Linux 4.9.243

[linux/fpc-iii.git] / arch / x86 / boot / compressed / kaslr.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;

        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 loads the identity mapping page table.
                 * This should only be done if a new physical address
                 * is found for the kernel, otherwise we should keep
                 * the old page table to make it be like the "nokaslr"
                 * case.
                 */
                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;
}