1 // SPDX-License-Identifier: GPL-2.0-only
2 // Copyright 2022 Google LLC
3 // Author: Ard Biesheuvel <ardb@google.com>
5 // NOTE: code in this file runs *very* early, and is not permitted to use
6 // global variables or anything that relies on absolute addressing.
8 #include <linux/libfdt.h>
9 #include <linux/init.h>
10 #include <linux/linkage.h>
11 #include <linux/types.h>
12 #include <linux/sizes.h>
13 #include <linux/string.h>
15 #include <asm/archrandom.h>
16 #include <asm/memory.h>
17 #include <asm/pgtable.h>
19 extern u16 memstart_offset_seed;
21 static u64 __init get_kaslr_seed(void *fdt)
23 static char const chosen_str[] __initconst = "chosen";
24 static char const seed_str[] __initconst = "kaslr-seed";
29 node = fdt_path_offset(fdt, chosen_str);
33 prop = fdt_getprop_w(fdt, node, seed_str, &len);
34 if (!prop || len != sizeof(u64))
37 ret = fdt64_to_cpu(*prop);
42 asmlinkage u64 __init kaslr_early_init(void *fdt)
46 if (kaslr_disabled_cmdline())
49 seed = get_kaslr_seed(fdt);
51 if (!__early_cpu_has_rndr() ||
52 !__arm64_rndr((unsigned long *)&seed))
56 memstart_offset_seed = seed & U16_MAX;
59 * OK, so we are proceeding with KASLR enabled. Calculate a suitable
60 * kernel image offset from the seed. Let's place the kernel in the
61 * 'middle' half of the VMALLOC area, and stay clear of the lower and
62 * upper quarters to avoid colliding with other allocations.
64 range = (VMALLOC_END - KIMAGE_VADDR) / 2;
65 return range / 2 + (((__uint128_t)range * seed) >> 64);