1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Copyright (C) 2020 - Google LLC
4 * Author: David Brazdil <dbrazdil@google.com>
5 *
6 * Generates relocation information used by the kernel to convert
7 * absolute addresses in hyp data from kernel VAs to hyp VAs.
8 *
9 * This is necessary because hyp code is linked into the same binary
10 * as the kernel but executes under different memory mappings.
11 * If the compiler used absolute addressing, those addresses need to
12 * be converted before they are used by hyp code.
13 *
14 * The input of this program is the relocatable ELF object containing
15 * all hyp code/data, not yet linked into vmlinux. Hyp section names
16 * should have been prefixed with `.hyp` at this point.
17 *
18 * The output (printed to stdout) is an assembly file containing
19 * an array of 32-bit integers and static relocations that instruct
20 * the linker of `vmlinux` to populate the array entries with offsets
21 * to positions in the kernel binary containing VAs used by hyp code.
22 *
23 * Note that dynamic relocations could be used for the same purpose.
24 * However, those are only generated if CONFIG_RELOCATABLE=y.
25 */
26
27 #include <elf.h>
28 #include <endian.h>
29 #include <errno.h>
30 #include <fcntl.h>
31 #include <stdbool.h>
32 #include <stdio.h>
33 #include <stdlib.h>
34 #include <string.h>
35 #include <sys/mman.h>
36 #include <sys/types.h>
37 #include <sys/stat.h>
38 #include <unistd.h>
39
40 #include <generated/autoconf.h>
41
42 #define HYP_SECTION_PREFIX ".hyp"
43 #define HYP_RELOC_SECTION ".hyp.reloc"
44 #define HYP_SECTION_SYMBOL_PREFIX "__hyp_section_"
45
46 /*
47 * AArch64 relocation type constants.
48 * Included in case these are not defined in the host toolchain.
49 */
50 #ifndef R_AARCH64_ABS64
51 #define R_AARCH64_ABS64 257
52 #endif
53 #ifndef R_AARCH64_ABS32
54 #define R_AARCH64_ABS32 258
55 #endif
56 #ifndef R_AARCH64_PREL64
57 #define R_AARCH64_PREL64 260
58 #endif
59 #ifndef R_AARCH64_PREL32
60 #define R_AARCH64_PREL32 261
61 #endif
62 #ifndef R_AARCH64_PREL16
63 #define R_AARCH64_PREL16 262
64 #endif
65 #ifndef R_AARCH64_PLT32
66 #define R_AARCH64_PLT32 314
67 #endif
68 #ifndef R_AARCH64_LD_PREL_LO19
69 #define R_AARCH64_LD_PREL_LO19 273
70 #endif
71 #ifndef R_AARCH64_ADR_PREL_LO21
72 #define R_AARCH64_ADR_PREL_LO21 274
73 #endif
74 #ifndef R_AARCH64_ADR_PREL_PG_HI21
75 #define R_AARCH64_ADR_PREL_PG_HI21 275
76 #endif
77 #ifndef R_AARCH64_ADR_PREL_PG_HI21_NC
78 #define R_AARCH64_ADR_PREL_PG_HI21_NC 276
79 #endif
80 #ifndef R_AARCH64_ADD_ABS_LO12_NC
81 #define R_AARCH64_ADD_ABS_LO12_NC 277
82 #endif
83 #ifndef R_AARCH64_LDST8_ABS_LO12_NC
84 #define R_AARCH64_LDST8_ABS_LO12_NC 278
85 #endif
86 #ifndef R_AARCH64_TSTBR14
87 #define R_AARCH64_TSTBR14 279
88 #endif
89 #ifndef R_AARCH64_CONDBR19
90 #define R_AARCH64_CONDBR19 280
91 #endif
92 #ifndef R_AARCH64_JUMP26
93 #define R_AARCH64_JUMP26 282
94 #endif
95 #ifndef R_AARCH64_CALL26
96 #define R_AARCH64_CALL26 283
97 #endif
98 #ifndef R_AARCH64_LDST16_ABS_LO12_NC
99 #define R_AARCH64_LDST16_ABS_LO12_NC 284
100 #endif
101 #ifndef R_AARCH64_LDST32_ABS_LO12_NC
102 #define R_AARCH64_LDST32_ABS_LO12_NC 285
103 #endif
104 #ifndef R_AARCH64_LDST64_ABS_LO12_NC
105 #define R_AARCH64_LDST64_ABS_LO12_NC 286
106 #endif
107 #ifndef R_AARCH64_MOVW_PREL_G0
108 #define R_AARCH64_MOVW_PREL_G0 287
109 #endif
110 #ifndef R_AARCH64_MOVW_PREL_G0_NC
111 #define R_AARCH64_MOVW_PREL_G0_NC 288
112 #endif
113 #ifndef R_AARCH64_MOVW_PREL_G1
114 #define R_AARCH64_MOVW_PREL_G1 289
115 #endif
116 #ifndef R_AARCH64_MOVW_PREL_G1_NC
117 #define R_AARCH64_MOVW_PREL_G1_NC 290
118 #endif
119 #ifndef R_AARCH64_MOVW_PREL_G2
120 #define R_AARCH64_MOVW_PREL_G2 291
121 #endif
122 #ifndef R_AARCH64_MOVW_PREL_G2_NC
123 #define R_AARCH64_MOVW_PREL_G2_NC 292
124 #endif
125 #ifndef R_AARCH64_MOVW_PREL_G3
126 #define R_AARCH64_MOVW_PREL_G3 293
127 #endif
128 #ifndef R_AARCH64_LDST128_ABS_LO12_NC
129 #define R_AARCH64_LDST128_ABS_LO12_NC 299
130 #endif
131
132 /* Global state of the processed ELF. */
133 static struct {
134 const char *path;
135 char *begin;
136 size_t size;
137 Elf64_Ehdr *ehdr;
138 Elf64_Shdr *sh_table;
139 const char *sh_string;
140 } elf;
141
142 #define elf16toh(x) le16toh(x)
143 #define elf32toh(x) le32toh(x)
144 #define elf64toh(x) le64toh(x)
145
146 #define ELFENDIAN ELFDATA2LSB
147
148 #define fatal_error(fmt, ...) \
149 ({ \
150 fprintf(stderr, "error: %s: " fmt "\n", \
151 elf.path, ## __VA_ARGS__); \
152 exit(EXIT_FAILURE); \
153 __builtin_unreachable(); \
154 })
155
156 #define fatal_perror(msg) \
157 ({ \
158 fprintf(stderr, "error: %s: " msg ": %s\n", \
159 elf.path, strerror(errno)); \
160 exit(EXIT_FAILURE); \
161 __builtin_unreachable(); \
162 })
163
164 #define assert_op(lhs, rhs, fmt, op) \
165 ({ \
166 typeof(lhs) _lhs = (lhs); \
167 typeof(rhs) _rhs = (rhs); \
168 \
169 if (!(_lhs op _rhs)) { \
170 fatal_error("assertion " #lhs " " #op " " #rhs \
171 " failed (lhs=" fmt ", rhs=" fmt \
172 ", line=%d)", _lhs, _rhs, __LINE__); \
173 } \
174 })
175
176 #define assert_eq(lhs, rhs, fmt) assert_op(lhs, rhs, fmt, ==)
177 #define assert_ne(lhs, rhs, fmt) assert_op(lhs, rhs, fmt, !=)
178 #define assert_lt(lhs, rhs, fmt) assert_op(lhs, rhs, fmt, <)
179 #define assert_ge(lhs, rhs, fmt) assert_op(lhs, rhs, fmt, >=)
180
181 /*
182 * Return a pointer of a given type at a given offset from
183 * the beginning of the ELF file.
184 */
185 #define elf_ptr(type, off) ((type *)(elf.begin + (off)))
186
187 /* Iterate over all sections in the ELF. */
188 #define for_each_section(var) \
189 for (var = elf.sh_table; var < elf.sh_table + elf16toh(elf.ehdr->e_shnum); ++var)
190
191 /* Iterate over all Elf64_Rela relocations in a given section. */
192 #define for_each_rela(shdr, var) \
193 for (var = elf_ptr(Elf64_Rela, elf64toh(shdr->sh_offset)); \
194 var < elf_ptr(Elf64_Rela, elf64toh(shdr->sh_offset) + elf64toh(shdr->sh_size)); var++)
195
196 /* True if a string starts with a given prefix. */
starts_with(const char * str,const char * prefix)197 static inline bool starts_with(const char *str, const char *prefix)
198 {
199 return memcmp(str, prefix, strlen(prefix)) == 0;
200 }
201
202 /* Returns a string containing the name of a given section. */
section_name(Elf64_Shdr * shdr)203 static inline const char *section_name(Elf64_Shdr *shdr)
204 {
205 return elf.sh_string + elf32toh(shdr->sh_name);
206 }
207
208 /* Returns a pointer to the first byte of section data. */
section_begin(Elf64_Shdr * shdr)209 static inline const char *section_begin(Elf64_Shdr *shdr)
210 {
211 return elf_ptr(char, elf64toh(shdr->sh_offset));
212 }
213
214 /* Find a section by its offset from the beginning of the file. */
section_by_off(Elf64_Off off)215 static inline Elf64_Shdr *section_by_off(Elf64_Off off)
216 {
217 assert_ne(off, 0UL, "%lu");
218 return elf_ptr(Elf64_Shdr, off);
219 }
220
221 /* Find a section by its index. */
section_by_idx(uint16_t idx)222 static inline Elf64_Shdr *section_by_idx(uint16_t idx)
223 {
224 assert_ne(idx, SHN_UNDEF, "%u");
225 return &elf.sh_table[idx];
226 }
227
228 /*
229 * Memory-map the given ELF file, perform sanity checks, and
230 * populate global state.
231 */
init_elf(const char * path)232 static void init_elf(const char *path)
233 {
234 int fd, ret;
235 struct stat stat;
236
237 /* Store path in the global struct for error printing. */
238 elf.path = path;
239
240 /* Open the ELF file. */
241 fd = open(path, O_RDONLY);
242 if (fd < 0)
243 fatal_perror("Could not open ELF file");
244
245 /* Get status of ELF file to obtain its size. */
246 ret = fstat(fd, &stat);
247 if (ret < 0) {
248 close(fd);
249 fatal_perror("Could not get status of ELF file");
250 }
251
252 /* mmap() the entire ELF file read-only at an arbitrary address. */
253 elf.begin = mmap(0, stat.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
254 if (elf.begin == MAP_FAILED) {
255 close(fd);
256 fatal_perror("Could not mmap ELF file");
257 }
258
259 /* mmap() was successful, close the FD. */
260 close(fd);
261
262 /* Get pointer to the ELF header. */
263 assert_ge(stat.st_size, sizeof(*elf.ehdr), "%lu");
264 elf.ehdr = elf_ptr(Elf64_Ehdr, 0);
265
266 /* Check the ELF magic. */
267 assert_eq(elf.ehdr->e_ident[EI_MAG0], ELFMAG0, "0x%x");
268 assert_eq(elf.ehdr->e_ident[EI_MAG1], ELFMAG1, "0x%x");
269 assert_eq(elf.ehdr->e_ident[EI_MAG2], ELFMAG2, "0x%x");
270 assert_eq(elf.ehdr->e_ident[EI_MAG3], ELFMAG3, "0x%x");
271
272 /* Sanity check that this is an ELF64 relocatable object for AArch64. */
273 assert_eq(elf.ehdr->e_ident[EI_CLASS], ELFCLASS64, "%u");
274 assert_eq(elf.ehdr->e_ident[EI_DATA], ELFENDIAN, "%u");
275 assert_eq(elf16toh(elf.ehdr->e_type), ET_REL, "%u");
276 assert_eq(elf16toh(elf.ehdr->e_machine), EM_AARCH64, "%u");
277
278 /* Populate fields of the global struct. */
279 elf.sh_table = section_by_off(elf64toh(elf.ehdr->e_shoff));
280 elf.sh_string = section_begin(section_by_idx(elf16toh(elf.ehdr->e_shstrndx)));
281 }
282
283 /* Print the prologue of the output ASM file. */
emit_prologue(void)284 static void emit_prologue(void)
285 {
286 printf(".data\n"
287 ".pushsection " HYP_RELOC_SECTION ", \"a\"\n");
288 }
289
290 /* Print ASM statements needed as a prologue to a processed hyp section. */
emit_section_prologue(const char * sh_orig_name)291 static void emit_section_prologue(const char *sh_orig_name)
292 {
293 /* Declare the hyp section symbol. */
294 printf(".global %s%s\n", HYP_SECTION_SYMBOL_PREFIX, sh_orig_name);
295 }
296
297 /*
298 * Print ASM statements to create a hyp relocation entry for a given
299 * R_AARCH64_ABS64 relocation.
300 *
301 * The linker of vmlinux will populate the position given by `rela` with
302 * an absolute 64-bit kernel VA. If the kernel is relocatable, it will
303 * also generate a dynamic relocation entry so that the kernel can shift
304 * the address at runtime for KASLR.
305 *
306 * Emit a 32-bit offset from the current address to the position given
307 * by `rela`. This way the kernel can iterate over all kernel VAs used
308 * by hyp at runtime and convert them to hyp VAs. However, that offset
309 * will not be known until linking of `vmlinux`, so emit a PREL32
310 * relocation referencing a symbol that the hyp linker script put at
311 * the beginning of the relocated section + the offset from `rela`.
312 */
emit_rela_abs64(Elf64_Rela * rela,const char * sh_orig_name)313 static void emit_rela_abs64(Elf64_Rela *rela, const char *sh_orig_name)
314 {
315 /* Offset of this reloc from the beginning of HYP_RELOC_SECTION. */
316 static size_t reloc_offset;
317
318 /* Create storage for the 32-bit offset. */
319 printf(".word 0\n");
320
321 /*
322 * Create a PREL32 relocation which instructs the linker of `vmlinux`
323 * to insert offset to position <base> + <offset>, where <base> is
324 * a symbol at the beginning of the relocated section, and <offset>
325 * is `rela->r_offset`.
326 */
327 printf(".reloc %lu, R_AARCH64_PREL32, %s%s + 0x%lx\n",
328 reloc_offset, HYP_SECTION_SYMBOL_PREFIX, sh_orig_name,
329 elf64toh(rela->r_offset));
330
331 reloc_offset += 4;
332 }
333
334 /* Print the epilogue of the output ASM file. */
emit_epilogue(void)335 static void emit_epilogue(void)
336 {
337 printf(".popsection\n");
338 }
339
340 /*
341 * Iterate over all RELA relocations in a given section and emit
342 * hyp relocation data for all absolute addresses in hyp code/data.
343 *
344 * Static relocations that generate PC-relative-addressing are ignored.
345 * Failure is reported for unexpected relocation types.
346 */
emit_rela_section(Elf64_Shdr * sh_rela)347 static void emit_rela_section(Elf64_Shdr *sh_rela)
348 {
349 Elf64_Shdr *sh_orig = &elf.sh_table[elf32toh(sh_rela->sh_info)];
350 const char *sh_orig_name = section_name(sh_orig);
351 Elf64_Rela *rela;
352
353 /* Skip all non-hyp sections. */
354 if (!starts_with(sh_orig_name, HYP_SECTION_PREFIX))
355 return;
356
357 emit_section_prologue(sh_orig_name);
358
359 for_each_rela(sh_rela, rela) {
360 uint32_t type = (uint32_t)elf64toh(rela->r_info);
361
362 /* Check that rela points inside the relocated section. */
363 assert_lt(elf64toh(rela->r_offset), elf64toh(sh_orig->sh_size), "0x%lx");
364
365 switch (type) {
366 /*
367 * Data relocations to generate absolute addressing.
368 * Emit a hyp relocation.
369 */
370 case R_AARCH64_ABS64:
371 emit_rela_abs64(rela, sh_orig_name);
372 break;
373 /* Allow 32-bit absolute relocation, for kCFI type hashes. */
374 case R_AARCH64_ABS32:
375 break;
376 /* Allow position-relative data relocations. */
377 case R_AARCH64_PREL64:
378 case R_AARCH64_PREL32:
379 case R_AARCH64_PREL16:
380 case R_AARCH64_PLT32:
381 break;
382 /* Allow relocations to generate PC-relative addressing. */
383 case R_AARCH64_LD_PREL_LO19:
384 case R_AARCH64_ADR_PREL_LO21:
385 case R_AARCH64_ADR_PREL_PG_HI21:
386 case R_AARCH64_ADR_PREL_PG_HI21_NC:
387 case R_AARCH64_ADD_ABS_LO12_NC:
388 case R_AARCH64_LDST8_ABS_LO12_NC:
389 case R_AARCH64_LDST16_ABS_LO12_NC:
390 case R_AARCH64_LDST32_ABS_LO12_NC:
391 case R_AARCH64_LDST64_ABS_LO12_NC:
392 case R_AARCH64_LDST128_ABS_LO12_NC:
393 break;
394 /* Allow relative relocations for control-flow instructions. */
395 case R_AARCH64_TSTBR14:
396 case R_AARCH64_CONDBR19:
397 case R_AARCH64_JUMP26:
398 case R_AARCH64_CALL26:
399 break;
400 /* Allow group relocations to create PC-relative offset inline. */
401 case R_AARCH64_MOVW_PREL_G0:
402 case R_AARCH64_MOVW_PREL_G0_NC:
403 case R_AARCH64_MOVW_PREL_G1:
404 case R_AARCH64_MOVW_PREL_G1_NC:
405 case R_AARCH64_MOVW_PREL_G2:
406 case R_AARCH64_MOVW_PREL_G2_NC:
407 case R_AARCH64_MOVW_PREL_G3:
408 break;
409 default:
410 fatal_error("Unexpected RELA type %u", type);
411 }
412 }
413 }
414
415 /* Iterate over all sections and emit hyp relocation data for RELA sections. */
emit_all_relocs(void)416 static void emit_all_relocs(void)
417 {
418 Elf64_Shdr *shdr;
419
420 for_each_section(shdr) {
421 switch (elf32toh(shdr->sh_type)) {
422 case SHT_REL:
423 fatal_error("Unexpected SHT_REL section \"%s\"",
424 section_name(shdr));
425 case SHT_RELA:
426 emit_rela_section(shdr);
427 break;
428 }
429 }
430 }
431
main(int argc,const char ** argv)432 int main(int argc, const char **argv)
433 {
434 if (argc != 2) {
435 fprintf(stderr, "Usage: %s <elf_input>\n", argv[0]);
436 return EXIT_FAILURE;
437 }
438
439 init_elf(argv[1]);
440
441 emit_prologue();
442 emit_all_relocs();
443 emit_epilogue();
444
445 return EXIT_SUCCESS;
446 }
447