_long(&raw)) {
	85	random ^= raw;
	86	use_i8254 = false;
	87	}
5bfce5ef KC	88	}
	89
	90	if (has_cpuflag(X86_FEATURE_TSC)) {
a653f356 KC	91	debug_putstr(" RDTSC");
a653f356 KC	92	rdtscll(raw);
5bfce5ef	93
a653f356 KC	94	random ^= raw;
	95	use_i8254 = false;
	96	}
5bfce5ef	97
a653f356 KC	98	if (use_i8254) {
	99	debug_putstr(" i8254");
	100	random ^= i8254();
5bfce5ef KC	101	}
5bfce5ef KC	102
e8236c4d PA	103	/* Circular multiply for better bit diffusion */
	104	asm("mul %3"
	105	: "=a" (random), "=d" (raw)
	106	: "a" (random), "rm" (mix_const));
	107	random += raw;
	108
a653f356 KC	109	debug_putstr("...\n");
a653f356 KC	110
5bfce5ef KC	111	return random;
5bfce5ef KC	112	}
8ab3820f	113
82fa9637 KC	114	struct mem_vector {
	115	unsigned long start;
	116	unsigned long size;
	117	};
	118
	119	#define MEM_AVOID_MAX 5
e290e8c5	120	static struct mem_vector mem_avoid[MEM_AVOID_MAX];
82fa9637 KC	121
	122	static bool mem_contains(struct mem_vector region, struct mem_vector item)
	123	{
	124	/* Item at least partially before region. */
	125	if (item->start < region->start)
	126	return false;
	127	/* Item at least partially after region. */
	128	if (item->start + item->size > region->start + region->size)
	129	return false;
	130	return true;
	131	}
	132
	133	static bool mem_overlaps(struct mem_vector one, struct mem_vector two)
	134	{
	135	/* Item one is entirely before item two. */
	136	if (one->start + one->size <= two->start)
	137	return false;
	138	/* Item one is entirely after item two. */
	139	if (one->start >= two->start + two->size)
	140	return false;
	141	return true;
	142	}
	143
	144	static void mem_avoid_init(unsigned long input, unsigned long input_size,
	145	unsigned long output, unsigned long output_size)
	146	{
	147	u64 initrd_start, initrd_size;
	148	u64 cmd_line, cmd_line_size;
	149	unsigned long unsafe, unsafe_len;
	150	char *ptr;
	151
	152	/*
	153	* Avoid the region that is unsafe to overlap during
	154	* decompression (see calculations at top of misc.c).
	155	*/
	156	unsafe_len = (output_size >> 12) + 32768 + 18;
	157	unsafe = (unsigned long)input + input_size - unsafe_len;
	158	mem_avoid[0].start = unsafe;
	159	mem_avoid[0].size = unsafe_len;
	160
	161	/* Avoid initrd. */
	162	initrd_start = (u64)real_mode->ext_ramdisk_image << 32;
	163	initrd_start \|= real_mode->hdr.ramdisk_image;
	164	initrd_size = (u64)real_mode->ext_ramdisk_size << 32;
	165	initrd_size \|= real_mode->hdr.ramdisk_size;
	166	mem_avoid[1].start = initrd_start;
	167	mem_avoid[1].size = initrd_size;
	168
	169	/* Avoid kernel command line. */
	170	cmd_line = (u64)real_mode->ext_cmd_line_ptr << 32;
	171	cmd_line \|= real_mode->hdr.cmd_line_ptr;
	172	/* Calculate size of cmd_line. */
	173	ptr = (char *)(unsigned long)cmd_line;
	174	for (cmd_line_size = 0; ptr[cmd_line_size++]; )
	175	;
	176	mem_avoid[2].start = cmd_line;
	177	mem_avoid[2].size = cmd_line_size;
	178
	179	/* Avoid heap memory. */
	180	mem_avoid[3].start = (unsigned long)free_mem_ptr;
	181	mem_avoid[3].size = BOOT_HEAP_SIZE;
	182
	183	/* Avoid stack memory. */
	184	mem_avoid[4].start = (unsigned long)free_mem_end_ptr;
185	mem_avoid[4].size = BOOT_STACK_SIZE;
186	}
187
188	/* Does this memory vector overlap a known avoided area? */
e290e8c5	189	static bool mem_avoid_overlap(struct mem_vector *img)
82fa9637 KC	190	{
82fa9637 KC	191	int i;
0cacbfbe	192	struct setup_data *ptr;
82fa9637 KC	193
	194	for (i = 0; i < MEM_AVOID_MAX; i++) {
	195	if (mem_overlaps(img, &mem_avoid[i]))
	196	return true;
	197	}
	198
0cacbfbe KC	199	/* Avoid all entries in the setup_data linked list. */
	200	ptr = (struct setup_data *)(unsigned long)real_mode->hdr.setup_data;
	201	while (ptr) {
	202	struct mem_vector avoid;
	203
20cc2888	204	avoid.start = (unsigned long)ptr;
0cacbfbe KC	205	avoid.size = sizeof(*ptr) + ptr->len;
	206
	207	if (mem_overlaps(img, &avoid))
	208	return true;
	209
	210	ptr = (struct setup_data *)(unsigned long)ptr->next;
	211	}
	212
82fa9637 KC	213	return false;
	214	}
	215
e290e8c5 KC	216	static unsigned long slots[CONFIG_RANDOMIZE_BASE_MAX_OFFSET /
	217	CONFIG_PHYSICAL_ALIGN];
	218	static unsigned long slot_max;
82fa9637 KC	219
	220	static void slots_append(unsigned long addr)
	221	{
	222	/* Overflowing the slots list should be impossible. */
	223	if (slot_max >= CONFIG_RANDOMIZE_BASE_MAX_OFFSET /
	224	CONFIG_PHYSICAL_ALIGN)
	225	return;
	226
	227	slots[slot_max++] = addr;
	228	}
	229
	230	static unsigned long slots_fetch_random(void)
	231	{
	232	/* Handle case of no slots stored. */
	233	if (slot_max == 0)
	234	return 0;
	235
	236	return slots[get_random_long() % slot_max];
	237	}
	238
	239	static void process_e820_entry(struct e820entry *entry,
	240	unsigned long minimum,
	241	unsigned long image_size)
	242	{
	243	struct mem_vector region, img;
	244
	245	/* Skip non-RAM entries. */
	246	if (entry->type != E820_RAM)
	247	return;
	248
	249	/* Ignore entries entirely above our maximum. */
	250	if (entry->addr >= CONFIG_RANDOMIZE_BASE_MAX_OFFSET)
	251	return;
	252
	253	/* Ignore entries entirely below our minimum. */
	254	if (entry->addr + entry->size < minimum)
	255	return;
	256
	257	region.start = entry->addr;
	258	region.size = entry->size;
	259
	260	/* Potentially raise address to minimum location. */
	261	if (region.start < minimum)
	262	region.start = minimum;
	263
	264	/* Potentially raise address to meet alignment requirements. */
	265	region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);
	266
	267	/* Did we raise the address above the bounds of this e820 region? */
	268	if (region.start > entry->addr + entry->size)
	269	return;
	270
	271	/* Reduce size by any delta from the original address. */
	272	region.size -= region.start - entry->addr;
	273
	274	/* Reduce maximum size to fit end of image within maximum limit. */
	275	if (region.start + region.size > CONFIG_RANDOMIZE_BASE_MAX_OFFSET)
	276	region.size = CONFIG_RANDOMIZE_BASE_MAX_OFFSET - region.start;
	277
	278	/* Walk each aligned slot and check for avoided areas. */
	279	for (img.start = region.start, img.size = image_size ;
	280	mem_contains(&region, &img) ;
	281	img.start += CONFIG_PHYSICAL_ALIGN) {
	282	if (mem_avoid_overlap(&img))
283	continue;
284	slots_append(img.start);
285	}
286	}
287
288	static unsigned long find_random_addr(unsigned long minimum,
289	unsigned long size)
290	{
291	int i;
292	unsigned long addr;
293
294	/* Make sure minimum is aligned. */
295	minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
296
297	/* Verify potential e820 positions, appending to slots list. */
298	for (i = 0; i < real_mode->e820_entries; i++) {
299	process_e820_entry(&real_mode->e820_map[i], minimum, size);
300	}
301
302	return slots_fetch_random();
303	}
304
f47233c2 JK	305	static void add_kaslr_setup_data(struct boot_params *params, __u8 enabled)
	306	{
	307	struct setup_data *data;
	308
	309	kaslr_setup_data.type = SETUP_KASLR;
	310	kaslr_setup_data.len = 1;
	311	kaslr_setup_data.next = 0;
	312	kaslr_setup_data.data[0] = enabled;
	313
	314	data = (struct setup_data *)(unsigned long)params->hdr.setup_data;
	315
	316	while (data && data->next)
	317	data = (struct setup_data *)(unsigned long)data->next;
	318
	319	if (data)
	320	data->next = (unsigned long)&kaslr_setup_data;
	321	else
	322	params->hdr.setup_data = (unsigned long)&kaslr_setup_data;
	323
	324	}
	325
	326	unsigned char choose_kernel_location(struct boot_params params,
	327	unsigned char *input,
8ab3820f KC	328	unsigned long input_size,
	329	unsigned char *output,
	330	unsigned long output_size)
	331	{
	332	unsigned long choice = (unsigned long)output;
82fa9637	333	unsigned long random;
8ab3820f	334
24f2e027 KC	335	#ifdef CONFIG_HIBERNATION
	336	if (!cmdline_find_option_bool("kaslr")) {
	337	debug_putstr("KASLR disabled by default...\n");
f47233c2	338	add_kaslr_setup_data(params, 0);
24f2e027 KC	339	goto out;
	340	}
	341	#else
8ab3820f	342	if (cmdline_find_option_bool("nokaslr")) {
24f2e027	343	debug_putstr("KASLR disabled by cmdline...\n");
f47233c2	344	add_kaslr_setup_data(params, 0);
8ab3820f KC	345	goto out;
8ab3820f KC	346	}
24f2e027	347	#endif
f47233c2	348	add_kaslr_setup_data(params, 1);
8ab3820f	349
82fa9637 KC	350	/* Record the various known unsafe memory ranges. */
	351	mem_avoid_init((unsigned long)input, input_size,
	352	(unsigned long)output, output_size);
	353
	354	/* Walk e820 and find a random address. */
	355	random = find_random_addr(choice, output_size);
	356	if (!random) {
	357	debug_putstr("KASLR could not find suitable E820 region...\n");
	358	goto out;
	359	}
	360
	361	/* Always enforce the minimum. */
	362	if (random < choice)
	363	goto out;
8ab3820f	364
82fa9637	365	choice = random;
8ab3820f KC	366	out:
	367	return (unsigned char *)choice;
	368	}