// SPDX-License-Identifier: GPL-2.0
/*
 * 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.
 *
 */

/*
 * isspace() in linux/ctype.h is expected by next_args() to filter
 * out "space/lf/tab". While boot/ctype.h conflicts with linux/ctype.h,
 * since isdigit() is implemented in both of them. Hence disable it
 * here.
 */
#define BOOT_CTYPE_H

#include "misc.h"
#include "error.h"
#include "../string.h"

#include <generated/compile.h>
#include <linux/module.h>
#include <linux/uts.h>
#include <linux/utsname.h>
#include <linux/ctype.h>
#include <linux/efi.h>
#include <generated/utsrelease.h>
#include <asm/efi.h>

/* Macros used by the included decompressor code below. */
#define STATIC
#include <linux/decompress/mm.h>

#define _SETUP
#include <asm/setup.h>  /* For COMMAND_LINE_SIZE */
#undef _SETUP

extern unsigned long get_cmd_line_ptr(void);

/* 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"


/* Only supporting at most 4 unusable memmap regions with kaslr */
#define MAX_MEMMAP_REGIONS      4

static bool memmap_too_large;


/*
 * Store memory limit: MAXMEM on 64-bit and KERNEL_IMAGE_SIZE on 32-bit.
 * It may be reduced by "mem=nn[KMG]" or "memmap=nn[KMG]" command line options.
 */
static u64 mem_limit;

/* Number of immovable memory regions */
static int num_immovable_mem;

enum mem_avoid_index {
        MEM_AVOID_ZO_RANGE = 0,
        MEM_AVOID_INITRD,
        MEM_AVOID_CMDLINE,
        MEM_AVOID_BOOTPARAMS,
        MEM_AVOID_MEMMAP_BEGIN,
        MEM_AVOID_MEMMAP_END = MEM_AVOID_MEMMAP_BEGIN + MAX_MEMMAP_REGIONS - 1,
        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;
}

char *skip_spaces(const char *str)
{
        while (isspace(*str))
                ++str;
        return (char *)str;
}
#include "../../../../lib/ctype.c"
#include "../../../../lib/cmdline.c"

enum parse_mode {
        PARSE_MEMMAP,
        PARSE_EFI,
};

static int
parse_memmap(char *p, u64 *start, u64 *size, enum parse_mode mode)
{
        char *oldp;

        if (!p)
                return -EINVAL;

        /* We don't care about this option here */
        if (!strncmp(p, "exactmap", 8))
                return -EINVAL;

        oldp = p;
        *size = memparse(p, &p);
        if (p == oldp)
                return -EINVAL;

        switch (*p) {
        case '#':
        case '$':
        case '!':
                *start = memparse(p + 1, &p);
                return 0;
        case '@':
                if (mode == PARSE_MEMMAP) {
                        /*
                         * memmap=nn@ss specifies usable region, should
                         * be skipped
                         */
                        *size = 0;
                } else {
                        u64 flags;

                        /*
                         * efi_fake_mem=nn@ss:attr the attr specifies
                         * flags that might imply a soft-reservation.
                         */
                        *start = memparse(p + 1, &p);
                        if (p && *p == ':') {
                                p++;
                                if (kstrtoull(p, 0, &flags) < 0)
                                        *size = 0;
                                else if (flags & EFI_MEMORY_SP)
                                        return 0;
                        }
                        *size = 0;
                }
                fallthrough;
        default:
                /*
                 * If w/o offset, only size specified, memmap=nn[KMG] has the
                 * same behaviour as mem=nn[KMG]. It limits the max address
                 * system can use. Region above the limit should be avoided.
                 */
                *start = 0;
                return 0;
        }

        return -EINVAL;
}

static void mem_avoid_memmap(enum parse_mode mode, char *str)
{
        static int i;

        if (i >= MAX_MEMMAP_REGIONS)
                return;

        while (str && (i < MAX_MEMMAP_REGIONS)) {
                int rc;
                u64 start, size;
                char *k = strchr(str, ',');

                if (k)
                        *k++ = 0;

                rc = parse_memmap(str, &start, &size, mode);
                if (rc < 0)
                        break;
                str = k;

                if (start == 0) {
                        /* Store the specified memory limit if size > 0 */
                        if (size > 0 && size < mem_limit)
                                mem_limit = size;

                        continue;
                }

                mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].start = start;
                mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].size = size;
                i++;
        }

        /* More than 4 memmaps, fail kaslr */
        if ((i >= MAX_MEMMAP_REGIONS) && str)
                memmap_too_large = true;
}

/* Store the number of 1GB huge pages which users specified: */
static unsigned long max_gb_huge_pages;

static void parse_gb_huge_pages(char *param, char *val)
{
        static bool gbpage_sz;
        char *p;

        if (!strcmp(param, "hugepagesz")) {
                p = val;
                if (memparse(p, &p) != PUD_SIZE) {
                        gbpage_sz = false;
                        return;
                }

                if (gbpage_sz)
                        warn("Repeatedly set hugeTLB page size of 1G!\n");
                gbpage_sz = true;
                return;
        }

        if (!strcmp(param, "hugepages") && gbpage_sz) {
                p = val;
                max_gb_huge_pages = simple_strtoull(p, &p, 0);
                return;
        }
}

static void handle_mem_options(void)
{
        char *args = (char *)get_cmd_line_ptr();
        size_t len;
        char *tmp_cmdline;
        char *param, *val;
        u64 mem_size;

        if (!args)
                return;

        len = strnlen(args, COMMAND_LINE_SIZE-1);
        tmp_cmdline = malloc(len + 1);
        if (!tmp_cmdline)
                error("Failed to allocate space for tmp_cmdline");

        memcpy(tmp_cmdline, args, len);
        tmp_cmdline[len] = 0;
        args = tmp_cmdline;

        /* Chew leading spaces */
        args = skip_spaces(args);

        while (*args) {
                args = next_arg(args, &param, &val);
                /* Stop at -- */
                if (!val && strcmp(param, "--") == 0)
                        break;

                if (!strcmp(param, "memmap")) {
                        mem_avoid_memmap(PARSE_MEMMAP, val);
                } else if (IS_ENABLED(CONFIG_X86_64) && strstr(param, "hugepages")) {
                        parse_gb_huge_pages(param, val);
                } else if (!strcmp(param, "mem")) {
                        char *p = val;

                        if (!strcmp(p, "nopentium"))
                                continue;
                        mem_size = memparse(p, &p);
                        if (mem_size == 0)
                                break;

                        if (mem_size < mem_limit)
                                mem_limit = mem_size;
                } else if (!strcmp(param, "efi_fake_mem")) {
                        mem_avoid_memmap(PARSE_EFI, val);
                }
        }

        free(tmp_cmdline);
        return;
}

/*
 * In theory, KASLR can put the kernel anywhere in the range of [16M, MAXMEM)
 * on 64-bit, and [16M, KERNEL_IMAGE_SIZE) on 32-bit.
 *
 * 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;
        unsigned long cmd_line, cmd_line_size;

        /*
         * 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;

        /* 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 = get_cmd_line_ptr();
        /* Calculate size of cmd_line. */
        if (cmd_line) {
                cmd_line_size = strnlen((char *)cmd_line, COMMAND_LINE_SIZE-1) + 1;
                mem_avoid[MEM_AVOID_CMDLINE].start = cmd_line;
                mem_avoid[MEM_AVOID_CMDLINE].size = cmd_line_size;
        }

        /* Avoid boot parameters. */
        mem_avoid[MEM_AVOID_BOOTPARAMS].start = (unsigned long)boot_params;
        mem_avoid[MEM_AVOID_BOOTPARAMS].size = sizeof(*boot_params);

        /* We don't need to set a mapping for setup_data. */

        /* Mark the memmap regions we need to avoid */
        handle_mem_options();

        /* Enumerate the immovable memory regions */
        num_immovable_mem = count_immovable_mem_regions();
}

/*
 * 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;
        u64 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;
                }

                if (ptr->type == SETUP_INDIRECT &&
                    ((struct setup_indirect *)ptr->data)->type != SETUP_INDIRECT) {
                        avoid.start = ((struct setup_indirect *)ptr->data)->addr;
                        avoid.size = ((struct setup_indirect *)ptr->data)->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 {
        u64 addr;
        unsigned long num;
};

#define MAX_SLOT_AREA 100

static struct slot_area slot_areas[MAX_SLOT_AREA];
static unsigned int slot_area_index;
static unsigned long slot_max;

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 = 1 + (region->size - image_size) / CONFIG_PHYSICAL_ALIGN;

        slot_areas[slot_area_index++] = slot_area;
        slot_max += slot_area.num;
}

/*
 * Skip as many 1GB huge pages as possible in the passed region
 * according to the number which users specified:
 */
static void
process_gb_huge_pages(struct mem_vector *region, unsigned long image_size)
{
        u64 pud_start, pud_end;
        unsigned long gb_huge_pages;
        struct mem_vector tmp;

        if (!IS_ENABLED(CONFIG_X86_64) || !max_gb_huge_pages) {
                store_slot_info(region, image_size);
                return;
        }

        /* Are there any 1GB pages in the region? */
        pud_start = ALIGN(region->start, PUD_SIZE);
        pud_end = ALIGN_DOWN(region->start + region->size, PUD_SIZE);

        /* No good 1GB huge pages found: */
        if (pud_start >= pud_end) {
                store_slot_info(region, image_size);
                return;
        }

        /* Check if the head part of the region is usable. */
        if (pud_start >= region->start + image_size) {
                tmp.start = region->start;
                tmp.size = pud_start - region->start;
                store_slot_info(&tmp, image_size);
        }

        /* Skip the good 1GB pages. */
        gb_huge_pages = (pud_end - pud_start) >> PUD_SHIFT;
        if (gb_huge_pages > max_gb_huge_pages) {
                pud_end = pud_start + (max_gb_huge_pages << PUD_SHIFT);
                max_gb_huge_pages = 0;
        } else {
                max_gb_huge_pages -= gb_huge_pages;
        }

        /* Check if the tail part of the region is usable. */
        if (region->start + region->size >= pud_end + image_size) {
                tmp.start = pud_end;
                tmp.size = region->start + region->size - pud_end;
                store_slot_info(&tmp, image_size);
        }
}

static u64 slots_fetch_random(void)
{
        unsigned long slot;
        unsigned 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 + ((u64)slot * CONFIG_PHYSICAL_ALIGN);
        }

        if (i == slot_area_index)
                debug_putstr("slots_fetch_random() failed!?\n");
        return 0;
}

static void __process_mem_region(struct mem_vector *entry,
                                 unsigned long minimum,
                                 unsigned long image_size)
{
        struct mem_vector region, overlap;
        u64 region_end;

        /* Enforce minimum and memory limit. */
        region.start = max_t(u64, entry->start, minimum);
        region_end = min(entry->start + entry->size, mem_limit);

        /* Give up if slot area array is full. */
        while (slot_area_index < MAX_SLOT_AREA) {
                /* Potentially raise address to meet alignment needs. */
                region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);

                /* Did we raise the address above the passed in memory entry? */
                if (region.start > region_end)
                        return;

                /* Reduce size by any delta from the original address. */
                region.size = region_end - 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)) {
                        process_gb_huge_pages(&region, image_size);
                        return;
                }

                /* Store beginning of region if holds at least image_size. */
                if (overlap.start >= region.start + image_size) {
                        region.size = overlap.start - region.start;
                        process_gb_huge_pages(&region, image_size);
                }

                /* Clip off the overlapping region and start over. */
                region.start = overlap.start + overlap.size;
        }
}

static bool process_mem_region(struct mem_vector *region,
                               unsigned long minimum,
                               unsigned long image_size)
{
        int i;
        /*
         * If no immovable memory found, or MEMORY_HOTREMOVE disabled,
         * use @region directly.
         */
        if (!num_immovable_mem) {
                __process_mem_region(region, minimum, image_size);

                if (slot_area_index == MAX_SLOT_AREA) {
                        debug_putstr("Aborted e820/efi memmap scan (slot_areas full)!\n");
                        return true;
                }
                return false;
        }

#if defined(CONFIG_MEMORY_HOTREMOVE) && defined(CONFIG_ACPI)
        /*
         * If immovable memory found, filter the intersection between
         * immovable memory and @region.
         */
        for (i = 0; i < num_immovable_mem; i++) {
                u64 start, end, entry_end, region_end;
                struct mem_vector entry;

                if (!mem_overlaps(region, &immovable_mem[i]))
                        continue;

                start = immovable_mem[i].start;
                end = start + immovable_mem[i].size;
                region_end = region->start + region->size;

                entry.start = clamp(region->start, start, end);
                entry_end = clamp(region_end, start, end);
                entry.size = entry_end - entry.start;

                __process_mem_region(&entry, minimum, image_size);

                if (slot_area_index == MAX_SLOT_AREA) {
                        debug_putstr("Aborted e820/efi memmap scan when walking immovable regions(slot_areas full)!\n");
                        return 1;
                }
        }
#endif
        return 0;
}

#ifdef CONFIG_EFI
/*
 * Returns true if we processed the EFI memmap, which we prefer over the E820
 * table if it is available.
 */
static bool
process_efi_entries(unsigned long minimum, unsigned long image_size)
{
        struct efi_info *e = &boot_params->efi_info;
        bool efi_mirror_found = false;
        struct mem_vector region;
        efi_memory_desc_t *md;
        unsigned long pmap;
        char *signature;
        u32 nr_desc;
        int i;

        signature = (char *)&e->efi_loader_signature;
        if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
            strncmp(signature, EFI64_LOADER_SIGNATURE, 4))
                return false;

#ifdef CONFIG_X86_32
        /* Can't handle data above 4GB at this time */
        if (e->efi_memmap_hi) {
                warn("EFI memmap is above 4GB, can't be handled now on x86_32. EFI should be disabled.\n");
                return false;
        }
        pmap =  e->efi_memmap;
#else
        pmap = (e->efi_memmap | ((__u64)e->efi_memmap_hi << 32));
#endif

        nr_desc = e->efi_memmap_size / e->efi_memdesc_size;
        for (i = 0; i < nr_desc; i++) {
                md = efi_early_memdesc_ptr(pmap, e->efi_memdesc_size, i);
                if (md->attribute & EFI_MEMORY_MORE_RELIABLE) {
                        efi_mirror_found = true;
                        break;
                }
        }

        for (i = 0; i < nr_desc; i++) {
                md = efi_early_memdesc_ptr(pmap, e->efi_memdesc_size, i);

                /*
                 * Here we are more conservative in picking free memory than
                 * the EFI spec allows:
                 *
                 * According to the spec, EFI_BOOT_SERVICES_{CODE|DATA} are also
                 * free memory and thus available to place the kernel image into,
                 * but in practice there's firmware where using that memory leads
                 * to crashes.
                 *
                 * Only EFI_CONVENTIONAL_MEMORY is guaranteed to be free.
                 */
                if (md->type != EFI_CONVENTIONAL_MEMORY)
                        continue;

                if (efi_soft_reserve_enabled() &&
                    (md->attribute & EFI_MEMORY_SP))
                        continue;

                if (efi_mirror_found &&
                    !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
                        continue;

                region.start = md->phys_addr;
                region.size = md->num_pages << EFI_PAGE_SHIFT;
                if (process_mem_region(&region, minimum, image_size))
                        break;
        }
        return true;
}
#else
static inline bool
process_efi_entries(unsigned long minimum, unsigned long image_size)
{
        return false;
}
#endif

static void process_e820_entries(unsigned long minimum,
                                 unsigned long image_size)
{
        int i;
        struct mem_vector region;
        struct boot_e820_entry *entry;

        /* Verify potential e820 positions, appending to slots list. */
        for (i = 0; i < boot_params->e820_entries; i++) {
                entry = &boot_params->e820_table[i];
                /* Skip non-RAM entries. */
                if (entry->type != E820_TYPE_RAM)
                        continue;
                region.start = entry->addr;
                region.size = entry->size;
                if (process_mem_region(&region, minimum, image_size))
                        break;
        }
}

static unsigned long find_random_phys_addr(unsigned long minimum,
                                           unsigned long image_size)
{
        u64 phys_addr;

        /* Bail out early if it's impossible to succeed. */
        if (minimum + image_size > mem_limit)
                return 0;

        /* Check if we had too many memmaps. */
        if (memmap_too_large) {
                debug_putstr("Aborted memory entries scan (more than 4 memmap= args)!\n");
                return 0;
        }

        if (!process_efi_entries(minimum, image_size))
                process_e820_entries(minimum, image_size);

        phys_addr = slots_fetch_random();

        /* Perform a final check to make sure the address is in range. */
        if (phys_addr < minimum || phys_addr + image_size > mem_limit) {
                warn("Invalid physical address chosen!\n");
                return 0;
        }

        return (unsigned long)phys_addr;
}

static unsigned long find_random_virt_addr(unsigned long minimum,
                                           unsigned long image_size)
{
        unsigned long slots, random_addr;

        /*
         * There are how many CONFIG_PHYSICAL_ALIGN-sized slots
         * that can hold image_size within the range of minimum to
         * KERNEL_IMAGE_SIZE?
         */
        slots = 1 + (KERNEL_IMAGE_SIZE - minimum - image_size) / CONFIG_PHYSICAL_ALIGN;

        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;

        if (IS_ENABLED(CONFIG_X86_32))
                mem_limit = KERNEL_IMAGE_SIZE;
        else
                mem_limit = MAXMEM;

        /* 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);
        /* Make sure minimum is aligned. */
        min_addr = ALIGN(min_addr, CONFIG_PHYSICAL_ALIGN);

        /* Walk available memory entries to find a random address. */
        random_addr = find_random_phys_addr(min_addr, output_size);
        if (!random_addr) {
                warn("Physical KASLR disabled: no suitable memory region!");
        } else {
                /* Update the new physical address location. */
                if (*output != random_addr)
                        *output = random_addr;
        }


        /* 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;
}