// SPDX-License-Identifier: GPL-2.0-only
// Copyright 2022 Google LLC
// Author: Ard Biesheuvel <ardb@google.com>

// NOTE: code in this file runs *very* early, and is not permitted to use
// global variables or anything that relies on absolute addressing.

#include <linux/libfdt.h>
#include <linux/init.h>
#include <linux/linkage.h>
#include <linux/types.h>
#include <linux/sizes.h>
#include <linux/string.h>

#include <asm/archrandom.h>
#include <asm/memory.h>
#include <asm/pgtable.h>

#include "pi.h"

static u64 __init get_kaslr_seed(void *fdt, int node)
{
        static char const seed_str[] __initconst = "kaslr-seed";
        fdt64_t *prop;
        u64 ret;
        int len;

        if (node < 0)
                return 0;

        prop = fdt_getprop_w(fdt, node, seed_str, &len);
        if (!prop || len != sizeof(u64))
                return 0;

        ret = fdt64_to_cpu(*prop);
        *prop = 0;
        return ret;
}

u64 __init kaslr_early_init(void *fdt, int chosen)
{
        u64 seed, range;

        if (kaslr_disabled_cmdline())
                return 0;

        seed = get_kaslr_seed(fdt, chosen);
        if (!seed) {
                if (!__early_cpu_has_rndr() ||
                    !__arm64_rndr((unsigned long *)&seed))
                        return 0;
        }

        /*
         * OK, so we are proceeding with KASLR enabled. Calculate a suitable
         * kernel image offset from the seed. Let's place the kernel in the
         * 'middle' half of the VMALLOC area, and stay clear of the lower and
         * upper quarters to avoid colliding with other allocations.
         */
        range = (VMALLOC_END - KIMAGE_VADDR) / 2;
        return range / 2 + (((__uint128_t)range * seed) >> 64);
}