/*
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Support for Kernel relocation at boot time
 *
 * Copyright (C) 2015, Imagination Technologies Ltd.
 * Authors: Matt Redfearn (matt.redfearn@mips.com)
 */
#include <asm/bootinfo.h>
#include <asm/cacheflush.h>
#include <asm/fw/fw.h>
#include <asm/sections.h>
#include <asm/setup.h>
#include <asm/timex.h>
#include <linux/elf.h>
#include <linux/kernel.h>
#include <linux/libfdt.h>
#include <linux/of_fdt.h>
#include <linux/panic_notifier.h>
#include <linux/sched/task.h>
#include <linux/start_kernel.h>
#include <linux/string.h>
#include <linux/printk.h>

#define RELOCATED(x) ((void *)((long)x + offset))

extern u32 _relocation_start[]; /* End kernel image / start relocation table */
extern u32 _relocation_end[];   /* End relocation table */

extern long __start___ex_table; /* Start exception table */
extern long __stop___ex_table;  /* End exception table */

extern void __weak plat_fdt_relocated(void *new_location);

/*
 * This function may be defined for a platform to perform any post-relocation
 * fixup necessary.
 * Return non-zero to abort relocation
 */
int __weak plat_post_relocation(long offset)
{
        return 0;
}

static inline u32 __init get_synci_step(void)
{
        u32 res;

        __asm__("rdhwr  %0, $1" : "=r" (res));

        return res;
}

static void __init sync_icache(void *kbase, unsigned long kernel_length)
{
        void *kend = kbase + kernel_length;
        u32 step = get_synci_step();

        do {
                __asm__ __volatile__(
                        "synci  0(%0)"
                        : /* no output */
                        : "r" (kbase));

                kbase += step;
        } while (step && kbase < kend);

        /* Completion barrier */
        __sync();
}

static void __init apply_r_mips_64_rel(u32 *loc_new, long offset)
{
        *(u64 *)loc_new += offset;
}

static void __init apply_r_mips_32_rel(u32 *loc_new, long offset)
{
        *loc_new += offset;
}

static int __init apply_r_mips_26_rel(u32 *loc_orig, u32 *loc_new, long offset)
{
        unsigned long target_addr = (*loc_orig) & 0x03ffffff;

        if (offset % 4) {
                pr_err("Dangerous R_MIPS_26 REL relocation\n");
                return -ENOEXEC;
        }

        /* Original target address */
        target_addr <<= 2;
        target_addr += (unsigned long)loc_orig & 0xf0000000;

        /* Get the new target address */
        target_addr += offset;

        if ((target_addr & 0xf0000000) != ((unsigned long)loc_new & 0xf0000000)) {
                pr_err("R_MIPS_26 REL relocation overflow\n");
                return -ENOEXEC;
        }

        target_addr -= (unsigned long)loc_new & 0xf0000000;
        target_addr >>= 2;

        *loc_new = (*loc_new & ~0x03ffffff) | (target_addr & 0x03ffffff);

        return 0;
}


static void __init apply_r_mips_hi16_rel(u32 *loc_orig, u32 *loc_new,
                                         long offset)
{
        unsigned long insn = *loc_orig;
        unsigned long target = (insn & 0xffff) << 16; /* high 16bits of target */

        target += offset;

        *loc_new = (insn & ~0xffff) | ((target >> 16) & 0xffff);
}

static int __init reloc_handler(u32 type, u32 *loc_orig, u32 *loc_new,
                                long offset)
{
        switch (type) {
        case R_MIPS_64:
                apply_r_mips_64_rel(loc_new, offset);
                break;
        case R_MIPS_32:
                apply_r_mips_32_rel(loc_new, offset);
                break;
        case R_MIPS_26:
                return apply_r_mips_26_rel(loc_orig, loc_new, offset);
        case R_MIPS_HI16:
                apply_r_mips_hi16_rel(loc_orig, loc_new, offset);
                break;
        default:
                pr_err("Unhandled relocation type %d at 0x%p\n", type,
                       loc_orig);
                return -ENOEXEC;
        }

        return 0;
}

static int __init do_relocations(void *kbase_old, void *kbase_new, long offset)
{
        u32 *r;
        u32 *loc_orig;
        u32 *loc_new;
        int type;
        int res;

        for (r = _relocation_start; r < _relocation_end; r++) {
                /* Sentinel for last relocation */
                if (*r == 0)
                        break;

                type = (*r >> 24) & 0xff;
                loc_orig = kbase_old + ((*r & 0x00ffffff) << 2);
                loc_new = RELOCATED(loc_orig);

                res = reloc_handler(type, loc_orig, loc_new, offset);
                if (res)
                        return res;
        }

        return 0;
}

/*
 * The exception table is filled in by the relocs tool after vmlinux is linked.
 * It must be relocated separately since there will not be any relocation
 * information for it filled in by the linker.
 */
static int __init relocate_exception_table(long offset)
{
        unsigned long *etable_start, *etable_end, *e;

        etable_start = RELOCATED(&__start___ex_table);
        etable_end = RELOCATED(&__stop___ex_table);

        for (e = etable_start; e < etable_end; e++)
                *e += offset;

        return 0;
}

#ifdef CONFIG_RANDOMIZE_BASE

static inline __init unsigned long rotate_xor(unsigned long hash,
                                              const void *area, size_t size)
{
        const typeof(hash) *ptr = PTR_ALIGN(area, sizeof(hash));
        size_t diff, i;

        diff = (void *)ptr - area;
        if (unlikely(size < diff + sizeof(hash)))
                return hash;

        size = ALIGN_DOWN(size - diff, sizeof(hash));

        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;
}

static inline __init unsigned long get_random_boot(void)
{
        unsigned long entropy = random_get_entropy();
        unsigned long hash = 0;

        /* Attempt to create a simple but unpredictable starting entropy. */
        hash = rotate_xor(hash, linux_banner, strlen(linux_banner));

        /* Add in any runtime entropy we can get */
        hash = rotate_xor(hash, &entropy, sizeof(entropy));

#if defined(CONFIG_USE_OF)
        /* Get any additional entropy passed in device tree */
        if (initial_boot_params) {
                int node, len;
                u64 *prop;

                node = fdt_path_offset(initial_boot_params, "/chosen");
                if (node >= 0) {
                        prop = fdt_getprop_w(initial_boot_params, node,
                                             "kaslr-seed", &len);
                        if (prop && (len == sizeof(u64)))
                                hash = rotate_xor(hash, prop, sizeof(*prop));
                }
        }
#endif /* CONFIG_USE_OF */

        return hash;
}

static inline __init bool kaslr_disabled(void)
{
        char *str;

#if defined(CONFIG_CMDLINE_BOOL)
        const char *builtin_cmdline = CONFIG_CMDLINE;

        str = strstr(builtin_cmdline, "nokaslr");
        if (str == builtin_cmdline ||
            (str > builtin_cmdline && *(str - 1) == ' '))
                return true;
#endif
        str = strstr(arcs_cmdline, "nokaslr");
        if (str == arcs_cmdline || (str > arcs_cmdline && *(str - 1) == ' '))
                return true;

        return false;
}

static inline void __init *determine_relocation_address(void)
{
        /* Choose a new address for the kernel */
        unsigned long kernel_length;
        void *dest = &_text;
        unsigned long offset;

        if (kaslr_disabled())
                return dest;

        kernel_length = (long)_end - (long)(&_text);

        offset = get_random_boot() << 16;
        offset &= (CONFIG_RANDOMIZE_BASE_MAX_OFFSET - 1);
        if (offset < kernel_length)
                offset += ALIGN(kernel_length, 0xffff);

        return RELOCATED(dest);
}

#else

static inline void __init *determine_relocation_address(void)
{
        /*
         * Choose a new address for the kernel
         * For now we'll hard code the destination
         */
        return (void *)0xffffffff81000000;
}

#endif

static inline int __init relocation_addr_valid(void *loc_new)
{
        if ((unsigned long)loc_new & 0x0000ffff) {
                /* Inappropriately aligned new location */
                return 0;
        }
        if ((unsigned long)loc_new < (unsigned long)&_end) {
                /* New location overlaps original kernel */
                return 0;
        }
        return 1;
}

static inline void __init update_kaslr_offset(unsigned long *addr, long offset)
{
        unsigned long *new_addr = (unsigned long *)RELOCATED(addr);

        *new_addr = (unsigned long)offset;
}

#if defined(CONFIG_USE_OF)
void __weak *plat_get_fdt(void)
{
        return NULL;
}
#endif

void *__init relocate_kernel(void)
{
        void *loc_new;
        unsigned long kernel_length;
        unsigned long bss_length;
        long offset = 0;
        int res = 1;
        /* Default to original kernel entry point */
        void *kernel_entry = start_kernel;
        void *fdt = NULL;

        /* Get the command line */
        fw_init_cmdline();
#if defined(CONFIG_USE_OF)
        /* Deal with the device tree */
        fdt = plat_get_fdt();
        early_init_dt_scan(fdt, __pa(fdt));
        if (boot_command_line[0]) {
                /* Boot command line was passed in device tree */
                strscpy(arcs_cmdline, boot_command_line, COMMAND_LINE_SIZE);
        }
#endif /* CONFIG_USE_OF */

        kernel_length = (long)(&_relocation_start) - (long)(&_text);
        bss_length = (long)&__bss_stop - (long)&__bss_start;

        loc_new = determine_relocation_address();

        /* Sanity check relocation address */
        if (relocation_addr_valid(loc_new))
                offset = (unsigned long)loc_new - (unsigned long)(&_text);

        /* Reset the command line now so we don't end up with a duplicate */
        arcs_cmdline[0] = '\0';

        if (offset) {
                void (*fdt_relocated_)(void *) = NULL;
#if defined(CONFIG_USE_OF)
                unsigned long fdt_phys = virt_to_phys(fdt);

                /*
                 * If built-in dtb is used then it will have been relocated
                 * during kernel _text relocation. If appended DTB is used
                 * then it will not be relocated, but it should remain
                 * intact in the original location. If dtb is loaded by
                 * the bootloader then it may need to be moved if it crosses
                 * the target memory area
                 */

                if (fdt_phys >= virt_to_phys(RELOCATED(&_text)) &&
                        fdt_phys <= virt_to_phys(RELOCATED(&_end))) {
                        void *fdt_relocated =
                                RELOCATED(ALIGN((long)&_end, PAGE_SIZE));
                        memcpy(fdt_relocated, fdt, fdt_totalsize(fdt));
                        fdt = fdt_relocated;
                        fdt_relocated_ = RELOCATED(&plat_fdt_relocated);
                }
#endif /* CONFIG_USE_OF */

                /* Copy the kernel to its new location */
                memcpy(loc_new, &_text, kernel_length);

                /* Perform relocations on the new kernel */
                res = do_relocations(&_text, loc_new, offset);
                if (res < 0)
                        goto out;

                /* Sync the caches ready for execution of new kernel */
                sync_icache(loc_new, kernel_length);

                res = relocate_exception_table(offset);
                if (res < 0)
                        goto out;

                /*
                 * The original .bss has already been cleared, and
                 * some variables such as command line parameters
                 * stored to it so make a copy in the new location.
                 */
                memcpy(RELOCATED(&__bss_start), &__bss_start, bss_length);

                /*
                 * If fdt was stored outside of the kernel image and
                 * had to be moved then update platform's state data
                 * with the new fdt location
                 */
                if (fdt_relocated_)
                        fdt_relocated_(fdt);

                /*
                 * Last chance for the platform to abort relocation.
                 * This may also be used by the platform to perform any
                 * initialisation required now that the new kernel is
                 * resident in memory and ready to be executed.
                 */
                if (plat_post_relocation(offset))
                        goto out;

                /* The current thread is now within the relocated image */
#ifndef CONFIG_CC_IS_CLANG
                __current_thread_info = RELOCATED(&init_thread_union);
#else
                /*
                 * LLVM may wrongly restore $gp ($28) in epilog even if it's
                 * intentionally modified. Work around this by using inline
                 * assembly to assign $gp. $gp couldn't be listed as output or
                 * clobber, or LLVM will still restore its original value.
                 * See also LLVM upstream issue
                 * https://github.com/llvm/llvm-project/issues/176546
                 */
                asm volatile("move $28, %0" : :
                             "r" (RELOCATED(&init_thread_union)));
#endif

                /* Return the new kernel's entry point */
                kernel_entry = RELOCATED(start_kernel);

                /* Error may occur before, so keep it at last */
                update_kaslr_offset(&__kaslr_offset, offset);
        }
out:
        return kernel_entry;
}

/*
 * Show relocation information on panic.
 */
static void show_kernel_relocation(const char *level)
{
        if (__kaslr_offset > 0) {
                printk(level);
                pr_cont("Kernel relocated by 0x%p\n", (void *)__kaslr_offset);
                pr_cont(" .text @ 0x%p\n", _text);
                pr_cont(" .data @ 0x%p\n", _sdata);
                pr_cont(" .bss  @ 0x%p\n", __bss_start);
        }
}

static int kernel_location_notifier_fn(struct notifier_block *self,
                                       unsigned long v, void *p)
{
        show_kernel_relocation(KERN_EMERG);
        return NOTIFY_DONE;
}

static struct notifier_block kernel_location_notifier = {
        .notifier_call = kernel_location_notifier_fn
};

static int __init register_kernel_offset_dumper(void)
{
        atomic_notifier_chain_register(&panic_notifier_list,
                                       &kernel_location_notifier);
        return 0;
}
__initcall(register_kernel_offset_dumper);