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// 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"
extern u16 memstart_offset_seed;
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;
}
memstart_offset_seed = seed & U16_MAX;
/*
* 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);
}
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