arch/x86/boot/compressed/kaslr.c - linux - Git at Google

 /*
  * 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;
 };

 #define MEM_AVOID_MAX 4
 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 theroy, KASLR can put the kernel anywhere in area of [16M, 64T). The
  * mem_avoid array is used to store the ranges that need to be avoided when
  * KASLR searches for a 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.
  *
  * How to calculate the unsafe areas is detailed here, and is informed by
  * the decompression calculations in header.S, and the diagram in misc.c.
  *
  * The compressed vmlinux (ZO) plus relocs and the run space of ZO can't be
  * overwritten by decompression output.
  *
  * ZO sits against the end of the decompression buffer, so we can calculate
  * where text, data, bss, etc of ZO are positioned.
  *
  * The follow are already enforced by the code:
  *  - init_size >= kernel_total_size
  *  - input + input_len >= output + output_len
  *  - kernel_total_size could be >= or < output_len
  *
  * From this, we can make several observations, illustrated by a diagram:
  *  - init_size >= kernel_total_size
  *  - input + input_len > output + output_len
  *  - kernel_total_size >= output_len
  *
  * 0   output            input            input+input_len    output+init_size
  * |     |                 |                       |                       |
  * |     |                 |                       |                       |
  * |-----|--------|--------|------------------|----|------------|----------|
  *                |                           |                 |
  *                |                           |                 |
  * output+init_size-ZO_INIT_SIZE   output+output_len  output+kernel_total_size
  *
  * [output, output+init_size) is for the buffer for decompressing the
  * compressed kernel (ZO).
  *
  * [output, output+kernel_total_size) is for the uncompressed kernel (VO)
  * and its bss, brk, etc.
  * [output, output+output_len) is VO plus relocs
  *
  * [output+init_size-ZO_INIT_SIZE, output+init_size) is the copied ZO.
  * [input, input+input_len) is the copied compressed (VO (vmlinux after
  * objcopy) plus relocs), not the ZO.
  *
  * [input+input_len, output+init_size) is [_text, _end) for ZO. That was the
  * first range in mem_avoid, which included ZO's heap and stack. Also
  * [input, input+input_size) need be put in mem_avoid array, but since it
  * is adjacent to the first entry, they can be merged. This is how we get
  * the first entry in mem_avoid[].
  */
 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[0].start = input;
 	mem_avoid[0].size = (output + init_size) - input;

 	/* 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[1].start = initrd_start;
 	mem_avoid[1].size = initrd_size;

 	/* 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[2].start = cmd_line;
 	mem_avoid[2].size = cmd_line_size;

 	/* Avoid params */
 	mem_avoid[3].start = (unsigned long)boot_params;
 	mem_avoid[3].size = sizeof(*boot_params);
 }

 /* 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;
 out:
 	return (unsigned char *)choice;
 }
	/*
	* 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;
	};

	#define MEM_AVOID_MAX 4
	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 theroy, KASLR can put the kernel anywhere in area of [16M, 64T). The
	* mem_avoid array is used to store the ranges that need to be avoided when
	* KASLR searches for a 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.
	*
	* How to calculate the unsafe areas is detailed here, and is informed by
	* the decompression calculations in header.S, and the diagram in misc.c.
	*
	* The compressed vmlinux (ZO) plus relocs and the run space of ZO can't be
	* overwritten by decompression output.
	*
	* ZO sits against the end of the decompression buffer, so we can calculate
	* where text, data, bss, etc of ZO are positioned.
	*
	* The follow are already enforced by the code:
	* - init_size >= kernel_total_size
	* - input + input_len >= output + output_len
	* - kernel_total_size could be >= or < output_len
	*
	* From this, we can make several observations, illustrated by a diagram:
	* - init_size >= kernel_total_size
	* - input + input_len > output + output_len
	* - kernel_total_size >= output_len
	*
	* 0 output input input+input_len output+init_size
	* \| \| \| \| \|
	* \| \| \| \| \|
	* \|-----\|--------\|--------\|------------------\|----\|------------\|----------\|
	* \| \| \|
	* \| \| \|
	* output+init_size-ZO_INIT_SIZE output+output_len output+kernel_total_size
	*
	* [output, output+init_size) is for the buffer for decompressing the
	* compressed kernel (ZO).
	*
	* [output, output+kernel_total_size) is for the uncompressed kernel (VO)
	* and its bss, brk, etc.
	* [output, output+output_len) is VO plus relocs
	*
	* [output+init_size-ZO_INIT_SIZE, output+init_size) is the copied ZO.
	* [input, input+input_len) is the copied compressed (VO (vmlinux after
	* objcopy) plus relocs), not the ZO.
	*
	* [input+input_len, output+init_size) is [_text, _end) for ZO. That was the
	* first range in mem_avoid, which included ZO's heap and stack. Also
	* [input, input+input_size) need be put in mem_avoid array, but since it
	* is adjacent to the first entry, they can be merged. This is how we get
	* the first entry in mem_avoid[].
	*/
	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[0].start = input;
	mem_avoid[0].size = (output + init_size) - input;

	/* 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[1].start = initrd_start;
	mem_avoid[1].size = initrd_size;

	/* 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[2].start = cmd_line;
	mem_avoid[2].size = cmd_line_size;

	/* Avoid params */
	mem_avoid[3].start = (unsigned long)boot_params;
	mem_avoid[3].size = sizeof(*boot_params);
	}

	/* 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;
	out:
	return (unsigned char *)choice;
	}