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, nodeoffset: node, name: seed_str, lenp: &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, node: 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 | |