OpenCloudOS-Kernel/arch/x86/boot/compressed/kaslr.c

476 lines
14 KiB
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 <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;
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_boot_seed(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;
}
#define KASLR_COMPRESSED_BOOT
#include "../../lib/kaslr.c"
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_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? If so, record the
* overlap region with the lowest address.
*/
static bool mem_avoid_overlap(struct mem_vector *img,
struct mem_vector *overlap)
{
int i;
struct setup_data *ptr;
unsigned long earliest = img->start + img->size;
bool is_overlapping = false;
for (i = 0; i < MEM_AVOID_MAX; i++) {
if (mem_overlaps(img, &mem_avoid[i]) &&
mem_avoid[i].start < earliest) {
*overlap = mem_avoid[i];
earliest = overlap->start;
is_overlapping = 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) && (avoid.start < earliest)) {
*overlap = avoid;
earliest = overlap->start;
is_overlapping = true;
}
ptr = (struct setup_data *)(unsigned long)ptr->next;
}
return is_overlapping;
}
struct slot_area {
unsigned long addr;
int num;
};
#define MAX_SLOT_AREA 100
static struct slot_area slot_areas[MAX_SLOT_AREA];
static unsigned long slot_max;
static unsigned long slot_area_index;
static void store_slot_info(struct mem_vector *region, unsigned long image_size)
{
struct slot_area slot_area;
if (slot_area_index == MAX_SLOT_AREA)
return;
slot_area.addr = region->start;
slot_area.num = (region->size - image_size) /
CONFIG_PHYSICAL_ALIGN + 1;
if (slot_area.num > 0) {
slot_areas[slot_area_index++] = slot_area;
slot_max += slot_area.num;
}
}
static unsigned long slots_fetch_random(void)
{
unsigned long slot;
int i;
/* Handle case of no slots stored. */
if (slot_max == 0)
return 0;
slot = kaslr_get_random_long("Physical") % slot_max;
for (i = 0; i < slot_area_index; i++) {
if (slot >= slot_areas[i].num) {
slot -= slot_areas[i].num;
continue;
}
return slot_areas[i].addr + slot * CONFIG_PHYSICAL_ALIGN;
}
if (i == slot_area_index)
debug_putstr("slots_fetch_random() failed!?\n");
return 0;
}
static void process_e820_entry(struct e820entry *entry,
unsigned long minimum,
unsigned long image_size)
{
struct mem_vector region, overlap;
struct slot_area slot_area;
unsigned long start_orig;
/* Skip non-RAM entries. */
if (entry->type != E820_RAM)
return;
/* On 32-bit, ignore entries entirely above our maximum. */
if (IS_ENABLED(CONFIG_X86_32) && 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;
/* Give up if slot area array is full. */
while (slot_area_index < MAX_SLOT_AREA) {
start_orig = region.start;
/* Potentially raise address to minimum location. */
if (region.start < minimum)
region.start = minimum;
/* Potentially raise address to meet alignment needs. */
region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);
/* Did we raise the address above this e820 region? */
if (region.start > entry->addr + entry->size)
return;
/* Reduce size by any delta from the original address. */
region.size -= region.start - start_orig;
/* On 32-bit, reduce region size to fit within max size. */
if (IS_ENABLED(CONFIG_X86_32) &&
region.start + region.size > KERNEL_IMAGE_SIZE)
region.size = KERNEL_IMAGE_SIZE - region.start;
/* Return if region can't contain decompressed kernel */
if (region.size < image_size)
return;
/* If nothing overlaps, store the region and return. */
if (!mem_avoid_overlap(&region, &overlap)) {
store_slot_info(&region, image_size);
return;
}
/* Store beginning of region if holds at least image_size. */
if (overlap.start > region.start + image_size) {
struct mem_vector beginning;
beginning.start = region.start;
beginning.size = overlap.start - region.start;
store_slot_info(&beginning, image_size);
}
/* Return if overlap extends to or past end of region. */
if (overlap.start + overlap.size >= region.start + region.size)
return;
/* Clip off the overlapping region and start over. */
region.size -= overlap.start - region.start + overlap.size;
region.start = overlap.start + overlap.size;
}
}
static unsigned long find_random_phys_addr(unsigned long minimum,
unsigned long image_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,
image_size);
if (slot_area_index == MAX_SLOT_AREA) {
debug_putstr("Aborted e820 scan (slot_areas full)!\n");
break;
}
}
return slots_fetch_random();
}
static unsigned long find_random_virt_addr(unsigned long minimum,
unsigned long image_size)
{
unsigned long slots, random_addr;
/* Make sure minimum is aligned. */
minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
/* Align image_size for easy slot calculations. */
image_size = ALIGN(image_size, CONFIG_PHYSICAL_ALIGN);
/*
* There are how many CONFIG_PHYSICAL_ALIGN-sized slots
* that can hold image_size within the range of minimum to
* KERNEL_IMAGE_SIZE?
*/
slots = (KERNEL_IMAGE_SIZE - minimum - image_size) /
CONFIG_PHYSICAL_ALIGN + 1;
random_addr = kaslr_get_random_long("Virtual") % slots;
return random_addr * CONFIG_PHYSICAL_ALIGN + minimum;
}
/*
* Since this function examines addresses much more numerically,
* it takes the input and output pointers as 'unsigned long'.
*/
void choose_random_location(unsigned long input,
unsigned long input_size,
unsigned long *output,
unsigned long output_size,
unsigned long *virt_addr)
{
unsigned long random_addr, min_addr;
/* By default, keep output position unchanged. */
*virt_addr = *output;
if (cmdline_find_option_bool("nokaslr")) {
warn("KASLR disabled: 'nokaslr' on cmdline.");
return;
}
boot_params->hdr.loadflags |= KASLR_FLAG;
/* Prepare to add new identity pagetables on demand. */
initialize_identity_maps();
/* Record the various known unsafe memory ranges. */
mem_avoid_init(input, input_size, *output);
/*
* Low end of the randomization range should be the
* smaller of 512M or the initial kernel image
* location:
*/
min_addr = min(*output, 512UL << 20);
/* Walk e820 and find a random address. */
random_addr = find_random_phys_addr(min_addr, output_size);
if (!random_addr) {
warn("KASLR disabled: could not find suitable E820 region!");
} else {
/* Update the new physical address location. */
if (*output != random_addr) {
add_identity_map(random_addr, output_size);
*output = random_addr;
}
}
/* This actually loads the identity pagetable on x86_64. */
finalize_identity_maps();
/* Pick random virtual address starting from LOAD_PHYSICAL_ADDR. */
if (IS_ENABLED(CONFIG_X86_64))
random_addr = find_random_virt_addr(LOAD_PHYSICAL_ADDR, output_size);
*virt_addr = random_addr;
}