Linux kernel mirror (for testing)
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linux
1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Read the intermediate KLP reloc/symbol representations created by klp diff
4 * and convert them to the proper format required by livepatch. This needs to
5 * run last to avoid linker wreckage. Linkers don't tend to handle the "two
6 * rela sections for a single base section" case very well, nor do they like
7 * SHN_LIVEPATCH.
8 *
9 * This is the final tool in the livepatch module generation pipeline:
10 *
11 * kernel builds -> objtool klp diff -> module link -> objtool klp post-link
12 */
13
14#include <fcntl.h>
15#include <gelf.h>
16#include <objtool/objtool.h>
17#include <objtool/warn.h>
18#include <objtool/klp.h>
19#include <objtool/util.h>
20#include <linux/livepatch_external.h>
21
22static int fix_klp_relocs(struct elf *elf)
23{
24 struct section *symtab, *klp_relocs;
25
26 klp_relocs = find_section_by_name(elf, KLP_RELOCS_SEC);
27 if (!klp_relocs)
28 return 0;
29
30 symtab = find_section_by_name(elf, ".symtab");
31 if (!symtab) {
32 ERROR("missing .symtab");
33 return -1;
34 }
35
36 for (int i = 0; i < sec_size(klp_relocs) / sizeof(struct klp_reloc); i++) {
37 struct klp_reloc *klp_reloc;
38 unsigned long klp_reloc_off;
39 struct section *sec, *tmp, *klp_rsec;
40 unsigned long offset;
41 struct reloc *reloc;
42 char sym_modname[64];
43 char rsec_name[SEC_NAME_LEN];
44 u64 addend;
45 struct symbol *sym, *klp_sym;
46
47 klp_reloc_off = i * sizeof(*klp_reloc);
48 klp_reloc = klp_relocs->data->d_buf + klp_reloc_off;
49
50 /*
51 * Read __klp_relocs[i]:
52 */
53
54 /* klp_reloc.sec_offset */
55 reloc = find_reloc_by_dest(elf, klp_relocs,
56 klp_reloc_off + offsetof(struct klp_reloc, offset));
57 if (!reloc) {
58 ERROR("malformed " KLP_RELOCS_SEC " section");
59 return -1;
60 }
61
62 sec = reloc->sym->sec;
63 offset = reloc_addend(reloc);
64
65 /* klp_reloc.sym */
66 reloc = find_reloc_by_dest(elf, klp_relocs,
67 klp_reloc_off + offsetof(struct klp_reloc, sym));
68 if (!reloc) {
69 ERROR("malformed " KLP_RELOCS_SEC " section");
70 return -1;
71 }
72
73 klp_sym = reloc->sym;
74 addend = reloc_addend(reloc);
75
76 /* symbol format: .klp.sym.modname.sym_name,sympos */
77 if (sscanf(klp_sym->name + strlen(KLP_SYM_PREFIX), "%55[^.]", sym_modname) != 1)
78 ERROR("can't find modname in klp symbol '%s'", klp_sym->name);
79
80 /*
81 * Create the KLP rela:
82 */
83
84 /* section format: .klp.rela.sec_objname.section_name */
85 if (snprintf_check(rsec_name, SEC_NAME_LEN,
86 KLP_RELOC_SEC_PREFIX "%s.%s",
87 sym_modname, sec->name))
88 return -1;
89
90 klp_rsec = find_section_by_name(elf, rsec_name);
91 if (!klp_rsec) {
92 klp_rsec = elf_create_section(elf, rsec_name, 0,
93 elf_rela_size(elf),
94 SHT_RELA, elf_addr_size(elf),
95 SHF_ALLOC | SHF_INFO_LINK | SHF_RELA_LIVEPATCH);
96 if (!klp_rsec)
97 return -1;
98
99 klp_rsec->sh.sh_link = symtab->idx;
100 klp_rsec->sh.sh_info = sec->idx;
101 klp_rsec->base = sec;
102 }
103
104 tmp = sec->rsec;
105 sec->rsec = klp_rsec;
106 if (!elf_create_reloc(elf, sec, offset, klp_sym, addend, klp_reloc->type))
107 return -1;
108 sec->rsec = tmp;
109
110 /*
111 * Fix up the corresponding KLP symbol:
112 */
113
114 klp_sym->sym.st_shndx = SHN_LIVEPATCH;
115 if (!gelf_update_sym(symtab->data, klp_sym->idx, &klp_sym->sym)) {
116 ERROR_ELF("gelf_update_sym");
117 return -1;
118 }
119
120 /*
121 * Disable the original non-KLP reloc by converting it to R_*_NONE:
122 */
123
124 reloc = find_reloc_by_dest(elf, sec, offset);
125 sym = reloc->sym;
126 sym->sym.st_shndx = SHN_LIVEPATCH;
127 set_reloc_type(elf, reloc, 0);
128 if (!gelf_update_sym(symtab->data, sym->idx, &sym->sym)) {
129 ERROR_ELF("gelf_update_sym");
130 return -1;
131 }
132 }
133
134 return 0;
135}
136
137/*
138 * This runs on the livepatch module after all other linking has been done. It
139 * converts the intermediate __klp_relocs section into proper KLP relocs to be
140 * processed by livepatch. This needs to run last to avoid linker wreckage.
141 * Linkers don't tend to handle the "two rela sections for a single base
142 * section" case very well, nor do they appreciate SHN_LIVEPATCH.
143 */
144int cmd_klp_post_link(int argc, const char **argv)
145{
146 struct elf *elf;
147
148 argc--;
149 argv++;
150
151 if (argc != 1) {
152 fprintf(stderr, "%d\n", argc);
153 fprintf(stderr, "usage: objtool link <file.ko>\n");
154 return -1;
155 }
156
157 elf = elf_open_read(argv[0], O_RDWR);
158 if (!elf)
159 return -1;
160
161 if (fix_klp_relocs(elf))
162 return -1;
163
164 if (elf_write(elf))
165 return -1;
166
167 return elf_close(elf);
168}