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

 #include "misc.h"

 #ifdef CONFIG_RANDOMIZE_BASE
 #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, 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 = (u64)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();
 }

 unsigned char *choose_kernel_location(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");
 		goto out;
 	}
 #else
 	if (cmdline_find_option_bool("nokaslr")) {
 		debug_putstr("KASLR disabled by cmdline...\n");
 		goto out;
 	}
 #endif

 	/* 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;
 }

 #endif /* CONFIG_RANDOMIZE_BASE */
	#include "misc.h"

	#ifdef CONFIG_RANDOMIZE_BASE
	#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, 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 = (u64)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();
	}

	unsigned char choose_kernel_location(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");
	goto out;
	}
	#else
	if (cmdline_find_option_bool("nokaslr")) {
	debug_putstr("KASLR disabled by cmdline...\n");
	goto out;
	}
	#endif

	/* 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;
	}

	#endif /* CONFIG_RANDOMIZE_BASE */