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_PREL64
54 #define R_AARCH64_PREL64 260
55 #endif
56 #ifndef R_AARCH64_PREL32
57 #define R_AARCH64_PREL32 261
58 #endif
59 #ifndef R_AARCH64_PREL16
60 #define R_AARCH64_PREL16 262
61 #endif
62 #ifndef R_AARCH64_PLT32
63 #define R_AARCH64_PLT32 314
64 #endif
65 #ifndef R_AARCH64_LD_PREL_LO19
66 #define R_AARCH64_LD_PREL_LO19 273
67 #endif
68 #ifndef R_AARCH64_ADR_PREL_LO21
69 #define R_AARCH64_ADR_PREL_LO21 274
70 #endif
71 #ifndef R_AARCH64_ADR_PREL_PG_HI21
72 #define R_AARCH64_ADR_PREL_PG_HI21 275
73 #endif
74 #ifndef R_AARCH64_ADR_PREL_PG_HI21_NC
75 #define R_AARCH64_ADR_PREL_PG_HI21_NC 276
76 #endif
77 #ifndef R_AARCH64_ADD_ABS_LO12_NC
78 #define R_AARCH64_ADD_ABS_LO12_NC 277
79 #endif
80 #ifndef R_AARCH64_LDST8_ABS_LO12_NC
81 #define R_AARCH64_LDST8_ABS_LO12_NC 278
82 #endif
83 #ifndef R_AARCH64_TSTBR14
84 #define R_AARCH64_TSTBR14 279
85 #endif
86 #ifndef R_AARCH64_CONDBR19
87 #define R_AARCH64_CONDBR19 280
88 #endif
89 #ifndef R_AARCH64_JUMP26
90 #define R_AARCH64_JUMP26 282
91 #endif
92 #ifndef R_AARCH64_CALL26
93 #define R_AARCH64_CALL26 283
94 #endif
95 #ifndef R_AARCH64_LDST16_ABS_LO12_NC
96 #define R_AARCH64_LDST16_ABS_LO12_NC 284
97 #endif
98 #ifndef R_AARCH64_LDST32_ABS_LO12_NC
99 #define R_AARCH64_LDST32_ABS_LO12_NC 285
100 #endif
101 #ifndef R_AARCH64_LDST64_ABS_LO12_NC
102 #define R_AARCH64_LDST64_ABS_LO12_NC 286
103 #endif
104 #ifndef R_AARCH64_MOVW_PREL_G0
105 #define R_AARCH64_MOVW_PREL_G0 287
106 #endif
107 #ifndef R_AARCH64_MOVW_PREL_G0_NC
108 #define R_AARCH64_MOVW_PREL_G0_NC 288
109 #endif
110 #ifndef R_AARCH64_MOVW_PREL_G1
111 #define R_AARCH64_MOVW_PREL_G1 289
112 #endif
113 #ifndef R_AARCH64_MOVW_PREL_G1_NC
114 #define R_AARCH64_MOVW_PREL_G1_NC 290
115 #endif
116 #ifndef R_AARCH64_MOVW_PREL_G2
117 #define R_AARCH64_MOVW_PREL_G2 291
118 #endif
119 #ifndef R_AARCH64_MOVW_PREL_G2_NC
120 #define R_AARCH64_MOVW_PREL_G2_NC 292
121 #endif
122 #ifndef R_AARCH64_MOVW_PREL_G3
123 #define R_AARCH64_MOVW_PREL_G3 293
124 #endif
125 #ifndef R_AARCH64_LDST128_ABS_LO12_NC
126 #define R_AARCH64_LDST128_ABS_LO12_NC 299
127 #endif
128
129 /* Global state of the processed ELF. */
130 static struct {
131 const char *path;
132 char *begin;
133 size_t size;
134 Elf64_Ehdr *ehdr;
135 Elf64_Shdr *sh_table;
136 const char *sh_string;
137 } elf;
138
139 #if defined(CONFIG_CPU_LITTLE_ENDIAN)
140
141 #define elf16toh(x) le16toh(x)
142 #define elf32toh(x) le32toh(x)
143 #define elf64toh(x) le64toh(x)
144
145 #define ELFENDIAN ELFDATA2LSB
146
147 #elif defined(CONFIG_CPU_BIG_ENDIAN)
148
149 #define elf16toh(x) be16toh(x)
150 #define elf32toh(x) be32toh(x)
151 #define elf64toh(x) be64toh(x)
152
153 #define ELFENDIAN ELFDATA2MSB
154
155 #else
156
157 #error PDP-endian sadly unsupported...
158
159 #endif
160
161 #define fatal_error(fmt, ...) \
162 ({ \
163 fprintf(stderr, "error: %s: " fmt "\n", \
164 elf.path, ## __VA_ARGS__); \
165 exit(EXIT_FAILURE); \
166 __builtin_unreachable(); \
167 })
168
169 #define fatal_perror(msg) \
170 ({ \
171 fprintf(stderr, "error: %s: " msg ": %s\n", \
172 elf.path, strerror(errno)); \
173 exit(EXIT_FAILURE); \
174 __builtin_unreachable(); \
175 })
176
177 #define assert_op(lhs, rhs, fmt, op) \
178 ({ \
179 typeof(lhs) _lhs = (lhs); \
180 typeof(rhs) _rhs = (rhs); \
181 \
182 if (!(_lhs op _rhs)) { \
183 fatal_error("assertion " #lhs " " #op " " #rhs \
184 " failed (lhs=" fmt ", rhs=" fmt \
185 ", line=%d)", _lhs, _rhs, __LINE__); \
186 } \
187 })
188
189 #define assert_eq(lhs, rhs, fmt) assert_op(lhs, rhs, fmt, ==)
190 #define assert_ne(lhs, rhs, fmt) assert_op(lhs, rhs, fmt, !=)
191 #define assert_lt(lhs, rhs, fmt) assert_op(lhs, rhs, fmt, <)
192 #define assert_ge(lhs, rhs, fmt) assert_op(lhs, rhs, fmt, >=)
193
194 /*
195 * Return a pointer of a given type at a given offset from
196 * the beginning of the ELF file.
197 */
198 #define elf_ptr(type, off) ((type *)(elf.begin + (off)))
199
200 /* Iterate over all sections in the ELF. */
201 #define for_each_section(var) \
202 for (var = elf.sh_table; var < elf.sh_table + elf16toh(elf.ehdr->e_shnum); ++var)
203
204 /* Iterate over all Elf64_Rela relocations in a given section. */
205 #define for_each_rela(shdr, var) \
206 for (var = elf_ptr(Elf64_Rela, elf64toh(shdr->sh_offset)); \
207 var < elf_ptr(Elf64_Rela, elf64toh(shdr->sh_offset) + elf64toh(shdr->sh_size)); var++)
208
209 /* True if a string starts with a given prefix. */
starts_with(const char * str,const char * prefix)210 static inline bool starts_with(const char *str, const char *prefix)
211 {
212 return memcmp(str, prefix, strlen(prefix)) == 0;
213 }
214
215 /* Returns a string containing the name of a given section. */
section_name(Elf64_Shdr * shdr)216 static inline const char *section_name(Elf64_Shdr *shdr)
217 {
218 return elf.sh_string + elf32toh(shdr->sh_name);
219 }
220
221 /* Returns a pointer to the first byte of section data. */
section_begin(Elf64_Shdr * shdr)222 static inline const char *section_begin(Elf64_Shdr *shdr)
223 {
224 return elf_ptr(char, elf64toh(shdr->sh_offset));
225 }
226
227 /* Find a section by its offset from the beginning of the file. */
section_by_off(Elf64_Off off)228 static inline Elf64_Shdr *section_by_off(Elf64_Off off)
229 {
230 assert_ne(off, 0UL, "%lu");
231 return elf_ptr(Elf64_Shdr, off);
232 }
233
234 /* Find a section by its index. */
section_by_idx(uint16_t idx)235 static inline Elf64_Shdr *section_by_idx(uint16_t idx)
236 {
237 assert_ne(idx, SHN_UNDEF, "%u");
238 return &elf.sh_table[idx];
239 }
240
241 /*
242 * Memory-map the given ELF file, perform sanity checks, and
243 * populate global state.
244 */
init_elf(const char * path)245 static void init_elf(const char *path)
246 {
247 int fd, ret;
248 struct stat stat;
249
250 /* Store path in the global struct for error printing. */
251 elf.path = path;
252
253 /* Open the ELF file. */
254 fd = open(path, O_RDONLY);
255 if (fd < 0)
256 fatal_perror("Could not open ELF file");
257
258 /* Get status of ELF file to obtain its size. */
259 ret = fstat(fd, &stat);
260 if (ret < 0) {
261 close(fd);
262 fatal_perror("Could not get status of ELF file");
263 }
264
265 /* mmap() the entire ELF file read-only at an arbitrary address. */
266 elf.begin = mmap(0, stat.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
267 if (elf.begin == MAP_FAILED) {
268 close(fd);
269 fatal_perror("Could not mmap ELF file");
270 }
271
272 /* mmap() was successful, close the FD. */
273 close(fd);
274
275 /* Get pointer to the ELF header. */
276 assert_ge(stat.st_size, sizeof(*elf.ehdr), "%lu");
277 elf.ehdr = elf_ptr(Elf64_Ehdr, 0);
278
279 /* Check the ELF magic. */
280 assert_eq(elf.ehdr->e_ident[EI_MAG0], ELFMAG0, "0x%x");
281 assert_eq(elf.ehdr->e_ident[EI_MAG1], ELFMAG1, "0x%x");
282 assert_eq(elf.ehdr->e_ident[EI_MAG2], ELFMAG2, "0x%x");
283 assert_eq(elf.ehdr->e_ident[EI_MAG3], ELFMAG3, "0x%x");
284
285 /* Sanity check that this is an ELF64 relocatable object for AArch64. */
286 assert_eq(elf.ehdr->e_ident[EI_CLASS], ELFCLASS64, "%u");
287 assert_eq(elf.ehdr->e_ident[EI_DATA], ELFENDIAN, "%u");
288 assert_eq(elf16toh(elf.ehdr->e_type), ET_REL, "%u");
289 assert_eq(elf16toh(elf.ehdr->e_machine), EM_AARCH64, "%u");
290
291 /* Populate fields of the global struct. */
292 elf.sh_table = section_by_off(elf64toh(elf.ehdr->e_shoff));
293 elf.sh_string = section_begin(section_by_idx(elf16toh(elf.ehdr->e_shstrndx)));
294 }
295
296 /* Print the prologue of the output ASM file. */
emit_prologue(void)297 static void emit_prologue(void)
298 {
299 printf(".data\n"
300 ".pushsection " HYP_RELOC_SECTION ", \"a\"\n");
301 }
302
303 /* Print ASM statements needed as a prologue to a processed hyp section. */
emit_section_prologue(const char * sh_orig_name)304 static void emit_section_prologue(const char *sh_orig_name)
305 {
306 /* Declare the hyp section symbol. */
307 printf(".global %s%s\n", HYP_SECTION_SYMBOL_PREFIX, sh_orig_name);
308 }
309
310 /*
311 * Print ASM statements to create a hyp relocation entry for a given
312 * R_AARCH64_ABS64 relocation.
313 *
314 * The linker of vmlinux will populate the position given by `rela` with
315 * an absolute 64-bit kernel VA. If the kernel is relocatable, it will
316 * also generate a dynamic relocation entry so that the kernel can shift
317 * the address at runtime for KASLR.
318 *
319 * Emit a 32-bit offset from the current address to the position given
320 * by `rela`. This way the kernel can iterate over all kernel VAs used
321 * by hyp at runtime and convert them to hyp VAs. However, that offset
322 * will not be known until linking of `vmlinux`, so emit a PREL32
323 * relocation referencing a symbol that the hyp linker script put at
324 * the beginning of the relocated section + the offset from `rela`.
325 */
emit_rela_abs64(Elf64_Rela * rela,const char * sh_orig_name)326 static void emit_rela_abs64(Elf64_Rela *rela, const char *sh_orig_name)
327 {
328 /* Offset of this reloc from the beginning of HYP_RELOC_SECTION. */
329 static size_t reloc_offset;
330
331 /* Create storage for the 32-bit offset. */
332 printf(".word 0\n");
333
334 /*
335 * Create a PREL32 relocation which instructs the linker of `vmlinux`
336 * to insert offset to position <base> + <offset>, where <base> is
337 * a symbol at the beginning of the relocated section, and <offset>
338 * is `rela->r_offset`.
339 */
340 printf(".reloc %lu, R_AARCH64_PREL32, %s%s + 0x%lx\n",
341 reloc_offset, HYP_SECTION_SYMBOL_PREFIX, sh_orig_name,
342 elf64toh(rela->r_offset));
343
344 reloc_offset += 4;
345 }
346
347 /* Print the epilogue of the output ASM file. */
emit_epilogue(void)348 static void emit_epilogue(void)
349 {
350 printf(".popsection\n");
351 }
352
353 /*
354 * Iterate over all RELA relocations in a given section and emit
355 * hyp relocation data for all absolute addresses in hyp code/data.
356 *
357 * Static relocations that generate PC-relative-addressing are ignored.
358 * Failure is reported for unexpected relocation types.
359 */
emit_rela_section(Elf64_Shdr * sh_rela)360 static void emit_rela_section(Elf64_Shdr *sh_rela)
361 {
362 Elf64_Shdr *sh_orig = &elf.sh_table[elf32toh(sh_rela->sh_info)];
363 const char *sh_orig_name = section_name(sh_orig);
364 Elf64_Rela *rela;
365
366 /* Skip all non-hyp sections. */
367 if (!starts_with(sh_orig_name, HYP_SECTION_PREFIX))
368 return;
369
370 emit_section_prologue(sh_orig_name);
371
372 for_each_rela(sh_rela, rela) {
373 uint32_t type = (uint32_t)elf64toh(rela->r_info);
374
375 /* Check that rela points inside the relocated section. */
376 assert_lt(elf64toh(rela->r_offset), elf64toh(sh_orig->sh_size), "0x%lx");
377
378 switch (type) {
379 /*
380 * Data relocations to generate absolute addressing.
381 * Emit a hyp relocation.
382 */
383 case R_AARCH64_ABS64:
384 emit_rela_abs64(rela, sh_orig_name);
385 break;
386 /* Allow position-relative data relocations. */
387 case R_AARCH64_PREL64:
388 case R_AARCH64_PREL32:
389 case R_AARCH64_PREL16:
390 case R_AARCH64_PLT32:
391 break;
392 /* Allow relocations to generate PC-relative addressing. */
393 case R_AARCH64_LD_PREL_LO19:
394 case R_AARCH64_ADR_PREL_LO21:
395 case R_AARCH64_ADR_PREL_PG_HI21:
396 case R_AARCH64_ADR_PREL_PG_HI21_NC:
397 case R_AARCH64_ADD_ABS_LO12_NC:
398 case R_AARCH64_LDST8_ABS_LO12_NC:
399 case R_AARCH64_LDST16_ABS_LO12_NC:
400 case R_AARCH64_LDST32_ABS_LO12_NC:
401 case R_AARCH64_LDST64_ABS_LO12_NC:
402 case R_AARCH64_LDST128_ABS_LO12_NC:
403 break;
404 /* Allow relative relocations for control-flow instructions. */
405 case R_AARCH64_TSTBR14:
406 case R_AARCH64_CONDBR19:
407 case R_AARCH64_JUMP26:
408 case R_AARCH64_CALL26:
409 break;
410 /* Allow group relocations to create PC-relative offset inline. */
411 case R_AARCH64_MOVW_PREL_G0:
412 case R_AARCH64_MOVW_PREL_G0_NC:
413 case R_AARCH64_MOVW_PREL_G1:
414 case R_AARCH64_MOVW_PREL_G1_NC:
415 case R_AARCH64_MOVW_PREL_G2:
416 case R_AARCH64_MOVW_PREL_G2_NC:
417 case R_AARCH64_MOVW_PREL_G3:
418 break;
419 default:
420 fatal_error("Unexpected RELA type %u", type);
421 }
422 }
423 }
424
425 /* Iterate over all sections and emit hyp relocation data for RELA sections. */
emit_all_relocs(void)426 static void emit_all_relocs(void)
427 {
428 Elf64_Shdr *shdr;
429
430 for_each_section(shdr) {
431 switch (elf32toh(shdr->sh_type)) {
432 case SHT_REL:
433 fatal_error("Unexpected SHT_REL section \"%s\"",
434 section_name(shdr));
435 case SHT_RELA:
436 emit_rela_section(shdr);
437 break;
438 }
439 }
440 }
441
main(int argc,const char ** argv)442 int main(int argc, const char **argv)
443 {
444 if (argc != 2) {
445 fprintf(stderr, "Usage: %s <elf_input>\n", argv[0]);
446 return EXIT_FAILURE;
447 }
448
449 init_elf(argv[1]);
450
451 emit_prologue();
452 emit_all_relocs();
453 emit_epilogue();
454
455 return EXIT_SUCCESS;
456 }
457