1 // SPDX-License-Identifier: GPL-2.0-only
2 // Copyright 2023 Google LLC
3 // Authors: Ard Biesheuvel <ardb@google.com>
4 // Peter Collingbourne <pcc@google.com>
5
6 #include <linux/elf.h>
7 #include <linux/init.h>
8 #include <linux/types.h>
9
10 #include "pi.h"
11
12 extern const Elf64_Rela rela_start[], rela_end[];
13 extern const u64 relr_start[], relr_end[];
14
relocate_kernel(u64 offset)15 void __init relocate_kernel(u64 offset)
16 {
17 u64 *place = NULL;
18
19 for (const Elf64_Rela *rela = rela_start; rela < rela_end; rela++) {
20 if (ELF64_R_TYPE(rela->r_info) != R_AARCH64_RELATIVE)
21 continue;
22 *(u64 *)(rela->r_offset + offset) = rela->r_addend + offset;
23 }
24
25 if (!IS_ENABLED(CONFIG_RELR) || !offset)
26 return;
27
28 /*
29 * Apply RELR relocations.
30 *
31 * RELR is a compressed format for storing relative relocations. The
32 * encoded sequence of entries looks like:
33 * [ AAAAAAAA BBBBBBB1 BBBBBBB1 ... AAAAAAAA BBBBBB1 ... ]
34 *
35 * i.e. start with an address, followed by any number of bitmaps. The
36 * address entry encodes 1 relocation. The subsequent bitmap entries
37 * encode up to 63 relocations each, at subsequent offsets following
38 * the last address entry.
39 *
40 * The bitmap entries must have 1 in the least significant bit. The
41 * assumption here is that an address cannot have 1 in lsb. Odd
42 * addresses are not supported. Any odd addresses are stored in the
43 * RELA section, which is handled above.
44 *
45 * With the exception of the least significant bit, each bit in the
46 * bitmap corresponds with a machine word that follows the base address
47 * word, and the bit value indicates whether or not a relocation needs
48 * to be applied to it. The second least significant bit represents the
49 * machine word immediately following the initial address, and each bit
50 * that follows represents the next word, in linear order. As such, a
51 * single bitmap can encode up to 63 relocations in a 64-bit object.
52 */
53 for (const u64 *relr = relr_start; relr < relr_end; relr++) {
54 if ((*relr & 1) == 0) {
55 place = (u64 *)(*relr + offset);
56 *place++ += offset;
57 } else {
58 for (u64 *p = place, r = *relr >> 1; r; p++, r >>= 1)
59 if (r & 1)
60 *p += offset;
61 place += 63;
62 }
63 }
64 }
65