#include "misc.h"

#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");
                raw = rdtsc();

                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 = (unsigned long)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(struct boot_params *boot_params,
                                      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

        boot_params->hdr.loadflags |= KASLR_FLAG;

        /* 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;
}