blob: 6cfcf2a2eb932ae023a9a925a1df2e0213fd49c9 [file] [log] [blame]
#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;
if (cmdline_find_option_bool("nokaslr")) {
debug_putstr("KASLR disabled...\n");
goto out;
}
/* 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 */