1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (C) 2023 - Google LLC
4 * Author: Ard Biesheuvel <ardb@google.com>
5 */
6
7#include <elf.h>
8#include <fcntl.h>
9#include <stdbool.h>
10#include <stdio.h>
11#include <stdlib.h>
12#include <string.h>
13#include <sys/mman.h>
14#include <sys/stat.h>
15#include <sys/types.h>
16#include <unistd.h>
17
18#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
19#define HOST_ORDER ELFDATA2LSB
20#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
21#define HOST_ORDER ELFDATA2MSB
22#endif
23
24static Elf64_Ehdr *ehdr;
25static Elf64_Shdr *shdr;
26static const char *strtab;
27static bool swap;
28
29static uint64_t swab_elfxword(uint64_t val)
30{
31 return swap ? __builtin_bswap64(val) : val;
32}
33
34static uint32_t swab_elfword(uint32_t val)
35{
36 return swap ? __builtin_bswap32(val) : val;
37}
38
39static uint16_t swab_elfhword(uint16_t val)
40{
41 return swap ? __builtin_bswap16(val) : val;
42}
43
44int main(int argc, char *argv[])
45{
46 struct stat stat;
47 int fd, ret;
48
49 if (argc < 3) {
50 fprintf(stderr, "file arguments missing\n");
51 exit(EXIT_FAILURE);
52 }
53
54 fd = open(argv[1], O_RDWR);
55 if (fd < 0) {
56 fprintf(stderr, "failed to open %s\n", argv[1]);
57 exit(EXIT_FAILURE);
58 }
59
60 ret = fstat(fd, &stat);
61 if (ret < 0) {
62 fprintf(stderr, "failed to stat() %s\n", argv[1]);
63 exit(EXIT_FAILURE);
64 }
65
66 ehdr = mmap(0, stat.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
67 if (ehdr == MAP_FAILED) {
68 fprintf(stderr, "failed to mmap() %s\n", argv[1]);
69 exit(EXIT_FAILURE);
70 }
71
72 swap = ehdr->e_ident[EI_DATA] != HOST_ORDER;
73 shdr = (void *)ehdr + swab_elfxword(ehdr->e_shoff);
74 strtab = (void *)ehdr +
75 swab_elfxword(shdr[swab_elfhword(ehdr->e_shstrndx)].sh_offset);
76
77 for (int i = 0; i < swab_elfhword(ehdr->e_shnum); i++) {
78 unsigned long info, flags;
79 bool prel64 = false;
80 Elf64_Rela *rela;
81 int numrela;
82
83 if (swab_elfword(shdr[i].sh_type) != SHT_RELA)
84 continue;
85
86 /* only consider RELA sections operating on data */
87 info = swab_elfword(shdr[i].sh_info);
88 flags = swab_elfxword(shdr[info].sh_flags);
89 if ((flags & (SHF_ALLOC | SHF_EXECINSTR)) != SHF_ALLOC)
90 continue;
91
92 /*
93 * We generally don't permit ABS64 relocations in the code that
94 * runs before relocation processing occurs. If statically
95 * initialized absolute symbol references are unavoidable, they
96 * may be emitted into a *.rodata.prel64 section and they will
97 * be converted to place-relative 64-bit references. This
98 * requires special handling in the referring code.
99 */
100 if (strstr(strtab + swab_elfword(shdr[info].sh_name),
101 ".rodata.prel64")) {
102 prel64 = true;
103 }
104
105 rela = (void *)ehdr + swab_elfxword(shdr[i].sh_offset);
106 numrela = swab_elfxword(shdr[i].sh_size) / sizeof(*rela);
107
108 for (int j = 0; j < numrela; j++) {
109 uint64_t info = swab_elfxword(rela[j].r_info);
110
111 if (ELF64_R_TYPE(info) != R_AARCH64_ABS64)
112 continue;
113
114 if (prel64) {
115 /* convert ABS64 into PREL64 */
116 info ^= R_AARCH64_ABS64 ^ R_AARCH64_PREL64;
117 rela[j].r_info = swab_elfxword(info);
118 } else {
119 fprintf(stderr,
120 "Unexpected absolute relocations detected in %s\n",
121 argv[2]);
122 close(fd);
123 unlink(argv[1]);
124 exit(EXIT_FAILURE);
125 }
126 }
127 }
128 close(fd);
129 return 0;
130}
131

source code of linux/arch/arm64/kernel/pi/relacheck.c