1 // SPDX-License-Identifier: GPL-2.0-only
2 // Copyright 2022 Google LLC
3 // Author: Ard Biesheuvel <ardb@google.com>
4
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.
7
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>
14
15 #include <asm/archrandom.h>
16 #include <asm/memory.h>
17 #include <asm/pgtable.h>
18
19 #include "pi.h"
20
21 extern u16 memstart_offset_seed;
22
23 static u64 __init get_kaslr_seed(void *fdt, int node)
24 {
25 static char const seed_str[] __initconst = "kaslr-seed";
26 fdt64_t *prop;
27 u64 ret;
28 int len;
29
30 if (node < 0)
31 return 0;
32
33 prop = fdt_getprop_w(fdt, node, seed_str, &len);
34 if (!prop || len != sizeof(u64))
35 return 0;
36
37 ret = fdt64_to_cpu(*prop);
38 *prop = 0;
39 return ret;
40 }
41
42 u64 __init kaslr_early_init(void *fdt, int chosen)
43 {
44 u64 seed, range;
45
46 if (kaslr_disabled_cmdline())
47 return 0;
48
49 seed = get_kaslr_seed(fdt, chosen);
50 if (!seed) {
51 if (!__early_cpu_has_rndr() ||
52 !__arm64_rndr((unsigned long *)&seed))
53 return 0;
54 }
55
56 memstart_offset_seed = seed & U16_MAX;
57
58 /*
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.
63 */
64 range = (VMALLOC_END - KIMAGE_VADDR) / 2;
65 return range / 2 + (((__uint128_t)range * seed) >> 64);
66 }
67
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